Continuous squeeze casting process by mass production

CHINA FOUNDRYNov.2006Continuous squeeze casting processby mass production*Yun Xia, Rich JacquesSPX Contech, Porage. MI 49024, USAAbstract: Squeeze casting has become the most compettive casting processithe automotive industrybecause of its many advantages over high pressure die casting (HPDC). Many squeeze casting R & D andsmall amount volume making have been implemented around the world, but the mass production control stillexists problem. SPX Contech squeeze casting process P2000 successully achieved the goal of massproduction; it includes lower metal turbulence, less gas entrapment, minimum volumetric shrinkage, and thusless porosity. Like other casting processes, however, the quality of squeeze castings is still sensitive toprocess control and gate and runner design. Casting defects can form in both diefilling and metalsolidification phases. The occurrence of casting defects is directly attributed to improper adjustment orlack of control of process parameters including metal flling velocity, temperature, dwell time, coolingpattern, casting design, and etc. This paper presents examples using P2000 techniques to improvepart quality in the fllowing areas: runner & gate design, casting & runner layout in the die, squeeze pinapplication, high thermal conductivity inserts, cooling/heating systems, spray & lubricant techniques,and part stress calculation from shrinkage or displacement prediction after stress relief.Key words: squeeze casting; die casting; casting processCLC mumber: TG249.2Document Code: AArticle ID:1672-6421(2006)04-0258-05( 1 queeze casting has been widely used for automotive strucmake a good casting without an optimum gating design and? tural parts because it offers a vast material selection fromprocess control. Many casting defects are caused due to pooraluminum and magnesium alloys. In comparison with low design and careless process control such as: metal stream jttingpressure die casting, squeeze casting also overcomes manyfrom an unbalanced runner and gate design, wrong casting layoutfluidity problems and thus it can use both hypereutectic andin the die, shrinkage porosity from solidification, lack of fillhypoeutectic alloys such as 319, 383 and 390.from improper temperature distribution and blisters fromSqueeze casting can also apply“spot solidification" technologyblocked heat transfer.in addition to directional solidification method. The shortcomingTo make a sound casting in the squeeze casting process, aof directional solidification is that in many cases the cross sectionscientific approach should be followed. All process parametersof a complex casting is not always reduced in the direction ofshould be under tight control. To do so, smart selection andrunner, because this part shrinkage can exist. Spot solidifcationbetter understanding of process parameters is the key. In squeezecan solve this problem by the use of squeeze pins, high thermalcasting high metal pressure must be applied to the casting inconductivity baffle, etc.order to squeeze gas and pack the material tightly. This mayThe use of a vertical paring line and slow flling in squeezecreate metal flow jetting because the liquid melt can be forcedcasting process alows for air removal without the use of a highinto small ingate areas. The runner and ingate should be largecost vacuum system, and still achieves the same desired effect enough to be able to pass the intensification pressure to theas a vacuum system. Because of a horizontal parting line incavity. The molten metal gravity may lead to an open galemany low pressure processes, air and gas are more likely to be shrinkage. In addition, the metal temperature should be keptentrapped, since some areas of the cavity can be above thehigh enough to have good fluidity, but high metal temperatureparing line. The entrapped air leads to surfacc oxidation andmay also produce blister defects. When these parameters aregas dects. The use of a vertical parting line in squeeze castingwell designed, an overall process control plan can be applied.overcomes these problems.Therefore, a good design and process control should be ableLike other casting processes, squeere casting process will not to manage temperature, pressure, velocity, and metallurgical中国煤化工)f these can be verified by*Yun Xiand metal soldification. ThisMale, Ph.D, work in Asia Business Development of SPXYHc N M H Ging proces siulation 10Corporation, USA.to improve part quality in the following areas including runnerE-mail:yun.xia@contech.spx.com& gate design, casting & runner layout in the die, squeeze pinReceived date: 2006-06-20 Adopted date: 2006-08-02application, high thermal conductivity inserts, cooling/heatingVol.3 No.4systems, spray & lubricant techniques, and part stress calculation..Equivalent Hydraulic Pressurefrom shrinkage or displacement prediction after stress relief.Shot Seeve1 Background of squeeze castingA-Plunger Areaprocess1.1 Process principle. A-Rod Section AreaSqueeze casting process can be divided into various categoriesP.rRod Pressurefoin terms of parting line orientation and the way liquid metal isintroduced into the cavity. One of these is vertical die openingwith vertical metal flling (VSC). A second is horizontal dieopening with vertical metal flling (HSVC). HVSC processdue to the horizontal parting line leaves many horizontal surfacese.-Hydraulic Pressuro A Hydraulic Cylinder Araand pockets which can make it hard for gas to escape. TheseFig.2 Squeeze casting pressure relationlead to trapped gas, oxidation and other casting defects. TheVSC process has a vertical parting line, allowing for the upperHydraulic pressure pushes the shot cylinder to work. But themost point to be near the parting line from which air and gasrod pressure will be a resistant force to push back. Thiscan be easily pushed out through overflows and vents. VSCcombination will create a resultant pressure PEM, which isalso directly flls the die without turbulence in slow velocity. Itsmaller than regular metal pressure as NADCA recommend.also meets the requirements to make high quality automotiveThis makes it possible to reduce the impact during the fast shot.casting. This paper is about VSC process. The machineTherefore, the squeeze casting machine will have less metalschematic is in Fig. I.pressure shock than conventional high pressure die castingEject Halr[ Cover Hatlmachine because it creates a rod pressure to resist the .[ Moving Platenintensification shock.Stationary Platen 11.2 Typical microstructure of squeezef Molten MetalcastingsSquccze castings have much finer microstructures, i.e. smallerdendrite arm spacing (DAS) in particular near the casting surfaceShot Cylinderin comparison with permanent mold castings. This is due tothe metal being pressurized and forced against the tool steel diecausing high heat transfer and very rapid solidification.Compared to conventional HPDC, overall microstructure of aFig.1 Schematic of a VSC squeeze casting machinesqueeze casting part has much less entrapped porosity. This isSqueeze casting utilizes a vertical shot sleeves and a horizontalbecause of the non-turbulent fill that reduces the entrapment ofdie parting line. The pressure calculation is shown belowgas, in conjunction with effective squeeze compressing the gas(Equation 1). The formula to calculate pressure in squeezeand shrinkage porosity. This improvement in microstructurecasting is different from conventional die casting machine. Itover HPDC leads to parts that can be heat treated and welded.considers the rod pressure, which is a resistant force that appiesThe comparison between a ADC-12 HVSC microstructure andwhen the plunger moves forward and fills the cavity. The sketchconventional ADC- 12 HPDC microstructure are shown in Figs.is shown in Fig. 2.3 and 4.PaN. A_=P. A..-PQ(A.rAR)(1)i Entrappedporosity中国煤化工MHCNMHG100umL 100um]Fig.3 VSC squeeze cast ADC-12 microstructureFig.4 Conventional ADC.12 HPDC microstructure2591QCHINA FOUNDRYNov. 2006A356 and A357 alloys, the ductility of squeeze castings is1.3 Mechanical properties of squeezesignificantly improved by one to two times in comparison withcastingsgravity permanent mold castings (GPM) even though the tensileTable 1 compares the mechanical properties of variousstrengths are comparable. In comparison with high pressurealuminum castings made by different casting processes. Fordie castings, squeeze castings not only show higher ductilitybut have better tensile strengths.Table 1 Propety comparison between squeeze and other processesYnekd城ongthTansile strenghElongationHardneseAlloyProcessMPaMPgA356.2-T6Squeeze221-234296-31010-1448-63GPM207-228283-3033-545-58357-T6241-262324-3388-10248-262331-3455-8750-653831-FDie cast140-160193-201-1.5N/A145-159269-2902.75-3.550-603831-T4234-255359-386-755-703831-T6296317379-42173-843902-F24127<13901.T6NIA352- 392180-90temperature is usually lower in VSC than that for HPDC. Figure2 Quality improvement through5 shows an example of mold flling simulation of a steering rackprocess simulation& pinion in the VSC process. As expected, a stable mold flingpattern is achieved by using the VSC process. As a result, a2.1 Gating design and process simulationpore-free and heat treatable steering rack & pinion is made.The key for gating design in squeeze casting process is to produceSolid metal is able to feed the shrinkage areas duringslow fling and drectional soidifcation.n Flling velocity must slidificacion. To take advantage of directional slidifcaion,be tightly controlled to guarantee reduction of any flow turbulencethe skin of the casting must be solidified prior to applyingand air entrapment. Unlike the HPDC, the bottom flling in intensification pressure. This requires the use of proper colingsqueeze casting can eliminate air generation during the metalwith cyclic water or oil lines in the die. The die cooling has to bemovement in the seeve Gate velocity also has tobe slow enough contoled tighly because coling too fast can cause misruns andto avoid any jetting. To solve the contradiction between non-poor fill defecls. Increased pressure after the skin formation canturbulent flling and cycle time, adjustable velocities are used atfurther push semi- solid metal to feed those areas where the :diferent stages. For accurate control of flow ptten, process possible porosity and shrinkage can occur. In this work, processsimulation is utilized to visualize the pressure, velocity andsimulation is used t0 decide if the feeding channel in the die designtemperature changes during mold filingn Melt temperature has is adequate to create a part that will meet the desired porositya significant effect on metal fluidity. shrinkage porosity andspecifications. Necessary corrections and changes should be madeblisters. The key in the process simulation is to seleet the critical to the runner size, position and design to guarantee the optimumtemperature that will llow the part to fll and provide the desired gating design. Figure 6 shows an example of a feding channelskin and microstructural quality. In general, the metal pouringin a pump house casting.