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ANALYSIS OF EFFECTS OF USING ALUMINIUM AS MOLD MATERIAL IN PLASTIC INJECTION MOLDING FOR AUTOMOTIVE HVAC DUCTS Sri Srinivasa Muktevi B.Tech., Jawaharlal Nehru Technological University, India, 2007 PROJECT submitted in partial satisfaction of the requirements for the degree of MASTER OF SCIENCE in MECHANICAL ENGINEERING at CALIFORNIA STATE UNIVERSITY,SACRAMENTO. FALL 2011

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  • ANALYSIS OF EFFECTS OF USING ALUMINIUM AS MOLD MATERIAL IN

    PLASTIC INJECTION MOLDING FOR AUTOMOTIVE HVAC DUCTS

    Sri Srinivasa Muktevi

    B.Tech., Jawaharlal Nehru Technological University, India, 2007

    PROJECT

    submitted in partial satisfaction of

    the requirements for the degree of

    MASTER OF SCIENCE

    in

    MECHANICAL ENGINEERING

    at

    CALIFORNIA STATE UNIVERSITY,SACRAMENTO.

    FALL

    2011

  • ii

    ANALYSIS OF EFFECTS OF USING ALUMINIUM AS MOLD MATERIAL IN

    PLASTIC INJECTION MOLDING FOR AUTOMOTIVE HVAC DUCTS

    A Project

    by

    Sri Srinivasa Muktevi

    Approved by:

    ________________________________, Committee Chair

    Dongmei Zhou, Ph. D.

    _________________________

    Date

  • iii

    Student:Sri Srinivasa Muktevi

    I certify that this student has met the requirements for format contained in the university

    format manual and this project is suitable for shelving in library and credit is to be

    awarded for the project.

    ________________________, Graduate Coordinator _____________________

    Akihigo Kumagai, Ph. D. Date

    Department of Mechanical Engineering

  • iv

    Abstract

    of

    ANALYSIS OF EFFECTS OF USING ALUMINIUM AS MOLD MATERIAL IN

    PLASTIC INJECTION MOLDING FOR AUTOMOTIVE HVAC DUCTS

    by

    Sri Srinivasa Muktevi

    Aluminum injection molds, primarily used in the past for prototypes are being

    investigated for use as production molds with the advent of a new generation of

    aluminum materials specifically tailored for this application.

    This project investigates the effects of using aluminum tooling while comparing the

    importance of other contributing factors in molding performance through the use of

    Moldflow software and Taguchi methods.

    The large number of variables studied, 13 at three different levels, contributed to some

    interesting results that were not seen on other published studies with smaller numbers of

    variables. The main focus, the mold material was found, not surprisingly, to be an

    important contributor in molding performance. However, unexpectedly the aluminum

    tooling in this instance was found to perform poorer than steel while beryllium-copper

    was found to be far superior to both. Factors such as melt temperature and mold

  • v

    temperature were important contributors. Other variables that were the focus of

    experiments with fewer variables, such as waterline geometries were found to be of little

    importance in comparison.

    ________________________________, Committee Chair

    Dongmei Zhou, Ph. D.

    _________________________

    Date

  • vi

    ACKNOWLEDGMENTS

    While working on this project, some people helped me to reach where I am today and I

    would like to thank all for their support and patience.

    Firstly, I would like to thank Professor Dr. Dongmei Zhou for giving me an opportunity

    to do this project. Her continuous support was the main thing that helped me to develop

    immense interest on the project that led to do this project. Dr.Dongmei Zhou helped me

    by providing many sources of information that needed from beginning of the project till

    the end. She was always there to talk and answer the questions that came across during

    the project.

    Special thanks to my advisor Dr Akihigo Kumagai for helping me to complete the writing

    of this dissertation, without his encouragement and constant guidance I could not have

    finished this report.

    Finally, I would also like to thank all my family, friends and Mechanical engineering

    department who helped me to complete this project work successfully. Without any of

    the above-mentioned people the project would not have come out the way it did. Thank

    you all.

  • vii

    TABLE OF CONTENTS

    page

    Acknowledgments.. .viii

    List of Tables.x

    List of Figuresxii

    Software Specifications.xv

    Chapter

    1. INTRODUCTION......1

    1.1 Background1

    1.2 Objectives..2

    1.3 Procedure and Methodology.4

    1.4 Computer Simulation Parameters for Taguchi Method DOE..5

    2. VARIABLE PARAMETERS OF INJECTION MOLDING ........................................ 6

    2.1 Mold Parameters ...................................................................................................... 6

    2.1.1 Mold Dimensions .......................................................................................... 6

    2.1.2 Mold Material ................................................................................................ 7

    2.1.2.1 Aluminum Alloy (Injection Molding Grade) - QC-10 ...................... 11

    2.1.2.2 Tool Steel - P-20 ................................................................................ 12

    2.1.2.3 Copper Alloy - Be-Cu C18000 .......................................................... 12

    2.2 Waterline Parameters ............................................................................................ 13

    2.2.1 Waterline Diameter ..................................................................................... 14

    2.2.2 Waterline Pitch ........................................................................................... 15

  • viii

    2.2.3 Waterline Depth ......................................................................................... 16

    2.3 Gating ..................................................................................................................... 18

    2.4 Part Design Parameters ........................................................................................... 19

    2.4.1 Plastic Types .................................................................................................. 19

    2.4.2 Plastic Families ............................................................................................ 20

    2.4.3 Fillers ........................................................................................................... 24

    2.4.4 Plastics Grades ............................................................................................. 24

    2.4.5 Part Thickness ............................................................................................. 25

    2.5 Processing Parameters ............................................................................................ 26

    2.5.1 Coolant Parameters ....................................................................................... 26

    2.5.2 Coolant Flow Rate ....................................................................................... 27

    2.5.3 Coolant Temperature .................................................................................. 28

    2.6 Mold Surface Temp .............................................................................................. 29

    2.7 Melt Temp ............................................................................................................ 30

    2.8 Ejection Temp....................................................................................................... 32

    2.9 Frozen Percentage ................................................................................................ 33

    3. TAGUCHI METHOD ORTHOGONAL ARRAY ....................................................... 35

    3.1 Setup .................................................................................................................... 36

    3.1.1 Equipment .................................................................................................... 36

    3.2 Finite Element Model ......................................................................................... 36

  • ix

    4. RESULTS AND DISCUSSIONS ................................................................................. 39

    4.1 Dimensional Stability ............................................................................................ 39

    4.1.1 Deflection Combined Effects.................................................................... 40

    4.1.2 Deflection Corner Effects ......................................................................... 42

    4.1.3 Deflection Differential Cooling ................................................................ 43

    4.1.4 Deflection Differential Shrinkage ............................................................ 44

    4.1.5 Deflection Orientation Effects .................................................................. 45

    4.1.6 Residual Stresses ......................................................................................... 46

    4.2 Cooling ............................................................................................................... 48

    4.2.1 Coolant Circuit Temperatures .................................................................... 48

    4.2.2 Mold Temperatures .................................................................................... 50

    4.2.3 Part Temperatures ...................................................................................... 53

    4.2.4 Time to Reach Ejection Time .................................................................... 55

    4.3 Pressure ............................................................................................................. 56

    4.4 Weld Lines ........................................................................................................ 57

