Is pre-conditioning supplier component before incoming inspection tests allowed?

[RealQualityGuy]

Hello all,

I work in a class 2 medical device manufacturing company, we have DC motors in our products. These are purchased parts, therefore, we have a motor tester that tests the motors to drawing specification. Before, running the test we do something called Pre-conditioning where we connect the motor to a power supply and run it for 10 minutes before testing it on the motor tester. The problem is if you do not pre condition motors, they fail acceptance criteria and are therefore rejected. This pre-conditioning process is not documented. There is no drawing criteria that calls for it. Moreover, I do not know if the pre-conditioning impacts the motors or simply makes them pass the test. Is this an acceptable practice? if not documented? If so where should we document it? we are currently in favor of the practice of using the pre-conditioning as a rework.

This could be an ethical or quality issue too.


Any guidance is appreciated.

Thanks,
RealQualityGuy

 

[normzone]

Outside my field, but I'd wager that if you run some in as a hedge against infant mortality, and scrap the fails, that's a legit use. It would need to be documented of course.

Whereas if you're warming them up so they will start reliably in your test, and the product is not expected to be used in the same manner, NOW you have a problem...

 

[RealQualityGuy]

Thank you, normzone.

We do not do any sort of Infant Mortality Testing. We get motors from the supplier, it gets rejected when we put it on the motor tester, we have found a work around by running them in and testing them. We always pass. All this has very little or no documentation at all.

Management says it is okay to do this. Under pressure as you might imagine. But, I have some serious concerns on this burn in practice.

also, we make medical devices that have this motor as an integral component. Product is not expected to be burnt-in by end user before use.

 

[Steve Prevette]

I can't answer from a medical perspective, but I do know in my hobby of model railroading it is well worth "breaking in" a motor in a model locomotive and run it in to allow the gears to wear in and mesh well. Once you do that, you've done it and don't have to do it again. So I assume you have a similar situation - it is well worth breaking in the motor but once it is "broken in" it is completed and doesn't have to be done again. So, I'd say that doesn't count as a test failure or infant mortality.

Why the supplier can't do a good break-in prior to shipping the motors may be a question to ask them. . .

 

[Bev D]

Steve makes a good point...
Do all of the motors get a run-in prior to use by the Customer? This may be at incoming or during your assembly/test process?

If so, then run-in is simply a part of your normal process - although as Normzone says it should be documented for the incoming test.

If not, then shouldn't the motors fail a the first Custoemr use as well as at Incoming? Or is the incoming test not predictive of Customer use/failure?

 

[RealQualityGuy]

Steve,

You raise a good point, however, I do know that the supplier does the "Burn-in" before shipping the motors from China to the USA. In this case, I have gathered some data (customer complaints, pre and post burn in motor data) which can point to the fact that the Burn-in feature is temporary. It wears out after time, so in order to meet drawing spec we have to run them in prior to Motor testing.


Bev,
The customer does no Burn in before use of the product. The incoming test is not predictive of the customer use.

 

[Miner]

What type of motors are these? AC, DC, Brushless DC, and are they attached to gearboxes? Are they continuous or intermittent duty?

I have a motor background, so I might be able to figure out what is going on.

 

[Miner]

Sorry. I just noticed that you had mentioned DC in your first post. Please respond about the gearbox and duty cycle, but the issue is probably related to run-in of the brushes.

The company I worked at would run DC motors for a period of time to seat the brushes to the commutator. This had a direct impact on the electrical performance characteristics of the motor. Many motor manufacturers skip this step to reduce lead times and expense.

 

[RealQualityGuy]

Miner, yes the motor does have a gearbox attached to it. Not sure about the Duty Cycle as it is controller based. Would have to do a little research to come up with it as it is not on the drawing.

I do understand that running in Motors for a period of time seats the brushes to the commutator. But in this case, the motor manufacturer has already Burnt in the motor so I assume it is strictly a one time process. That is not the case with us because we had to burn it in twice.

 

[Miner]

The exact time of the duty cycle is not important. It is the contrast between continuous duty and intermittent duty.

Since you do have a gearbox attached, it is probably an intermittent duty motor. The mechanical resistance of the gearbox will have a significant impact on measured characteristics of the motor. You could be seeing the effect of warm up on the gearbox lubricants, which would typically reduce the viscosity and reduce friction.

Regarding burn-in of brushes, it is a one-time process for the brushes, but should be repeated each time the brushes wear out and are replaced.