Many times we receive a drawing with demanding tolerances, a 3D design that turn on all alarms, for example big accumulation of mass, with paralelism, perpendicularity or flatness in raw materials like polyamide with high percent of glass fiber. By this reason, we think it is necessary to bear in mind some considerations about design of injection molding based on more than 25 years of knowledge, that probably it could be of help.
In ZATEC we can advise to customer collaborating in this first phase of design, checking the feasibility analysis to optimize the design of piece, according to adequate raw material depending onf inal application and our process of injection molding, to reduce the investment if it is possible. As you can read as follow, we have remarked some examples about it:
although sometimes it is not possible to avoid changes of thickness, is very important to have homogeneus thickness without sudden cahnges always it will be possibe. An irregular thickness could generate problems like deformations due to differences of shrinkage in the mentioned thickness, or sink marks in the opposite face.
the sharp edges are stress concentrations (Kc) weakening the piece. Although we can do radii in some areas could complicate the mold, also we improve the design considerably. It is necessary to take acocunt the big accumulation of mass in the perimeter when we round this area. A good example is a plastic part like a box, and the barrel efect.
If we want a rigid piece, it is better to add nerves like reinforcement than increase the thickness. It is very important to bear in mind the crosses of nerves due to possible accumulation of mass, that as you know, this accumulation can generate asthetic defects. In areas with flat surfaces, besides of mentioned nerves, it is necessary to take account the cooling in mold with variations of temperatute, location and size of injection gate(s) and the chosen of adequate engineering plastic based on final application.
Towers and spigots
It should be designed to avoid big accumulation of mass, bubbles… theredore the important consideration is the difference between exterior radius and inner radius.
if it is possible, avoid the thread’s pitch too thin. In case of female thread, avoid the fillet ends up to final of piece by possible breaks. In case of male threads demolded by sliders, can be stopped at height of union line, avoiding if it is possible the problem of wear. As we have mentioned, is important to avoid the sharpd edges with weak mechanical properties, by this reason a good option is to reduce them.
Parts with Inserts
The inserts must not weakening the around material, by this reason the optimum thickness of around material of insert, it must be verified. The shrinkage of plastic on the metal can generate an overflow. This overflow could be removed, doing a ribbed uniform and crossed in the insert part. Based on our knowledge, it is recommended to heat the insert before injectioning.
If we can help you with a project of plastic part, based on our expertise of engineering plastics and injection molding, do not hesitate to contact us like company of technical plastic injection located in Muel, Zaragoza (Spain), where we can collaborate actively with our customers.