Injection molding design tips

Injection molding is a manufacturing process that injects molten materials into molds to produce components. This process can use different materials, such as thermoplastic, polymer, or elastomer. The molten material is fed into a bucket through a funnel, where it is heated, melted, and mixed. Then inject it into the mold. After solidification, the material occupies the shape of the mold cavity. Injection molding technology is widely used in large-scale production because it generates relatively low waste production and has high repeatability.
The universality of injection molding technology requires broader design considerations. Most design considerations will be made on the mold after developing product requirements. Some factors that affect design include: how the parts will be used (as a single product or for assembly), their size and mechanical requirements, and their ability to withstand chemical or pressure factors. Below are some important techniques to consider when designing injection molding.
Carefully select the materials that are suitable for your design
Different materials provide different characteristics. For example, some injection molding materials provide more dimensional stability than other materials. Similarly, some bonds with adhesives are better than others. The material design considers the following factors: temperature, pressure, biological and chemical interactions. Thermoplastic resins can be roughly divided into amorphous and semi crystalline. Although semi crystalline thermoplastic plastics provide better chemical resistance and electrical resistance, their amorphous counterparts have much higher dimensional stability and impact resistance. Material selection can affect the required tolerance level or certain features (such as wall thickness).
Consider part tolerances
Molds are usually prepared with strict tolerances and typically have CNC tolerances up to 0.005 mm. But as the plastic cools, shrinkage occurs, depending on the material. Some polymers contract more than others. For example, although the maximum shrinkage rate of PLA can be expected to be 0.5%, the shrinkage rate of PEEK may be as high as 1.5%. When designing parts and applying tolerances, it is important to consider shrinkage and the type of material used.
Choose the appropriate wall thickness
The following are recommended wall thicknesses for different materials:
ABS: 1.143 mm -3.556 mm
Acetaldehyde: 0.762 mm -3.048 mm
Acrylic acid: 0.635 mm -12.7 mm
Liquid crystal polymer: 0.762 mm -3.048 mm
Long fiber reinforced plastic: 1.905 mm – 27.94 mm
Nylon: 0.762 mm -2.921 mm
Polycarbonate: 1.016 mm – 3.81 mm
Polyester: 0.635 mm -3.175 mm
Polyethylene: 0.762 mm -5.08 mm
Polyphenylene sulfide: 0.508 mm -4.572 mm
Polypropylene: 0.889 mm – 3.81 mm
Polystyrene: 0.889 mm -3.81 mm
Polyurethane: 2.032 mm – 19.05 mm
In addition, the walls should be uniformly thick. Uneven wall thickness can lead to indentation marks. Sinking marks are local surface depressions caused by slow cooling of thicker parts. Try to maintain a uniform wall thickness as much as possible. However, when there is inevitably uneven wall thickness, the thickness difference shall not exceed 15% of the nominal thickness. We also recommend using gradient or smooth transitions.