    4.5 Air Traps ............................................................................................................ 58

    4.6 Fiber Orientation............................................................................................... 59

    4.7 Economics and Performance............................................................................. 60

    5. CONCLUSION AND FUTURE WORK63

    5.1 Conclusion .......................................................................................................... 63

    5.2 Future Work ........................................................................................................ 64 Bibliography ..................................................................................................................... 65

  • x

    LIST OF TABLES page

    1. Table 1 Thermal properties of mold materials...10

    2. Table 2 Variables selected-waterline diameters....15

    3. Table 3 Variables selected-waterline pitch...16

    4. Table 4 Variables selected-waterline depth..17

    5. Table 5 Typical processing parameters for generic classes of resins....21

    6. Table 6 Materials selected with filler type and percentage25

    7. Table 7 Selected part thickness.26

    8. Table 8 Selected flow rates as measured by Reynolds numbers...28

    9. Table 9 Selected collant temperatures...29

    10. Table 10 Selected mold surface temperatures30

    11. Table 11 Recommended mold surface temperatures (molfdlow)..30

    12. Table 12 Selected melt temperatures...31

    13. Table 13 Recommended melt temperatures (mold flow)...32

    14. Table 14 Selected ejection temperatures.....33

    15. Table 15 Recommended ejection temperatures..33

    16. Table 16 Select frozen temperature...34

  • xi

    17. Table 17 Resulting L27 orthoginal array (taguchi method)...35

    18. Table 18 Hardware & software used...36

    19. Table 19 Finite element model statistics.37

    20. Table 20 Results considered........39

    21. Table 21 Deflection and Ejection time compared for aluminium,steel and copper

    tool62

  • xii

    LIST OF FIGURES

    page

    1. Figure 1 HVAC duct ...................................................................................................... 3

    2. Figure 2 L27 (13 factors with 3 levels) orthogonal array .............................................. 5

    3. Figure 3 Mold geometry ................................................................................................ 7

    4. Figure 4 Thermal diffusivity as a function of endurance limit of mold materials .......... 9

    5. Figure 5 Thermal conductivity vs Thermal diffusivity of engg materials at room

    temperature10

    6. Figure 6 Modulus versus strength of engineering materials ........................................ 11

    7. Figure 7 Typical dimensions for cooling channels..14

    8. Figure 8 Waterline depth as measured for this project. .17

    9. Figure 9 A typical view of the mold with part and waterlines connected in series.18

    10. Figure10 Part with various gate locations20

    11. Figure 11 Processing window for melt temperature of generic plastics..23

    12. Figure 12 Processing window for mold temperature of generic plastics..24

    13. Figure 13 Recommended ejection temperatures of generic plastics.24

    14. Figure 14 Finite Element Model..39

    15. Figure 15 An example of dimensional deflection41

    16. Figure 16 Effect of studied parameters on combined deflection effects....41

    17. Figure 17 An example of corner effects on a box shape. .42

  • xiii

    18. Figure 18 Effect of studied parameters on corner effects.43

    19. Figure 19 Effect of studied parameters on differential cooling.44

    20. Figure 20 Effect of studied parameters on all differential shrinkage..45

    21. Figure 21 Effect of studied parameters on orientation effect....46

    22. Figure 22 Effect of studied parameters on all 1st residual stress.47

    23. Figure 23 Effect of studied parameters on 2nd

    residual stress.47

    24. Figure 24 Effect of studied parameters on highest circuit cooling temperature

    bottom........................................49

    25. Figure 25 Effect of studied parameters on highest circuit cooling temperature

    top..............................................................................................................49

    26. Figure 26 Effect of studied parameters on highest mold temperature - top50

    27. Figure 27 Effect of studied parameters on lowest mold temperature top51

    28. Figure 28 Effect of studied parameters on mold T - top..51

    29. Figure 29 Effect of studied parameters on highest mold temperature bottom52

    30. Figure 30 Effect of studied parameters on lowest mold temperature - bottom..52

    31. Figure 31 Effect of studied parameters on mold temperature T top.53

    32. Figure 32 Effect of studied parameters on temperature differential..54

    33. Figure 33 Effect of studied parameters on heat flux - bottom54

    34. Figure 34 Effect of studied parameters on heat flux - top..55

    35. Figure 35 Effect of studied parameters on time to reach ejection temperature..56

    36. Figure 36 Effect of studied parameters on pressure at the V/P switchover57

  • xiv

    37. Figure 37 Weld lines are indicated by the multicolored lines58

    38. Figure 38 Fiber orientation with air traps..59

    39. Figure 39 Typical Fiber Orientation..60

  • xv

    SOFTWARE SPECIFICATION

    The work was performed utilizing Autodesk Moldflow software. The exact

    configuration is detailed in below.

    Hardware and Software Used

    Computer Dell Dimension 9100

    Processor GenuineIntel x86 Family Model 15 Stepping 6 ~2393 x2

    Memory 2045 Mbytes

    Operating

    System

    Windows XP Service Pack 3

    Software Autodesk Moldflow (ami2010-main (Build 09114-001) 32-bit

    build

  • 1

    Chapter 1

    INTRODUCTION

    1.1 Background

    As discussed in the article exploration of use of advanced aluminium alloys for

    improved productivity in plastic injection molding( Nerone et. al,. 2000) for many years,

    the automotive industry has used both aluminum molds and steel molds for injection

    molding. Aluminum molds have been used primarily for prototype tooling. Due to the

    relative softness of aluminum compared to steel, aluminum tools are able to be quickly

    and cheaply manufactured which is an advantage for a prototype tool. Unfortunately, the

    types of aluminums used were prone to wear and fatigue issues. Aluminum tools

    generally were assumed to last in the range of hundreds of parts rather than the tens of

    thousands of parts needed for an automotive production application. Thus, automotive

    parts required the use of steel tooling for production parts. Additionally, the different

    thermal properties of aluminum compared to steel made it difficult to apply the lessons

    learned in the processing of the prototype parts to production parts.

    Recently, aluminum companies such as Alcoa and Alcan have introduced new grades of

    aluminum that are purported to be a viable replacement to steel as a mold material in

    many applications. The new aluminum tools hold the promise of reducing tool

    manufacturing time and cost, decreasing cycle time and thereby piece cost, and

    improving part quality.In a paper by name exploration of use of advanced aluminum

  • 2

    2

    alloys for imporved productivity in plastic injection molding, a comparision of the

    thermal conductivity of new aluminium alloys and tool steel is been made, so as an

    extension to the project I have conducted an experimental investigation of the effect of

    these two mold materials in molding performance,This project focuses on dimensional

    stability of part produced when these mold materials have been used and also the effects

    of variuos parameters on molding performance.

    1.2 Objectives

    This study had two objectives:

    Investigate the effect on the part molding process of aluminum tooling while

    investigating whether the contribution of the tooling or other factors such as

    design or molding parameters are more important

    Investigate the molding performance of aluminum tooling versus steel tooling

    The focus of this study was to examine an automotive part that would be a prime

    candidate for the use of the new aluminum molds. The largest downside with the new

    aluminum molds appears to be they still do not retain texture on the mold as well as a

    steel mold; therefore, non-visible parts which will not have texture are great candidates.

