HPT and MPI: still viable and necessary or outdated bureaucracy?

[orionz06]

Agreed. But but don't take it for granted that any given bolt is checked for dimensional accuracy. The Internet is making them MPI but no one is making them gauge dimensions.

All bolts break after a certain number of rounds.

That is likely because they have not been told that matters. Off hand, how many bolts have you seen that have passed everything else make it onto the shelves for sale? I am not suggesting that we step back on the dimensions, but I am curious if cases of good bolts not being correct even exist.

We know that untested bolts will break, just google it, but I am unsure of any dimensional issues.

[aquajon]

In my mind dimensional tolerances are more important then MPI, but I would have considered it a given that manufactures tested dimensions anyway. MPI, if done, should be on top of that.

Does anyone have any information that would suggest the "left side" of the chart (those who MPI test bolts) also skip dimensional testing? Wouldn't this be relatively simple to accomplish with laser gauges in the large scale and custom gauges/jigs in the small scale?

ETA: If QC budget is the restriction, maybe MPI testing can be considered a marketing expense and taken from that pot instead?

[d90king]

Absolutely important when working out a new design and process for verification. Once none of the parts are failing, the design is proven, and one would phase out the procedure unless bound by contract. We HPT 100% because it is company policy.

I am missing your point... The testing that is being referenced is about the overall integrity of the materials used. It is not testing to see if the design is sound and works the way it is intended to work. The testing prevents an end user from ending up with a part that doesn't have the needed integrity to last the way it was manufactured to last, which in the end could affect the reliability of a tool that is used to defend life. And yes, IMHO the standard testing should be done as it has been proven to find faulty manufacturing and or materials.

Based on your scenario how can you be assured that every part you are using meets your own standards if you don't test to make sure? I'm certain that you don't want end user failures to determine the quality of your materials and manufacturing. Just because it worked in the past does not mean that it will work in the future even though it might be a good early indicator that you are using good materials at the start.

Once again as a side note you need to clarify the WE in your post as to avoid any future conflict and conform with the forums guidelines. AAC should be listed in your sig (if memory serves that is the company that employs you)

[d90king]

I would also add that dimensional testing should be done as a basic step to the manufacturing process... It is just as important as making sure that the materials used are up to the manufactures standards.

[SteveL]

Once again as a side note you need to clarify the WE in your post as to avoid any future conflict and conform with the forums guidelines. AAC should be listed in your sig (if memory serves that is the company that employs you)

Thanks for posting this. I was just about to ask specifically who this "we" is that rsilvers keeps referring to.

[rob_s]

It is, I think, important to understand what MPI, properly utilized, is looking for. From the linked thread

4.7.4.3 Bolt inspection. The bolt shall be magnetic
particle inspected in accordance with MIL-STD-1949 utilizing
standard five turn magnetizing coil with a current of 200 to 300
amperes. Both circular and longitudinal continuous magnetization
with wet fluorescent solution shall be used. The bolts shall be
examined for evidence of cracks, seams and other injurious
defects.

More info here
http://www.ing.unlp.edu.ar/aeron/cat...L-STD-1949.pdf

[5pins]

Isn’t the point of HPT to reveal any defects that can be found with MPI? I don’t understand why you would HPT without MPI. To me that would be like filling your condom with water then not looking for leaks.

[Sierrahotel83]

I am a little confused as to why this has become a dimensional vs. MPI, the 2 do not seem to be to the exclusion of the other, as has been stated, it would seem that they would be done at different times in the process.

I do not understand how HPT the part then visually Inspecting it would really suffice as stress fractures and imperfections are not going to be of a visible nature, and therefore the MPI makes sense as it gives the ability to check for these problems.

As stated Bolts eventually fail, I am sure no one is going to argue that one, I am pretty sure it is well documented that after extended use they do fail, but this is not a reason to avoid doing proper tests and inspections to make the part last as long as possible.

[HES]

IMO HPT and MPI is an important part of the process. Look at it this way using the car analogy that was mentioned earlier. If a cylinder in an engine fails the worst that will happen is that you are broken down and have an expensive repair bill. Now if your weapon fails and KBs you are at a minimum looking at a very high potential for personal injury. If you are in a self defense situation the consequences of a failure are even higher.

Yes I do think that verifying that parts are within tolerances is important. In fact I do think that guaging should be a standard part of the production process. However just as important is verifying that there is not a material production defect present that is not able to be checked by visual inspection. Even using the correct metal composition and manufacturing processes problems can occur.

The only way to verify that is HPT and MPI. Personally if I am betting my life on a weapon I would want the testing done for the assurance factor. If the statements in this thread are correct, that it is only an additional cost of $15 per unit to do this, then charging an extra $20 per unit (includes profit) and marketing the virtues of HPT and MPI would seem to be a no brainer.

[mike_556]

Simple question for any mfg's that may be on here..when your parts are produced, are they not CMM'ed, or are they just batch tested? Tolerance stacking in certain military aircraft is no longer accepted as they were in the past--I would think in small weapon parts such as the bolt it would be fairly simple and inexpensive to verify the dimensions are in spec?