Application of Lean Production Concept in Organisation of Gear Wheels Manufacturing

Transcription

1 Application of Lean Production Concept in Organisation of Gear Wheels Manufacturing Legutko Stanislaw; Staniszewski Maciej; Legutko Zygmunt Abstract: The purpose of the paper is to show the advantages of applying lean manufacturing as exemplified by an enterprise making gear wheels. The basic assumptions of the concept, an example of modified production process are shown in the paper, as well as profits obtained as the result of the modifications. Key words: lean manufacturing, gear wheels, production process 1. INTRODUCTION The word lean, when referring to a human figure, means slimness and adaptation. When referring to manufacturing systems, the word denotes slimming of production in respect of the necessary material resources, maintained reserves of ready-made products and running production, as well as the used room of the production halls. The term Lean Manufacturing (LM) describes production systems with significant degree of slimming as compared to the traditional ones, existing in most enterprises of mass production. The name itself has been invented by the scientists of the Massachusetts Institute of Technology in Boston: James P. Womack, Daniel T. Jones and Daniel Ross. It was first used in their work, The Machine that Change the World published in The work was a result of a survey of the world automotive industry within the international program named International Motor Vehicle Program. Comparing the parameters of investments and results in Japanese, American and European enterprises, they have stated the prevalence of Japan. Among Japanese firms, was Toyota Motor Corporation with its system called Toyota Production System. Toyota s system of production is known as the first slimmed manufacturing system and that is where the roots of LM should be sought. According to Womack and Jones, slimmed production gives the possibility to produce more and more using less and less less human effort, devices, time and room, while getting closer to the target which is providing the customers precisely what they want. This is possible due to reorganization of all the actions of the enterprise: the sequence of the design, administrative and execution operations, organization of material resources, machine functions and human actions [2]. The method rests on three pillars: Total Quality Management, Just in and transparency of the production state. 44 The most important objective of Toyota Production System and the slimmed production is elimination of wasting, that is all that increases the cost of production without contributing any useful input to it. TPS names 7 kinds of losses: overproduction producing more than necessary or too early; unnecessary traffic surplus traffic due to bad organization of working stands; waiting long idling periods of people, machines, parts, materials; unnecessary transport relocation of elements, parts, semi products, products more often than necessary; reserves too much materials in the production process, too many ready made products; defects refers to both products and documentation, supplies, information; surplus machining execution of unnecessary steps in the process of machining [1]. In Poland, it is considered that the best way of cost reduction is to use the scale effect or to reduce employment while maintaining the process proceeding used so far. Looking at the state of Polish enterprises one can see that the methods are not effective and meet strong objections of the employees who have to work more productively under the same working conditions. It is obvious that a man has limited production ability and is not able to perform an unlimited of actions in a unit of time and the faster he works the more mistakes he makes. Hence the problem of meeting the customers requirements and orders under the circumstances of strongly limited resources. One of the solutions of the problem is a closer look at the production processes, actions performed in them and methods used in their realization. In them one should seek the possibilities to cope with the challenges of the market and difficult economic situation of enterprises. The first step to introduce the Lean Manufacturing concept in the enterprise under discussion was the analysis and modification of the production process.

