iSixSigma

marklamfu

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  • #117149

    marklamfu
    Participant

    The samples(subgroup) used to calculate control limit need come from different shift /operator , at least 20 subgroups is need, so, one day ‘s test-data is not enough.
    It is need to remind the control limit need to modify (CL may advise) if process capability is changed.
    Best regards
    Mark

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    #117148

    marklamfu
    Participant

    Hi:
    I believe we need to know the process capability of the control chart establishment.
    If the control chart is generated based on a capable process (e.g. Cpk>1.33), the in-control plot-point can ensure good shipment, because the possible escaped rate under this situation is less than the escaped rate of performing normal sample plan inspection(e.g. mill-std-105).
    If the control chart is generated under a incapable process (e.g. CKP<1) , It is difficulty to explain the question, at that time, "in-control chart" only state the process is stable, but, can not ensure outgoing product quality.
    Thanks!
     

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    #104703

    marklamfu
    Participant

    Hi 2 sigma:
    We can category CPK as “process CPK” and “product CPK”, for the multi-assemble process, we only need to know individual process CPK ( generally, not include inspection stations) as to improve,  a overall process Cpk seem no meaning.
    If we want to know overall qulity of final product which passed all assemble process, we also can use term “product Cpk”
    It is easy to get product CPK:
    1. To take a adequate samples from final product
    2. To measure and gain the specific value of one parameter for the product
    3. To calculate specific CPK referring to common CPK formular
    Here, it is need to remind the product CPK indicate the parameter’s CPK , a product maybe have many parameters, at this situation, we can not get a intergrated CPK, if want , we have to use attributed method , e.g. overall Yield, Over sixsigma level(DPPM)
    Regards
    Mark
     

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    #94614

    marklamfu
    Participant

    Dear sir:
    The problem what you met is common issue, in fact, in some situations, it is very difficulty to directly measure a product by quantified indexs, my opinion is:
    1. According to SixSigmg basic rules, the defect means the defect of CTQ(critical to quality), it does not directly equal to defect of  product. so, your performance metric must cover CTQs.   but sometimes, can not cover product directly.
    2. Sometimes, we deem know a feature is critical to product quality, but, we can not quantify its impact to product , this feature still is a CTQ.
    3. For yuor case, I think the most important thing is to identify CTQ and its measuring criteria.
    Thank you for your attention!

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    #94275

    marklamfu
    Participant

    The direct DMMP chart is not a variable control chart, generally, for process or product control , we perfer to use variable chart ( e.g. X_bar &R chart , IX_MR chart,etc.), DPPM chart is used to review the product performance achieved,
    If no chance to do variable control due to product nature (only attribute parameter) we also can use DPPM to control process or product qulity, at this situation, DPPM chart are similar with a np-chart or P-chart.
     

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    #91202

    marklamfu
    Participant

    What you described seem be Champion rather than MBB.

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    #90648

    marklamfu
    Participant

    The attributed chart(e.g. P-chart, np-chart,etc) do not fit the so low ppm, please use variable method to control the process, X_bar chart is OK, CPK trend is OK yet.

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    #90647

    marklamfu
    Participant

    If the data is from a normal distribution, I think the minimum sample size is 30, >50 is perfer

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    #89620

    marklamfu
    Participant

    Do not worry!I am QA manager yet, and ever handled ISO9001:2000/ISO14001:1996 certification and many similar projects, I would like to share my a few opinions here for your reference:1. Before start the project, the justfication for the project should be confirmed and promoted within senior meanagement team, and get their consensus and commitment2. The objective /deliverables of the project need confirmed with sponsor . the sponsor shall be top management.3. Regular report(biweekly) the status to top management, have them know the positive result and difficult areas as to keep management attention and get more support. 

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    #89619

    marklamfu
    Participant

    It is a interested case!
    One operator to perform R&R stduy is not adequate, as you said, only one R (Repeatability) is done.
    You known, the aim of perform R&R study is to control the measurement as a suitable condition to meet customer requirement. Lack of another R, the status of this measurment can not be confirmed. 
    In fact, the persons involved  the process should be more than one , the measuring data may be verified by supervisor or other person, the outgoing product may be inspected by customer,etc. So, I propose you to invite related persons (even indirect) to do another R with this operator together.
     
