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Aluminium die casting

Die casting China is a manufacturing process that is used to produce complex metal parts by using die-casting molds, or dies, die casting tooling, etc., The die casting process involves the use of a furnace, metal alloy like aluminum, zinc, magnesium, die casting machine, and die casting mold. The alloy such as aluminum die casting or Zamak is melted in the furnace and then injected into the die casting mold which is assembled in the die casting machine. There are two main types of die casting machines – hot chamber casting machines (used for alloys with low melting temperatures, such as zinc) and cold chamber casting machines (used for alloys with high melting temperatures, such as aluminum). The differences between these two types of machines will be detailed in the sections on equipment and tooling. However, in both machines, after the molten metal is injected into the die casting tooling, it rapidly cools and solidifies into the end alloy part, called the die casting part. The casting process is the same for both die casting machines.

The casting parts that are created by this process can vary greatly in size and weight, ranging from a couple of grams to 40 kg. One common application of die casting parts is housings thin-walled enclosures, often requiring many bosses & ribs on the interior of casting. Metal housings for a variety of appliances and equipment are often using die casting parts. Lots of automobile components are also manufactured using the die casting process, including propellers, gears, bushings, pumps, and valves, Other normal die casting parts include pistons, cylinder heads, and engine blocks.

China Die casting Process Cycle time

The die casting process cycle time for die casting consists of five main stages, see below in detail about those die casting process stages.

1. Clamping force

The first step is assembly and clamping of the die casting mold into the die casting machine. There are two half in the die casting mold and machines, Injection half and ejection half. Each die half is first cleaned from the previous injection and then lubricated to facilitate the ejection of the next part. The lubrication time increases according to the casting part size, as well as the number of cavities and cores. Also, lubrication may not be required for every cycle, but requires 2 or 3 cycles, depending upon the material and casting part feature. After lubrication, the two die halves, which are closed together in the die casting machine by the clamping force. Sufficient force must be applied to the die casting mold to keep it securely closed while the metal alloy is injected. The time required to close and clamp the die casting tooling is dependent upon the machine large machine requires more time buy produce a large die casting mold/part.

2. Injection

The molten metal alloys, which is maintained at a melt temperature in the furnace, is next transferred into a chamber where it can be injected into the die casting mold. The method of transferring the molten metal alloy is dependent upon the type of die casting machine (hot chamber or cold chamber machine is being used). The difference in this equipment will be detailed in the next section. Once melt alloy material is transferred, then injected at high pressures into the die casting mold. basically, injection pressure ranges from 1,000 to 20,000 psi. This pressure holds the molten metal alloys in the dies during solidification. The amount of metal alloy that is injected into the die casting mold is referred to as the shot. The injection time is the time to fill all of the channels and cavities in the die casting tooling. This time is very short, normally less than 0.1 seconds, in order to prevent early solidification of any one part of the metal. The proper injection time can be determined by the thermodynamic properties of the alloy material, casting part size, part feature, as well as wall thickness of the casting part. A thicker wall thickness, big part size, and complex part feature will require a longer injection time.

3. Cooling systems

The molten metal alloy that is injected into the Alu die casting mold will begin to cool and solidify by die cooling systems. When the entire cavity is filled and the molten metal solidifies, the final casting part is formed. The die casting mold can not be opened until the cooling time has elapsed and the casting is solidified. The cooling time can be adjusting according to the thermodynamic properties of the metal alloy, the wall thickness of the casting part, and the complexity of the die part. A greater wall thickness and the geometric complexity of the die part require a longer cooling time because of the additional resistance to the flow of heat.

4. Ejection

After the predetermined cooling time has passed, the die halves open and an ejection mechanism will push the casting part out of the die mold cavity. The time to open the die casting mold can be estimated from the dry cycle time of the machine and the ejection time is determined by the size of the casting’s envelope and should include time for the casting to fall free of the die casting mold. The ejection mechanism must apply some force to eject the part because during cooling the die part shrinks and adheres to the die. Once the casting part is ejected, the die casting mold is ready for the next injection cycle.

5. Trimming

During cooling and high pressure of injection, the material in the channels of the die will solidify attached to the casting part. This excess alloy material, along with any flash that has occurred, must be trimmed from the casting part either manually cutting or sawing, or using a trimming press tooling. The time required to trim the excess alloy material can be estimated from the size of the casting part feature. The scrap alloy material from the trimming process is either discarded or reused in the die casting process. Recycled alloy material may need to be reconditioned to the proper chemical composition before it can be combined with non-recycled metal alloy and reused in the die casting process.

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