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Modern High Pressure Die-casting Processes for Aluminium ...

| 1 |TRANSACTIONS OF 61st INDIAN FOUNDRY CONGRESS 2013 INTRODUCTIONA luminium was discovered in the year 1825 by a Denmarkscientist Mr. Hans, using chemical process. Due to veryhigh cost, equivalent to that of silver, there was no majordevelopments until the Electrolysis method wasinvented by Charles M Halls. New developments the year 1876, the first Aluminium casting wasproduced using sand moulds. By 2010, there about 33plus different methods are available. Out of these, one ofthe most commercially successful process is Conventional high Pressure Die-casting . But it has somemajor drawbacks as well, such as air and gas blow holes, shrinkages, severe surface defects like cold shuts, swirl,sink and many more. These are also unable to weld andheat-treat to enhance the mechanical properties of thecastings. To overcome these defects, many newerprocesses have come up. In these, the above drawbacksare overcome, casting strength is increased, castablecasting minimum wall thickness has come down from 6mm (sand casting ) to mm in the Vacuum die-castingsand still upto marvellous achievements are very muchadvantageous to the highly competitive auto high Pressure Die-casting Processesfor Aluminium CastingsABSTRACTT here are about 33 Processes commercially available for the production of Aluminium castings.

| 5 | TRANSACTIONS OF 61st INDIAN FOUNDRY CONGRESS 2013 parts which require high strength, endurance, ductility are now made using this process. Hitachi Vacural Process ( HIVAC–V ): This is also a modified form of ‘Vacural Process’ which is used for

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Transcription of Modern High Pressure Die-casting Processes for Aluminium ...

1 | 1 |TRANSACTIONS OF 61st INDIAN FOUNDRY CONGRESS 2013 INTRODUCTIONA luminium was discovered in the year 1825 by a Denmarkscientist Mr. Hans, using chemical process. Due to veryhigh cost, equivalent to that of silver, there was no majordevelopments until the Electrolysis method wasinvented by Charles M Halls. New developments the year 1876, the first Aluminium casting wasproduced using sand moulds. By 2010, there about 33plus different methods are available. Out of these, one ofthe most commercially successful process is Conventional high Pressure Die-casting . But it has somemajor drawbacks as well, such as air and gas blow holes, shrinkages, severe surface defects like cold shuts, swirl,sink and many more. These are also unable to weld andheat-treat to enhance the mechanical properties of thecastings. To overcome these defects, many newerprocesses have come up. In these, the above drawbacksare overcome, casting strength is increased, castablecasting minimum wall thickness has come down from 6mm (sand casting ) to mm in the Vacuum die-castingsand still upto marvellous achievements are very muchadvantageous to the highly competitive auto high Pressure Die-casting Processesfor Aluminium CastingsABSTRACTT here are about 33 Processes commercially available for the production of Aluminium castings.

2 About 70%of the castings are produced using conventional high - Pressure Die-casting process. It s main drawbacks are 1)Air and gas blow holes 2) Unable to weld 3) unable to heat treat to enhance mechanical properties. To overcomethese, many Modern Processes have been invented. A few of them are 1) high Integrity Die-casting processessuch as 1) Squeeze casting 2) Local casting spot pressurising 3) Ultrahigh vacuum process 4) Massive ventprocess 5) Vacural process 6) Minimum fill time process 7) Nissan Innovative process 8) Controlled fillingprocess 9) Vacuum high vac V process 10)Semi -solid casting Processes . In this paper a brief account of theabove such Processes are : Aluminium high pressue Die-casting , Turbulence, Air and gas blow holes, high integrity Die-casting Processes , Ultra high vacuum process, Semi-solid casting Processes , reduce casting weight,increase casting quality, minimum casting wall thickness, squeeze pins, suppress blow holes, pin of money had been invested in developing the modernprocesses through process R&D by several companiesin the world.

3 By this their components are of betterquality and they gain competitive advantage. In thispaper, a brief account of some of the new Processes ,that resulted in the above marvellous achievements, OF HPDC From , it can be noted that in the year 1915 the firsthigh Pressure Die-casting machine was brought to marketby At first, Zinc die-castings wereproduced, then Aluminium . In the year 1928, , Switzerland , brought out a PDC machine whichattracted the market. This is a landmark in PDC. Then,many changes took place due to the advancements inhydraulics , electrical and high Pressure DIE-CASTINGS PROCESSESM achines are available with the locking forces from 60to 7200 tonnes for production .Castings ranging fromabout 50 grams to 50 kg are being produced. Two typesof machines are used in ThirugnanamE-mail: Mobile No. : 98402 56816| 2 |TRANSACTIONS OF 61st INDIAN FOUNDRY CONGRESS 20131)Horizontal Cold Chamber high Pressure Die-casting machines, for most types of )Vertical high Pressure Die-casting machineespecially for electrical motor parts with OF THE ABOVE CONVENTIONALPROCESSESBy nature, the HPDC process is very violent andturbulent.

4 It is like a strong, wild Horse. Metal is injectedinto the die cavity at a Pressure between 200 to 1000 kg/cm2 max. Molten Aluminium enters in the die cavity withthe speeds from about 20 to 45 meters /sec, limited tothe maximum gate speed of 60 meters results in a lot of turbulence causing air injection takes place in milli-seconds. Hence, thereis no sufficient time available for the air in the cavity quantity of air and gases still remain insidethe casting itself even after providing air venting in thedie. Moreover, there is a need to maintain the impurityelement Iron in the alloy composition to a level of max, to avoid sticking of castings with the affects the strength of the casting . Scientists andEngineers have pushed the Conventional HPDC processto the edge of its limits. But not able to meet the presentday product design requirements. Hence ,there is pressingneed for developing newer Processes .

