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.
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.
Molded parts are everywhere — from highly cosmetic housings hiding in plain sight to internal components where a fine polish is unnecessary. Most people pay no attention to the surface finish on those parts, but for product designers and engineers, it’s an important design consideration.
Identifying the right surface finish is dependent on a few important elements, namely the development or production stage that your parts are in, the materials they’re being manufactured in and their end-use applications.
On custom finishes, use color coding to provide a clearly marked image of your CAD model with its required finishes.
This month’s tip discusses:
- available surface finishes for injection molded parts at Proto Labs
- how to create a custom surface finish involving two or more finishes
- navigating finishes within ProtoQuote
- why gating and ejection play a limited role in liquid silicone rubber parts
- secondary options applied to magnesium components
Read the full design tip here.
There are hundreds of thermoplastic materials available for injection molding, and various grades provide strength, durability, impact resistance and many other beneficial attributes. By adding compounded fillers to the equation, you can further increase the durability of your parts.
A component molded with glass-filled nylon to improve durability.
Glass is the most commonly used additive in plastics. Glass-filled materials provide a higher level of strength and rigidity to a part versus an unfilled base material. You can adjust the level of glass in a material depending on your needs, but be cautious as glass can affect how a part turns out dimensionally and cosmetically. We typically see 13 percent and 33 percent glass-filled materials, but occasionally it pushes upwards to 45 percent.
Other Additives and Fillers
There more additives than just glass fiber, and many of these are easily compounded by material manufacturers for your specific needs (or they may already have a pre-compounded material that meets your needs). Glass bead, mineral, metal, carbon, glass mica, talk and Teflon are just a few that Proto Labs has worked with in the past. These fillers can improve:
Designing luminaires or lenses with clear materials? Our tip this week looks at the material selection and surface finishes available for prototyping and low-volume production of lighting applications.
Prototype built in clear WaterShed XC 11122 material with stereolithography.
If you haven’t considered using additive manufacturing (3D printing) for your lens design, you may want to check it out. Proto Labs offers stereolithography (SL) with three options for clear parts.
- Somos WaterShed XC 11122 — ideal for lens and high-humidity applications
- 3D Systems Accura 60 (10 percent glass-filled) — creates a clear part with slight blue tint and high stiffness
- 3D Systems Accura 5530 — high temperature resistance, suitable for under-the-hood applications
Prototyping small volumes of microfluidic parts has traditionally been difficult using CNC machining or injection molding, but Proto Labs offers microfluidic fabrication through additive manufacturing (3D printing) for just this purpose.
Microfluidics typically requires very flat surfaces, and clear and thin/shallow features that are difficult to produce in a mold that is milled and hand polished. These tiny features are not easily distinguishable, requiring careful polishing and injection molding pressures can sometimes role the edges even further, not to mention the effect that the ejector pins have on the part surface. Ejector pins play a huge factor in removing the part from the mold and can cosmetically impact microfluidic parts that are molded. We will continue to injection mold microfluidics, but please first discuss these projects with a customer service engineer at Proto Labs.
Additive microfluidics changes all of this as ejector pins are a non-factor. We use stereolithography (SL) to produce parts using an ultraviolet laser drawing on the surface of a thermoset resin, primarily our Somos WaterShed XC 11122 material. High-resolution SL is able to produce features as thin as 0.002 in. layers to provide the fine detail that microfluidics require. We recommend channel sizes of 0.025 in. square cross sections with a minimum wall thickness of 0.004 in. for X and Y dimensions and 0.016 in. for the Z dimension. Of course, we can produce features smaller than this, but it would need to be carefully reviewed by our engineers before the build begins.