DC ProcessTechnologies

8/13/2019 DC ProcessTechnologies

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2008

PROCESSTECHNOLOGIES

Turn Research into Action

Business Solutions Based on NADCA Research

NORTH AMERICAN DIE CASTING ASSOCIATION


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Turn Research into Action Business Solutions Based on NADCA Research

Leak Testing for Die CastingsJ. Brevick & C. Adams, Ohio State Universi ty

Project Objectives: The topic of leak testing can

be a confusing one for the individual whose specialty is

in another field such as the die casting practitioner. The

questions of How do I measure a specified leakage

rate? and How is a maximum allowable leakage rate

assured in a production setting? lead to a myriad ofother questions for which the answers can be ambigu-

ous or difficult to obtain. One objective of this project

was to review standard leak testing technology as ap-

plied to die castings to provide the industry with a place

to begin for understanding leak testing for die castings.

The determination of maximum allowable leakage rates

for die castings is based on functional requirements and

is made by the designer or customer of the die casting.

In many situations casting designers and customers are

uncertain about which method of leak testing is appropri-

ate for their die casting applications. More than one leak

test method is sometimes even used for the same casting

in different production facilities. Leak testing in produc-

tion is usually an accelerated test using a fluid (gas) other

than that (liquid) used in service. Castings may demon-

strate measurable leakage in an accelerated test, but not

leak in service. Ideally, the level of leakage acceptable

in the accelerated production test should have a known

correlation to the leak rate in service. This correlation is

typically done via empirical testing of the casting under

conditions that the casting encounters in its service life.

Another objective of this project was to generate a

mathematical model which would directly correlate thegaseous flow or leakage through a die casting during

accelerated production testing with the actual fluid leak-

age which would occur during its service life.

Approach: The literature on leak testing was ex-

plored and the most common methods for leak testing

die castings were reviewed. A report was subsequently

written, which documents many of the technical aspects

of leak testing of die castings and provides empirical

data used in industry to correlate accelerated leak test-

ing with actual leaks in the field.

Specifically, the following technical areas relevant toleak testing were summarized:

Physical behavior of gases.

o Physics of gases.

o Fluid dynamics of gases.

Gaseous flow through leaks.

Leak testing technology as applied to die castings.

Methods of leak testing die castings.

Results: The project resulted in a comprehensive

summary of the technologies relevant to leak testing of

die castings, including the physical behavior of gases,

gaseous flow through leaks, and leak testing technol-

ogy. Additionally, a description of and a procedure for

the most common methods for leak testing a die castingwere presented. The methods addressed were: Pres-

sure Decay and Flow Rate Testing, Bubble Emission

Leak Testing, Mass Spectrometer Leak Testing, and

Halogen Tracer Gas Leak Detection.

These efforts were intended to provide die casting

practitioners with a place to begin with assurance of

leakage rates for die castings. The original proposal

from NADCA for this project was to investigate the

possibility of analytically correlating the flow of vari-

ous liquids encountered in the application of castings

(e.g. transmission fluid) where leakage is a concern,

to the flow of gaseous testing media (e.g. air). It was

the intent of the project to provide for the die casting

industry a means to escape the empirical nature of de-

termining appropriate gaseous leakage rates to which

to test a casting to assure acceptable leakage rates of

liquid media in service.

This objective was not accomplished. Analytically

correlating liquid flow to gaseous flow would be a very

difficult task. Before one could attempt such a corre-

lation, analytical modeling of each type of flow would

have to be completed. Although fairly detailed model-

ing of gaseous flow is detailed in the project report,application of these models to liquid flow is applicable

under very limited conditions at best. To complicate

issues further, a variety of operating liquids with widely

varied viscosities and included additives are encoun-

tered in use with die castings, as well as a myriad of

operating temperatures and pressures and varied fluid

leakage mechanisms.

The table below does describe the maximum production

test air leak rates that have been reported for some die

cast products and the corresponding field leak rates.

Implementation Strategy: The results of thisproject, contained in the final report, provide compre-

hensive discussions concerning the physics of leak

testing, detailed explanations of the various types of

leak testing systems, and input into how each of these

technologies can be used effectively. Those who wish

to better understand the leak testing requirements for

die casting products or wish to adopt effective speci-

fications for leak testing components should read and

understand the final report on this project.


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Monitoring Task Force: Process Technology Task Force

Sponsored by: NADCA

This research is featured in more detail in the following transaction

Transaction: T04-023

Casting / Fluid ContainedTypical Test Pressure

Range bars (psig)Typical Leakage Rate - cc/min (air)

Transmission Case / Automatic Transmission Fluid 0.2 to 0.4 (3 to 5) 10 to 20

Carburetor Assembly / Gasoline 0.4 to 0.7 (5 to 10) 1 to 5

Master Cylinder / Brake fluid 1.4 to 7.0 (20 to 100) 5 to 20

Engine Block / Water/Glycol/Oil 0.3 to1.4 (4 to 20) 10 to 30

Cooling Systems/Water 1 to 2 (15 to 30) 4 to 7

Oil (various) 0.1 to 7 (1.5 to 100) 6 to 15Diesel Fuel 1 to 10 (15 to 145) 0.1 to 15

Gasoline 1 to 5 (15 to 75) 3 to 15

Air Conditioning/Refrigerant 2 to 20 (30 to 290) 5 to 15 gm/year (tracer gas method)

Electrical Housings/Connectors 0.1 to 1 (1.5 to 15) 0.01 to 1

For further information, contact:

North American Die Casting Association

847.279.0001 phone847.279.0002 facsimile

www.diecasting.org/[email protected]


241 Holbrook Drive Wheeling, IL 60090Email: [email protected]

www.diecasting.org/research


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ENERGY AND TECHNOLOGYASSESSMENT FOR DIE CASTING PLANTSS. Udvardy and J. Wilkey, NADCA

Project Objectives: The purpose of this project

was to:

Review recent NADCA research project results to

identify the new technologies that can be utilized to

enhance the energy efficiency of die casting plants.

Develop an audit form to assist in conducting anenergy and technology assessment of two die casting

plants to assist the plants in improving its use of energy

and in reducing costs associated with the use of energy.

Approach: The initial task of the project was to

identify die casting technologies that have the capability

of providing energy benefits to the die casting indus-

try. Based on a review of completed and mature R&D

projects, several technological results that were directly

transferable to the die casting shop floor were identi-

fied. In some cases, projects had been implemented

by a die casting industry partner that participated in a

specific project in order to validate the laboratory test

results. In these instances, the successes noted by an

industry partner were captured and formed the basis for

the estimated amount of energy savings improvements.

The results of each project identified as having viable

results were summarized on a single PowerPoint slide.

The projects with successes noted by an industry part-

ner were included as case studies on the same slide or

on additional slides. The case studies were intended to

provide the industry at large with tangible evidence of

the true opportunities that exist for energy savings and

technological advancement. PowerPoint was selectedas the format for compiling the results for ease of pre-

senting viable technologies to the plants for which the

assessment was performed and to have a presentation

prepared for future die casting plant assessments.

The second task of the project was to establish an audit

form to be used as a tool in performing an energy and

technology assessment of die casting plants. Hence,

subsequent to the identification and compilation of

viable energy related technological results or new

technologies, key questions were developed, targeted

at determining whether die casting plants were aware

of or were using the technologies. The questions weremade specific enough to determine the awareness or

use of a technology but general enough to not have

too many questions. These questions were used to

develop the technology related portion of the audit form

and were categorized in five topical areas Cast Ma-

terials, Die Materials, Design Aids, Sensors & Controls,

and Process Technologies.