    An example of a larger non-visible part is an HVAC defroster duct. The traditional

    HVAC duct is generally made from two halves (Figure 1) that are attached together

    forming a tube, often with considerable bends and twists to go around other components

  • 3

    or to reach distant window demister locations. Generally both halves are formed in a

    family mold and warp in nearly all directions is a very real concern.

    This study utilized mold flow software and Taguchi methods to determine whether

    replacing steel tooling with aluminum tooling makes sense from a molding performance

    point of view. At the same time, this study investigated many input parameters from the

    design stage, though the tooling stage, and finally to processing to determine what were

    the key contributors.

    Figure 1 HVAC duct

  • 4

    1.3 Procedure and Methodology

    The primary focus was to study the two parts using Moldflow software. The effect of

    different mold design, part design, and processing considerations were considered in

    terms of part quality and cycle time. Using information gained from the CAE analysis

    performed, a discussion of whether aluminum tooling is feasible in terms of molding

    performance will be discussed.

    Autodesk Moldflow plastic injection molding simulation software, part of the Autodesk

    solution for Digital Prototyping, is a tool that help manufacturers validate and optimize

    the design of plastic parts and injection molds, and study the plastic injection molding

    process. Auto desk mold flow simulation software helps to reduce the need for costly

    physical prototypes, avoid potential manufacturing defects, and get innovative products

    to market faster.

    To analyze if aluminium can be replaced with steel as mold material in plastic injection

    molding, the following parameters have been supplied to autodesk mold flow software as

    input variuables: mold parameters, part design parameters, process parameters.The output

    of simulation would be the effects of dimensional stability of the part, varying pressures

    in part, weld lines, fiber orientation are being studied as outputs of simulation which are

    discussed in chapter 4 of this report.

  • 5

    1.4 Computer Simulation Parameters for Taguchi Method DOE

    The first section of the report, chapter 2 and part of chapter 3 will explain many of the

    important parameters that effect the final part condition. Each parameter will be grouped

    into either a mold parameter, part design parameter, or process parameter. The study

    explains the reason for choosing or not choosing a parameter and if chosen what factor

    levels will be used. Finally, a full L27 (13 factors with 3 levels) orthogonal array (

    Figure 2) will be presented with a discussion of the results .

    Figure 2 L27 (13 factors with 3 levels) orthogonal array

  • 6

    Chapter 2

    VARIABLE PARAMETERS OF INJECTION MOLDING

    2.1 Mold Parameters

    A tool engineer when designing a mold will make key decisions that influence the

    molding process. Primarily, the key considerations to be made by the mold engineer are

    the mold size, what mold material will be selected, how the waterlines will be laid out,

    and the method of runners and gates.

    2.1.1 Mold Dimensions

    There are many considerations for a mold engineer to consider when choosing the core

    and cavity block size such as packaging any actions and ensuring structural integrity of

    the mold. The mold itself can act as a heat sink, and affect the molding process. But,

    typically other considerations such as mass and cost of the mold material and the ability

    to fit the mold between the platens and tie rods of the molding machine, dictate that the

    smallest mold possible be used. The mold dimensions for this project are fixed and are

    based on the actual cavity and core dimensions of the real life part. The die draw of the

    mold is shown in Figure 3. For clarity, the two mold halves are referred to as top and

    bottom rather than cavity and core.

  • 7

    Figure 3 Mold geometry

    2.1.2 Mold Material

    Selection of the mold material is an important decision for any mold engineer. Two

    typical scenarios can explain the importance of mold material selection.

    In the first scenario, a prototype mold to produce a prototype part needs to be constructed

    quickly. Build time and fabrication cost are important considerations for a prototype

    mold. An aluminum mold is often selected because of the ability to quickly and cheaply

    fabricate the mold due to relative ease of machining aluminum. However, there are

    drawbacks. The aluminum mold typically wears relatively quickly and therefore is not

    suitable for production volumes. Additionally, when the part is eventually built on a

  • 8

    production tool, it is often observed that the processing characteristics of the part are

    quite different than what was observed on the prototype tool. Typically this is attributed

    to the substantial differences in thermal properties of the aluminum prototype mold

    versus the steel production mold.

    In the second scenario, a production mold is built. Cost and timing are important, but

    when weighed against the possibility of premature wearing and ultimately the failure of

    the tool, which could shut down production of an automotive assembly line, durability is

    the key factor. For this reason, tool steels are typically chosen for production injection

    mold tools. While machining can be onerous by comparison, creating higher cost and

    taking longer to manufacture, steel molds are durable and can produce a very high

    quantity of parts.

    Typically mold material selection is a tradeoff of mechanical property versus thermal

    properties. High mechanical properties are desired as well as high thermal properties.

    Unfortunately, as can be seen from Figure 4 through Figure 6 and in Table 1, typical

    mold materials such as steel, aluminum, and copper do not meet all the requirements

    simultaneously. Steel typically has high mechanical properties whilst low thermal

    properties and copper and aluminum typically have high thermal properties but low

    mechanical properties.

    Three different mold materials were chosen as variables. The first is a new generation of

    high strength aluminum professed to be engineered to meet the requirements of a

  • 9

    production injection mold, QC-10. The second is the workhorse material of injection

    molding, P-20 (Kazmer, 2007, p. 85). Third is a copper alloy C18000, which is typically

    used in molds for its very high thermal properties.

    Figure 4 Thermal diffusivity as a function of endurance limit of mold materials

    (Kazmer, 2007, p. 85)

  • 10

    Table 1 - Thermal Properties of Mold Materials

    Figure 5 - Thermal conductivity vs Thermal diffusivity of engg materials at room

    temperature

    (Ashby M. F., 2005, p. 66)

  • 11

    Figure 6 - Modulus versus strength of engineering materials

    (Ashby, Shercliff, & Cebon, 2010, p. 118)

    2.1.2.1 Aluminum Alloy (Injection Molding Grade) - QC-10

    Aluminum alloys have traditionally been used in injection molding for prototype

    tooling. While having thermal properties superior to steel, they typically are not

    suitable to meeting the high number of cycles of an injection mold. Aluminum

    manufacturers, notably Alcoa with its QC-10 grade and Alcan with its Alumold

    500 line have attempted to break into the production mold market with new

    aluminum alloys specifically engineered to be used in high cycle production

  • 12

    molds. While still not matching the strength of steel, it is noted to be sufficiently

    strong and offers the advantages over steel of easy tool manufacturing and

    superior thermal properties (Skillingberg, 2004).

    2.1.2.2 Tool Steel - P-20

    P-20 steel is a commonly chosen high grade forged tool steel for injection molds.

    Basically, P-20 is an AISI-4130 or AISI-4140 steel (sometimes this group of

    chromium-molybdenum steels is referred to chrome moly steels) with more

    stringent requirements resulting in less impurities and a more homogenous

    microstructure. It is a good mold material due to its high toughness, lack of

    internal defects, uniformity, pre-hardened state, and ability to be textured or

    polished to nearly any finish. (Rosato, Rosato, & Rosato, 2000, pp. 334-7)

    2.1.2.3 Copper Alloy - Be-Cu C18000

    Copper alloys such as that shown in Error! Reference source not found., have a

    lace in mold manufacturing due to their high heat transfer which can be 10 times

    that of tool steels. Unfortunately, they have low resistance to wear, low

    toughness, and low compressive strength. (Rosato, Rosato, & Rosato, 2000, p.

