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BASICS FOR CONTROLLING DEFECTS IN DIE CASTING OF ALUMINUM HPDC PARTS
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EC-515 Die CastingDefects
Dr. Steve Midson
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BASICS FOR CONTROLLING DEFECTS
You cant correct and control defectswithout first measuring and reportingthem.
The scrap reporting system must be setup for those who have to make
improvements, not just for the frontoffice.
The scrap report should be available toeveryone in the plant. In fact, it shouldbe posted on the bulletin board so
everyone can see it.
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BASICS FOR CONTROLLING DEFECTS
The daily scrap report must have the followingfeatures as a minimum:
1. It must be available first thing in themorning for the previous day
2. It must categorize scrap (as a minimum):
By defect type,By part number,
By die,
By shift,By operator,
By machine.
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The scrap reporting system should show longterm trends and be able to predict the customerrejects based on the current scrap activity -
Pareto charts are good ways to show theproblems
The report should include defects that are not
detected until the parts are downstream - and asystem developed so these defects can betracked to the shift and machine that produced
them All shots should be reported, even warm-up and
scrap that is returned to the furnace at the
machine (they cost in die life)
BASICS FOR CONTROLLING DEFECTS
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The process is complex, and a continuousreporting system must be set up to provide realtime feedback and effective process control if
defects are to be controlled.
The two major defects in die casting are surface
quality and porosity. Both of these requirejudgment decisions about severity.
This means a method of measuring the severityof defects is a requirement and must bedevised for many situations.
BASICS FOR CONTROLLING DEFECTS
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A rating system is intended to tell you if the defectproblems are getting better or worse, or whetherchanges made in the process are making a
difference.
What you are looking for is the ability to track anychanges or trends, and to know when corrections
are needed. This system also allows corrections tobe made before the defect level becomes a crisis.
The standards used for the rating system may notcoincide with the customer standards or the qualitydept. Ratings; they are for a different purpose anddo not need to coincide.
BASICS FOR CONTROLLING DEFECTS
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For example, you may rank a porosity defectfrom the worst to the best with rankings from 1to 5.
A capability study could be done as follows:
Take 6 sets of samples of 5 sequential castings
at intervals of 1/2 hr to 2 hr.
Rate each casting and average the total. This
gives the average quality level; this should bechecked against similar studies to determine ifthe process is improving or degenerating
BASICS FOR CONTROLLING DEFECTS
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One of the most difficult problems indeveloping a rating system is finding a methodof reporting and rating porosity
The most typical methods are x-ray, machining,or sawing.
A cheap and effective method is to use an oldlathe to approximately duplicate the customersmachining.
Always select examples for the rating systemand save them. They must not be used forany other purpose.
BASICS FOR CONTROLLING DEFECTS
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Thus defect corrections must start with a goodscrap reporting system
Developing this system may start with definingthe names of defects, which means a
document or board with samples and names ofdefects
Bottom line: YOU CANT IMPROVE IT IF YOUCANT MEASURE IT!
BASICS FOR CONTROLLING DEFECTS
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Die Casting Defects
1. Surface defects2. Laminations
3. Gas porosity
4. Blisters
5. Shrink porosity
6. Sinks7. Leakers
8. Cracks
9. Inclusions
10.Solder
11.Carbon12.Erosion/cavitation
13.Outgassing
14.Bending/warping
15.Flash
16.Stained castings17.Waves/lakes
18.Drags
19.Ejector pin defects
20.Cold flake
21.Excessive flux
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Surface Defects
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Causes Of Surface Defects
This part of the class is about those types ofdefects that appear on the surface of a diecasting
These defects are called by one of the followingnames:
Cold Flow Cold Shut Flow Lines Cold
Chill Non-fill
No-fill Poor-fill Laps Lines
Run Marks Misruns
Others:
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Pictures - Surface Defects
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Factors Controlling Surface Defects
A general list of the factors that control thiskind of defect is shown below. These arecontrolled by different people, maybe even
different companies The wall thickness
The casting shape
The fill time The flow pattern (gate design)
The die temperature
The metal temperature The type of alloy
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The first 2 factors on the list are controlled bythe part design Wall thickness and casting shape
Very important Regarding surface defect problems The wall thickness is the most critical,
Controls many casting parameters Required fill time
Required die temperature Distance the metal will flow Length of defect free surface that can be made
Good surface quality requires consistent wall
thickness, The designer and the die caster should focus on
reducing heavy sections
Try to make the wall thickness constant
Who Controls Surface Defects?
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The operating parameters for thin walls arevery different than for thick walls
A thin wall causes the flow to freeze and
develop cold flow quickly, For aluminum and magnesium, a typical
minimum wall thickness will be about 1.5mm
For a flow distance of about 150 mm or more For zinc, the minimum wall thickness would be
about 1.0 mm
Wall Thickness And Surface Defects
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Wall Thickness And Surface Defects
For example, see the change in fill timerequired by change in wall thickness:
Change in Wall
Thickness Fill Time Change Required
2 mm to 1.5 mm 25% reduction in fill time
3.5 to 3.0 mm 12% reduction in fill tim2
Thus a small variation in plunger speed (filltime) on a thin wall (say 2.0 mm ) casting is
very noticeable for surface defects, while therewould not be much noticeable for the same filltime variation in a thicker wall (i.e. 5.0 mm)
aluminum casting
ll h k d f f
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The die temperature will also become muchmore critical and, in addition to becomingmuch more sensitive, the reduced mass of
the part will not provide enough heat for thedie
The basic requirement for making a thin wallcasting is a very fast fill time in a hot diewith a high gate velocity
Wall Thickness And Surface Defects
W ll Thi k A d S f D f
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Summary of wall thickness issues for thin wallparts: Talk to designer early
Get wall thickness the same (consistent) Keep wall thickness variation down with narrow
range to toolmaker
Expect much a smaller process window, and set upmuch tighter process controls
Use low or very low fill times
Use direct feed from gate
Use high gate velocities (but within normal range) Use high die temperatures
Wall Thickness And Surface Defects
Fill Ti A d S f D f t
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Fill Time And Surface Defects
Fill time has a major impact on surface quality
The fill time is defined as the time beginningwhen the metal first arrives at the gate andending when the cavity is full of metal (includingthe overflows and vacuum runners)
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Fill Ti A d S f D f t
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Fill Time And Surface Defects
The fill time can be calculated from the formulagiven in the NADCA gating course, which is:
Max fill time =
Where:
K = A constant
T = Average casting wall thickness
ti = Metal injection temperature
tf= Metal flow temp (solidus)td = Die temperature
S = Percent solids at cavity full
Z = Conversion for latent heat
K T t t S Z t t
i f
f d
* ( * )
Fill Ti A d S f D f t
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For some rough guidelines, the following aremaximum fill times based on calculations andexperience and will be reasonable for most
castings:Thin wall Average wall
2 mm
Al, approx. 2 kg .09 sec .1 secZn, approx. 1.4 kg .03 sec .05 sec
Mg, approx. 1 kg .02 sec .03 sec
Note: for high quality surface finish, reduce thefill times shown by about 50%
Fill Time And Surface Defects
Fill Time And Surface Defects
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Fill Time And Surface Defects
Predicting the fill time is best done withthe PQ2 calculation
The PQ2
calculation predicts the change infill time and gate velocity from changingany of the following:
The gate areaThe plunger size
The machine hydraulic pressure
The plunger speed setting
Fill Time And Surface Defects
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Fill Time And Surface Defects
The PQ2 calculation provides the only way thatthe fill time can be predicted accurately
Without it you must guess, and this is expensive
Fill Time And Surface Defects
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Fill Time And Surface Defects
This list shows some of the things that canaffect the plunger speed, which in turn changesthe fill time and the casting surface finish.