The third task of the project was to utilize the audit form

and perform a plant-wide energy and technology as-

sessment of two the plants.

Initially, a copy of the audit form was sent to each facil-

ity. The form was completed by staff members of eachfacility and submitted back to NADCA for review. The

no responses on each of the audit forms were viewed

as potential opportunities for identifying energy sav-

ings improvements for each respective facility. Next, a

walk-through audit was conducted at each facility and

interviews were conducted with members of each staff

to obtain information pertinent to the facility, including

the current manufacturing processes and programs in

use, as well as past and current efforts in conserving

energy and controlling costs.

Results: An assessment tool has been developedto assist die casters in determining where opportuni-

ties exist to apply new technologies. The application of

these technologies will assist in enhancing the energy

efficiency of plants through improved design, process

and operational efficiencies.

A presentation to aid in reporting/presenting findings to

plants has been established. The presentation can be

easily tailored to address specific improvement opportu-

nities sited through the use of the assessment tool. The

information in the presentation has been formulated to

assist in encouraging the implementation and use of

new die casting technologies.

The assessment tool was utilized to perform audits of

two die casting facilities. Over 40 improvement op-

portunities were identified. The combined potential

improvement in energy usage is anticipated to be a 10-

20% reduction in energy use for the facilities. Projected

savings may be realized through a 10% increase in pro-

ductivity in die casting operations, a 30-40% improve-

ment in die life, and a 10-15% reduction in scrap.

Implementation Strategy: Each die casting facil-

ity should utilize the developed technology presentation

and audit form to assess the degree to which NADCAresearch results are being utilized. These can be uti-

lized in several ways:

1. Secure the audit form from NADCA and conduct a

self-audit of the plant, which will identify areas which

offer potential energy efficiency improvement.

2. Secure the presentation on the implementation of

R&D results to be sure plant personnel are aware of the

latest research findings.


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3. Request an on-site plant audit by technical experts

from NADCA to develop a list of potential areas for

improved energy efficiency.

4. Once an initial audit has been performed, request

a follow-up audit to quantify the savings realized and

identify new opportunities resulting from new re-

search results.

Monitoring Task Force: NADCA Staff

Sponsored by: U.S. Department of Energy and NADCA



847.279.0001 phone847.279.0002 facsimile






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Sensors for Die CastingC. Smith , G. Allgood & S. Viswanathan, Oak Ridge National Laboratory

Project Objectives: The objective of this projectwas to investigate the use of a vibration sensor for die

casting process diagnostics. During the project, the ef-

fect of three different process variables on the vibration

signal obtained during die casting was analyzed.

Approach: Vibration sensors, or accelerometers, de-tect motion or acceleration, and translate mechanical vi-

brations into electronic signals. Typically, an accelerom-

eter contains a piezoelectric crystal, which is configured

such that vibrations cause the crystal to be compressed.

The compression of the crystal causes it to produce an

electronic signal that is proportional to the amplitude and

frequency of the vibration. This electronic signal can

then be amplified, filtered, recorded, and analyzed.

For use in die casting, vibrations arising from the move-

ment of the die casting machine and from the flow of metal

are converted into electrical signals by a vibration sensor

attached to the die. These signals are electronically con-

ditioned and digitized. Mathematical algorithms analyze

the timing, frequency, and amplitude of the vibrations and

correlate them with process variables to form a vibra-

tion signature. This vibration signature is then compared

against a reference vibration signature that is known to

have resulted in an acceptable quality part. The com-

parison of specific signature characteristics between the

test vibration signature and reference vibration signatures

can be used to determine the quality of the part as well as

operational characteristics of the die casting machine.

For this project, 10 castings were made at each of 5

test conditions, for a total of 50 castings. The parts

were produced on a 125 ton cold chamber die casting

machine with 380 aluminum alloy at a nominal pouring

temperature of 1280 Fahrenheit. A visual examination

criterion and rating system was developed. Each of the

50 castings was examined visually and rated according-

ly. Four castings from each sample were selected for

detailed analysis. These 20 castings were analyzed by

x-ray radioscopy to determine their internal soundness.

An x-ray rating criteria was developed and utilized.

During production of the test castings, vibration read-ings were obtained through the use of a low-cost com-

mercially available Endevco Model 7701-100 acceler-

ometer mounted to one side of the die block. A simple

vibration signature was formed by calculating the band

limited Root Mean Square of the vibration signal from

the accelerometer. A more complex vibration signature

was formed by calculating a vibration spectrum over a

period of time that corresponds to a specific length of

ram travel. The effect of different shot profiles on the

vibration signature and vibration spectrum was studied

by varying the intermediate and fast portions of the shot

profile by approximately 50 percent. The slow portion

of the shot was held constant.

Results: The following results were obtained from theexperimentation in this project:

Each step in the die casting process, such as door

closing, injection, and part extraction can be related to a

characteristic feature in the vibration signature.

Each shot profile can be identified by its vibration

signature. In particular, increasing or decreasing the

fast shot (or intermediate shot) significantly changed

the vibration signature.

The frequency based segment analysis demonstrated

that a frequency spectrum containing broad peaks indi-

cates atomized metal flow, while a frequency spectrum

dominated by harmonic resonance indicates laminar (ornon-atomized) flow of the molten metal.

The vibration signature also displays unique charac-

teristics during the solidification of the casting.

The results of the project have demonstrated that vibra-

tion signatures can identify shot profile parameters and

provide insight into the flow characteristics of the metal.

The identification of flow characteristics is the first step

in correlating the vibration signature with part quality.

As refinements are made in the analysis of the vibration

signatures, it is expected that the vibration characteris-

tics will correlate with part quality. Once these charac-

teristics have been identified, they can be incorporated

into real-time machine diagnostics for use in production

to instantly differentiate between good and bad parts.

Implementation Strategy: The results of thisproject showed the potential for using vibration sensors

to monitor the die casting process. Vibration sensors

have been used for many years by industrial mainte-

nance personnel to locate eminent failures of drives,

motors and bearings. This same technology could pos-

sibly be used provide immediate feedback from the die

casting process as well.

This project was a preliminary study on using vibration

sensors to monitor the die casting process. Significant

additional work is required to correlate vibration signa-

tures to part quality. However, for die casters already

familiar with the use of vibration signatures for main-

tenance purposes, their application to the die casting

process could provide additional useful data.


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For further info rmation, contact:


847.279.0001 phone847.279.0002 facsimile









Figure 2.Vibration signature showing events in the casting cycle.

Figure 1.Location of vibration sensors.


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Understanding the Relationship BetweenFilling Pattern and Part Quality in Die CastingJ. Brevick & A. Miller, Ohio State University

Project Objectives: The overall objective of thisproject was to investigate phenomena involved in the

filling of die cavities with molten alloy in the cold chamber

die casting process. It has long been recognized that

the filling pattern of the molten metal entering a die cav-

ity influences the quality of the resulting die cast parts.However, the relationship between fill parameters and

part quality is not completely understood. Fill parameters

typically include the velocity of the molten alloy through

the gate(s) at the start of cavity filling, molten alloy tem-

perature, die temperature, time to fill the cavity, intensifi-

cation pressure, and gate location, size and geometry.

Approach: The methods available for assessing fillingpatterns for high pressure die casting are rather limited be-

cause the process occurs in an optically opaque steel die.

The water analog technique and computer simulation are

two commonly used techniques to study filling patterns.

Observation of filling patterns in sand, lost foam and

permanent mold casting has been done with radiography,

and in this project, real-time radiographic observation of

die casting filling patterns was evaluated. This method is

considerably more challenging in die casting because of

the short time (milliseconds) and high pressure involved.

