APPLICATION OF LEAN METHODS FOR IMPROVEMENT OF MANUFACTURING PROCESSES

Transcription

1 APPLICATION OF LEAN METHODS FOR IMPROVEMENT OF MANUFACTURING PROCESSES György KOVÁCS 1,a ABSTRACT: Changing market environment, increasing global competition and fluctuating customer demands require efficient operation of production and logistical processes. The essence of Lean manufacturing is the cost reduction and improvement of productivity. There are lots of Lean methods for improvement of the production performance. The paper shows the essence, characteristics and advantages of application of Lean production philosophy. The article describes the theoretical background relating to the process improvement and a practical design method is also introduced in a case study. This case study which is a part of a real R+D project shows how can be improved the efficiency of a real assembly line by application of 4 Lean methods: Takt- analysis, Line balance, Cellular design and One-piece flow. KEY WORDS:Lean production, waste, efficiency improvement, takt- analysis, cellular manufacturing. 1 INTRODUCTION The growing market globalization, global competition, and more complex products require efficient operation of logistical processes where the enterprises have to focus on cost reduction and productivity. This research study is very important and actual, because the improvement of productivity and the cost reduction are very important for manufacturing enterprises. Lean manufacturing is an often applied production philosophy at more and more companies in many sectors including automotive, electronics, etc. to increase their competitive advantage. In the study the essence, characteristics and methods of the Lean philosophy is introduced. The article is original and unique, because the theoretical background relating to the process improvement is introduced and a practical design method is also described in a case study. The described case study confirms that the Lean manufacturing philosophy is an effective tool for process improvement. Significant results can be 1 University of Miskolc, Faculty of Mechanical Engineering and Informatics, Institute of Logistics, Miskolc-Egyetemvaros, 3515 Miskolc, Hungary a altkovac@uni-miskolc.hu realized by the application of a U-shape assembly cell instead of a linear assembly layout by the application of several Lean tools which are Onepiece flow, Takt- analysis, Line balance and Cellular design. 2 LEAN PRODUCTION PHILOSOPHY The focus of Lean philosophy is to decrease the cost of production, to evaluate activities which do not add value to the product from the customer point of view. The main perspective of the Lean production system is to improve quality, decrease wastes and optimize the cost of production processes (Womack & Jones, 1996; Holweg, 2007). The aim of the philosophy is the cost reduction by eliminating non-value added activities. In today's increasingly global marketplace, many manufacturers are adopting Lean manufacturing practices in order to optimize costs and efficiency, thereby gaining a competitive advantage. 2.1 Lean principles There are many literatures in topic of Lean production principles and application of it (Fawaz & Jayant, 2007; Fullerton et al., 2003) Lean manufacturing techniques are based on the application of five principles which are the followings (Figure 1.): Figure 1. Lean principles 1. Value: The foundation for the value stream that defines what the customer is willing to pay for. ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL.15, ISSUE 2/

