Sometimes Size Does Matter - Why Clamp Tonnage is Important

Vince Farrell

By Chris Ma

When using SOLIDWORKS Plastics, injection pressure, air trap and weld line locations, sink marks, and fill time are all some common things that are considered when designing plastic parts. However, clamp tonnage (the force imparted by the injection machine on the mold halves to keep them from separating during the injection process) is often overlooked by novice plastic designers. Let’s look at two reasons why you should design with clamp tonnage in mind:

Reason #1: Undersizing Your Machine

When the clamp force supplied by your injection molding machine is insufficient to manufacture the part you have designed, you may get some flash around your part.

Clamp Tonnage - Flash Example

What is flash? During the injection process, pressure builds up within the mold and the injection molding machine has to counteract that pressure by applying a clamping force. If it can’t produce enough force, the mold halves can open slightly and molten plastic can flow into unintended places. This unwanted plastic is called flash.

Reason #2: Oversizing Your Machine

Okay, so why not just run the part on the biggest machine you can find? Well, let’s consider running a part on a 610-ton machine. You may be avoiding flash in your part, but typically the larger the injection machine the more it will cost to run.

So like the title says, size matters. Using a tool like SOLIDWORKS Plastics will allow you to accurately calculate the clamp tonnage required for your part so you can pick an optimally sized injection machine.

Recently I helped a manufacturing company prove to their customer that a part could not be molded, because the required clamp tonnage was too high. I'll be presenting a webinar on September 24th highlighting that project, titled You Can’t Mold That Part - Here’s Why - click here to join the webinar.

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