Production time analysis at a ring mill

Sammanfattning: Ovako Ajax me, in York, South Carolina, USA manufactures seamless steel rings. The rings are made from blocks, which are heated, pressed, punched and then rolled to desired size and shape. Due to tougher competition on the seamless steel ring market, it is necessary to know the total production time for an order of specific rings, in order to be able to price the rings correctly and plan the production as efficiently as possible. This project establishes a model that predicts the total production time per order on one of the ring rolling lines. This general model is presented below. = n(30 + f31'CE + r32'Diameter Growth + 33' Block Weight) + S = Estimated value of the total production time per order n = Number of pieces in the order [3,, = Estimated coefficients 5 = Non productive time (set up time, adjustment time and down time) CE, Diameter Growth, Block Weight are product variables. Knowledge of the type of rings in the order also implies knowledge of the product variables. All ring types manufactured on the ring rolling line, have been divided into groups. Each ring group has its own specific set of values on the estimated coefficients and the non productive time. When it is known which ring group the rings in the order belong to, it is possible to calculate the total production time for the order. Through discussions and an Ishilcawa survey, the most significant product variables for the total production time were identified. The coefficients, [3, were established through linear regression analyses, based on data from production logs from 1992. The non productive times, 5, were analyzed separately and are in the models expressed by a mean and a standard deviation. Despite the great variance in the measured variables, we believe the result is a useful guideline for the company. During our research, some interesting facts regarding production flow were revealed. The product variable that affects the total production time the most is block weight. The induction heaters usually turned out to be bottlenecks, although they were designed not to be.