Ultem Machining, brittel material?
Ultem Machining, brittel material?
(OP)
Please see attached picture.
Not sure why it crack. It seems that the crack start at internal slotting area.
It does not crack when we receive the part, but after a while, it break into two pieces.
1. This might due to the stress concentration at one point?
2. I assume that: When the bottom surface of the machine part is not flat to the ground (let say flatness is about .012", bow in one direction) , when install it to the base, due to the strain it start cracking. I think Ultem is kind of brittle after looking at the cross sectional view.
What do you guys think?
Not sure why it crack. It seems that the crack start at internal slotting area.
It does not crack when we receive the part, but after a while, it break into two pieces.
1. This might due to the stress concentration at one point?
2. I assume that: When the bottom surface of the machine part is not flat to the ground (let say flatness is about .012", bow in one direction) , when install it to the base, due to the strain it start cracking. I think Ultem is kind of brittle after looking at the cross sectional view.
What do you guys think?





RE: Ultem Machining, brittel material?
You've got stress raisers everywhere.
A little bow is all it takes to complete the fracture.
Taken purely on its own, lacking context with which to defend or justify it, it's an awful design.
Sorry. You asked.
Mike Halloran
Pembroke Pines, FL, USA
RE: Ultem Machining, brittel material?
Based on my observation, the Right side has more meat but somehow the crack seems to be started at that area.
RE: Ultem Machining, brittel material?
Counterbored slots, everywhere, intersecting, from both sides, with small/no radius at the bottom 'corner' of the c-bore.
Do you anneal the material before or after machining?
Use a machining coolant that's known to not affect the material?
Mike Halloran
Pembroke Pines, FL, USA
RE: Ultem Machining, brittel material?
If the material is critical rather than the manufacturing process, you might consider that. It may also free you up some on the geometry to eliminate some problematic features.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Ultem Machining, brittel material?
How could you have a radius at the corner of the c-bore? I don't see this in many application.
RE: Ultem Machining, brittel material?
RE: Ultem Machining, brittel material?
The crack seems to start from a sharp corner and the surface finish shows some indications of being pushed by the cutters at times.
You have created stress risers by both extreme changes of section thickness and by creating very sharp edges in high load areas.
You should make sure you use very sharp tools with moderate rake and lots of back clearance. Sabic should have a technical information sheet on this.
You should also use your cutters have a rasius at the edge of the cutting surface.
You must anneal the parts.
Reducing section thickness in some areas might help with load sharing, but I will presume you are locked into the part geometry for reasons required for fit or function.
Regards
Pat
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RE: Ultem Machining, brittel material?
Patprimmer and Mike: What is the minumum radius?
See attached.
RE: Ultem Machining, brittel material?
Regards
Pat
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RE: Ultem Machining, brittel material?
I.e., you don't want a screw head bearing on the radius, and you want the c-bore diameter large enough to leave a visually noticeable radius at the bottom of the pocket. I.e. the outer diameter of the flat part at the bottom of the c-bore would be derived from the max screw head diameter plus an allowance representing the screw position tolerance, plus a little fudge.
Mike Halloran
Pembroke Pines, FL, USA