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Design for Six Sigma Optimal, Confidential 1 Error Proofing Francis Xu May 10, 02 Acknowledgment: Special thanks for the majority of the training material from HS Yam of Seagate Design for Six Sigma Optimal, Confidential 2 Agenda 1. Presentation on Error-proofing 2. Brainstorming a. Error-proofing Optimal (AMAP) b. More Error-proofing? c. Timeline update Design for Six Sigma Optimal, Confidential 3 What is Error-Proofing? Why need Error-Proofing? Errors Analysis 10 different kinds of Errors 10 causes of Errors 3 types of Inspection for Errors How to do Error-Proofing? Summary Examples Contents Design for Six Sigma Optimal, Confidential 4 Error proofing is a process improvement system targeted at prevention of personal injury promotion of job safety prevention of faulty products or service prevention of machine damage What is Error Proofing? Design for Six Sigma Optimal, Confidential 5 Also denoted as Fool proofing, Poka-Yoke, mistake- proofing, etc. * Error proofing the design and the production process *Strives for zero defects *Leads to Quality Inspection Elimination *Respects the intelligence of workers *Minimizes tasks that rely on memory What is Error Proofing? Design for Six Sigma Optimal, Confidential 6 On Error Resume Next Defer error handling. Error 11 Simulate the “Division by zero“ error. This example uses the Error statement to simulate error number 11. An VBA example Design for Six Sigma Optimal, Confidential 7 Elevator Speech Disaster I didnt mean to press the alarm! Alarm 1 2 3 4 5 6 Design for Six Sigma Optimal, Confidential 8 Quality and Stability is essential in a lean manufacturing environment Human error is a natural occurrence; all humans make errors Machines are not defect-free Why do Error Proofing? Design for Six Sigma Optimal, Confidential 9 Enforces operational procedures or sequences, thus insuring quality Signals or stops a process if an error occurs or a defect is created Eliminates choices leading to incorrect actions Prevents product damage Prevents machine damage Prevents personal injury Eliminate inadvertent mistakes which increase work load What are the Benefits? Design for Six Sigma Optimal, Confidential 10 Process Flow ERROR To Next Process An error is any deviation from an intended process. Occurs when any condition necessary for successful processing is improper or absent All defects are created by errors Not all errors result in defects POSSIBLE DEFECT Definition of an Error Design for Six Sigma Optimal, Confidential 11 Almost all defects are caused by human errors. However, there are at least ten kinds of human errors. 1. Forgetfulness: Sometimes we forget things when we are not concentrating. For example, the stationmaster forgets to lower the crossing gate. Safeguards: Alerting operator in advance or checking at regular intervals. 2. Errors due to misunderstanding: Sometimes we make mistakes when we jump to the wrong conclusion before were familiar with the situation. For example, a person not used to a car with automatic transmission steps on the brake, thinking it is the clutch. Safeguards: Training, checking in advance, standardizing work procedures. 3. Errors in identification: Sometimes we misjudge a situation because we view it too quickly or are too far away to see it clearly. For example, a $1 bill is mistaken for a $10 bill. Safeguards: Training, attentiveness, vigilance. The Different Kinds of Errors Design for Six Sigma Optimal, Confidential 12 4. Errors made by amateurs: Sometimes we make mistakes through lack of experience. For example, a new worker does not know the operation or is just barely familiar with it. Safeguards: Skill building, work standardization. 5. Willful errors: Sometimes errors occur when we decide that we can ignore rules under certain circumstances. For example, crossing a street against a red light because there are no cars in sight at the moment. Safeguards: Basic education and experience. 6. Inadvertent errors: Sometimes we are absentminded and make mistakes without knowing how they happened. For example, someone lost in thought tries to cross the street without even noticing that the light is red. Safeguards: Attentiveness, discipline, work standardization. 7. Errors due to slowness: Sometimes we make mistakes when our actions are slowed down by delays in judgement. For example, a person learning to drive is slow to step on the brake. Safeguards: Skill building, work standardization. The Different Kinds of Errors (cont.) Design for Six Sigma Optimal, Confidential 13 8. Errors due to lack of standards: Some errors occur when there are no suitable instructions or work standards. For example, a measurement may be left to an individual workers discretion. Safeguards: Work standardization, work instructions. 9. Surprise errors: Errors sometimes occur when equipment runs differently than expected. For example, a machine might malfunction without warning. Safeguards: Total productive maintenance, work standardization. 10. Intentional errors: Some people make mistakes deliberately. Crimes and sabotage are examples. Safeguards: Fundamental education, discipline. Mistakes happen for many reasons, but almost all can be prevented if we take the time to identify when and why they happen and then take steps to prevent them by using poka-yoke methods and the safeguards listed above. The Different Kinds of Errors (cont.) Design for Six Sigma Optimal, Confidential 14 There are ten common causes of errors which Error Proofing is designed correct or eliminate. 1. Processing omissions: Leaving out one or more process steps. 2. Processing errors: Process operation not performed according to the standard work procedures. 3. Error in setting up the workpiece: Using the wrong tooling or machine settings for the current product. 4. Missing parts: Not all parts included in the assembly, welding, or other processes. 