Cecil Rice Export operates a facility in Alexandria, Egypt, where bulk white rice is bagged for export in 70-pound grain bags. The bagged rice is then palletized and brought by truck to a quay in the harbor and loaded onto a break-bulk ship for transport to foreign customers.
Cecil Rice Export has experienced good growth in the past decade due to a concentration on continuous improvement and Lean techniques. It has gained an enviable reputation for being a lowcost, high-value supplier. This growth has led to the need to increase capacity by expanding the number of shifts at Cecil Rice Export’s facility. In 2005, it operated only one shift, from 08:00 to 16:00. In 2007, a second shift was added, and the facility operated from 04:00 to 20:00, switching shifts at 12:00. Since the start of 2009, the company has increased to three shifts, operating from 00:00 to 08:00, 08:00 to 16:00, and 16:00 to 00:00. As these shifts were added, most of the more experienced employees, due to their seniority, chose to remain on the day shift. Those originally on the second shift added in 2007 (at that time the 12:00 to 20:00 shift) mostly moved onto the 16:00 to 00:00 shift. Those on the shift added in 2009, the greenest shift, were therefore left with the 00:00 to 08:00 shift. As the new shifts were added, some senior personnel were assigned to the new shifts to break in the new workers. Eventually, these experienced hands returned to their preferred day shift. Traditionally, working bonds between shift members have resulted in a good amount of cohesion in the workforce, and shift members are usually quite averse to changing shifts.
Rice is delivered to the Cecil Rice Export facility and stored in a silo. From the silo, an air-powered transport system moves the grain to the hopper of the bagging machine. The bagging machine fills bags from the hopper to a specific weight, 70 pounds, and past records indicate that the mean is in fact 70.0 pounds, with a standard deviation of 1.0 pounds. This machine, however, is very sensitive and must be calibrated by trained personnel. In the past, this was not a problem due to the experience of the personnel in the original production shift. As shifts were added, there was no effort to examine whether the weight of the bags remained within acceptable limits. Recently, during the loading of the pallets on the merchant ship, the ships’ officers have detected abnormalities in the pallets. The pallets are loaded with 30 bags each, for a presumed weight of 2,100 pounds. When confronted with abnormalities, plant management initially suspected the bagging operation, specifically over- or underweight bags. Both under- and overweight bags are undesirable from the firm’s point of view. Overweight bags decrease Cecil Rice Export’s revenue as product is given away in the overage. Underweight bags, on the other hand, present a customer service issue. Cecil Rice Export’s customers have come to expect bags to have a proper weight and are disappointed when the bags are underweight. For these reasons, over- and underweight bags are equally undesirable. The table shows the minimum, maximum, and average from hourly samples of five bags per hour, taken over 3 days.
1. What control charts should be used to determine whether the process is in control or out of control?
2. Develop a control chart for each shift. Does there appear to be a difference between the shifts?
3. Cecil Rice Export is planning on providing incentives for senior personnel to rotate into other shifts to better mix personnel among the shifts. If the same control charts were used for all three shifts, what would be the control limits of these charts?