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Quality control methods


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Quality control is a process that is used to ensure a certain level of quality in a product or service. It might include whatever actions a business deems necessary to provide for the control and verification of certain characteristics of a product or service. Most often, it involves thoroughly examining and testing the quality of products or the results of services. The basic goal of this process is to ensure that the products or services that are provided meet specific requirements and characteristics, such as being dependable, satisfactory, safe and fiscally sound.

Check sheet
Control chart
Ishikawa Diagram
Pareto Chart
Scatter diagram
Flow chart

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Quality control methods

  1. 1. Quality Control Methods Mohamed Sharique. V
  2. 2. What is Quality Control? Quality control is a process that is used to ensure a certain level of quality in a product or service. It might include whatever actions a business deems necessary to provide for the control and verification of certain characteristics of a product or service. Most often, it involves thoroughly examining and testing the quality of products or the results of services. The basic goal of this process is to ensure that the products or services that are provided meet specific requirements and characteristics, such as being dependable, satisfactory, safe and fiscally sound.
  3. 3. • Manufacturers of food products often have employees who test the finished products for taste and other qualities. • Clothing manufacturers have workers inspect garments to ensure that they are properly sewn. • Service-oriented companies often have representatives who observe the services being performed or who do follow-up checks to ensure that everything was done properly. Basic examples of Quality Control
  4. 4. When does Quality Control occur? 1. When raw materials are received prior to entering production. 2. Whilst products are going through the production process. 3. When products are finished - inspection or testing takes place before products are despatched to customers. 4. Evaluating people. (Applicable with service-oriented companies.)
  5. 5. 7 Basic Tools of Quality • Check sheet • Control chart • Histogram • Ishikawa Diagram • Pareto Chart • Scatter diagram • Flow chart
  7. 7. WHY THE NEW SET OF TOOLS • To structure the brainstorming process • Simplify • Remove fear • To help create a comfort fit (minimal dependence on statistics) • Improve penetration • Increase application
  8. 8. LIST OF TOOLS • Affinity Diagram • Interrelationship diagraph • Tree Diagram • Matrix Diagrams • Matrix Analysis • PDPC, process decision program charts • Arrow diagrams
  9. 9. AFFINITY DIAGRAM Definition An Affinity Diagram is a special type of brainstorming process that is used for organizing large groups of information into meaningful categories. It helps us to clarify and make sense of a large or complex problem
  10. 10. AFFINITY DIAGRAM Process • Record each idea on cards or notes • Look for ideas that seem to be related • Sort cards into groups until all cards have been used.
  11. 11. AFFINITY DIAGRAM Example How to implement a process of continual improvement throughout the organization? Which causes of waiting time in the hospital should we be working on?
  12. 12. AFFINITY DIAGRAM Example
  13. 13. AFFINITY DIAGRAM Example
  14. 14. INTER RELATIONSHIP DIAGRAPH Definition This tool displays all the interrelated cause-and-effect relationships and factors involved in a complex problem and describes desired outcomes. The process of creating an interrelationship diagraph helps a group analyze the natural links between different aspects of a complex situation. `
  15. 15. INTER RELATIONSHIP DIAGRAPH Process • Agree on the issue or question. • Add a symbol to the diagram for every element involved in the issue. • Compare each element to all others. Use an "influence" arrow to connect related elements. • The arrows should be drawn from the element that influences to the one influenced. • If two elements influence each other, the arrow should be drawn to reflect the stronger influence. • Count the arrows. • The elements with the most outgoing arrows will be root causes or drivers. • The ones with the most incoming arrows will be key outcomes or results. `
  16. 16. INTER RELATIONSHIP DIAGRAPH Example The quality issue is the potential causes or factors contributing to late deliveries.
  18. 18. INTER RELATIONSHIP DIAGRAPH Example The inference is that Potential causes for late delivery are: • ‘Poor scheduling practices’ (6 outgoing arrows), • ‘Late order from customer’ (5 outgoing arrows), and • ‘Equipment breakdown (3 outgoing arrows).