    343) Traditionally they are an alloy of Beryllium-Copper (Be-Cu). More

    recently, health concerns with the machining of beryllium have caused the

    creation of beryllium free alloys in which nickel replaces the beryllium. (Baranek)

    Some Be-Cu thermal conductivity copper alloy. (Engelmann & Dealey,

  • 13

    Maximizing Performance Using Copper Alloys, 1999) Be-Cu C18000 , having

    both good mechanical and thermal properties whilst being beryllium free was

    chosen for this study.alloys typically chosen for mold cores are Be-Cu C17200, a

    high hardness Be-Cu; Be-Cu C17510, a high thermal conductivity Be-Cu; and Be-

    Cu C18000 a Ni-Si-Cr hardened high

    2.2 Waterline Parameters

    Waterline geometry is an important consideration when designing a mold. One of the

    primary functions of the mold is its ability to efficiently and evenly pull heat from the

    part to solidify it. Different geometry choices of waterlines result in different cooling

    performances depending on which mold materials are used. Three important geometry

    choices are waterline diameter, depth, and pitch (Figure 7). (Shoemaker, Hayden,

    Engelmann, & Miller, 2004)

  • 14

    Figure 7 Typical dimensions for cooling channels

    2.2.1 Waterline Diameter

    Waterlines are typically circular due to the fact that machining a feature for a

    waterline in a mold is most efficiently performed with a gun drill. This leaves the

    diameter to be the only variable. Previous studies have indicated that waterline

    size was not found to have a significant effect on temperature uniformity of the

    molding surface but did significantly affect the average temperature of the

    molding surface. (Shoemaker, Hayden, Engelmann, & Miller, 2004, p. 824)

    National Pipe Thread (NPT) sizes are typically used in mold construction in the

    US; the sizes used in this study are in

    Table 2. (Rees, 2002, p. 298)

  • 15

    Table 2 Variable selected - Waterline diameters (ANSI/ASME B1.20.1 - 1983 (R1992))

    Pipe Size (in) Drill Size

    Drilled Waterline Diameter

    (in) (mm)

    1/4 NPT 7/16" 0.4375 11.1

    3/8 NPT 9/16" 0.5625 14.3

    1/2 NPT 11/16" 0.6875 17.5

    2.2.2 Waterline Pitch

    Waterline pitch is the spacing between each waterline as shown in Figure . The

    pitch is often calculated as a multiple of the waterline diameter (Rees, 2002, p.

    300). While waterline pitch is fairly standardized in steel molds, it has been

    shown that the introduction of mold materials with high thermal conductivity

    creates a need to reevaluate waterline pitch and depth. Typically larger pitch can

    be used to achieve equal or improved surface temperature uniformity due to the

    higher thermal conductivity. (Shoemaker, Hayden, Engelmann, & Miller, 2004)

    The waterline pitch values investigated in this study are listed in table 3.

  • 16

    Table 3 Variable selected - Waterline pitch as measured by multiple of waterline

    diameter

    Waterline Pitch

    2.5 x Diameter

    5 x Diameter

    10 x Diameter

    2.2.3 Waterline Depth

    Waterline depth is often measured as a multiple of waterline pitch which is itself a

    multiple of waterline diameter. (Rees, 2002, p. 300) Typically the depth of the

    waterline is calculated such that the waterline is as close to the surface as possible

    while maintaining adequate distance from the surface in order to ensure the

    structural integrity of the mold. The waterline depths investigated in this study

    are listed in table 4. However, as 27 unique waterlines were required for this

    experiment, it was beyond the scope of this study to optimize waterlines for each

    scenario. The Moldflow waterline wizard was used which only allows one level

    and no baffles. While perhaps a thickness of only 8.3mm of steel between

    waterline and part would be judged by a tooling engineer to be insufficient in a

    real mold due to structural integrity, for the purpose of this study it was judged

    adequate. The 8.3mm was an acceptable compromise as the dimension measured

  • 17

    is to the closest point of waterline and part which only occurred in a small

    localized area. In the case of the largest distance, the waterline depth was

    35mm.

    Table 4 Variable selected - Waterline diameter as measured by multiple of

    waterline diameter

    Refer to Figure 8 andFigure 9 for actual examples of waterline diameter, pitch, and depth

    from this study.

    Figure 8 Waterline depth as measured for this project.

    Note that because the waterlines reside in one plane, waterline depth is measured to the

    closest point from the plane in which the waterlines are to the part.

    Waterline Depth

    0.75 x Diameter

    1.5 x Diameter

    2 x Diameter

  • 18

    Figure 9 - A typical view of the mold with part and waterlines connected in series.

    Note-diameter, pitch, and depth vary.

    2.3 Gating

    The gating location of the part is an important consideration. Typically the flow length of

    the material determines how many gates are needed and the gates are then spread out in a

    manner such that each gate fills approximately the same amount of material volume. The

    gate positions for this project were positioned to have equal filling amounts from the

    center of the tool along the parting line (Figure 10). Different gating geometries were not

    investigated as part of this study.

  • 19

    Figure10 Part with various gate locations

    Arrows indicate gate location and colored zones are typical fill regions for each gate

    2.4 Part Design Parameters

    The design engineer makes many choices during the engineering of a plastic part that will

    affect molding results such as cycle time and part warpage. Two important items the

    design engineer will select are material and geometry. While material is easier to define

    for the purpose of this study, geometry is not as an infinite amount of shapes could be

    chosen. However, one very important geometry parameter, thickness (assuming that it is

    uniform) is easy to define.

    2.4.1 Plastic Types

    One of the biggest decisions any design engineer has is the selection of material.

    Injection molded parts are no different. A basic introductory course in plastics will

    introduce the general rule of thumb that amorphous parts are typically more

  • 20

    dimensionally stable then semi-crystalline parts. Also, fillers, especially fiber fillers, can

    create complex anisotropic properties. Therefore it is logical that to examine the

    influence of material selection.

    2.4.2 Plastic Families

    For this study, generic plastic families were chosen based on two primary criteria,

    common usage in the automotive industry and a similar processing window. The

    first criteria being important as the part under investigation is automotive, the

    latter being important so as to be able to consider processing parameters as

    variables and use similar process settings regardless of the specific material being

    used on a sample.

    The first step to determine the material choices was to consult a table of common

    generic plastics (Table 5). Polypropylene is a very common commodity plastic

    used in HVAC parts. Two additional materials were then sought with similar

    processing criteria in terms of melt temperature, mold temperature, and ejection

    temperature(Figure 1 - Figure 3). ABS has nearly identical processing

    parameters. It is a common automotive material and as a bonus for this study, it is

    an amorphous plastic as opposed to the semi-crystalline polypropylene allowing

    for the study of whether this may have influenced the results. Finally polystyrene

    was chosen to have a third material; while not as typical of an automotive

  • 21

    material, the very similar processing characteristics made it a workable choice for

    this study.

    Table 5 - Typical processing temperatures for generic classes of resins with the choices

    for this project

    are highlighted in green (Shoemaker, 2006, p. 289)

    Generic

    Name

    Melt Temp (C) Mold Temp (C) Ejection

    Temp (C)

    Min. Rec. Max. Min. Rec. Max. Rec.

