Why are plastic injection molding parts needed?
Plastic injection molding suits high-volume production runs extremely well. The low per-unit cost when manufacturing thousands or millions of identical plastic parts offsets the high upfront costs of designing and fabricating the injection molds. Injection molding of plastic can produce highly complex and intricate plastic components with tight tolerances. Injection molding can produce parts with complex internal structures, threads, integrated hinges, and moving parts. This allows for part consolidation and design optimization.
Properly fabricating injection molds can produce plastic parts with an excellent surface finish. Designers can also build a variety of decorative effects and textures into the mold. This allows them to create aesthetic plastic components without secondary processing. Compared to some other manufacturing methods, injection molding can be extremely cost-effective for mass production, especially with simpler part geometries. It results in a very low cost per part.
What are injection molding parts?
Engineers commonly use thermoplastic polymers like ABS, nylon polycarbonate, and polyethylene for plastic injection molding parts. They select these materials based on mechanical requirements, chemical compatibility, and temperature resistance.
Designers incorporate uniform wall thicknesses, internal radii, corners, and draft angles into well-designed plastic injection-molded parts to ease ejection and account for shrinkage in the design. They can incorporate complex geometries and living hinges. Steel tooling molds with cavities machined to the required shape are needed. Designers include feed systems, cooling channels, ejector pins sliders, etc. in the mold. They use multi-cavity molds for mass production.
Operators gravity-feed raw plastic pellets from a hopper into a heated barrel. As the plastic melts, a reciprocating screw injects it into the mold cavity at high pressure. After adequate cooling time, the mold opens and the operator ejects the solidified part.
How to design Injection Molded Parts?
Designers should consider draft angles. First, they should add some degree of taper (typically 1-3 degrees) to allow the part to be ejected from the mold. Internal surfaces and deep ribs will need more draft angles. Designers should avoid thin walls below 0.4–0.5 mm, as they may not fill properly in the mold. They should consider thickening thin sections or adding ribs for strength.
Designers are minimizing variation in wall thickness across the part to prevent uneven cooling, shrinkage, and warpage. If there are thick and thin areas next to each other, they should use graduations. Adding generous fillets and rounds helps them avoid stress concentrations. Sharp corners are difficult to fill in the mold. Designers can avoid sink marks and warpages by using ribs or gussets to add material to the inside of thick walls and bosses. They need to make sure the part can be molded in a two-piece mold with proper shut-offs for the mating surfaces. Designers should avoid undercuts.
Engineers should consider the plastic material choice early as it affects critical dimensions, tolerances, strength, clarity, etc. Common choices include ABS, polypropylene, nylon, and acetal. Engineers should talk to their injection molder during the design phase for advice on improving moldability and manufacturability.
The injection molders can help refine the details. Prototype molds can validate the design before engineers commit to full-hard tooling.
Engineers should allow time and budget for potential design revisions. The key is to design for proper flow, cooling, and ejection while minimizing residual stresses; gaining experience with the plastic injection molding process will help with this.
Why is Injection Molding Needed?
Plastic injection molding suits high-volume production runs extremely well. The low per-unit cost when manufacturing thousands or millions of identical plastic parts offsets the high upfront costs of designing and fabricating the injection molds. Injection molding of plastic can produce highly complex and intricate plastic components with tight tolerances. Injection molding can produce parts with complex internal structures, threads, integrated hinges, and moving parts. This allows designers to consolidate parts and optimize designs.
Engineers can use a wide range of plastic polymers in plastic injection molding, from common ones like ABS, polypropylene, and nylon to specialized high-performance plastics. Engineers select the material to meet specific application needs for strength, temperature resistance, chemical compatibility, etc. Properly fabricating injection molds enables production of plastic parts with an excellent surface finish. Designers can also build a variety of decorative effects and textures into the mold. This allows them to create aesthetic plastic components without secondary processing. Compared to some other manufacturing methods, injection molding can be extremely cost-effective for mass production, especially for simpler part geometries. It results in a very low cost per part.
Engineers create durable plastic parts meeting complex design needs at low costs using plastic injection molding, making it an essential manufacturing process for mass production in many different industries. Engineering thermoplastics into the right shapes and configurations is key.