Work during the project was focused on water analog test-

ing, computer modeling, development of real-time radio-

graphic testing, and corresponding casting trials.

Results: The water analog method involves the use

of a high-speed camera to record water or low melting

point alloy flow in transparent dies. The water is typi-cally colored using dyes to make the flow patterns eas-

ily visible. Room temperature water has pertinent fluid

properties that are very similar to molten aluminum.

One drawback of the water analog approach is that it is

isothermal, no heat is lost in the system and therefore

no solidification or changes in viscosity occur as they

would in a real die casting operation.

A variety of water analog tests were conducted using

two different geometries, various gate velocities and

pre-fill percentages. Pre-filling is a departure from NA-

DCA recommendations that many die casters use suc-

cessfully. Pre-filling involves partially filling the castingvolume at a very low gate velocity, then quickly ramping

up to high gate velocity to complete filling before the

alloy solidifies. The results of the water analog work

demonstrated that pre-filling certainly does influence

the fill pattern observed. The complex flat plate geom-

etry showed a significant filling pattern improvement

using various percentages of die cavity pre-fill. The

simple geometry showed virtually no improvement in

filling pattern using pre-fill. However, pre-fill is only a

feasible option when the casting geometry is massive

enough (thick wall sections) to allow longer total cavity

filling times. Otherwise the molten alloy would solidify

before the cavity could be filled.

The objective of the computer modeling work was toconduct computer simulations of filling patterns for the

simple and complex geometries using commercially

available software. The computer simulations were

generated to compare with the water analog simulation

fill patterns and with the fill patterns from the radio-

graphic experiments. In order to accomplish the vari-

ous computer simulations, the parametric solid models

for both geometries and the gating systems were

constructed in Unigraphics. The models were then

exported from Unigraphics as STL models and loaded

into the commercial simulation software packages. The

commercial software programs utilized were: CastView,

MAGMASOFT, NovaCast, Flow3D, and dieCAS.

Generally, the water analog and computer filling pat-

tern simulations, using the same geometries and filling

parameters, yielded results that were strikingly similar.

Certainly, there are minor local differences that can be

seen from one simulation to the next, so the level of

precision is still an issue for discussion. From one point

of view the similarity is surprising because according to

current wisdom, the flow at the gate exit into the cavity

is supposed to be atomized. Yet none of the computer

simulation tools was capable of modeling atomized

flow. However, as demonstrated in this project via com-parison with actual castings, on a macroscopic scale,

computer simulations of filling patterns have the ability

to predict flow related defects in castings.

For the radiographic testing, it was necessary to design

and build an experimental apparatus suitable for real-

time radiography experiments to observe die cavity filling

patterns and the molten metal flow regime from the point

of exiting the gate. Information about flow regime at the

gate as a function of gate velocity and time during cavity

filling could be very useful for die casters. Fundamental

static and dynamic experiments were conducted and

showed that such a technique is feasible. An electricmotor was used to spin step blocks of lead and zinc

through the x-ray beam at various velocities in the die

casting range. The lead sample step block can clearly

be observed through 2 inches of aluminum with a resolu-

tion of 0.4 milliseconds. Likewise, the zinc can be seen

easily at 1.3 milliseconds and with some difficulty at

0.4 milliseconds. Based on these tests, an aluminum

die was chosen for use with both lead and zinc casting

alloys. An experimental apparatus for conducting the


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Monitoring Task Force: Process Technologies &

Computer Modeling Task ForcesSponsored by: U.S. Department of Energy and NADCA






847.279.0001 phone847.279.0002 facsimile





radiographic experiments was designed and was nearing

completion at the conclusion of the project.

Implementation Strategy: The results of thisproject showed that water analog simulations and

computer simulations can predict defects found in

actual die castings. Die casters should utilize these

tools to better understand die filling and optimize die

casting parameters.

Figure 1.Water Model vs. Computer Model Results


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results from computer programs (BINORM and MagmaSoft)

for the experimental die and casting cycle. The experiments

with the thermal probes were short duration tests accom-

plished on an experimental die, so the longevity of the thermal

sensors is unknown.

Longer duration Beta-site tests were conducted with multiple

thermocouple sensors located throughout the die, but not at or

near the cavity surface. The "composite" die temperature

based on these temperature sensors was found to be one of

the principal process variables needed to predict the volume

and weight of the die castings produced.

In-Cavity Direct Pressure Sensors: The in-cavity direct

pressure sensors evaluated in this project were manufactured

by Kistler Instrument Corporation (Kistler Instrument Corporation

part #6175A2). The Kistler direct pressure sensors demon-strated sufficient response time capability to measure the

metal pressure in its local cavity region during cavity filling and

intensification. However, once a skin solidified on the surface

of the pressure sensor, the reported sensor pressure

decreased in comparison with the metal pressure inferred

from the hydraulic records.

The direct pressure sensors provide complimentary data to the

machine hydraulic record. Specifically, the hydraulic pressure

sensors on die casting machines are of limited value for meas-

uring the inertial pressure spike that occurs in the cavity at the

end of filling. However, the direct pressure sensors were ableto monitor the pressure during the final stages of cavity filling,

the pressure spike at the end of filling, and the pressure

during the onset of intensification. These data are very useful

during initial trials with a new die to determine the preferred

injection system parameters as part of machine set-up to

produce the desired casting quality without flashing the die.

Data from the156 shots at the GM CADC beta site experi-

mental campaign were collected using the Kistler direct pres-

sure sensors with no reliability problems with the sensors or

the associated data acquisition equipment.

Vent Gas Flow Sensors: OSU experiments indicated that

thermocouples and microphone transducers are adequate to

determine if a die cavity vent is open or closed during a given

shot. However, the need exists to develop robust sensors and/

or systems that can be used for multiple sequential determi-

nations. Access to the vent exhaust location is a major problem

in attempting to utilize the vent gas flow sensors on dies

currently in use. If vent gas sensors are to be used to monitor


DIE CAVITY INSTRUMENTATION

C. Mobley and J. Brevick, Ohio State University

Business Benefit: This project provides the die caster with

information on the use of monitoring equipment to better

understand the die casting process and improve the quality of

parts. The monitoring observed the relationships between

casting weight, volume and density, with die temperature,

mean cavity pressure during solidification and intensification

stroke length.

Project Objectives: The primary objective of this project was

to evaluate the performance characteristics and usefulness

of near-cavity temperature, liquid pressure, and gas flow rate

sensors for improved monitoring and control of die casting

processes. Three types of near cavity sensors were evaluated:

1. A multi-thermocouple probe used for determining the surface

and near-cavity thermal history of the die.

2. A commercially available direct cavity pressure sensor for

measuring the pressure history of the liquid and solidifying

alloy in the die cavity.

3. A vent gas flow sensor for monitoring whether gas exits the

cavity vent during cavity filling.

Approach: As part of the evaluation of the near or in-cavity

process sensors, die casting experiments were conducted at

the Manufacturing Laboratory of the Ohio State Universitys

Engineering Research Center for Net Shape Manufacturing. A

beta site die casting campaign was also performed at the GM

Casting Advanced Development Center (CADC), at Bedford,

IN. One hundred and fifty six rear axle aluminum alloy trans-mission cases were die cast during the GM CADC beta site

experimental campaign. Detailed shot profile, die tempera-

ture, and cavity pressure data were collected for each shot.

The cycle time for each of the 156 shots in the campaign was

121 seconds and there were no operating delays or breaks

during the campaign. The volumes, densities and weights of

the individual castings were determined and correlated with

the measured casting variables.

