1、Designation: F 1503 02 (Reapproved 2007)Standard Practice forMachine/Process Capability Study Procedure1This standard is issued under the fixed designation F 1503; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers provision of a proper method fordetermining process capability for new or existing machineprocesses. I
3、t is recommended that available statistical softwarebe used for the calculation of the descriptive statistics requiredfor decision making when using this practice. Where softwareis not available, Section 8 and Tables 1 and 2 are provided formanual calculations.2. Referenced Documents2.1 ASTM Standar
4、ds:2F 1469 Guide for Conducting a Repeatability and Repro-ducibility Study on Test Equipment for NondestructiveTesting3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 bilateral specificationsspecifications that have bothupper and lower values.3.1.2 Cpan index that indicates the
5、 variability of theprocess with respect to tolerance.3.1.3 Cpkan index of process variability and centering.This is a widely-used index which considers the process mean,range, and its relation to the specification nominal.3.1.4 inspection plana set of instructions defining productcharacteristics, sp
6、ecifications, frequency of inspection, accep-tance criteria, and methods of inspection for product at aspecified operation.3.1.5 process parameterscombination of people, equip-ment, materials, methods, and environment that produce out-put.3.1.6 unilateral specificationsspecifications that haveonly u
7、pper or lower values.3.1.7 san estimate of the standard deviation of a processcharacteristic.4. Summary of Practice4.1 A machine/process capability (MPC) study is conductedto provide a level of confidence in the ability of a machine/process to meet engineering specification requirements. This isacco
8、mplished through statistical process control techniques asdefined in this practice.4.2 For new equipment purchases, the purchasers manufac-turing engineering department, or equivalent discipline, shallhave primary responsibility for ensuring that the requirementsof this practice are met. The purchas
9、ers quality assurancedepartment shall be available to assist on an as-requested basis.4.3 New machines/processes will not be accepted for use inproduction with Cpvalues less than 1.67. If a manufacturingprocess must be conditionally accepted, a processimprovement/product control plan shall be develo
10、ped.4.3.1 The machine/process control plan shall identify spe-cific process improvement activities, which will be imple-mented to make the process more capable as well as an interiminspection plan to ensure that nonconforming product is notshipped to a customer.4.4 Product Specifications:4.4.1 Prior
11、 to any MPC study, the product specifications(nominal dimension and tolerances) must be identified, and anappropriate method of variables type inspection selected.4.4.2 This practice is limited to bilateral specificationswhose distributions can be expected to approximate a normalcurve. This practice
12、 should not be applied to unilateral speci-fications (flatness, concentricity, minimum tensile, maximumhardness, etc.).4.5 Gage Capability Analysis:4.5.1 All gaging systems used to evaluate product involvedin the study must have documentation for a gage repeatabilityand reproducibility study in acco
13、rdance with Guide F 1469before the machine/capability study is conducted.4.5.1.1 Gaging systems which consume #10 % of theapplicable product tolerance are considered acceptable.1This practice is under the jurisdiction of ASTM Committee F16 on Fastenersand is the direct responsibility of Subcommittee
14、 F16.93 on Quality AssuranceProvisions for Fasteners.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 1994. Last previous edition approved in 2002 as F 1503 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at se
15、rviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, U
16、nited States.4.5.1.2 Gaging systems which consume over 10 to 30 % ofthe applicable product tolerance are generally considered to beunacceptable. However, users of this guide may authorize theiruse depending on factors such as the criticality of the specifi-cation in question, the cost of alternative
17、 gaging systems, andso forth.4.5.1.3 Gaging systems which consume more than 30 % ofthe product tolerance are unacceptable and must not be used.4.5.2 All gaging systems must be certified as accurate usingstandards traceable to NIST, other recognized standards orga-nizations, or the equivalent manufac
