Archive for Září 20th, 2011

Guidelines For Avoiding Costly Mistakes Injection Molded Plastic Parts

Guidelines For Avoiding Costly Mistakes Injection Molded Plastic Parts

Mistakes, which newcomers regularly make whilst beginning to design plastic components can regularly be discovered via Rapid prototype parts before starting to construct an injection mold. I will point out a number of usually made mistakes and present some pointers for designing the perfect plastic components.

The method of manufacturing plastic components is different from producing other components such as metal components. An important practice in designing plastic components is to try to maintain identical wall thickness. Parts with irregular wall thickness are likely to cool unevenly and leave nasty shrink marks that are visible on the outside. In addition, this might cause stress at the junction of high and low shrinkage and cause the part to warp.

Given that plastic components are shaped by injection molding, they ought to 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 a lot of appliances. Draft angles of 1.5 to 2 degrees are regarded customary for plastic injection molding.

Whilst using a thin wall thickness, now and then it is crucial to raise the rigidity of a part. One usually used technique is to add ribs. While inserting ribs, be sure to make the thickness of the ribs less than the thickness of the wall. Normally, ribs have 60% to 80% of the wall thickness. When multiple ribs are utilized, they must be spaced at the least 2 times the wall thickness apart. It is best to keep the height of the ribs less than 3 times the wall thickness and rather add more ribs instead of increasing the height of the ribs.

Bosses are another design building block used for mounting and assembly purposes. Regularly, bosses are designed with thick wall sections that can influence the appearance of the plastic component and the finished product.  As a guideline , the wall thickness around a boss ought to 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 ought to be adhered to while determining the height of the boss. Ideally the greatest height of the boss should be no more than 2.5 times the boss hole diameter.

When designing plastic components, sharp corners ought to be avoided. Sharp corners can lessen part strength and act as stress risers. Sharp corners moreover effect plastic flow producing parts with unappealing surface patterns. The inside radius of bosses and ribs ought to be one quarter of the part thickness, but a minimum of 0.015. The internal radius of other corners should be at the least half the wall thickness. The outer radius should be the inside radius added to the part thickness.