material for checking die clearances

Plastigage is often used for this purpose. It doesn't need to be warmed, unless, I suppose, the ambient temp was very low.

Plastigage was my first guess too Ken, but I have never seen (or looked for it) in any other than cord form (like for bearing clearances)

Bill

I haven't seen it in anything other than the cords, either -- it's strength, and probably its patents, have to do with the ease of measuring tight clearances by the squished width -- which is easy to see. To check a die, you'd need to lay up a matrix of the stuff -- and even then might not find exactly what you want to know. (If I recall, the stuff is incredibly expensive, too.)

I never used warmed plastic sheeting or observed it being used, but that is mmaterial. You said that the material was used in sheet form. I suspect that it was "Mylar" -a DuPont product otherwise known as Polyethylene Terephthalatea or PET.

Mylar is available in fairly precise thicknesses, so one could use varying thicknesses to determine if the punch/die clearance was sufficient to bend, rather than cut it. I guess that it would be better than using brass shimstock (my old favourite) as there should be less chance of locking the die should the clearance be insufficient.

Best Regards,

Ing. Robert Forbus

I remember a "string" of precise diameter plastic from, IIRC, Plastigage. You select the appropriate dia, then close the die. Measuring the width of the flattened cross section gave the clearance.

I've never seen the sheet you are looking for, but a plastic supplier should be able to help you find one with a low softening point and low thermal expansion.

Polyethylene might work. It's used for vacuum forming at fairly low temperatures.

Plastigage is the material. I've used it to the check clearances in engine rebuilding for main and connecting rod bearings. I would imagine it would work with a die as well. Here's the company info I didn't find a web site.

2917 Wildwood, Box 1167
Jackson, MI , 49204-1167
Phone: 517-788-8000
FAX: 517-788-8215

Dear "well I reckon",

A previous comment was made on plastigage, I do not believe that this is a good choice for what you are describing. Plastigage is useful to check the likes of bearing clearances in cars, and perhaps small close pinch areas in a small number of dies with specific material thicknesses.

There are many methods for checking DIE CUTTING CLEARANCES - I assume that is what you were asking about. Generally the most precise way to check clearances is to have the die closed with the strippers and blocks removed which may interfere with access to the area to be inspected, then the die is closed without the need of the press, using its guiding system (pins), and a crane for heavy dies. The upper and lower die shoes are then rested on accurately ground equal height parallels, all 3 more at maximum distances reasonable for the accuracy required and distances to space the upper and lower die halves equally and parallel such that the cutting edges are engaged.

Now to the checking:

Once the Die is closed and it is assured that it seats tightly on the paralles, and that the cutting edges are engaged to a point that a feeler gauge can be used to check the clearance between the upper and lower steel cutting edges very accurately.

Talking about accuracy: What you did not mention in your question is the type of material being pierced, the type of die set, and the type of die - ie. progressive, trim, combination, form trim, pinch trim etc... this has a profound effect on the method of die clearance examination for cutting edges.

For checking cutting clearances which are near zero, a layout blue can be applied to one side of the tool with the stripping device removed, the die is then to be closed preferably in the press where the tool runs, and the amount of scraping on the cutting edges observed. Near zero cutting clearances are sometimes desirable for soft materials as well as thin materials.

If you were referring to die clearance in terms of "squeeze distance" a chunk, or small ball of plasticine can be placed on the die, with a drop of oil, and after a complete cycle the thickness can be observed with a small graduated steel rule. This is not truly accurate, but is a good indicator of initial distance. For observing tool form pressures, a trained individual can use Die Blue to observe "tight" spots in a die, this needs to be performed by specialized individuals, that are trained in the ability to "read the spot", and the proper application of this technique. False readings can lead to disastrous and excessive clearances if re-cuts of the tool is initiated.

Please note that the simplest way to determine clearances is to simply look at the material which was pierced - unless there are other undue pressures in the tool distorting results - simply look for the shear and break zone of the steel material which contacted the die cutting edges during the cutting action. you should see about 1/3 to 1/2 shear, (shiny, and the rest dull (the break or fracture zone of the material) as well as the die roll (Radius on the leading edge of cutting edge entry- this indicates a good balance of tool longevity, most economical tonnage requirement, and least burr condition on the material. Of course try to use the same material as used in your production. As the shear zone increases, generally the die clearance decreases. This holds true for conventional stamping, and not for fine blanking or shaving processes.

