Development of a suitable manufacturing system for developing country.

Park, Hong Seok ; Mun, Si Hwan ; Choi, Hung Won 等

1. INTRODUCTION

Recently, the latest automobile industry has unfavorable conditions of cost and customers' demand. To survive in global market environment with such conditions, opening up new markets is very important for manufacturers. Therefore, fufillment of quality and cost competition are very important factors to obtain competition in a new market opened up. Automobile enterprises are trending to transfer technologies to developing countries due to lower cost. There are not same conditions in different countries. So, it is difficult to expect the same goals of productivity and economical efficiency in different countries.

To develop the optimum manufacturing system under any production conditions, various studies are carried out. Specially, studies that search problem of current manufacturing systems and develop new manufacturing systems using 3D virtual simulation of Digital Manufacturing technique are becoming salient issues recently.

Jayaraman and Agarwal (1996) introduced the method that designs factory of automobile engine for processing and assembly efficiently. The method simulates main parts processing system (Micro Level Simulation), then it simulates whole engine factory (Macro Level Simulation).

Jayaraman and Gunal (1997) used simulating problem solution method for buffer operation between special quality and process of engine assembly line when designing automobile engine assembly process and Park et al. (2002) presented operation strategy using virtual automobile body shop. The operation strategy prevented expected problem beforehand analyzing material flow before building a factory.

However, creating alternatives to use a heuristic algorithm is still on study until now. This algorithm has problems that a lot of time and expenses are invested and improvements appear only in some parts of system, not the whole.

To solve this problem in this paper, Transmission gear processing factory builds in overseas to construct optimal Transmission gear processing factory in early time without consumption of needless capital and time is developed logically. Moreover, we also used Thinking Process of TOC (Theory of constrains), 3D Simulation of digital Manufacturing methodology to achieve our goals.

2. CURRENT PROCESS ANALYSIS

In order to have most suitable model of automobile transmission manufacturing systems in developing countries we should analyze the current manufacturing system first. We analyze the products whose the same (or similar) material flows processes and analyze the same operations. However, processing time of the same operations is different due to the difference in the dimensions and the shape of the products.

The specifications of each gear processing line to produce other items are 2 kinds. This is according to the schedule for each machine tool. In addition, the processing gear up for the process, because most of the cutting process perform an operation based on the life cycle of Tool and Tool must be changed. The cycle of changing machine tool for each process will be applied differently. In addition, each of the standards process to determine the actions that were in process, the flow of logistics, equipment and tools with the distance, loading/unloading of stock, the worker can bring in and sequence of the overall process. Based on sequence of a defined process and the cycle time, work, latency, machine broken rate, waste, and 4M (Material, Machine, Man, and Method) analysis of the process and time is defined as constraints. That is the basis for 3D virtual simulation.

[FIGURE 1 OMITTED]

3. DEVELOPMENT STRATEGY AND METHODOLOGY

There would be many problems when we apply the current manufacturing system to developing countries, by using Effect-Cause-Effect analysis we pointed out all the problems and solved them with methodology of Thinking Process, which is one of the methods of TOC (The theory of constraints) and its tool -Logical Tree. With Logical Tree, we could find out the objective and logical optimum solution.

The first phase of Logical Tree was used to define all the problems when applying the current system to developing countries. The problems were called UDE (Undesirable Effect). UDE defined based on the core problem of manufacturing system was solved to find out the developing countries' unreasonable manufacturing system. Next, CRT (Current Reality Tree) was also used to point out the causal relationship in the UDE.

EC (Evaporation Cloud) resolve core problem in order to find out the antagonistic relationship between alternatives so that we could have the most appropriate solution. And we decided to change the automation level of production system according to the analysis of product volume. To take full use of manpower, the automatic conveyor must be removed and then the system used worker to put items in the machines and take them out from the machines. Moreover, transporting items from one station to the other was also done by manpower. Such a system was called Manual one. On the contrary, in Automatic system, all the above works were done by automatic machines. Both of Manual system and Automatic one are not suitable for developing countries and our task was to determine the most appropriate automation level for the new system.

The new system is not neither Manual system nor Automatic one; it could be called semi-automatic system. In this system, the Loading / Unloading items processes were done by automatic machines, otherwise the Transporting items processed were done by workers. A batch of items for each time of transportation had 10 items. In semi-automatic system, however, the production capacity is only 65.1 UPH, which is lower than the production requirement- UPH 67. Due to the using more workers in all processes, especially in moving parts from one station to the other, the total processing time increased. That resulted the UPH of the semi-automatic system did not fulfill the requirement of 67 UPH.

