Process controls on attribute data - Chrome plating manual buffing line

L

liquified56 - 2009

#1
Hey everyone,

I have a question on CPK i hope you can help with. We make chrome plated parts for the plumbing and auto industry and are currently using Control charts in our plating line and diecast line. In a recent Customer audit one of our primary customers mentioned they wanted to see some cpk data or process control data from our manual buffing line. I have alot of history with being able to run charts with actual dimensions to check(variable data) but im not sure how to do this on a purely cosmetic operation. I do have some existing data i can work off of though that we record on a daily basis. Mainly Parts produced/and rejected by operator/shift. Fallout is very high in this operation just due to its nature and we run a wide variety of parts so a cluster map or U chart i think its called isnt feasible.

What i am thinking is running data with a 0 LCL and a management set UCL and setting triggers at the UCL to notify the supervisor that something is happening with that particular operator. Over time we can adjust the UCL as the process tightens(people know we are monitoring). One of the main issues is the Cpk data will be off and the chart will be one sided considering we cant fall below 0 on the LCL. Any ideas or other charts/process studies i should be looking at instead where i can get a measureable cpk/cp?

Thanks for your help
 
Elsmar Forum Sponsor

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#2
Re: Process controls on attribute data?

In a recent Customer audit one of our primary customers mentioned they wanted to see some cpk data or process control data from our manual buffing line.
Cpk on manual buffing....oh, brother. To what specification on their print did they want this capability compared to? Was a reflectance range called out, or something? Cpk really only relates to bilateral tolerances, and typically with normal distributions.

Although measuring fallout may be statistical, it really offers little for control. That is what I am guessing is the customer's issue: How do you control a manual process? Training and testing? PM on the buffing wheels? Specification of compounds? Frequency of adding compound? Moreover, how do you prove these activities are effective - which is where the measurable would be handy.

Where are you at in the relationship with the customer? Do you have the order? If no, you might want to reconsider the cost of meeting what the customer is asking for - because it seems like they want a lot of overhead for free.
 
L

liquified56 - 2009

#3
Re: Process controls on attribute data?

To what specification on their print did they want this capability compared to?
Not a print requirement a Quality System requirement for all processes related to their product.

How do you control a manual process? Training and testing? PM on the buffing wheels? Specification of compounds? Frequency of adding compound? Moreover, how do you prove these activities are effective - which is where the measurable would be handy.
Buffing wheels/adding compound is controlled in the preventive maintenance WI & operator WI. Training/effectiveness is done through CAR/NCMR history and operator production outputs. Also we have compound and wheel testing results in our PAR history.

Where are you at in the relationship with the customer? Do you have the order?
One of our biggest customers and where we want to grow our business. We are currently one of their best suppliers and this is getting into potential future/new parts and production.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#4
Re: Process controls on attribute data?

Not a print requirement a Quality System requirement for all processes related to their product.
If there is no specification, there is no cpk. It is a fundamental part of the calculation! Their Quality System should not indicate requirement for all processes related to their product, it should indicate requirement for all critical specifications related to their product. I am surprised there is no measurable callout for the finish - especially for a end-customer visual area.

One of our biggest customers and where we want to grow our business. We are currently one of their best suppliers and this is getting into potential future/new parts and production.
That is understandable. I just feel the approach you are considering is adding a layer of effort to your system with little value added - just to meet their 'system'.
 
L

liquified56 - 2009

#5
There are cosmetic finish requirements, spec analysis, dirt/pit size criteria, Surface grade callouts. Im trying to meet their requirements with data we already are recording so i dont overwelm production with more inspection/paperwork requirements.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#6
let's try an alternative approach. This is something that has worked effectively for me when dealign with manual processes and categorical requirements (aka attributes data)

I firmly believe that we need to monitor the performance of any critical process output and it appears that your customer feels this is a critical output for them. SO, first principles takes us to a simple run chart of the number of rejections per lot (p chart) or the number of discreet defects per part (c or u chart). IF the different parts are similar enough that the defect rate is more dependent on the process than the part (eg simple vs complex geometries) then a single chart could be used for all parts. only the actual data will tell us which way to go.

