SPC for Short Runs (Control Limits) vs. Precontrol charts (Specification Limits)

[Don Winton]

Folks,

I received this recently and require assistance. Years ago (too many, I’m afraid), I studied SPC for short runs but do not remember a lick of it. All my reference material has “vanished” from the time and I would like comment. I will forward (with appropriate credit, of course) if someone can help, or provide a location where this information is available. I have already suggested the pre-control method, but he still wants details on short run SPC (Which, IMHO, is an oxymoron, but that is another story). All for now.

Thanks in advance and Best Regards,

Dear Don,
I am a Quality engineer at Hindustan motors Ltd, Mfgr of Earthmoving equipment incollabration with CAT, USA We process components for which the batch qty is less and hence the need for Short run SPC, with moving avg & moving range method I find it to be more sensitive than normal SPC. Precontrol charts are used in the existing system but that involves use of specification limits instead of control limits. I prefer control limits to process control. Please let me know if there is material available in this regard.

Bye

Venu

[Roger Eastin]

Don,
The ASQ Publications catalog has several SPC texts that have short-run SPC as a topic. I used it several years ago on a machine that made several different types of product and the biggest problem I had was interpreting how much to change a setting if it was out of control. Anyway, if I remember correctly, the first book that I saw on this topic was authored by a guy named Bothe. It is probably easy to go to the ASQ website and do a search.

[barb butrym]

try DPMO ..it can be done for runs of 1.

[Roger Eastin]

I am not always real good at acronyms: what is DPMO? (Shoot, I just found out last week what IMHO meant!) Thanks.

What does IHMO stand for?

[barb butrym]

IMHO In My humble opinion
another i use often.......
LOL laugh Out loud

[Don Winton]

Roger and barb,
I forgot. Thanx for your comments and suggestions.

Best Reagrds,
Don

[Don Winton]

Defects Per Million Opportunities: an attribute chart used in assembly operations when an item or part contains many opportunities for a defect to occur. For example, a circuit board assembly contains many components and operations that must be successfully completed to make the final assembly. This type of operation typically uses a DPMO control chart during final inspection for monitoring the processes involved.

[This message has been edited by Don Winton (edited 10-09-98).]