International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING

Transcription

1 INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING RESEARCH AND DEVELOPMENT (IJIERD) ISSN (Print) ISSN (Online) Volume 4, Issue 3, September - December (2013), pp IAEME: Journal Impact Factor (2013): (Calculated by GISI) IJIERD I A E M E A DETAILED STUDY ON PROCESS FAILURE MODE AND EFFECT ANALYSIS OF PUNCHING PROCESS J. Arun 1, S. Pravin Kumar 2, M. Venkatesh 3, A.S. Giridharan 4 1 UG Graduate, Department of Mechanical Engineering, Government College of Technology, Coimbatore. 2 UG Graduate, Department of Mechanical Engineering, Government College of Technology, Coimbatore. 3 UG Graduate, Department of Mechanical Engineering, Government College of Technology, Coimbatore. 4 UG Graduate, Department of Mechanical Engineering, Government College of Technology, Coimbatore. ABSTRACT An FMEA (Failure Mode and Effect Analysis) is a systematic method of identifying and preventing product and process problems before they occur. FMEAs are focused on preventing defects, enhancing safety, and increasing customer satisfaction. Ideally, FMEAs are conducted in the product design or process development stages, although conducting an FMEA on existing products and processes can also yield substantial benefits. FMEA is used in the manufacturing industry to improve production quality and productivity by reducing potential reliability problems early in the development cycle where it is easier to take actions to overcome these issues, thereby enhancing reliability through design. It is a method that evaluates possible failures in the system, design, process or service. In this paper, Failure mode and Effect Analysis is done on the process of Punching. A series of ing operation is done on various work pieces and the defects are found. Based on the evidence found, the ratings are given and risk priority number is given. Based on the RPN, the preventive measures are given. The FMEA is a proactive approach in solving potential failure modes. These works serve as a failure prevention guide for those who perform the ing operation and works towards effective ing operation. KEYWORDS: Failure Modes, Punching, Risk Priority Number, FMEA Table, Chipping. 1

2 1. INTRODUCTION In today s market, the expectancy of the customer towards high quality, reliable and cost effective products is really high. So this expectancy proves a burden for the manufactures as they strive to satisfy the customers with defect free, reliable product. So the manufacturers switch to a newer technique which helps them to achieve the expected standards. The challenge is to design a quality and reliability product early in the development cycle. Such challenges are met with latest techniques and strategies implemented in both the design and product manufacturing. One such technique is Failure Mode and Effect Analysis (FMEA). Failure Mode and Effect Analysis (FMEA) is used to identify potential failure modes, determine their effect on the operation of the product, and identify actions to mitigate the failures [1-2]. 1.1 FAILURE MODE & EFFECT ANALYSIS FMEA is a tool originated by SAE reliability engineers. It continues to be associated by many with reliability engineering. It analyzes potential effects caused by system elements ceasing to behave as intended. The purpose of FMEA is to identify possible failure modes of the system, evaluate their influences on system behavior and propose proper countermeasures to suppress these effects. FMEA enhances further improvisation of both the design and manufacturing processes in the future as it serves as a record of the current process in formations [4-5]. FMEA is an engineering technique used to identify, prioritize and alleviate potential problems from the system, design, or process before the problems are actualized (According to Omdahl, 1988). What does the term Failure Modes imply? Lots of definitions for this term can be obtained. According to the Automotive Industry Action Group (AIAG), a failure mode is the way in which a product or process could fail to perform its desired function (AIAG, 1995). Some sources define failure mode as a description of an undesired cause-effect chain of events (MIL-STD-1629A, 1994). Others define failure mode as a link in the cause-effect chain [3] (Stamatis, 1995: Humphries, 1994). To conclude with we consider the term failure mode as any errors or defects in a process, design, or item, especially those that affect the customer, and can be potential or actual. The term Effect Analysis also invites various definitions. The effect analysis is the analysis of the outcome of the failure on the system, on the process and the service (Stamatis, 1995: Humphries, 1994) [2-5]. To put it simply Effects analysis refers to studying the consequences of those failures. FMEA is a tool that allows us to: Discover potential failures in a system, product or process Prioritize actions that decrease risk of failure Evaluate the system/design/processes from a new vantage point Guide design evaluation and improvement Troubleshoot and monitor the performance of systems 1.2 IMPORTANCE OF FMEA IN PUNCHING Punching process is a stamping or pressing type of metal removal process in which the product is formed by pressing the work between die [7]. The metal removal is by shearing force between the work and the die. Various components contribute to the accuracy, 2

