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Rockford Powertrain Training Workshop Process Capability and Cpk

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## Rockford Powertrain Training Workshop Process Capability and Cpk

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**1. **Rockford PowertrainTraining WorkshopProcess Capability and Cpk

**2. **Training materials, reference documents, and functional SPC templates are available free on the Rockford Powertrain web site. Go to:www.rockfordpowertrain.com/supplier

**3. **Process Capability Enables successful manufacturing and sales
Prevents scrap, sorting, rework
Allows jobs to run well
Has major impact on cost and schedule

**4. **“Process Capability” is the ability of a process to make a featurewithin its tolerance.

**5. **Everything Varies (and the variation can be seen if we measure precisely enough) Heights
Weights
Lengths
Widths
Diameters
Wattage
Horsepower
Miles per Gallon Pressure
Roughness
Strength
Conductivity
Loudness
Speed
Torque
Etc. etc. etc.

**6. **Eli Whitney in 1798 Won a U.S. Military contract to supply 10,000 guns
Reduced variation and created interchangeable parts for assembly and service by:
Installing powered factory machinery
Using specialized fixtures, tools, jigs, templates, and end-stops
Creating drawings, routings, operations & training

**7. **Manufacturing in the 21st Century International competition to provide defect-free products at competitive cost
Reducing variation and providing interchangeable parts for assembly and service by:
Using machine tools
Using specialized fixtures, tools, jigs, templates, and end-stops
Using drawings, routings, operations & training

**8. **Graphing the tolerance and a measurement

**9. **Graphing the tolerance and a measurement

**10. **Graphing the tolerance and a measurement

**11. **Graphing the tolerance and a measurement

**12. **Graphing the tolerance and measurements

**13. **Graphing the tolerance and measurements

**33. **Review Question 1 What is “Process Capability?”

**34. **Review Question 2 How is the “process average” calculated or estimated?

**35. **Review Question 3 What is a “Standard Deviation”?
(also known as a “sigma”)

**36. **Review Question 4 What is Cpk used for?

**37. **Review Question 5 Suppose that a feature tolerance is .750”/.760”,
and the process average is .759”,
and the process standard deviation is .002”
…is the process satisfactory and capable?

**38. **Review Question 6 Suppose that a torque tolerance is 25 foot pounds minimum,
and the process average is 26 foot pounds,
and the process standard deviation is 3 foot pounds…
…is the process capable?

**39. **Review Question 7 Suppose that a diameter tolerance is 8.010” to 8.060”,
and the process average is 8.041”,
and the process standard deviation is .002”…
…is the process capable?

**40. **Review Question 8 Fred is cutting an outside diameter on a lathe and the diameter is easily adjustable.
The diameter tolerance is 5.050” to 5.090”,
the process average is 5.090”,
and the process standard deviation is .001”…
What is the Cpk?
What should Fred do with the process?

**41. **Review Question 9 Joe is boring an inside diameter on a lathe.
The diameter tolerance is 1.980” to 2.020”.
Joe has measured three random samples at
2.005”, 2.004”, and 2.006”.
Estimate the process average.
Estimate the standard deviation (best guess).
Estimate whether the process can be capable.

**42. ** Review Question 10 TechCorp is demonstrating a new “high-precision” grease dispenser machine.
TechCorp claims that they can “dispense grease all day with an accuracy of plus or minus half an ounce.”
During the demo, ten samples of grease in a row were dispensed (in ounces) as follows:
2.3, 2.0, 2.6, 3.0, 2.1, 2.7, 2.9, 2.5, 2.0, 2.4
Based on the sample data, evaluate TechCorp’s claim that they can “dispense grease all day with an accuracy of plus or minus half an ounce.”

**43. **Quiz Question 1 True or False?
“Process Capability” can be defined as
the ability of a process to make a featurewithin its tolerance.

**44. **Quiz Question 2 True of False?
We can estimate the process average
by taking a set of sample measurements,
adding them up, and dividing by the number of measurements.

**45. **Quiz Question 3 True or False?
A “Standard Deviation” can be thought of as the “typical” distance of the measurements from the average;
about 68% of the individuals will fall within
+ or – 1 standard deviation of a bell curve.

**46. **Quiz Question 4 True or False?
When using Cpk, the goal is to keep the Cpk value as low as possible.

**47. **Quiz Question 5 True or False?
If the feature tolerance is .350”/.360”,
and the process average is .351”,
and the process standard deviation is .004”
…then the process should be called “capable.”

**48. **Quiz Question 6 True or False?
If a pressure tolerance is 250 PSI minimum,
and the process average is 260 PSI,
and the process standard deviation is 4 PSI,
…then the process is “capable.”

**49. **Quiz Question 7 True or False?
If a height tolerance is 7.010” to 7.060”,
and the process average is 7.042”,
and the process standard deviation is .002”…
…then the process is “capable.”

**50. **Quiz Question 8 True or False?
If Larry is cutting an O.D. and the diameter is easily adjustable, the tolerance is 4.055” to 4.095”, the process average is 4.095”, and the standard deviation is .001”…
…then Larry should be able to make the process fully “capable” by adjusting the process.

**51. **Quiz Question 9 True or False?
If Jill is boring an I.D. with a tolerance of 1.475” to 1.525”, and has measured three samples at 1.501”, 1.500”, and 1.499”…
…then the average of the samples is 1.501”, the standard deviation is probably larger than .010”, and the Cpk is probably zero.

**52. **Quiz Question 10 True or False?
If HiTechCo is demonstrating a new “high-precision” surface coating machine, and claims that their machine “can coat all day with an accuracy of plus or minus .010 inches,” and during the demo the coating thickness readings (in inches) were as follows:
.027, .028, .027, .029, .028, .029, .028, .029, .028, .027
…then the sample readings suggest that HiTechCo might be telling the truth about being able to hold plus or minus .010 inches.

**53. **Appendix Cpk and PPM
(Parts Per Million Defective)