This document provides guidance on calculating and interpreting the process capability index Cpk. It defines Cpk as a ratio that compares the specification tolerance to the process variation expressed in terms of standard deviations. It explains how to calculate Cpk and discusses factors that influence Cpk values such as sample size, process centering, and measurement uncertainty. The document also provides examples of the expected defective parts per million that correspond to different Cpk values and factors to consider when improving Cpk, such as machine, tooling, workholding, and workpiece variables.
Chapter 1
1.1 Introduction 5
1.2 Definitions of quality 6
1.2.1 Traditional and Taguchi definition of Quality 7
1.3 Taguchi’s quality philosophy 8
1.4 Objective of Taguchi Methods 10
1.5 8-Steps in Taguchi Methodology 10
Chapter 2 (Loss Function)
2.1 Taguchi Loss Function 11
2.2 Variation of Quadratic Loss function 17 Chapter 3 (Analysis of Variation)
3.1 Understanding Variation 19
3.2 What is ANOVA 19
3.2.1 No Way ANOVA 19
3.2. 1.1 Degree of Freedom 20
3.2.2 One Way ANOVA 24
3.2.3 Two Way ANOVA 30
3.3 Example of ANOVA 36
Chapter 4 (Orthogonal Array)
4.1 What is Array 46
4.2 History of Array 46
4.3 Introduction of Orthogonal Array 47
4.3.1 Intersecting many factor- A case study 49
4.3.1.1 Example of Orthogonal Array 50
4.3.2 A Full factorial Experiment 58
4.4 Steps in developing Orthogonal Array 60
4.4.1 Selection of factors and/or interactions to be evaluated 60
4.4.2 Selection of number of levels for the factors 60
4.4.3 Selection of the appropriate OA 62
4.4.4 Assignment of factors and/or interactions to columns 63
4.4.5 Conduct tests 65
4.4.6 Analyze results 66
4.4.7 Confirmation experiment 69
4.5 Example Experimental Procedure
Measurement System Analysis (MSA) course is essential for successful Six Sigma DMAIC and DFSS projects. It is also key for implementation of SQC, and efficient process management.
Reliable measurement processes are critical to the success of any effort dependent on measurement data and process analysis, including Six Sigma DMAIC improvement projects, DFSS project, SPC, SQC, Supplier Quality, and business process management and continuous improvement. Without validation that measurements are accurate, repeatable with multiple measurements by the same person, reproducible from person to person (gage Repeatability and Reproducibility or gage R&R), all conclusions are suspect, and process management is therefore fragile and ineffective.
Organizations typically focus on measurement accuracy and calibration, but this course also emphasizes the essential elements of reliable measurement procedures.
Chapter 1
1.1 Introduction 5
1.2 Definitions of quality 6
1.2.1 Traditional and Taguchi definition of Quality 7
1.3 Taguchi’s quality philosophy 8
1.4 Objective of Taguchi Methods 10
1.5 8-Steps in Taguchi Methodology 10
Chapter 2 (Loss Function)
2.1 Taguchi Loss Function 11
2.2 Variation of Quadratic Loss function 17 Chapter 3 (Analysis of Variation)
3.1 Understanding Variation 19
3.2 What is ANOVA 19
3.2.1 No Way ANOVA 19
3.2. 1.1 Degree of Freedom 20
3.2.2 One Way ANOVA 24
3.2.3 Two Way ANOVA 30
3.3 Example of ANOVA 36
Chapter 4 (Orthogonal Array)
4.1 What is Array 46
4.2 History of Array 46
4.3 Introduction of Orthogonal Array 47
4.3.1 Intersecting many factor- A case study 49
4.3.1.1 Example of Orthogonal Array 50
4.3.2 A Full factorial Experiment 58
4.4 Steps in developing Orthogonal Array 60
4.4.1 Selection of factors and/or interactions to be evaluated 60
4.4.2 Selection of number of levels for the factors 60
4.4.3 Selection of the appropriate OA 62
4.4.4 Assignment of factors and/or interactions to columns 63
4.4.5 Conduct tests 65
4.4.6 Analyze results 66
4.4.7 Confirmation experiment 69
4.5 Example Experimental Procedure
Measurement System Analysis (MSA) course is essential for successful Six Sigma DMAIC and DFSS projects. It is also key for implementation of SQC, and efficient process management.
