Initiatives of six-sigma in an automotive ancillary unit: A case study

Article history: Received: November 26, 2017 Received in revised format: January 31, 2018 Accepted: April 26, 2018 Available online: April 27, 2018 It is a commonly visible scenario in todays’ market, especially in small and medium sized enterprises (SMEs), where the focus is on quantity rather than quality. This paper explains the common high rejection problem of a SME and how the productivity levels were enhanced after the successful implementation of Six-Sigma DMAIC methodology. Once the project completion industry was able to acquire many tangible and intangible benefits, this paper offers a systematic step by step illustration of DMAIC methodology to help the other firms start similar productivity improvement initiatives. © 2018 by the authors; licensee Growing Science, Canada


Introduction
Six-Sigma was introduced by Motorola, and in very short time, due to its enormous benefits, it was introduced in many large scale manufacturing organizations across the globe (Kaushik et al., 2012;Kaushik & Mittal, 2015;Kaushik, 2016a,b;Srinivasan et al., 2016;Uluskan, 2016).But the problem still exists on how to apply it in SMEs.The evidences of Six-Sigma application in small and medium scaled industries are very little.In large industries, Six-Sigma is an emerging and one of the most effective business strategies all over the world.As for big manufacturing industries Six-Sigma achieved positive results over different productivity problems, so it can also provide useful results for small scale industries as well (Sreedharan & Raju, 2016).For SME sector to become successful in the present competitive scenario, the strategy needs to be innovative (Biswas & Chowdhury 2016).SME sector needs immediate attention due to its participation in global progress in form of breakthrough strategy other than Statistical Process Control (SPC) (Kaushik et al., 2017a).In order to achieve customer satisfaction, researchers and industrialists around the world have worked over various tools (Kaushik et al., 2017b,c) and techniques like Total Quality Management (TQM), Quality circles (Mittal & Prajapati 2014), APQP (Mittal, Kaushik, & Khanduja 2012;Mittal et al., 2011Mittal et al., , 2012)), Shainin system (Mittal et al., 2017b), Quality Function Deployment (QFD) (Mittal & Kaushik 2011;Tewari et al., 2017), Decision Tree Analysis (Mittal et al., 2017;Mittal et al., 2017a), Fuzzy logic (Mittal et al. 2016a), Total Preventive Maintenance (TPM), Business Process Reengineering (Mittal et al., 2016b), Lean and Six Sigma (Kaushik et al., 2012;Kaushik et al., 2016a).The most popular of the techniques named above is Six-Sigma.It aims to find out the basic causes in process and eliminates them to achieve business excellence (Kaushik et al., 2016b).Various aspects of DMAIC strategy have been analyzed by researchers in great details in their own terms and literature suggests that so far, Six Sigma has been mostly thought of quality management tool for large manufacturing industries alone.With this in mind, an attempt has been made to visualize the application of Six-Sigma in a SME explained in form of a case study.
The organization under consideration is a SME manufacturing automobiles components such as valves, locks, carburetor repair parts, float needle, main jet, slow jet, throttle needle, chock piston, jet holder, gasket kit, slide screw, air screw, etc.The company was established in the year 1987 with a vision to deliver quality automobile components to fulfill the requirements of the Overall Equipment manufacturers (OEMs).It owns a sophisticated manufacturing unit and is equipped with the latest technology and tools to fabricate quality products which render long term service.The name of the company is withheld at its behest, to maintain confidentiality of the company records.
The main product of company is locks and one variety of lock is hood latch lock as shown in Fig 1 .The company was facing high rejection rates due to tight movement of lock's hood which ultimately results in "Hook not return" complaint in long stay.Hence, it became essential to validate the design of the product without changing the riveting specification due to high rejection rate and willingness of staff and management to improve quality.Lock is the main component of any automobile vehicle and it should not cause any problem to any customer while making it lock-unlock.Six-Sigma DMAIC methodology (Fig. 2) was selected to solve problem and to reduce effort while locking-unlocking.Various phases and their implementation are as follows: 1.1 Define This is the first phase of any Six-Sigma project and mainly deals with following the voice of customer.Customers' provided specifications are refolded and relooked in this phase.Various brainstorming sessions were held and process flow diagram and SIPOC diagram were drawn.Process flow diagram is a representation of the activities performed on the raw material till the final product is manufactured.It is a systematic flow or step by step procedure that will be followed on the raw material until the final required product is manufactured.Process flow diagram for making hood latch lock is shown in Fig. 3.

