Design Tip - 3

Wall thickness.

This is one of the easiest issues, at least easiest in theory. As most of plastic part design documentation say, the walls have to be as uniform as possible.

If it's so easy why we have a lot of problems with the wall thickness? The point is that a lot of plastic part could not be done using a constant wall thickness. In my opinion there are two main reasons, one is the part function, sometimes to give the desired function to a part we have to use different wall thickness; the second reason is that sink marks are not accepted in most of our parts, so we need to make thiner walls to avoid the marks.

My suggestion is to try to use uniform walls where possible but if wall thickness needs to be changed try to use smooth thickness changes (not sharp changes). Try to minimize the changes. Try to add recesses in the not visible areas to keep the thickness uniform (if you are lucky and your part has not visible areas). Finally use the thinnest thickness possible (cost reduction is a must nowadays).

If you really need big thickness differences, you are not able to make smooth changes and it is not possible to add recesses on the b-side of the part, be careful! Your part will warp, will be difficult to fill & pack and it is probable you will have marks (sink marks, flow marks and others). In this case try to think on a different design to fulfill the specification, try to think if you are able to split the part in 2 or if you are able to give some of the function of the part to any of the surrounding parts.