Reliable measurement processes are critical to the success of any effort dependent on measurement data and process analysis, including Six Sigma DMAIC improvement projects, DFSS project, SPC, SQC, Supplier Quality, and business process management and continuous improvement. Without validation that measurements are accurate, repeatable with multiple measurements by the same person, reproducible from person to person (gage Repeatability and Reproducibility or gage R&R), all conclusions are suspect, and process management is therefore fragile and ineffective.
Organizations typically focus on measurement accuracy and calibration, but this course also emphasizes the essential elements of reliable measurement procedures.
This is a presentation to the top management as to why reliability is important and what is the difference between a maintenance engineer and a reliability engineer.
7 QC Tools are simple statistical tools used for problem solving. Nilesh Arora presented basics of 7 QC Tool training and details about Pareto Diagram.
Process Quality Control
SPC, SQC Defined
Difference between SQC and SPC
Controlling Process Inputs (independent variables)
Process Capability with MINITAB
Monitoring process outputs (dependent variables)
7QC-Tools with MINITAB
This is a presentation to the top management as to why reliability is important and what is the difference between a maintenance engineer and a reliability engineer.
7 QC Tools are simple statistical tools used for problem solving. Nilesh Arora presented basics of 7 QC Tool training and details about Pareto Diagram.
Process Quality Control
SPC, SQC Defined
Difference between SQC and SPC
Controlling Process Inputs (independent variables)
Process Capability with MINITAB
Monitoring process outputs (dependent variables)
7QC-Tools with MINITAB
ANALYZING THE PROCESS CAPABILITY FOR AN AUTO MANUAL TRANSMISSION BASE PLATE M...ijmvsc
The industry today is working intensively on a goal-oriented way towards introducing regular studies in
manufacturing. The current study is part of a large overall spanning project aiming towards an increase in
productivity, i.e. more products produced per year with availability. In this paper we have analyze what
Process Capability is and how it is implemented on a current process. All the steps are listed out in an easy
to understand manner. In current scenario, specifications for products have been tightened due to
performance competition in market. Statistical tools like control charts, process capability analysis and
cause and effect diagram ensure that processes are fit for company specifications while reduce the process
variation and improve product quality characteristic. Process capability indices (PCIs) are used in the
manufacturing process to provide numerical measures on whether a process is capable of producing items
within the predetermined limits. For the analysis purpose MINITAB 16.0 is used and is found that the
process is placed exactly at the centre of the control limits. Analysis also shows that process is not
adequate. The cause and effect diagram is prepared to found out the root cause of variation in diameter of
work. In this study, a process-capability analysis was also carried out in a medium-sized company that
produces machine and spare parts.
1. (25 points) Temperature, Pressure and yield on a chemical .docxaulasnilda
1. (25 points) Temperature, Pressure and yield on a chemical process is given below. Use the SPSS package to model this problem as a DOE problem and answer the questions below?
a. What factors are sensitive?
b. Give the complete table of analysis of variance.
c. What is the best combination of temperature and pressure to run this system?
(Figures inside the table are yield in pounds for the same starting batch size for a chemical reaction.)
Pressure lbs/sq. in.
Temperature in centigrade given below
250
300
350
100
44
74
85
100
43
72
81
100
49
73
72
100
56
60
84
100
50
78
78
100
49
76
71
100
54
67
86
100
55
74
89
100
47
72
83
100
59
80
72
150
49
60
78
150
54
77
86
150
47
64
79
150
59
73
72
150
53
71
80
150
50
62
74
150
42
61
72
150
42
78
89
150
53
66
85
150
48
64
76
200
59
60
73
200
52
71
80
200
42
72
72
200
55
79
87
200
44
78
82
200
49
76
84
200
53
70
72
200
42
78
80
200
50
69
83
200
58
69
77
2. (20 points) Solve the following problem using logistic regression using SPSS. Data on admission to Top MBA programs and student profiles are given below. Answer the questions at the bottom of the page. (Science major =1 and non-science major =0, Admission is 1 and rejection is 0.)
