Nonconformances and Rework in a Machine Shop

[aceystay]

I'm tasked with implementing a nonconformance process for a machine shop that has a high failure rate. (They are working on the process capability) In the mean time we still need some of the parts, any ideas on the best way to keep parts moving while rework is being done?

I'm thinking of starting with a master lot then splitting the nonconforming parts into a sublot for rework, but allowing the conforming parts to continue.

Anyone know of a hybrid batch/piece flow manufacturing process?
We're just brainstorming for ideas, I figure we can make it compliant with procedures and documentation.

thanks for the help!!

[silentrunning]

Let me ask a few questions to see if we can get some response on this. Are you presently using parts that do not meet requirements? If so, is this under release of an internal MRB or the customer? You ask for a non-conformance process, but are you aiming at developing a Corrective Action?

Maybe this will get some answers for you.

[Wes Bucey]

In Reply to Parent Post by aceystay

I'm tasked with implementing a nonconformance process for a machine shop that has a high failure rate. (They are working on the process capability) In the mean time we still need some of the parts, any ideas on the best way to keep parts moving while rework is being done?

I'm thinking of starting with a master lot then splitting the nonconforming parts into a sublot for rework, but allowing the conforming parts to continue.

Anyone know of a hybrid batch/piece flow manufacturing process?
We're just brainstorming for ideas, I figure we can make it compliant with procedures and documentation.

thanks for the help!!

Sounds to me like you have a bigger problem than "sorting"

I owned and operated a high tech precision contract machining shop for ten years. I've written about our successful operations for years here in the Cove.

The key to success is inserting in-process inspection in the process to avoid making ANY nonconforming parts to sort out in final inspection.

To be fair, there are a whole slew of things which need to be considered:
It is critically important to understand and implement a systematic root cause investigation when a nonconformance is detected anywhere in the process, then to deploy corrective action, evaluating that action for effectiveness and efficiency.

Even before accepting the contract, Contract Review and Failure Mode & Effect Analysis (FMEA) should be a routine part of every job.

In a precision machining environment, it is not a good practice for in-process inspection to be informal, rather, it should be part of a well-thought out Control Plan for each different product, taking into consideration such things as critical characteristics dictated by the customer and machining "checkpoints" before a final dimension.

Following are links to posts about some practices I deployed in a precision machining environment - perhaps something similar will work for your organization.

Quote:
Wes Bucey on an efficient shop - empowerment (This is a single post (#18) in a longer thread - the url leads directly to the post - it is associated with a follow-up in post #20)
http://elsmar.com/Forums/showpost.php?p=105469&postcount=18
Wes Bucey on quoting and empowerment (This is a single post (#20) in a longer thread - the url leads directly to the post)
http://elsmar.com/Forums/showpost.php?p=105566&postcount=20

In process and final inspection:
Re: Inspection Dimensional Check Sheets - Over 500 part numbers

Who inspects?
I, too, ran a shop where primary responsibility...

Control Charts
In my high tech machining business (1990 -2000),...

What makes sense?
In point of fact, I have seen several operations...

[aceystay]

The nonconformances are being detected by QC inspection prior to release to our mfg group. Nonconforming material is not used in production; it is reworked, scrapped, or transferred to engineering for salvage. Since the machine shop is an in-house supplier to our mfg. group we’re all under one quality system. I'm not involved in the mfg. process (but I know they are looking at it in terms of scale up and capability) I think it’s going to be a while before those improvements are implemented, so I'm strictly looking how to manage the lots, so that I’m not holding up the conforming parts while rework is performed.

73s — kb6zis here J

[Wes Bucey]

In Reply to Parent Post by aceystay

The nonconformances are being detected by QC inspection prior to release to our mfg group. Nonconforming material is not used in production; it is reworked, scrapped, or transferred to engineering for salvage. Since the machine shop is an in-house supplier to our mfg. group we’re all under one quality system. I'm not involved in the mfg. process (but I know they are looking at it in terms of scale up and capability) I think it’s going to be a while before those improvements are implemented, so I'm strictly looking how to manage the lots, so that I’m not holding up the conforming parts while rework is performed.

73s — kb6zis here J

I recognize I'm probably

Frankly, it doesn't matter whether the "customers" are at the next machine or on the other side of the planet. The process of PDCA is always valid.

Another point to consider - just because a company has some machines doesn't mean those machines are capable of making the parts they need for other processes. Just because a company has employees doesn't mean those employees have enough training and experience to do the job in an efficient, effective manner (assuming the machines they use have the capability and capacity to do the job.)

We talk about "gap analysis" when we plan to elevate a company/organization to achieve registration to an international quality management Standard. That same sort of technique of gap analysis is used to determine the capacity and capability of machines and personnel to make products.

Bottom line:
Sorting for quality is a fool's errand.

[Michael_M]

One of the methods we use is an inspection check list. EVERY dimension and/or specification is listed on the inspection check list. The machine operator is responsible for recording the dimension(s) on this check list. This has 'slowed' down production a bit, but has increased the good parts quantity per day. Since the operator is responsible for recording the dimensions on the parts they make, this makes them more aware of what (and how) to do. On the inspection check list we have the frequency of check so some dimensions (threads, +/-.0003) are checked 100% while 45 degree chamfer call outs are checked 2x per day. I have discovered (and have even done this myself in the past when I was a machinist), people will get so focused on tight dimension, or frequent check dimensions that they fail to check the 'open' tolerances and run 100's of parts bad for failure to check thus the check EVERY dimension or requirement at least 2x per day.

Hope this helps

[Cari Spears]

In Reply to Parent Post by aceystay

I'm thinking of starting with a master lot then splitting the nonconforming parts into a sublot for rework, but allowing the conforming parts to continue.

Yes - this sounds like an acceptable process. If your "sublot" records are traceable to the original lot and it's material certs, etc., I don't see a problem.