Scrap % Calculation Formula

[swanny297]

Alright, need your quick math skills, there is a bit of an ongoing debate on scrap calculation and I would like to see your answers:

Vendor Scrap - 0pcs
Internal Scrap - 29pcs
Internal Set up Scrap - 155pcs
Good product run (put in boxes to go to customer) - 514pcs

What scrap percentage for this run do you calculate - we use all forms of scrap in the calculation and don't separate anything out.

Thanks
Clint

 

[Statistical Steven]

Re: Scrap % Calculation

Clint

My thought is an easy calculation would be:

Good 514
Scrap 184
Total 698
Scrap Rate 26.4%

 

[hogheavenfarm]

Re: Scrap % Calculation

"...we use all forms of scrap in the calculation and don't separate anything out...."

Then this is your own formula, every company may be different, depending upon what they want to see. In one company I worked at, set up scrap was in a different category than "bad parts", and was used to monitor die change times and equipment and tooling lines. Bad parts are defects, these were monitored directly, although separated into an "internal category". Parts that made it out and were bad (shipped to customer) were another "external" category, and supplier defects could be listed under "internal" or "external" depending upon what you intend to do with the data.

 

[PaulJSmith]

Re: Scrap % Calculation

I agree with Steven. If you are considering all scrap with no distinction, then the simple formula is the best. Even if you divide it into categories, your overall scrap rate will still be that simple formula.

 

[Ninja]

Re: Scrap % Calculation

I would note that if I was interested in (vendor scrap %), I would use vendor scrap # divided by total received....
You may not have used all received in your production run....

 

[Candi1024]

Re: Scrap % Calculation

I curious about what the debate could possibly be, especially since you already stated that everything is included in scrap so that doesn't seem to be the issue.

 

[Bev D]

perhaps it is whether or not the denominator is only the good parts put in the box or the good parts put in the box and scrapped parts?

I have seen this with people who never really understood percentages

 

[Helmut Jilling]

Depends on what you want to know. If you want to know your performance, why would you include setup scrap? If you do stamping, there is trim (offall). Both are quoted in the production. If you want to know your performance, then simply calculate the inverse of Yield. If you make 100 parts, how many of them must be scrapped? Produce 100 pieces, scrap 3 pcs, that is a 3% scrap rate.

 

[maria1]

Re: Scrap % Calculation

This method by separating setup from production scrap, while it does not decrease the overall amount, or the percent remains the same, it does allow for occurrence monitoring that should be then driven into process improvements at either level.

 

[Helmut Jilling]

Re: Scrap % Calculation

This method by separating setup from production scrap, while it does not decrease the overall amount, or the percent remains the same, it does allow for occurrence monitoring that should be then driven into process improvements at either level.

True, if the different categories are not lumped into one bucket... I ask clients "what do you want to know?" That should guide how the metric is set up.