GRE
GPA
Experience
Science_Major
Admission_top_MBA_Program
420
2.989713
4
1
0
410
3.062205
0
0
0
460
3.95905
2
0
1
740
3.969431
5
0
1
400
2.964876
3
1
0
740
3.016192
4
0
1
750
3.798612
1
0
1
610
3.779912
0
0
0
540
3.959263
4
0
1
460
2.873084
0
0
0
790
2.969328
2
0
1
420
2.952248
3
0
0
410
2.929681
3
0
0
670
2.853553
4
0
0
620
3.047547
5
1
0
550
3.660386
3
0
0
530
2.893152
5
0
0
790
3.193752
3
0
1
480
3.023745
2
0
0
580
3.902819
2
1
1
730
3.899274
1
0
0
480
3.869059
1
1
0
600
2.924105
2
0
0
700
2.960273
2
0
0
410
3.730714
0
0
0
720
3.934777
1
0
1
560
3.559107
3
1
0
620
3.088629
2
0
0
560
2.904412
3
0
0
610
3.897915
3
1
0
a. Run the logistic regression using SPSS and this data.
b. Write down the logit function from your output.
c. Using the logistic regression equation and input data, generate the probability of admission for each of the 30 students and compare it with SPSS produced probabilities.
3. (15 points) Data on Yield % against two variables (temperature and catalyst level) is given below.
a. Do a spreadsheet based analysis of the data and report on which factors (temperature, catalyst level or interaction: temperature*Catalyst) is significant.
b. If interaction is significant at 0.05 level, report on the best combination of the two factors that will maximize the yield percent.
Temperature (C )
600
650
700
Catalyst Level
Low
70
74
94
Low
61
73
74
Low
57
77
52
Morerate
95
60
93
Moderate
87
79
82
Moderate
97
54
84
High
53
69
58
High
73
66
65
Hjigh
71
74
76
Yield % in a chemical reactor
Data to be used in SPSS if you wanted to check your answer is given below.
Cat Level
Temp
yield
Low
600
70
Low
600
61
Low
600
57
Low
650
74
Low
650
73
Low
650
77
Low
700
94
Low
700
74
Low
700
52
Moderate
600
95
Moderate
600
87
Moderate
600
97
Moderate
650.
Tuning the model predictive control of a crude distillation unitISA Interchange
Tuning the parameters of the Model Predictive Control (MPC) of an industrial Crude Distillation Unit (CDU) is considered here. A realistic scenario is depicted where the inputs of the CDU system have optimizing targets, which are provided by the Real Time Optimization layer of the control structure. It is considered the nominal case, in which both the CDU model and the MPC model are the same. The process outputs are controlled inside zones instead of at fixed set points. Then, the tuning procedure has to define the weights that penalize the output error with respect to the control zone, the weights that penalize the deviation of the inputs from their targets, as well as the weights that penalize the input moves. A tuning approach based on multi-objective optimization is proposed and applied to the MPC of the CDU system. The performance of the controller tuned with the proposed approach is compared through simulation with the results of an existing approach also based on multi-objective optimization. The simulation results are similar, but the proposed approach has a computational load significantly lower than the existing method. The tuning effort is also much lower than in the conventional practical approaches that are usually based on ad-hoc procedures.
Estimating Reliability of Power Factor Correction Circuits: A Comparative StudyIJERA Editor
Reliability plays an important role in power supplies, as every power supply is the very heart of every electronics equipment. For other electronic equipment, a certain failure mode, at least for a part of the total system, can often be tolerated without serious (critical) after effects. However, for the power supply no such condition can be accepted, since very high demands on the reliability must be achieved. At higher power levels, the CCM boost converter is preferred topology for implementation a front end with PFC. As a result significant efforts have been made to improve the performance of high boost converter. This paper is one the effort for improving the performance of the converter from the reliability point of view. In this paper a boost power factor correction converter is simulated with single switch and interleaving technique in CCM, DCM and CRM modes under different output power ratings and the reliability. Results of the converter are explored from reliability point of view.
Core technology of Hyundai Motor Group's EV platform 'E-GMP'Hyundai Motor Group
What’s the force behind Hyundai Motor Group's EV performance and quality?
Maximized driving performance and quick charging time through high-density battery pack and fast charging technology and applicable to various vehicle types!
Discover more about Hyundai Motor Group’s EV platform ‘E-GMP’!
What Exactly Is The Common Rail Direct Injection System & How Does It WorkMotor Cars International
Learn about Common Rail Direct Injection (CRDi) - the revolutionary technology that has made diesel engines more efficient. Explore its workings, advantages like enhanced fuel efficiency and increased power output, along with drawbacks such as complexity and higher initial cost. Compare CRDi with traditional diesel engines and discover why it's the preferred choice for modern engines.