5 Air / gas blow holesare inevitable in the conventional HPDC. Also thesecastings cannot be heat-treated and are not are really some major drawbacks in spite of severalplus OF A FEW Modern casting PROCESSESWITH BRIEF OUTLINESlow Shot Die-casting Processeszzzzz Squeeze casting Process: Molten metal is pouredinto an injection sleeve, which is kept in an inclinedposition at the start .Then it is straightened andconnected to the die cavity through the gate. Metal isinjected into the die at a very slow speed of about max ;unlike the very high speeds of (45meters/sec) conventional HPDC . Very quite andturbulent free cavity filling is achieved. Then a pressureof 500 to 1100 kg/cm2 is applied on the castings untilthe solidification is completed. Shrinkage porosity andgas voids are suppressed out. Due to slow metal injection,air entrapment is very much reduced.

6 Gas inclusion isFig. 1: Traces 9 years of development of the Processes .| 3 |TRANSACTIONS OF 61st INDIAN FOUNDRY CONGRESS 2013as low as 1cc/100 gm of Aluminium . Hence, T6 heattreatment and welding are possible. Iron is limited only, hence the casting strength is improved. Thereare two types of machines available i) Horizontal ii)Vertical types. The typical process parameters are: Metaltemperature 720 oC, Die temp: 300 oC, Injection m/sec upto the gate, gate velocity: to m /sec, Alloy :356.. The method of metal injection is shownFigs. 2 and Acurad Process: (Fig. 5) This was introduced byGeneral Motors Corporation, USA. One of the features isa thick gate and low injection speed for laminar fillingfor reducing air blow holes. Another one is directionalsolidification by judicial temperature control and forcedfeed by another plunger to squeeze gas and shrinkageporosity.

7 By slow injection of metal, turbulence is reducedto a large extent. Hence air entrapment is minimised (Fig4). Plunger 1 injects metal slowly into the die cavity .Whenthe casting becomes just semi solid, the 2nd plunger, whichis located annularly in the 1st plunger, moves forward andapply high Pressure until the solidification is Pressure suppresses the shrinkage and gas voids toa large extent. This process is NOT suitable for thincastings. Machine problems are very much, hence notpopular. Yet its basic idea is utilised in the recent moderndie- casting Pressurising Processe (Fig. 6): In thisprocess, high Pressure is applied, using moving pins,located within the die itself, on the casting spots whereshrinkage is occurring and there is no way to providecooling or core pins. The Pressure is applied when thecasting is in the semi-solid condition. The squeeze pinengagement time is kept between 1and sec.

8 For eachtype of situation, this time and also the start and endtimings are determined by experimentation only. Thereare 3 types are available. 1) Local casting - spot pressurising process, 2) Squeeze pin feedback controlsystem 3)Local runner spots pressurising process. Outof these Local casting -spot pressurising process iswidely used in India by many Pin Feedback Control System: This wasdeveloped by Toyota of Japan. The squeeze pinmovement is regulated in accordance with reaction forcemeasured during pushing of the Injection Process: In this process metal is directlysupplied to the die cavity by an electro magnetic pumpor by air Pressure . Then, Pressure is applied by a plungeruntil the solidification is completed. Powder typelubricant is applied for avoiding the casting sticking tothe die cavity. In this process, conventional high speedfilling is used. After a set time, a pressurising pin is pushedforward in an appropriate location of the casting , whereFig.

9 : 2 Fig.: 3| 4 |TRANSACTIONS OF 61st INDIAN FOUNDRY CONGRESS 2013shrinkage occurs. By this high Pressure , the shrinkage Die-casting Processes . In the conventionalvacuum process, vacuum is 20 to 50 kP and the gascontained in the casting is 5 to 20 cc/ 100 gmsAluminium. And hence, T6 heat treatment and weldingare not Ultra high Vacuum Process: In the ultra vacuumprocess, vacuum Pressure is below 10 kp. In this process(Fig. 7), air and gas content is below 5 cc per 100 gramsof Al, hence the castings are heat-treatable and Vacural Process: In this process, to achieve heattreatment of castings, many improvements are sealing at the parting line, ejector pins, plungertip, metal injection method are also improved. The moltenmetal in the holding furnace is sucked in to the shot sleevethrough a pipe by lowering the Pressure in the die cavityand shot sleeve (Fig. 8). The sucking is continued for along time until the Pressure becomes as low as 5 kp.

10 Thegas /air content in the casting is as low as 1 to 3 cc / 100grams of Aluminium . Hence, T6 heat treatment andwelding is possible. This process is being followed byDaimler-Chryslers for making engine parts, Porche andNissan for suspension parts and Hitachi for making Snowmobile Innovative casting Process (NICS): Thisis a modified version of Vacural Process . Suspension The microstructure in the squeezecasting is not as fine as that observed inconventional die casting , & the dendritesare much more cycle time is longer than theconventional Die-casting due to slowinjection & longer solidification timesFig.: : Acurad : 6| 5 |TRANSACTIONS OF 61st INDIAN FOUNDRY CONGRESS 2013parts which require high strength, endurance, ductilityare now made using this Vacural Process ( HIVAC V ): This is alsoa modified form of Vacural Process which is used forproducing Snow mobile ( pore free) Process : In this process, air in thecavity, runner, shot sleeve is replaced by oxygen reacts with the molten Aluminium which is injectedat high speed through pin gates.


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