Plastic injection molding is the primary process for manufacturing plastic parts. Plastic is known to be a very versatile and economical material that is used in many applications. Although the tooling is expensive, the cost per part is very low. Complex geometries are possible and limited only to mold manufacturability. Injection molding is a plastics manufacturing process where a liquid thermoplastic or thermo set is injected into a tool or die under pressure. It is suitable for very high volume production runs. Your computer monitor, mouse and keyboard, automobile parts and home appliances are injection molded plastics.
Plastic injection molding can form most plastics including:
Plastic injection molding is an extremely versatile process for producing a wide range of simple or complex plastic parts with a good finish. Almost any 2D or 3D shape can be achieved. However draft is required in most cases as the shape must allow ejection from the mold. Side holes and even threaded holes are possible though they complicate the tooling.
Injection molding involves taking plastic in the form of pellets or granules and heating this material until a melt is obtained. Then the melt is forced into a split-die chamber/mold where it is allowed to “cool” into the desired shape. The mold is then opened and the part is ejected, at which time the cycle is repeated. In spite of the relatively expensive tooling cost, injection molding remains the most popular manufacturing process for plastic materials in mass production, thanks to its low operational cost, high precision, and the flexibility to make parts with complex shapes.
Plastic injection molding produces plastic parts by forcing molten plastic into a mold where it cools and hardens. In plastic injection molding granular plastic is fed by gravity from a hopper into a heated barrel. As the granules are moved forward by a screw-type plunger, the plastic is forced into a heating chamber, where it is melted. As the plunger advances further, the melted plastic is forced through a nozzle into the mold cavity. The mold remains relatively cold so the plastic solidifies almost as soon as the mold is filled. Custom steel tooling is required and adds to the initial cost but is quickly amortized.
Many value added services like printing and hot stamping are generally done in the post injection molding process. These additional operations are only done after the molding process because they cannot be done during the molding process or at the molding machine. This is often because the post injection molding process is for example, placing the part into a CNC machining center after "aging" the part. Aging the part is used for the purpose of allowing the part to reach its maximum shrink properties so that in the machining process dimensions will not continue to move thereby rendering the part a reject after the machining process.
For fine plastic finishing services, they include:
Screen printing : Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink as a sharp-edged image onto a substrate. A roller or squeegee is moved across the screen stencil, forcing or pumping ink past the threads of the woven mesh in the open areas. Screen printing is also a stencil method of print making in which a design is imposed on a screen of silk or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced through the mesh onto the printing surface. It is also known as "silk screening" or "serigraphy".
Hot-stamping : The advantages of hot stamping include increased productivity, multiple colors in one step, and a variety of available materials and finishes. The Hot Stamping, Heat Transfer Decoration of a wide array of plastic parts and molds are possible due to the secondary production services available. Some of the assembly and sub-assembly services as well the following: flame treatment, hot stamping, point of sale packaging, labeling, and drilling.
Tempo printing : Tempo printing technique consists of transferring ink from the stereotype on an object by means of a silicone plug. This impression makes it possible to reproduce a logo or text on.
Spray painting : Spray Paint Injection Molding Technology is a sub-assembly operation on automotive industry, it's a low cost, novel in-mould painting system for injection molding that can be retrofitted to existing machine technology.
Ultrasonic welding : Principle benefits of ultrasonic welding include the ability to mold and assemble components with complex interiors, allow for designs not achievable in one shot and allow for final assemblies with internal components such as springs, chips, electronics and mechanical parts.