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ASTM F1503-02(2012)

Standard Practice for Machine/Process Potential Study Procedure
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1.1Ā This practice covers provision of a proper method for determining process capability for new or existing machine processes.

It is recommended that available statistical software be used for the calculation of the descriptive statistics required for decision making when using this practice.

Where software is not available, Section 8 and Tables 1 and 2 are provided for manual calculations.

TABLE 1 Machine/Process Average and Range

Calculate the average Range (R) and the Process Average X For the study period, calculate:

Ā 

Equation F1503-02R12_1


where:
k Ā Ā =Ā Ā  the number of subgroups,
R1 Ā Ā =Ā Ā  the range and average of the first subgroup,
X1 Ā Ā =Ā Ā  the range and average of the first subgroup,
R2 Ā Ā =Ā Ā  from the second subgroup, and
X2 Ā Ā =Ā Ā  from the second subgroup, etc.

TABLE 2 Machine/Process Standard Deviation

Ā 

Estimate the process standard deviation (the estimate is shown as σ^ ā€œsigma hatā€).

Using the existing sample size calculate:

σ^ = R/d2

Where R is the average of the subgroup ranges (for periods with the ranges in control) and d2 is a constant varying by sample size, as shown in the table below:

n

2

3

4

1.1 This practice covers provision of a proper method for determining process capability for new or existing machine processes. It is recommended that available statistical software be used for the calculation of the descriptive statistics required for decision making when using this practice.

Where software is not available, Section 8 and Tables 1 and 2 are provided for manual calculations.

TABLE 1 Machine/Process Average and Range

Calculate the average Range (R) and the Process Average X. For the study period, calculate:

Equation F1503-02R12_1

where:
k Ā Ā =Ā Ā  the number of subgroups,
R1 Ā Ā =Ā Ā  the range and average of the first subgroup,
X1 Ā Ā =Ā Ā  the range and average of the first subgroup,
R2 Ā Ā =Ā Ā  from the second subgroup, and
X2 Ā Ā =Ā Ā  from the second subgroup, etc.
TABLE 2 Machine/Process Standard Deviation

Estimate the process standard deviation (the estimate is shown as σ^ ā€œsigma hatā€).

Using the existing sample size calculate:

σ^ = R/d2

Where R is the average of the subgroup ranges (for periods with the ranges in control) and d2 is a constant varying by sample size, as shown in the table below:

n 2 3 4 5 6 7 8 9 10
d2 1.13 1.69 2.06 2.33 2.53 2.70 2.85 2.97 3.08

5.1 This practice is designed to evaluate a machine or process isolated from its normal operating environment.

In its normal operating environment, there would be many sources of variation that may not exist at a machine/process builder's facility; or put another way, this study is usually conducted under ideal conditions.

Therefore, it should be recognized that the results of this practice are usually a ā€œbest caseā€ analysis, and allowances need to be made for sources of variations that may exist at the purchaser's facility.

SDO ASTM: ASTM International
Document Number F1503
Publication Date Oct. 1, 2012
Language en - English
Page Count 4
Revision Level 02(2012)
Supercedes
Committee F16.93
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