Control limits

#1
Hi,
Wondering if it’s helpful to use control limits on operations metrics like customer complaints, supplier DPPM, on time deliver for a start up company - simple responses would be greatly appreciated . Thanks
 
Elsmar Forum Sponsor

John Predmore

Trusted Information Resource
#3
In a start-up company situation, there has to be some modicum of predictability in order to have "helpful" predicted limits. The math of SPC gives us a way to judge whether a process is "in control".

Statistical Process Control limits can show expected ranges for process metrics. It is helpful to know what is expected, so to recognize and react when the process behaves unexpectedly, both in a favorable and unfavorable direction. Planning and budgeting for a stable, predictable process is far more reliable than for operations which are not in a state of statistical control.

Where your team is working to improve quantities with negative consequences, such as complaints and DPPM, it is helpful to judge whether minor month-to-month improvements are large enough for the team to take credit, or whether the minor improvements could just as likely be random month-to-month fluctuation.
 

Miner

Forum Moderator
Leader
Admin
#4
Early in my career as a quality manager, we would have monthly reviews with division leadership of various plant performance metrics. These meetings would last 4-6 hours as every negative movement of an indicator would have to be explained and plans made to address each. These explanations were always smoke and mirrors because no one had any idea what had happened. My company at that time briefly had the wisdom to hire a good VP of Quality that was also the head of ASQ. He suggested that we plot all these metrics on I-MR charts and only explain when the metrics exceed the control limits. Meetings then only took 1.5-2 hours and managers actually knew why the metrics had changed and were able to come prepared with good plans to address it.

So, yes it is helpful.
 

Steve Prevette

Deming Disciple
Leader
Super Moderator
#5
Miner - I posted your comment (with attribution) to my students in Statistical Applications (ITEC 265 at Southern Illinois University at Carbondale) since they just finished a discussion topic that touched on SPC and management use (and misuse) of data.
 

RoxaneB

Change Agent and Data Storyteller
Super Moderator
#6
Early in my career as a quality manager, we would have monthly reviews with division leadership of various plant performance metrics. These meetings would last 4-6 hours as every negative movement of an indicator would have to be explained and plans made to address each. These explanations were always smoke and mirrors because no one had any idea what had happened. My company at that time briefly had the wisdom to hire a good VP of Quality that was also the head of ASQ. He suggested that we plot all these metrics on I-MR charts and only explain when the metrics exceed the control limits. Meetings then only took 1.5-2 hours and managers actually knew why the metrics had changed and were able to come prepared with good plans to address it.

So, yes it is helpful.
We had a similar approach in my previous organization.

Part of our culture was to also colour-code the metrics or data points, and our conversations focused on the "red" results. It didn't matter if the point was a "good" red or a "bad" red. Red was red and it meant outside of the control limits. With that said, our conversation on a "good" red was different than on a "bad" red. For "bad" reds, we discussed cause and course correction. For "good" reds, we discussed cause and repeatability - could the "good" red become part of the new norm and result in an adjustment to our control limits.
 

outdoorsNW

Quite Involved in Discussions
#7
I like investigating good days as well as bad.

Sometimes on a good day it is easier to identify what is different. Suppose you have 40 machines all doing the same thing that affect the quality at a later process. If on a good day machines 27 and 35 are down for some reason, I would investigate if one or both of those machines is a significant contributor to quality problems. It is al lot easier to run a study on two machines than 40, especially if the later process where problems are easily detectable also has multiple machines.
 
