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Quality Tools. ISQA 552 MBA Mellie Pullman. Quality Specifications. Design quality : Inherent value of the product in the marketplace Dimensions include: Performance, Features, Reliability, Durability, Serviceability, Response, Aesthetics, and Reputation.
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Quality Tools ISQA 552 MBA Mellie Pullman
Quality Specifications • Design quality: Inherent value of the product in the marketplace • Dimensions include: Performance, Features, Reliability, Durability, Serviceability, Response, Aesthetics, and Reputation. • Conformance quality: Degree to which the product or service design specifications are met • Quality as fitness for use • Quality as excellence
Judging Fitness for Use What are desired benefits received by the customer from the product?
Common Improvement Tools • Value Stream mapping • Cause and effect diagrams (aka “Fishbone” or Ishikawa diagrams) • Check sheets • Pareto analysis • Run charts and scatter plots • Bar graphs • Histograms
Cause and Effect Diagram • ASKS: What are the possiblecauses? • Root cause analysis — open and narrow phases
Problem: Late Room Service • No one is sure why, but plenty of opinions • “Management by Fact” • Tools we will use: • Fishbone diagram • Check sheets • Pareto analysis
Pareto Analysis(sorted histogram) Late Elevator Late food 100 Lacking cart 85 Few runners 70 Other (160) 65
Percent of each out of 480 total incidents ... Late elevator 21% Late food 18% Late cart 15% Runners 14% Other 33%
The PDCA Cycle Do Plan Check Act
Discovering “problems” • Inspect every item • Expensive to do • Testing can be destructive, should be simply unnecessary • Statistical techniques Statistical process control (SPC) Acceptance Sampling
Appraisal Costs Prevention Costs Internal Failure Costs External Failure Costs Costs of Quality: Four Sources Costs associated with discovering the condition of products and raw materials (e.g., inspection) Costs from product defects found before shipment to the customer (e.g., rework, scrap) Costs associated with defects found after shipment to customer (e.g., warranty) Costs associated with preventing defects and limiting failure and appraisal costs (e.g., training, improvement projects, data gathering, analysis)
Appraisal Costs Costs of Quality External Failure Costs Prevention Costs Internal FailureCosts Costs of Poor Quality • Rule-of-Thumb: $1 spent in prevention leads to $10 of saved internal, external, and appraisal costs.
Cost of Quality Defects found at Ownprocess Nextprocess End of theline Finalinspection End user’shand Cost tothecompany • Very minor • Minor delay • Some rework • Rework (mat’l, labor, capacity, etc) • Reschedule of work • Significant rework • Delivery delay • Inspection costs • Warranty cost • Loss of market share • Reputation Impact tothecompany
Quality Awards & Programs • Malcom Baldridge: Most extensive • Focus: customer satisfaction & quality • ISO 9000: Quality standards requiring companies to “say what they do and do what they say” • Focus: conformance to specs, customer requirements, continuous improvement, leadership • ISO 14000: Environmental standards requiring companies to keep track of their raw materials use, their generation, treatment, and disposal of hazardous materials. • Focus: performance improvement, labeling and life cycle assessment
SPC: Statistical Process Control Control Charts are tools for tracking variation based on the principles of probability and statistics
Variation • Exists in any process • error rate made by receptionist entering guest record data, • bus time between two points, • ounces of beverage in a bottle, • number of minutes past the alarm that you stay in bed in the morning.
Sources of Variation: 2 Types • Common (random) causes: chance or generally unidentifiable sources of variation. • Slight variation in walking speed • Slight variation in raw material • Controllable or Assignable causes: A reason why the change occurred • people blunder, faulty setup, or a batch of defective raw material,worn equipment, fluctuating temperature • Super huge peanuts arrived from supplier so we only got 8 in each bag.
Common Causes 425 Grams
Controllable Causes Average Grams (a) Location
Controllable Causes Average Grams (a) Location
Controllable Causes Average Grams (a) Location
Controllable Causes Average Grams (b) Spread
Controllable Causes Average Grams (b) Spread
Controllable Causes Average Grams (c) Shape
Mean -3 -2 -1 +1 +2 +3 68.26% 95.44% 99.74% The Normal Distribution = Standard deviation
How variation impacts our process: • Generally random variation cannot economically be eliminated from a process. • Controllable variation can be detected and elimination of its causes is economically justified. • Observations beyond the control limits are attributed to controllable variation.
Process Control Chart Activities • Periodically sample from our operation or process. • Calculate some characteristic like average, standard deviation, or range. • Plot the characteristic in time order on the chart.
Purpose of Charts • To ensure the process variation is in control • To ensure that the process is capable of meeting the requirements (specifications and tolerances of the organization)
Variable Control Charts (X bar & R) • Measurement charts: some characteristic we can measure (weight, time, distance) • X: average measurement for the sample • R: range of the measurements in the sample • Variable charts have lots of information, better for advanced analysis of a process
Control Limit Formulas & Constants (A2, D3, & D4) In Textbook chapter 9 pg. 190 Our sample size n= ?
Control Chart Examples UCL Nominal Variations LCL Sample number Appears to have normal variation
Attribute Chart: P-Charts • Number of defective units in a sample. Yes/No, Pass/Fail, Go/No Go criteria • p- easy to measure (pass/fail) but sample size must be big enough to detect at least one defective item on average • p=percentage faulty in sample • N= size of the sample
UCLp = p + 3p LCLp = p - 3p p = p(1 - p)/n Control Charts for Attributes P-Chart
“Six Sigma Quality” When a process operates with 6σ variation inside the tolerance limits, only 2 parts out of a million will be unacceptable.
Process Capability • Can the process provide acceptable quality consistently?
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.
Shown Graphically: Process Capability ratio of 1 (99.7% coverage)
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 ?
Process Capability Ratio (Cp) Upper Tolerance Limit – Lower Tolerance Limit 6σ (7000-6000)/(6*150)= 1.11 Capable?
Process Capability Index (Cpk) • Used when the process is not precisely centered • Assume process mean is actually m= 6300 • Cpk = min [(6300-6000)/(3*150), (7000-6300)/(3*150)]