𝘼𝙣𝙩𝙞𝙦𝙪𝙚 𝙋𝙡𝙖𝙨𝙩𝙞𝙘 𝙏𝙧𝙖𝙙𝙚𝙧𝙨 𝙞𝙨 𝙫𝙚𝙧𝙮 𝙛𝙖𝙢𝙤𝙪𝙨 𝙛𝙤𝙧 𝙢𝙖𝙣𝙪𝙛𝙖𝙘𝙩𝙪𝙧𝙞𝙣𝙜 𝙩𝙝𝙚𝙞𝙧 𝙥𝙧𝙤𝙙𝙪𝙘𝙩𝙨. 𝙒𝙚 𝙝𝙖𝙫𝙚 𝙖𝙡𝙡 𝙩𝙝𝙚 𝙥𝙡𝙖𝙨𝙩𝙞𝙘 𝙜𝙧𝙖𝙣𝙪𝙡𝙚𝙨 𝙪𝙨𝙚𝙙 𝙞𝙣 𝙖𝙪𝙩𝙤𝙢𝙤𝙩𝙞𝙫𝙚 𝙖𝙣𝙙 𝙖𝙪𝙩𝙤 𝙥𝙖𝙧𝙩𝙨 𝙖𝙣𝙙 𝙖𝙡𝙡 𝙩𝙝𝙚 𝙛𝙖𝙢𝙤𝙪𝙨 𝙘𝙤𝙢𝙥𝙖𝙣𝙞𝙚𝙨 𝙗𝙪𝙮 𝙩𝙝𝙚 𝙜𝙧𝙖𝙣𝙪𝙡𝙚𝙨 𝙛𝙧𝙤𝙢 𝙪𝙨.
Over the 10 years, we have gained a strong foothold in the market due to our range's high quality, competitive prices, and time-lined delivery schedules.
Ever been troubled by the blinking sign and didn’t know what to do?
Here’s a handy guide to dashboard symbols so that you’ll never be confused again!
Save them for later and save the trouble!
Things to remember while upgrading the brakes of your carjennifermiller8137
Upgrading the brakes of your car? Keep these things in mind before doing so. Additionally, start using an OBD 2 GPS tracker so that you never miss a vehicle maintenance appointment. On top of this, a car GPS tracker will also let you master good driving habits that will let you increase the operational life of your car’s brakes.
"Trans Failsafe Prog" on your BMW X5 indicates potential transmission issues requiring immediate action. This safety feature activates in response to abnormalities like low fluid levels, leaks, faulty sensors, electrical or mechanical failures, and overheating.
Fleet management these days is next to impossible without connected vehicle solutions. Why? Well, fleet trackers and accompanying connected vehicle management solutions tend to offer quite a few hard-to-ignore benefits to fleet managers and businesses alike. Let’s check them out!
Symptoms like intermittent starting and key recognition errors signal potential problems with your Mercedes’ EIS. Use diagnostic steps like error code checks and spare key tests. Professional diagnosis and solutions like EIS replacement ensure safe driving. Consult a qualified technician for accurate diagnosis and repair.
5 Warning Signs Your BMW's Intelligent Battery Sensor Needs AttentionBertini's German Motors
IBS monitors and manages your BMW’s battery performance. If it malfunctions, you will have to deal with an array of electrical issues in your vehicle. Recognize warning signs like dimming headlights, frequent battery replacements, and electrical malfunctions to address potential IBS issues promptly.
In this presentation, we have discussed a very important feature of BMW X5 cars… the Comfort Access. Things that can significantly limit its functionality. And things that you can try to restore the functionality of such a convenient feature of your vehicle.
Why Is Your BMW X3 Hood Not Responding To Release CommandsDart Auto
Experiencing difficulty opening your BMW X3's hood? This guide explores potential issues like mechanical obstruction, hood release mechanism failure, electrical problems, and emergency release malfunctions. Troubleshooting tips include basic checks, clearing obstructions, applying pressure, and using the emergency release.
Comprehensive program for Agricultural Finance, the Automotive Sector, and Empowerment . We will define the full scope and provide a detailed two-week plan for identifying strategic partners in each area within Limpopo, including target areas.:
1. Agricultural : Supporting Primary and Secondary Agriculture
• Scope: Provide support solutions to enhance agricultural productivity and sustainability.
