New metrics and scheduling rules for disassembly and bulk recycling

In recent years, growing quantities of end-of-life electronics have increased the amount of attention devoted to product recovery. Research on end-of-life electronics returns has primarily focused on manual disassembly operations. In this paper, we focus on the scheduling problem for a facility with staging, manual disassembly operations, and bulk recycling. In bulk recycling, shredding or grinding reduces the size of the material fragments while magnetic, eddy current or other density separation techniques separate the material fragments. Unlike production, there are often no due dates in materials recovery processing. Recyclers can sell the recovered materials to material commodity buyers at any time. However, recyclers wait to accumulate a shipment of material to reduce transportation costs and meet minimum sales quantities. Another important difference between production and recycling is that manufacturers purchase raw materials while recyclers may be paid to receive products. When due dates do not apply to scheduling products for materials recycling and product receipts generate revenue for recycling services, we propose two new metrics: the staging space turnover and the shipment fill time. We use our metrics to analyze new scheduling rules for disassembly and bulk recycling and to evaluate their performance. Using discrete-event simulation models, we test our scheduling rules on seven product families, where product families are defined based on material composition and separation operations. Of the rules we test, the disassembly scheduling rule which ranks product families based on the ratio of product size to disassembly time (SDT) most quickly empties the staging space. Shipment fill time is less sensitive to our scheduling rules. Our results illustrate how a recycler can reduce incoming product inventory with a new scheduling rule.