Results: Each of the three types of sensors provided valuable

information.

Thermal Probes:Thermal sensors located at the die cavity

surface demonstrated sufficient response time to successfully

measure gate freezing time as well as near-surface heat fluxes

from molten alloy entering the cavity and from spray cooling of

the die surfaces. These data can be extremely useful to die

designers, in terms of validating their approach for thermal

management of the die. Data gathered from the near-cavity

temperature sensors were consistent with thermal analysis


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intensification stroke length with shot number for the GM

CADC campaign is shown in Figure 2. Linear regression

analysis indicated that the volumes of the GM beta site

castings were also given by the relation:

Vc = 281.911 0.052327 T + 14.6116 [2]

where T is the composite die temperature (in degrees

Fahrenheit) and is the intensification stroke length (in inches),

and the casting volume is in units of cubic inches. The R2

correlation coefficient for the Equation [2] fit was 0.973.

Density:The measured densities of the GM CADC castings

as a function of shot number are shown in Figure 3. Based on

the model presented in the 1993 NADCA Transactions paper

entitled "Equations for Predicting the Percent Porosity in Die

Castings", it was anticipated that the density of the castings

would depend primarily on the quantity of gas contained in the

casting, the pressure applied during solidification, and the

amount of liquid fed to the die cavity during intensification. For

the GM CDCA beta site castings, the density of the individual

trimmed cases was fit by the expression:

= 0.0988 - 4.0345/Pmean + 0.4470 0.19/Vc [4]

All of the variables are expressed in English units; in pounds

per cubic inch; Pmean in pounds per square inch; intensification

stroke length () in inches, and casting volume (Vc )in cubic

inches. The R2 correlation coefficient for the Equation [4] fit

was 0.933.

Figure 2. Intensification Stroke Length versus Shot

Number For GM Beta-site Campaign

Figure 3. Casting Density versus Shot Number for GM

Beta-site Campaign

the gas flow from the cavity during filling, their placement

should be considered in the early design of the die vent and

means provided for the sensor placement and replacement.

Additional effort is required to demonstrate the robustness of the

thermocouple or microphone transducer type vent flow sensors.

Implementation Strategy: Die casters can use the information

to correlate near-cavity sensor data with casting properties.

The volume, density and weight of the trimmed castings

produced during the GM CADC beta site campaign were

determined using the Archimedes method. All three charac-

teristics (volume, density and weight) were determined to five

significant figures.

Volume:The volumes of the aluminum alloy rear axle trans-

mission cases die cast during the GM CADC campaign are

plotted as a function of the shot number in Figure 1. It was

anticipated that the volume of the casting is primarily a

function of die cavity temperature and the liquid pressure in

the die cavity. The casting volume is unique or specific to a

given machine and die, as it depends on the dimensional

stability/response of the die casting system. For the GM CADC

die and machine system used in the beta site campaign, the

volume of the die castings, Vc, was related to the die casting

conditions by the expression:

Vc = 281.088 0.0524 T+ 0.0003862 Pmean + 6x10-8 Pmean

2 [1]

where T is the composite die temperature (in degrees

Fahrenheit) at the start of a given shot and Pmean is the mean

or average pressure in the liquid during solidification (in

pounds per square inch, psi). The R2 correlation coefficient for

the relation given in Equation [1] is 0.970.

Figure 1. Casting Volume versus Shot Number for GM

Beta-site Campaign

The die temperature significantly influences the volume of the

die-casting. This is consistent with the observation that casting

volumes and weights differ significantly during startup and

during or following production stoppage or delays. The volume

of the casting is greater when the die is cold and decreases

with increasing die temperature.

The volume of the castings correlated well with the intensification

stroke length or plunger travel past impact. The variation of



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Weight:The weight of the GM CDCA beta site castings as a

function of the shot number is shown in Figure 4.

Figure 4. Casting Weight versus Shot Number for GM

Beta-site Campaign

The weight of the casting is the product of its density and

volume, that is:

W = Vc [5]

As the volume of the casting depends on the die temperature

and mean pressure applied to the liquid during solidification


(and/or the intensification stroke length), and the density

depends on the mean pressure and intensification stoke

length, the weight of the casting (for a completely filled and

non-flashed cavity) is expected to depend primarily on the die

temperature, mean applied pressure, and intensification

stroke length. A regression analysis for the trimmed casting

weight gave the best-fit relation:

W = 28.303 0.00515 T 1713.5/Pmean + 1.4962 [6]

All the variables in Equation [6] are expressed in English units.The R2 correlation coefficient for Equation [6] was 0.985.

The observed relations between casting weight, volume, and

density with die temperature, mean cavity pressure during

solidification, and intensification stroke length clearly show the

value of using existing and near cavity measurements to bet-

ter monitor and understand the die casting process and

resultant parts. The observed dependence of casting weight

with the selected process variables also suggests the moni-

toring and use of weight data as part of a process and prod-

uct quality control procedure as the weighing of castings does

not require complex equipment and/or long time measurement

procedures.

Monitoring Task Force: Process Technologies Task Force







847.279.0001 phone847.279.0002 facsimile



14/32


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The measured response was the gas volume (air) trapped in

the casting cavity at the moment the metal filling the cavity

sealed off the vents. The outcome of the designed experiment

was a regression model demonstrating the influence of the

factors investigated on the volume of gas entrapped in cast-

ings. The computer generated cavity fill patterns were also

very useful in identifying the probable locations (distribution)

of trapped gas in the castings. Interim results of the computer

flow modeling work have been presented at the 1999 NADCA

Technical Congress in Cleveland, OH, and at the 2000 NADCA

Technical Congress.

The results of the computer flow analyses were compared with

results from water analog physical simulations. Water analog

experiments were conducted using a Prince test stand with a

VisiTrak Worldwide shot controller/monitor. Experimental dies

having geometries matching the computer models weremachined from transparent acrylic blocks. Injection parame-

ters were controlled to match the computer model using the

VisiTrak equipment. Cavity flow patterns were captured using

a high-speed camera capable of 4,500 frames per second.

Filling patterns were recorded on S-VHS tapes and reviewed

in slow motion.

Results: Three significant finding were discovered during

the testing:

1. The cavity filling patterns predicted using computer flow

models were in excellent agreement with the filling patterns

observed with high speed video camera recordings of the

water analog physical simulation experiments.

2. It was observed that filling patterns in die cavities were

significantly different when employing cavity pre-fill. A major

benefit when employing cavity pre-fill was the unilateral

expansion of entering metal flow in die cavities. Compared to

the fill patterns that develop when inertia dominated jet flow

occurs at the gates, in some cases pre-fill helped create more

uniform cavity fill pattern. In those cases, the amount of air

entrapped could be significantly reduced using cavity pre-fill.

3. Major factors influencing air entrapment in die cavities

turned out to be: the geometry of the die cavity itself, along

with the locations of associated gate(s), and vents; and the

percentage of cavity pre-fill and associated interactions with

slow shot (pre-fill) velocity and transition time from slow to fast

shot velocity. Therefore, for a given cavity geometry an appro-

priate combination of pre-fill (if any) and other injection param-

eters should be employed to minimize air entrapment. This

result could possibly explain why the influence of cavity pre-fill


ASSESSMENT OF THE INFLUENCE OF SLOW TO FAST SHOT TRANSITION

POINT ON CAVITY FILLING PATTERNS IN COLD CHAMBER DIE CASTING

J. Brevick, Ohio State University


information about using flow modeling to minimize porosity

related scrap. This knowledge may also preclude the need for

costly additional equipment, such as a vacuum system or

casting impregnation equipment, to reduce the amount of air

entrapped.,

Project Objectives: The purpose of this project was to evalu-

ate the influence of cavity pre-fill percentage, slow shot (pre-

fill) velocity, and transition time from slow to fast shot velocity

on filling patterns and gas porosity in die castings.