Some of these are: Dragging tip Plunger lubrication Poor sleeve condition
Poor plunger condition Poor cooling water flow to the plunger Sleeve deflection Gooseneck and plunger ring conditions Hydraulic pressure Low (or high) nitrogen charge Gate size
Fill Time And Surface Defects
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Fill Time And Surface Defects
Summary of fill time adjustments:Set fill time maximum values with
calculations and experience, then use adisciplined process
Use PQ2 to predict adjustments to get the
right values and eliminate costly trial anderror
Measure and control process variables with a
monitor systemMaintain control of sleeve and gooseneck
conditions to keep the fill time within limits
Flow Pattern And Surface Defects
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Flow Pattern And Surface Defects
The metal flow pattern is the criteria in gatedesign
The gate design is a function of design rules as
taught in the NADCA gating classes Flow the short way across the casting
Avoid mixing flows if possible
Flow pattern can be simulated with computerprograms and reviewed with short shots
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Flow Patterns And Surface Defects
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These rules include:
Use PQ2 to size the gate and the plunger, using theappropriate gate velocity, fill time, and cavity
pressure criteria Divide the casting into zones
Proportion gates so as to fill each zone at the same
time Flow the short way across the casting
Avoid mixing flows if possible (unless close to gate)
Gate into heavy section porosity and/or importantsurface finish areas
Flow Patterns And Surface Defects
Flow Patterns And Surface Defects
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Flow pattern rules (continued): Avoid jet flows at all times and distribute flow as
much as possible
If possible, set gate location so venting can be usedopposite the gate
Avoid flow directly on cores if possible (but do it ifneeded for best flow pattern
Keep runner lengths equal (avoid tree typerunners)
Eddies in the flow path (from cores or openings) will
cause swirls, gate to avoid this Gate to allow for high momentum (cores can be
bypassed)
Flow Patterns And Surface Defects
Die Temperature And Surface Defects
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Die Temperature And Surface Defects
The die temperatures effect on surface defectsand the die temperature operating window willbe discussed next
A low die temperature affects surface defects bycooling the fluid metal stream and increasing thepercent of solidified metal in the metal stream
If the percent of solidified metal is high, then it
becomes stiff and solid and does not knittogether well; And the flow forms "wrinkles", orcold flow
A cold die can be compensated for by having ashorter fill time - this means a higher plungerspeed
In other words, we can exchange plunger speedfor die temperature.
Die Temperature And Surface Defects
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Measuring die temperature should be done onevery job - most dont do it enough, but it isrequired to really minimize surface defects
In general, measuring can be done three ways: Hand held probe Thermocouple in the die Infra red device
Each has advantages and disadvantages: Hand held probe: accurate, but must stop the
machine Thermocouple in die: continuous, but does not
measure surface temperature Infra red: easy, but not as accurate
Die Temperature And Surface Defects
Die Temperature And Surface Defects
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Die Temperature And Surface Defects
Temperature ranges for good surface finish:(Measured with a hand held surface probe
just after the casting ejects)
Metal Good Finish Average Finish
Al 250 315oC 190 - 315oC
Zn 230 - 290oC 190 - 290oC
Mg 220 - 290oC 200 - 290oC
Die Temperature And Surface Defects
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The operator can control die temperature withthe following controls:
Die spray
Water/oil flow ratesCycle time
The engineer can change the design and affect
how much difference some of these make, butthe operator often controls the actual use of allof them. Thus the operating temperature of the
die is often controlled directly by the operatorand this die temperature control is probably themost important activity of the operator on thefloor. We will review these in sequence
Die Temperature And Surface Defects
Die Temperature and Surface Defects
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Die spray is lubricant mixed with water It is mostly water The water controls the temperature, not the die
spray itself The spray cools the die quickly because of the
large amount of heat quickly pulled out of the
die as the water in the spray boils away
Die Temperature and Surface Defects
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Die Temperature And Surface Defects
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Some techniques include: spray in 2-3 secondincrements with careful adjustment of thespray pattern - spray the areas that need
cooling, not just where the casting might stick- automatic sprayers with a set manifold foreach job are a good way to keep spray to aminimum
Keep spray equipment in good shape, the mostimportant factor is consistency
Document pressures, nozzles sizes, flowadjustments, and spray times in detail -undocumented changes should not be allowed(changes should not be stopped, just
documented)
Die Temperature And Surface Defects
Die Temperature And Surface Defects
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Factors in the spray actions that are veryimportant in controlling die temperature:
Length of time of spray
Spray nozzle adjustment, or spray pattern
Distance from nozzle to the die
Balance between air pressure and lube pressure
(drop size and velocity) Minimize over spraying
Document everything - spray time, pressures, spray
location, mixtures, etc... Be consistent
e e pe atu e d Su ace e ects
Die Temperature and Surface Defects
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The second die temperature control factor is theadjustments made to the water or the hot oilsystems for internal die cooling- this can be
done by the operator or technician
e e pe atu e a d Su ace e ects
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Die Temperature And Surface Defects
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With water, flow rate is usually more important thanthe temperature of the fluid. A small difference inflow rate will do more than a large difference in
temperature
Measuring flow rate is a very desirable way to
improve process control Using flow meters is more and more common
Keeping the pressure constant is another way
A constant flow rate can help to eliminate the coldflow that seems to come and go without explanation
p
Die Temperature And Surface Defects
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The flow rate is determined by the smallestopening in the supply line - this is usually thequick connect fitting
Water (or oil) manifolds affect the flow rate ifthey are not carefully designed - there often ismore output area than input area
Then which line gets the most flow? Adjustment valves should be easy to see, easy
to use, and have large openings for good flow
The water pressure at each machine should beconsistent, and not vary Many plants should have new piping installed
p
Die Temperature And Surface Defects
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Hot oil systems will often make a significantdifference in the surface defect rate for tworeasons:
It keeps the die hot during stoppages - thestart up scrap is often a high percentage ofthe total scrap, (this is where hot oil caneasily pay for itself)
It can add heat to the die as needed to getbetter surface conditions
Hot oil units cool about half as effectively aswater, so the thermal design must accountfor this to get the cycle times desired Use higher flow rates, move lines closer, make
larger, etc..
