Home Chapter 13: Aggregate Planning Additional Case Studies

Cornwell Glass

Cornwell Glass produces replacement automobile glass for all makes of cars. Cornwell has a sophisticated forecasting system that uses data from past years to find seasonal factors and long-term trends. The system uses data from past weeks to find recent trends. The following table presents the forecasted demands for the coming year on a weekly basis.

 Week Demand Week Demand April 15 1,829 November 4 1,864 22 1,820 11 1,989 29 1,887 18 2,098 May 6 1,958 25 2,244 13 2,011 December 2 2,357 20 2,063 9 2,368 27 2,104 16 2,387 June 3 2,161 23 2,402 10 2,258 30 2,418 17 2,307 January 6 2,417 24 2,389 13 2,324 July 1 2,434 20 2,204 8 2,402 27 2,188 15 2,385 February 3 2,168 22 2,330 10 2,086 29 2,323 17 1,954 August 5 2,317 24 1,877 12 2,222 March 3 1,822 19 2,134 10 1,803 26 2,065 17 1,777 September 2 1,973 24 1,799 9 1,912 31 1,803 16 1,854 April 7 1,805 23 1,763 30 1,699 October 7 1,620 14 1,689 21 1,754 28 1,800

Cornwell uses these forecasts for its production planning. It manufactures several types of glass, and demand is aggregated across products and measured in pounds.
It is obvious from the demands that there is a great deal of seasonality/cyclicality in the demand pattern. Cornwell will need to take this into account in developing a production plan for the coming year.

Cornwell must consider the costs of hiring or firing workers; using overtime; subcontracting; and holding inventory or running out of the product. The holding cost for glass is \$.12 per pound per week. The company estimates that the cost of a late order is \$20 per pound per week late.
Cornwell currently costs out each hire at \$5.63 per pound (based on training costs and production rates per worker). It costs out each fire at \$15.73 per pound (based on unemployment compensation and loss of good will). The company currently has the capacity to manufacture 1,900 pounds of glass per week. This capacity cannot be exceeded under any plan. At most, 2,000 pounds can be subcontracted in a given week, and overtime is limited to 250 pounds per week. Glass that is manufactured during overtime costs \$8 per pound more than glass manufactured during regular time. Glass that is subcontracted costs \$2 more per pound than glass that is produced during overtime.

The current inventory is 73 units, and currently production is working at full capacity, 1,900 units. Cornwell has not been able to determine whether demands not met in the current month can be met later or whether these orders are lost.

DISCUSSION QUESTIONS

1. Find the production schedule Cornwell should follow under the various assumptions and policies, and detail the differences among these schedules.