Thread starter Similar threads Forum Replies Date
Z Setting the Control limits on Minitab Using Minitab Software 4
D Locking Control Limits and SPC Sample Sizes (AIAG/Automotive Requirements) Six Sigma 2
Nihls Quality Control (stability) Chart for CMM's - How the control limits are to be calculated Capability, Accuracy and Stability - Processes, Machines, etc. 2
Z Why Control Limits are not the same depending on type of exclusion of data points Using Minitab Software 7
N Apply control limits to a non-normal distribution Statistical Analysis Tools, Techniques and SPC 13
G I-Chart and X bar Chart Control limits Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
V Correlating Maximum 'Range' of Values for a given "RSD" (Control Limits) Statistical Analysis Tools, Techniques and SPC 3
H Control limits for varying subgroup sizes Statistical Analysis Tools, Techniques and SPC 1
T What to do if parameters are found to be Outside of Control Limits Document Control Systems, Procedures, Forms and Templates 5
K Historical Data to establish Control Limits Manufacturing and Related Processes 4
B Cleanroom Control Limits: Cumulative or individual? Statistical Analysis Tools, Techniques and SPC 11
D Calculating Lower and Upper 3 Sigma Control Limits Statistical Analysis Tools, Techniques and SPC 2
K Advice on Calculating Control Chart Control Limits Statistical Analysis Tools, Techniques and SPC 13
K Determining Control Limits from a desired Cpk Using Minitab Software 19
P Critical Limits for Air Blower as CCP (Critical Control Point) Food Safety - ISO 22000, HACCP (21 CFR 120) 6
I Shewhart Constants vs Central Limit Theorem in calculating Control Limits Statistical Analysis Tools, Techniques and SPC 18
S Is a Stable Process (within Control Limits) required for Calculating Pp, Ppk? Capability, Accuracy and Stability - Processes, Machines, etc. 6
D Are Four Sigma Control Limits based on Shewhart's work Statistical Analysis Tools, Techniques and SPC 3
K How to Calculate UCL (Upper Control Limits) and LCL (Lower Control Limits) Statistical Analysis Tools, Techniques and SPC 18
T Conducting the "are all points within the control limits" test when there is no LCL? Statistical Analysis Tools, Techniques and SPC 2
D One-Two-Three Sigma Control Limits - Calculating Control Limits for X-bar Charts Statistical Analysis Tools, Techniques and SPC 3
B Precision Machining and Compressed Control Limits Capability, Accuracy and Stability - Processes, Machines, etc. 13
S Calculation of Upper and Lower Control Limits for Control Chart? Statistical Analysis Tools, Techniques and SPC 7
C Cleanroom Class 8 (100,000) Particulate Control and Warning Limits Statistical Analysis Tools, Techniques and SPC 1
M Control Limits for Wildly Out of Control Processes Statistical Analysis Tools, Techniques and SPC 14
S Computing Control Limits in Minitab Statistical Analysis Tools, Techniques and SPC 6
S Setting Control Limits for Particle Counts Statistical Analysis Tools, Techniques and SPC 9
B If I know x-bar, spec limits, and Cpk, can I calculate the control limits? Capability, Accuracy and Stability - Processes, Machines, etc. 16
A Finding Control Limits for a Non-Normal Distribution Statistical Analysis Tools, Techniques and SPC 3
P Help on Treatment of Points Outside of Control Limits Statistical Analysis Tools, Techniques and SPC 4
W Estimated Sigma and Control Limits Statistical Analysis Tools, Techniques and SPC 2
N Variable Control Limits Calculation - P Chart Statistical Analysis Tools, Techniques and SPC 8
J Moving Range Upper and Lower Control Limits when alpha=0.002 Statistical Analysis Tools, Techniques and SPC 4
K Calculating Control Limits in Average and Range Charts Statistical Analysis Tools, Techniques and SPC 3
J Choice of Control Limits - Customer wants to control at 4.5 sigma Statistical Analysis Tools, Techniques and SPC 23
G Adjusted Control Limits - Usage of Control Charts Statistical Analysis Tools, Techniques and SPC 26
J Control limits for one sided control charts using WECO rules Statistical Analysis Tools, Techniques and SPC 5
V Subsets vs. Subgroups - Calculating the control limits of a process Statistical Analysis Tools, Techniques and SPC 6
S Calculating 1 sigma and 2 Sigma limits in Control Charts Statistical Analysis Tools, Techniques and SPC 1
P Help on p-chart - Computing new control limits and chart suitability Statistical Analysis Tools, Techniques and SPC 4
M Control Charts - Points TOUCHING Limits = Stable? Statistical Analysis Tools, Techniques and SPC 12
CycleMike Setting Process Control Limits - Is this process out of control? Statistical Analysis Tools, Techniques and SPC 38
J Calculating Control Limits for nonconformities - 1000 accounting transactions per day Statistical Analysis Tools, Techniques and SPC 2
B Calculation for extending control limits Statistical Analysis Tools, Techniques and SPC 7
M Interpreting my R+R chart - NDC's and Out of Control Limits Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
W How to justify Widened Control Limits - No Assignable Cause scenario Statistical Analysis Tools, Techniques and SPC 26
A Control Chart and Limits For Large Sample Size Statistical Analysis Tools, Techniques and SPC 6
A Tight Control Limits - Tape & Reel Process, the process of packaging ICs Statistical Analysis Tools, Techniques and SPC 27
Marc When to Recalculate Control Limits? SPC Statistical Analysis Tools, Techniques and SPC 14
S To take into account the tool wear during calculating control limits Statistical Analysis Tools, Techniques and SPC 6

Similar threads

Top Bottom