p
Die Temperature and Surface Defects
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Adding overflows are another method ofincreasing die heat
p
41
Die Temperature And Surface Defects
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Some things to consider: Do not place water lines around the outside edge of
the cavities (cool the cold areas)
Give priority to cooling/heating lines, even if thismeans moving ejector pins or other changes
Do not use the same line to control temperatures in
both a hot area and a cold area Depth of the line is critical, set depths carefully
Size of line must match the flow rate
Treat water because deposits of only .005 cut heattransfer by about 40%
Die Temperature And Surface Defects
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Another important control for the dietemperature is the cycle time.
The die temperature at any given time is
the direct result of the number of pounds ofmetal that went through the die in the lastone to two hours.
A consistent cycle time is one of the mostimportant factors in good defect control
The cycle time should be measured and
displayed to the operator or technician insome way to get good control
Die Temperature And Surface Defects
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Die temperature changes slowly, which can causesome delayed effects, and perhaps some confusion
Example: A change that adds nozzles to the spray
manifold, and shortens the spray time with evenmore cooling than before, and also shortens thecycle time
There will be two effects, short and long term. The
short term from the increase in spray cooling, thelong term from the change in cycle time
Increasing the cooling from spray will reduce the
die temperature quickly (short term) Reducing the cycle time will increase the die
temperature (long term)
Die Temperature And Surface Defects
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Summary of correcting surface defects with dietemperature: Measure die temperature to know where to
change and how much Establish temperature goals for minimum defects Increase die temperature in the defect area by:
Reducing spray Reducing water flow rate Adding overflows
Increase overall die temperature by:
Reducing cycle time Increasing hot oil temperature and flow rate
Die Temperature And Surface Defects
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Summary (cont.): Use good spray practices and keep consistent
Use good computer aided thermal analysis for
cooling/heating line design Measure flow rates and control
Use good engineering to develop good quality
water at consistent pressures Minimize start up scrap and marginal production
situations with die pre-heating; Keep die hot
during short stops
Metal Temperature And Surface Defects
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The metal temperature can make a significant differencein the surface finish
In general, the most desirable situation is to keep themetal temperature at a high range, but not high enough
to cause a lot of other problems Keeping the zinc at 430oC max,
and the aluminum at about 690oC
magnesium should be kept at about 677oC
Control metal temperature on furnaces to within +/- 5oC
Use consistent times between ladling and shot
If possible, control temperatures in shot sleeve
Use consistent set point, do not use metal temperature as avariable unless absolutely necessary
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Laminations
Laminations
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Laminations have several sources
Usually they are the result of metal flowconditions where one flow lays on the top of
another, and the flows were too cold to mix asthey came to rest
This is shown in the next overhead
Laminations
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Flow paths 1 and 2 meet, and are relativelythin layers at this point - they can be peeledaway from the layer underneath (flow 3) by
grit blasting, machining or similar activity
FLOW 1FLOW 2
FLOW 3
DIE SURFACE
COLD FLOW LINE
Laminations
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The correction of these kinds oflaminations is to correct the processconditions, which include:
Flow pattern (gating design)
Gate location
Gate velocity Fill time
Die temperature
Metal temperature
Laminations
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These layers can come from the way the metalflows inside the casting, which may be due tothe geometry of the casting
In this case, the flow pattern can be difficult tochange with gate modifications, so theimportant corrections would be:
Decrease fill time Increase die temperature
Increase metal temperature if possible
Changing gate velocity (either up or down) may also
affect these kinds of laminations
Laminations
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Generally changing fill time is the best It is very common that laminations are due
to some metal being splashed into the cavity
while the plunger is at slow speed; In thiscase the correction would be increase thelength of fast shot (move the switch towards
the pour hole) Laminations are also possible from a flexing
die - when the intensifier comes in, the die
may flex and another layer of metal could beadded outside the initial casting skin - thecorrection is add support to the die
Laminations
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Laminations can also come from oxide skins.These skins come from the holding furnace, ormay be formed in the cold chamber duringinjection
These will be random in location, and usuallyare fairly small, perhaps .08 (2mm) in size.When dislodged by machining or sanding, they
can be mistaken for porosity The corrections are good metal handling,
including:
Skimming the holding pot properly Keep the time in the cold chamber to a minimum Filtering Fluxing and degassing properly
Laminations
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Another cause of laminations is flash capturedin the casting
This happens when the die is not cleaned
properly, and the flash left on the die drops intothe cavity as the die closes
The incoming metal will not remelt the flash
and cause it to mix with the rest of the casting;In fact, the molten metal may barely adhere tothe flash
This flash can make a very weak spot in thecasting, causing cracks in addition to layers onor near the surface (laminations)
Laminations
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The corrections include those activitiesthat reduce flash, such as:Cleaning the die between shots
Not postponing die repairs
Using good process design to selectappropriate metal pressures
Proper adjustment of intensifier settings
Engineering the die cooling to keep dieexpansion as even as possible
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Porosity
Porosity
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Porosity is the biggestproblem in die casting.
The two basic types of
porosity in die castingsare:
Shrinkage
Gas
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It is critical that those who are responsible forsolving defects determine the kind of porosity
before trying to correct it Each kind takes a completely different
corrective action, but they can look alike
Porosity
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It is important that some time be taken toreview porosity before starting to makecorrections
A quick examination can be misleading
Generally, a porosity defect should be
examined under 5 to 10 powermagnification
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Gas Porosity
Gas Porosity
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Gas porosity is the biggest singleproblem in die casting
The high gas content prevents heattreating or welding and makes thestrength unpredictable
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Gas Porosity
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There are three major sources of gasporosity for die castings:
Trapped air
Steam
Gas from lubricant
Gas porosity is round and generally smooth,
although it can be flattened to some extentby pressure
The actions to reduce gas porosity, ingeneral, are not the same as the actions forreducing shrink porosity
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Gas Porosity
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Gas Porosity Trapped Air
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Any turbulence in the metal movement thatallows some air bubbles to be trapped in themetal These bubbles will remain trapped when the casting
solidifies
Air can be trapped in: Shot sleeve
Gating system
Die cavity
Starting with the shot sleeve, we will reviewpotential sources of trapped air and possiblecorrections
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Gas PorosityTh fi t t i t i t i th t
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The first step is to maintain the same pour rateand shot delay time Especially important if the fill % is below about 50%.
