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Aluminum alloy die casting Advantage

As a professional enterprise of product design, aluminum alloy melting, aluminum die-casting and machining,it covers an area of 153,335 square meters .

The new machining workshop invested US$ 2.5 million has been put into production at the end of 2005. Up to now, our company employs 382 persons, among them 52 people are technicians. Because of the practice of scientific management of computer network, the researching and developing process has been accelerated. We always strictly implement 5S-administration and SPC-statistical process control. We had been approval ISO9001:2000 and TS16949 Quality System Certification.

Our company has advanced digital control processing and detection equipment. We successively introduced the horizontal cold chamber die casting machine from Japan, the digital control machining centre and lathe from Japan-Taiwan jointly funded company, the three-dimensional measuring machine from Italy, Alang direct reading spectrograph from Britain and other 260 machining equipments. All products are manufactured by means of digital control and of high manufacturing quality. We also have 6 sets reflecting smelter with annual production capacity of 20000 tons aluminum alloy ingots.

We have our own new product R&D centre. We have self-contained production line for more than 80 types of products in such categories as aluminum alloy melting, aluminum alloy die casting and machining.

The products are mainly automobile engine mission and aluminum die casting for traffic transport industry

Die-casting is similar to permanent mold casting except that the metal is injected into the mold under high pressure of 10-210Mpa (1,450-30,500) psi . This results in a more uniform part, generally good surface finish and good dimensional accuracy, as good as 0.2 % of casting dimension. For many parts, post-machining can be totally eliminated, or very light machining may be required to bring dimensions to size.

Die-casting can be done using a cold chamber or hot chamber process.
•In a cold chamber process, the molten metal is ladled into the cold chamber for each shot. There is less time exposure of the melt to the plunger walls or the plunger. This is particularly useful for metals such as Aluminum, and Copper (and its alloys) that alloy easily with Iron at the higher temperatures.
•In a hot chamber process the pressure chamber is connected to the die cavity is immersed permanently in the molten metal. The inlet port of the pressurizing cylinder is uncovered as the plunger moves to the open (unpressurized) position. This allows a new charge of molten metal to fill the cavity and thus can fill the cavity faster than the cold chamber process. The hot chamber process is used for metals of low melting point and high fluidity such as tin, zinc, and lead that tend not to alloy easily with steel at their melt temperatures.
Die casting molds (called dies in the industry) tend to be expensive as they are made from hardened steel-also the cycle time for building these tend to be long. Also the stronger and harder metals such as iron and steel cannot be die-cast


Common Alloys in Die Casting
Aluminum, Zinc and Copper alloys are the materials predominantly used in die-casting. On the other hand, pure Aluminum is rarely cast due to high shrinkage, and susceptibility to hot cracking. It is alloyed with Silicon, which increases melt fluidity, reduces machinability. Copper is another alloying element, which increases hardness, reduces ductility, and reduces corrosion resistance.
Aluminum is cast at a temperature of 650 ºC (1200 ºF). It is alloyed with Silicon 9% and Copper about 3.5% to form the Aluminum Association 380 alloy (UNS A03800). Silicon increases the melt fluidity, reduces machineability, Copper increases hardness and reduces the ductility. By greatly reducing the amount of Copper (less than 0.6%) the chemical resistance is improved; thus, AA 360 (UNS A03600) is formulated for use in marine environments.
A high silicon alloy is used in automotive engines for cylinder castings, AA 390 (UNS A03900) with 17% Silicon for high wear resistance. Common aluminum alloys for die casting are summarized as follows:


Material

Silicon

Copper

Tensile Strength
MPa (ksi)

Properties

AA 380
(UNS A03800)

8.5 %

3.5 %

324
(47)

Fair easy to fill

AA 384
(UNS A03840)

11 %

4 %

331
(48)

Easy to fill

AA 386
(UNS A03860)

9.5 %

0.6 %

317
(46)

Good corrosion resistance

AA 390
(UNS A03900)

17 %

4.5 %

283
(41)

Good wear resistance

Zinc can be made to close tolerances and with thinner walls than Aluminum, due to its high melt fluidity. Zinc is alloyed with Aluminum (4%), which adds strength and hardness. The casting is done at a fairly low temperature of 425 ºC (800 ºF) so the part does not have to cool much before it can be ejected from the die. This, in combination with the fact that Zinc can be run using a hot chamber process allows for a fast fill, fast cooling (and ejection) and a short cycle time. Zinc alloys are used in making precision parts such as sprockets, gears, and connector housings.
Copper alloys are used in plumbing, electrical and marine applications where corrosion and wear resistance is important.
Minimum wall thicknesses and minimum draft angles for die casting are


Material

Min. Thickness
mm (in)

Min. Draft Angle (º)

Aluminum alloys

0.9 mm
(0.035 in)

0.5

Zinc alloys

0.6 mm
(0.025 in)

0.25

Copper alloys (Brass)

1.25 mm
(0.050 in)

0.7

Die-castings are typically limited from 20 kg (55 lb) max. for Magnesium, to 35 kg (77 lb) max. for Zinc. Large castings tend to have greater porosity problems, due to entrapped air, and the melt solidifying before it gets to the furthest extremities of the die-cast cavity. The porosity problem can be somewhat overcome by vacuum die casting.
From a design point of view, it is best to design parts with uniform wall thicknesses and cores of simple shapes. Heavy sections cause cooling problems, trapped gases causing porosity. All corners should be radiused generously to avoid stress concentration. Draft allowance should be provided to all for releasing the parts-these are typically 0.25º to 0.75º per side depending on the material.

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