Measure
This phase generally involves measuring the extent of problem and recording the results of process.Firstly, in this phase factors which are critical to quality were listed and after that Gauge R&R study (Mittal et al., 2018;Mittal & Kaushik, 2018) was performed to determine whether the tool used for measuring the diameter of spring is working properly or not.

Gauge R&R study:
The aim behind this study is to categorize variation due to appraisers/operators and measuring instruments.In the current study, sample size of 20 was taken over two operators taking two readings on each sample, making a total of 40 readings as shown in Table 1 and Table 2.The instrument used for measuring spring diameter is Screw Gauge.Result of Gauge R&R showed Repeatability at 25.60 and Reproducibility at 0.00 percent, putting average percentage study variation at 25.60 percent < 30 percent.Hence, it indicates that Screw Gauge was correct.

Analysis
In this phase, the real root-cause analysis is performed using various statistical tools.After knowing the extent of the problem in measure phase, various brainstorming sessions are held and a list of suspected source and causes of rejection is prepared.In this case, one by one, components were analyzed to see the main cause of problem in the lock movement.First suspected source of variation was Rivet height.Modified component search tool was selected for its analysis.This tool is used when the problem is on an assembled product and parts will get damaged during disassembling and rivet pin will get damaged during disassembly during analysis.Also, the component was replaced with new pin for the First trial and Second trial run.A Best of Best (BOB) and Worst of Worst (WOW) sample was collected based on Attribute Index.Both BOB & WOW assemblies were disassembled two times and response is shown in Table 3.Based on the results obtained from Table 3, D/d ratio was calculated which tells whether rivet pin is causing problem or not.Here, 'D' refers to difference of Medians of BOB and WOW, whereas 'd' indicates the average sum of range of BOB and WOW.If D/d is equal to or more than 3 then it is concluded that the component is not problem.Table 4 shows the results of the modified component search.Since, in this search D/d ratio comes out to be equal to 3. Hence it can be stated that Assembly Process or Replaced component is not causing any problem, the other parts are causing problem.Secondly, the spring diameter was checked, whether it is causing problem or not.The dimension of spring diameter is 0.98mm +/-.5mm.A histogram (Fig. 6) for the 40 spring diameter readings was drawn.Histogram displays the large data that is difficult to interpret and also indicates process capability.The Histogram clearly shows that the data for spring diameter is centric.Hence, it is not the reason for the tightness of the hook of Hood Latch Lock.After the conclusion on spring diameter, three components (Hook, Washer and Hook base plate) were left that might be causing problem.One by one component was disassembled from Good and assembled in the bad and the response is taken as shown in Table 5, Table 6 and Table 7.
List of suspected components are 1) Hook -A (A-R+, A+R-) 2) Washer -B (B-R+, B+R-) 3) Hook Base Plate -C (C-R+, C+R-) 1 .0 2 1 .00 0 .98 0 .96 0 .9 4 0 .9 2 A conclusion table for the above analysis was drawn as Table 8.Finally, it is evident form the Table 8 that washer was the component causing problem.In the next step, validation of the results obtained from analysis was done.The component identified i.e.Washer was swapped to the original assemblies and checked for complete reversal as a part of validation as shown in Table 9, which validated the root cause.

