Chapter 6 – Part 4. Process Capability. Meaning of Process Capability. The capability of a process is the ability of the process to meet the specifications. A process is capability of meeting the specification limits if at least 99.73 % of the product falls within the specification limits.
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USL = upper specification limit
LSL = Lower specification limit
Width of spec limits = USL - LSL
Spread of Process = USL - LSL
Spread of process matches the width of specs.
99.73% of output is within the spec. limits.
If , what does this imply regarding the spec. limits?
Spread of process is less than the width of specs.
More than 99.73% of output is within the spec. limits.
Spread of process is greater than the width of specs.
Less than 99.73% of output is within the spec. limits.
USL = 20 grams
LSL = 10 grams
Estimated Process Fraction Defective
p-bar = F1 + F2
z = 3Cp
(See last side for deviation of this result.)
z = 3(0.627) =1.88
be the area under the standard normal curve between 0 and z.
Area(z) = Area(1.88) = 0.4699
F2 = % above USL = .5000 - 0.4699 = .0301
z = 3Cp = 3(0.33) = 0.99
Area(z) = Area(0.99) = 0.3389
p-bar = 2[.5 - Area(0.99)]
= 2[.5 - 0.3389]
Process Mean = Target Value = (LSL + USL)/2
If process is centered on target,
If process is off target,
LSL = 10, USL = 20, estimated standard deviation =
5.0 and estimate process mean = 15.33. Compute
If process mean is adjusted to target,
is the maximum amount by which we can increase CTby adjusting the mean to the target value.