The main Plastic injection mould process used is machin […]
The main Plastic injection mould process used is machining, where the shape to be generated is cut to the required size on a lathe or milling machine. It is difficult to cut very hard steel, so use softer steel and then harden or nitride it. During the hardening process, the heat treatment that the metal receives may relieve the stress present in the metal block and may cause slight deformation. The use of normalized steel can reduce this, but as the processing progresses, very precise work is required to perform many annealing treatments. Most metals can be processed. For simple circular shapes, a lathe is the most useful tool. An improvement in processing is die sinking, where a negative pattern is used, and the zoom tool will follow the negative pattern to generate a suitable shape.
Compared with graphics, the arrangement of pantographs can be reduced by up to 10:1 in size, so high accuracy can be achieved. Engraving also uses scaled graphics, mainly for engraving-where repetitive work is done. Using numerical control (NC) machinery is expensive, and before it can be used reasonably, the workload requires considerable work and saves a lot of labor. Very hard steels can be machined by electrochemical machining (ECM) or electric discharge machining, commonly referred to as spark erosion. ECM is very fast, it can remove 1 in3 / min of metal per 10,000 amperes of current per minute, which is obviously at a very low voltage.
The surface finish is very good, but the electrode of the shape suitable for the desired shape is expensive. EDM is usually used for smaller jobs and replaces wafer sinking. Blind holes are produced quickly, and may form acute angles, and it is easy to obtain sizes larger than 001. The latest machines using transistorized pulse generators generate very fast sparks, with minimal electrode wear and high surface finish. Electrodes are relatively easy and cheap to manufacture, and graphite and copper are the preferred materials. These mold manufacturing methods include cutting metal from the mold. The other two methods used involve the opposite method, namely building the metal to provide the desired shape.
Electroforming is a process in which metal is electrodeposited on a reverse model of the shape to be formed, and a fusible casting alloy, such as Hoyt Metal or Kirkst, is used to support the resulting metal casing. The cooling coil of soft copper tubing can be incorporated into the alloy backing. In metal spraying, a low melting point alloy is flame sprayed onto the positive electrode model, and similar alloys are pasted on the formed shell. Since the alloys used in both processes are softer than required, the formwork is installed in the steel pillow, and the locking force is absorbed on the hardened steel pad incorporated in the pillow. Cast metal molds of aluminum, zinc, Kirksite and beryllium copper can also be used for injection molding.