2 2. The Value Stream: The mapping and identifying of all the specific actions required to eliminate the non-value added activities from design concept to customer usage. /Tools: 1.) Identification of wastes, 2.) 5 Why, 3.) Value stream mapping/ 3. Flow: The elimination of all process stoppages to make the value stream flow without interruptions. /Tools: 1.) JIT, 2.) One piece flow, 3.) Takt- design, 4.) Heijunka, 5.) SMED, 6.) Jidoka/ 4. Pull: The ability to streamline products and processes from concept through customer usage. /Tools: 1.) Pull system, 2.) Kanban, 3.) Supermarket/ 5. Perfection: The ability to advocate doing things right the first through the application of continuous improvement efforts. /Tools: 1.) Standardization, 2.) Kaizen, 3.) 5S/ 2.2 Main types of Lean activities Activities can be categorized into three groups: - value added activities (e.g. assembly, manufacturing, welding, etc.), - required but non-value added activities (e.g. exchange of die, etc.), - wastes are any element that does not add value, or that the customer is not prepared to pay for (e.g. over-production, warehousing, etc.). (Liker & Lamb, 2000; Kovács, 2014) The results of the Lean philosophy are described in Figure 2. In case of Lean manufacturing the ratio of the value adding and non-value adding activities will be improved compared to traditional manufacturing by elimination of wastes in processes. Figure 2. Traditional manufacturing compared to Lean manufacturing 2.3 Lean wastes Seven types of wastes (Figure 3.) can be identified in processes (McLachlin, 1997; Holweg, 2007). 1. Over production Producing more final products than is needed for the customer. 2. Waiting Worker or machine is waiting for material or information. 3. Motion Any unnecessary motion that does not add value to the product. 4. Transportation Moving material does not increase the value of the product to the customer. 5. Inventories Material sits taking up space, costing money, and potentially being damaged. 6. Over- processing Extra processing not essential to value-added from the customer point of view. 7. Producing defective products Defective products impede material flow and lead to wasteful handling, and effort. 8. Other additional wastes Underutilized worker creativity and resource, application of non adequate equipments and systems, wasted energy and water, damage of environment. Figure 3. Seven types of wastes These wastes are appeared in every manufacturing company. Companies who identify, manage, and minimize these wastes are able to be the best in the very competitive marketplace. 3 MAIN TOOLS AND TECHNICS OF LEAN MANUFACTURING Lean tools and techniques focus on areas of the manufacturing process in order to help reduce costs and improve efficiencies of the processes. The main tools and techniques of Lean manufacturing (Womack et. al, 1990; Kovács, 2012, Intă & Muntean, 2015) are for example Value Stream Mapping, Takt analysis, Pull system, JIT, Kanban, One-piece flow, Heijunka, Single Minute Exchange of Dies (SMED), Jidoka, Supermarket, Kaizen, Standardised processes, 5S, layout for flow, Work group team error proofing, Zero defects, Poke-yoke, Line balance, etc. 32 ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL.15, ISSUE 2/2017

3 4 ADVANTAGES OF LEAN MANUFACTURING AND LEAN METHODS 4.1 Advantages of Lean manufacturing The Lean production philosophy utilizes the advantages of Pull philosophy, therefore the Lean philosophy is also provide the same advantages of Pull production philosophy. From the philosophical point of view the Push approach (make to stock) is replaced by Pull approach (make to order), the traditional mass production is replaced by unique production (or smaller batches). Push philosophy production planning is based of forecasted data (not actual customer demand), so that the result is high amount of products, including unsalable stock is created. On the contrary the Pull production (uniqueness of production) starts only when an actual customer demand appears (with detailed specification), which starts procurement and manufacturing processes. Pull system only produces what a customer needs and has asked for. Production and distribution are demand driven, coordinated with true customer demand rather than forecasted demand. The advantages of Lean manufacturing are the followings (Kovács, 2012): - higher productivity, - reduced lead, - reduced inventory since inventory levels increase with lead s, - flexible reaction to the changing customer demands, - smaller place for production, - higher utilization of human resources and equipment, etc. 4.2 Advantages of Lean methods and tools Application of Lean methods and tools provides the following advantages: - Lean tools are easy to use due to their simplicity. - Lean tools provide the possibility to gain a better understanding of the current production processes and to point out potential for improvement. - Bottlenecks and wastes can be found easily. - Most of lean tools and methods require only a pen and a single sheet, nothing more expensive equipment. (The value stream with the most important production parameters are sketched on-site by hand.) - Use excellent visualization techniques, which support the transparency of the process and the optimal production design. - The examined process can be visualized in the current state map and in the future state map. - Lean method requires very little effort. The application of Lean production philosophy can result the improvement of the following Key Performance Indicators (KPI): shorter lead s, shorter set up s, smaller stocks, increase of free production area, increased quality of products, general increase of the efficiency of production, increase of productivity. 5 CASE STUDY FOR PRACTICAL APPLICATION OF LEAN METHODS Significant practical results can be gained by the application of Lean methods which are the cost reduction and productivity improvement. A case study is introduced for an assembly process improvement which is a part of an R+D project. The analyzed assembly process can be seen in Figure 3., which including 14 assembly processes organized into 5 workstations. The main profile of the analyzed company is manual assembling activity. The material flow between the workstations is also showed in Figure 4. by red arrow. Cycle s of the different assembly processes and workstations are listed in Table 1. Table 1. Data relating to the actual assembly process Workstation 1. Workstation 2. Workstation 3. Assembly processes Cycle 1. 6,7 2. 3,5 3. 8,8 4. 3,4 5. 7,2 6. 6,4 7. 5,8 8. 8,2 9. 7, ,2 Total cycle ,5 ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL.15, ISSUE 2/

