# What’s the Calculation for Calculating Store Size?

Six Sigma – iSixSigma Forums General Forums Implementation What’s the Calculation for Calculating Store Size?

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• #55867

68rs327
Participant

I am trying to calculate a store size in a manufacturing process. I know part of the calculation is cycle time, lead time, and OEE.
Here is the break down Example

Work cell “A” runs 5 different models, each model has a 30 second cycle time and OEE on this line is 70%. Change over time is 45 minutes

A cart picks up parts and delivers them to process “B” which is a paint process that has a cycle time of 25 seconds and has an OEE of 90%. No Change Over
A cart picks up painted parts and delivers them to a store.

The cart picks up the parts from the store and delivers them to Process “C” which is an assembly process that has a cycle time of 37 seconds and has an OEE of 65%. Change Over time is 30 minutes.

All 5 models that run on “A” also run on “B” and “C”.

The cart delivery route is every 30 minutes.

How many parts should my store that feeds process “C” hold?
Lot size on “A” and “C” is 500 pcs.

Hope this is enough information to explain how to calculate the store size and if someone knows of an excel spreadsheet that can calculate this.. That would be awesome.

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#201982

68rs327
Participant

No Ideas?

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#201983

Katie Barry
Participant

@68rs327 You asked your question on a Friday night. You’re more likely to get a faster response during the work week.

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#201984

68rs327
Participant

Thanks,
I’m anxious to see if anyone can help. I know this is a common thing in a factory setting. I think I have enough information for someone with experience to walk me through it.
Thanks,

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#201987

Chris Seider
Participant

A simulation model would be great but some confusion exists reading the blog. If the lot size is 500 parts which are created in less than 30 seconds, it seems you’d limit operation of steps A and B since step C is your bottleneck or else you’ll pile up inventory before Step C.

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#201990

68rs327
Participant

I need to clear up the confusion.
The cycle time of the machine is 30 seconds, but the pickup delivery route is 30 minutes. And the machine changes over every 500 pieces. Machine A runs 5 models as does B and C, but they run all the same model. Machine B runs the parts that A does, material delivery is parts are picked up at A and dropped off At B to be painted. Their cycle time is the same.
Parts are picked up at B and delivered to C’s future store.
Now, Machine cell “C” also runs the same 5 models as “A” but they may not be running the same model at the same time… this is why I need a store. Uptime on “A” and “C” is anywhere from 50 – 65%. Scrap on “A” is about 3% and scrap on “B” is less than 1%.
If you need more info. please let me know.

If the problem is to difficult to calculate without seeing the process… Can someone give the calculations on how to calculate a “Store Size” .

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#201993

Chris Seider
Participant

I wish I could help but get confused. You quote 90% and 65% OEE but also quote in a later post that you have 50-65% uptimes which are in conflict with quoted OEE’s.

Don’t forget my suggestion on modeling software to “see” how the process might perform after getting the stats clear enough.

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#201994

68rs327
Participant

Let’s try this again.
1. Process “A” is a machining process. OEE ranges anywhere from 50% to 70%, due to massive amounts of downtime. I know we need to work on uptime, but engineering can’t seem to fix the downtime. Changeover time is 45 minutes. They run 500 pcs. then changeover, per our shipping dept. Cycle time per piece is 30 seconds. The variation in uptime is what kills things.

2. Process “B” is a painting process, it’s uptime is 90% and OEE ranges from 90-95%. Cycle time on this process is 30 seconds. No changeover time.

3. Process “C” is an assembly process. Their OEE ranges from 50% to 70%. Their change over time is 30 minutes. Their cycle time is 30 sec to 37 sec. depending on what part they are running. All three process run the same 5 models. This process runs 500 pcs and changes over.

4. I am wanting to put in a store to feed process “C” because it may not be running the same model that process “A” is running.

5. Route pick up and deliver from “A” to “B” to “Store” to “C” is every 30 minutes.

I believe there is enough info here to recommend a store size?
If not, can someone post the calculations on how to calculate a “Store” size.
I know it calculated off cycle time, lead time, OEE, fluctuation, Etc.
I need the calculation….

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