5. Improper part/item: Wrong part installed in assembly. 6. Processing wrong workpiece: Wrong part machined. Error Proofing: Ten Causes of Errors Design for Six Sigma Optimal, Confidential 15 7. Operations errors: Carrying out an operation incorrectly; having the incorrect revision of a standard process or specification sheet. 8. Adjustment, measurement, dimension errors: Errors in machine adjustments, testing measurements or dimensions of a part coming in from a supplier. 9. Errors in equipment maintenance or repair: Defects caused by incorrect repairs or component replacement. 10. Error in preparation of tooling: Damaged blades, poorly designed jigs, or wrong tools. Error Proofing: Ten Causes of Errors Design for Six Sigma Optimal, Confidential 16 Shigeo Shingo identified three different types of inspection: judgment inspection informative inspection source inspection Purpose of inspection is to improve the process and prevent defects, not intended to sort out the defects Types of inspection for Error Shigeo Shingo was one of the industrial engineers at Toyota who has been credited with creating and formalizing Zero Quality Control (ZQC), an approach to quality management that relies heavily on the use of poka-yoke devices Design for Six Sigma Optimal, Confidential 17 judgment inspection involves sorting the defects out of the acceptable product inspecting in quality not an effective quality management approach Types of inspection for Error-1 Design for Six Sigma Optimal, Confidential 18 informative inspection uses data gained from inspection to control the process and prevent defects traditional SPC is a good example successive checks / self-checks in ZQC self-checks are preferred to successive checks whenever possible Both checks provide information after the fact Types of inspection for Error-2 Design for Six Sigma Optimal, Confidential 19 source inspection determines before the fact whether the conditions necessary for high quality production exist. Poka-yoke devices ensure that proper operating conditions exist prior to actual production. Types of inspection for Error-3 Design for Six Sigma Optimal, Confidential 20 Red Flag Conditions Types of Error-Proofing devices Six Steps to Error-Proofing How to do Error-Proofing? Design for Six Sigma Optimal, Confidential 21 A condition in a process which might provoke an error Red Flag Conditions Design for Six Sigma Optimal, Confidential 22 Each of the common Red Flag conditions may lead to production errors. 1. Adjustments 2. Tooling and tooling changes Red Flag: Workers having to make adjustments to parts or equipment to complete a process step. 3. Dimensions/ specifications/ critical conditions The use of perishable tools in production and/or tools that are changed between production runs. Operations which require the use of measurements to position a part in operations, or situations which require operations to be performed within designated critical conditions. (e.g, temperature, pressure, speed, etc.) Red Flag Conditions Design for Six Sigma Optimal, Confidential 23 4. Many / mixed parts A process which involves a wide range of parts in varying quantities and mix. 5. Multiple steps A process that requires many small operations or sub-steps to de done in a strict preset order. 6. Infrequent production An operation or task which is not performed regularly. 7. Lack of an effective standard Standard operating procedures (SOPs) that are vague or do not fully describe the correct and proven way to perform a production process. Red Flag Conditions Design for Six Sigma Optimal, Confidential 24 8. Symmetry Machining or assembly operations which use an object whose opposite sides are similar or identical. 9. Asymmetry Operations which use a part, tool or fixture whose opposite sides may look identical but are different in size, shape or relative position. 10. Rapid Repetition A process which requires quickly performing the same operation over and over again. Red Flag Conditions Design for Six Sigma Optimal, Confidential 25 11. High/Extremely High Volume A process which requires quickly and repeatedly performing a task with time pressure. 12. Environmental Conditions Physical circumstances within and around the workplace that can influence quality and workmanship. Red Flag Conditions Design for Six Sigma Optimal, Confidential 26 Guide / reference / interference rod or pin Template Limit switch / microswitch Counter Odd-part-out method Sequence restriction Standardize and solve Critical condition indicator Detect delivery chute Stopper / gate Sensor Mistake-proof your Error Proof device Eliminate the condition Redesign for symmetry Redesign for asymmetry Automated lock outs The following is a list of Error Proofing devices which can be used to respond to Red Flag conditions. These devices are described in more detail in Appendix A. Types of Error Proofing Devices Design for Six Sigma Optimal, Confidential 27 Step 1: Identify and describe Identify and describe the defect / red flag condition in detail. In the case of a defect, examine the history of the defect. In order to establish accountability, a team member should be identified to follow up on the defect/red flag. Step 2: Determine the root cause Conduct cause and effect diagramming to assess the root cause. This determination is critical for applying error proofing techniques to eliminate the defect/ red flag. Step 3: Review the current standard procedure. Document each element / step in the operation where the defect occurs. Error proofing opportunities will be based upon this careful procedure identification. These steps provide a framework for implementing Error Proofing in the factory. These steps should be implemented: Reactively, in response to the observation of defects Proactively, after identifying Red Flag conditions which exist in a process. Six Steps to Error Proofing Design for Six Sigma Optimal, Confidential 28 Step 4: Identify deviations from