When the fill is less than 50%, a wave isgenerated by the pouring action This wave travels back and forth from the parting
line to the shot tip
The time at which the plunger tip starts tomove and its speed and acceleration aredesigned so air is not trapped
A surfing wave traps air
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Gas Porosity
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If the wave is met by the tip as it movesforward, then extra splashing and sloshing isgenerated, and this captures some bubbles.
However, if the tip is started forward justafter the wave has been reflected from it,then the tip chases the wave, and this will
give the best chance for minimizing airentrapment
The timer that sets the time delay between
the end of pour and the start of shot willdetermine when the tip starts forward inrelationship to this wave
Gas Porosity
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The next part of the sequence that can addtrapped air (bubbles) and porosity is theacceleration of the plunger to the slow shot
speed This acceleration rate should be slow enough
to keep the metal from tumbling over
(surfing), and fast enough to preventtrapped air between the generated wave andwaves reflected from the die
This acceleration rate will vary with thepercent fill and the length of the sleeve, butthe usual range will be between 2 and 2.8
inches per second per inch of travel
Gas Porosity
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The optimum acceleration profile can be closelyapproximated by a straight line (linearacceleration) when the sleeve fill is below about50% (which is where most of the problems occur)
Above about 50% fill, the optimum accelerationtrace will be more of a curve
Using these methods, the acceleration will
normally cause the plunger to reach the criticalslow shot speed 1 or 2 inches before sleeve full
This is very close to the start of fast shot, so
there is little time to spend at the slow shotspeed The trace shown on the next page is for a fill
percentage less than 50%
Gas Porosity
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0
5
1 0
1 5
2 0
2 5
3 0
0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4P l u n g e r P o s i t i o n ( i n )
PlungerVelocity(in
/sec)
Optimum acceleration profile with a 32% full sleeve, (3 in.sleeve, 20 in. length, 400 ton cold chamber machine)
Note that the straight line closely approximates the
optimum profile
OPTIMUM
Gas Porosity
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Typical overall shot profile at 32% fill, using linear
acceleration. 400 ton cold chamber machine
Gas Porosity
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The next phase of the shot profile will be thecritical slow shot speed - this will be the speedthat minimizes the trapped air during the slow
shot phase. This speed is calculated from theformula:
Css = k x [(100 - %fill)/100 ] x tip dia
Where k = 22.8 for ips (inch system)
This speed will minimize the air trapped in thisportion of the shot
Wave Formation in Sleeve
Sl h t l it t l Sl h t l it t f t
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Slow shot velocity too slow
Ideal slow shot velocity
Slow shot velocity too fast
The following settings should be considered
Gas Porosity
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The following settings should be consideredimportant when trying to reduce air trapped inthe shot sleeve. While one of these settings maynot seem to be important by itself, there are
interactions and its recommended they berepeated as close as possible once a good settingis foundPour rateDelay time before shotPour hole speedChange over point from pour hole speed to
slow shot speedSlow shot accelerationSlow shot speed
Fast shot start point73
Gas Porosity
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The next location of trapped air is likely to be inthe runners. Any sharp corners or small to largearea changes in the metal flow path in therunner system will cause air entrapment
The main rule is that the runner has smooth,rounded corners, that it has ever decreasingarea from the plunger to the gate
74
VERY POOR RUNNER
DESIGN, SWIRLS TRAPAIR AND GENERATE
GAS POROSITY
CASTING
Gas Porosity
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Effect of short ejector pins
TRAPPEDAIR
BUBBLES
(POROSITY)
SHORT EJECTOR PIN
RUNNER
75
Gas Porosity
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Once the metal starts to enter the cavity, it willnormally flow at a high velocity, very turbulentflow condition, and will trap some of the air
present as gas porosity The flow pattern design should be such that themetal tends to push the air through the cavityto the vents
Much of the air in the shot sleeve and the cavitycan be pushed out the vents or the vacuumsystem
Vents must be sized correctly and go to theedge of the die if they are to be effective
Vents must be kept clean of flash & lubricant
buildup76
Gas Porosity To summarize, the control of trapped air porosity
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, pp p ywill involve a check list like the following:Plunger control settings
Pour rate
Delay before shooting Pour hole speed Start slow shot point Slow shot speed
Fast shot start pointRunner area No square corners No low or high ejector pins
Decreasing runner area in the metal flow pathCavity
Vent location at last place to fill Vents sized right and go to edge of die
Vents to be kept clean77
Gas Porosity
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Steam is the second source of gas porosity Steam comes from water on the cavity surface
when the metal arrives
This gas is mostly trapped in the metalbecause there is little chance to push the gasout the vents - the gas is not present until themetal arrives, and so is mixed with theturbulent metal flow as soon as it is generated
78
Gas Porosity
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The water is mostly from the die spray but itcan also be from other sources
Some of the water will evaporate from a hot
die, but you cannot count on this happening Therefore, it is critical that the die be dry
when it is closed
Other sources of water on the die:Leaking water lines
Dripping overhead sprayers
Leaking hydraulic cylinders
79
Gas Porosity
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Steam porosity tends to be either a few largelarge bubbles or a group of smaller bubbles
If it is from a water line leak, the bubbles may
always congregate in about the same location
80
Gas Porosity
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Checklist to reduce gas porosity fromsteam:
To much water based die lubricants on the die
(the die must be dry as it closes)Leaking water lines
Leaking water pipe connections
Crack in the die into a water line
Sprayer dripping on the die as it closes
Water glycol hydraulic fluid getting on the die
81
Gas Porosity The third source of gas porosity is lubricant
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g p y
The lubricant used on the dies or on theplunger can generate gas when heated by the
incoming metal This gas (like the steam) is only formed when
the metal arrives, and so it is not possible to
force most of the gas out the vents ahead of themetal flow
All lubricants give off some gas when heated to
the temperature of the molten metal - theamount and type of gas will vary from lubricantto lubricant
82
Gas Porosity
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The biggest single lubricant source of gasporosity is the plunger lubricant The usual problem is that the lubricant is
applied ahead of the plunger much heavierthan is needed This is especially true when a dragging or
worn tip is nursed along with extra lubricant
83
Gas Porosity
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Check list of actions for gas porosity fromlubricants:Check the amount of plunger lubricant
Reduce the die spray lubricantLook for pockets where the lubricant can
accumulate on a cold die
84
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Blisters
Blisters
Blisters are another version of gas porosity, the
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gas just happens to be near the surface of thecasting.
