Module 5: Quality Flashcards
Performance quality
To what extent the product or service provided meets customer expectations
Conformance quality
Whether the process is carried out the way that we intend it to be carried out
Cause for conformance quality issues
Variability
Yield of a resource
% of units the resource produces according to specification
Yield of process
% of units the process produces according to specification
= y_1 * y_2 * … * y_n = (1-p)^n
Swiss cheese model
Probability of an overlapping defect (hole) in all slices of cheese
Cost of defect: Input or output price?
Depends on point of detection - before or after bottleneck
Starved (resource)
Resource is not utilized due to rework at preceding resource
Blocked (resource)
Resource has completed processing but cannot progress due to rework at next resource
Buffer vs Toyota argument on inventory
Buffer: Increase inventory to avoid flow rate impact from production issues
Toyota: Decrease inventory to expose problems and address them
Kanban system
Visual way to implement a pull system. Amount of WIP is determined by number of cards
Why is inventory the worst form of waste?
Operators grow comfortable with current amount of defects instead of trying to improve
Upper specification limit (USL)
Level above which a unit will be considered defective
Lower specification limit (LSL)
Level below which a unit will be considered defective
Capability score
(USL - LSL) / (6 * sigma)
ppm
Parts per million. Used to describe number of defective units per one million produced
Common cause variation
Signified by variation within control limits
Assignable cause variation
Signified by variation outside control limits
Control limits (LCL and UCL)
Measure level of variation in a product relative to its usual fluctuations (ie. w/in 3sd in each direction). Not related to whether or not defective
Process control chart
[TBD]
Capability analysis
1st step in process control: What is the inherit capability of my process when it is “in control”?
Conformance analysis
2nd step in process control: Identify when control has likely been lost and assignable cause variation has occurred
Investigate for assignable cause
3rd step in process control: Find root causes of potential loss of statistical control
Eliminate or replicate assignable cause
4th step in process control: Need corrective action to move forward
Information turnaround time (ITAT)
Amount of time before a defective is detected => slow feedback and improvement
Jidoka
If equipment malfunctions / gets out of control, it shuts itself down to prevent further damage. Requires three steps: 1) Detect, 2) Alert, 3) Stop
Andon Board / Cord
Assembly line version of Jidoka. When a worker notices a defect, s/he pulls the andon / cord. Station # appears on andon board.
Toyota quality system diagram
[TBD - ]
3 commonalities between Toyota Quality System & Six Sigma
1) Avoid defects by eliminating variation
2) If variation exists, create an alarm and trigger process
3) Process is never perfect - repeat steps
Ishikawa diagram
Brainstorming technique of what might have contributed to a problem.
Fish-shaped.
5 Why’s
Technique from Toyota to get to the root of a problem
Pareto chart
Maps out the assignable causes of a problem in the categories of the Ishikawa diagram. Order root causes in decreasing order of frequency of occurence - 80/20 logic.
Pareto principle
80% of the problems are caused by 20% of the root causes
Three enemies of operations
Variability, Waste, Inflexibility