    ABS 200 230 280 25 50 80 88

    PA 12 230 255 300 30 80 110 135

    PA 6 230 255 300 70 85 110 133

    PA 66 260 280 320 70 80 110 158

    PBT 220 250 280 15 60 80 125

    PC 260 305 340 70 95 120 127

    PC/ABS 230 265 300 50 75 100 117

    PC/PBT 250 265 280 40 60 85 125

    HDPE 180 220 280 20 40 95 100

    LDPE 180 220 280 20 40 70 80

    PEI 340 400 440 70 140 175 191

    PET 265 270 290 80 100 120 150

    PETG 220 255 290 10 15 30 59

  • 22

    PMMA 240 250 280 35 60 80 85

    POM 180 210 235 50 70 105 118

    PP 200 230 280 20 50 80 93

    PPE/PPO 240 280 320 60 80 110 128

    PS 180 230 280 20 50 70 80

    PVC 160 190 220 20 40 70 75

    SAN 200 230 270 40 60 80 5

    Figure 11 Processing window for melt temperature of generic plastics

    150

    200

    250

    300

    350

    400

    450

    Tem

    pe

    ratu

    re

    C

    Generic Plastics

    Melt Temperature of Generic Plastics

    Melt Temp (C) Max.

    Melt Temp (C) Min.

    Melt Temp (C) Rec.

  • 23

    Figure 12 Processing window for mold temperature of generic plastics

    Figure 13 Recommended ejection temperatures of generic plastics

    0

    50

    100

    150

    200

    Tem

    pe

    ratu

    re

    C

    Generic Plastics

    Mold Temperature of Generic Plastics

    Mold Temp (C) Max.

    Mold Temp (C) Min.

    Mold Temp (C) Rec.

    0

    50

    100

    150

    200

    SAN

    P

    ETG

    P

    VC

    LD

    PE PS

    PM

    MA

    A

    BS

    PP

    H

    DP

    E P

    C/

    AB

    S P

    OM

    P

    BT

    PC

    / P

    BT

    PC

    P

    PE/

    PP

    O

    PA

    6

    PA

    12

    P

    ET

    PA

    66

    P

    EI

    Tem

    per

    ature

    (C

    )

    Generic Plastics

    Ejection Temperatures

    Ejection Temp (C) Rec.

  • 24

    2.4.3 Fillers

    Fillers were chosen as a key part design criteria that could affect both cooling

    time and warpage. Materials were sought with common filler and loading

    percentages of 0, 10, and 30%. Glass fiber was chosen as the filler due its

    common use and because it was predicted that the high aspect ratio of glass fiber

    as opposed to other common fillers such as talc or glass beads would play an

    important role. (Fischer, 2003, p. 29) Unfortunately even with common materials,

    common fillers, and common loading percentages, it was not possible to find

    examples of all the materials with each filler type and loading percentage in the

    Moldflow library. In the case of PS, a 10% mineral filled PS had to be substituted

    for a 10% glass filled PS. For ABS, a 15% glass filled ABS had to be substituted

    for a 10% glass filled ABS.

    2.4.4 Plastics Grades

    Given the criteria of plastic families and fillers presented above. Materials were

    chosen from the Moldflow library. They are listed in table 6

  • 25

    Table 6 Materials selected with filler type and percentage

    Generic Name Manufacturer Trade Name FILLER FILLER

    %

    PP Basell Pro-fax SD242 N/A N/A

    PP Arkema Pryltex V4010HL12 Glass Fiber 10%

    PP Arkema Pryltex V4030HL12 Glass Fiber 30%

    PS Chevron Phillips MC3200 N/A N/A

    PS SABIC CM-3260 Mineral 10%

    PS RTP RTP 0405 Glass Fiber 30%

    ABS DOW Magnum 3404 N/A N/A

    ABS SABIC Thermocomp AF-1003M Glass Fiber 15%

    ABS LG Chemical Lupos GP-2300 Glass Fiber 30%

    2.4.5 Part Thickness

    The geometry of a part is important, especially in terms of warpage. Consider the

    difficulties in molding a five sided box with no warpage. (Bakharev, Zheng, Costa, Jin, &

    Kennedy, 2005) However, to study the effects of different geometries was too large in

    scope to attempt due to the need to create models for each unique geometry and an

    infinite amount of geometries to choose from. One aspect of geometry, part thickness, is

    easy to model in Moldflow when using mid-plane analysis. Part thickness was chosen

  • 26

    for its obvious effect on cooling time and less obvious effects on warpage such as

    different shear stress and orientation effects.

    A typical range of part thickness for automotive HVAC parts of 2.0 to 3.0mm was

    selected. The parts are modeled with standard injection molding guidelines of uniform

    thickness. (Malloy, 1994, pp. 64-65)

    Table 7 Selected part thickness

    Part Thickness (mm)

    2.0

    2.5

    3.0

    2.5 Processing Parameters

    The processing engineer has the complicated task of selecting the proper settings for the

    injection molding process. Some of the more important parameters were chosen as

    variables and the details of each are explained below.

    2.5.1 Coolant Parameters

    While the coolant can be various fluids, water and oil are the most common. In the case

    of using the coolant only to cool the mold (as opposed to heating coolant material for this

    experiment. Water is often recirculated in a closed loop system that typically has two

  • 27

    variables, coolant flow rate and coolant temperature.it), water is commonly used although

    ethylene glycol and oil are sometimes used. Water is selected as the

    2.5.2 Coolant Flow Rate

    Coolant flow rate needs to be sufficient enough to prevent the water from raising

    in temperature a significant degree while it is in the mold. If the water

    temperature rises too much, it could cause different amounts of cooling across the

    part. Typical recommendations are to keep the coolant temperature from rising

    more than 6C between the inlet and outlet. (Rees, 2002, p. 303) However, it

    should be noted that some sources advocate keeping the temperature delta to less

    than 0.1C for precision parts. (Kazmer, 2007, p. 208) Additionally, liquids cool

    less efficiently with laminar flow than with turbulent flow. Because the diameter

    is also a variable thereby complicating any use of volumetric rate as a variable, it

    then made most sense to use the Reynolds number to describe the flow rate. In

    laminar flow with water, the outer layer can prove to be significantly higher in

    temperature at the outer laminate than near the core. Turbulence begins in circular

    cooling channels at a Reynolds number about Re 2300. (Osswald, Turng, &

    Gramann, 2008, p. 302) To ensure efficient cooling a Reynolds number of Re

    4000 (Kazmer, 2007, p. 209) to 10000 (Osswald, Turng, & Gramann, 2008, p.

    302) is recommended. This study used Re 4000, Re 10000, and Re 20000 to

    determine the effect of lower versus higher turbulence (Table 8).

  • 28

    Table 8 Selected flow rate as measured by Reynolds numbers

    2.5.3 Coolant Temperature

    Setting coolant temperature is a balance between cycle time and part quality. The

    lower the coolant temperature, the lower the cycle time. However, lower coolant

    temperature can result in higher residual stresses. Typically the coolant

    temperature is selected to be slightly above the freezing temperature of the liquid.

