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Injection Moulding Technology - Part 3
CoWC 0410
Injection Moulding Technology
Part 3
Quality
Injection Moulding Technology - Part 3
CoWC 0410
To improve the delegates understanding of quality issues, relating to injection moulding and how the process can be optimised and monitored.
Session aim
Injection Moulding Technology - Part 3
CoWC 0410
By the end of the session you will be able to:
Calculate Cm and Cmk values.
Explain how weight can be used to monitor the process.
State 3 Quality Improvement tools.
Session objectives
Injection Moulding Technology - Part 3
CoWC 0410
The manufacturing process
Methods People Material
Environment Equipment
Output
Information on quality
Decisions taken
Quality control - Detection systems
Injection Moulding Technology - Part 3
CoWC 0410
ImproveDesigns Update
PerformanceDoE
Information on qualitySPC
FMEA
The manufacturing process
Method People Material
Environment Equipment
Output
Decisions taken
Quality assurance - Prevention systems
Injection Moulding Technology - Part 3
CoWC 0410
Quality tools
A combination of trials to identify optimum process conditions. e.g. L8 – 7 variables with 2 levels.
DoE (Design of Experiments)
Step-by-step approach to identify all possible failures in a design, manufacturing or assembly process.
FMEA (Failure Mode & Effects Analysis)
SPC (Statistical Process Control)
A mathematical technique to measure and improve performance.
Injection Moulding Technology - Part 3
CoWC 0410
1. Process function – Capability study on m/c.
2. Potential failure modes – Zero cushion position
3. Potential effects of the failure – High scrap rate
4. Potential causes of the failure – Worn/damaged check ring
5. Current process controls – None
6. Recommended actions – a) Barrel tolerances +/- 100C. b) Monitor cushion position c) Visual check every 6 months (Abrasive polymers) PC & GF grades
Failure Mode & Effects Analysis
Injection Moulding Technology - Part 3
CoWC 0410
SPC - More detail
Collecting, representing and analysing data,developing and understanding patterns.
A sequence of operations, not only themachine cycle.
Statistical
Process
Control
Measuring performance, taking action onthe data.
Injection Moulding Technology - Part 3
CoWC 0410
TargetBottom
LimitTopLimit
Total Tolerance
x x xx x x x x x
Terminology
xx
Injection Moulding Technology - Part 3
CoWC 0410
Measured sizes
Target piston diameter = 60 mm (+/- 1mm)
Case study
60.0
x x x x xx xx x xx
xx
x
61.2
60.8
60.6
60.4
60.2
61.0
58.8
59.8
59.4
59.2
59.0
59.6
Target
Total Tolerance
xx
xx xx
x xx x
x
x
xx
xx
xx
x
xx
x x x
xxx
xx
x
xxx
x
xx
Total Variation in Sample
Injection Moulding Technology - Part 3
CoWC 0410
Normal distribution curves
x
Injection Moulding Technology - Part 3
CoWC 0410
Normal distribution curves
x
6 x std dev (6 Sigma) = 99.9997%
Injection Moulding Technology - Part 3
CoWC 0410
Why choose 6 sigma?
x
1 sigma = 691,462 DPM or 30.9% Defect free
2 sigma = 308,538 DPM or 69.1% Defect free
3 sigma = 66,807 DPM or 93.3% Defect free
4 sigma = 6,210 DPM or 99.4% Defect free
6 sigma = 3.4 DPM or 99.9997% Defect free
Injection Moulding Technology - Part 3
CoWC 0410
Machine capability
Total tolerance6 x Sigma
CmCm =
CmCm = Measure of the variation present, in relation to the available tolerance.
Injection Moulding Technology - Part 3
CoWC 0410
Capability = Cm = Total tolerance = 1.2 = 36 x Sigma 0.4
Curve fits into tolerance 3 times.
High capability
Tolerance = +/- 0.6
6 Sigma
( = 0.4 )
Injection Moulding Technology - Part 3
CoWC 0410
Curve does not fit inside the tolerance.
Low capability
Capability = Cm = Total tolerance = 1.2 = 0.756 x Sigma 1.6
Tolerance = +/- 0.6
6 Sigma
( = 1.6 )
Injection Moulding Technology - Part 3
CoWC 0410
LSL USL
Cm = 1.67 or greaterCm = 1.67 or greater
Minimum capability
Injection Moulding Technology - Part 3
CoWC 0410
LSL USL
Cm is still = 1.67
Minimum capability
but some samples are outside limits.
Target
Injection Moulding Technology - Part 3
CoWC 0410
Targeting
CmkCmk = Difference between the Avg. and nearest limit
3 x Sigma
CmkCmk = Measure of the variation present in relation to the available tolerance, combined targeting of the set-up.
Injection Moulding Technology - Part 3
CoWC 0410
LSL USL
Worked example
TARGETAvg.(Mean)
Cmk = Difference between Avg. and nearest Limit
3 x 0.035 (Sigma)=
Cmk = 1.67Cmk = 1.67 or greateror greater
0.215
0.105
3 x sigma
= 2.04
0.215
Injection Moulding Technology - Part 3
CoWC 0410
Injection Moulding Technology
Part 3
Quality