How to Calculate UCL (Upper Control Limit) & LCL (Lower Control Limit) & CL

mmjj3259 said:

2.66=3/1.128

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chvrajus said:

Hi

Is it possible to calculate LCL & UCL without Spec limits????

Thanks in advance

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Stijloor said:

Yes, because UCL and LCL are dependent on the variation in the process.
The spec limits come only into play when process capability is estimated.

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chvrajus said:

Our process is low volume mfg assembly.

We only produce 30 parts per month.

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chvrajus said:

Thanks for your quick replay.

I have few questions.

Our's process is low volume mfg assembly.

We only produce 30 parts per month.

Q1. how to calculate LCL&UCL for 30 parts (Some parts will have spce limits & some don't). can you give me some example and charts for parts which has spec limint and which don't have spec limit

Note - I seen couple of control charts online but it only shows ucl & lcl in the chart but not USL,LSL & UCL,LCL.

Q2. If production only produces 20 parts in one month and 30 parts in other month. So then LCL & UCL will it change???

Q3. Below is our sample data. Value field is our ploting data. can you please give some chart and the forumla how to calculate LCL&UCL

Part NumberSerial Number ValueUSLLSL2304545410235487406030102355454010235603421023566140102357194810235777401023583550102358935010235951411023600945102360674210236125401023618341
Thanks in advance

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Bev D said:

Let's start with some basics:
how much do you know about SPC? have you been trained or are you being asked to do this without training?
WHY are trying to do SPC?
Why do you want spec limits on the chart?

It is helpful to understand the process/characteristic being measured in order to select the correct chart type. For example knowing that you are low volume, I would look first to try a individuals, moving range chart (aka I, MR or X, MR) for continuous data.

Please attach your data in an excel spreadsheet as teh posting you have is one great big number...

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chvrajus said:

Hi-

I have very little knowledge about SPC.
We want to implement this to predict failures ahead of time.

Yes ours production is very low volume.
As I asked in my previous post, if one month production is 20 parts and another month production is 30 parts. Will it be the same formula to calculate control limits?


Example – can we create charts if production produces (20-30) parts per month?
Is their any limit like (X number of parts should be produced per month to calculate the control limits)

I attached some sample data.

Please let me know if you need any more information.

Please excuse me if I had not explained you clearly.

Thanks in advance

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