Recommendations For Designing The Perfect Injection Molded Plastic Components

First-time designers of plastic parts commonly make a large amount of errors. Rapid prototyping may reveal various errors prior to committing to the price tag of a injection mold still other errors become obvious just once the final components emerge. I will point out various generally made mistakes. I will moreover explain the impact that those types of mistakes will have on the final parts. I will moreover give various pointers that are good design procedures to adhere to whilst designing parts.

The first guideline to abide by when designing plastic components is to try to sustain unvarying wall thickness. In this respect, plastic parts differ from other components. As such designing plastic parts needs a entirely different design strategy than for example metal components. Components which include irregular wall thickness tend to cool irregularly during the manufacturing. The result are shrink marks which are visible on the outside. Another effect is warping. Warping can be created thanks to stress at the junction of places of dissimilar shrinkage.

Plastic components are shaped by injection molding. During this process, two halves of the mold have to be detached from the part during manufacturing. For this reason, plastic components should at all times be designed with a draft. Draft means the angle of taper of a side wall or rib. A draft is vital such that the tooling can be detached easily from the part. Too small draft angles can make manufacturing of the part difficult. A further probable difficulty are noticeable surface marks that are caused throughout removal of the tooling. Most mainstream devices make use of draft angles between 1.5 to 2 degrees.

An often utilized design element are ribs. Ribs can increase the stiffness of a part. Whilst adding ribs, be sure to make the thickness of the ribs less than the thickness of the wall. Generally ribs are 60% to 80% of the wall thickness and spaced no less than 2 times the wall thickness apart. The height of ribs ought to be kept to a minimum. At most the height ought to be 3 times the wall thickness. It is better to insert extra ribs rather than raising the rib height.

Bosses are one more often utilized element. Bosses are valuable while parts have to be mounted or assembled. Frequently bosses include thick wall sections. Those can lead to surface imperfections of the plastic components. Usually the wall thickness around the boss should be between 40 and 60 % of the part thickness depending on the part thickness. The next rule is going to further help avoid surface imperfections such as sink marks and voids. The height of the boss ought to be no more than 2.5 times the diameter of the hole in the boss.

Sharp corners should be avoided while designing plastic parts. Sharp corners can lead to stress risers. Those can cause part failures and lessen the strength of a part. The inside radius of ribs and bosses should be at least 0.015. The inside radius of other corners ought to be at the least half the wall thickness. The outside radius ought to be the inside radius added to the part thickness.