What you had described:

I understand what you had described, this type of check is generally used for larger stamping dies piercing material thicknesses upwards of .040". This process should be conducted by a trained tool and die maker, as the accuracy of determination by using a hardening non shrinking compound, as well as prep work for adhesion and the physical process of opening the die exactly parallel is vital to accuracy. After all usually cutting clearances are measured in a few thousands of an inch.

Now to point you in the right direction for your question:

General rule for looking for materials for what you described - fast dry time, 2 component material, steel properties, and most importantly - non shrinking. Keep in mind that there is a lot more required to do this properly, even if you have found the material.

I hope this helps in your search for the correct material for the checking application you had described, please describe your process in some more detail.

To send me a mail direct:

mircog@canstampconsulting.com

Have a great day.

In the event that you don't have one of the products mentioned, here is a cheap easy solution that will work if you are checking cavity wall thickness. Take a small ball of modeling clay and put a piece of cellophane tape on either side of it. Put it in the die or mold and close it up. If you are checking a vertical wall you can leave a tail of tape to stick to the wall so the clay ball stays in place. You have to be careful not to squeeze the clay too much when you take your measurement, but it will work. You can check down to about .015 with this method.

Microconsultant offered a fairly thorough answer to your question; I just want to add that I have also used lead solder to check form and pressure in many instances.

If you are attempting to center a punch with a die, women's nylon hosiery work very well when a spread evenly around the cutting edges. Loosen the punch holder bolts, close the tool and then tighten. Use more layers for more clearance. Grocery store plastic bags also work, but I have had more consistant success using my wife's old stockings.

Lead Solder...

Lead actually used to be available as sheet, and works well for determining various die settings, however Lead is poisinous and generally banned, as it is readily absobed into your skin, and doesn`t like to leave your body once inside, as far as I understand. Lead free solder wire does not yield as accurate clearance detection results compared to older leaded solders, as it "smears" differently.

Back to the original question: I know that the epoxy type of material exists, however the art is in the excecution and use. Check your local plumber supply store for 2 part non liquid epoxy, even Home Depot should carry it, I am not sure if it is non shrinking.

Bye for now.

Back to the original question: I know that the epoxy type of material exists, however the art is in the excecution and use. Check your local plumber supply store for 2 part non liquid epoxy, even Home Depot should carry it, I am not sure if it is non shrinking.

Virtually all epoxies are both non-shrinking and non expanding (+/- a percent or two). However, most are quite adhesive -- an in my experience will stick to surfaces carefully prepared with mold release, and refuse to stick to surfaces carefully cleaned and sanded for best adhesion. (I'm exaggerating here, but I've actually had to throw out a mold from which epoxy would not release, and have had failures of the bond in carefully prepared materials.)

Another issue with epoxy in a closed space is that if it is dimensionally thick, it can exotherm, generating heat, bubbles and expanding to perhaps 5 times its original volume -- so in a closed mold it could end up in places where you do not want it. In a steel die, the heat sink effect should reduce this likelihood, but it is something to be aware of.

The other Murphy's Law, re epoxy, is that if the assembly is complex and time consuming to put together, then the epoxy cures too fast. If the assembly is quick, then you have to wait forever for the stuff to cure.

Thanks for all the imput folks.

I believe the product you are referring to is called Verifilm®. We used it to verify bond line thickness when assembling the speed brake for the space shuttle. The part was assembled with the Verifilm® in place of the film adhesive and the part was run through an autoclave cure cycle. The part was then dissassembled and the film was measured with a caliper or micrometer to determine the actual bond line thickness. Unlike Plastigage, this material only flows at elevated temperature. At room temperature, the product is solid and allows precise measurement of the clearance.

If you try to masure Plastigage with a caliper or mic, it will just mush out.

Thanks for all the great suggestions!

Problem solved and moving on to the next task