    Depending on whether the water is cooled from a central location or press side,

    and depending on the season, coolant temperature may vary. (Osswald, Turng, &

    Gramann, 2008, p. 303) Coolant temperatures of 10, 20, and 30C were selected

    for this study to range from a temperature above freezing to the room temperature

    of a hot summer day (table 9)

    Flow Rate (Reynolds Number)

    4000

    10000

    20000

  • 29

    Table 9 - Selected Coolant Temperatures

    Coolant Temperature C

    10

    20

    30

    2.6 Mold Surface Temp

    High mold surface temperatures can allow a processing window of lower pressure

    resulting in lower shear stress. The effect of mold surface temperature on pressure and

    shear stress is usually found to be lower than that of melt temperature. (Shoemaker,

    2006, p. 22) Additionally, lower injection speed can be used with higher mold surface

    temperatures due to slower cooling of the melt flow. Mold surface temperatures of 35,

    50, and 65C were chosen for this study (table 10) to fall within the range of

    recommended mold surface temperatures for each material studied (table 11)

    Table 10 Selected Mold Surface Temperatures

    Mold Surface Temperature C

    35

    50

    65

  • 30

    Table 11 - Recommended Mold Surface Temperatures (Moldflow)

    Generic

    Name Manufacturer Trade Name FILLER FILLER %

    Min.

    Mold

    Surf.

    Temp.

    C

    Rec.

    Mold

    Surf.

    Temp.

    C

    Max.

    Mold

    Surf.

    Temp.

    C

    PP Basell Pro-fax SD242 - - 20 50 80

    PP Arkema Pryltex V4010HL12 Glass Fiber 10% 40 50 60

    PP Arkema Pryltex V4030HL12 Glass Fiber 30% 20 40 60

    PS Chevron Phillips MC3200 - - 25 48 70

    PS SABIC CM-3260 Mineral 10% 20 50 70

    PS RTP RTP 0405 Glass Fiber 30% 40 50 65

    ABS DOW Magnum 3404 - - 25 50 80

    ABS SABIC Thermocomp AF-1003M Glass Fiber 15% 40 60 80

    ABS LG Chemical Lupos GP-2300 Glass Fiber 30% 25 50 80

    2.7 Melt Temp

    Melt temperature is an important process variable. Low melt temperatures will result in

    higher viscosity melt, requiring a higher pack pressure and resulting in high shear

    stresses. High melt temperatures reduce the pressure needed, but also results in high

    volumetric shrinkage. If temperatures are too high, the material can also degrade.

    Additionally, higher melt temperatures result in longer cooling time, but not as markedly

  • 31

    as higher mold temperatures. (Shoemaker, 2006, p. 22) Melt temperatures of 210, 230,

    and 250C (table 12) were chosen for this study , which span the recommended melt

    temperature processing window of the three main material families (table 13)

    Table 12 - Selected Melt Temperatures

    Melt Temperature C

    210

    230

    250

    Table 13 -Recommended Melt Temperatures (Moldflow)

    Generic

    Name Manufacturer Trade Name FILLER FILLER %

    Min.

    Melt

    Temp. C

    Rec.

    Melt

    Temp.

    C

    Max.

    Melt

    Temp.

    C

    PP Basell Pro-fax SD242 - - 200 230 280

    PP Arkema Pryltex V4010HL12 Glass Fiber 10% 220 235 290

    PP Arkema Pryltex V4030HL12 Glass Fiber 30% 200 240 300

    PS Chevron Phillips MC3200 - - 200 230 300

    PS SABIC CM-3260 Mineral 10% 180 230 320

    PS RTP RTP 0405 Glass Fiber 30% 210 230 265

    ABS DOW Magnum 3404 - - 200 230 320

    ABS SABIC Thermocomp AF-1003M Glass Fiber 15% 220 240 280

    ABS LG Chemical Lupos GP-2300 Glass Fiber 30% 200 230 320

  • 32

    2.8 Ejection Temp

    Ejection temperature is the surface temperature of the part when ejected. Because it

    would take many minutes for the part to reach an equilibrium state, with a uniform

    temperature throughout the part, the part is often ejected as soon as the part has reached a

    temperature cool enough to maintain its shape during and after ejection. The part will

    continue to shrink during the cooling phase, so by keeping the part in the mold longer

    (lowering the ejection temperature), it can help to prevent warp. However, the longer it is

    kept in the mold, the longer the cycle time, so a balance must be reached. The ejection

    temperature is usually recommended by the material manufacturer (table 15). For this

    project, ejection temperatures of 80, 90, and 100C were chosen (table 14)

    Table 14 - Selected Ejection Temperatures

    Ejection Temperature C

    80

    90

    100

  • 33

    Table 15 -- Recommended Ejection Temperatures (Moldflow)

    Generic

    Name

    Manufacturer Trade Name FILLER FILLER

    %

    Rec. Eject.

    Temp. C

    PP Basell Pro-fax SD242 - - 116

    PP Arkema Pryltex V4010HL12 Glass Fiber 10% 113

    PP Arkema Pryltex V4030HL12 Glass Fiber 30% 95

    PS Chevron Phillips MC3200 - - 86

    PS SABIC CM-3260 Mineral 10% 80

    PS RTP RTP 0405 Glass Fiber 30% 89

    ABS DOW Magnum 3404 - - 88

    ABS SABIC Thermocomp AF-1003M Glass Fiber 15% 95

    ABS LG Chemical Lupos GP-2300 Glass Fiber 30% 88

    2.9 Frozen Percentage

    An alternative method of determining when to eject plastic is by checking the frozen

    percentage. This is easy to do in a software simulation, but less easy to do in reality.

    How can one on a processing floor instantly cut into a part and then measure how much

    has solidified and how much is liquid? But, it is an interesting observation to check not

    only the surface temperature from the previous section, but also to check solidification on

    a volumetric temperature approach, which in this case is how much of the part has

    reached a temperature below the melt temperature in cooling. Frozen percentages of 100,

    95, and 90 were selected table 16.

  • 34

    Table 16 -- Selected Frozen Percentage

    Frozen Percentage

    100%

    95%

    90%

  • 35

    Chapter 3

    TAGUCHI METHOD ORTHOGONAL ARRAY

    The previously described variables in chapter 2 result in a L27 (13 factors with 3 levels)

    orthogonal array. The array is shown in Table 17 below. Taguchi methods were used to

    analyze the results and are described in this chapter. The taguchi method is used over

    here to come up with a optimum set of parameters to achieve otpmised results in the

    simulation.

    Table 17 - The resulting L27 (13 factors with 3 levels) orthogonal array for the

    experiment

  • 36

    3.1 . Setup

    3.1.1 Equipment

    The study was performed utilizing Autodesk Moldflow software. The exact

    configuration is detailed in table 18.

    Table 18 - Hardware and Software Used

    Computer Dell Dimension 9100

    Processor GenuineIntel x86 Family Model 15 Stepping 6 ~2393 x2

    Memory 2045 Mbytes

    Operating

    System

    Windows XP Service Pack 3

    Software Autodesk Moldflow (ami2010-main (Build 09114-001) 32-bit

    build

    3.2 Finite Element Model

    A mid-plane mesh of the part was created and is shown in Figure . A midplane mesh was

    chosen for this experiment primarily due to the ability to vary the part thickness in

    Moldflow which is not possible in a full 3d mesh. Additionally the mid-plane mesh

  • 37

    keeps the computing time reasonable as some runs can take up to 8 hours and full 3-D

    analysis would have extended the computing time needed even further. Information

    regarding the mesh is provided in table 19.

    Table 19 -- Finite Element Model Statistics

    Mesh type Midplane

    Number of nodes 17778

    Number of beam elements 1342

    Number of triangular

    elements

    31494

    Number of tetrahedral

    elements

    0

  • 38

    Figure 14 - Finite Element Model

  • 39

    Chapter 4

    RESULTS AND DISCUSSIONS

    The results considered are listed in Table 20 below. The results discussed are obtained

    from computer simulation done in autodesk mold flow software.

    Table 20 - Results Considered

    4.1 Dimensional Stability

    Dimensional stability or as some may refer to it, deflection or warpage is the difference

    between the nominal position and actual molded position. In terms of dimensional

    stability, the smaller the deflection, the better the quality of the part. When it comes to

  • 40

    the automotive industry today, it is not uncommon for parts to have tolerances in the

    tenths of millimeters.

    Dimensional stability will be evaluated by measuring the distance from nominal position

    to the as molded position of a point at the extreme edge of the part which was seen to

    have some of the worst warpage issues (figure 5).

    Figure 15 An example of dimensional deflection

    The measurement for all deflection values is the difference between the nominal and

    actual values of a key point at the extremity of the upper arm.

    4.1.1 Deflection Combined Effects

    Deflection is one of the primary considerations in this report. The Deflection

    Combined Effects result (Figure 6) is the most important deflection result as it

  • 41

    shows the final part condition and incorporates all the other deflection categories

    into a sum total.

    Somewhat surprisingly, the variable with the largest effect is melt temperature.

    Plastic type, mold material, and fillers also all have significant contributions.

    Waterline and coolant made almost no difference. Also, as it is typically taught

    that the longer the part is held in the mold, the more dimensionally stable it is, one

    would have expected ejection temperature or frozen percentage at ejection to

    make a larger contribution, but they didnt. Also unexpectedly, the QC-10 had

    higher deflection then the P-20.

    Figure 16- Effect of studied parameters on combined deflection effects

  • 42

    4.1.2 Deflection Corner Effects

    Corner effects, is the condition in molding which causes a part to shrink to the

    warmer side of the part. Consider a curve with thickness. The outside of the

    curve has more length then the inside of the curve. In a mold, the outside of the

    curve has more mold material to cool the plastic then the inside of the curve does.

    The inside of the curve takes longer to cool and causes the part to warp to the

    inside. An example is shown in figure 17.

    The Deflection Corner Effects result is similar to the Combined Affects (Figure

    6) result, except ejection temperature is less of a contributor (figure 18).

    Figure 17 - An example of corner effects on a box shape.

    The black is the nominal shape and the red is the molded shape due to corner effects

  • 43

    Figure 18 Effect of studied parameters on corner effects

    4.1.3 Deflection Differential Cooling

    Differential cooling is caused by different cooling rates at different locations of

    the plastic part. Differential cooling can be caused by either the part or the mold.

    For instance, if a part has both thick and thin areas, the thick areas will take longer

    to cool then the thin areas. Also, a certain area of the mold may be more difficult

    to cool causing differential cooling.

    The Deflection Different cooling result (Figure 19) shows a much tighter

    grouping of contributors then the Combined Effects result(Figure 6)However

    melt temperature and plastic type are still the strongest contributors along with

    mold temperature. The waterlines and coolant temperature make a difference, but

    not nearly as much as I would have thought.

  • 44

    Figure 19 Effect of studied parameters on differential cooling

    4.1.4 Deflection Differential Shrinkage

    Differential shrinkage can be thought of as differences in shrinkage of certain

    areas caused by factors such as the position relative to key factors such as the gate

    location or end of fill. (Shoemaker, 2006, p. 161)

    The melt temperature and plastic type make significant contributions to the

    Deflection Differential Shrinkage result (Figure 0) while mold material and

    fillers are also important. The graph is very similar to the Combined Effects

    result (Figure 16), except the contributions of the top four variables are even

    stronger in comparison to the other variables.

  • 45

    Figure 20 Effect of studied parameters on all differential shrinkage

    4.1.5 Deflection Orientation Effects

    Orientation effects are attributed to the alignment of the plastic molecules and

    fiber fillers due to the flow direction of the injected material.

    The orientation effects (figure 21) was strongest with the melt temperature and

    plastic type. Mold material and not surprisingly fillers also were strong

    contributors. What is somewhat surprising is that the fillers were not stronger

    contributors.

  • 46

    Figure 21 Effect of studied parameters on orientation effect

    4.1.6 Residual Stresses

    Residual stress is a state in which a part is mechanically stressed while there are

    no applied external forces. Residual stress is typically caused by differential

    cooling. (Potsch & Michaeli, 2007, pp. 147-148)

    Moldflow generates reports for biaxial stress. For 1st residual stresses (

    Figure 2) there were only two strong contributors, melt temperature and mold

    material. It makes sense that melt temperature was a strong contributor since it

    was also a strong contributor in differential cooling. Interestingly, the aluminum

    and Be-Cu material caused higher stresses then the steel. The 2nd

    residual stress

    results (figure 23) had no clear strong contributors, other than melt temperature.

  • 47

    Figure 22 Effect of studied parameters on all 1st residual stress

    Figure 23 - Effect of studied parameters on 2nd

    residual stress

  • 48

    4.2 Cooling

    For the cooling section, the study will look at results the input variables have in terms of

    the cooling circuit temperatures, mold temperatures, part temperatures, and heat flux.

    While none of these are characteristics of the final part, they can shed important light

    onto how some of the characteristics of the final part came to be.

    4.2.1 Coolant Circuit Temperatures

    As previously noted, coolant circuit temperatures are important because they can

    affect the temperature of the mold and the mold affects the temperature of the part

    and how quickly it can cool. It is recommended that the temperature differential

    between coolant inlet and outlet be small in order to make dimensionally stable

    parts.

    The strongest factor in the highest coolant temperature is the inlet temperature.

    However, this is really not of any interest since of course a higher inlet coolant

    temperature results in a higher outlet coolant temperature. The only other factor

    making a strong contribution is the Reynolds number. Low Reynolds numbers,

    which correspond with low flow rates, experienced a strong correlation with high

    outlet temperature. The longer residence time seems to be a stronger contributor

    then the higher turbulence. Results of coolant circuit temperatures are shown in

    figure 24 and figure 25.

  • 49

    Figure 24 Effect of studied parameters on highest circuit cooling temperature bottom

    Figure 25 Effect of studied parameters on highest circuit cooling temperature top.

  • 50

    4.2.2 Mold Temperatures

    For mold temperatures, a series of results are presented on figure 26 through

    figure 31. Shown in these results are the highest mold temperature during the

    cycle, the lowest mold temperature during the cycle, and the difference between

    the two values. The highest mold temperature is dominated by the mold material

    and mold temperature setting. The lowest mold temperature is primarily

    dependant on the coolant temperature. The difference between these two values

    is dependent on the three previously noted variables.

    Figure 26 Effect of studied parameters on highest mold temperature - top

  • 51

    Figure 27 Effect of studied parameters on lowest mold temperature top

    Figure 28 Effect of studied parameters on mold T - top

  • 52

    Figure 29 - Effect of studied parameters on highest mold temperature bottom

    Figure 30 Effect of studied parameters on lowest mold temperature - bottom

  • 53

    Figure 31 - Effect of studied parameters on mold temperature T top

    4.2.3 Part Temperatures

    Shown in Figure 2 through Figure 35 are graphs related to the part temperature

    properties. The temperature differential of the part is mostly dependant on the

    coolant temperature and the mold temperature. The heat flux shows a strong

    correlation with the mold material, coolant temperature, and mold temperature.

