7 Tips to Design for Injection Molding
Injection molding is a manufacturing method that uses plastic and rubber and is subject to many potential design flaws, so please read on for 7 tips to design for injection molding. Implementing all 7 tips will create a more consistent, better product. If you are unfamiliar with the process please review the basics of injection molding.
Tips to design for injection molding.
- Keep a uniform wall thickness
The wall thickness of the injection molded part has a huge impact on the finished product. Ideally, you should use thinner walls to reduce cost and cooling time. The thicknesses should range from .020-.150 inches or more depending on the type of plastic being molded. Thicker walls take longer to cool than thinner walls, and unequal cooling of the part may warp or even crack where the two different thicknesses meet.
- Appropriately apply draft
To properly release the part from the injection mold, the product must have an angled draft on the faces that touch the tooling. The draft will help release the part from the tool without damaging the surface finish. In most products it is best to have a draft of around 2 degrees. If the part has a medium to rough texture, the part will need a draft of 3 degrees.
- Strategically place you parting lines
Hiding your parting lines is always a challenge. Ideally, you want smooth transitions on the surfaces that are visible. If you can get the parting lines on a face that is not visible once the product is assembled it will hide some of the potential defects like flash.
- Watch your corners
This one tends to be problematic for most new engineers and designers, who put the same fillet on the inside and outside of the part resulting in a thick section in the corners. Another common corner problem is applying fillets before the draft. By applying the draft first, the fillet will automatically have the correct draft applied.
- Shrink your ribs
If you have a rib that is the same thickness as the nominal wall thickness it will cause sink on the back face of the surface. Rib and boss thicknesses should not exceed 60% of the nominal thickness.
- Keep your bosses thin
We often need to mount lids or covers to our products. This can be a challenge since the material thickness should not exceed 60% of nominal thickness. Bring your bosses away from the outside walls and add ribs that run across. This allows you to use a smaller boss and at the same time stiffens the entire part.
- Implement features into the tooling
Part of efficient manufacturing is minimizing production steps. Let’s say you need a through hole for a fastener. Design the part so you can use a slide in the tool to make the through hole. How about branding labels or stickers? Just mold the logo directly into the plastic. The tooling costs for these added features will be minimal compared to the time saved on the extra processing, not to mention consistency, which is the key for quality.
Following these simple tips to design for injection molding and you will have fewer issues with your injection moldings.
If you found these tips useful, please share them with you colleagues.