In cold chamber die casting, the acceptability of castings is

often dependent upon the location, size distribution and total

volume of contained gas porosity. These attributes of gas

porosity are influenced by the approach chosen to fill the cav-

ity with molten alloy. Specifically, metal injection parameterssuch as slow shot velocity, acceleration from slow to fast shot

velocity, slow to fast shot transition point (amount of cavity

pre-fill) and fast shot velocity can all influence the size, loca-

tion and amount of gas porosity in castings.

With respect to slow to fast shot transition point, the most

common approach among die casters is to start the fast shot

when the metal is just arriving at the gate(s). An alternative

method is the practice of cavity pre-filling, where the transition

to fast shot is delayed until the casting cavity is partially filled

at the slow shot velocity. The practice of pre-filling has been

shown to produce castings having equal or superior quality interms of porosity and surface finish. However, the best

approach for "engineering" the shot profile to obtain cavity fill

patterns that minimize contained gas casting defects is

not known.

Approach: Two approaches were taken; computer flow mod-

eling and physical simulation using the water analog approach.

Both approaches assumed an isothermal system; no heat flow

was considered in either approach. Several casting geome-

tries, ranging from simple to complex, were selected for eval-

uation using these methods. The computer flow modeling was

accomplished using the finite element based software

Flow3D. Filling pattern analyses were conducted using

experimental design approach. The factors investigated were:

1. Cavity pre-fill percentage

2. Slow shot (pre-fill) velocity

3. Transition time from slow to fast shot velocity

4. Complexity of cavity geometry.


16/32

(by itself) on porosity in die castings has been somewhat

controversial in industry.

Implementation Strategy: Die casters should consider the

filling strategy early in the die and process design phases.

Computer flow models can be invaluable aids in determining

where air will be trapped in the cavity. For a given casting

geometry, the pre-fill percentage, slow to fast shot transition

time, gate geometry and location, and vent location need to be

considered together to achieve filling patterns that will mini-

mize air entrapment during metal injection.

It should be noted that employing the cavity pre-fill approach

will increase cavity fill time. Therefore, the die caster should

be careful to calculate the available fill time for the casting to

avoid filling problems due to heat loss before considering the

use of cavity pre-fill. Typically, pre-fill can be used with die-

castings that are relatively thick in wall section, such as auto-

motive parts, which allow longer filling times. Also, in thick wall

castings employing the pre-fill approach, thicker gates may

advantageous because they can be used to feed solidification

shrinkage during intensification.

Cavity pre-fill can also increase die life on components locat-

ed close to the gates, where impinging metal may cause rapid

erosion of the die. Also, design (location) of gates and vents

are very important factors influencing air entrapment, which

can be reduced by cavity pre-fill. Accordingly, to minimize air

entrapment and maximize the benefit of using cavity pre-fill,

the cavity pre-fill approach should be considered not only in

the process design phase but also in the die design phase.

In the die and process design phases, it is also important toknow the capabilities of the die casting machine to be used in

the production of the casting. Important machine capabilities

include the degree of shot velocity control, and acceleration

rate from slow to fast shot velocity.

Using flow modeling in conjunction with knowledge about die

casting machine shot end capabilities, filling patterns can be

designed to minimize, or change the distribution of, entrapped

air in die castings. Casting scrap attributed to visual porosity

on machined surfaces, or pressurized leak test failures can be

minimized.

The results of this research demonstrate that in many cases

casting porosity can minimized by designing the shot profile

while concurrently considering die geometry and die casting

machine capabilities. This approach can minimize porosity

related scrap and may obviate the need for costly additional

equipment to reduce the amount of air entrapped, such as a

vacuum system or casting impregnation equipment. Also, the


time required for pre-production try-out, scrap generated

during start-up due to trial and error, and shot parameter setup

time can be significantly reduced. The use of pre-fill can also

potentially reduce tool repair expenses by reducing premature

erosion failures near the gate(s).

Case Study

Problem: The problem was a high scrap rate situation due to

visual porosity on machined surfaces for an aluminum cold

chamber die-casting (see Figure 1).

Figure 1. Near-surface entrapped air porosity in subject

A380 casting (100X)

Implementation/Action: The project results suggested per-

forming a computer flow analysis to identify a combination of

slow to fast shot transition point, pre-fill percentage, and tran-sition time from slow to fast shot velocity that would minimize

entrapped air volume. In this case, the die and gate geometry,

and gate and vent locations were already fixed. Also, the tran-

sition time from slow to fast shot velocity in this case could not

be changed because of limitations in the die-casting machine

hydraulic and control systems.

Computer flow analysis suggested that changing the slow to

fast shot transition point from existing practice (13.5 inches) to

a low pre-fill percentage (greater than 16 inches) would reduce

entrapped air porosity during filling.

Results: An experimental casting campaign was conducted

where the slow to fast shot transition point was varied

between 13.5 and 18 inches. The castings made during the

experiment were then tested by the Archimedes method for

total percent porosity. The results of the experiment are shown

in Figure 2.


17/32

Figure 2. Casting porosity as a function of slow to fast

shot transition point






847.279.0001 phone

847.279.0002 facsimile


[email protected]


Castings made with a slow to fast shot transition point of 16

inches or less had an average porosity of 3.5 %. Castings

made with a slow to fast shot transition point of 16.5 to 18

inches had an average porosity of less than 1%. Also, the vari-

ation in porosity among the experimental castings was much

lower when the slow to fast shot transition point was greater

then 16 inches. The die-casting machine was programmed

with a new shot profile having a slow to fast shot transition point

of 17.5 inches. Subsequent to this change, porosity related

scrap was significantly reduced.




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19/32

and solidification times of critical portions of castings.

Computer models showing filling patterns and hot spots can be

invaluable in helping designers and engineers identify potential

problems early in the design of a casting and process.

Since most military die castings are "short-run", the gating and

machine injection parameters should be designed to generate

a desirable filling pattern even when the die is cold during

start-up. Designing injection parameters to minimize air

entrapment in the shot sleeve and during mold filling can also

minimize visual porosity on machined surfaces.

Also, die casters should monitor metal quality and practice

melting methods to ensure that oxides and sludge are mini-

mized or eliminated. Clean metal will minimize unexpected

filling pattern problems due to poor fluidity and also minimize

the occurrence of hard spots during machining.

Integration of the part, tooling, and process design will

minimize the overall design time (administrative lead-time).

The time required to manufacture tooling, try out tooling and

cast acceptable parts will also be reduced. Casting defect

problems can also be identified and eliminated early in the

design process.

Die-casters employing these strategies can reduce scrap

during start-up as well as scrap in regular production. Start-

up times can also be minimized, thus increasing machine

utilization and labor efficiency. Savings in broken tooling anddowntime during subsequent casting machining operations

can be significant.

Case Study #1

Problem: A Weapon Efficiency Recorder Housing (see Figure

1) for the F-18 Hornet aircraft was being cast by a custom die-

caster in a cold chamber machine. This thin-walled aluminum

alloy casting was experiencing an unacceptable level of

misrun and flow line defects particularly during start-up (see

Figure 2).

Figure 1. Weapon

Efficiency Recorder

Housing with gating

and overflows shown.


DEFECTS CAUSING REJECTION OF DIE-CASTINGS

AFTER MACHINING (PHASE 2)J. Brevick, Ohio State University

Business Benefit: This project provides die casters with

information on ways to achieve savings by integrating the part,

tooling and process design. Incorporating these strategies can

reduce lead time as well as scrap.

