How to design for plastic injection molding?
How to Design for Plastic Injection Molding?
The injection molding process is a dominant method for mass production, mainly due to its efficiency in minimizing scrap and its high precision in manufacturing. Given the flexibility of this technique, designers must take various elements into account for optimal results. Much of the design intricacies gets finalized around the mold after outlining the product specifications.
Several key elements influence the design when creating parts for injection molding, such as the intended usage (whether it's a standalone product or part of a larger assembly), the dimensional and mechanical specifications required, and the need for resilience against external factors like chemicals or pressure. Below, we delve into essential considerations for successful injection molding designs.
Choosing the Right Materials for Your Design
Each material used in injection molding comes with distinct properties that play a crucial role in the final product's performance. For instance, different materials can vary significantly in their dimensional stability and their ability to bond with adhesives. When selecting materials, factors such as temperature resistance, pressure tolerance, and interaction with biological or chemical agents must be evaluated.
Thermoplastics can be divided into two categories: amorphous and semi-crystalline. While semi-crystalline thermoplastics provide better resistance to chemicals and electricity, the amorphous ones typically exhibit greater dimensional stability and impact resistance. The choice of material can substantially influence the tolerances required and specific features like wall thickness.
Consider Part Tolerances
Part tolerances can be influenced by the degree of shrinkage that occurs during the cooling phase. Generally, amorphous materials such as PLA maintain tighter tolerances compared to semi-crystalline materials like PEEK. Tight tolerances may lead to increased production costs, but they could be critical for ensuring that parts fit and operate as intended, particularly in assembly scenarios.
It is advisable to consult your supplier early in the design phase to clarify their tolerance standards. For reference, DIN standards provide a general tolerance table for various materials, which can guide your specifications. If your project requires tighter tolerances, be prepared to provide detailed 2D drawings to your supplier.
Deciding on Wall Thickness
It is essential to assess specific factors that inform the decision on wall thickness for injection molding parts:
- Thinner walls can reduce cycle times and lower overall production costs. For many applications, a wall thickness of 1.5 to 2.5 mm is adequate, but consulting recommended specifications based on material is wise.
- Unlike CNC machined components, plastic injection molded parts benefit from uniform wall thickness. Variations can lead to issues like sink marks.
- Non-uniform wall thicknesses may cause warping as the walls cool and shrink at different rates. Where variance is necessary, thickness changes should not exceed 15% of the baseline dimension, ensuring smooth transitions for quality results.
Add Draft Angles
Injection molding components should incorporate draft angles to enhance ejection success. Unlike traditional machining processes which can create vertical walls, verticality in injection molding can result in parts becoming lodged in the mold as they cool and contract. Applying a slight draft helps facilitate easier removal, protecting both the part and the ejector system from potential damage.
Integration of Ribs and Gussets
Ribs and gussets can greatly enhance the structural integrity of certain parts while minimizing cosmetic defects like warping and sinks. These features are vital in strengthening components without merely adding thickness, which can exacerbate shrinkage issues. Maintaining rib thickness around 50-60% of the wall thickness they are attached to helps mitigate such risks.
Enhancing the Design with Radii and Fillets
Incorporating radii and fillets improves the flow of material during molding and enhances the product's structural stability. Sharp corners can create weak points and complicate the molding process; therefore, smoothing these areas can lead to better part ejection and reduced stresses. This refined design approach not only improves manufacturing efficiency but can also lower production costs as it allows for simpler molds.