MIT 2.810 Manufacturing Processes and Systems Homework 4...
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MIT 2.810 Fall 2016 Homework 4 1 MIT 2.810 Manufacturing Processes and Systems Homework 4 Injection Molding and Heat Transfer Revised 6 October 2016 Problem 1. Wax casting. (a) Consider the open (aluminum) mold casting of a wax candle as shown in Figure 1. Assume that L >> D, D = 2 cm, the mold is at a constant temperature of 30°C and the wax is poured at 100°C. Estimate the time to cool the wax to 37°C. Note that wax has similar thermal properties as polymers. Discuss what the consequences would be if L and D were of the same order. Note: You will need to refer to the chart of transient temperature distribution in a cylinder (from Lienhard’s A Heat Transfer Textbook,4 th ed., Figure 5.8). (a) Assuming L = D, draw the solidified shape of the candle. Explain how this shape would evolve. If this were glass, would there be any possibility of cracking? Where? What is important about the difference between glass and wax for this problem? Figure 1: Open Mold for Candle Casting
Transcript of MIT 2.810 Manufacturing Processes and Systems Homework 4...
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MIT2.810ManufacturingProcessesandSystemsHomework4
InjectionMoldingandHeatTransfer
Revised6October2016Problem1.Waxcasting.
(a) Consider the open (aluminum)mold casting of a wax candle as shown in Figure 1.AssumethatL>>D,D=2cm,themoldisataconstanttemperatureof30°Candthewaxispouredat100°C.Estimatethetimetocoolthewaxto37°C.Notethatwaxhassimilarthermalproperties aspolymers.Discusswhat the consequenceswouldbe if L andDwereofthesameorder.
Note: Youwillneed to refer to thechartof transient temperaturedistribution ina cylinder(fromLienhard’sAHeatTransferTextbook,4thed.,Figure5.8).
(a) AssumingL=D,drawthesolidifiedshapeofthecandle.Explainhowthisshapewouldevolve. If thiswereglass,would therebeanypossibilityof cracking?Where?What isimportantaboutthedifferencebetweenglassandwaxforthisproblem?
Figure1:OpenMoldforCandleCasting
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Problem2.Injectionmolding.Considertheinjectionmoldingofthetapeholder(weight=0.5oz,wallthickness=1.6mm)showninFigures2and3.Pleaseanswerthefollowingquestionsaboutthemanufactureofthispart:
(a) Estimatethecoolingtime.(b) Indicate any special features thatwould result inmoving parts for themold.Were
ejectorpinsused?(c) Indicatethemoldfillingsequenceandlocationsofthegateandweldlines(ifany).(d) Specify roughly the sizeof the injectionmoldingmachineneeded tomold4of these
partsatatimeusinga4-cavitymold.
Figure2:TapeDispenser
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Figure3:TapeDispenserDimensions
Problem3.Designforinjectionmolding.TwoconceptualdesignsforthetoolingforthepartshowninFigure3(aftereliminatingthe0.25in.ridgeatthebase)areshownindrawings(A)and(B).
(a) Whatwouldbethedifferencebetweenthesetwoapproaches?(b) DoanyfeaturesonthesedrawingsviolateDFMrules?(c) Drawinthelocationofthepartimmediatelyafteropeningthemold.(d) Pleaseshowwhereyouwouldputastripperplateand/orejectorpinsonthesemolds.(e) Considertwodifferentgatingsituations.Ononedrawthegateandspruelocationif
theyaretoremainconnectedtothepartondieopening.(f) Inanother,showthegateandspruelocationiftheyaretoseparatefromtheparton
dieopening.
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Figure3.Injectionmoldedpart(alldimensionsininches).
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Problem4.Diecastingversusinjectionmolding.Onenoticeabledifferencebetweendiecastingtoolingandinjectionmoldingtoolingisthesizeoftherunnersystem.Figure4showsamulti-cavitydiefordiecasting.Notethattherunnersystem is quite large and changing in size. In comparison, the runner system for injectionmoldingisusuallyofsmallerandconstantdiameter.Canyouexplainwhythesearedifferent?Isthereafeatureofthediecastingdiethatismissinginthispicture?
Figure4.Multiple-cavitytoolfordiecasting.Notetherunnersizecomparedtopartsize.Problem5.Coolingtime.Showthatequation8.5inBoothroydetal.reducestoourresult
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