• Target Areas: Polokwane, Tzaneen, Thohoyandou, Makhado, and Giyani.
2. Automotive Sector: Partnerships with Mechanics and Panel Beater Shops
• Scope: Develop collaborations with automotive service providers to improve service quality and business operations.
• Target Areas: Polokwane, Lephalale, Mokopane, Phalaborwa, and Bela-Bela.
3. Empowerment : Focusing on Women Empowerment
• Scope: Provide business support support and training to women-owned businesses, promoting economic inclusion.
• Target Areas: Polokwane, Thohoyandou, Musina, Burgersfort, and Louis Trichardt.
We will also prioritize Industrial Economic Zone areas and their priorities.
Sign up on https://profilesmes.online/welcome/
To be eligible:
1. You must have a registered business and operate in Limpopo
2. Generate revenue
3. Sectors : Agriculture ( primary and secondary) and Automative
Women and Youth are encouraged to apply even if you don't fall in those sectors.
4. A Guide to Using Cpk
a Process Capability Index
1
Introduction
The purpose of this guide is twofold. The first is to provide
information on the process capability index Cpk. The second is
to list various actions that can be taken or parameters checked
in order to reduce process variation.
The idea of comparing the specification of a part parameter to
the measured variation or distribution of the process producing
the parameter has been with us for many years. It has only
been in recent years that the comparison has been given a for-mal
name and a means of calculation.
All authors and analysts writing on Cpk hasten to point out that
the index is a statistic based on measurements and, like all such
statistics, has an associated degree of uncertainty. However,
most practitioners consider Cpk to be a fixed number without
regard to the nature of the data that produced it. We will point
out the uncertainty involved in any statement of Cpk.
This guide assumes the reader has knowledge of control charts
and methods for calculating standard deviations. A good refer-ence
is the NIST/SEMATECH Handbook of Statistical Methods.
The complete Handbook is on the Internet and may be accessed
at www.itl.nist.gov/div898/handbook.
What is Cpk?
Cpk is a Process Capability Index. The term index is used
because the value is a comparison or ratio. It is the ratio of the
5. workpiece specification or tolerance (allowed variation) com-pared
to the process variation (produced variation) expressed in
terms of ± 3 standard deviations. When standard deviation is
used in a calculation, the assumption is that the underlying
measurements form a normal distribution.
Therefore, in the case of calculating Cpk, all known assignable
causes for variation in the process should be minimized before
measurements are taken that will be used in the final calcula-tion.
In other words, the process should be stable and in statis-tical
control.
Some processes may use a positive stop or an in-process gage
to produce part size. In those cases, the size distribution may
not be normal, and the calculations described here will not be
valid. Other sources should be consulted on how to deal with
skewed distributions.
In other cases, the specification is not bimodal nor is it given as
a range. Examples might be “hardness at least – ” or “surface
finish not to exceed –.” In those situations a Cpk cannot be cal-culated
since the part specification is not stated as a range. Of
course, the standard deviation for the process output can still be
calculated, and an estimate made about the probability of stay-ing
within the specification. But this is not a comparison such
as Cpk.
The importance of sample size in acquiring data cannot be over
emphasized. As we shall see, the calculated value of Cpk
depends on what is technically termed an “estimate” of the
standard deviation. The larger the sample size, the more accu-rate
is the estimate.
2
6. Calculating Cpk
Once data on the process has been gathered and analyzed, and
the standard deviation calculated, a comparison to the product’s
specification can be made. This simple comparison yields the
process potential Cp. In some cases, the mean of the process is
at the center of the product’s specification limit as shown in
Figure 1. The term Cp assumes centering and should be equal
to or greater than 1.
Specification Width
−
Process Spread
Specificat ion Pr s
USL is the upper specification limit
LSL is the lower specification limit
X is the process mean
Note: The symbol σ is used for standard deviation when very
large samples are used that accurately represent the total popu-lation.
In most cases, it is not feasible to use large samples,
and the resultant standard deviation is represented by s.
3
=
ocess USL LSL
6
Cp =
7. However, in most cases, the process will not be centered on the
specification as shown in Figure 2. The actual process capabili-ty
Cpk then becomes
X Nearest Specificat ion Limit
X Nearest Specification Limit
USL X
−
X LSL
In Figure 2, the nearest specification limit is USL. An
inspection of Figure 2 will show that the first step in increasing
Cpk should be to take action to align the center of the process
spread with the center of the specification spread. This
assumes that the two spreads are close to equal, or the process
spread is actually less than the specification spread.
