Injection molding part design is the tone setter for any production run. Nailing the design ensures multiple aspects of a successful component including functionality, shape, lifecycle expectancy, repeatability, scalability, and much more.
Every injection molding project is different. It requires different thermoplastics, considerations for environmental exposures, varying wall thicknesses, geometries, and cooling times post-injection.
Agape Plastics’ guide on injection molding part design accounts for some of the best practices we’ve seen over the years with regards toward manufacturability and performance.
Core Design Principles
While every injection molding part design is going to be different – millions upon millions of unique parts are created yearly through this manufacturing process – there are some unifying design characteristics and principles that guide engineering teams during the design process.
It all starts off with wall thickness. Teams that keep wall thickness consistent throughout the part experience fewer defects like sink marks, voids, warpage, and uneven cooling. These defects are minimized or even outright eliminated from proper wall thickness because even material flow and uniform cooling are more easily achievable. In the event that wall thickness must change, gradual transitions in thickness are recommended to keep defects at bay.
Part of the design process includes accounting for ejection from the mold, and this is possible when draft is added to all vertical faces. A clean ejection means smooth surfaces and a ready-to-use component.
A final standard principle in part design is the avoidance of sharp internal corners. To better improve part strength and overall mold life, use radii rather than corners.
Balancing Strength with Material Usage
There’s a delicate balance between obtaining component strength and material usage. It’s a common thought that the more material that’s used, the stronger the part will be, but that isn’t necessarily true.
When injection molding part design factors in ribs and bosses, material usage can be lowered while maintaining desirable product strength. This ultimately keeps wall thickness in check as well. A best practice is to keep ribs thinner than the main wall while limiting the height of a rib. As mentioned above, add draft and radii at the root to minimize sink and stress. Bosses should be kept proportionate to the nominal wall and tied to ribs.
The less material that’s used for your component, the lower costs will be and less waste is created, which further drives down costs.
The Moldability and Cost Relationship
Moldability and cost have a direct relationship with one another. The simpler a mold ejection is, the more cost-effective the project becomes. The best way to achieve this is by utilizing a straight-pull mold. When undercuts, side actions, or lifters are considered or incorporated, complexity is added to the project, and complexity equates to rising costs.
Consider the locations of gates and ejector pins early on in your design so they aren’t entangled with cosmetic or stressed areas.
Contact Agape Plastics for More Injection Molding Part Design Best Tips
Agape Plastics opened its doors to customers in the mid-1970s, and we made our name as one of the most reliable injection molders for the automotive industry. Over the course of 50-plus years, our work touches multiple industries by serving OEMs and Tier 1 suppliers across the country and throughout the world, including all of North America.
Injection molding part design is one of the most critical aspects of the manufacturing process and should be considered part of the technical process by teams. While we are not part-design-responsible, we work closely with your team to ensure design for manufacturability so that we can create the component with minimal to no defects. Our quality management systems include thorough testing and validation to correctly account for proper cooling, part functionality, and all dimensions are accurate to the design.
Contact our team today for more information regarding our injection molding part design operations and how we can best serve your project’s needs today.