REDUCING SETUP TIME THROUGH SMED TECHNIQUE IN A DIE CASTING PRODUCTION LINE

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1 REDUCING SETUP TIME THROUGH SMED TECHNIQUE IN A DIE CASTING PRODUCTION LINE Nithin.S 1, K. N. Ganapathi 2 1-M. Sc. [Engg.] Student, 2- Asst Professor, Department of MME M. S. Ramaiah School of Advanced Studies, Bangalore Abstract The present manufacturing scenario demands low quantity and high variety parts. Only through lean manufacturing, this target can be achieved. Just-in-Time manufacturing demands smaller production quantities which in turn mean more setup times (non-productive time). Companies should focus on reducing down time in order to remain competitive. In this project work, die casting process and setup evaluation is carried out in Jeng Fong (JF DC H30) die casting machine. The Rotor casting is found as the bottle neck by studying the process in detail. With the help of pareto analysis the 4 major causes of more setup time were focused. They include nozzle change, coolant system assembly, parameter setting and inspection. The corrective actions were taken systematically to reduce the listed setup time. This included designing and manufacturing a new cooling system, inspection gauge, SOP for ease in setting of moulding parameters. 5S and kaizen activities were initiated in the company. Also training was given to the operators in SMED (converting of internal activities to external). The project also focuses on reduction of manufacturing lead time of rotor part. Reduction of manufacturing lead time was brought into action by reducing the cycle time of the moulding process. With the help of new design of cooling assembly, the cycle time of cooling and spraying was brought down. Comparative study was done and the results were validated. Tools used for achieving the goals are SMED, 5S, SIPOC diagram, SOP, Poka-Yoke etc. The project implementation resulted in bringing down the setup time to 27% (from 69 min. to 19 min.) and manufacturing lead time reduction by 19 % (70.5 hrs to 57.2 hrs). Keywords: SMED, SOP, Die Casting 1. INTRODUCTION The present manufacturing scenario demands low quantity and high variety parts. Only through lean manufacturing, this target can be achieved. Just-in-Time manufacturing demands smaller production quantities which in turn mean more setup times (non-productive time). Companies should focus on reducing nonproductive time in order to remain competitive. Thus quick change over is critical element in lean manufacturing. Quick changeover is also known as setup reduction which focuses on eliminating or reducing non value added activities during the setup. This helps companies to efficiently change the tool/mould from one part to another. Changeover time is referred to as the total time required for change from one product to the second product. As shown in figure 1, total changeover time is considered as lost production which includes rampdown time, setup time and ramp-up time. Ramp down time: Run down period is the time between the end of a batch production till the lot quantity is completed. Setup Time: Setup time is the non production time in which change over takes from one part to another. Ramp up time: The time between setup is completed and the full production is achieved. Implementation of SMED starts from identifying the change over process and sorting it into internal and external activity. Internal activity: Activities that are done after stopping the machine. External activity: Operations that can be done without stopping the machine. PRODUCT 1 Fig. 1Total changeover time [1] PRODUCT 2 Internal activities have to be converted to external wherever possible. Then focus should be on minimizing external activities. Maintaining of 5S is important at each levels of implementation. At each stage of advancement, the process has to be standardized and again scope of improvement has to be analysed and implemented focusing on continuous improvement. With the help of continuous improvement, the total changeover has to be brought down to single minute, i.e. aim of SMED [2]. Production consists of different processing and assembly operations. Between the operations there are tasks related to material handling, inspection and other non-productive activities. The activities in production are divided into three main categories; operation and non-operation elements. MLT is the sum of setup time, processing time, and non-operation time [3 ]. The nonoperation elements are handling, storage, inspections, and other sources of delay. When a worker completes the processing of one batch, the machine must be set up for the processing of the next batch. This time between the changeovers is known as setup time. SASTECH 63 Volume 10, Issue 2, Sep 2011

