Injection molding is the manufacturing process by which different parts are produced by injecting molten material into a shaped mold or die. This process is done, when there is a need to produce parts in bulk volumes and when the same part is created thousands or even millions of times in succession. This process is widely used for producing items such as automotive body panels, water bottles, and cell phone cases from toys and plastic trinkets.
In the injection molding, there are commonly two things used. The first one is thermoplastic and the second one is thermosetting plastic. In this process, the raw material is heated to turn into a molten form, then this molted material is injected into the clamping unit to give it the desired shape.
1) Injection moldings types
There are several injection molding types, but some of the most important ones are as the following.
The die casting process is the injection molding process by which the molten metal is forcibly put into the mold cavity under high pressure. The mold cavity is made up of two hardened tool steel dies which have been machined into the product’s shape. The die casting provides the two main features of a molded material, i.e., surface finishing and dimensional consistency.
Metal Injection Moldings (MIM)
Metal injection molding is the injection molding process in which finely-powdered metal is mixed with the binder material to produce a feedstock that is shaped and then solidified. Metal injection molding machine produces the molded product in the form of a ‘shot’. The current equipment can only use shots with the weight of 100 grams or less to make a product. Due to this limitation, Metal Injection Molding (MIM) process is cost-effective only for small and high-volume products.
Thin-wall injection moldings
Thin-wall injection molding is another type of injection molding that is extensively used to save the cost and make the cycle time as short as possible. This technology is similar to the standard injection molding but is specifically used for mass production of plastic parts such as bottles, cans, …where the product is thin and light. Thin walls can be as small as 0.5 mm.
Injection molding of liquid silicone rubber (LSR)
This is the type of the injection molding in which high purity platinum cured silicone with low compression set, great stability and ability to resist extreme temperatures of heat and cold are used. This technology produces pliable and durable parts in high volumes. The process is used to make electrical surface insulation, seals, sealing membranes, electric connectors, multi-pin connectors, infant products where smooth surfaces are desired.
This process is similar to the injection molding; however, unlike conventional injection molding, RIM process makes use of low-viscosity liquid polymers in a thermoset. This process of molding involves two parts. Polymers are mixed together by injecting them under high pressure into an impinging mixer. This mixture is then injected with a low pressure into a mold. After that, the mixture is allowed to sit inside the mold long enough for it to expand and cure. During this process, thermosetting polymers are used to make new parts. This process is commonly used for making automotive bumpers, air spoilers, and fenders. This technology is by far more advantageous than conventional injection molding. While its production time is longer, it is more beneficial regarding the wide range of part size, design uniqueness, flexibility and of course cost-efficiency.
2) The molds building process
The injection molding machines consist of two main units, an injection unit, and a clamping unit. The injection unit consists of the feed hopper, the heater barrel, and the ram. The feed hopper feeds the plastic into the machine which is being heated by a heater barrel to make it in a molted form. This molded material is then forcibly moved to the clamping unit by the screw-ram where clamped parts of the machine mold this melted material according to the given shape. This material cools down and conducts its heat away. The process is then cycled to remove the moldings.