4
s
3
−
s
3
−
s
3
Cpk =
This is usually stated as
Cpk = Min [ , ]
FIG. 2
8. Of course, if the process spread greatly exceeds the specifica-tion
spread, steps must be taken to reduce the process spread.
In Figure 2, Cpk would be about 0.5. However, if the process
spread were aligned with the specification, Cpk would be about
1.0.
Putting Cpk in Perspective
For the sake of simplicity, let’s assume that the process is cen-tered
on the product specification. How many defective parts
per million (parts out of tolerance) would we expect for differ-ent
values of Cpk? Table 1 lists some values:
Table 1: Expected number of defective parts
for values of Cpk
Cpk Parts per million defective
1.00 2,700.0
1.10 967.0
1.20 318.0
1.30 96.0
1.40 26.0
1.50 6.8
1.60 1.6
1.70 0.34
1.80 0.06
2.00 0.0018
It should be noted that a Cpk of 2 equates to roughly two parts
per billion defective! Such a number highlights the signifi-cance
of sample size and the related issue of uncertainty associ-ated
with the actual value of Cpk.
5
9. Suppose we would like to start with a 90% confidence level
that a calculated value of Cpk based on measured data is equal
to or greater than a specified value. What value would we have
to see based on various sample sizes? Table 2 provides some
examples:
Table 2: Required Test Cpk Values for 90% Confidence
in Specified Value
Specified Value for Cpk
Sample
Size 1.00 1.30 1.50 1.70 2.00
200 1.08 1.40 1.61 1.82 2.14
100 1.11 1.44 1.66 1.88 2.21
50 1.17 1.51 1.74 1.97 2.31
30 1.24 1.60 1.84 2.07 2.45
10 1.50 1.93 2.22 2.52 2.95
Most experts agree that the sample size should be at least 30.
For derivation of how to calculate the values in Tables 1 and 2
above, see the referenced NIST/SEMATECH Handbook (noted
on page 1), section 7.1.4.
Things to Remember About Cpk
Cpk is used to provide some expectation about the future
capability of a process. However, the number calculated
is based on a snapshot of the process at only one point
in time. The calculated Cpk is only an estimate of how
the process might be expected to perform.
The confidence level we can assign to the calculated
value is a function of sample size.
6
10. We should not lose sight of the fact that establishing process
capability gives us a benchmark for improvement. Continuous
improvement is the ultimate goal of making the measurements.
Factors to Consider in Improving Cpk
Measurement
The key element in establishing Cpk with a customer is reach-ing
agreement on the measurement method and gauges to be
used. The condition of the measurement equipment, and gauge
reproducibility and repeatability (RR) should be stated. In
fact, for tight tolerances, the conditions used to determine RR
should be stated – such as the number of appraisers and the
number of repeat measurements. In order to be able to analyze
data for events that happen during a test run, make sure that
measurements are recorded chronologically.
See Section 2.4 in the NIST/SEMATECH referenced Handbook
for a complete discussion on gauge RR.
Machine
Thermal deformation is one of the greatest contributors to
change in the output of a machine tool. All elements respond-ing
to temperature change should be understood and monitored.
Machine accuracy and repeatability should be determined using
statistical techniques. Factors such as alignment, spindle
runout and balance, and dynamic stability should be accessed
with respect to the contribution to desired workpiece parame-ters.
Machine maintenance is useful to restore parameters that have
deteriorated and are contributing to variations. Company pro-cedures
should be established for maintaining machine calibra-tion.
7
11. Tooling
Changes in tool condition are a common source of shift in
workpiece size or surface finish. These changes can best be
analyzed from a histogram of data taken chronologically.
Changes are not limited to tool wear, but may also be created
by dirt on the toolholder, a balance condition, or repeatability
when changing inserts.
Workholding
The ability of the workholding device to position each part con-sistently
is critical to maintaining uniform output. Tests should
be made to determine the repeatability of workholding devices.
The rigidity of the workholding device in relation to the rigidity
of the workpiece and process-induced forces can also influence
size variation.
Workpiece
Variations in workpiece initial stock conditions are a common
source of output variation. Workpieces should be checked for
incoming size and hardness. Both parameters cause changes in
process forces. Cpk of incoming parts would be desirable.
8