Plastic Injection Molders – Designing Products for Injection Molding

Plastic injection molding is an efficient process that produces high-quality parts at lower cycle times than alternative techniques. It can make hundreds of identical parts in an hour without creating much waste. Get the Best information about MH vertical plastic injection molding machines.

Most of this work can be automated and performed by one operator, reducing overhead costs and allowing production costs to remain at levels that can be passed along to customers.
Material Selection

Material selection for injection-molded parts has a dramatic impact on their durability and strength, as well as cost and quality. Therefore, it’s crucial that potential materials be evaluated according to their mechanical properties (strength, elasticity, and toughness), thermal characteristics (heat resistance and conductivity), chemical and electrical properties, and environmental considerations.

Plastics such as polypropylene, acrylonitrile butadiene, nylon, and styrene are among the most frequently utilized materials. They offer affordability, durability, and chemical resistance. Not all plastics offer equal performance; those seeking higher-performance options should look into PEEK or ULTEM for optimal results.

Engineering thermoplastics are known for their superior toughness and mechanical properties, good chemical and weather resistance, durability, and dimensional stability. Unfortunately, however, one significant drawback of using engineering thermoplastics for engineering applications is they do not comply with UL 94 fire standards.

Polycarbonate thermoplastic is a strong, lightweight thermoplastic with excellent impact resistance, heat stability, and chemical resistance properties. It is easy to fabricate with low shrinkage and precise dimensional control. Unfortunately, polycarbonate contains bisphenol A, which could pose potential health concerns when used in food-contact applications.

Note that plastic injection molding materials don’t only include these two options. There are other materials available for injection molding with unique advantages and drawbacks. Acetals are one such material, though they typically don’t meet UL 94 fire safety regulations and have relatively high shrinkage rates. They do, however, possess the durability to withstand high loads, making them great choices for parts such as gears and pumps, conveyor links, or automotive switches.
Design for Manufacturability

When designing products to be manufactured using injection molding, the designer must consider all factors that could affect the final result. The strength of the finished product must be balanced against costs and assembly time. Special attention must also be given to assembly process needs such as sterilization or biocompatible materials. Designing easy-to-assemble products can save both production time and cost while decreasing errors or defects due to complex designs with components that must be placed exactly right.

Plastic injection molding allows manufacturers to quickly produce intricate or complex shapes with high levels of accuracy, eliminating manual adjustments and guaranteeing that every finished product meets standards uniformly. This precision makes plastic injection molding ideal for manufacturers, as each finished product meets standards consistently.

For optimal injection molding results, designers must carefully examine part geometry. Stock sizes must minimize material removal, while tolerances should be within tolerances that can be met using their chosen manufacturing method. If fasteners need to be attached, consideration must be given to threading options that work with both material selection and the design of the injection mold.

Another consideration should be how often a product will be molded, which can have an impact on overall tooling costs. For instance, products requiring side-action cores will increase cycle times as their movement moves across the cavity wall. To minimize cycle times and save on tooling costs, designers should make sure that parts have minimal areas of overhang while placing any side-action cores away from areas where injection molding will occur.
Tooling

Engineers employ computer-aided design (CAD) and manufacturing (CAM) software to translate product specifications and requirements into detailed mold designs for injection molding. Once this step is completed, machinists use 3D printing, CNC machining, or cast urethane casting techniques to fabricate low-volume prototype tools as troubleshooting aids; these prototype tools help minimize risks while saving both time and money during production and assembly processes.

An “A” side, also called cavity half, attaches to a fixed platen in an injection molding machine and contains guide pins that fit into holes on its mobile B side half to maintain optimal alignment during injection molding processes. A stationary A-side may include sprue bushings and cooling lines. Sprue bushes are channels carved into molds that carry plastic melt from an injection unit directly to cavities in mold cavities. Cold and hot runner systems may use cartridge heaters to keep sprue and injectors warm during injection; hot runners use cartridge heaters instead. Once the injection has taken place, pressure is released from the mold by drawing back its screw, leaving the plastic to cool for milliseconds to minutes, depending on its thermoplastic and part complexity, before finally being released from its holding period and released by opening up the tool and ejecting.

Short shots in injection molding occur when molten plastic does not fill its mold cavity evenly. This is often caused by trapped air, uneven wall thickness, or abrupt geometry changes in parts. To reduce short shots in design, part designers can utilize smooth walls with few holes and decrease volume by decreasing internal and external undercuts in their product designs.
Automation

Plastic injection molding is an efficient manufacturing technique used to produce plastic components used worldwide in vehicles, electronics, medical devices, and household appliances. Injection molding provides manufacturers with an economical means of producing large volumes of identical parts at consistent quality levels with rapid turnaround times. Once an injection mold has been designed and ready for use by an injection machine (usually hydraulic or electric), plastic is melted, injected, and set in its desired form and placed within it.

Injection molding machines are specifically designed to deliver thermoplastic pellets into mold cavities through an injection barrel equipped with an inlet nozzle for injection into the cavity of a mold. Once thermoplastic enters an injection barrel, it is quickly heated to an extremely high temperature that disarms Van der Waals forces that resist movement among individual molecules and makes the substance fluid. Mechanical shear shearing of thermoplastic by the reciprocating screw causes it to be mechanically sheared and moved towards a nozzle for injection into the mold via either sprue bushings or gates. Sprue and gate hardware is then attached to the A and B plates of an injection mold to direct liquid plastic towards part-forming cavities, creating channels called “sprues and gates,” leaving behind marks called parting lines, sprue marks, or runner marks on final injection molded parts.

According to The Society of Plastics Industry, surface finishes on molds vary depending on the desired look and feel of a finished plastic component. Although surface finishes serve primarily cosmetic purposes, their rough surfaces may also influence performance by increasing friction during injection.
Quality Control

Quality assurance (QA) and inspection play vital roles in injection molding production processes. They help reduce costs by minimizing waste, improving efficiency, and adhering to industry standards. Furthermore, these practices identify risks and help prevent defects, which could prove costly to customers and production lines alike.

Injection molders that invest in quality control enjoy a competitive edge over their peers who don’t. A comprehensive quality control system includes processes, procedures, and work instructions; employee training; documentation; advanced technology tools and techniques; and quality testing processes and techniques. Although investing in quality control may require time, money, and resources, it is absolutely essential for any plastic injection molding company seeking to offer high-quality products.

Quality-control processes ensure every molded piece is free of flaws and functions properly, starting with raw material analysis and progressing through injection molding and its post-molding phase. Visual and nondestructive testing techniques are utilized to detect any issues that might impede product quality—this may include burn marks, smudges, flashing, and knit lines that might otherwise alter the final output.

Knit lines are hairlike discolorations that appear where two areas of an injection-molded part come together initially. They are typically caused by variations in resin cooling rates or wall thickness between sections meeting in a mold. They may result in soft corners or gaps where sections meet, thus altering the part’s final appearance.

Flashing refers to plastic that leaks out from an injection molding cavity during its formation process and into various locations on a part, including its sprue and runner channels, parting line, or ejector pin holes. It can be identified by its visible presence as dark or black coloration on its surface.