18、turers standard.4.6 Process Parameter Selection:4.6.1 For studies conducted at the equipment vendorsfacility, all machine/process parameters (for example, infeedrates, coolant, dies, pressures, fixtures, etc.) must be estab-lished and documented prior to the MPC study so the require-ments of 9.5 can
19、 be met.4.6.1.1 Machine/process parameters may not be changedonce an MPC study has begun.4.6.1.2 All machine/process adjustments made during theMPC study must be documented and included with informationrequired in Section 10.1 of this practice.NOTE 1Machine/process adjustments are defined as those a
20、djust-ments made due to internal machine/process gaging (or other sources offeedback control), or by the operator as part of the normal operation of themachine/process.4.6.2 The selection of machine/process parameters is theresponsibility of the purchasers manufacturing engineering orequivalent disc
21、ipline, or, in some cases, the machine supplierdepending on preestablished contractual agreements.4.6.2.1 The machine/process parameters selected must beconsistent with those intended to be used in production.4.6.3 Machine/process parameters may be systematicallyvaried after a study is completed and
22、 additional MPC studiesperformed for optimization purposes.5. Significance and Use5.1 This practice is designed to evaluate a machine orprocess isolated from its normal operating environment. In itsnormal operating environment, there would be many sources ofvariation that may not exist at a machine/
23、process buildersfacility; or put another way, this study is usually conductedunder ideal conditions. Therefore, it should be recognized thatthe results of this practice are usually a “best case” analysis,and allowances need to be made for sources of variations thatmay exist at the purchasers facilit
24、y.6. Material Selection6.1 Material (for example, steel slugs, bar, wire, prefinishedparts, etc.) used for MPC studies shall be selected at random.The variability of material used for MPC studies should beconsistent with the variability of material the machine is likelyto see in production. However,
25、 all selected samples shallconform to their applicable product engineering standards.6.2 Presorting of material is not permissible for machine/process qualification purposes.6.3 In some cases, machine/process capability results maybe influenced by the specific product specifications selected forthe
26、study. The specific product selected for qualifying a newmachine/process should be based on that which will yield themost conservative results. If the relationship between specificproduct specifications and machine/process capability is un-known, two or more distinct studies should be performed with
27、different products to qualify and accept the new machine/process.7. Procedure-Machine/Process Capability Study7.1 Operate the machine/process for a sufficient period oftime to ensure that the machine/process is stable and all initialsetup adjustments are complete.7.2 Control charting techniques shou
28、ld be utilized to deter-mine the stability and capability of the machine/process.7.2.1 When possible, a standard X,Rchart should be usedwith subgroup size n equals 2 through 5.7.2.1.1 Sampling frequencies shall be established to ensurethat all likely sources of variability occur.7.2.1.2 A minimum of
29、 25 subgroups are required to estab-lish control.7.2.2 When the quantity of sample measurements cannot bepractically obtained, it is permissible to utilize a chart forindividuals and moving ranges.7.2.2.1 A minimum of 25 subgroups are required to estab-lish control.7.2.3 After the study is complete,
30、 calculate and plot thecontrol limits, Xand R(or MR), for each specificationidentified in 4.4.1 (see Table 1). If during the study themachine/process was out of control, the MPC study is notvalid. The root cause(s) of the out-of-control condition(s) mustbe identified and eliminated and the study rep
31、eated.7.2.3.1 If the out-of-control condition is associated with nomore than two subgroups on the range chart, one point on theXor individuals chart and the root cause of the out-of-controlcondition is identified and corrected, new control limits may becalculated by excluding the out-of-control poin
32、ts. A secondstudy is not required.7.2.3.2 In some instances, control chart analysis may revealout-of-control conditions that are inherent to the machine/process. Trends due to tool wear or grinding wheel wear aretypical examples. If the cause of the out-of-control condition isknown, the out-of-contr