2 2. DESCRIPTION OF GEAR WHEEL MACHINING METHODS IN THE ENTERPRISE UNDER DISCUSSION Gear wheels are the most common and cheapest mechanisms of driving transmission. The common use has resulted in that various methods of forming the toothing have been created. The selection of the machining method depends on the required execution accuracy and the production scale. The technological process of toothing machining depends on the kind of production and the destination of the gear wheels. Machining of gear wheels in the soft state, i.e. ones with the hardness of about 3-4 HRC is applied to remove excess material while leaving allowance for finish machining. There are two major methods of cutting gear wheel teeth: forming and orbital [3]. Figure 1 shows the methods used in the enterprise under discussion to obtain toothing inside a gear wheel. Fellows method, pull broaching and chiselling are used in series production, roller gear shaper milling, on the other hand, in manufacturing single wheels in tool-rooms. Fig. 1 Methods of forming gear wheels with internal toothing used in the enterprise under discussion It should be pointed out, however, that only pull broaching id applied as finish machining. The other methods only give the initial shape to the teeth which obtain their ultimate dimensional and shape accuracy during further machining on grinding machines. 3. COMPARISON OF A SELECTED TECHNOLOGICAL PROCESS PRIOR TO AND AFTER MODIFICATIONS The two technologies of manufacturing straight gear wheels differ in the time of the process duration (table 1 and 2). Table 1. The process of part manufacturing according to the technology used so far distribution room Preparation 2 1,3 Injector cleaner Cleaning 5 Saw Cut-off 25,3 Polisher Precleaning 1 distribution room Preparation to the transport 21 Interoperational check Check 15 8,6 Tug-4 Turning 215 Conservation 2,5 Marking Marking 22,8 Dot peen marking Marking 25 2,85 Tug-4 Turning 295 5,5 Okuma CNC turning 3 Hanson 31 2,9 Dot peen marking Marking 35 2,25 Furnace Hardening 32 2,11 Heald rotary Grinding 4,25 Washer Washing 325 4,61 Toyoda Grinding 45 2,25 Furnace Tempering 33 4 Mikron Milling 5,3 Sharpening machine (ds-25) Precleaning 332 2,1 Fadal Milling 55 Interoperational check Check 335 1,64 Ironworker s shop Ironworker s 6 1 Cleaner (dcm-89a) Cleaning 34 7,87 Heald Special grinding 65 Conservation Opal Teeth grinding 7 5,4 Okuma CNC turning Kapp Teeth grinding 75,5 Marking Marking 36 9,47 Ironworker s shop Ironworker,s Hanson 45

3 8 3,2 Okuma CNC turning 37 Magnetic check Magnetic check Washer with rotary table 9 Copperizing 38 Surface condition check Etching 95 3,4 Toyoda Grinding 385 Washer with table of (dt 4x48e-2) 1 3,65 Liebherr Milling of toothing 39 2,4 Drier Seasoning 11 14,9 Pfauter Milling of toothing 395 2,1 Bore blast Stream processing 15 3,52 Ironworker s shop Ironworker s 4 Washer with table of (dt 4x48e-2) 11 Hanson Mycie wg instr Check Final check 115 C Check 42 4,2 Fassler Teeth honing 12 Copperizing II 425 Washer (jumbo) 123 Chemical purification 43 Chec Final check ,3 Injector cleaner Cleaning 435,8 Dot peen marking Marking 13 Interoperational check Check 44 Preservation acc. to instr ,75 Furnace Carbonizing 49 Preparation 14,2 Marking of samples Marking of samples 495 Washer (jumbo) Preservative removal 145 Copperizing of samples 5 Washing - line Washing 15 Furnace Samples heat treatment 55 5,2 Press Ironworker s -assembly 155 Interoperational check Check 51 Washer (jumbo) 16 Copper plating removal 515 8,43 Weiler Turning of special sleeve 165 1,3 Injector cleaner Cleaning 53 3,7 Dot peen marking Marking 17 Copperizing 535 Washer (jumbo) 175 1,87 Furnace Hardening 54 Check Check 18,25 Washer Washing Corrections Iroworker s 185 2,25 Chamber Sub-zero treatment 55 Preservation acc. to instr ,25 Se l11 Low tempering 555 Packing 195 Cooperator Copper plating removal Table 2.The process of part manufacturing with the application of lean production elements Preparation 335 9,9 Heald Special grinding 5 4,2 Saw Cut-off 34 2 Heald rotary Grinding 1 Preparation for transport Opal Teeth grinding 7 5,4 Okuma CNC turning Kapp Teeth grinding 75,5 Marking Marking 36 9,5 Ironworker s shop Ironworker s 8 3,2 Okuma CNC turning 365 Hanson 85 Hanson 37 Check (h81) Magnetic check 46