The trapped gas is under high pressure at the
end of fill and the metal may shrink andsqueeze it more.
When the casting is taken out of the die, and
the die surface is no longer there to hold thecasting shape, pressure from the trapped gas isable to push up a blister.
86
Blisters
h d f
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The same corrections used for gas porosityapply to blisters:
Reduce trapped air
Reduce spray and plunger lubricant
Eliminate water on the die
Correct venting and vacuum problems
87
Blisters
Bli t h ld b li i t d b ti
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Blisters should be eliminated by correctingthe gas porosity problem. However, youcan:
Cool the die in the immediate area wherethe blisters occur Cool the blister area with die spray Cool the blister area by adjusting water lines
Cool the whole die by slowing the cycle time
Cool the casting immediately after ejectionby quenching in water (this will keep the
skin strong and resist blister formation)
Reduce metal temperature (but watchfor other problems)
88
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Shrinkage Porosity
Shrink Porosity Shrinkage develops because the metal
i l h lid th it did
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occupies less space when solid than it didwhen it was liquid.
For die casting alloys, the difference involume will be about 6% to 8%
This extra space will be concentrated atthe last point to solidify, which is thehottest spot in that section of the casting
90
Shrink Porosity
Si th l ti f h i k it il h h i h i f
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Since the location of shrink porosity isalso the hottest spot in that section ofthe casting, it is usually in the center of a
heavy section This hot spot location can be controlled to
some extent by die temperature
The hot spot can often be moved bychanging the die temperature, therefore
the shrinkage porosity can be moved
91
Shrink Porosity An even casting temperature will cause the
porosity to spread out and to be roughly on
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porosity to spread out, and to be roughly onthe center line (the last point to solidify)
WARM WARM
centerline
porosity
92
Shrink Porosity
If there is a large temperature difference
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If there is a large temperature difference,then there will be large porosity at the lastpoint to solidify
The spray and the water line keep one end
of the casting cold, the gate keeps the otherend hot, and the shrink porosity will tend tobe at the hot end
HOT
COLD
93
Shrink Porosity
If the hot and cold spot can be reversed then
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If the hot and cold spot can be reversed, thenthe shrink porosity will follow the hot spot.
Shrink porosity will always be in a hot spot in
the casting
HOTCOLD
94
Shrink Porosity
Note that the temperatures that effect thel ti f h i k it i id th ti
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location of shrink porosity are inside the castingitself
The die temperatures will influence the internalcasting temperature, but they are not alwayseffective in controlling it completely
Shrink porosity in a heavy section will be harderto move, shrink porosity in a thin section will berelatively easy to move
95
Shrink Porosity Shrink porosity is rough and irregular in shape
and this characteristic is the quickest and
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and this characteristic is the quickest andeasiest way to identify shrink porosity
The shape and appearance of the porosity
comes from the way the casting solidifies
96
Shrink Porosity
The first metal to contact the die surface freezes
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The first metal to contact the die surface freezesquickly and forms the skin
The skin is a very strong, dense, and fine grained
surface with very low porosity, due to the rapidsolidification/freeze rate
Once the skin has formed, the rate slows down
and a dendritic structure starts to appear
SKIN FORMS
97
Shrink Porosity
Dendrites are tree like structures that form inthe solidifying liquid
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the solidifying liquid
The dendrites grow slowly, and by the time the
last metal solidifies, there will be a lot ofdendrites in this area
98
Shrink Porosity It will be difficult to identify shrink porosity in
some castings and without identifying it you
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some castings, and without identifying it youmay very well take the wrong action forcorrection thus the identification is a key factor.
You should know that the walls of shrinkporosity have a characteristically roughstructure
The shrink porosity is usually crack like inappearance, and is jagged, rough and irregularin general
Occasionally it can have a rounded and smoothappearance, when this happens it is sometimescalled worm holes
99
Shrink Porosity
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Shrink Porosity To summarize on the effect of temperature - it
will move the porosity or spread it out - not
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will move the porosity or spread it out notnecessarily reduce it - controlling porosity withdie temperature is possible only on some
castings The shrink porosity location is determined by the
temperature difference between areas in the
casting - the hot and the cold spots determinethe location of the porosity
Watch temperature difference between die
halves Remember, you can heat up the cold spot as wellas cool the hot spot
101
Shrink Porosity
Shrink porosity can be reduced with metalpressure
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pressure
Die casting is a high pressure process and the
only reason die casting machines use highpressure is to reduce shrink porosity
The pressure can fill some of the voids as they
develop, but timing and temperature arecritical and very hard to control
102
Shrink Porosity The intensifier systems used with die casting
machines are there only to add pressure during
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machines are there only to add pressure duringsolidification and thus to reduce shrink porosity
Timing is critical because: the porosity is not
there when the metal is liquid, so pressure atthat time doesnt help (it will only add toflashing)
After the casting is solid, the pressureobviously will not help
Therefore, the only time pressure can be used
to feed more metal into the developing porosityholes is during solidification
103
Shrink Porosity The most common die casting alloys have a
freezing range - which means they go through
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g g y g ga mushy stage as they solidify
It is during this mushy stage that we can addpressure and reduce shrinkage porosity byfilling some voids as they are forming
Some typical freezing ranges for the mostcommon die casting alloys would be as follows:
380 aluminum 45oC
384 aluminum 65oC
413 aluminum 8oC
104
Shrink Porosity Using pressure to fill the emerging shrinkage
voids during this mushy stage is a key factor in
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g y g ycontrolling shrinkage porosity. Several keycontrol elements important in the use of
pressure are: The casting configuration, especially between the gate
and the point of interest (most important factor) The amount of metal pressure available at the end of
the plunger stroke - the packing pressure The intensified metal pressure The die temperature The gate freeze time The injection temperature
Solid
Liquid
Mushy Zone
105
Shrink PorosityTypical values for minimum pressures would be:
Static Intensified
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ALUMINUM 3,000 psi 8,000 psi
20 MPa 55 MPa
These should be regarded as minimum for goodcasting quality internally - lower pressures are
sometimes used when the internal quality is notthat critical
For heavier section castings, some die casters use10,000 psi (70 MPa) as the minimum intensifierpressure
106
Another operational factor is biscuit size
Cavity pressure decreases very rapidly once the
Shrink Porosity
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Cavity pressure decreases very rapidly once thebiscuit reaches a certain minimum size
This minimum varies with the size of the shotsleeve, the metal temperature, the fill time andother factors
Below this minimum, the internal soundness ofthe casting will deteriorate very rapidly
107
Shrink Porosity
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D E N S I T Y V S B I S C U I T T H I C K N E S S
00 . 2
0 . 4
0 . 6
0 . 8
1
0.