4 Workstation 4. Workstation , , , ,4 10,4 11,6 85,5 Figure 4. Actual layout Goals of the process improvement: - increase productivity, - balance and optimize the assembly line, - realize perfect one-piece-flow in the assembly process, - reduce the amount of WIP inventories, - reduce movement of raw materials, components, equipment and workers. 6 REDESIGN OF AN ASSEMBLY PROCESS The process redesign is based on the application of 4 Lean tools which are Takt- analysis, Line balance, Cellular design and Onepiece flow. 6.1 Takt-Time Analysis method The rhythm of the production is defined by the customer demands. The takt- is the average between the start of production of a product and the start of production of the next product. Takt- can be calculated by the next equation: T takt TS Q sec unit, (1) where: T S is the net available to work [work per shift: sec], Q is the customer demand [final products required per shift: unit]. Net available is the amount of available for assembly which includes break s. In this case 8 hours in a shift minus 30 minutes break. Totally the net available to work is 7,5 hour which is equal to sec/shift. The customer demand is 1200 units/shift sec sec T takt 22, unit unit The takt- at the assembly line is 22,5 sec/unit which is a real customer demand and the base of the production scheduling. There are a number of benefits of application of takt- analysis: - Activities at workstations (human and equipment resources) that require more than the takt- are bottlenecks in the assembly process. These bottlenecks can be identified very easy. - Activities at workstations that need less than the takt- are also critical sections in the assembly process, because the unutilized human and equipment resources are also wastes. Figure 5. shows the current loading of 5 workstations. Figure 5. Current loading of 5 workstations It can be seen that the total cycle of assembly processes at workstation 3. is longer than the takt-. It results that the customer demands are not fulfilled in (the required number of final products can not be manufactured in ), deliveries are late and customers are unsatisfied. Assembly processes at workstations 1., 2., 4. and 5. are less than the takt-, the human- and equipment resources are unutilized, lot of waiting and free capacity are realized. 6.2 Line balance method The next step of the design is to define how many workstations and workers are needed to run the manufacturing cell. The required number of workstations can be calculated by: Ttotal NWS [unit], (2) T takt where: 34 ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL.15, ISSUE 2/2017

5 T total is the total manufacturing cycle of a final product, T takt is the takt- [sec/unit] , ,4 85,5 In our case: 85,5 NWS 3,8 4 unit. 22,5 It shows that at least 4 workstations and operators are needed to produce one product every 22,5 seconds. Assembly line balancing is dealt with reconfiguration (balancing) of size and assignment of the workforce on the assembly line. Line balance can be realized if the consumption of workstations (task groups) is approximately equal, close to the takt-. Line balancing is levelling the workload of all processes in the assembly cell to remove bottlenecks and free capacities. In the assembly line every operator is doing the same amount of work in, no one overloaded and no one unloaded. Based on the above mentioned principle of line balancing the balanced assembly process is described in Figure 6. and Table 2. It can be summarised that the cycle s of the 4 workstations are near the same, close to takt-, therefore the perfect one piece flow can be realized in the process. This perfect flow can result a shorter lead and the reduction of WIP stocks between the workstations. Figure 6. Balanced production 6.3 Cellular design method The goal of cellular manufacturing is to design cells to improve productivity of the assembly line and create perfect material flow in the assembly process (Massoud, 1999, Miltenburg, 2001; Miltenburg, 2001). The redesigned U-shape cell can be seen in Figure 7. The assembly process is including the same 14 assembly processes organized into 4 workstations, the material flow direction and the task groups are also depicted in Figure 7. Table 2. Data relating to the balanced assembly process Workstation 1. Workstation 2. Workstation 3. Workstation 4. Assembly processes Cycle 1. 6,7 2. 3,5 3. 8,8 4. 3,4 5. 7,2 6. 6,4 7. 5,8 8. 8,2 9. 7, , , ,8 Total cycle 22,4 19,4 21,7 22 Figure 7. U-shape cell as a new layout It can be summarized that the cellular manufacturing has lot of advantages. The performance of the assembly line was improved due to the perfect one-piece flow, balanced assembly line, reduced movement of goods and reduced amount of inventories. The compactness of the assembly cell minimized the required space of the assembly process on the shop floor. 7 CONCLUDING REMARKS In a competitive market the manufacturing companies have to produce cost effective products which can be realized by minimized production cost and higher effectiveness. ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL.15, ISSUE 2/

