What is the appropriate PPM Level for Sheet Metal Fabrication?

[ARM129]

morning,

I work for a sheet metal fabrication company, we manufacture yellow goods, military, railway, refuse components, fruit machines, hospital beds, harvester equipment. We offer laser cutting, machining, brake press, resistance nut welding, power presses, manual welding, robot welding, wet and powder painting and full mechanical assembly.

We do not have any production lines but the listed work centres above, with parts moving through different work centres based on their routing through the company, which is controlled by the MRP system. We do not regularly manufacture the same part, we have contracts for parts and in some instances might only make 200 of one part and not see if again for a year, some times never again.

We have a customer who normally produces electrical components, but they have been using us to manufacture steel and aluminium boxes, plates and other fixings. They have set us a figure of 500 PPM. We delivered 3806 parts to them with 4 rejects, giving us a PPM of 4972. The rejects are subjective, they do not understand welding and want visually pleasing welds, but a good looking weld in aluminium is not always the strongest etc. They have also rejected parts on paint, which was quite subjective on their part. Other issues are resistance nuts snapping off, yet we torque check every 10 parts, calibrate the machine monthly, spc the tooling etc.


Firstly does anyone believe that 500PPM is the correct figure for a company of our type, secondly should we be more aggressive in our handling of rejects?

cheers in advance.

Andy

 

[Umang Vidyarthi]

Re: Sheet metal fab PPM level

morning,

I work for a sheet metal fabrication company, we manufacture yellow goods, military, railway, refuse components, fruit machines, hospital beds, harvester equipment. We offer laser cutting, machining, brake press, resistance nut welding, power presses, manual welding, robot welding, wet and powder painting and full mechanical assembly.

We do not have any production lines but the listed work centres above, with parts moving through different work centres based on their routing through the company, which is controlled by the MRP system. We do not regularly manufacture the same part, we have contracts for parts and in some instances might only make 200 of one part and not see if again for a year, some times never again.

We have a customer who normally produces electrical components, but they have been using us to manufacture steel and aluminium boxes, plates and other fixings. They have set us a figure of 500 PPM. We delivered 3806 parts to them with 4 rejects, giving us a PPM of 4972. The rejects are subjective, they do not understand welding and want visually pleasing welds, but a good looking weld in aluminium is not always the strongest etc. They have also rejected parts on paint, which was quite subjective on their part. Other issues are resistance nuts snapping off, yet we torque check every 10 parts, calibrate the machine monthly, spc the tooling etc.


Firstly does anyone believe that 500PPM is the correct figure for a company of our type, secondly should we be more aggressive in our handling of rejects?

cheers in advance.

Andy

Hello Andy, Welcome to the cove

I too manufacture sheet metal components, and the target of 500 PPM sounds unrealistic. Check with your customer, there might be a typo error, this could be 5000 PPM which is considered good, while 3000 PPM is considered very good in our industry.

Let others too chime in.

Umang

 

[CarolX]

Re: Sheet metal fab PPM level

Hello Andy, Welcome to the cove

I too manufacture sheet metal components, and the target of 500 PPM sounds unrealistic. Check with your customer, there might be a typo error, this could be 5000 PPM which is considered good, while 3000 PPM is considered very good in our industry.

Let others too chime in.

Umang

I agree - 500ppm for sheet metal parts is unrealistic unless you have dedicated lines, which usually is not possible in a sheet metal job shop. As Umang stated, a 3000-5000ppm range is more realistic.

 

[ARM129]

hi guys, thanks for the welcome. I have been a bit of a stalker tbh, i have been on the site quite a few times, reading up on the opinions of others and it really offers a good range of opinions.

I thought we should be looking at around 5000ppm, possibly up to 4 sigma/ 6210 ppm, but there isnt really anyone else here that has any knowledge of ppm, and i started to question whether it was just me.

I understand that we aim for zero defects, but there needs to be some reality there or workers would become demotivated trying to hit a figure that is possibly not cost effective to hit.

Currently our customer offers us the same ppm figure as the company supplying them copper wire, and other electrical components. As stated they have dedicated production lines, which they therefore can control parameters, possibly through DOE, and use SPC to monitor the process.

We plan to offer them an alternative PPM figure, but also inform them of the additional cost to production for us to hit the 500ppm. i think it would be pretty much 100% inspection.

The forecast for this customer for next year is 9000 pieces across 115 different parts/ assemblies, which i calculate allows us 4 rejects for 2010.

 

[DrM2u]

hi guys, thanks for the welcome. I have been a bit of a stalker tbh, i have been on the site quite a few times, reading up on the opinions of others and it really offers a good range of opinions.

I thought we should be looking at around 5000ppm, possibly up to 4 sigma/ 6210 ppm, but there isnt really anyone else here that has any knowledge of ppm, and i started to question whether it was just me.

I understand that we aim for zero defects, but there needs to be some reality there or workers would become demotivated trying to hit a figure that is possibly not cost effective to hit.

Currently our customer offers us the same ppm figure as the company supplying them copper wire, and other electrical components. As stated they have dedicated production lines, which they therefore can control parameters, possibly through DOE, and use SPC to monitor the process.

We plan to offer them an alternative PPM figure, but also inform them of the additional cost to production for us to hit the 500ppm. i think it would be pretty much 100% inspection.

The forecast for this customer for next year is 9000 pieces across 115 different parts/ assemblies, which i calculate allows us 4 rejects for 2010.

ARM, the PPM is going to vary based on the sheet metal process (stamping vs. fabrication vs. laser cutting) and on the complexity of the final part (just a piece or welded components). The best source for what is acceptable for a PPM value is your customer since it is their requirement. This does not mean however that the customer knows it all and could not use some 'education' on what is realistic. This is your job since you are the 'specialists' for your processes and should know what can be done. The idea is to come to a common agreement as far as what is to be expected else someone will not be happy.

Laser cutting usually can be controlled easily and the PPM should be low, probably around 100-200 PPM. Some capability studies will pinpoint when the laser cutter needs maintenance (new mirrors, lenses, etc) and adjustment (speed, power, offset, etc) and alow for predictable adjustments based on in-process inspection.

Sheet metal stamping is also a process that can be controlled as dimensional changes could be predicted based on die life time studies. The short term capability is very good but the long term looks horible because of die wear. The process variation is fairly small and one of the biggest factors is variation in sheet metal thickness. Anyway, the PPM should be around 500 PPM without much difficulty, depending how well you controll the process and how far you want to push the variables.

Sheet metal fabrication (bending, cutting, slitting, etc) is a whole other animal as it requires looser tolerances because of the higher variations. The number of variables and the size of variation change depending on how much manual labor vs. use of equipment and automation. Unrealistic tolerances can skyrocket your PPM but realistic tolerances shoud facilitate the achievement of 500-1000 PPM.

The PPM can go even higher as multiple components are joint together via welding, riveting, folding or any otheer process that you could think of. In such casses the variations could compile into something out of control or could cancel and yield the perfect part.

Bottom line, you know what is realistic and need to agree with your customer on common expectations. Be prepared to support your position with data so an objective decision can be reached. Well, that's my two-pennies worth.

 

[haefjjh]

I have taken a prior employer fabricator to 300 PPM. This involved rewriting ISO procedures to a process approach, correcting some setup and tooling issues, and working with production to properly monitor processes. Monitoring processes involved operator quality checks using standard check sheets and some statistical process control. The real breakthrough, however, was via solid quality engineering, statistical analysis, and process control of chronic problem parts. What made the job easy was that quality had unilateral power and authority to contain and sort parts. In addition, the plant was managed by individuals who cooperated in stopping the practice of "ship and see".