3 reliability of the product. When these components are defective, this leads to the failure of the product. Some of the failures in the ing process are like Punch chipping, Slug jamming, Galling etc. [7]. These result in unfavorable consequences like failure of the system or production of inaccurate products. Hence it is essential to conduct a FMEA in this process so that the failure is avoided totally or reduced. Prior notification of these failures can prevent them by following control measures. 2. IMPLEMENTATION OF FMEA The purpose of performing an FMEA is to analyze the product's design characteristics relative to the planned manufacturing process and experiment design to ensure that the resultant product meets customer needs and expectations. When potential failure modes are identified, corrective action can be taken to eliminate them or to continually reduce a potential occurrence [3-4]. In FMEA, failures are prioritized according to how serious their consequences are, how frequently they occur and how easily they can be detected. Ideally, FMEA begins during the earliest conceptual stages of design and continues throughout the life of the product or service. Results can be used to identify high-vulnerability elements and to guide resource deployment for best benefit. An FMEA can be done any time in the system lifetime, from initial design onwards. The various steps in Process Failure and Effect Analysis are as follows Reviewing the process List the potential effects and modes of failure Assign a severity rating Assign an occurrence rating Assign a detection rating Calculate the risk priority number (RPN) for each mode of failure Take action to eliminate or reduce the high-risk failure modes Calculate the resulting RPN as the failure modes are reduced or eliminated [4]. 2.1 STEP 1: PROCESS REVIEW The blueprint (or engineering drawing) of the product and a detailed flowchart of the operation are reviewed. The process parameters of the conducted tests are as follows: Capacity : 60 Ton Maximum stroke : 6" Bed Area : 42" X 32" Speed : 40 Strokes per minute Floor to Bed : 33" Dimensions : 10'10" High, 8'6" RL, 6' FB Weight : 15,000 Lbs Tool used : Tungsten steel Work piece : Silicon steel Several trials are to be conducted with the above mentioned parameters. 3

4 Fig 1: High Speed Press Fig 2: Defective product from ing process Burr formation Fig 3: Burr formation in the ed product 2.2 STEP 2: POTENTIAL EFFECTS & FAILURE MODES Based on the trials conducted the failures are listed. In this, previously recorded failures are also added. The effects of these failure modes are also tabulated. These failure modes and their effects are charted separately for the sake of calculating and assigning the ratings and risk priority numbers. With the failure modes listed on the FMEA Worksheet, each failure mode is reviewed and the potential effects of the failure should it occur are identified. For some of the failure modes, there is only one effect, while for other modes there may be several effects. This step must be thorough because this information will feed into the assignment of risk rankings for each of the failures. It is helpful to think of this step as an ifthen process: If the failure occurs, then what are the consequences [4]. 2.3 STEP 3: ASSIGN SEVERITY RATING The severity ranking is an estimation of how serious the effects would be if a given failure did occur. In some cases it is clear, because of past experience, how serious the problem would be. In other cases, it is necessary to estimate the severity based on the 4

5 knowledge of the process. There could be other factors to consider (contributors to the overall severity of the event being analyzed) [4]. Calculating the severity levels provides for a classification ranking that encompasses safety, production continuity, scrap loss, etc. user. Each effect is given a severity number (S) from 1 (no danger) to 10 (critical). A failure mode with severity number of 10 results in severe dissatisfaction of the customer and may even result in the physical injury due to the failure. Severity ratings in the range of 4-6 result in mild dissatisfaction of the customer whereas those in the range of 1-3 are not so severe and may even be not detected [2-6]. Table 1gives the guidelines based on which severity ratings were given. Severity Rating Table 1: Severity Ratings Description Failure is of such minor nature that the customer (internal or external) will probably not detect the failure. Failure will result in slight customer annoyance and/or slight deterioration of part or system performance Failure will result in customer dissatisfaction and annoyance and/or deterioration of part or system performance. Failure will result in high degree of customer dissatisfaction and cause non-functionality of system Failure will result in major customer dissatisfaction and cause non-system operation or non-compliance with regulations 2.4 STEP 4: ASSIGN THE OCCURANCE RATINGS Occurrence ratings denote how often such failures occur. In this step it is necessary to look at the number of times a failure occurs. This can be done by looking at similar products or processes and the failure modes that have been documented [4]. A failure mode is given an occurrence ranking (O), again If a failure is inevitable or occurs often, then it is given a rating in the range of Those with mild occurrences are given 4-6 whereas those with low or eliminated failure have 1-3 occurrence ratings [2-6]. Table 2 gives the occurrence ratings based on which FMEA table is designed in this paper. Occurrence Rating Table 2 Occurrence Ratings Meaning 1 Failure eliminated or no know occurrence 2,3 Low or very few 4,5,6 Moderate or few occasional 7,8 High or repeated failure occurrence 9,10 Very high rate of failure or inevitable failures 5

