Six Sigma is a methodology that aims to improve processes by eliminating defects. It was developed at Motorola in 1986 and uses a "sigma level" to measure a process's capability and quality. There are two approaches: DMAIC focuses on improving existing processes, while DMADV creates new processes. Process capability indices like Cp, Cpk, Pp and Ppk are used to measure the variation within a process compared to specifications and determine if a process is capable and centered. These indices help identify issues to target for improvement and ensure stable, high quality processes.

1. - Lalit B. Padekar

2.  Initially developed at Motorola by Bill Smith in 1986
 Way of systematically improving processes by eliminating
defects
 The term " Sigma " is used to designate the distribution or
spread about the mean (average) of any process or
procedure.
 The higher the sigma value, the better. Sigma measures the
capability of the process to perform defect-free-work.

3. Formula for σ (sigma):
 ;
Where N= Sample Size.
μ = Mean of the data.

4.  There are 2 methods to implement 6σ
DMAIC
• Define
• Measure
• Analyze
• Improve
• Control
DMADV
• Define
• Measure
• Analyze
• Design
• Verify

5. DMAIC DMADV
 Define:
◦ Define the requirements and expectations of
customer.
◦ Define the project boundaries.
◦ Define the process by mapping the business flow.
 Measure:
◦ Develop Data collection plan.
◦ Measure all the critical and relevant data.
 Analyze:
◦ Find the critical processes.
◦ Analyse the causes of defects and sources of
variation
◦ Prioritize opportunities for future improvement.
 Improve:
◦ Improve process to eliminate variations.
◦ Develop creative alternatives and implement
enhanced plans.
 Control:
◦ Prevent reverting to old ways.
◦ Ensure any variances are corrected before they
result in defects
◦ Ensure any variances are corrected before they
result in defects
 Define:
◦ Define the requirements and expectations of
customer.
◦ Define the project boundaries.
◦ Define the process by mapping the business flow.
 Measure:
◦ Develop Data collection plan.
◦ Measure all the critical and relevant data.

 Analyze:
◦ Find the critical processes.
◦ Analyse the causes of defects and sources of
variation
◦ Prioritize opportunities for future improvement.
 Design
◦ Design details
◦ Optimize design
◦ Run simulations if necessary
◦ Prepare for design verification.
 Verify:
◦ Verify the design
◦ Set up pilot runs,
◦ Implement the production process and hand it over
to the process owner(s).
DMAIC is used to improve an existing process and DMADV is used to
create new process

6.  Process Capability means the ability to do a particular work without
producing or producing least defects.
 It measures the “goodness of a process” comparing the “voice of the
process” with the “voice of the customer”.
 Process-capability analysis helps to determine the ability to
manufacture parts within the tolerance limits and engineering
values.

7.  The process capability index or process capability ratio is a
statistical measure of process capability, the ability of
a process to produce output within specification limits.
 They measure how much ”natural variation” a process
experiences relative to its specification limits
 It allows different processes to be compared w.r.t each other
and determine the most capable process amongst them.
 The process capability indices are Cp, Cpk, Pp and Ppk.

8.  Cp = Process Capability ; Pp = Process Performance
 Both Cp and Pp are a monitoring indices for the spread of your
process compared to the specification spread.
 Used to see if a process is capable.
 They do not provide information about process centralization.
 They tell us whether the process is capable or not but not
whether the process is acceptable.
Cp or Pp = (USL-LSL)/6σ
Where; USL = Upper Specification Limit
LSL = Lower Specification Limit

9.  Cpk = Process Capability Index ; Ppk = Process Performance Index
 Cpk and Ppk are used to indicate the spread of process about the
centre.
 They give us the idea of how well the process is centered or how
much it has deviated from the centre.
 They can tell us whether the process is acceptable or not as well as
whether the process is capable or not.
Cpk or Ppk = Min of [(Mean – LSL)/3σ] or[(USL-Mean)]/3σ]

10.  Cp and Cpk consider the deviation mean within rational subgroups,
while Pp and Ppk set the deviation based on the studied data
 In most of the practices, when process is unstable or has just begun then Pp
and Ppk values of that process are considered for statistical analysis.
 When the process is stable and in control then Cp and Cpk values are
considered for statistical analysis.
New Process or process Not
under Statistical control
Existing Process under
statistical control
Measure of Spread Fit Pp Cp
Measure of Centering Ppk Cpk

11. a) Just began learning. Aims at
center but the result is hilarious
( Pp ok but Ppk not ok)
b) Finally shot the center but is
still amateur ( Pp and Ppk ok)
c) Decides to concentrate on
controlling the spread and
finally increases accuracy
(Good Cp but bad Cpk)
d) After gaining stability finally
targets the center and the
result is excellent ( Good Cp
and Cpk).
For further explanation see the Notes

12. It tells us the condition of the output.
It compares the natural variation with the specification of
customers.
It tells us whether the process is capable to produce the
desired output or not.
It compares two or more processes, to tell which process is
most capable.
It helps us to predict the variations occurring in process.
It helps us to identify and eliminate the special causes.

13.  www.isixsigma.com
 www.searchcio.techtarget.com
 Benefits, obstacles and future of six sigma approach – Young
Hoon Kwak and Frank T. Anbari.
 Six Sigma Green Belt and Black Belt training book
 Process capability and stability analysis in Track grinding of
Taper Roller bearings – Shrikant Jadhav, Ravi Shekhar, T.P Singh.
 Process Capability Improvement of an Engine Connecting Rod
machining process – GVSS Sharma and P Shrinivasa Rao.