  19. 19. TREE DIAGRAM Definition This tool is used to break down broad categories into finer and finer levels of detail. It can map levels of details of tasks that are required to accomplish a goal or task. It can be used to break down broad general subjects into finer and finer levels of detail. Developing the tree diagram helps one move their thinking from generalities to specifics.
  20. 20. TREE DIAGRAM Process • Develop a statement of the goal • Ask a question that will lead you to the next level of detail. • Brainstorm all possible answers. Write each idea in a line below. Show links between the tiers with arrows. • Do a “necessary and sufficient” check. Are all the items at this level necessary for the one on the level above? • Each of the new idea statements now becomes the subject: a goal, objective or problem statement. • Continue to turn each new idea into a subject statement and ask the question, till you reach a root cause • Do a “necessary and sufficient” check of the entire diagram. Are all the items necessary for the objective?
  21. 21. TREE DIAGRAM Example The Pearl River, NY School District, a 2001 recipient of the Malcolm Baldrige National Quality Award, uses a tree diagram to communicate how district- wide goals are translated into sub-goals and individual projects. They call this connected approach “The Golden Thread.” The district has three fundamental goals. The first, to improve academic performance, is partly shown in the figure below. District leaders have identified two strategic objectives that, when accomplished, will lead to improved academic performance: academic achievement and college admissions.
  22. 22. TREE DIAGRAM Example
  23. 23. MATRIX DIAGRAM Definition This tool shows the relationship between items. At each intersection a relationship is either absent or present. It then gives information about the relationship, such as its strength, the roles played by various individuals or measurements. Six differently shaped matrices are possible: L, T, Y, X, C, R and roof-shaped, depending on how many groups must be compared.
  24. 24. MATRIX DIAGRAM Example A personnel department wanted to improve social activity within the company in order to increase loyalty levels. A theory was put forwards that soft-skills training contributed significantly towards this in-house socializing. The personnel manager consequently decided to use a Matrix Diagram to investigate this. The steps taken were: Objective: Investigate effect of soft-skills training on social activity. Matrix: T-matrix, with people on main stem, in-house training courses to left, attendance of social clubs to right, plus an extra column for years of service. Comparison: In-house training - tick for attendance within last three years; social clubs - three bands corresponding to under 30%, 30% to 70% and over 70% attendance in the same period.
  25. 25. MATRIX DIAGRAM Example
  26. 26. MATRIX DIAGRAM Example The resultant matrix, showed that people with higher levels of social training also tended to be more committed members of social clubs. It was also noticed that there seemed to be a particular increase in commitment after going on the team-building course. The length of service showed no particular pattern. As a result, the training was expanded, and people were given more encouragement to attend (particularly the team-building course). This resulted in a steady increase in social activity and a reduction in attrition rates.
  27. 27. PRIORITISATION MATRIX Definition This tool is used to prioritize items and describe them in terms of weighted criteria. It uses a combination of tree and matrix diagramming techniques to do a pair-wise evaluation of items and to narrow down options to the most desired or most effective.
  28. 28. PRIORITISATION MATRIX Example Problem To identify the most important factors effecting motivation in a team
  30. 30. PRIORITISATION MATRIX Example Pay and work overload, as the highest scoring motivational problems, were selected for carrying forward for further investigation. As a result of consequent work in the project, the pay structure for certain grades was revised and training on job scheduling was introduced. In the following year, the survey improved in these areas by 2 and 3 points, respectively.
  31. 31. PDPC Definition A useful way of planning is to break down tasks into a hierarchy, using a Tree Diagram. The PDPC extends the tree diagram a couple of levels to identify risks and countermeasures for the bottom level tasks. Different shaped boxes are used to highlight risks and identify possible countermeasures (often shown as 'clouds' to indicate their uncertain nature). The PDPC is similar to the Failure Modes and Effects Analysis (FMEA) in that both identify risks, consequences of failure, and contingency actions; the FMEA also rates relative risk levels for each potential failure point.
