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OEM die casting mold or molding process

26 Jul 2017 - OEM die casting,die casting mold,molding process

OEM die casting mold or molding process

The following are the four steps in traditional OEM die casting molding process, also known as high-pressure OEM die casting mold or molding process, these are also the basis for any of the OEM die casting variations: die preparation, filling, ejection, and shakeout. The dies are prepared by spraying the mold cavity with lubricant. The lubricant both helps control the temperature of the die and it also assists in the removal of the casting. The dies are then closed and molten metal is injected into the dies under high pressure; between 10 and 175 megapascals (1,500 and 25,400 psi). Once the mold cavity is filled, the pressure is maintained until the casting solidifies. The dies are then opened and the shot (shots are different from castings because there can be multiple cavities in a die, yielding multiple castings per shot) is ejected by the ejector pins. Finally, the shakeout involves separating the scrap, which includes the gaterunnerssprues and flash, from the shot. This is often done using a special trim die in a power press or hydraulic press. Other methods of shaking out include sawing and grinding. A less labor-intensive method is to tumble shots if gates are thin and easily broken; separation of gates from finished parts must follow. This scrap is recycled by remelting it.The yield is approximately 67%.

The high-pressure injection leads to a quick fill of the die, which is required so the entire cavity fills before any part of the casting solidifies. In this way, discontinuities are avoided, even if the shape requires difficult-to-fill thin sections. This creates the problem of air entrapment, because when the mold is filled quickly there is little time for the air to escape. This problem is minimized by including vents along the parting lines, however, even in a highly refined process there will still be some porosity in the center of the casting.

Most die casters perform other secondary operations to produce features not readily castable, such as tapping a hole, polishing, plating, buffing, or painting.


OEM die casting mold or molding process

Inspection

After the shakeout of the casting it is inspected for defects. The most common defects are misruns and cold shuts. These defects can be caused by cold dies, low metal temperature, dirty metal, lack of venting, or too much lubricant. Other possible defects are gas porosity, shrinkage porosityhot tears, and flow marks. Flow marks are marks left on the surface of the casting due to poor gating, sharp corners, or excessive lubricant.

Lubricants

Water-based lubricants, called emulsions, are the most used type of lubricant, because of health, environmental, and safety reasons. Unlike solvent-based lubricants, if water is properly treated to remove all minerals from it, it will not leave any by-product in the dies. If the water is not properly treated, then the minerals can cause surface defects and discontinuities. There are four types of water-based lubricants: oil in water, water in oil, semi-synthetic, and synthetic. Oil in water is the best, because when the lubricant is applied, the water cools the die surface by evaporating while depositing the oil, which helps release the shot. A common mixture for this type of lubricants is thirty parts water to one part oil, however in extreme cases a ratio of 100:1 is used.

Oils that are used include heavy residual oil (HRO), animal fatsvegetable fats, and synthetic fats. HROs are gelatinous at room temperature, but at the high temperatures found in die casting, they form a thin film. Other substances are added to control the emulsions viscosity and thermal properties; these include graphitealuminium, and mica. Other chemical additives are used to inhibit rusting and oxidationEmulsifiers are added to water-based lubricants, so that oil based additives can be mixed into the water; these include soapalcohol esters, and ethylene oxides.

Historically, solvent-based lubricants, such as diesel fuel and kerosene, were commonly used. These were good at releasing the part from the dies, but a small explosion occurred during each shot, which led to a build-up of carbon on the mold cavity walls. However, they were easier to apply evenly than water-based lubricants.


OEM die casting mold or molding process

Advantages of OEM die casting molding process:

  • Excellent dimensional accuracy (dependent on casting material, but typically 0.1 mm for the first 2.5 cm (0.005 inch for the first inch) and 0.02 mm for each additional centimeter (0.002 inch for each additional inch).
  • Smooth cast surfaces (Ra 1–2.5 micrometres or 0.04–0.10 thou rms).
  • Thinner walls can be cast as compared to sand and permanent mold casting (approximately 0.75 mm or 0.030 in).
  • Inserts can be cast-in (such as threaded inserts, heating elements, and high strength bearing surfaces).
  • Reduces or eliminates secondary machining operations.
  • Rapid production rates.
  • Casting tensile strength as high as 415 megapascals (60 ksi).
  • Casting of low fluidity metals.

The main disadvantage to OEM die casting molding process is the very high capital cost. Both the casting equipment required and the dies and related components are very costly, as compared to most other casting molding processes. Therefore, to make die casting an economic process, a large production volume is needed. Other disadvantages are that the process is limited to high-fluidity metals, and casting weights must be between 30 grams (1 oz) and 10 kg (20 lb). In the standard OEM die casting molding process the final casting will have a small amount of porosity. This prevents any heat treating or welding, because the heat causes the gas in the pores to expand, which causes micro-cracks inside the part and exfoliation of the surface. Thus a related disadvantage of die casting is that it is only for parts in which softness is acceptable. Parts needing hardening (through hardening or case hardening) and tempering are not cast in dies.


Alpine Mold is an OEM die casting mold manufacturer, having specialized in OEM die casting mold or molding process for more than 25 years with good quality and pretty competitive price. Please contact us by kerry@alpinemold.com.

Shenzhen Alpine Mold Engineering Factory
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