6 Recently more and more companies apply the Lean production philosophy which focuses on cost reduction and productivity improvement by eliminating non-value added activities. In this study the author defined the essence and characteristics of the philosophy and emphasized the importance of application of Lean manufacturing, techniques and tools. The article is original and unique, because beside the description of theoretical background of Lean philosophy, a practical design method was also introduced in a case study, in which an existing linear assembly line was redesigned for a U-shape assembly cell. So in this case study it was showed that how can be improved the efficiency and reduced manufacturing cost of a manufacturing system by application of Lean tools which were the One-piece flow, Takt- analysis, Line balance and Cellular design. Based on the above mentioned facts, it was confirmed that the Lean manufacturing philosophy is an effective tool for process improvement, because a perfect goods flow was realized to provide one-piece flow in the assembly process, number of workstations and operators were reduced, assembly line was balanced and the amount of inventories was reduced. 8 ACKNOWLEDGEMENTS This project has received funding from the European Union s Horizon 2020 research and innovation programme under grant agreement No REFERENCES Fawaz, A. A., Jayant, R. (2007). Analyzing the benefits of lean manufacturing and value stream mapping via simulation: A process sector case study, International Journal of Production Economics, 107, pp Fullerton, R. R., McWatters, C. S., Fawson, C. (2003). An examination of the relation ships between JIT and financial performance. Journal of Operations Management, 21 (4), pp Holweg, M. (2007). The genealogy of lean production. Journal of Operations Management, 25 (2), pp Intă, M., Muntean, A. (2015). Application of lean principles to optimize production. Case study - Connectors department of the Harting company. Academic Journal of Manufacturing Engineering, 13 (2) Page42-47 Kovács, Gy. (2012). Productivity improvement by lean manufacturing philosophy. Advanced Logistic Systems: Theory and Practice, 6 (1), pp Kovács, Gy. (2014). Lean production philosophy, textbook, (in Hungarian), University of Miskolc, Institute of Logistics, ISBN: Kovács, Gy., Kot, S. (2016). New Logistics and Production Trends as the Effect of Global Economy Changes. Polish Journal of Management Studies, 14 (2), pp Liker, J. K., Lamb, T. (2000). Lean manufacturing principles guide DRAFT. Version 0.5, University of Michigan Massoud, B. L. (1999). Layout designs in cellular Manufacturing. Original Research Article European Journal of Operational Research, 112 (2), pp McLachlin, R. (1997). Management in initiatives and just-in- manufacturing. Journal of Operations Management, 15 (4), pp Miltenburg, J. (2001). U-shaped production lines: A review of theory and practice. International Journal of Production Economics, 70, pp Miltenburg, J. (2001). One-piece flow manufacturing on U-shaped production lines: A tutorial. IIE Transactions, 33, pp Womack, J. P., Jones, D. T., Roos, D. (1990). The machine that changed the world: The story of lean production. Harper Collins Publishers, New York Womack, J. P., Jones, D. T. (1996). Lean Thinking: Banish waste and Create Wealth in Your Corporation. New York: Simon & Schuster 10 NOTATION The following symbols are used in this paper: T takt = takt- [sec/unit]; T S = net available to work [work per shift: sec]; Q = customer demand [final products required per shift: unit]; N WS = required number of workstations [unit]; T total = total manufacturing cycle of a final product. 36 ACADEMIC JOURNAL OF MANUFACTURING ENGINEERING, VOL.15, ISSUE 2/2017