6 2.5 STEP 5: ASSIGN DETECTION RATING This section provides a ranking based on an assessment of the probability that the failure mode will be detected given the controls that are in place. The proper inspection methods need to be chosen. The probability of detection is ranked in reverse order. For example, a "1" indicates a very high probability that a failure would be detected before reaching the customer; a "10" indicates a low zero probability that the failure will not be detected [2-6]. Table 3 shows the guidelines based on which the detection ratings of a product are given. Table 3: Detection Rating Detection Rating Description 1 Very certain that the failure will be detected 2-4 High probability that the defect will be detected 5-6 Moderate probability that the failure will be detected 7-8 Low probability that the failure will be detected 9 Very Low probability that the defect will be detected. 10 Fault will be passed to customer undetected 2.6 STEP 6: CALCULATE THE RISK PRIORITY NUMBER The risk priority number (RPN) is simply calculated by multiplying the severity ranking times the occurrence ranking times the detection ranking for each item. Risk Priority Number = Severity Occurrence Detection The total risk priority number should be calculated by adding all of the risk priority numbers. This number alone is meaningless because each FMEA has a different number of failure modes and effects. The small RPN is always better than the high RPN. The RPN can be computed for the entire process and/or for the design process only. Once it is calculated, it is easy to determine the areas of greatest concern. There could be less severe failures, but which occur more often and are less detectable. These actions can include specific inspection, testing or quality procedures, redesign (such as selection of new components), adding more redundancy and limiting environmental stresses or operating range. Once the actions have been implemented in the design/process, the new RPN should be checked, to confirm the improvements [1,2,6]. S. Problem No 1 Punch Chipping & Point Breakage Table 4: FMEA Table for Punching Process Effects Severity Occurrence Detection Rating Rating Rating Causes Solutions RPN Deformation High impact Change 336 or compressive s and failure diameter Leading to 5 6 Misalignment 210 downtime resulting in Check overall lateral forces die alignment Additional 3 3 Part Use a retainer 63 die damage movement or mounted stripper 6

7 5 1 Poor control 3 6 Excessive stripping force Review die, press, & feeder setup Reduce -to-die entry Increase -to-die button Consider coatings to add lubricity Punch point hardness too low 1 1 Improper selected 8 2 Sharpening damage Regrind burr Tight die Sharp corners on shaped es Flat face 3 4 Improper heat treatment 4 3 Improper stagger 7 2 Improper finish on point and/or face Verify hardness Change Use Coolant, correct speeds and feeds for grinding Remove regrind burr Increase Change Use Coatings and surface treatments Increase in the corners of die button Use shear angles and use edge breakers Triple tempered for high-speed and follow the guided speeds Cut-off operation & large point first to enter Ensure there are no harsh grinding Excessive burr Stress concentration at edges Incorrect Restore correct 98 7

8 Decreases resistance to fracture Shortens fatigue life 5 1 Worn tools 4 1 Misalign components Sharpen or replace tools Check alignment Slug Jamming Punch breakage Punch point deformation Tight die 6 1 Excessive land length Increase die Change relief from counter bore to taper Land length should not exceed four times thickness Taper in the land of the die button 6 2 Inadequate taper relief in die button 9 2 Worn die button 9 3 Worn or chipped 5 1 Rough land in die button Verify there is no reverse taper in the land of the die button Increase per side taper Sharpen, replace, and/or change die button Sharpen or replace Use die buttons with smooth wire cut, or ground land 3 2 Slug tipping Check lubrication consider lubricating both sides of part 7 1 Obstruction in slug relief hole Examine slug path Consider increasing the size of the relief hole in lower plate Slug Pulling Punch point deformation Excessive wear on and die Surface defects Bell mouth wear in die button Increase die Check alignment Change die button 54 8

9 Broken es and dies 8 2 Punch entry too deep 3 3 Punch entry not deep enough 9 1 Excessive die 3 2 Slug not held in the land 3 1 Sticky lubricants 3 4 Not enough relief on die Use slug control system Reduce entry Increase entry Reduce die Use slug control system Use vacuum slug sucker Blow air through center hole in Use negative taper in land Check lubrication Increase taper relief or use counter bore die Punch Wear and/or Galling Reduced die performance Reduced and die life Requires heat treatment of parts High stress concentration in parts Tight die 6 2 Punch entry too deep Increase die Change s Reduce entry 3 2 Misalignment Check die & press alignment 4 2 Regrind burr Remove regrind burr break sharp 6 1 Improper sharpening of 3 1 Improper 5 1 Sharp corners on shaped es 4 1 Punch surface too rough Use flood coolant, and correct grinding wheel speed & feed for steel type Change s Increase in the corners of the die button Consider finish improvements