1
0.
3
0.
5
0.
7
0.
9
1.
1
1.
3
B IS C U IT T H IC K N ES S
AP
PROXIMATE
DENSITY
A P P R O X IM A T E
D E N S IT Y ,
P E R C E N T
Shrink Porosity Corrective actions for shrink porosity
Check the process design for appropriate
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p g pp pmetal pressure, both static pressure andintensified pressure (plunger size, pressure
settings)Check plunger tip and sleeve condition
Check biscuit thickness for consistency and
the appropriate value
109
Shrink Porosity Other considerations
If possible, move the gate close to the
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problem area to feed metal duringsolidification phase
Use squeeze pins to add pressure on thecasting after the gate is frozen
These pins are usually activated from 2 to 12seconds after the end of fill - the castingconditions must be the same from shot to shot tomake them effective, (something many die
casters cannot do because they dont control theprocess adequately)
The squeeze pins are also effective on leaker
problems, (leakers will be discussed later)110
Shrink Porosity
Hot chamber machines have similarproblems mostly they have metal leaking by
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problems, mostly they have metal leaking bythe plunger - this causes low pressure at theend of the shot and lack of pressure justwhen you need it
Trying to run too close to machine capacityin hot chamber machines can cause low
pressure at the end of the stroke Shrink porosity can occur at the gate
because this tends to be a local hot spot -
porosity in this location should respond tobetter pressure management (temperaturecontrol also)
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Sinks
Sinks Sinks (surface depressions) are a form of
shrink porosity
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A sink forms when the shrink porosity isclose to the surface, and as it cools it pullsthe thin skin on the die surface in towardsitself
The shrink porosity is close to the surfacebecause the surface of the casting is thehottest point in that area of the casting
113
Sinks
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114
Sinks The shrink porosity is formed in the location
shown when the casting is first made. As theti i l d l th di
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casting is run longer and longer, the dietemperature gets hotter and hotter in the areas
marked hotCOLD
HOT
POROSITY
115
Sinks It is typical to have a section that is heavy
enough so the gate is frozen before the areawith the shrink porosity has solidified (so the
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with the shrink porosity has solidified (so theshrink porosity cannot be fed from the gate as
it solidifies) The three hot areas shown in the last diagramcause the shrink porosity to gradually movedown towards the flat surface - the flat surfacewill likely get hotter than any other area
T H E H E A T F L U X
A R R O W S C R O W D
T O G E T H E R H E R E A N D
T H E H E A T C A N N O T
E S C A P E F A S T , S O T H E
C O R N E R G E T S V E R Y
H O T
T H E H E A T F L O W F L U X
A R R O W S H A V E L O T S
O F R O O M , A N D M O V E
H E A T O U T F A S T , S O
T H E C O R N E R S T A Y S
V E R Y C O L D
116
Sinks The flat surface gets very hot also, then the hot
spot gradually moves very close to the surface As the shrinkage porosity starts to contract it
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As the shrinkage porosity starts to contract, itpulls the skin away from the surface
As soon as the skin is pulled away from thesurface, heat flow is blocked to the die whichmakes the conditions worse
DIE SURFACE
SHRINK POROSITY
SINK FORMING
CASTING SKIN
117
Sinks
Eventually, the casting solidifies with the sink inthe surface
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The clue that the spot is getting hot and that a
sink might form is when the surface of thecasting starts to get rough (or frosty inappearance)
The operator should notice this condition, andstart to spray and/or adjust cooling line flow
What is needed is a change in temperature
balance between the hot and cold areas
118
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Leakers
Leakers Leakers are another form of shrinkage problems
There may not be any large voids, in fact theremay not be any visible porosity
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may not be any visible porosity
All that is needed is a continuous path and
enough space for gas or liquid to get through
120
Leakers This size of the space between dendrites
depends on the temperature differences thatexisted at the time of freezing and the ability to
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existed at the time of freezing and the ability tofeed new metal in during freezing
The center of the casting, or the last point tosolidify will have a loose dendritic structure thatis porous
The skin, however, is not porous - thus mostcasting would allow at least a little gas to passthrough if it were not for the dense non-porousskin
121
Leakers It takes a break in the skin (usually on both
sides of the casting) to generate a leak throughthe wall
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the wall
A typical situation is shown below
122
Leakers One way that a break occurs is when the last
point to solidify is on the surface. When thishappens, the surface generally has the rougher
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pp , g y gor frosty appearance, and the dendritic
structure is close to the surface Another way is to expose a break by machining
off some of the surface
123
Leakers The break in the surface often is from a
machining action on one side and a shapecondition on the other so that a hot spot is
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generated on the surface
GROOVEMACHINED HERE
HOT SPOTS DUE TOSHAPE OF THE
CASTING
LEAK PATH
124
Leakers The first correction should be to try to minimize
the temperature problem on the surface This can be done (sometimes) by running this
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This can be done (sometimes) by running thisarea cooler in the die; changing spray patterns,
changing or adding a water line; changing toone of the high heat transfer die materials
The temperature difference between die halves
is something to look out for (not over 100 deg fmax)
Remember that heating up a cold section can
also help restore thermal balance
125
Leakers Adding radius where possible around the leaker
area is a good idea, but can only help so much- adding more than about a .18 to .32 inch (4
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g (to 8 mm) radius does not help much
Adding pressure in that area can help -squeeze pins can work well; Moving a feedergate near the leaker area can help if the
pressure is managed correctly
126
Leakers
Also check the metal temperature - a lowerinjection temperature may make a littledifference but it may also cause other
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difference, but it may also cause otherproblems
It is best to give every opportunity for a goodskin to develop in the area where the leakerappears, be sure the die surface in this areais very smooth and clean.
127
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Cracks
Cracks Cracks, or tears, or hot cracks have many
causes, but usually are at least partially causedby shrinkage cracks on the surface
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Most often, the casting is stretched in the die as
it cools because the die doesnt changedimensions while the casting is cooling andcontracting. The stretching causes cracks at theweak point (the last point to solidify)
129
Cracks Shrinkage cracks on the surface occur during
solidification, and have a dark surface - cool thecorners or heat up the adjacent areas, add radiito the corners for this type of crack
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to the corners for this type of crack
For castings that crack while cooling in the die,the crack will also be at a hot spot increaseradii
130
Cracks Mechanical stress can cause cracks when the
die opens or the casting ejects (or during slideoperations)
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p )
Cracks at the base of long cores or fins,dragging or sticking of projections into one diehalf may indicate die shift when the diesseparate
The factors in die alignment should be checked,such as: die droop (no die carrier), wornguide pins, worn linkage, worn tie bar bushings,worn shoes under the moving platen, uneventie bar stress, etc.