4 9 Cooperator Copperizing ,7 Liebherr Toothing milling ,5 Ironworker s shop Ironworker s 385 Washer with rotating table Surface condition checks sti(ceim-5) Washer with rotating table Etching 11 Hanson 39 2,4 Drier Seasoning 125 1,3 Injector cleaner Cleaning 395 2,1 Bore blast Stream processing 13 Interoperational check check 4 Washer with rotat. table 135 3,8 Furnace Carbonizing 42 4,2 Fassler Teeth honing 14,2 Marking of samples Marking of samples 425 Washer (jumbo) 15 Furnace Heat treatment of samples 43 Check Final check 155 Interoperational check Check of samples 435,8 Dot peen marking Marking 175 1,9 Furnace Hardening 44 18,3 Washer Washing 49 Work preparation In Preservation acc. to instr Preparation 185 2,3 Chamber Sub-zero treatment 495 Washer(jumbo) Preservative removal 19 2,3 Se l11 Low tempering 5 Washing - line Washing 195 Cooperator Copper plating removal 55 5,2 Ironworker s press Assembly 2 1,3 Injector cleaner Cleaning 51 Washer (jumbo) 25,3 Polishing machine precleaning 515 8,4 Weiler Special sleeve turning 21 Interoperational check Check 53 3,7 Dot peen marking Marking 295 5,1 Okuma CNC turning 535 Wsasher (jumbo) 35 4 Mikron Milling 54 Check Check 31 1,6 Ironworker s room Ironworker s Corrections Ironworker s 32 3,7 Dot peen marking Marking ,6 Grinding machine (s4) Grinding 555 Preservation acc. to instr Packing The major difference of the two technologies of manufacturing the same part presented here is the elimination of some elements of the technology, which has significantly reduced the time of manufacturing the given gear wheels. The reduction resulted from the change of the material of which the wheel is made and from the elimination of unnecessary technological operations which had increased the cost of the wheel manufacturing. The operations eliminated from the process were grinding, second copperizing and the first checking operations. Elimination of grinding and copperizing from the manufacturing process, as very energy and time consuming operations, has allowed to shorten the production process from 63 to 51 working days. The elimination of these two operations has necessitated designing of new machining fixtures and modernization of the existing ones. According to the technology used so far, the parts were coated with copper all over and the surfaces from which copper was removed, were most often ground. In the new technology the copper coated surfaces are much reduced and, consequently, some operations could be given up in manufacturing of those parts. Another profit from the new manufacturing process is the economical aspect. The cost of production has been reduced in this way. The money saved allowed the part prices to be maintained at the same level although, generally, they have brought great profit to the firm. However, the new technological concept has brought problems which had to be solved. First of all, new mandrels necessary in the process of copperizing had to be designed and executed. The other task imposed to the process engineers was to select adequate materials of which the parts are made. Collaboration of all the team created for the introduction of lean production principles has made quick introduction of the necessary processes and principles of the concept. 47

5 4. ADVANTAGES The data in table 3 and in Figure 2 show the actual time of gear wheels production in the period of four subsequent s. At the moment, the of working days necessary to make the parts is 51. Emphasis is still put on the part manufacturing time reduction to obtain a result below 48 days. Table 3. Comparison of part execution time according to the old technology and according to the new one Number of days necessary to make Quarter 1 Quarter 2 Quarter 3 Quarter 4 one serie Part execution time acc. to the old technology Part execution time acc. to the new technology old technology new technology 5. CONCLUSIONS Fig. 2. Graphical image of part manufacturing cycle reduction [time in days] Introduction of only several elements of the lean production concept has brought much profits. Those include not only the economical profit (large sums of money saved), but also the profit originating from the production sphere. Reduction of the part manufacturing time from 65 days down to 51 working days has improved and strengthened the enterprise s position in the market of spare part suppliers. The enterprise has become more elastic and competitive. Another important aspect of introducing the lean production concept was reduction of the of errors and, consequently, the of claims concerning the parts made by the enterprise. However, one cannot confine oneself to the production process modification alone. Further steps will be: optimization of machines location in the production line, improvement of part transfer in a department, introduction of KAIZEN and TQM, adaptation of warehouse handling to the JIT concept. REFERENCES [1] Taiichi, O., (1998). Toyota Production System. Productivity Press Inc., New York. [2] Womack, J.; Jones D., (21). Slimming of firms. Elimination of wastage a key to success. Manager Information Centre, Warsaw. [3] Wójcik, Z., (1991). Toothing machining. Engineer s handbook, WNT, Warsaw. 48 Authors addresses: Stanislaw Legutko Prof. DSc. PhD. MSc. Eng., Prof. h. c. Faculty of Mechanical Engineering and Management Poznan University of Technology 3 Piotrowo street, Poznan, Poland stanislaw.legutko@put.poznan.pl Maciej Staniszewski MSc. Eng. Faculty of Mechanical Engineering and Management Poznan University of Technology 3 Piotrowo street, Poznan, Poland maciejstaniszewski@op.pl Zygmunt Legutko MSc. Eng. 22 os. Wichrowe Wzgorze street, Poznan, Poland legutko@gmail.com Contact person Stanislaw Legutko stanislaw.legutko@put.poznan.pl