10 5 2 Lack of lubrication on part and/or incorrect lubrication Check lubrication 70 6 Punch Head Breakage Increase in -to-die Punch breakage Excessive shear on es and die Deflection of head Punch pumping 6 3 Insufficient chamfer in retainer 4 7 Backing plate too hard 3 6 Head is too hard 5 4 High impact or high compressive load on head Verify head thickness is properly fit in the retainer counter-bore Chamfer retainer to clear head fillet on Draw back backing plate to reduce hardness RC Draw back head of to lower RC Increase head diameter and thickness Increase shank diameter Punch does not extract Increased delay Incorrect 3 2 Lack of lubrication 5 1 Tough s 6 1 Ineffectual extraction system Restore correct Use proper lubrication or coated es Revise Replace with a spring or reloaded assembly Work part deformation Imprecise components Incorrect 2 2 Lack of lubrication 6 1 Holes too close in sequence Restore correct Use proper lubrication or coated es Reprogram alternate ing sequence Wear Reduced tool life Speed too fast Slow down, use more coolant

11 Dimensional inaccuracies 3 7 Hard Use higher grade tool, add surface treatment 4 8 Improper feed rate (too slow) 4 5 Improper -die angle 4 5 Improper angle Increase feed rate Change to correct ing angle Give proper angle Reduced tool life High cost Too much shearing force during ing 5 6 Tough work 4 6 Frequent resharpening of tool Select proper tool s Select premium tool Resharpen the tool periodically RESULTS & DISCUSSIONS From the table 4, which shows FMEA table for ing process, it is observed that the chipping and point breakage due to the high impact or compressive force has the highest risk priority number. This can be minimized by the proper selection of -die s and by maintaining the correct between and die. The burr and slug formations also have detrimental effect on the overall quality of the final product. These undesirable developments can be curtailed by varying the feed rates and speed of the machine. To reduce the breakage of tool and burr formation due to excessive feed rate and high cutting speeds, we have to perform the process in rated speed and acceptable feed rates. In order to produce the ed products without any deformations or distortions, better tool and work holding devices are to be used. To reduce metal chipping, initial speed has to be minimum and proper cutting speeds should be employed. The tool life can be increased by proper lubrication, minimizing the wear and other parameter perfection has to be achieved. 4. CONCLUSION Thus the high speed ing process in motor manufacturing section has been analyzed and the expected failure modes have been noted. From the results of the critical analysis made on the ing process, the failure modes with greater risk priority number has been selected. The causes, effects and possible alternate solutions are given along with the ratings and priorities of action that decrease risk failure. The risk priority numbers are specified which indicates the necessity of care for producing defect-free ing process and its products. Thus this process analysis will serve as a helpful tool to detect the failure 11

12 modes occurring in the ing process and also assures in the effective functioning of the process. This study provides a documented method for selecting a design with a high probability of successful operation and safety. As a result of this approach, the system development cost and time, the possibility of occurrence of same kind of failure in future are reduced along with improved quality, reliability and safety of process/product. Consequently, the productivity of the product is also increased. This approach can be well suitably applied to consumer products like automotives, home appliances, etc., and other fields such as manufacturing, aerospace, instrumentation, medical, chemical processing, etc. REFERENCES 1. V Janarthanan, D Rajenthira Kumar. Root Cause analysis & process failure mode and effect analysis of TIG Welding on SS 3041 (Proceeding of NC MISAA 2013, copyright 2013 PSGCT) 2. Aravind.P, Rooban Babu.R, Arun Dhakshinamoorthy, Venkat Prabhu.N, Subramanian.SP An integrated approach for prediction of failures by process failure mode and effect analysis (PFMEA) in MIG Welding-a predictive analysis (ISBN ) 3. D.H.Stamatis. Failure mode and effect analysis : FMEA from theory to execution (Book 2 nd Edition (1995)) 4. Robin E. McDermott, Raymond J. Mikulak, Michael R. Beauregard. The basics of FMEA-Productivity press (1996) 5. Aravind.P, Subramanian.SP, SriVishnu.G, Vignesh.P. Process failure mode and effect analysis on TIG Welding process - a criticality study (ISSN ) 6. Failure modes and effects analysis (FMEA) - Copyright 2004 Institute for Healthcare Improvement. 7. Jim Szumera, James. A. Szumera. The Metal Stamping Process (Industrial Press Inc, 2003). 8. A.Mariajayaprakash, Dr.T. SenthilVelan and K.P.Vivekananthan, Optimisation of Shock Absorber Parameters using Failure Mode and Effect Analysis and Taguchi Method, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp , ISSN Print: , ISSN Online: Pravin Kumar.S, Venkatakrishnan.R and Vignesh Babu.S, Process Failure Mode and Effect Analysis on End Milling Process- A Critical Study, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 5, 2013, pp , ISSN Print: , ISSN Online: