Reduction of Hub Diameter Variation In High Pressure Pump Cylinder Head by using Shainin Problem Solving Technique

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1 Reduction of Hub Diameter Variation In High Pressure Pump Cylinder Head by using Shainin Problem Solving Technique Shashikumar S PG scholar, Department of industrial & production engineering, The national institute of engineering Mysore shashikumarsolur@gmail.com M S Sham Prasad Associate professor, Department of industrial & production engineering, The national institute of engineering, Mysore shamprasad_nie@yahoo.co.in Raghuveer Prasad Deputy manager, QMM4, Bosch limited. Adugodi Bengaluru Abstract: in this study, the control parameters for grinding process are improved for reduction in diameter variation while keeping up quality standards in a cp1h high pressure pump s cylinder head hub diameter manufacturing company. The shainin problem solving technique which is a powerful tool to design optimization for quality is used to find the optimal control parameters. The present paper deals with one of the quality issues resolved by using shainin methodology in diesel systems plant, bosch ltd., bengaluru. Keywords: shainin technique, factual, multivari, diameter variation, dressing, ofat, ***** I. INTRODUCTION: II. APPROACH AND EXPERIMENTATIONS Parts that require fine surface finishes and extremely close tolerance are candidates for precision grinding; precision grinding is becoming increasingly important for automotive industries. High pressure pumps have to produce bar pressure by eliminating all losses, this can to achieve by its components which are used. Cylinder head is the one of the important part in the high pressure pump, it s hub diameter play a very important role, if diameter is higher cannot do assemble, if less then fuel spillage will happen and it s diameter tolerance is 33µm. Hub diameter is grind by using CNC machine. The CNC grinding machine is unstable process. In Bosch company, bahmuller CNC grinding machine module1 have diameter variation, it can t predictable nature, for this reason operator can t maintain diameter within specification, by this critical condition 3% of parts rejection found. The FACTUAL (Focus Approach Converge Ttest Understand-Apply-Leverage) approach has been followed here to solve the underlying problem of reducing process variation and improving the process yield. This paper explores how a manufacturing process can use a systematic methodology to move towards world-class quality level. The application of the shainin problem solving technique methodology resulted in reduction of variation of hub diameter in the grinding process from 3% to 0%. The factual methodology has had a significant financial impact on the profitability of the company in terms of reduction in scrap cost, man-hour saving on rework and increased output. A saving of approximately 3lakhs per annum was reported from this project. Pareto diagram, isoplot, box plot, strategy diagram, shainin doe techniques are used to find out the root cause. This project carried out in Bosch ltd. Adugodi Bengaluru. The problem solving methodology follows the discipline of Focus- Approach- Converge- Test- Understand- Apply- Leverage, which has been discussed in detail in the following sections. 1.1 FOCUS Since the focus of project in the business point of perspective will be about 3% section created will be dismisses because of hub diameter less(<21.747mm) and hub diameter more (>21.78mm),it has revamp amid last examination. Fig2.1. Pareto diagram of part rejection The important defects that occur during the production of cylinder head are patch on hub diameter, patch on internal diameter, patch on face, internal diameter, taper, hub diameter low and hub diameter high.etc when the percentage defects for various defects in the year 2014 were drawn, hub diameter high and low were found to be of major concern and were contributing 80% of the defects. Pareto analysis shows that hub diameter variation which constitutes 20% of the type of defects is the cause for the 80% the total defectives. Pareto law suggests that these two 43

2 defects should be concentrated upon. This technique saves resources like money, time, etc. If we divert our attention to trivial matter then our resources get wasted. If we concentrate on Pareto causes then the rejection can be brought down by more than half, which is actually the aim of the project then there will be a considerable decrease in the overall rejection. Fig. 2.3: GREENY categorization as feature 1.3 CONVERGE Fig. 2.2: illustration of problem definition tree. The representation of issue identification and definition are indicated in fig. 2.2.rolling top 5 issues, dismissal found because of quality problem.cp1h pump it goes under the common rail pump segment, cylinder head rejected part because of hub diameter variety. Two sorts of cylinder head are assembling, F01M part higher creation. converging towards the RED X causing the GREENY has been achieved by strategy diagram technique. The solution tree for the GREEN Y to determine the RED X is illustrated in fig FEATURE (RADIUS) STRATEGY DIAGRAM DESIGN FAMILY 1.2 APPROACH The effective utilization of the statistical tool and quickness of the root cause identification relays on the selection of samples with two extreme characteristics, that is WOW (worst of worst) and BOB (best of best). The type of problem that is being tackled is apparently limited to variation problems. Out of four GREEN Y types the present problem was identified as defect. The defect could have occurred during the process stage which could be easily identifiable and has a probability distribution which does not meet the demands. The hub diameter variations are detected only after inspection. At review the cp1h cylinder head are examined for their hub diameter, face flatness and different other characteristics. The characterized GREENY is a "feature" as demonstrated in fig Under "feature" come length, radius, true position and thickness. This variety of problems could be efficiently handled primarily by doing validation of measurement system through variable data and use of ISOPLOT followed by process flow diagram, strategy diagram, multivari. Fig Feature (radius) strategy diagram design family 44

3 Density International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE) ISSN: FEATURE (RADIUS) STRATEGY DIAGRAM PROCESS FAMILY Thumb rule for eliminating gauge variation as main contribution in the total process variation. p/ m 6 called as discrimination ratio, since discrimination ratio 6, so existing gauge variation won t be an issue to find out the major cause for variation FREQUENCY DIAGRAM Histogram of NO Interruption, Interruption Normal Variable NO Interruption Interruption Mean StDev N variation Fig Frequency distributed diagram Fig Feature (radius) strategy diagram process family Worst of worst (WOW) and best of best (BOB) are selected two extreme position in the specifications of the part. In the design family comparison of WOW and BOB are illustrated in the fig Feature (radius) strategy diagram design family. Radius to radius same arc have small contrast maximum 4µm variation in wow part. Arc to arc in a same circle have low contrast, maximum 8µm variation in wow part at arc compared to circle to circle in a same cylinder small contrast and it is less than 2 µm. Considering process family feature strategy diagram in the fig , cylinder to cylinder in a same grinding cycle have small contrast, variation within grinding cycle maximum variation is 15µm this high contrast because of occasions and machine stoppages. Grinding cycle to grinding cycle in a same batch have higher contrast, variation of parts just before and after dressing maximum variation found 25µm. Batch to batch in a same module have less contrast, variation is around 10µm. Interruption in the machining process can cause unstable condition in the machine these can be validated through frequency distributed diagram, y axis indicate the frequency and x axis indicates the difference between after dressing 1 st part hub diameter and before dressing last part hub diameter. Variation in grinding cycle without interruption is higher than interruption grinding cycle, interruption grinding cycle was treated as PINK X problem solution tree ISO PLOT Fig ISOPLOT P is a process and M is the measurement system, by utilizing ISOPLOT we can validate no issues with measurement system. By strategy diagram approve issue with grinding cycle to grinding cycle. No interruptions produce higher variation, so interruption can regard as PINKX. At long lost left two REDX, one is grit of grinding 45

4 Density International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE) ISSN: wheel behavior by effect of dressing cycle and axis scale malfunction of the grinding wheel OFAT Histogram of Initial, Feed change, Depth of cut cha, set back to inti Normal Variable Initial Feed change Depth of cut change set back to intial Mean StDev N average of 5 at before dressing (that is 26 to 30) in the same grinding cycle, and it clearly shows the 50% of variation in the process, existing condition process having higher variation then the better, that is the dressing depth of cut 0.030mm is better. Better Test for Equal Variances: Better, Current F Test P-Value Current Hub Diameter Fig frequency disribution plot % Bonferroni Confidence Intervals for StDevs Fig test for variances The part of cp1h high pressure pump cylinder head import to plant having hub diameter of to mm. Initially checked relation between before grinding and after grinding process, around mm to mm stack will removes in the grinding but it shown zero contribution of regression, it indicates that machine grinding process takes place as per program feed in the control system. We observed most of the hub diameter at the final inspection time, standard variation was found around to In this machine after every 30 parts dressing will takes places. Each time of grinding changes the hub diameter pattern in the graph, so we mainly concentrated dressing operation. We changed existing feed during dressing from 500mm/min to 250 mm/min, after measured output of grinding process, we got standard deviation And our next observation with changed dressing depth of cut from existing mm to 0.030mm we observed standard deviation After our experiments settings has set back to the initial condition that trail we observed standard deviation was TEST Boxplot of Better, Current The hub diameter variation is minimized by change setting in the dressing cycle depth of cut (better) then the existing grinding process (current) validated by using anova. Considering, null hypothesis h 0 is equal to all variances are equal and alternative hypothesis h 1 is equal to at least one variance is different with significance level α = Method F test. We obtained p valve lesser than 0.05 that is Threfore null hypothesis h 0 is rejected and alternative hypothesis h 1 is accepted. And the better process has implemented. 2.5 UNDERSTAND Dressing is the process of sharpening the abrasive elements in the wheel. The process breaks down the bond and removes dull abrasive grain to expose new and sharp abrasive particles. Without proper dressing, it s impossible to achieve the best consistency and adherence to specs from even the highest quality abrasive wheel. 2.6 APPLY A simple program change to the bahmuller CNC grinding machine, depth of cut has 0.030mm instead of mm during dressing cycle. Better 2.7 LEVERAGE There were one more lines manufacturing this product. control plan was implemented all production lines. Actual savings were 3lakh annually. Current variartion Fig box plot The box plot has drawn considering difference of average of five at after dressing (that is part 1 to 5) and 46

5 application of shainin doe techniques,vikalpa,vol. 34/01, jan-mar 2009, [6] Application of six sigma methodology to reduce defects of a grinding process by E. V. Gijo, johny scaria and jiju antony. (wileyonlinelibrary.com) doi: /qre.1212 III. CONCLUSION Shainin provides a set of problem solving tools to determine the root cause of a technical problem in manufacturing, successively eliminate potential causes by play the dictionary game, try to avoid many measurements and sophisticated statics. In this case study, grinding machine has very sensitive, small act can give big result. Improper dressing as redx, depth of cut during dressing cycle change has reduced the variation in the grinding cycle, part diameter tolerance is in micron level so OFAT doe principle used and finally we get effective reduction of hub diameter variation in the process. It can be reduced rejection rate and as well as rework and save money 3 lakh in annual. REFERENCE [1] Bosch automotive handbook, 5 th edition, robert bosch gmbh, sae international, 2000 [2] Quality improvement during camshaft keyway tightening using shainin approach by nagaraja reddy k m, dr. Y s varadarajan. International journal of scientific and research publications, volume 4, issue 7, july 2014 issn [3] 3. Quality improvement of pumping element used in diesel fuel injection pump by nagarjun.s, dr.h.n.divakar international journal of scientific and research publications, volume 4, issue 7, july issn [4] Root cause analysis of control rod friction problemin dfip using shainin approach by bhaskar p, k m subbaiah, raghuveer prasad, g l shekar international journal of mechanical engineering and technology (ijmet) issn [5] Sunil sharma and anuradha r chetiya, Simplifying the six sigma toolbox through 47