Measuring die expansion and or movement with a dial indicator 1

[WillKMI]

Greetings, looking for suggestions on a problem I'm trying to troubleshoot with a compression mold. Part of the challenge is the fact that the upper half of the mold is electrically heated to 300 degrees F (mold surface at about 250, not sure what temperature the outer faces of the tool reach.

What I want to set up is dial indicators on both sides to monitor the expansion and either confirm that it is expanding uniformly or whether the expansion is not uniform and the billet is shifting. I want to do this on the cheap using $17 harbor freight indicators rather than risk something more expensive, I was thinking that the ambient air probably means the heat won't transfer all the way to the dial indicator internals but I could try insulating the tip with a ceramic knob just in case.

Any better ideas?

 

[MikeHalloran]

Indicate a planar surface on the die.
Use a convex tip on the indicator.
Better, use an extra long convex tip.
Insulate the indicator back/mount or support it from something that's isolated from the heat.


Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Faster:
Jam beer bottles (yes, full) between the die and the frame of the machine.
If the die is shifting, only the bottles on one side will fracture.
If the die is expanding uniformly, most of the bottles will fracture.


Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

You may want to consider using an insulated tip for another reason: the thermal load of the tip could change the thermal uniformity of the mold and alter the behavior.

If you can afford a bit more coinage, there are 3D scanners that could be used; even a Kinect could potentially be applied to your application. The main benefits are:
> non contact, so no perturbation of the thermal condition of the mold
> multiple points of inspection, so even small area distortions can be detected
> less concern about fiducials, etc., because the data can be self-registered, and there's no worries about the heat affecting the mounting of the dial indicators

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[hendersdc]

Could you set up fixed reference surfaces around the tool that are a known distance from the tool surface when it is cool and then measure the distance using calipers after the tool is heated? Calipers may not be the right solution, if the distance is small gauge pins could work nicely. The point is to use a means of measurement you already have lying around.

 

[EdStainless]

We used to attach long ceramic rods to dial indicators (4"-6") when we needed to do hot work.
This way we could use good indicators and still keep them safe.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[ctopher]

I this is important, and you want to measure the expansion of a mold, I would not use $17 harbor freight indicators.

Chris, CSWP
SolidWorks '16
ctophers home
SolidWorks Legion

 

[Tmoose]

How much expansion are you anticipating?
If several 0.001s of an inch, I'd probably buy the HP ( edit - HF )indicators a few weeks in advance and test them for smooth operation, then against gage blocks for full range accuracy, then full stroke them 100 times and test them again.

To deflect the (completely justified) skeptics maybe these would be a better choice.

http://www.mscdirect.com/product/details/76450071

It's pretty easy to "calibrate" a dial indicator by lifting the stem, sliding precision shim stock into the gap, and releasing the stem.
Used that method to reveal a big problem when somebody used one of those "centering" indicators that reads 1/2 of the actual motion.

 

[WillKMI]

If I ran my calculations correctly, linear expansion of a 48" piece of aluminum going from 70 to 300 F should mean around 0.040" of expansion per side.

I wanted to keep this test simple, I know that it could run away in cost and complexity if I was doing everything I want to in an ideal manner. I'd like to measure all 4 corners for growth in the width direction and the length direction, measuring the growth of the billet with respect to the base plate and movement of the base plate with respect to the platen of the press. That's 32 measurements with an assumption that the movement of the platen is purely linear and repeatable.

If a quick and dirty test with a couple $17 HF indicators suggests a more detailed and accurate study is needed, I'd probably get the tool builder involved, but my expectation is I'll either see equal movement on both sides or I'll see a significant difference from one side to the other, at which point I'll ask the tool builder if one of the keyways is sheared or something.

The tool is going into the press next Monday, so it's not a timeframe where I can go through any sort of purchase approval process, I just want what I can get reasonably out of pocket, throw in my suitcase and take with me to western Kentucky.

I'm interested in more than just thermal expansion, I want to see if the tool moves during closing and cycling as well, and it's inside a safety cage which locks out electrical and hydraulic power except on one side where parts are manually loaded and unloaded, and on that side it is protected by a light curtain to keep the tool from cycling while an operator is there, so some of my measurements I want to watch while the tool is running couldn't be done by caliper.

This discussion has prompted me to think through the problem some more... Does the base plate heat up and expand? There isn't really anything to positively locate the baseplate on the platen, it's just clamped in place with the tool closed. I'd presume that the billet heat transferring to the steel base plate transfers to the platen so it doesn't heat as much, but it must heat up some, and maybe that expansion is happening non-uniformly.

ETA: Discussed with our tooling engineer, and the billet is on risers so heat should dissipate before it gets to the base plate, so there shouldn't be an issue with the base plate expanding and causing a shift of the billet.

 

[1gibson]

My first thought is a frame with rods mounted in holders that slide, then stay. Touch the rods off on critical areas, heat it up, cool it off, measure the gap that remains.