Project Objectives: The Defense Logistics Agency (DLA)

objective of this project was to investigate manufacturing

processes that could potentially reduce procurement costs for

military replacement parts. A major thrust of the program was

for Army Materiel Command (AMC) participants to identify

components that were produced by methods other than casting

(fabrications, forgings, and machined parts) and to assist the

DLA in evaluating the potential benefits of changing the man-

ufacturing method to casting. A secondary goal of the DLA

was to conduct studies that would demonstrate methods to

improve the quality and reduce the costs of castings. In

Phase 2, the project objective was to select military die cast-ings experiencing defects and apply process engineering

methods to demonstrate the application of these techniques to

reduce the frequency of defects.

Approach: In Phase 2, a group of military die castings

experiencing a high scrap rate subsequent to machining were

analyzed for defects. Process engineering techniques such as

PQ2, engineering of the slow shot profile, and evaluation of

the casting filling pattern and hot spots using computer simu-

lation were employed to minimize or eliminate the defects.

Results: In Phase 2, the primary defects discovered in militarydie castings were visual and structural problems such as visual

porosity on machined surfaces, and cold shuts. The defects

were caused by undesirable filling patterns and hot spots

related primarily to the existing gate and overflow designs.

Machine injection parameters were also not appropriate in

some cases to provide the best opportunity to fill the cavity

without entrapped air porosity, or to fill the cavity when the die

was cold. Since most military die castings are made in pro-

duction runs of less than 200 castings, the scrap castings

made during the start-up of each run can be a significant

percentage. For example, if 20 warm-up shots are required for

a run of 200 shots, that is a 10% in-house scrap rate.

Therefore, it is important to reduce the number of shots

required to make the first acceptable casting.

Implementation Strategy: Die casters should employ Design

for Manufacturing (DFM) techniques whenever possible.

Concurrently, they should consider the impact of the design of

casting geometry, gates and overflows, as well as machine

capabilities and injection parameters on the filling patterns


20/32

Figure 2. Photomicrograph showing a flow defect

(100x, A380 aluminum).

Action/Implementation: Since no previous flow analysis had

been conducted during the design of the gating system, a

computer filling analysis using the existing gating system was

performed. Corrective revisions to the gating system were

evaluated so as to obtain an acceptable filling pattern even

with a cold die.

The gating inlet areas were revised by changing the geometry

of the gates - transitioning more gradually from gate to casting

using 45 degree angles rather than existing single 90 degree

angle.

Results: The computer flow analysis demonstrated better

flow patterns, even with cold dies. Misruns and visible flow

lines were minimized over a wider range of die temperature,

hence, fewer shots were required to obtain acceptable cast-

ings during start-up. Figures 3 and 4 illustrate the filling pat-

terns predicted by computer simulation for the WeaponEfficiency Recorder Housing for the old and new gating,

respectively.

Figure 3. PEI 2640 Old

Gating and Filling Pattern

Case Study #2

Problem:A Weapon Efficiency Recorder Bracket (see Figure 5)

for the F-18 Hornet aircraft was being produced by a custom

die-caster in a cold chamber machine. The company was


experiencing drill and tap breakage during machining of two

bosses on the aluminum alloy part.

Action/Implementation: The plan called for conducting radi-

ographic and optical microscopic evaluation of the problem

bosses, and conducting computer simulations of filling and hot

spot analysis. Also, the existing injection profile on the die-

casting machine was evaluated.

Radiographic and optical microscopy revealed the existence

of solidification shrinkage in bosses, causing small diameter

drills and taps to wander and break during machining (Figure

6). Computer solidification simulations were conducted and

showed inadequate gating and overflows in the boss areas.

Overflows connected to bosses were enlarged and gates

were added to boss the areas to improve the solidification

pattern (Figures 7 & 8). The metal injection profile was also

modified to improve filling.

Results: The changes resulted in reduction in the amount of

shrinkage in the bosses and reduced drill and tap breakage.

Figure 5. Weapon Efficiency Recorder Bracket with

gating and overflows shown.

Figure 6. Photomicrograph showing boss shrinkage

defects (50x, A380).

Figure 4. PEI 2640 Revised

Gating and Filling Pattern


21/32


Figure 7. Thermal results

with prior overflow design

Figure 8. Thermal results

with revised overflow design


Sponsored by: U.S. Department of Defense (Defense Logistics

Agency) and NADCA, Through the American Metalcasting Consortium






847.279.0001 phone847.279.0002 facsimile



22/32


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Business Benefit: This project provides the designer and die

caster with guidelines to determine when short-run die casting

may be a cost-effective alternative to other production methods,

increasing the potential market for die cast products.

Project Objectives: The objective of this project was to inves-

tigate the reasons why short-run die casting is not economical.

Based on a literature review and an industry survey, dies are

the biggest cost factor in short-run casting. One of the ways to

make short runs economical is by making the tool cheaper

while maintaining the quality. If improvements can be made in

the biggest cost factors, the cost of the die will go down and

short run die casting will be more economical. Another aspect

of the research was analyzing the biggest variables adding to

the lead time for dies.

Approach: Die casting is a near net shape manufacturing(NSM) process that produces components that are widely

used in many industries, including automotive, aerospace,

computer, telecommunication and consumer appliances.

Their use has been increasing due to their quality, low cost

and low weight. Typical reasons for the selection of the die

casting process include:

High production volume and rate with good repeatability

from part to part

Part accuracy and dimensional stability

Long die life

Several small components with different shapes can be

combined into a single die casting

Elimination of machining operations and few or no

secondary operations

Recyclability

Die castings made today have complicated features and main-

tain very high dimensional accuracy. Significant technological

advances such as controlling the process and equipment,

and by producing precise dies have helped achieve these

requirements. However, expensive equipment and dies have

made die casting a capital oriented business. To reduce costper part, the production volume of die cast parts usually

exceeds 10,000 units because of the high die cost. Therefore,

die casting is usually considered only when high part volume

is required. However, there is demand for low volume die cast

parts as functional prototypes or low volume production parts.

The production of these castings is described as short-run die

casting production. In this research, short-run die casting is

defined and classified as follows:


Type 1 3,000 parts or less are produced in total for the life

of the product

Type 2 Demand calls for 200-500 parts periodically, but the

product life extends over several years

Type 1 short-run die casting is used for prototyping or situa-

tions where die castings are required for functional reasons

but the total number of parts required is small.

Type 2short-run die casting typically is not envisioned at the

start of the project. However, it turns out that it is very common

for military and other applications. A weapon system or com-

ponent may stay in inventory for long periods of time but few

are destroyed or damaged. The demand for new components

or replacement parts is low and castings are required only

periodically. The die will sit on the casters shelf for extended

periods and be infrequently placed in production for shortproduction runs. This type of casting operation has its own

special problems.

The objectives of the research were to understand the char-

acteristics of the die casting industry as it relates to short-run

production and to determine how short-run die casting can be

made more economical. Part of the question was to determine

the technical and business barriers. A two-pronged approach

was utilized. The process structure and cost structure of the

industry were mapped and causes of cost and lead time leak-

age were analyzed. A case study was carried out using a mil-

itary part as the test case to determine the feasibility and cost

of short-run production. The second aspect of the work was to

determine the characteristics of the industry and the current

nature of short run practice. This was accomplished by a survey

and plant visits.

