A good rule of thumb is to apply 1 degree of draft per 1 inch of cavity depth.
There are multiple paths to injection molding. Some parts are first prototyped through 3D
printing where moldability considerations are of limited concern. Others take a more
traditional machining route that allows for iterative testing in engineering-grade materials
similar to that of molding. And many simply jump right to injection molding.
Before production begins, there are important design considerations that will improve the
moldability of the parts, and ultimately, reduce the chance of production hiccups,
cosmetic defects and other issues.
In this month’s design tip, we walk through these key design elements:
- Draft and radii
- Wall thickness
- Coring out and ribbing
- Ramps and gussets
- Gating and ejection
Read the full design tip here.
In this week’s tip, we look at best practices for designing text on parts, and answer questions like raised or recessed, which fonts to use and alternative options.
Raised or Recessed?
Features can either be raised up or recessed in to part surfaces, but which way is best? Because molds are machined, we prefer to mill the actual text or logo instead of milling around those features. This allows for faster machining, easier polishing and eliminates very small mold features that may break off.
Please extrude the text/logo features by a minimum of 0.010 in. and a maximum of 0.020 in. This allows your text to be legible and not stick in the features while molding — any deeper and you risk having the text peel off and remain in the mold. So, design raised features on your CAD model to improve moldability during manufacturing and legibility on final parts.
Raised text on part is recommended.
If you must have recessed features on your part, many of the same guidelines still exist, but there is one additional concern that you will need to address in regards to the spacing between characters. Having text recessed on your part now means that the features in the mold are raised and we need to machine between each character. Features with less than 0.125 in. of clearance require spacing between each character at a minimum of 0.020 in. to properly remove all material to ensure the legibility of text.
How do you know if you should use low-volume injection molding or traditional methods? What benefit does soft aluminum tooling provide? These are just a few questions we hear regularly, so we wanted to shed some light on these important molding considerations.
Before Proto Labs began in 1999, prototyping with injection molding was costly and took months to receive the very first sample parts. We took a low-volume approach to injection molding where it was possible to get a handful of parts in a few days rather than the large-scale approach that nearly all other manufacturers used that involved part minimum in the tens of thousands and full-scale production in the millions of parts.
Proto Labs specializes in aluminum molds that use high-speed CNC machines to create a standard single cavity mold in as fast as one business day with the ability to produce up to 10,000 parts or more. Complex parts are also possible by using pin-actuated slides as well as hand-loaded mold inserts. We try to take the difficulty out of injection molding design by simplifying it.
Conventional molding uses a much more complex molds that take weeks to design, where Proto Labs is highly automated. Complex multi-plate mold designs using lifters, collapsible cores and multi-cavities are able to produce much more complex parts at high volumes, and typically, mold creation for these molds take anywhere from four to 12 weeks.
We discovered that there was a much greater need for low-volume manufacturing. Customers were placing additional orders for a few thousand parts that were being used to set-up production lines and even limited short-run production while the conventional tooling was being built.
Conventional tooling is your production mold. It’s difficult to have a bridge tool produced without having your production molder hold off on manufacturing while they create a bridge tool. Using both methods allows you to have two manufacturers producing molds side-by-side to ultimately have parts produced faster.
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.