Otherwise, Automatic and Manual systems also had low machine utilization in Deburring processes. And this problem still existed in the semi-automatic system. Semi-automatic system, however, had an advantage that the automatic did not have. In automatic system, if one station had to stop for any reason, all the other had to stop also. In a working day, the average stop time in the entire line is 1 hour and 30 minute, but in the semi-automatic system, it was only 11 minutes. Additionally, blocking situation took 1 hour and 20 minutes per day on average, but it was 0 in the semi-automatic. With Evaporating Cloud diagram we had found out the solution, Semi-automatic system, but it was not the optimum one.

4. MANUFACTURING SYSTEMS DEVELOPMENT FOR DEVELOPING COUNTRIES

So, we changed to another tool to find the optimum solution, it were Logical tree of Future Reality in Thinking process.

In Semi-automatic system, blocking situation maintained a low rate of machine utilization in Deburring process. After analyzing Deburring station ability, we decided to eliminate some machines in Deburring process. Because the processing time of Deburring process is lower than all the others, there were up to 2 hours of idle time on Deburring process per day. As said in the above, we had to eliminate some machines in Deburring process in order to increase the machine utilization. Then, we had to determine how many machines to be eliminated exactly.

After eliminating one machine at Deburring process, one item would be processed on 2 different lines. And then, the system became mixed process manufacturing system. However, the mixed production happened at only Deburring process. As we had known, the number of machines had been reduced by 1, but we still kept the number of workers. So, we would build a new production plan. At Hobbing station, each different type of items was processed on one different machine, but at Deburring station one machine would process 2 different types. Namely, speed gear number 1 and number 2 would be processed on one Deburring machine; similarly, speed gear number 2 and number 3, speed gear number 3 and number 4, Speed Gear number 4 and number 5. We must be aware that there was time of changing tools before changing to process the other types. And in our process scheduling, the time of changing tool was taken into account. Therefore, at Deburring stations the time of changing tools had been added

[FIGURE 2 OMITTED]

Thanks to all the improvements on the above, the machine utilization ratio of Deburring process was improved to 81.28% and the one of the entire line was 78.4%. The values were significant improvement if we put them in comparison the values of the semi-automatic system, 63.32% and 76.0%, respectively. As a result, the mixed process system had 37 units/day more than the capacity of the semi-automatic system. Namely, the capacity of the mixed process system was 1209 units/day, and it satisfied our target.

In addition, due to the characteristics of mixed process system, we had to use 10 workers (higher than 7 of automatic manufacturing system); the worker utilization ratio was 85.63%, which was also higher than 70.43% of automatic manufacturing system. This result met our goal of maximizing the use of manpower. Therefore, due to the reduction of 1 machine at Deburring station, it was not only that the machine utilization ratio had been improved, but also we got cost effective

5. CONCLUSION

In this study, we had used Logical Tree of Thinking Process in Theory of Constraints to solve a problem in automobile transmission manufacturing system. Also, we used 3D virtual simulation technique to get out the problem and analyze the current system. And the solution came out based on the objective-oriented analysis. After building mixed process semi- automatic manufacturing system, we used the 3D virtual simulation method to get the results of the system working. There was only the output/day of the new system that was not better than the automatic system's, the output/day still satisfied our goal. All the others were better than the automatic system's. The main problem which had happened at Deburring station was also solved clearly. The solvent also gave us cost effective.

6. ACKNOWLEDGEMENT

This research was supported by the Ministry of Knowledge Economy, Republic of Korea under the development program of regional industry technology.

7. REFERENCES

Jayaraman, A. & Agarwal A. (1996). Simulating an Engine Plant, Manufacturing Engineering, 117/5, 60-68

Jayaraman, A. & Gunal, A. (1997). Applications of Discrete Event Simulation in the Design of Automotive Power train Manufacturing Systems, Winter Simulation Conference, 1/1, 758-764

Park, Y. J.; Shin, H. S.; Chung, K. H.; Hong, S. W. & Noh S. D. (2002). Material Flows Analysis and Storage Plans Evaluations by Virtual Automotive Body Shop, Conference Proceedings of KSAE, 1/1, 1005-1010