standards. Observe the actual process and identify areas where the methods being applied deviate from the standard operating procedure. These deviations will point to areas where procedural improvements are needed. Step 6: Create device(s) and test for effectiveness Create and test the device for effectiveness. Modifications are made until the device proves effective in preventing the defect. Step 5: Identify the type of error-proofing device type required. Identify the type of error-proofing device most likely to effectively eliminate the defect. Remember to error-proof your error-proof devices Six Steps to Error Proofing Design for Six Sigma Optimal, Confidential 29 Summary Mistakes happen for many reasons, but almost all can be prevented if we take the time to identify when and why they happen, and take steps to prevent them Poka-yoke methods are powerful tools for error- proofing, or can inexpensively inspect each item that is produced to determine whether it is acceptable or defective. Design for Six Sigma Optimal, Confidential 30 Appendix Examples Types of Error Proofing Design for Six Sigma Optimal, Confidential 31 small plate pins jig large plate small plate medium plate Guide / reference/ interference rod or pin Example : Mis-aligning plates in setup was causing defects. Locator pins built into the jig correspond to double holes drilled in the center of every plate so that all sizes of plates are automatically positioned correctly by merely setting them on the jig. Processing errors due to misalignment in setup are eliminated. A guide or reference rod is a solid piece of material like a stem or peg that positions or orients a part, tool or fixture and guarantees its correct placement. An interference pin refers to a peg that blocks, obstructs, or prevents the incorrect positioning of a part, tool or fixture. This pin or “boss”, as it is sometimes called, can be fixed onto the part itself, or on a tool or fixture. reference holes in plate jig pins Types of Error Proofing Design for Six Sigma Optimal, Confidential 32 Templates Ensures that work-pieces are machined to the desired profile with consistency. Profiler Cutting Wheel offset is fixed Template Work-Piece Types of Error Proofing Design for Six Sigma Optimal, Confidential 33 button button positioning jig sleeve position for 1st button needle button positioning jig position for 2nd button position for 3rd button Template A template is a pattern used to represent an accurate copy of an object used to guarantee accurate positioning. Templates are frequently used in inspection procedures and are often made of thin metal, plastic, or paper. An existing jig or fixture may be modified to serve as a template. Example: Buttons were not being sown in the correct position and spacing. A positioning jig was developed for sewing buttons which positions buttons by putting the cuff end against the jig mounted on the sewing machine. This positions the cuff accurately for the required number of buttons and they come out neatly in a row and evenly spaced. Types of Error Proofing Design for Six Sigma Optimal, Confidential 34 buzzer limit switch 1 limit switch 2 switch 1 confirms beginning of drilling switch 2 confirms penetration Limit switch / microswitch Example: Holes were not being drilled to the appropriate depth. Two limit switches were mounted on the drill press. Faulty drilling is indicated if limit switch 1 is released before limit switch 2 has been tripped (indicating the start of drilling without penetration). A buzzer is sounded to alert the operator. A limit switch or microswitch is an electrical device or instrument that, with a light contact on its antenna section, can confirm the presence, position, dimension, breakage or degree of use (wear) of a part, tool, or fixture. They are also called proximity switches, photoelectric switches, and touch switches. Types of Error Proofing Design for Six Sigma Optimal, Confidential 35 Example: In a process where parts are manufactured for several different models, ten holes are tapped on each work piece, using a single-spindle drill press. Before Improvement: The operator had to visually check and count the number of holes they had tapped. This method of control relied strictly on the workers vigilance and tapping was omitted now and then. After Improvement: A counter was added to the tapping machine. The operator clears the counter for each work piece and checks that the number of taps is correct for the current model. Although this amounts only to a method method for assisting the vigilance of the operator, it almost completely eliminates omissions of tapping. Counter A counter is an indicator that keeps track of a number - the number of parts, turns, strokes, output, or abnormalities of a given machine or operation. counter clear button Breakthrough Types of Error Proofing Design for Six Sigma Optimal, Confidential 36 part 1 part 2 part 3 The worker is given exactly the right number of parts for the number of products to be made Odd-part-out method The odd-part-out method is a form of counting that does not rely on a counting device. Instead, it isolates the pre-counted correct number of parts visually, and the visual display tells us if all the parts are not used. Example : The parts needed for a given run of products are counted out in advance and given to the worker. If some parts remain after the planned number of products have been assembled or if there are not enough parts, it is immediately clear that there is an abnormality. This method of checking prevents units with missing parts from being sent out into the market. Types of Error Proofing Design for Six Sigma Optimal, Confidential 37 Sequence Restriction A sequence restriction is useful when order is so important that any change or omission in the order can result in costly errors. Look for concrete ways to restrict the sequence so it can only follow the pre-set order. Sequ