Conclusions based on Paired Comparison
 From the response Table 10, it can be definitely concluded that Washer more than 1.02mm diameter is creating the problem. The washer should be less than .95mmand washer tolerance should also be considered for revision.
 Considering Washer Thickness as the response Multi Variant Analysis for the 10 Cavity Mold Tool was conducted.Multi Variant Analysis is used only when the problem is generated from a manufacturing process.Table 11 shows the multi variant analysis done for washer thickness as response.Cavity to Cavity variation is found to be more than part to part, so the corrective action is required for the cavities.0.9 0.9 0.9 0.9 1 0.9 0.9 1 0.9 0.9 Part to Part 0.02 Cavity to Cavity 0.1

Improvement phase
This is the fourth phase of Six Sigma DMAIC methodology and in this phase, improvement is made in the cause of problem by implementing the corrective measures recommended by the team in analysis phase.As in current case study, washer thickness is found to be the source of problem so the improvement action for the same is taken into account.The washer is manufactured by molding process, so as a first corrective step, mold tool was improved at the manufacturing end by revising tolerance.Improvement required in size for various parts is shown in Table 12.Tolerance Revised ( 0.90 -0.0/ +0.05) Fig. 7 and Fig. 8 show the picture of molded component and 10 Cavity mold for washer.Various tests including flexure strength testing (Kaushik et al., 2017;Kaushik et al., 2017) were also performed for changes made in the thickness of washer.

Control Phase
This is the final phase of Six Sigma DMAIC Methodology.In this phase results of the improvement phase are checked.The true aim of this phase is to cross check the implementation and raise a feedback system if deviation is visualized.In present case study, as the mold tool is the only component which required improvement.After the implementation of recommended actions, defects in hood latch locks were reduced to a great extent.Results shows the decrease in PPM in four months after the improvement done in the mold tool used for making washer.Initially, PPM was about 1550 which has been reduced to nearly 100 PPM in a short period of four months.Additionally, a control plan for the mold tool has been prepared to keep a check on the variation in washer thickness.

Results and Discussion
The results showed a huge monetary gains when calculated.Successful implementation of SIX-Sigma DMAIC methodology brought a financial benefit of Rs. 104000 per month.Similar measures were applied to the products of same part family which raise the extrapolated annual benefit to around Rs. 1500000, which is a huge amount for SME.The calculation for the same is as follows: Before Improvement, Cost of Poor Quality = Rs 1, 20,000 per month Rejections per month =300 per month on average Cost of poor quality per rejection = Rs 400 per rejection After Improvement, Rejections per month = 40 per month (reducing) Cost of poor quality per rejection = Rs 16,000 per month Savings in cost after improvement = Rs (1, 20,000 -16000) = Rs 1, 04,000 One can understand and gain profit from Six Sigma strategy by its project by project application in small sized enterprise.For the upliftment of the enterprise in the global market and strengthening of the bottom line in small sized enterprise, Six Sigma can play a vital role and is much awaited strategy.To extract the benefits from Six Sigma one should believe in it and prepare the road map and implement it into the industry and proceed earnestly.So for the observation of impact of Six Sigma in SME's, an attempt has been made to implement it in car lock manufacturing organization.The study was an attempt to allay myths and fears of Six Sigma implementation in small scale industries.Since small industries have their own constraints and resource limitations, so efficacy of Six Sigma to improve productivity, without major investments, has been highlighted by the results of the study.

Conclusions
It can be concluded that Six Sigma is not only a strategic tool, but it can be used as a process improvement tool as well.In present work, an effort has been made to implement Six Sigma on a small hood latch lock manufacturing industry.The results have shown an impressive reduction in rejection rates.The main reason identified for the rejection was washer thickness.After the application of paired comparison and multi vary analysis, it has been found that the thickness of washer was varying from cavity to cavity which is causing problem.During the improvement phase, the tolerance of the washer thickness has been revised from 1mm +/-0.25mm to 0.90mm -0.00/ +0.05mm and accordingly the mold has been corrected.After the improvement phase, the results have shown a high improvement and reduce the cost of poor quality from Rs 1, 20,000 per month to Rs 16,000 per month making the savings of Rs 1, 04,000 per month which is indeed a great achievement for industry of such stature.Apart from tangible benefits, intangible savings such as reduction in consumer complaints and inspection, personnel development of employees, organization culture improvement etc. were also noticed.This case study clearly challenges the saying that Six Sigma has the domain of only large companies.

Table 1
Minitab Data Sheet of Spring Diameter for Gauge R&R Study