Now we can add REAL control limits using the formulas for the appropriate chart type. Just because you have categorical doen't mean SPC can't be used as intended - to assess the statistical control or stability of a process. I woulf run away from 0 and some arbitrary upper goal line as fast as possible - that flawed ineeffective approach was debunked decades ago and is exactly what SPC was intended to replace.

Next we can calculate a Cpk value by going backwards thru the Z table - calculate the ppm value, determine the corresponding Z value and divide by 3 Of course this isnt' a Cpk value in teh traditional sense of understanding the process spread vs the tolerances, adn I personally prefer to just deal with yield numbers over silly Cpk/Ppk values, but some customers just HAVE TO HAVE a single number: Cpk. So we can give it to 'em. Why argue the point? in this case the whole Normal distribution problem for continuous data that relates standard deviation to a ppm value is irrelevant. It's a small thing and everyone gets to check their box. The real value add comes from teh control chart itself: concentrate on that. It will be invaluable in understanding your process.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#7
I am curious - did they ever require a capability study (versus ongoing control)? And if so, how would you perform one? Did they offer any suggestion as to what they would like to see studied? Maybe it's just me, but if a vendor asks me, I would offer up all kinds of ideas. Of course, they would then generally discuss with me the limitations of each of them...but it sparks a good dialog.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#8
Now we can add REAL control limits using the formulas for the appropriate chart type. Just because you have categorical doesn't mean SPC can't be used as intended - to assess the statistical control or stability of a process. I would run away from 0 and some arbitrary upper goal line as fast as possible - that flawed ineffective approach was debunked decades ago and is exactly what SPC was intended to replace.
This is absolutely true - and I hope they can sell it to their customer. Usually, when the drop the "cpk" bomb, their expectation is that the process is 'capable' - as is in not only not making bad parts - but not near making bad parts. Using attribute charts with upper control limit above zero will preclude that, although you will be able to determine control, such as shifts in the process (as in making more bad parts than the usual amount of bad parts indicating a special cause). You know - it's the old control versus capability thing.

Best of luck any way you slice it...
 

Stijloor

Staff member
Super Moderator
#9
I have the impression that the customer's representative has no clue what they're asking for. Yes, we must be very sensitive to Customer's needs and expectations, but if it does not make (satatistical) sense, then it's OK to diplomatically push back. Regretfully, some (automotive) suppliers have no adequate (alternative) approach to offer resulting in a lot of wasted time and non-value added work.

Stijloor.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#10
I have the impression that the customer's representative has no clue what they're asking for. Yes, we must be very sensitive to Customer's needs and expectations, but if it does not make (statistical) sense, then it's OK to diplomatically push back.
:agree1: I agree...to whatever degree that makes sense.

Regretfully, some (automotive) suppliers have no adequate (alternative) approach to offer resulting in a lot of wasted time and non-value added work.
.
Not always - it depends on the customer. Most reasonable customers will defer AIAG books. There is enough detail in them to find appropriate exceptions when needed. My experience has shown that it is generally more than the other fields have to work with.
 