33、ol condition is both repeatable andpredictable, and the condition cannot be eliminated, the MPCstudy may be considered acceptable and Cpand Cpk valuescalculated in accordance with 8.1-8.3, or through the use ofstatistical software.TABLE 1 Machine/Process Average and RangeCalculate the average Range
34、(R) and the Process Average XFor the study period, calculate:R1+R2+.+RkR= kX1+X2+.+XkX= kWhere k is the number of subgroups, R1and X1are the range and average ofthe first subgroup, R2and X2are from the second subgroup, etc.F 1503 02 (2007)28. Calculating Results8.1 Estimate the process standard devi
35、ation as follows:s5R/d2(1)where:d2= constants for sample size 2 to 10, see Table 2.8.2 Calculate Cpby dividing the total product tolerance by6 s.8.3 Calculate Cpk as follows:Cpk 5 minimum of USL 2 X!/3 s or X2 LSL!/3 s (2)whereUSL = upper specification limit, andLSL = lower specification limit.9. An
36、alysis of Results9.1 The qualification of a machine/process shall be based ona review of the statistical parameters CpandCpk. CpandCpk areboth numerical indexes that provide a measure of a processsvariability relative to predefined product specifications. Cpconsiders the tolerance range only, wherea
37、sCpk considers boththe tolerance range as well as how close the process averagewas to the nominal specification. Cpand Cpk will have thesame numerical value when the process average is centeredaround nominal. As the process average moves away fromnominal, Cpk will decrease.9.2 The decision to accept
38、 or qualify a manufacturingprocess shall be based on the following criteria:9.2.1 AcceptCpk equals 1.67 or greater. Process is capableof consistently producing product within specification, if con-trolled properly, using statistical process control (SPC) tech-niques.9.2.2 Conditional AcceptanceCpk e
39、quals 1.33 to 1.67.Machine/process is marginally capable. SPC techniques maybe used; however, special care must be taken to ensure that themachine/process average is as close to nominal as possible.Occasional 100 % sorting of product may be required.9.2.3 RejectCpk equals less than 1.33. Process is
40、inca-pable of producing product within specification. This willrequire 100 % sorting by the machine/process operator.9.3 A process with Cpk 1.33 may also be accepted if bothof the following conditions exist.9.3.1 Cp$ 1.67, and9.3.2 The machine/process is such that the machine/processaverage can be c
41、ontrolled by the machine operator throughnormal machine/process adjustments.9.3.3 The requirements identified in 4.3 shall be imposed onany machine/process that receives conditional acceptance.9.4 In many cases, capability may vary depending on thedegree of control exercised during the study (that i
42、s, the typeand frequency of adjustments made). The purchaser is respon-sible for reviewing all adjustments made during the study andensuring that the same level of control can/will be used inproduction.9.5 If the original machine/process capability study is con-ducted at the equipment vendors facili
43、ty, a follow-up studymust be performed after the machine/process is set up andrunning in the appropriate manufacturing facility to confirmresults.10. Documentation10.1 It is recommended that documentation of each gagerepeatability/reproducibility study and MPC study conductedbe maintained and used a
44、s a benchmark for continuousimprovement of the machine/process.11. Keywords11.1 bilateral specification; capability; Cp; Cpk; fasterners;gage capability; inspection plan; machine capability; machinecapability study; process capability; process capability study;process parameters; sampling; SPC; stat
45、istical process control;unilateral specificationTABLE 2 Machine/Process Standard DeviationEstimate the process standard deviation (the estimate is shown as s “sigmahat”).Using the existing sample size calculate:s=R/d2Where Ris the average of the subgroup ranges (for periods with the ranges incontrol
46、) and d2is a constant varying by sample size, as shown in the tablebelow:n2 3 4 5 6 7 8 910d21.13 1.69 2.06 2.33 2.53 2.70 2.85 2.97 3.08F 1503 02 (2007)3SUMMARY OF CHANGESThis section contains the principal changes to the standard that have been incorporated since the last issue(F 1503 95).(1) Revi
47、sed the title from Potential to Capability Study, andthroughout the body of the standard to reflect current industrypractices.(2) Changed the capability measure index from Ppand Ppk toCpand Cpk to align the pracice with short-run studies.(3) Removed the figures of variables and individuals controlch
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