  32. 32. PDPC Process From the bottom level of some activity box, the PDPC adds levels for: •identifying what can go wrong (failure mode or risks) •consequences of that failure (effect or consequence) •possible countermeasures (risk mitigation action plan)
  33. 33. PDPC Example A dress production team at a clothes manufacturer was improving the cutting-out process in order to minimize material wastage. They decided to use PDPC on the work breakdown structure to identify potential problems and ways of avoiding them. As the most expensive element is the material itself, they defined a significant risk as, 'Anything that might cause the cut cloth to be ruined', and viable countermeasures as, 'Anything that will reduce the risk, and which costs less than 100 pieces of cloth' .
  34. 34. PDPC Example
  35. 35. PDPC Example As a result of this, the cutting was tested on cheaper material, resulting in the material clamp being redesigned to prevent drag, a start notch provided for the cutter and the general area being inspected for sharp corners to minimize snag problems. The cutting operator was involved in the PDPC process and the subsequent tests, resulting in her fully understanding the process. The final cutting process thereafter ran very smoothly with very little error.
  36. 36. ACTIVITY NETWORK DIAGRAM Definition This tool is used to plan the appropriate sequence or schedule for a set of tasks and related subtasks. It is used when subtasks must occur in parallel. The diagram enables one to determine the critical path (longest sequence of tasks). Two Types •Arrow on Node •Arrow on Arrow
  37. 37. ACTIVITY NETWORK DIAGRAM Process Drawing the Network List all the necessary tasks in the project or process. One convenient method is to write each task on the top half of a card or sticky note. Across the middle of the card, draw a horizontal arrow pointing right. Determine the correct sequence of the tasks. Do this by asking three questions for each task: Which tasks must happen before this one can begin? Which tasks can be done at the same time as this one? Which tasks should happen immediately after this one? It can be useful to create a table with four columns —prior tasks, this task, simultaneous tasks, following tasks.
  38. 38. ACTIVITY NETWORK DIAGRAM Process First do a forward pass to note down the duration and the Earliest finish and start times Then a backward pass is done to fill in the Latest finish, start and total float times
  39. 39. ACTIVITY NETWORK DIAGRAM Example ActivityActivity Time (days)Time (days) ImmediateImmediate PredecessorsPredecessors AA 22 -- BB 77 -- CC 44 AA DD 33 AA EE 22 B,CB,C FF 33 D,ED,E
  40. 40. ACTIVITY NETWORK DIAGRAM Process float time and critical path 0 2 2 1 1 3 A 0 7 7 0 0 7 B 2 4 6 3 1 7 C 2 3 5 6 4 9 D 7 2 9 7 0 9 E 9 3 12 9 0 12 F
  41. 41. Some problems concerning Quality Control: • The inspection process does not add any "value". If there were any guarantees that no defective output would be produced, then there would be no need for an inspection process in the first place. • Inspection is costly, in terms of both tangible and intangible costs. For example, materials, labour, time, employee morale, customer goodwill, lost sales. • It is sometimes done too late in the production process. This often results in defective or non-acceptable goods actually being received by the customer
  42. 42. • It is usually done by the wrong people - e.g. by a separate "quality control inspection team" rather than by the workers themselves • Inspection is often not compatible with more modern production techniques (e.g. "Just in Time Manufacturing") which do not allow time for much (if any) inspection. • There is often disagreement as to what constitutes a "quality product". For example, to meet quotas, inspectors may approve goods that don't meet 100% conformance, giving the message to workers that it doesn't matter if their work is a bit sloppy. Or one quality control inspector may follow different procedures from another, or use different measurements.
  43. 43. Difference between Quality Control & Quality Assurance • Though the two are similar, but there are some basic differences. Quality control is concerned with examining the product or service — the end result - and quality assurance is concerned with examining the process that leads to the end result. • A company would use quality assurance to ensure that a product is manufactured in the right way, thereby reducing or eliminating potential problems with the quality of the final product.
  44. 44. "Inspection with the aim of finding the bad ones and throwing them out is too late, ineffective, costly. Quality comes not from inspection but from improvement of the process." - W. Edwards Deming “Any tool is a weapon if you hold it right” - Ani DiFranco
  45. 45. Thank you