Hi all, Just added a request in the knowledge base for an article on the differences in component design from Thermoplastic to Thermoset, and thought i'd put a little shout out here as well. I've designed a part which needs to be made from Urea (plastic!), and have a rough idea of the ‘do's and ‘do not’s - for example, as far as i know, the wall thickness is not so important in Thermoset as it doesn't suffer from shrinkage, but I've been warned off undercuts as the hot mould tool will wear out quickly. Can anyone shed and light on the do's and don'ts of Thermoset moulding compared to thermoplastic? Failing that, does anyone know of a design guide online (Dupont or Distrupol do similar guides for their own branded materials, but can't find anything for Urea specifically). Any help welcome!
Try this link http://www.akronporcelain.com/Plastics/DesignGuide.pdf for a thermoset plastic design guide.
Generally injection type thermoset molding is done with the "RIM" (reaction injection molding) process although much more of it is done using more of a casting methodology except with precision molds. All kinds of data out there on both of these process, so check with your prospective fabrication vendors. Most commonly used for "rubber" like parts but common for automotive bumpers and lots of other things as well. Since it is generally done at a low enough temperature for manual handling of molding equipment all kind of things not normally done with injection molding can be done. Parts can have metal structural components embedded inside the plastic as well as inserts. While comparatively biodegradable, these days urea based plastics are generally not used in favor of less carcinogenic materials. So why urea? Importantly don't be an "over the wall engineer"! These kinds of questions are not the exclusive province of design and should be addressed with a collaborative engineering effort that involves all the stake holders from concept to end user.
Back in the early 80's I worked for a company making brush holders for Black & Decker. We used a process called "injectoset". As a mold maker and designer I was responsible for understanding what could and what could not be done. To say that these plastics do not shrink is incorrect, they do. Especially using an injection type process. Sharp corners and undercuts are the two worst enemy's of a sucessful application. The bestthing about these materials is that they are not conductive, thats the main and only reason to use them.
Hi, I was designing mould tools and moulding Thermoset Plastics in Commutators 30yrs ago. Remember the tools are hot and any components have to be pre heated. After moulding it is best to post cure the thermoset material to stabilise it. You can have undercuts providing you have enough meat around the part to support it, as well at having anough room for any side actions etc. Cheers
