Archive for Září 23rd, 2011

Guidelines For Avoiding Costly Mistakes Plastic Parts

Guidelines For Avoiding Costly Mistakes Plastic Parts

Errors, that newcomers regularly make whilst beginning to design plastic parts can often be discovered by Rapid prototype parts before commencing to construct an injection mold. I am going to point out some frequently made mistakes and present several suggestions for designing the perfect plastic parts.

The procedure of producing plastic parts differs from making other components like metal parts. An important practice in designing plastic components is to attempt to sustain identical wall thickness. Parts with uneven wall thickness are likely to cool irregularly and leave bad shrink marks which are noticeable on the outer surface. In addition, this might bring about tension at the junction of high and low shrinkage and cause the part to warp.

Given that plastic components are shaped by injection molding, they must be designed with a draft. Draft is the angle of taper of a wall. A draft angle of 0.5 degrees is considered as a bare minimum for many appliances. Draft angles of 1.5 to 2 degrees are regarded normal for plastic injection molding.

Whilst using a thin wall thickness, every so often it is required to increase the stiffness of a component. One frequently used technique is to include ribs. Yet, when adding ribs a few guidelines have to be adhered to. The thickness of the rib ought to be smaller than the wall thickness. Typically ribs are 60% to 80% of the wall thickness and spaced no less than 2 times the wall thickness apart. Don’t make the height of the rib upwards of 3 times the wall thickness. It is better to increase the quantity of ribs as opposed to the rib height.

Bosses are utilized as components need to be mounted and are now and then designed with thick wall sections that may affect the look of the final parts.  As a guideline , the wall thickness around a boss should be 60% of the nominal part thickness if that thickness is smaller than 1/8 inches. If the part thickness is more than 1/8 inches, the nominal part thickness ought to be 40% of the wall thickness. In order to avoid sink marks and voids, the next rule should be observed when determining the height of the boss. Ideally the maximum height of the boss ought to be no more than 2.5 times the boss hole diameter.

When designing plastic components, sharp corners should be avoided. Sharp corners can lessen part strength and act as stress risers. Sharp corners moreover effect plastic flow causing parts with nasty surface patterns. The internal radius of bosses and ribs should be one quarter of the part thickness, yet a minimum of 0.015. The inside radius of other corners ought to be a minimum of half the wall thickness. The exterior radius should be the internal radius plus the part thickness.