defects/voids

[eclarkmx]

Not so long ago while doing a part we found a very strange void. It had happened before we thought that a substance in the surface of the mold could be the problem (oil, water, Etc)this last time it appear without going all the way down to the mold, and we are puzzled how it could happened.the line you see in the bottom is not metal or anything like that it seems to be a stress mark. the profile if we had a section of it would be of half an hour glass. I wonder if someone has an idea of what could make this type of a void.

 

[lisa247]

What type of test have you done? What composite material is it? WHat is the large thing in the centre of the photograph?

 

[berkshire]

What is the process you are using?
It looks like a trapped air bubble that has not had time to come to the surface before the resin hardened. This can happen with vacuum bagged lay ups and with resin transfer molding, it is not so common in pre preg lay ups.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[eclarkmx]

The material is HDPE. We are extruding it the large thing is the void after some layers were machined. As I mentioned before we thought it was a contaminant we know it isn't a bubble because we video taped the process and there is no indication of bubbles at all. We felt it was a contaminant that gasified because of the concentration of heat but we do not find any type of residue.

 

[berkshire]

So what we are looking at in the Photo is a breakout on the surface of a machined part.
How are you molding the part, is it an extrusion, or is this a hot melt press dropping into a cavity mold?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[berkshire]

Forget the question, I just re read the post and realised you were extruding it. You may get better answers on,

http://www.eng-tips.com/threadminder.cfm?pid=712

B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor