Is 100% Inspected Lot of Machined Parts requires Cp > 1.67

rnsvasan

Involved In Discussions
#1
We do valve retainer body. During machining we are able to achieve process capability morethan 1.67. But after Case hardeneing some of the dimensions like taper bore distance, wall thickenss are not meeting Cp 1.67. After heat treament no machining is done. We are analysing the issue and hopefully we can able to bring in control.

In the mean time we informed our customer regarding this and told them that we will do 100% inspection and send the parts that meets the specification. But customer is asking the lot only with in 1.67. For this we may have to reject lot of parts even if it is with in the specificaiton. Only because we could'nt achieve 1.67 we do 100% inspection, in this condition is it right to demend for cp level. pl. suggest how to go about in this situation.
 
Elsmar Forum Sponsor
A

anil123

#2
We do valve retainer body. During machining we are able to achieve process capability morethan 1.67. But after Case hardeneing some of the dimensions like taper bore distance, wall thickenss are not meeting Cp 1.67. After heat treament no machining is done. We are analysing the issue and hopefully we can able to bring in control.

In the mean time we informed our customer regarding this and told them that we will do 100% inspection and send the parts that meets the specification. But customer is asking the lot only with in 1.67. For this we may have to reject lot of parts even if it is with in the specificaiton. Only because we could'nt achieve 1.67 we do 100% inspection, in this condition is it right to demend for cp level. pl. suggest how to go about in this situation.
In case if the Cpk is not equal or more than 1.67, then we have to inspect it 100% which you have suggested is correct measure. Cpk is less than 1.67 mean that process is not under the statistical control due to which the process may produce some non-conformig parts. To aviod such events of passing the non-conforming materials we have to do 100% inspection and only OK material will be shifted to customer. You have to tell this to your customer as he is not understanding the practical meaning of Cpk.
 
C

cochran

#3
Explain to your customer in this way:

If we use SPC, we are not measuring 100% of the parts. Because of this, we need to be able to show you a level of confidence that you will only receive good material from us. This is the purpose of showing you a 1.67 capability.

If we are sorting 100%, and we've shown you good GRR on the measurement system, then we don't need to provide a statistical prediction of process quality, as we have guaranteed our product quality for this limited run.

Good luck!
 
A

anil123

#4
Explain to your customer in this way:

If we use SPC, we are not measuring 100% of the parts. Because of this, we need to be able to show you a level of confidence that you will only receive good material from us. This is the purpose of showing you a 1.67 capability.

If we are sorting 100%, and we've shown you good GRR on the measurement system, then we don't need to provide a statistical prediction of process quality, as we have guaranteed our product quality for this limited run.

Good luck!
you are right
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#5
We do valve retainer body. During machining we are able to achieve process capability more than 1.67. But after Case hardening some of the dimensions like taper bore distance, wall thickness are not meeting Cp 1.67. After heat treatment no machining is done. We are analyzing the issue and hopefully we can able to bring in control.

In the mean time we informed our customer regarding this and told them that we will do 100% inspection and send the parts that meets the specification. But customer is asking the lot only with in 1.67. For this we may have to reject lot of parts even if it is with in the specification. Only because we couldn't achieve 1.67 we do 100% inspection, in this condition is it right to demand for cp level. pl. suggest how to go about in this situation.
I am afraid the biggest problem is your customer is rubber stamping a lack of understanding of statistical process control onto your process. They should be willing to accept the all of the product if it is 100% inspected. In fact, if you use the correct statistical process control and analysis of the machining operation,a 1.33 is all that is truly necessary. You would be unnecessarily overcontrolling the process at 1.67. You may realize you have to run to a tighter process tolerance to compensate to heat treating to a final dimension. All the more important to use the correct statistical analysis - which is likely the X hi/lo-R chart, found elsewhere in this site.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#6
Cpk is less than 1.67 mean that process is not under the statistical control due to which the process may produce some non-conformig parts.
just for clarity: not meeting a specific Cpk value does not mean that the process is out of statistical control; it merely means that it is not capable to the specified level.

As for the comment Bob made - I agree. It sounds like the custoemr is blindly imposing requirements it doesn't understand. Time to educate the Customer...
 
A

anil123

#7
just for clarity: not meeting a specific Cpk value does not mean that the process is out of statistical control; it merely means that it is not capable to the specified level.

As for the comment Bob made - I agree. It sounds like the custoemr is blindly imposing requirements it doesn't understand. Time to educate the Customer...
As customer is not knowing the sinificance of SPC and 100% inspection, customer to educated to aviod such problems
 

rnsvasan

Involved In Discussions
#8
THanks to all for giving the clarity. I will probably take up this with the customer and let you know about his view.

In the meanwhile, can someone help me about "X hi/lo-R chart".
 
M

martin elliott

#9
Here is another take on this.

If the component is part of a assembly of components which the ultimate customer has placed a Capability requirements on for example the Stack of, then if the component is not capable then you might be commiting your customer to 100% inspection on his assembly.