2 2. PROBLEM STATEMENT [1] The project aims to reduce the manufacturing lead time on the bottleneck part. With the help of literature review, it was found that, cycle time and setup time contributes for manufacturing lead time. Hence reduction in cycle time by reducing the cooling and spraying time is also focused to reduce. 5S and Kaizen activities has made compulsory in the company for all employees. This helped to strive continuous improvement through incremental changes. [2] Reducing the changeover time on the bottleneck part from 69 minutes to 12 minutes through lean principles by emphasizing on setup time reduction and to reduce the manufacturing lead time from 70 hrs to 60 hrs is the aim of the project. 3. METHODOLOGY Literature reviewed on SMED and lean principles carried out by referring books, journals and manuals. Detailed study of the operations and existing changeover procedure done by video recording. Converted internal activity to external by ensuring availability of tools, fixture. Standardized the mould shut height with respect to the machines they are loaded. Implemented 5S for safety and serene work place. 3.1 Bottleneck Identification Table 1 refers the monthly production schedule (August & September) for lock assemblies. As per this schedule the bottle neck assembly is identified considering the criteria of maximum manufacturing lead time. Part # , Lock assembly is identified as the bottle neck. The manufacturing of this assembly is taking more lead time because of more cycle time for production and less number of cavities in the mould. Table 1. Monthly production schedule SANDHAR COMPONENTS (Production Schedule) SL PART NO PART NAME No. of MLT Parts TOTAL QTY AUG SEPT Lock Assy Lock Assy Lock Assy Table 2. Identifying the bottleneck part in assembly T Fig. 2 Existing changeover vs target Figure 2 refers to the target planned for reducing setup time. The setup time was planned to reduce to 12 minutes from 69 minutes. 4. CURRENT STATE ANALYSIS Die casting process and setup evaluation is carried out in Jeng Fong (JF DC H30) die casting machine. The Rotor casting is found as the bottle neck by studying the process in detail. Tools used for setup time reduction are SMED,7 QC tools [4], 5S, SOP, Poka-Yoke etc. Analysis is carried out by various stages such as: Identification of the bottleneck assembly, followed by the part. SIPOC analysis [5]. Detailed time study and attributes contributing for setup. Selection of major areas of focus. Why-Why Analysis [6] FMEA [7] Developing the new model. Planning (WBS) [8] & Implementing. Validating the results. From Table 2, the Rotor part is identified as the bottleneck in the assembly. The manufacturing lead time required for Rotor is hrs and the maximum setting time for the mould is 1.15 hrs. The cycle time required for producing a part is 20 seconds. The production time is calculated using the below listed formula Production Time = (25000 x 20) / (2 x 60 x 60) = Hours. Total Manufacturing Lead Time = Production Time + Setting Time = Hours. Fig. 3 refers to the SIPOC diagram in which the casting process is represented diagrammatically. It includes Supplier-Toolroom, Inputs-Mould clamping fixtures, Process-Changeover that includes getting corrected mould from maintenance department, carrying it to the machine, search for tools and clamping fixtures, Unloading and loading of the mould to the machine, clamping, changing the nozzle (if any), assembly of ejector assembly, parameter setting, cooling system assembly and inspection. SASTECH 64 Volume 10, Issue 2, Sep 2011

3 Setting. Any improvement in reducing the listed distribution will result in tremendous reduction in setup time and thereby reducing the manufacturing lead time. Fig. 5 refers to the selection of the areas of focus for setup time reduction. It includes reducing the time for coolant system assembly, nozzle change, inspection, parameter setting and also generating 5S and kaizen within the production line. Incremental improvements from the production side help the company to strive towards excellence. Fig. 3 SIPOC diagram Time study for the sequential operation is done by video recording. The detailed time taken for the operations is listed below Table 3. SL # Table 3. SMED analysis sheet ACTIVITY TIME IN SEC. TIME IN MIN. 1 Inspection Cooling System Assy Parameter Setting Nozzle Change Ejection Assy Loading & Clamping Search for Trolley Search for Tools Carrying the trolley and mould to machine Unloading TOTAL Fig. 5 Areas on focus 5. PROBLEM SOLVING 5.1 Cooling System Assembly External cooling is done after every shot for the die casting mould. This helps to reduce the defects on the part and also to have an optimum cycle time. In a process, cooling time constitutes about 40-45% of casting cycle time. Any improvement in reduction of cooling time will result in reduced cycle time and thus improved productivity. In the setup, cooling system assembly was contributing 14%. Observations: Coolant and air mixed up together and ejected with the help of pump after every shot (Fig. 6). The coolant covers only limited area (Ø28mm). More time taken for cooling for large components simultaneously cycle time gets increased. Setting of this coolant system takes more time to focus on core/cavity area. Standard spray gun available in market is one sided. Fig. 4 Pareto analysis for time study Fig. 6 Coolant system before From the pareto diagram (Fig. 4) 64% of the changeover time is contributed by Cooling System Assembly, Nozzle Change, Inspection, Parameter SASTECH 65 Volume 10, Issue 2, Sep 2011

4 Table 4. Why why analysis coolant system Fig. 8 denotes the manufactured new cooling system and the advantage of covering more surface area of coolant. Coolant spray Focusing the Why cooling covers limited area Cooling System coolant spray to system setup while spraying Assembly- the core and taking more since the coolant 10min (14%) cavity takes time? and air is mixed more time? and sprayed. FMEA analysis (design) has been carried out to understand and find the potential failure modes. According to this analysis, corrective actions and steps were taken for improving the coolant system design. Summary of DFMEA and corrective actions includes: Fouling of coolant system with mould daylight - Defining minimum width and length with respect to minimum daylight of mould. Leakage of coolant & air Separate coolant, air transformation and air spatters the coolant at the end point. Coolant and air mix up Press fit of plug must be ensured and functioning of coolant system by movement of piston. Cross feeding air and coolant pipes Separate colour codes for air and coolant pipe and also diameter change incorporated. Less cooling area - Rotary head at the end for effective spraying. Fig. 7 Coolant system 3D model Table 5. BOM for cooling system BOM-Cooling System Sl# Description Qty Matl. Size 1 Base Block 1 MS 20x21x110 2 Piston 1 MS Ø6x20 3 Side Block 1 1 MS 15x20x20 4 Side Block 2 1 MS 15x20x20 5 Spray Gun 2 MS Ø25x35 6 Inlet Nipple 3 STD 7 Spring 1 STD Ø6x7 8 SHCS 4 STD M5x15 Fig. 8 New coolant system Result: Coolant and air taken separately to the end point of spray gun and spatters the coolant droplet. More area of contact for the cooling i.e. Ø60mm. Cooling offered on both core and cavity side. Easy setting. Poka-yoke integrated for the design. 5.2 Nozzle Change The molten casting material (Zamak 3) is injected through the nozzle from gooseneck arrangement. The nozzle is having a radius which matches with the sprue bush radius, through which the material enters into the mould. The material is transferred from the goose neck furnace to the spru bush of the mould. The sprue bush inlet diameter ranges from Ø5 to Ø6 depending upon various moulds. In the setup, nozzle change was contributing 11%. Observations: Moulds manufactured from different suppliers are having different attributes. Nozzle inlet diameter varies from Ø5 to Ø6 mm. No standardised design for mould base is provided to suppliers with respect to machine criteria. Mould setter was not trained to change the nozzle. Pre heating of nozzle is required after clamping; this also increases the setup time. Table 6. Why why analysis nozzle change Nozzle Change- 7.5min (11%) Why nozzle change taking more time? Different moulds Moulds having different manufactured at is sprue diameter with different suppliers which the nozzle having different diameter (Ø5-Ø6). attributes. SASTECH 66 Volume 10, Issue 2, Sep 2011

5 Solution: Standardise the sprue bush inlet diameter of moulds. Supplier coordination and standard mould base design to be generated. Table 7. Comparison for nozzle rework Ø5 Nozzle Ø6 Nozzle Angular Relief = 3 0 Angular Relief = Volume = Volume = = 3.14x80/3[2.5 2 = x80/3[ (3x6.9) +(2.5x6.7)] = ] = 83.7[ ] 83.7[ ] mm mm 3 Weight = Volume x Weight = Volume x Density x 10-6 Density x 10-6 = x 6.8 = x 6.8 x 10 = kg = kg Difference: = kg. As shown above (Table 7), a comparative study is carried out for understanding the shot weight difference and it was observed that only a fractional increase of 0.004kg is increased by incorporating new design and standardising. The volume is calculated by substituting the sprue area as the volume of a frustum of cone. Standardized Mould Base Design: From Jeng-Fong H30 machine manual, the standard slot size on the machine bed has being analysed. This helped to design the areas of clamping for the die casting mould. The total mould size and the setting attributes are also standardized. Table 8 was generated with the help of machine manual and being circulated among the suppliers with the control points in design. Design Standard for Mould Base Machine JF-DC-H30 Machine # PDC 09 Locking Force 30 T Die Stroke 180mm Injection Force 2.69 T Injection Pressure 137Kg/cm 2 Ejector Stroke 50 mm Ejector Force 2.7 T Sl# Description Dimension Min Max 1 Height [H] Length [L] Breadth [B] Clamping Block [P1, P2] Inspection The critical dimension of the castings has to be ensured before production run. Inspection time is contributing 25% of the total setup time. Observation: Fitment of the part is checked and assembly takes more time since it is done with 6 brass clips. QA department carries out the inspection and gives clearance for production. Components after 5-10 shots are taken for inspection. Apart from fitment, the weight is also checked. Inspection Time-17 min. (25%) Table 9. Why-why analysis inspection Why inspection taking more time? Fitment of Inspection done the part is for pilot lot in checked assembly by using mating QA department. parts (6 brass clips) Solution: Introduce gauge in production line. The upper limit of the slot is controlled in the core and gauge introduced to check within the lower limit specification. Table 8. Design standard for mould base Result: Standard design for mould base helps to manufacture identical moulds at different suppliers. Nozzle change time is completely eliminated since the sprue bush inlet is reworked and standardized to Ø6. Fig. 9 Inspection gauge SASTECH 67 Volume 10, Issue 2, Sep 2011

6 5.4 Parameter Setting After each lot production, the moulding parameters have being updated through trial and error method. The parameters include shot weight, temperature, holding time, cooling time, and idle time. Setting of parameters has to be precise since they directly contribute to the cycle time. Observation: The machine is running on analogue mode and not having any facility to store the program (parameters) and recall when it is needed. Parameter setting requires skilled setters with higher efficiency in casting process. About 14% of the setup time was lost in setting of parameter. Parameter Setting-10 min (14%) Solution: Table 10. Why-why analysis parameter setting Why parameter setting takes more time? Mould setter sets Machine running it by trial & error in analogue mode. method through No program visual inspection. saving facility in (Highly efficient the machine and manpower required) also parameter log is not available. Track the moulding parameters while production and introduce SOP. Time study being carried out and noted for the Rotor part. The parameter setting log was tracked at 6 different points. Average Cycle time for ROTOR part was tracked as 20 sec. The first step of parameter setting reduction involved developing a standard work instruction. Standard work instruction which was developed tracking down all the steps involved for mould changeover. With the help of tracked down parameter setting data, an SOP was developed with the standard work instruction of the bottleneck part and parameter range. This range helped to reduce the parameter setting time. Complete elimination of this attribute in setting time was not incorporated since because of no memory saving facility in the machine. Result: Unskilled worker can do setting (parameter). Parameter range helps operator to program efficiently and less time consuming. Accurate when compared to old input system (trial & error). Ease in training new operators S & Kaizen Observation: Tool maintenance, storage area away from production line. Movement of tool to machine consumes more time (12.8 mtrs). No display of work instruction and SOP near machine. Solution: Plant layout to be changed by expanding PMD and tool maintenance, storage area to be shift near to production line. Moulds ready for production has to be planned and moved near to production line at the starting of shift. In the modified plant layout, the tool room area is brought near to the production line (1.8mtrs). Moulds ready for production is shifted near to the production line at the starting of every shift. The old tool room area was expanded to PMD and rework area was also merged with it. Distance Travelled: D da = ni x dj ni = Avg visit dj = Xj + Yj (Total Distance) ni = 10/day (average tool setup in 3 shifts taken as 10 times) Table 11. Man movement for loading in a day Description New layout Total Avg visit per Avg Distance Average Storage (meter) distance Location dj = Xj+yj traveled (ni) dda(m) Old Layout Total Avg Distance Average (meter) distance dj = Xj+yj traveled dda(m) Mould Shifting per day Total 18 Total 128 Table 11 shows the formulation and calculation of average distance travelled in daily basis. Kilom Fig. 10. Man movement reduction trend per month Fig. 10 denotes the mould movement for loading brought down to 0.9km from 6.4 km/month. 6. RESULTS After implementation of the above listed improvements, studies have being done to check the updated results. From the comparison study of new setup time, it was noticed that setup time was reduced from 1.15 hrs to 0.32 hours. This was made happen by training the operators, tool setters regarding the importance of setup time reduction and also by SASTECH 68 Volume 10, Issue 2, Sep 2011

7 converting internal activities to external. The manufacturing lead time has reduced from 70.5 hrs to 57.2 hrs. Figure 11 demonstrates the comparison of setup time and manufacturing lead time before and after. The manufactured new model of cooling system helped to reduce the cooling time and hence that resulted into reduction of cycle time. [6] Unknown, Why-Why Analysis, retrieved on 20 th Oct [7] Unknown, Failure Mode & Effect Analysis, retrieved on 20 th Oct [8] Unknown, Work Breakdown Structure, retrieved on 25 th Oct Time Fig. 11 Project result comparison 7. SUMMARY Implementation of SMED technique in die casting production line helped to understand various aspects of attributes contributing for setup (non value added time). The project focused on reduction of manufacturing lead time of rotor part. Reduction of manufacturing lead time was brought into action by reducing the cycle time of the moulding process. The new design of cooling assembly, cooling and spraying time was brought down this helped in reduction of cycle time. Comparative study was done and the results were validated. Tools used for achieving the goals are SMED, 5S, SIPOC diagram, SOP, Poka-Yoke etc. The project implementation resulted in bringing down the setup time to 27% (from 69 min. to 19 min.) and manufacturing lead time reduction by 19 % (70.5 hrs to 57.2 hrs). 8. REFERENCES [1] Unknown, Total Changeover Time, retrieved on 15th October [2] Dr.Shigeo Shingo, A Study of the Tovota Production System From an Industrial Engineering Viewpoint, [3] R. Władysiak, Reengineering of Permanent Mould Casting with Lean Manufacturing Methods, Archives of Dry Engineering., Poland. ISSN ( ), Volume 7, Issue 3/2007, pp [4] Dr. Deming & Juhran, Seven QC Tools, retrieved on 20 th Oct [5] Unknown, SIPOC Analysis, retrieved on 15 th Oct SASTECH 69 Volume 10, Issue 2, Sep 2011