Production flow improvements : a simulation study of the Frame factory at Volvo Trucks

In Tuve outside of Gothenburg one of Volvo Trucks’ factories for final assembly is located. In the same plant the Frame factory is located, manufacturing frame sides for the Tuve assembly lines, as well as other foreign plants. Companies in the heavy trucks market have been operating in high capacity utilization for several years and the Frame factory at the Tuve plant is no exception. Customer demand is exceeding current production rate at the Tuve Frame factory and volume increases have been incremental since last major reconstruction in 2005. Shifting bottlenecks are a major issue at the Frame factory and an investigation of the production line and the planning process is requested to detect possibilities for capacity increases without major investments in new machines. The purpose of the thesis is to investigate Volvo Trucks’ frame side production line and give recommendations for controlling order releases and increasing line capacity. The goals are to define the current state of the production line and its’ constraints, develop an order release method, and to build a simulation model for testing of order release methods and examining constraint behavior. The authors examined the production line with first hand observations of the process flow and work methods. Logging statistics, process documents, time studies and interviews with personnel at the Frame factory were used as input for the empirical description, constraint analysis and simulation testing. A tool for analysis and experiments was discrete event process simulation in AutoMod™. The current state of the Frame factory is a high volume general flow shop with small buffer stocks and closely arranged resources similar to lines described under the Just-in-time ideology. Highest utilization is found in two early stations for punching and plasma cutting. The Overall Equipment Effectiveness (OEE) is close to 60 percent in both stations which show high levels of down time and speed losses. Product types with varying operating times in Capacity Constraint Resources (CCR) create shifting bottlenecks unless scheduling of order releases is leveled. Since buffers are small in the Frame factory, unleveled scheduling will risk starving or blocking CCRs which reduces throughput. Recommendations are to focus on the punching machines and the plasma cutter as bottlenecks. According to Theory of Constraints, concentrating on other resources will not increase throughput but could reduce lead time and WIP. A short setup time in the Rollformer is critical to avoid starving the punching machines. Keeping the Punching buffer stocks filled before the setup begins allows setup time variations without decreasing throughput. The largest contributor to differences in lead time, WIP and throughput is high variations in availability in CCRs. The current manual logging of machine losses cannot account for all losses at current rate and recommendations are to install automatic logging in CCRs. The product mix should be monitored to maintain a leveled workload in resources to avoid the shifting bottleneck phenomenon. Releasing orders with consideration of short term loading in CCRs gives small increases in throughput of the production line.Validerat; 20101217 (root