A SMULATON STUDY OF QUALTY NDEX N MACHNE-COMPONF~T GROUPNG By Hamd Sefoddn Assocate Professor ndustral and Manufacturng Engneerng Department Unversty of Wsconsn-Mlwaukee Manocher Djassem Assstant Professor Department of ndustral Studes Unversty of Wsconsn-Plattvlle ABSTRACT Smulaton modelng s employed to determne the effectveness of qualty ndex n screenng machne-part matrces for the development of cellular manufacturng systems. NTRODUCTON Cellular manufacturng s the organzaton of producton nto ndependent manufacturng unts called "machne cells." A machne cell has the capablty of processng a range of parts (part-famly) wth smlar manufacturng requrements. Ths reduces the need for formaton of lots of large szes for achevng the economy of scale. Consequently, cellular manufacturng systems are more effcent and provde more flexblty n respondng to consumers demand [2,6,7,9]. The man data for machne cell formaton s organzed n a machne-part matrx wth one/zero entres representng presence/absence of operatons on machnes. A machne-part matrx s converted nto a block dagonal form before t s used for the development of a cellular manufacturng system. n the block dagonal form, one entres are concentrated nto blocks along the dagonal of matrx representng the machne-component groups. The structure of a machne-part matrx has a great mpact on the performance of the correspondng cellular manufacturng system [3]. To evaluate the block dagonal machne-part matrx for the development of cellular manufacturng systems, a number of groupng measures have been developed [3,8]. Among these measures, qualty ndex (Q) s more effectve n evaluatng the performance of a cellular manufacturng system based on ts machne-part matrx [8]. Q s based on the data n the machne part matrx, the producton volume of parts n the product mx, and the processng tmes of manufacturng operatons.
v Create Part Demand, Arrval of Pm~s to "Enter SUtton" dentfy Part Famly Membershp, Machne Cell Assgnment Request a Ctrt, Transfer Arrvng Batch to Frst Machne ~,~.1 Free the Cart/Operator, Wat n Machne's Queue Seze the Operator and Release After Setup Tme Seze the Machne, Start the Operaton, Assgn Setup Tme of Next Part n Queue,... them.chne Compute Effcency Measures "EL" Pcked by Operator ntra-cell Transfer to Next Machne n Cell Compute Move Tme.mf SextMove7 J-" ntertcell k Watng for Other Batch Members Request a Cart Transfer the Batch to Next Cell, Compute Move Tme & Number of Moves NO [ Last Operaton7 Yes Collect Statstc! Ext System ] 4 Prnt Summary Reports and Data Fles Fgure 1. Flow Chart of the Procedure for Performance Evaluaton
n ths paper, smulaton modelng wll be used to determne the effectveness of Q n screenng the machne-part matrces for the development of cellular manufacturng systems. DEFNTON OF THE PROBLEM Though cases of successful mplementaton of cellular manufacturng systems are numerous, the converson from job shop to cellular manufacturng may not always result n hgher productvty. Some studes show that the converson from job shop to cellular manufacturng leads to longer watng lnes, hgher-n-process nventores, and lower machne utlzaton [1,5]. Therefore, pror to the development of a cellular manufacturng system, t s necessary to evaluate the manufacturng system for determnng ts sutablty for cellular manufacturng. Q has been specfcally developed to evaluate manufacturng systems based on ther block dagonal machne-part matrces. A smulaton study by authors show that Q s the most consstent groupng measure n predctng the performance of a cellular manufacturng system based on the structures of ts block dagonal machne-part matrx. Therefore, ths measure can be used to quantfy the characterstcs of a machne-part matrx. Snce Q s only a measure of the qualty of the machne-part matrx, t s necessary to evaluate the performance of the cellular manufacturng system before and after converson to cellular manufacturng to determne ts effectveness. SOLUTON METHODOLOGY The flow chart of the procedure for the comparson of job shop and cellular manufacturng systems based on Q and smulaton modelng s presented n Fgure 1. The detaled descrpton of the model, ts nput, and ts output s gven n reference [4]. The procedure ncludes three mportant functons as lsted below. 1. Formaton of machne-component groups 2. Calculaton of Q for machne-part matrces 3. Performance evaluaton of manufacturng systems under job shop and cellular manufacturng. The machne-part matrx and other detaled data on manufacturng systems used n ths study are gven n reference [4]. The smulaton results for two extreme values of Q, 0.68 and 1.0 are gven n Tables 1 and 2. Table 2. Smulaton Results for Q =.68 Type of Mean Flow Mean Mean WP Manufacturng Tme Setup (parts) Systems (hours) Tme % Mean Operator Productvty Parts/Shft Job Shop 128 3.02 19.9 3.17 Cellular Manufacturng 154 4.71 5.4 3.40
Table 3. Smulaton Results for Q = 1.00 Type of Mean Flow Mean Mean WP Manufacturng Tme Setup (parts) System (hours) Tmes % Mean Operator Productvty Parts/Shft Job Shop 82 2.96 18.8 3.48 Cellular Manufacturng 66.3 2.13 3.9 3.94 As can be seen, an ncrease n the value of Q leads to substantal mprovement n the performance measures for the cellular manufacturng system. CONCLUSON The evaluaton of block dagonal matrces provdes useful nformaton on the sutablty of a manufacturng system for converson to cellular manufacturng. Q s an effectve groupng measure for the evaluaton of machne-part matrces. Smulaton modelng serves as an effectve tool for performance evaluaton n the development of cellular manufacturng systems. REFERENCES [1] Ang, C. P., Wlley, P. C., "A Comparatve Study of the Performance of Pure and Hybrd Group Technology Manufacturng Systems Usng Computer Smulaton Technques," nt. J. Prod. Res., ol. 22, No. 2, pp. 193-233, 1984. [2] Burbdge, J., "Change to Group Technology: Process Organzaton s Obsolete," nt. J. Prod. Res., ol. 30, No. 5, pp. 1209-1220, May 1992. [3] Chandrasekharan, M. P. and Rajagopalan, R., "Groupablty: An Analyss of the Propertes of Bnary Data Matrces for Group Technology," nt. J. Prod. Res., ol. 27, No. 6, pp. 1035-1052, 1989. [4] Djassem, M., "The Use of Machne-Groupng Effcency n Comparson of Job Shop and Cellular Manufacturng Systems: A Smulaton Study," Unpublshed Ph.D. Dssertaton, 1994, Department of ndustral and Manufacturng Engneerng, Unversty of Wsconsn-Mlwaukee. [51 Flynn, B. B. and Jacobs, F. R., "A Smulaton Comparson Group Technology wth Tradtonal Job Shop Manufacturng," nternatonal Journal of Producton Research, 1986, ol. 24, No. 5 pp. 1171-1192. [6] Hyer, N. L., "The Potental of Group Technology for U. S. Manufacturng," J. of Operaton Management, ol. 4, No. 3, pp. 183-201, 1984. [7] Hyer, N. L., Wemmerlov, "Group Technology and Productvty," Harvard Busness Revew, July/August 1984.
[8] Sefoddn, H. and Djassem, M., "Analyss of Effcency Measures for Block Dagonal Machne-Component Charts," 16th nternatonal Conference on Computers and ndustral Engneerng, Ashkaga, Japan, 1994. [9] Wemmerlov, U. and Hyder, L., "Cellular Manufacturng n the U. S. ndustry: A Survey of Users," nt. J. Prod. Res., ol. 21, No. 9, pp. 1511-1530, 1989.