     

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    #89162

    marklamfu
    Participant

    The selection criteria of  BB is different because the product and culture of  organization are  different , Now,  I would like to share my company’s consideration for BB selection:
    1. To show out following behaviours: 
    Teamwork,  Information seeking and Analytical Thinking
    2. Skills:
    SPC knowledge, Project management,  risk analisis skill and communication skill
    3. Experience
    Familiar with the product
     

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    #89161

    marklamfu
    Participant

    No way to 100% ensure right implementation all time. I recommend you to follow the process below to implement new process:
    1. Document the new process
    2. Train up & quaify the every user with the document
    3. Monitor and audit the implement
    4. Identify and correct the deviation
    5. Review and enhance the step1~step4.

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    #89160

    marklamfu
    Participant

    For electrical test, usually, the variable sampling plan(e.g. Mil-std-414) is used to control outgoing parameter’s distribution.If you used attribute sampling plan, in order to smooth your process to reduce the WIP , you can reduce lot size, or apply CSP-1 sampling plan. 

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    #88560

    marklamfu
    Participant

    It is for striving for Zreo defect and enhacing the sensitivity to defect, 0.1% defect rate =1000 ppm, 0.01%=100 ppm, 0.001% =10 ppm, when quality achieved a high level, using % to measure defect seem not sensitive, e.g. six sigma process defect is 3.4 ppm, (0.00034% seem ….), as if  to buy gold, we say to buy 10 gram not say to buy 0.001 kg , because the kg is not sensitive for this case.

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    #88559

    marklamfu
    Participant

    Yield is typical attribute data , t-test is used to comparing 2 sets variable data, if you want to use T-test or Poisson for attribute data, I believe, it is not accurate, Generally, we can plot unit(daily, weekly) yield as a trend for comparing, or transfer attribute as a variable data and then use t-test or other tool(s) for comparision,

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    #88383

    marklamfu
    Participant

    The high CP(2.29) means the process variation is small (the Spec. have cover about 13.8 std.), for 6 sigma process, only CP>2.0 is not enough, at same time, the CPK >1.5( with 1.5 sigma mean shift) and DPPM<=3.4ppm.
    Th cause of CP high but process out of control is big mean shift. the fianl index to measure process capability is CPK not CP, CPK =(1-K)CP, K is mean shift factor, the more of mean shift , the lower of CPK value .
    A few of reminders for your reference:
    1. to recheck& confirm whether the process ture average is OK.
    2. The setting/location of process machine or tool,  the process seem have systemic problem. i suggest you to find the cause of mean shift prior to set control chart. 

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    #87946

    marklamfu
    Participant

    Answer your question:
    1. Small std. compare to product spec. and  expected process capability , if  expected CPk>1, small std means that 6std 1.33, small std means that 8std<(USL-LSL).
    2. For grinding process you mentioned, if machine setting have limited change, the parameter mean of product will be shifted, but, the std. may be  no change. in other words, CPK is lower, CP is not change, if CPK is not lower than your expected value, the process still stable.
    For a six sigma process, even process mean shifts 1.5 sigma , the process capability still enough (CPK = 1.5, CP=2, dppm=3.4), at that time, the process still is stable!
    3. Any process have variation , “variation” is not “unstable”.
    I am very gold to discuss this issue with you! 

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    #87888

    marklamfu
    Participant

    Firstly, the most important condition of a stable process is to have small std, the high variation means process data can not follow statistical rules, at that time, we can not to precisely control process & predict what will be happen for the process because the population of process can not determined through samples analysis.
    Secondly, if process have a small std, the mean will be limited as small swing range even have shift comparing to normal value.
    A no-shift mean can not indicate process is stable, “mean shift” also do not equal to “mean unstable”.

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    #87473

    marklamfu
    Participant

    I do not think Champion equal to BU Head or Sponsor, I think Champion is only a honorary title for the BBs who have successfully completed serveal big six sigma projects. Champion may be a project leader , perhaps, he/she also may be a sponsor  in another project.

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    #87187

    marklamfu
    Participant

    For getting a reliable control limit of X_bar chart, generally, number of subgroups is 20 at least , each subgroup include a few samples ( >3), total samples 60~100, for individual chart, every subgroup only have 1 sample, considering the nature of normal distribution, 30 samples is recommended.