中国煤化工.MHCNM H G_Fig. 6 Directional solidification pattern produced forFig. 5 Steering rack & pinion flling patternpump housingVol.3 No.42.2 Some techniques used in moderngeometry changes to the casting. Figure 8 shows an examplesqueeze casting P2000of squeeze pins being applied on a runner.The key point for squeeze pin design is to accurately controlIn some cases. isolaled hot spots exist. The directional the pin size, travel distance, velocity, timing and pessre.solidification channel is separated into several segments. ForProcess simulation can be used to optimize the squeeze pinthose cases, spot oriented solidification techniques have to bedesign and in particular the timing. which guaranees a pinapplied through the use of squeeze pin or highly thermalpressure high enough to push semi-solid metal to feed theconductivity materials.shrinkage. Because of the complex geometry of automotiveIn conventional die casting or squeeze casting, aluminumcastings the ideal directional solidification is not alwaysalloys shrink about 4% .6%. Undesirable shrinkage porositypractical. The local spot solidification techniques need to benormally occurs in the heavy cross sectional areas. Successfulused. This can be realized by using certain high thermalprocess control and casting design is not just to eliminate theconductivity tools such as baffles, bubblers, and super cools orshrinkage, but maybe to relocate shrinkage porosity to otherother highly thermal conductive material to create a local coolingunimportant loeations where mechanical properties are not environment and to asist the whole systematic directionalhighly rquired. Figure 7 shows a pacical suee pin design slication.. Figure 9 shows the design of a cpper bryliumfor this application,insert and super cooling insert/system to assist solidification.Squeeze pins can also be used on runners or overflows to avoidShrinkageSquoeze pinused hore|Fig. 7 An example showing application of a squeeze pin in a castingl Super Coolig PinCuBo Insern-Water Line中国煤化工YHCNMHGFig.9 Cooling system assists directionalFig. 8 Squeeze pins applied to runnersolidification⑨CHINA FOUNDRYNov. 20062.3 Simulation used to improve qualitydesign, material, process and manufacturing engineers.Continuing advancement and increasing in understanding ofFurthermore, simulation results need to be validated withmolten metal flow and solidification simulation have led to aexperimental data.significant improvement in aluminum castings quality. The3 Summaryeffective use of process simulation can ensure a non-turbulentflow during mold flling by the use of proper gating, thus greatlySqueeze casting process P2000 is a good process to makeimproving part quality. The use of simulation also allows for automotive castings with fewer defects, better microstructurethe trial of different cooling configurations or use of different and mechanical properties. Several techniques that are currentlyspot solidification methods to improve part quality in a cost used in squeeze casting process are discussed in this paper sucheffective manner well before any parts are produced.as the spot cooling, squeeze pin, and directional solidification.Some simulation packages, when correlated, can accuratelyProcess P2000 can be a very powerful tool for engineers topredict DAS of the microstructure. This data can then be used optimize product design and manufacturing processes. Into dctermine mechanical properties in different areas of the part, squeeze casting process, simulation can be applied to achieveand can also be used to determine if quality specifications can better results in die filling and solidification. Simulationbe met when certain DAS is required.engineers should accurately interpret simulation results.Numerical simulation is now advancing in ways other thanApplication of simulation tools must be combined withmerely fllig and soldification prediction. The use of part stress engineers' knowledge and experience.determination during solidification can predict tendency of hotcracking. This capability can help to optimize the part geometry, Referencestooling, and cooling system to avoid such problem in early part1] Xia Yun et al. Several Techniques Applied in Squeeze Castingdevelopment. Another simulation tool is heat treatmentDefect Reduction. NADCA 2003, Indianapolis, Septembersimulation. This simulation tool can be used to predict part2003, T03- 061relaxation and distortion during heat treatment. Thus this can [2] Xia Yun et al. Thixo-Casting Flow Pattern Study and Defectbe used to design heat treating fixtures and loading schedule.Prediction. NADCA 2003, Indianapolis, September 2003 .T03-012.One important aspect that needs to be considered is that[3] Dasgupta B, Xia Yun. Squeeze Casting: Principles andsimulation is a numerical method that solves traditional fluidApplications. Die Casting Magazine, January, 2004.flow and heat transfer equations. How to interpret and use the [4] Xia Yun, Cncilla J. Mohley E ptimized Fluid Flow Patternsimulation results correctly is critical for a simulation engineer.for Automotive Lightweight Component Castings. SAEThis requires not only individual engineer's knowledge andTechnical Paper, 2004, 04ANNUAL 106.experience but also frequent communication among product中国煤化工MYHCNMHG126万数据