Thread starter Similar threads Forum Replies Date
A UDI and Design Controls - Labeling change via the Design Control process 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
M IATF 16949 - 8.5.6.1.1 Providing a list of process controls: Does this requirement add value to QMS? IATF 16949 - Automotive Quality Systems Standard 4
F CQI-23 Special Process Molding - Controls IATF 16949 - Automotive Quality Systems Standard 7
G More on IATF 8.5.6.1.1 - Temporary Change of Process Controls IATF 16949 - Automotive Quality Systems Standard 4
T Temporary Change of Process Controls - IATF 16949 Clause 8.5.5.1.1 IATF 16949 - Automotive Quality Systems Standard 16
P IATF 16949 Clause 8.5.6.1.1 - Temporary Change of Process Controls IATF 16949 - Automotive Quality Systems Standard 21
J How to understand IATF 16949 Clause 8.5.6.1.1 - Process Controls IATF 16949 - Automotive Quality Systems Standard 2
R Calibration of processing equipment - 21 CFR 820.70 Production and process controls 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 3
M Interpreting Process Controls - 21 CFR Part 820.70(a) 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 5
M Process Controls - Wood Glue Adhesive Failure Manufacturing and Related Processes 7
V Transforming the Attitude and Culture towards Documentation and Process Controls US Food and Drug Administration (FDA) 2
Q Current Process Controls (Prevention) and Incoming Raw Material Inspections FMEA and Control Plans 8
A Setup Controls in a Process Control Plan FMEA and Control Plans 2
P Detection Rating in PFMEA and Process Controls FMEA and Control Plans 6
D Checking Rib Thickness on a Part and Necessary Process Controls Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
Q Required Supplier Process Controls under 4.1 and 7.4 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 9
T Current Process Controls Prevention - Process FMEA before Control Plan FMEA and Control Plans 5
J ?Current Process Controls? and the ?Detection Rank? assigned to them FMEA and Control Plans 16
M Audit of Goods In as part of the QSIT "Production & Process Controls" Schedule 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 4
K Supplier Questionnaire about statistical process controls and where we use them Supplier Quality Assurance and other Supplier Issues 2
R Clause 4.1 - What qualifies as an outsourced process? What controls are required? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 17
A At what point do you need to formalize process controls? QS-9000 - American Automotive Manufacturers Standard 4
J Need Help with FPY Data in Assembly Process Manufacturing and Related Processes 7
A When someone refuses to follow a process.... Misc. Quality Assurance and Business Systems Related Topics 21
E Software maintenance Process Software maintenance Process to IEC 6204? IEC 62304 - Medical Device Software Life Cycle Processes 3
R AS5553 Clause 3.1.7 f - "Implement a returns process....." AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
normhowe "The Problem with Quality Management: Process orientation, controllability and zero-defect processes as modern myths" Book, Video, Blog and Web Site Reviews and Recommendations 2
Judy Abbott General temperature used in the blasting process and laser process Manufacturing and Related Processes 2
B SOP for CNC turret punching machine for sheet metal process Manufacturing and Related Processes 0
A API Monogram audit review process Oil and Gas Industry Standards and Regulations 4
R AS9102 FAI Change in Material / Process Supplier AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 4
A Process mapping Process Maps, Process Mapping and Turtle Diagrams 1
R MDEL Process Canada Medical Device Regulations 4
optomist1 Rates Daily or Hourly Process Improvement Training Consultants and Consulting 2
S Manufacturing Process FDA FOIA Medical Device and FDA Regulations and Standards News 3
S Manufacturing Process FDA FOIA US Food and Drug Administration (FDA) 4
B Toyota PPAP Process - Three Questions APQP and PPAP 3
R Changes vs CMO - How can we simplify this process? Supplier Quality Assurance and other Supplier Issues 3
A Ethics Committee Review Process for IVD Products EU Medical Device Regulations 2
V Laser Welding Process - Impact on Electrical Properties Reliability Analysis - Predictions, Testing and Standards 4
Q Process: Knowledge Section 7.1.6 of ISO 9001:2015 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 10
L Documented Information in Internal Audits Process (9.2) ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 4
A Sampling plan for in-process QC (medical devices) Inspection, Prints (Drawings), Testing, Sampling and Related Topics 13
R MRB (Material Review Board) Process using MS Sharepoint or MS Teams Manufacturing and Related Processes 2
M Clinical Benefit of device that only aids in a process for managing or treating disease EU Medical Device Regulations 2
C In-process inspection - Tooling and assembly lines for automotive companies AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 6
M Efficacy of an IT process after a cyber attack ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
N Sterilization Protocol Change in Validation Process and further impacts ISO 13485:2016 - Medical Device Quality Management Systems 1
N Riveting - special process Manufacturing and Related Processes 11
M Material incoming to the production process reflected in PFMEA FMEA and Control Plans 9

Similar threads

Top Bottom