Side Action Flash, Part 1, Mold Engineering Software

Have you ever seen a mold with the side action flashing across the split face? Have you checked the design and the steel over and over only to find that the dimensions appear to be correct? The flash problem may be due to an under-designed mold plate. This is particularly true with “A”-side action molds for large parts, and even more so when the side action is contained in a mold plate with a “through-pocket”, like the one shown below.

In this case, each part has 1.25 square inches of surface area for the cavity pressure to generate force on. This force must be overcome by the strength of the plate. Let’s assume that the cavity pressure is 10,000 p.s.i., which is not an unreasonable assumption. This is a 4-cavity mold, so the force trying to separate the slide faces is 50,000 pounds.

You have two types of plate distortion to calculate here: one is the stretching of the 2 legs that form the upper and lower boundaries (the ends) of the pocket. You can get a better visualization of that in the DZynSource Mold Engineering Software screenshot shown below. The other distortion is the “bow” of the sides of the pocket, again see the DZynSource screenshot.

You can see from the calculation here that the center of the plate, left as designed, would blow apart approximately .0012 inches, which would probably flash when molding a polypropylene part. In this case, as you can see in the drawing, the plate weakness was overcome by installing an interlock between the slide pocket plate and the stripper plate. This interlock gave the plate enough additional strength to mold flash-free parts. Of course, if the designer had the DZynSource Mold Engineering Software, this problem could have been avoided by doing “what if” scenarios with plate sizes and thicknesses to come to a more robust design that would not flash without extra mold components.