Results: The research has shown that "economy of scale" is

not the only way to make die casting economically viable. A

case study was conducted to carefully review the die making

process. A die casting die was designed and manufactured at

The Ohio State University and 500 parts were produced on the

laboratory machine. This case study demonstrated that time

and cost can be cut from the machining of the die, and as long

as die tryout is not excessive, the costs are very competitive.

Extensive use was made of computer simulation to optimize

the design and a soft insert was used to minimize the material

delivery lead time and the machining time. Measurements

taken from the parts showed relatively little die wear over the

500 parts but there were some difficulties with die soldering

due to the process.

GUIDELINES FOR SHORT RUN DIE CASTING

A. Miller, V. Shah, and K. Wee Chau, Ohio State University


24/32

The case study demonstrated that Type 1 short-run production

can be very competitive with machining even with production

runs as low as a few hundred parts. The survey, however,

clearly showed that most die casters avoid both types of short-

run production. Very few casters devote more than 10% of their

machine utilization to these runs. Even though a premium is

usually paid for short-run castings, the casters believe that

the risk of problems outweighs the benefits and they prefer

conventional business when it is available.


The results of this project identified two opportunities for die

casters:

1. The techniques identified in the project which reduced both

the cost and lead time for die construction can provide savings

to die casters engaged in both short-run and conventional part

production.

2. Opportunities exist for the production of more short-run die

castings for those die casters willing to accept the risks

involved.

Monitoring Task Force: Computer Modeling

Sponsored by: U.S. Department of Defense and NADCA


241 Holbrook Drive Wheeling, IL 60090

Email: [email protected]




847.279.0001 phone847.279.0002 facsimile



25/32


information on methods to monitor and reduce energy con-

sumption in order to reduce costs.

Project Objectives: The primary objective of this research

project was to develop models for die-casting operations that

can be used to assess the influence of equipment or process

changes on energy consumption.

Molten metal processing is inherently energy intensive and

roughly 25% of the cost of die-cast products can be traced to

some form of energy consumption. The obvious major energy

requirements are for melting and holding molten alloy in

preparation for casting. The proper selection and maintenance

of melting and holding equipment are clearly important factors

in minimizing energy consumption in die-casting operations. In

addition to energy consumption, furnace selection also influ-ences metal loss due to oxidation, metal quality and mainte-

nance requirements. Other important factors influencing ener-

gy consumption in a die-casting facility include geographic

location; alloy(s) cast; starting form of alloy (solid or liquid);

overall process flow; casting yield; scrap rate; cycle rates;

number of shifts per day; days of operation per month; type

and size of die-casting machines; related equipment (robots,

trim presses); and downstream processing (machining, plat-

ing, assembly, etc.). Each of these factors also may influence

the casting quality and productivity of a die casting enterprise.

In a die casting enterprise, decisions regarding these issues

are made frequently and are based on a large number of fac-tors. Therefore, it is not surprising that energy consumption

can vary significantly from one die casting enterprise to the

next, and within a single enterprise as a function of time.

The influence of local decisions within a die casting enterprise

on energy consumption is often difficult to determine because

of the scale and complexity of die casting operations. A

change made in one aspect of the system may not have the

degree of impact anticipated on the entire die casting system.

In addition, individual components of the die casting system

are not often metered for energy consumption, making it very

difficult to assess the actual influence of enterprise decisions

on energy consumption.

Approach: The general approach of this project was to con-

duct a literature review regarding energy use in die casting,

and then create and distribute a survey regarding energy con-

sumption to North American Die Casting Association (NADCA)

corporate members. The survey responses were then collect-

ed and evaluated. The goal of these activities was to establish


an accurate flow chart capable of mapping energy inputs for

the die casting industry. Also, these data were used to deter-

mine the relative importance of various energy-consuming

operations in die-casting, and to determine the amount and

quality of energy data available in the industry. In addition to

energy survey data, selected energy audits of die-casting

operations at The Ohio State University (OSU) die casting lab-

oratory and at industry sites were conducted. The purpose of

these audits was to establish the relative amount of energy

required by various die-casting operations, such as alloy melt-

ing, alloy holding and the die casting operation itself. Based on

the information derived from the energy survey and on-site

energy audits, computer-based models were developed that

allow the energy "journey" in die-casting operations to be

assessed.

Results: A literature review regarding energy use in die cast-ing was conducted and yielded pertinent information regarding

energy consumption of melting and holding furnaces used for

die casting. An energy survey instrument was developed, dis-

tributed to North American Die Casting Association (NADCA)

corporate members, and the data collected and analyzed. It

was determined that the amount and quality of energy data

available in the die casting industry is generally poor. Using

data from the literature and survey an accurate flow chart for

mapping energy inputs for the die-casting industry was devel-

oped.

The relative importance of various energy-consuming opera-tions in die casting, such as alloy melting, alloy holding and die

casting, were determined via energy audits conducted at the

OSU die casting laboratory and at industry sites. Based on the

information derived from the energy survey and on-site energy

audits, the computer-based models TEAM and iThink were

developed. The Energy Assessment Model (TEAM) is based

on Absorbing State Markov Chains (ASMC). A dynamic energy

model was created using iThink software. These models

allow the energy "journey" in die-casting operations to be

assessed.

Both the TEAM ASMC and iThink models can be applied to

individual plants or industry aggregates although some analy-

sis is needed to see if aggregation introduces any significant

systematic bias into the estimates that come from the models.

The ASMC model does not directly capture the dynamic

effects of time as will the I-Think model. However, once the

dynamic effects are well understood, it may be possible to

incorporate them in the spreadsheet with the TEAM model.

ENERGY CONSUMPTION OF DIE CASTING OPERATIONS

J. Brevick, C. Mount-Campbell & C. Mobley at Ohio State University


26/32

Implementation Strategy: Die casters should give more

attention to the energy consumption and energy costs of their

operations. Many operations do not have the necessary

metering or accounting techniques to properly identify energy

costs. The following approaches could provide significant

benefit to die casting operations:

Quantify the cost per pound of metal melting and holding

equipment

Measure the energy cost per pound of finish product shippedand set goals for improvement


Utilize the models demonstrated in this project to help make

equipment and operational decisions based on their energy

impact and cost

Maintain knowledge about new energy-efficient equipment

that could provide savings in energy costs








847.279.0001 phone847.279.0002 facsimile



27/32


information to analyze die casting conditions, such as extremely

long shot delay times, that affect the microstructural features

of cast products.

Project Objectives: The objective of this project was to deter-

mine the effects of externally solidified product (ESP), also

referred to as "cold flakes", on the quality of die cast aluminum

components. It was anticipated that the amount of ESP

formed in the shot sleeve would increase with shot delay time,

and that this increased amount of ESP would influence the

microstructures and associated tensile and axial fatigue prop-

erties of the resulting die castings.

Approach: Modified 383 aluminum alloy die castings were

produced using selected shot delay times and amounts of

plunger lubricants. The die castings were produced at Briggs& Stratton Corporation during June, 2001. The total shot weight

(total quantity of alloy poured) for the sump cover casting pro-

duced was about 5.25 pound, and the resultant weight of the

casting and overflows was 4.0 pounds. Twenty or more die

castings were produced at each of three shot delay times (0.5,

6.5, and 13 seconds) and two amounts of plunger lubricant

(1.3 and 2.6 grams), providing a 3 by 2 matrix for a total of six

processing conditions. The other machine setup conditions

were left as constants.

The castings were cut at selected locations in the runners,

near the main gate, at a point two-thirds of the way through themetal flow path, and near the casting overflows. The selected

dimensions of the tensile and fatigue samples were consistent

with the recommended dimensions set forth in ASTM Standard

for Tensile of Metallic Materials E-8). The normal thickness of

the tensile and fatigue samples was 0.114 inches.

