19. Process Capability Flashcards

1
Q

Process Capability P.365

A

Inherent variability of the characteristics of a process. A process is capable when the output always conforms to the process specifications (6σ).

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2
Q

Process Capability Index P.365

A

Used to represent the ability to meet customer specification limits..

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3
Q

Cp Index

A

Describes process capability in relation to the specified tolerance of a characteristic divided by the natural process variation

Cp = USL - LSL / 6σ 
1 = capable
2= represent 6σ performance
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4
Q

Cpk Index

A

Cpk = min (Cpkl, Cpku)

Cpkl = x̅- LSL / 3σ
Cpku = USL - x̅ / 3σ
  1. 33 = goals
  2. 67 = mission critical / safety items
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5
Q

Cpm Index

A

Process capability index of the mean. An index that accounts for the location of the process average relative to a target value.

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6
Q

Process performance P.370

A

Statistical measure of the outcome of a characteristic from a process that may not have been demonstrated to be in a state of a statistical control.

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7
Q

Process Performance Index P.371

A

A dimensionless number that is used to represent the ability to meet specification limits on a characteristic of interest.

Tend to be a bit larger than their corresponding process capability indices since they are often based on smaller sample sizes.

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8
Q

Pp Index

A

Pp = USL - LSL / 6s

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9
Q

Ppk Index

A

Ppk = min. (Ppkl, Ppku)

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10
Q

Ppm Index

A

Analogoous to Cpm

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11
Q

Conducting a Process Capability Study P.372

A
  1. Select a quality characteristic of a specific process for study.
  2. Confirm the measurement system.
  3. Gather the data.
  4. Verify process stability and ensure that the process is in control.
  5. Verify that the individual data are normally distributed.
  6. Obtain the process specifications.
  7. Determine process capability indices and interpret them.
  8. Update the process control plan.
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12
Q

Lower confidence Limit on the Cpk P.373

A

LCL Cpk = Cpk - Zα√(1/9n+(Cpk^2)/(2n-2))

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13
Q

Process Capability for Attributes Data P.374

A

Equivalent Ppk% = Equivalent Ppk based on percent

Equivalent Pp% = Equivalant Pp based on percent

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14
Q

Process Capability for Non-Normal Data P.377

A
  • Find another known distribution that fits the data.
  • Use nonlinear regression to fit a curve to the data.
  • Transform the date to produce a second variable that is normally distributed.
  • Box-Cox
  • Johnson transformation
  • Weibull
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15
Q

Natural Process Limit P.381

A

+- 3σ limits (6σ spread) around a process averages. (VoP)

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16
Q

Specification Limits P.381

A

Customer determined (VoC)

17
Q

Process Performance Metrics P.381

A
  • Percentage Defective
  • PPM
  • Defects per Unit (DPU)
  • Defects per Million Opportunities (DPMO)
  • Throughput Yield (TPY), first time yield
  • Rolled Throughput Yield (RTY)
18
Q

Short-Term Capability P. 388

A
  • Cp, Cpk, Cpm
  • Process must be in statistical control
  • These indices are derived using an estimate of short-term variation.
  • It is assumed approximately normal distribution
  • Specification limits are based on customer requirements
19
Q

Long-Term Capability

A
  • Pp, Ppk, Ppm
  • Process does not need be in statistical control
  • These indices are derived using an estimate of long-term variation.
  • It is assumed approximately normal distribution
  • Specification limits are based on customer requirements
20
Q

Relationship between Long/ Short term Capability P.389

A

Long-term variability = Short-term variability +- 1.5σ shift.