Void Detection in Molded Plastic Part

Detecting voids could be done by checking the density of the molded part.

X-ray would also work. Sectioning would destroy the part, so you might not want to do that.

Fix the process. You can't inspect quality into a part. You need to tune your injection parameters so that you are not putting voids in the part.

Your units are not clear. "less than 40000th inch from surface." What are you measuring?

Hello Lyn,

Thanks for your reply. We are considering product failure if we found void at that distance from surface. Currently we are cutting part and perfoming manual inspection of Void. We want to get rid of this.

Yes we can improve process but still we need to perform quality check on product.Failure do that can cause damage when we do welding with other part.

So we must need to have non destrutive method to perform testing. Is any thing better than Ultrasonic??

How X-ray work in terms of uneven and very small width and performance on detection of damage at certain distance?

Appreciate your help.

Have you considered transmitting through a stream of water, free falling on your test piece. Flowing water makes an excellent waveguide.

YOU NEED TO EXPLAIN HOW YOU WILL TEST 40,000 th of inch. Looks like a mistake

No existing ultrasonic equipment could detect such void measured in 0.000635mm....

I think he meant 40 thousandts of an inch (0.040") .

Yes You are right. Thanks for more clarifications. But experts we already tried to approach 2-3 vendors and they are in process in their Labs. But my company wants to know what else can be use if Ultrasonic not worked. We desperately need something to get rid of those defects.

"We desperately need something to get rid of those defects."

Testing will not get rid of defects. It only identifies the parts that you can't sell.

Without knowing the physical properties, further processing requirements (welding) end use, etc. there's not much we can do.

What material are you using now? What type of tooling? What type of machine?

Have you tried simply weighing each part on an analytical balance?

You need a process engineer to fix this. All the QA in the world will not result in void-free parts.

Hello Lyn,

Thanks for your reply.

I am looking solution for Battery Cover. As i am new being this discussion helping me to learn.

It is Molded Plastic. We are going to weld it with bottom cover(which also require to be void free). Currently we are cutting it manual and perfoming Visual Inspection to identify Voids. As you seen from above, we just need to identify void at certain distance from Suraface. So we have process developed at previous stage, but we want to double check of Voids during Quality Check.

We can do balance check, but we wont care if void presence more than 0.040" from Surface. Because we are welded upto that point.

THanks Again

Voids generally occur when the material transitions from thin section to thicker section.

How many different thichnesses is this cover? The entire part should be the same thickness for proper molding. Differing cross sectional thicknesses will require more injection and hold pressure.

Can you post a picture of a part that has been sectioned to show us where the viods are and are they always in the same place, etc.

What is tolerable limit of voids?

Consider TRANSILLUMINATION: it is a cheap and easy technique we have used in medicine way before the discovery of X-rays! Depending on the thickness and type of material you are using, it simply may work!