  • 54

    Figure 32 Effect of studied parameters on temperature differential

    Figure 33 Effect of studied parameters on heat flux - bottom

  • 55

    Figure 34 Effect of studied parameters on heat flux - top

    4.2.4 Time to Reach Ejection Time

    Figure shows the effect on the time to reach ejection temperature, more

    commonly referred to as the cycle time. This is one of the key performance

    indictors in terms of the economic viability of a part as the quicker the cycle time;

    the more parts can be made. Mold material, mold temperature, coolant flow rate,

    and part thickness were all important contributors. It was expected that mold

    material, mold temperature, and part thickness, would play important results in

    ejection time. Unexpectedly, ejection temperature and frozen percentage were of

    little importance. Also unexpectedly, the QC-10 tended to take longer to reach

    ejection temperature then P-20. The coolant flow rate had some unusual results

    with both high and low Reynolds number resulting in relatively high cycle time,

  • 56

    while the Reynolds number of 10000 showed significant improvement in cycle

    time.

    Figure 35 Effect of studied parameters on time to reach ejection temperature

    4.3 Pressure

    Pressure is equivalent to describing how hard the injection molding machine must work

    to force the plastic into the mold. A recommendation for pressure is that to mold a part it

    should not take more than fifty percent of the pressure that the injection molding machine

    can create. (Shoemaker, 2006, p. 28) Not surprisingly, the melt temperature especially,

    but also the fillers were strong contributors to pressure (figure 36).

  • 57

    Figure 36 Effect of studied parameters on pressure at the V/P switchover

    4.4 Weld Lines

    Weld Lines are areas where two flow fronts meet forming a weaker area know as a weld

    line or knit line.

    Moldflow presents weld lines as a graphical representation (figure 37). There was little

    difference between weld lines based on different processing parameters.

  • 58

    Figure 37 Weld lines are indicated by the multicolored lines.

    4.5 Air Traps

    Air traps are areas that plastic failed to fill. Typically they are created because either a

    flow front reaches an area of the mold that has inadequate venting or two flow fronts

    meet head on trapping a pocket of air between the flow fronts.

    The data Moldflow is able to report for air traps is a graphical representation of the

    locations of air traps. Shown in Error! Reference source not found., one can see there is

    little distinguishable difference between a part judged to have a high amount of air traps

    and one that has a low amount of air traps. Therefore, the processing parameters will not

    be investigated as to the affect on air traps. What can be noted is that the air traps are

    well aligned to weld lines shown in the previous section.

  • 59

    4.6 Fiber Orientation

    Fiber orientation was checked for each part containing fillers. Fiber orientation is

    reported by Moldflow graphically. There was no distinguishable difference for fiber

    orientation with the given variables. Typical fiber orientation is presented in Figure 39 .

    Figure 38 fiber orientation with air traps

    This figure shows there is little difference between what can be considered a part exhibiting high

    quantity of air traps (top set, run 25) and a part exhibiting low quantity of air traps (bottom set,

    run 23). The red circles show the areas of highest concentrations of air traps.

  • 60

    Figure 39 Typical Fiber Orientation

    4.7 Economics and Performance

    The justification for manufacturing a mold from high grade aluminum (QC-10) rather

    than traditional mold steel (P-20) in this case is difficult to justify based on the results.

    This report was meant to study the general effects of various part, mold, and processing

    parameters, not to choose the optimal set of conditions to make a specific part. One

  • 61

    cannot say that for any specific part whether aluminum or steel may make a better mold

    choice based on these results. However, the evidence from Figure and Figure shows

    that whether aluminum or steel is chosen, the part should have nearly the same deflection

    and ejection time results with the steel having slightly better results in both cases.

    Certainly this was unexpected, as one would have thought the superior heat transfer

    characteristics of the aluminum would at minimum cool the part quicker. Additionally

    there is case study evidence that would have led one to predict the aluminum to perform

    better. (Nerone, Iyer, & Ramani, 2000)

    The data obtained from the Taguchi experiment was looked at for further explanation.

    There were 27 experiments run, 9 for each mold material. The mean, minimum, and

    standard deviation were examined for each set of nine runs in Table 21. Since this data

    came from an orthogonal array set up for a Taguchi experiment, it was not intended to be

    set up to examine data from each run as though it was an independent optimized run so

    one might question the validity of examining these results in such a way. But it is

    illustrative that only in the case of minimum ejection time, did QC-10 perform better then

    P-20 and that BE-CU performed better than either.

    So, unless two Moldflow simulations are performed on a part, one for aluminum and one

    for steel, and the results compared, one should not assume that aluminum will perform

    better. Moreover, the recommendation should be to make the tool of steel for the

    superior wear and large amount of experience molders and toolmakers have with it unless

  • 62

    substantial improvements can be shown to exist for using aluminum through Moldflow

    simulation.

    Finally, while aluminum was not shown to have substantial advantages over steel, Be-Cu

    was and more investigation would be warranted in this material. Some studies have

    already suggested this (Engelmann, Dawkins, Shoemaker, & Monfore, 1997) , but real

    world use in terms of full molds seemed to be even less common then aluminum tooling.

    Typically, any use was restricted to small inserts.

    Table 21 - Deflection and Ejection Time Compared for Aluminum, Steel and Copper

    Tools.

    QC-10:aluminium alloy

    P-20: Tool Steel

    Be-CU :beryllium copper alloy

  • 63

    Chapter 5

    CONCLUSION AND FUTURE WORK

    5.1 Conclusion

    As predicted the mold material was a strong contributor in many aspects of the molding

    criteria. However, the QC-10 did not show the favorable results that were predicted. At

    the same time, some of the other criteria showed their importance while others were

    determined to be of little significance.

    From the variables studied, several proved to be dominant contributors. Melt temperature

    proved to be especially important in the deflection and stress criteria along with the

    material choice and to a lesser degree the mold material. The mold material and mold

    temperature proved to be especially important in terms of cycle time and heat removal

    from the part.

    Unexpectedly, there were several variables that when compared at the same time with

    other variables, made little or no difference in comparison to the dominant variables in

    any of the results studied. Amongst such variables were the waterline variables;

    diameter, depth and pitch as well as ejection signal variables; ejection temperature and

    frozen percentage. So while some studies, such as that by Shoemaker et al. (Shoemaker,

    Hayden, Engelmann, & Miller, 2004) found important the waterline variables, when

    compared against more variables, their significance was reduced.

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    5.2 Future Work

    An automotive hvac duct part is choosen to conduct of the tests to investigate the

    effects of replacing steel with aluminium alloy. With aluminium alloy as the

    mold material, it is being said that the high qualities of tetures of part cannot be

    achieved. So work can be extended to do a comparison of surface texture obtained

    when using steel as mold material to aluminum..

    Work can be extended by investing the effects on various products manufactured

    through injection molding process.

    Work can be extended by doing finite element analysis on parts generated from

    different mold materials, to have a better understanding of their behavior.

    FEA analysis of the mold can be conducted using CAE software's like catia, solid

    works etc.

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