1. Process Capability
BA 339
Mellie Pullman

2. 4/16/2017
Process Capability
Can the process provide acceptable quality consistently?

3. Process Capability Ratio (Cp)
4/16/2017
Process Capability Ratio (Cp)
Upper Tolerance Limit – Lower Tolerance Limit 6σ
σ is the estimated standard deviation for the individual process observations (SPC)
Tolerance or specifications are dictated by the customer, part drawings, laws, or other non-process related entities.
Upper and lower tolerance limits are also called the upper and lower specification limits (USL and LSL).

4. Process Capability ratio of 1
4/16/2017
Shown Graphically:
Process Capability ratio of 1
(99.7% coverage)

5. Climbing Carabineer In the lab, average breaking strength is:
m = 6500 lbs and s = 150 lbs
Industry Safety Specification = 6000 lbs lower limit and 7000 lbs upper limit.
Can the process make a product to this specification 99.7 % of time ?

6. Process Capability Ratio (Cp)
4/16/2017
Process Capability Ratio (Cp)
Upper Tolerance Limit – Lower Tolerance Limit 6σ
( )/(6*150)= 1.11
Capable?
Upper and lower tolerance limits are also called the upper and lower specification limits (USL and LSL).

7. Process Capability Index (Cpk)
4/16/2017
Process Capability Index (Cpk)
Used when the process is not precisely centered
Assume process mean is actually m= 6300
Cpk = min [( )/(3*150), ( )/(3*150)]

8. 4/16/2017
“Six Sigma Quality”
When a process operates with 6σ variation inside the tolerance limits, only 2 parts out of a million will be unacceptable.

9. 3 Lines of Defense PREVENT defects from occurring
4/16/2017
3 Lines of Defense
PREVENT defects from occurring
TQM and continuous improvement
DISCOVER problems early
Process control charts
CATCH DEFECTS before used or shipped
inspection