After machining, selected samples were visually examined

and subjected to X-ray radiography to assess their porosity

and related defect occurrence. The accepted samples were

then subjected to either uniaxial tension or axial fatigue test-

ing at room temperature. Following completion of the tension

or fatigue tests, the fracture surfaces of selected samples

were examined with the naked eye, low magnification optical

microscope, and scanning electron microscope (SEM)

equipped with energy dispersive X-ray analysis (EDAX).

Results: The tensile data indicate no statistically significant

difference between the 0.5- and 6.5-second shot delay condi-

tions. The tensile fracture stress and fracture strains are

significantly lower with the 13 second shot delay. There is no


significant effect of the two levels of plunger lubricant at any

given shot delay time. The lower fracture stress and strain

values associated with the 13-second shot delay condition are

attributed to:

1. An anticipated larger volume fraction of ESP.

2. An increased porosity level (decreased density)

3. A greater oxide content

4. An increased occurrence of "cold shuts"

The NADCA Specification values for the yield strength and

fatigue strength of 383 aluminum alloy are 22 and 19 ksi,

respectively. However, according to the fatigue data cited in

the NADCA Specification, the number of cycles to failure for

the samples should have been in excess of ten million at the

stress level used (12 ksi). Only one sample of all those tested

survived more than 4 million cycles. The average number ofcycles to failure was 537,900 or less for all of the conditions

tested. The significantly lower fatigue lives is in part attributed

to the rectangular cross section of the samples and the asso-

ciated stress concentration effect of the corners. The lower

number of cycles to failure for the 13 second shot delay

samples is attributed primarily to the increased occurrence of

cold shuts and surface flow lines observed for those samples.

All of the tensile samples and most of the axial fatigue sam-

ples contain at least one feature on the fracture surface that

can be detected with the naked eye. The presence of those

features is extremely detrimental to the tensile and fatigue

properties. These features are classified into four categories:

cold shuts, surface flow marks, ESP or oxide films, and

macroporosity. Cold shuts are the dominant feature observed

in the 13-second shot delay time samples for both lubrication

conditions. Surface flow marks are the dominant feature in the

6.5-second shot delay samples and the ESP/oxide film feature

is dominant in the 0.5-second shot delay samples. Within

those four features, cold shuts reduce the tensile strength and

ductility the most, the macroporosity is next most influential,

and the surface flow marks and ESP/oxide films have nearly

equal, and lesser, effect on the tensile properties.

Implementation Strategy: The results of this study support

the premise that the tensile and fatigue properties of die cast-

ings are strongly dependent on the microstructural features

present in those products. The microstructural features observed

(cold shuts, surface flow marks, ESP/oxide films, and macro-

porosity) influence the tensile and fatigue properties of the

modified 383 aluminum alloy die castings. The extent of

occurrence of the four microstructural features was dependent

EFFECTS OF EXTERNALLY SOLIDIFIED PRODUCT

ON WAVE CELERITY AND QUALITY

T. Liang, C. Mobley, The Ohio State University


28/32

on the die casting conditions, with cold shuts occurring most

frequently with extremely long shot delay times. Accordingly,

die casters should minimize the shot delay time to optimize

casting mechanical properties.









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had to be adjusted to eliminate the time required to get 10%

more quality castings per hour. Emission factors should be

lower with increased production rates. The 10%increase in

parts per hour should reduce consumption of energy, the same

level or slightly more based on initial calculations with a total

energy savings of around 1.5 times the cycle time savings.

Further work is needed to fully characterize the savings in

energy with improved productivity.

Implementation Strategy: The results of this project suggest

that there is very little, if any, residue that is exhausted into the

environment from aluminum die casting machines in operation.


The emission factors and emission rates were two magnitudes

below those for typical iron foundries. A simple filter design

should be sufficient to control emissions. The project also

demonstrated that significant improvements in die casting

operations can be made by maximizing the dilution ratio of the

die lubricant, minimizing the spray time for the die lubricant,

and increasing the cycle rate of the process to reduce the

energy required for each casting produced.


Sponsored by: U.S. Department of Energy (NICE3) and NADCA






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The thermo-physical properties of the die lubricants and the

interactions between the lubricant and the die and liquid cast

alloy are critical to developing stable system operation to pro-

duce acceptable quality die-castings. However, the LTA is not

capable of characterizing the influence of deposited lubricants

on the heat transfer coefficient between molten aluminum and

H13 die steel. In a second part of this research, the chill block

melt spinning (CBMS) process was evaluated as a possible

laboratory method to assess the heat transfer coefficient

between the die and the solidifying alloy, with and without die

lubricants. A CBMS apparatus was constructed and used to

assess the heat transfer coefficient between an aluminum-

silicon eutectic alloy melt stream and an H13 tool steel wheel.

The influence of two die casting lubricants on heat transfer

coefficient was evaluated and reported.

Results: The results regarding the influence of the spraysystem on the lubricant performance were as follows:

1. The Externally Mixed Nozzle provides a faster cooling than

the Internally Mixed Nozzle. Externally Mixed Nozzles are

characterized by small size droplets in a close spray. The heat

transfer is better with this light spray in the film boiling regime

to break down the vapor barrier. The design also provides for

independent control of air and lubricant line pressures for

control of the droplet size and velocity.

2. Increasing lubricant line pressure with constant air pressure

leads to a smaller SMD for the droplets and also adds kinetic

energy to the droplets. A light spray with fast moving dropletsgives a better cooling performance than a dense spray.

3. Heat flux goes on increasing with increase in lubricant mass

flow rate for both Internally and Externally Mixed Nozzles.

Flow rate is more important a factor than the Sauter mean

diameter (SMD) because of the interaction of the droplets

downstream which is difficult to capture with an equation.

4. Study of spray patterns introduced the concept of spray flux

(spray flow over a unit area). A tight solid cone spray would

be helpful in cooling hot spots effectively because of concen-

tration of spray over a small impingement area. Widening

cone spray design can cover a large area and is useful to

remove heat from bulk of the die.

5. Pulsating spray is an interesting method of spray lubrication.

Experiments on the LTA did prove its merit. Pulsations in the

range of 360 pulsations per minute were capable of removing

heat from the plate at temperature of 315 deg C (i.e. 600 deg

F) at a faster rate as compared to a continuous spray.

Pulsation rate was correlated to the time required for vapor

barrier break down and the rebound of heat in the plate (when


INVESTIGATION OF SPRAY LUBRICANTS

J. Brevick, Ohio State University

Business Benefit: This project provides die casters with

information about techniques that can be used to control the

cooling rate provided by the die spray and other techniques,

such as pulsing the spray, which can further increase the

cooling rate.

Project Objectives: Since the early 1990s General Motors

Power Train Division (GMPT) pursued the development of a

reliable off-line testing method to evaluate the performance of

commercially available spray lubricants. A Lubricant Testing

Apparatus (LTA) was constructed for this purpose and since

1995, the LTA has been utilized at The Ohio State University

(OSU). This project continues the research conducted with the

LTA at OSU.

The first primary objective of this research was to investigate

the influence of the spray system on the thermal coolingperformance of water and lubricants. Specifically, the first goal

was to evaluate the cooling performance of internal versus

external style atomization nozzles at various flow rates

and pressures. A second goal was to evaluate the cooling

performance of commercially available spray tip patterns. A

third goal was to evaluate the influence of pulsating spray on

cooling performance.

A second primary objective was to investigate the potential of

employing a melt spinning technique for measuring the heat

transfer coefficient of commercially available lubricants on

H13 die steel.

Approach: In an effort to optimize the performance of the

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