It is a situation I am faced with so it may not be quite so simple
 
Thread starter Similar threads Forum Replies Date
Ninja Windows 10 100 % disk use after update Coffee Break and Water Cooler Discussions 33
A 21 CFR part 11 - section 11.100 - Electronic Signature Certification Other US Medical Device Regulations 6
Stoic Manual soldering processes - 100% verifiable, or always requiring validation? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 15
E Correct way to certify hydrostatic testing when it is not 100% (and Sample Size) Various Other Specifications, Standards, and related Requirements 6
A What to do when 100 % verification is not 100 % Manufacturing and Related Processes 5
Nicole Desouza ISO / AS Certification - Small business with less than 100 employees ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
M EU – Chemical Safety Report – CSR – REACH Authorisation decisions – Triton X-100 – Ortho-clinical-Use1 REACH and RoHS Conversations 0
D Measuring fine tubing (< 0.100") "Wall by weight" General Measurement Device and Calibration Topics 11
Marc Anniversary of the First Trans-Atlantic Flight 100 years ago - June 2019 Coffee Break and Water Cooler Discussions 2
Y IEC 62304 Section 4.3(a) - 100% probability of failure IEC 62304 - Medical Device Software Life Cycle Processes 3
BHobbs_Busche All Measurements taken with a Variable Gage have to be Recorded 100% IATF 16949 - Automotive Quality Systems Standard 14
Pmarszal Clarification for 21 CFR Part 11.100 - General Requirements Other US Medical Device Regulations 14
S 100% Final Inspection Requirements of Active Medical Devices (MDD or IEC Standards?) EU Medical Device Regulations 4
B Is Gage R&R required on a 100% Dimensional Layout? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
K IEC 61010-2-100 Labeling question - IVD equipment Other ISO and International Standards and European Regulations 1
D Long length measurement of 18" up to 100" with an accuracy of .005 min General Measurement Device and Calibration Topics 8
F Yield reaction higher than 100% Manufacturing and Related Processes 3
S Suggestions for a 100% Paperless Manufacturing Shop Floor Quality Tools, Improvement and Analysis 10
M Can OEE (overall equipment effectiveness) exceed 100%? Manufacturing and Related Processes 2
G Sampling Question - Random Sample of 100 pcs and 11 pcs. have been rejected Inspection, Prints (Drawings), Testing, Sampling and Related Topics 30
Marc 100 Years of Change in the United States - 1913 - 2013 Coffee Break and Water Cooler Discussions 5
E Is there a specific regulatory requirement for 100% inspection of IFUs? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
N Switch to 100% inspection when lot fails sampling? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 9
K 100 years war aviation - A plane is used for bombing World News 3
S ATA (Aerospace Testing Alliance) Specifications 100, 200 and 300 AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
K SPC to apply for Particle in Clean Room Class 100 Statistical Analysis Tools, Techniques and SPC 7
N What Makes Life 100% (joke) Funny Stuff - Jokes and Humour 0
V Supplier Capability and 100% Sort causing Gage Wear APQP and PPAP 1
P Sample Size to Test Products used for 100 hours in a Test Environment Reliability Analysis - Predictions, Testing and Standards 2
R Problems with Supplier - Always with 100% Sorting - No Corrective Actions Supplier Quality Assurance and other Supplier Issues 22
R Why do outgoing QA Sample Testing again when Product is tested 100% Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
Ajit Basrur China to launch 100 rockets, 100 satellites by 2015 Coffee Break and Water Cooler Discussions 1
V PPAP - Requirements when Cpk is <1.67 - 100% Sort for Defectives APQP and PPAP 8
G Is Controlled Shipping requirement Sampling Based or 100% Inspection? Misc. Quality Assurance and Business Systems Related Topics 3
J MSA Emergency - PV%=100(PV/TOL)in American? And that is correct? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 13
C What to expect in a GE Aerospace Audit of a 100 Person Machine Shop Customer and Company Specific Requirements 5
R Research involving a very small population (100 approx) - Help with Sampling Statistical Analysis Tools, Techniques and SPC 3
N 100% Inspection in Retail Warehouse which Ships Products to Customers Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
P FDA Part 820 Clause 820.100 Corrective and Preventive Action 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 3
J Can a Major Nonconformance be Open but 100% Resolved? IATF 16949 - Automotive Quality Systems Standard 6
K 100% Inspection or do the usual IQ, OQ, PQ Validation - Medical Molding Design and Development of Products and Processes 3
C Cleanroom Class 8 (100,000) Particulate Control and Warning Limits Statistical Analysis Tools, Techniques and SPC 1
S 100 Places to Remember Before They Disappear Coffee Break and Water Cooler Discussions 8
J Functional Test Sampling - Determining Sample Size to eliminate 100% Testing Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
S Taking samples in a 100 cavity mold for Xbar-R chart Statistical Analysis Tools, Techniques and SPC 1
Stijloor 100 Best companies to work for. Career and Occupation Discussions 0
A Elsmar's Social Group "Mexican Curious" reached 100 Members Coffee Break and Water Cooler Discussions 8
J What Control Chart should be used for Microbial Limit (NMT 100 cfu/m3) Statistical Analysis Tools, Techniques and SPC 12
R Sample Size for P Chart - 100% Leak Test for Condensor Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
Rameshwar25 MSA Manual 4th Edition, Page 100 - What is wrong in the Linearity graph? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8

Similar threads

Top Bottom