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    #86745

    marklamfu
    Participant

    BB is not a consultant to guide team to apply DAMIC process, he is a full time project leader and need to lead a team to achieve objective(s) defined in project charter following DAMIC approach, so, his duty is bigger than a experienced member(expert involved in project), because the member’ responsible is to complete one or more key task(s )under this project. 
    In addition, many critical work need to be directly done by BB , align objective with sponsor, break down objectve as actionable tasks, analyze the possible risk , prepare contigency plan, organiz review meeting,etc. BB must understand the problems need to resolve and control project progress.

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    #86544

    marklamfu
    Participant

    The aim of QA audit is to verify system conformity and the effectiveness of action taken by operation, is to identify ,analyze and report your findings for correcting /improvement, not ensure operation always “do right thing”, production shall ensure himself to do right thing.
    I can not say that installing video in some monitoring poings is totally wrong ,but, it can not ensure production to always do right thing.
    In order to facilitate to detect root cause of product failure or track special process , sometimes, video is selected as monitoring tool, at the time, video is part of  process, for production, management, and QA, not only for QA.

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    #86291

    marklamfu
    Participant

    The small company also can implement ISO9000 or six sigma, I was tolded the smallest company obtained ISO9000 only have 2 persons, total document is stated on 1 A4 paper.
    The aim of implementing ISO/six sigma or other system is to improve organization quality/business , thus,  you have to  justify what is your approach based on your business nature& expectation, select a completed quality management system to implement or select a few elements from one system fitted your business nature to implement? Beginning, I suggest you select a few elements to implement.

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    #85995

    marklamfu
    Participant

    It means the dept./resources that take direct function during the processes from material purchasing to product outgoing shipping of organization

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    #85724

    marklamfu
    Participant

    If the project team failed to achieve the objective(s) of the six sigma project, my opinion is:
    1. The sponsor organize this team to perform formal F.A(failure analysis).
    2. The team identify the root cause of failure, Is objective defined too high? poor time control, skill adequate? etc.
    3. The leader chair meeting to review the findings with sponsor
    4. Define the inprovement area or corrective action plan
    5. Encourage the team to restart this project or shoulder other new project.
     

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    #85376

    marklamfu
    Participant

    I believe the TS you mentioned is TS19649.
    ISO/TS 16949 is an exciting new set of quality system requirements designed specifically for the automotive industry. It encompasses ISO 9000, and aligns existing automotive quality system requirements within the North American and European automotive industries, making it the only registration you’ll need to supply to these markets.
    Both  TS16949 and QS9000 are used in Automative industry£¬ but£¬ the  application scope of TS16949 is wider than QS9000¡£

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    #85270

    marklamfu
    Participant

    No. of statistical data is related to the character of the case. If you want to study process capability, 30 data are minimum, generally, 100 or more data are perferable. For X_bar control chart, you can get 5 data as a subgroup to plot chart, for variable sampling plan(e.g. Mil-std-414), we can get 5, 10, 15, 20… samples based on Lot Size&AQL to calculate and determine the Lot’ acceptance or rejection 

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    #85006

    marklamfu
    Participant

    I suggest you to break the visual critiria as more grades, 4 levels seem less and 7 levels is basic requirement, try to do so, perhaps, the distribution have a change.
    In addition, Abnormal data also can be used to calculate process capability, it is need get the values of X0.00135 and X0.99865, you can use the software of SPC1to directly gain abnormal CPK.
     
     

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    #84915

    marklamfu
    Participant

    The related procedures should issued by individual organization to reflect ISO9001:2000 requirements , generally, Quality policy, Quality manual, Document control, Quality record, Internal audit, etc, is minimum requirements.
    Of course, only procedures is not enough to ensure compliance, the many requirements of ISO9000 do not demand to define special procedure, e.g. Quality Objective, management review ,etc., but, if you want ensure the system, the actual operation must cover full requirements and provide adequate evidence/record to show system’ effectiveness.

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    #84460

    marklamfu
    Participant

    For the process capability calculation of unilateral tolerance, the book named Measuring Process Capablity define specific method:
    If only USL is available:
    C’pu=Max[(USL-T)/3sigma, (USL-u)/3sigma] 
    If only LSL is available:
    C’pl=Max[(T-LSL)/3sigma, (u-LSL)/3sigma]
    where T=target process average
    u=actual process average.
    if no target is specified:
    C’pu=Cpu=(USl-u)/3sigma
    C’pl=Cpl=(u-LSL)/3sigma

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Viewing 30 posts - 1 through 30 (of 30 total)