Kaivanya Extrusion – Tips and Tricks for a Successful Injection Molding Design

Part of being a supplier is coaching a customer to a successful design for the manufacturing process. Here are some pointers to help you and your parts succeed.

Getting early feedback on your CAD model can save you time and money later. Bringing in your supplier early to help review your needs against geometry limitations will prevent surprises and added delays once you are ready to order.

How thickness affects parts

Suppliers love seeing uniform wall thicknesses in models. It tells them that you visualized how injection molded parts cool and harden. Having uniform wall thicknesses between 0.060 and 0.120 in. (1.5 to 3.0 mm) is crucial to ensuring that parts cool evenly.

 

Be wary of saving too much weight or you might end up with:

➱   cracking
➱   suppressed cooling and possibly warp
➱   incomplete filling or shorts
➱   weak knit lines and fracture points
➱   excessive or premature wear at the parting line

Overly thick walls could cause:

➱   sink
➱   porosity
➱   warp
➱   flow lines

draft picks
The draft is that slight angle that helps parts pop out of molds. Adding a draft early in a design helps communicate your expected parting line to the molder. Adding it into your sketch or feature tree of the model makes it part of your design and not an afterthought.

Cosmetic parts need more drafts, especially when applying textures and polish. Functional parts may not need as much, but 1° should be the minimum draft for all parts, especially with aluminum tooling.

Draft and uniform wall thicknesses let parts cool within the injection mold without bending or twisting, avoiding internal stress to the part and mold. If your part “potato chips” are inside the mold, the added locking force of the part binding adds stress to the ejection system. That can bend ejector pins and other components, risking damage to molds, which, in turn, delays your parts. Neither party wants this.

Getting early feedback on your CAD model can save you time and money later. Bringing in your supplier early to help review your needs against geometry limitations will prevent surprises and added delays once you are ready to order.

How thickness affects parts
proto lab-thickness-injection-molding-transparent-part-100.png
Suppliers love seeing uniform wall thicknesses in models. It tells them that you visualized how injection molded parts cool and harden. Having uniform wall thicknesses between 0.060 and 0.120 in. (1.5 to 3.0 mm) is crucial to ensuring that parts cool evenly.

Be wary of saving too much weight or you might end up with:

❖   cracking
❖   suppressed cooling and possibly warp
❖   incomplete filling or shorts
❖   weak knit lines and fracture points
❖   excessive or premature wear at the parting line
❖   Overly thick walls could cause:

➱   sink
➱   porosity
➱   warp
➱   flow lines

#1 draft picks draft is that slight angle that helps parts pop out of molds. Adding a draft early in a design helps communicate your expected parting line to the molder. Adding it into your sketch or feature tree of the model makes it part of your design and not an afterthought.

Cosmetic parts need more drafts, especially when applying textures and polish. Functional parts may not need as much, but 1° should be the minimum draft for all parts, especially with aluminum tooling.

Draft and uniform wall thicknesses let parts cool within the injection mold without bending or twisting, avoiding internal stress to the part and mold. If your part “potato chips” are inside the mold, the added locking force of the part binding adds stress to the ejection system. That can bend ejector pins and other components, risking damage to molds, which, in turn, delays your parts. Neither party wants this.

Why radii deserve love

Resin hates to be forced into a sharp corner, especially as it cools and relaxes. Radii help reduce shear and turbulence caused by sharp corners and abrupt flow changes. As we think about filling a mold, we have a fluid that flows through the cavity — smooth bends make for better fill and stronger parts.

Visualize this: Your part is the positive form. The mold is the negative form split in half. So, a part’s inside corner is an outside corner on the mold. As the part cools, it shrinks. Now, that inside resin corner is pressed harder against the mold’s outside corner. If that outside corner is sharp, the mold will bite into the part and stick harder than necessary. That leads to grabbing, pinching, or binding on that sharp corner. Ejector systems must push this “bite” off, which creates stress in the mold and on the part. You end up with broken parts, possible broken molds, and poorly processed parts as the molder tries to reduce the risk to the injection mold and parts.

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