131
Cracks The cracks at ejection are usually
accompanied by drag marks of some sort.
Check the ejector plate for worn bushings be
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Check the ejector plate for worn bushings, besure the ejector plate operates straight. Lookfor undercuts from erosion in the die thatcause the casting to hang up
132
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Inclusions
Inclusions
What are Inclusions/Nonmetallic Inclusions a) Particles of foreign material in a metalmatrix; b) any nonmetal material in the die
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matrix; b) any nonmetal material in the diecasting alloy.
Usually oxides, refractory particles, andsludge, but can be any material foreign to,
and essentially insoluble in, the metalmatrix.
134
Inclusions
Inclusions are mostly a problem inaluminum die casting, but there are issuesin zinc and magnesium also
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in zinc and magnesium also
Can cause quality issuesStrengthHard spots
Flow issues The most prevalent type ofinclusions are oxides
135
Oxide Inclusions The cast alloy is shiny, as evidenced by a
casting that has been machined or a furnacethat has been just skimmed
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j
The gray surface on castings or on the surfaceof the liquid metal is oxide.
This oxide layer on a casting can be very thin -
from a few microns thick to a few thousands
136
Oxide Inclusions Oxides in the furnace can not be totally
eliminated Aluminum we use is recycled, has had a lot of
i d h d id
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exposure to air and has generated oxide
Oxygen is picked-up during metal melting andhandling
Once formed in the furnace, the oxide
particles or skins remain
137
Oxide Inclusions Aluminum, zinc, and magnesium oxidize to
form dross When aluminum oxide is first formed
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Fairly soft
Less dense than the molten metal
Gamma Al2O3, dross
138
Oxide Inclusions Exposed to 1800oF (1000oC) or higher in the
presence of more oxygen gamma aluminumoxide transforms to very hard more dense phase
Al h Al O d
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Alpha Al2O3, corundum
Next to diamond on the Mohs scale Grinding wheel material
139
Oxide Inclusions Corundum can form in the melting or holding
furnaces in most plants The oxides stick to the wall and are scraped off
in the cleaning procedures
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in the cleaning procedures
Oxidesformathotcorners
1800 TO 2000 DEG
HOT CORNER
AL ALLOY - 1350
ALLOY
LEVEL
GOES UP
AND DOWN
140
Oxide Inclusions
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Casting which contained dross from dip-out well
141
Oxide Inclusions
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Cross-section of a casting containing dross
Oxide Inclusions
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Residual corundum particle from improper furnace cleaning
143
Oxide Inclusions
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Dispersion of corundum particles that can look like porosity
144
Refractory Particles Furnace refractory particles come off
the wall during furnace cleaning
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145
Refractory Particles Typical forms: brick, mortar,
castable, crucible
Some common refractory materials
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Some common refractory materials
alumina alumino-silicates
zircon
graphite
clay-graphite
silica silicon carbide
146
Refractory Particles
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Refractory particles, corundum, and flux
147
Intermetallic compounds whose formationis composition and temperature dependent
Factors contributing to sludging
Sludge
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Factors contributing to sludging
Metallic impurities
Some alloying elements
Low holding temperatures
Swings in temperature
Once formed almost impossible to dissolve
148
Fe (iron), Mn (manganese) and Cr (chromium)
can form sludge in aluminum alloys if theconcentration is high enough
Sludge
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149
Aluminum sludge factorFe + 2Mn + 3Cr3Fe + 2Cr + 3Mn
Sludge
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Hold to
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Sludge particles in aluminum alloy
151
Sludge
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152
X-ray of a hard spot (more dense inclusion)
Excess Flux Fluxes are used for various functions
Cover fluxes protect the melt from oxidation
Wall-cleaning fluxes react with wall build-up
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Degassing fluxes remove hydrogenDrossing or cleaning fluxes assist in partial
removal of oxides and reduction/recovery of
metal from drossRefining fluxes may modify, grain refine, or
remove specific metallic impurities
Too much flux gets entrained in the metal
153
Excess Flux
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Flux inclusion
154
Excess Flux
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Mixture of flux and oxide
155
Control of Inclusions
What we dont want!
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156
Inclusions To control dross
Minimize exposure to air and metal tempUse proper drossing procedures
Allow enough time after disturbing molten
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Allow enough time after disturbing moltenmetal bath
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Inclusions To control corundum
Minimize formation of Al drossDont use higher than necessary metal
temperature
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p
Allow at least 30 minutes after furnacecleaning for settling of particles
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Inclusions To control refractory particles and sludge
Use proper furnace cleaning procedures
Control furnace temperature
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Stay below sludge factor of 1.8
Allow at least 30 minutes after furnacecleaning for settling of particles
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Inclusions Oxides can be removed by filtering, fluxing, or
by de-gassing the liquid metal
Refractory particles, sludge, intermetallics canbe removed by filtering
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y g
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Solder
Soldering phenomenon occurs when the molten
aluminum enters the die and contacts directly onsteel die cavity
Soldering
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The molten aluminum stream removes theapplied surface lubricant film and the iron oxidelayer or other coatings then erodes grain
boundaries and pits the die surface At a high enough temperature and pressure a
reaction takes place that causes the formation of
an aluminum-iron intermetallic and a directfusion between the die and the casting
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Soldering Keep the gate velocity to a minimum, calculate
the gate velocity to stay below about 1600 ips(40 m/s) in aluminum, 2500 ips in zinc (60m/s), and about 3000 ips (75 m/s) in
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magnesium - this is to avoid washing thecoating off the steel
Zinc alloys tend to solder in areas away from
the main metal flow The zinc alloys do not form a compound withthe die steel on the surface of the die (seebuild up), but build a layer on top of the steel
Die temperature is most important to keepthis type of zinc solder from forming
Soldering Surface roughness is also important,
a polished die surface will reduce thetendency to form the die solder in
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zinc (it is probably better called abuild up)
Keeping the die temperature is most
important to keep this type of zincsolder from forming
Draft angle is also important,especially if the die temperaturecannot be controlled
Soldering
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Soldering The best solution is keeping the die steel cool -
solder will not start then Cooling methods include die spray, adding
water channels, slowing the cycle speed, and
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reducing metal temperature. Also consider other die materials Anvilloy
Bi-metallic cores
Niobium
Other solutions Draft angle add to die
Gate velocity keep low
Die surface roughness keep smooth
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Build Up A die build up usually comes from lubricant that
was not evaporated from the die If it is darker in color, it is often referred to as
carbon
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Review the die temperatures with the die spraysupplier to get the proper lubricant - keep ratiounder control
Use of hard water in the die lubricant cansometimes cause build up
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Build Up Review the die temperatures with the die spray
supplier to get the proper lubricant Keep die spray dilution ratio under control
Dont spray too long
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Be consistent
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Erosion
Erosion and burn out refer to defects in the
casting that come from the effects of havingsome die steel eroded away
Erosion generally occurs in aluminum die
Erosion - Burn Out
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casting, usually where there are high metalvelocity and high steel temperatures
The biggest factor in erosion is usuallyuncontrolled and poorly managed gate velocities
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The gate velocity should be kept about in the
following ranges:Aluminum, 1000 to 1600 ips (25-40 m/s)
Zinc, 1200 to 2000 ips (30-50 m/s)
( / )
Erosion - Burn Out
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Magnesium, 1200 to 3000 ips (30-75 m/s) Die temperature is next most important, and
should be kept as low as possible
Additional factors include the metaltemperature, the inclusions in the metal, thetype of alloy, proper gate design and flow
pattern
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Burn out is a term usually applied to zinc
dies, and is mostly the result of cavitation Cavitation comes from gas bubbles in the
metal imploding when the go from a high
i th t l
Erosion - Burn Out
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pressure area in the runner to a lowpressure area in the cavity - if theyhappen to be in contact with the die steelwhen this happens, then cavitation occurs
Sometimes the gate location can bechanged so the metal doesnt impact onthe die steel just past the gate opening
The best correction for this is to minimize
the air bubbles - this includes factors suchas the following:
Using two speed plungers
Erosion - Burn Out
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Using runner sprue designs
Using proper and carefully designed
runners and gates
O t i
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Outgassing
Gate Porosity - Outgassing This defect occurs when the casting is heated,
usually for a secondary operation like painting,and gas comes out of the casting
This is due to the expansion of the trapped gasin the casting that escapes through a porous
ti f th ti
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section of the casting
It is not be possible to eliminate all the trappedgas, so most of the work should be focused onreducing the porous-ness of this section of thecasting
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Gate Porosity - Outgassing To reduce the problem in the overflows,
minimize the number of overflows used andkeep the gate to the overflow as thin aspossible
For outgassing at the gate keep the gate as
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For outgassing at the gate, keep the gate asthin as possible, keep the gate area cool asmuch as possible, and increase metal pressure
Ensure there is enough pressure to feed theshrinkage
For all types of gate entrances to the casting,
do not have thin die sections that can build-upheat.
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Gate Porosity - Outgassing
CASTING
GATE
HOT SPOT
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HOT SPOT INSTEEL
HOT SPOT,
POROUS AREA
This hot spot increases the amount of shrinkporosity formed at the gate which contributesto outgassing problems
B di W i
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Bending, Warping
Bending - Warping Bent and warped castings have many different
causes, starting with design, die build, machineconditions, and operating conditions
Once the design is set, the major operating
factor is that the casting and the die always be
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factor is that the casting and the die always beat the same temperature when the casting isejected
The use of a thermocouple to eject the castingat the same temperature every time is avaluable aid to precise dimensional control
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The die and the machine must be maintained in
good condition to minimize bending and warping
Bending - Warping
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Flash
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Flash Flash occurs when liquid metal flows into an area
of the die where it is not expected, such as theparting line, under a slide, or along side anejector pin
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Flash Flash can be almost eliminated if proper attention
is applied to tool design and operational factors
A robust die is required, there can be no diedeflection
Good thermal balance is required so the die fitswell at operating temperature
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well at operating temperature
The machine locking conditions must be proper;such as equal load on the tie bars, proper die set
up, linkage not worn, platens flat, etc Metal pressures and impact force should be no
more than necessary
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Flash Flashing can occur for one of three
reasons:1. The die seal-off is poor.
2. The die and machine do not work together
to seal off the mold cavity
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to seal off the mold cavity.3. The impact force at the end of the cavity
fill exceeds the clamping force of the
machine. To understand the reason why flashing
occurs, you must understand the
condition of the machine, the tool, andthe forces occurring within the machineat the end of cavity fill.
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Flash Determining the root cause of a flashing
problem is sometimes quite complex. As an operator, you need to observe the die:
If the casting flashes in exactly the same way
every shot, then the tool or machine is likely
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every shot, then the tool or machine is likelythe problem.
If the flash pattern around the cavity changes
drastically, especially as a die heats up duringstartup, then it indicates two possible causes:
The impact force is exceeding the clamping
force of the machine. Thermal expansion within the tool is allowing
metal to escape the die cavity.
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Flash Summary The two keys to minimizing flashing
are:Die design.
Machine maintenance.
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Machine maintenance. Die design.
Die squareness.Thermal design.
Die seal-off.
Centering the part within the die.
Wear plate and lock design.
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Stained Castings
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Stained Castings
Stained Castings Dark gray or black discoloration
Almost always involves die or plunger lube
Typically, too much lube has been applied
Check:A t f l b b i li d
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Amount of lube being applied
Dilution ratio
Application procedure
Other sources dirt scrap
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Waves and Lakes
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Waves and Lakes
Waves & Lakes Typically in zinc
Caused by metal flow problems Two flow fronts meet, one cooler than the
other, however, enough heat for re-melting
for the two fronts to attach this is thediff b t l i ti d &
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difference between laminations and waves &lakes.
Waves & Lakes Check:
Plunger acceleration needs to beaccelerated before metal hits the gate
Fast shot transition early enoughGate design
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y gGate design
Flow pattern
Die temperature
Metal temperature
Drags
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Drags
Drags Looks similar to solder, but is caused by the die
dragging on the part during ejection
Check:
Draft angles
Ejection problem, such as bendingErosion that may have caused an undercut
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Erosion that may have caused an undercut
Distorted, mushroomed cores
Flash on slides Die temperature
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C ld l k
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Cold Flakes
Cold Flakes PSP - ESP Occurs in only cold chamber machines
Causes irregular breakout at the gate Most collects at the gate
Can cause flow problems
May be difficult to see without microstructural
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examination
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Cold Flakes PSP - ESP Corrections
Minimize shot delay time
Keep fill % in sleeve as high as possible
Keep sleeve temperature as high aspossible
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possible
Keep metal temperature high
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