Mark s' rusco ferris state university

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Mark s. ruscoferris state university

• Managing Your SPC Program for Results

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Why do my parts vary???
Part Variation
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Why do my parts vary???
Injection Temp
Hold Pressure
Mold Temp
Cycle Time
Dwell Time
Ambient Temp
Melt Temp
Injection Pressure
Part Variation
Material Dryness
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Goal for your process

• 1. Have a Process Control System that alerts the
  operator to stop the process and look for
  problems. Adjust the process to compensate.
• 2. Have a Process Control System that allows the
  operator to continuously run the process with
  little to no adjustment.
• Whats the difference?

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Part variation

• Your process causes parts.
• Variation in your process causes variation in
  your parts.
• To control part variation, you must control
  process variation.

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Minimize part variation

• Step 1. Talk to the operator and ask them to be
  more careful.
• Step 2. Hang Quality message posters reminding
  the operators that The Customer is the Next
  Inspector.
• Step 3. Write-up operators.
• Step 4. Accomplish actual process improvement by
  applying Quality tools.

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Using spc to minimize part variation

• To minimize part variation, you must minimize
  process variation.
• SPC does nothing to minimize variation.
• SPC is a tool used to maintain a process i.e.
  continue doing what youve always done.
• SPC improves a process in the same way that an
  accountant makes money for the company. It just
  keeps score.

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Using spc to minimize part variation

• SPC belongs in a larger framework of Continuous
  Improvement.
• Identify the important process characteristics.
• Measure them for a while using SPC to create a
  baseline
• Do project based Continuous Improvement.
• Continue using SPC to monitor the results.

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Steps to implement Spc
What do we do?
Do we do it the same?
Do we do it right?
Process Definition
In-Control
Capability
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Capability

• In-control means a process is stable and
  predictable, i.e., it will make the same kind of
  stuff that it always has.
• Capable means that the stuff the process makes is
  good according to specification.

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Capability

• Capability is a Ratio
• Ratios are tricky things.
• Its unitless
• Compared against some standard (1.33, 1.67, etc.)
• No further analysis in terms of adding them,
  multiplying them, etc.
• Can be converted to an equivalent PPM

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Capability

• Pp vs PPM Summary table
• You create this by solving the Z-score problem
• Notice that its not a linear connection

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Capability

• Interpreting Pp
• Changes in Pp are driven by changes in Sigma.

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Capability

• Pp

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Capability

• Interpreting Pp and Ppk
• Notice that if Sigma doesnt change, then Pp
  doesnt change
• Notice that if Mean changes, Pp doesnt change
  but Ppk does change.

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Capability

• Ppk

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Capability

• Pp (and Cp) measure how well your process COULD
  be if it were centered.
• Ppk (and Cpk) measure the actual performance of
  your process, based on how far off center it is.
• Ppk is easier to fix than Pp
• Its easier to move the mean (adjust some knob)
  than to reduce standard deviation

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Interpreting Capability
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The End
Injection Temp
Hold Pressure
Mold Temp
Cycle Time
Dwell Time
Ambient Temp
Melt Temp
Injection Pressure
Part Variation
Material Dryness