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김근표,박창순 중앙대학교 통계연구소 1997 統計論文集 Vol.- No.4
공정관리는 크게 통계적 공정관리와 자동공정관리로 나뉠 수 있다. 본 논문에서는 공정조정을 목적으로 하는 자동공정관리의 피드백 조정 중 일반적으로 사용되고 있는 IMA(0,1,1) 잡음모형에 대하여 각 평활계수 λ의 변화에 다른 목표치로부터의 손실을 모의실험을 통하여 제품의 조정비용과 검사비용 그리고 목표치로부터의 제곱편차로 이루어진 손실함수식에 접합시킴으로써 공정의 한 생산 주기동안 발생되는 기대 비용을 최소화할 수 있는 최적의 공정에 대하여 연구하였다. Process control can be categorized into two fields, statistical process control(SPC) and automatic process control(APC). The objective of APC is to adjust the process while SPC is to monitor the process. A feedback adjustment of APC is considered in this paper. We consider a bounded adjustment scheme where the inherent disturbance occurring during production is expressed as an IMA(0,1,1) process. The bounded adjustment scheme adjucts the process when the deviation from target exceeds the boundaries. The expected cost per unit interval of the scheme is expressed in terms of the sampling cost, the adjustment cost, and the mean squared deviation from target. The mean squared deviation from target is approximated for various values of the smoothing parameter λas a function of the sampling internal, the adjustment interval, and the boundaries by using simulations. The performance of the approximation is compared to results of Taguchi and Woodall. It is shown that our method is better than Taguchi's and Woodall's in approximating the cost per unit interval. The approximation method seems to be useful in calculating the cost per unit interval although it is getting worse as the smoothing parameter decreases. The approximation is improved by correcting the expectation of the reciprocal of the adjustment interval for small values of the smoothing parameter. Finally, we find the optimal process parameters, such as the sampling interval and the boundaries, which minimize the cost per unit interval occurring between adjustments.
High Energy Ball Mill에 의해 제조된 75w-25Cu 의 치밀화 거동에 관한 연구
이성,송흥섭,노준웅,홍문희,김근표,김용우 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.2
Solid and liquid phase sintering behaviors of ball-milled 75W-25Cu have been studied by using a dilatometry technique. The ball-milled 75W-25Cu was prepared by high energetic ball milling under argon atmosphere of 1 atm with duration times of 50 to 400 hrs. The sintering was performed in the dilatometer under flowing hydrogen atmosphere with a heating rate of 3℃/min. To compare with the ball milled 75W-25Cu, blended 75W-25Cu was also prepared and sintered. Sintering shrinkage, dl/1, increased with increasing milling time from 50 to 400 hrs. The shrinkage versus temperature plots of the ball-milled 75W-25Cu can be divided into three regions, while for that of the blended 75W-25Cu two regions. The characteristics of ball-milled 75W-25Cu were analyzed by energy dispersive spectroscopy (EDS), differential scanning calorimeter(DSC) and scanning electron microscopy (SEM). The considerable grain growth of W particles was observed during the liquid phase sintering of the ball-milled 75W-25Cu. From these results, the solid and liquid phase sintering behaviors were discussed in terms of the size, the stored energy, and the distribution of W and Cu particles embedded in the ball-milled 75W-25Cu composite powders. (Received August 18, 1992)