Correcting Warpage in Molded Parts

Our CT scan data and formulas combined with the shop’s expertise of their part makes for a winning recipe.

Victoria Russman
Victoria Russman

Correcting Warpage in Molded Parts

A tooling manager who creates molds, a CT scan, and a little art are the ingredients for our modus operandi today. This is the story of a high-level, problem-solving case of correcting warpage in molded parts to bring them into tolerance. The tooling manager brought us a small plastic gear. It’s a 2″ tall cylinder, 1″ in diameter. It has a hole in the middle created by a a steel pin. The hole is too big and it would seem they need to shave the pin to make the hole smaller to bring the part into tolerance. Sounds simple enough so far. Not so. It gets a little more knotty as these things sometimes do.

We are not dealing with a smooth cylinder. It has some bumps. During the cooling process there is a dimensional change as the plastic shrinks and collapses. Sometimes this can happen while a part is still in the mold or it can even happen after the part is taken out of the mold. Building windage can help solve the problem of distortion in molded parts. Windage is an adjustment made to the mold to correct for warpage. By building the pin out it should account for the warping of the gear as it shrinks.

Think of an hourglass. Let’s say this is what the hole looks like after it is taken out of the mold. If we change the pin to a whiskey barrel shape, we can correct the hole. We will CT scan the part. We export the scan data as individual points or a cloud of points with millions of X, Y, Z coordinates into Microsoft Excel. We will apply engineering and mathematical formulas to calculate distances and vectors on each point relative to CAD nominals. Then, we reverse the values and vectors based on how far each point deviates from CAD. The idea is to end up with an inverted shape of the original part. These may end up being 1/4 mm adjustments. It’s not a perfect science and there is a little art involved. Our CT scan data and formulas combined with the shop’s expertise of their part makes for a winning recipe. If done properly we will be able to take the guesswork out of the tuning needed to bring their part to tolerance. This is a complex problem, but Nel is confident in our people, process, and platform to ultimately save this tooling manager time and money. We will update you as things progress. Check back on our blog or social media platforms for the latest.

Warpage in molded parts
We will reverse values and vectors to form a whiskey-barrel shaped pin to correct the hourglass distortions; taking the guesswork out of tuning using CT scan data and formulas.