Tech|Tips – 3DL: Milky “Stretch” Marks On 3DL Surface

Recently I worked with a 3DL component producer that was experiencing wrinkles across the width of very large parts. After working our way through the process the primary culprit was an excessively large membrane belly upon press closing. (See the previous blog)

In the process of working through one issue, another was created, albeit very briefly. Immediately after eliminating the large wrinkles by reducing the press temperature, preheat time and membrane belly, we began to see what looked like stretch marks.

However, there were no differences in surface quality to the touch. It was just a slight irregularity in appearance in certain lighting. (See photos 1 & 2)

Example #1

Example #1

Example #2

Example #2

This is a problem that is rarely seen but can appear when trying to make fine changes to temperature and preheat time. When the 3DL has not been conditioned completely via heat to stretch evenly throughout all of its layers, this type of issue can arise. The solution is simple – make very slight increases in press temperatures and/or preheat times until the problem disappears.

Bill Formella is President of Formella Contour Solutions and is the owner and moderator of the LinkedIn group Membrane Pressing & 3D Laminating Design. You can reach Bill at bformella@formellacsi.com. For more tips and ideas, follow us on Facebook and Twitter.