TIPS WITH TONY: Watch Out for Warp, Sink and Voids!

In my years of working closely with product designers, I’ve seen some really great designs, but on occasion, I’ve encountered part designs by both novice and experienced designers and engineers that have needed some work to improve moldability and reduce cosmetic defects. Let’s look at some common design mistakes that could result in parts with sink, warp and voids.

Wall Thickness
Why is uniform wall thickness important? Thermoplastics simply don’t like transitioning from thin to thick sections due to the ununiformed cooling. All thermoplastics shrink as they cool but when thin areas cool before thick areas, stress is created. The results may vary depending on material selection and part design, but if you’re not following the proper material guidelines for wall thickness and mold design, you may end up with unsightly voids, sink and possibly even warp within your parts.

How can you reduce the risk of these molding concerns? Provide proper wall thickness through appropriate coring, rib and boss design, which in turn, helps you avoid excessive thick or thin wall sections.

Material Selection
How does material factor into to sink and warp? Not all materials are alike. You have high shrink/low shrink, non-filled/filled, and blended materials. Each material has unique characteristics, so let’s look at a few quick examples:

Example 1: Are you molding with ABS or a PC? You may want to consider using ABS/PC-blended materials. The ABS/PC blend improves the overall molding process, and while it doesn’t completely remove sink, there’s a good chance that it’ll reduce it.

Example 2: Are you molding with a clear PC? Acrylic may be a good alternative as PC has a tendency to have voids and sink on thick parts. Acrylic provides excellent option for lighting and optics applications, but will lose some impact resistance inherent with PC.

Example 3: How about glass-filled material? There are many reasons to add fillers to your base materials and glass-filled is one of the most commonly used. Glass provides increased thermal properties and strength to many materials as well as decreasing the mold shrink that can decrease sink. This is all great, but you’ll need to follow proper design guidelines more closely as glass-filled materials create more internal stress that can result in warp. You can help minimize this with proper gate selection to align the fibers in the longest flow path and most structurally sound direction.

Upload your part today for an interactive quote with free design for manufacturing feedback that will highlight sections where sink and warp could be an issue.

Tips with Tony is a weekly feature focused on improving the manufacturability of your parts.

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About Tony Holtz

Tony is a technical specialist at Proto Labs with more than 10 years of experience ranging from CNC mill operator to mold designer to customer service engineer. While his formal education is in industrial machinery operations, he has extensive knowledge and experience in both traditional and advanced manufacturing processes and materials. Throughout his tenure at Proto Labs, Tony has worked with countless designers, engineers and product developers to improve the manufacturability of their parts.

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