Die/Mould Machining

The Die/Mold industry comprises of the following processes:

  • Injection molding

  • Die casting

  • Forging

  • Sheet metal stamping

Injection Molding

Injection molding is a manufacturing technique for making parts from both thermoplastic and thermosetting plastic, rubber and glass materials. Molten material is injected at high pressure into a mold, which has the shape of the component. The molten material forms the shape of mold thus assumes the shape of the required component. After an Engineer designs a product, molds are made by a moldmaker (or toolmaker) from metal (usually steel) and precision-machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to the entire body panels of cars. Injection molding is the most common method of production.

Example: Bottle caps, Speaker covers, Television covers, Rubber tyres.

Die Casting

Die casting is process where metal is injected into the mold under high pressure of 10-210Mpa (1,450-30,500 psi). This results in a more uniform part with generally good surface finish and good dimensional accuracy that is 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 achieved through cold chamber or hot chamber process. The cold chamber process is used for metals having high melting points such as aluminum, and copper (and its alloys) that alloy easily with iron at higher temperatures. On the other hand, 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 melting temperatures.

Die casting molds (called dies in the industry) tend to be expensive as they are made from hardened steel and the cycle time required for building these molds tend to be long. Stronger and harder metals such as iron and steel cannot be die-cast.

Example: Automobile engines, Die cast machine structures.

Forging

For forging, metal is heated and shaped by plastic deformation whereby compressive force is applied suitably. This force is usually in the form of hammer blows using a power hammer or a press.

Forging refines the grain structure and improves physical properties of the metal. With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use. Grain flow is the direction of the pattern that the crystals take during plastic deformation. Physical properties (such as strength, ductility and toughness) are much better in the forged metal than in the base metal, which contains randomly oriented crystals.

Forgings are consistent from piece to piece, without porosity, voids, inclusions or other defects. Thus in the finishing operations such as machining, no void is exposed and little preparation is required during coating operations such as plating or painting due to the good surface. Forging yields parts that have high strength to weight ratio, thus is often used in the design of aircraft frame members.

A Forged metal can result in the following:

  • Increased length, decreased cross-section – drawing out the metal.

  • Decreased length, increased cross-section – upsetting the metal.

  • Changes length, changes cross-section, by squeezing in closed impression dies.This results in favorable grain flow for strong parts.

Examples: Screws, nuts and bolts

Sheet Metal Stamping

Stamping is a metalworking process by which sheet metal strips are punched using a press tool, which is loaded on a machine press, or stamping press to form the sheet into a desired shape. This could be a single stage operation where every stroke of the press produce the desired form on the sheet metal part, or could occur through a series of stages.

The most common stamping operations are:

  • Piercing

  • Fine blanking

  • Bending

  • Forming

  • Coining

  • Progressive stamping

  • Deep drawing

  • Embossing

  • Extrusion

Example: Car bonnets, Tin covers.