Bottleneck Analysis and Theory of Constraints Each work area has its own unique capacity based on the station process time required Capacity analysis determines the throughput capacity of workstations in a system A bottleneck is a limiting factor or constraint A bottleneck has the lowest effective capacity in a system

Process Times for Stations, Systems, and Cycles The process time of a station is the time it takes to produce a unit at that workstation The bottleneck time is the time of the longest process time in the system The throughput time is the time it takes for a product to go through production from start to end (assuming no waiting)

A Four-Station Assembly Line 20 min/unit 8 min/unit 15 min/unit A B C 10 min/unit D

Capacity Analysis Two identical sandwich lines Each line has two workers and a toaster to perform the three operations All completed sandwiches are wrapped Wrap 37.5 sec/sandwich Order 30 sec/sandwich Bread Fill Toast 15 sec/sandwich 20 sec/sandwich 40 sec/sandwich © 2011 Pearson Education, Inc. publishing as Prentice Hall

Capacity Analysis With Parallel Stations The bottleneck is the operation with the longest process time after dividing by the number of parallel operations The system capacity is the inverse of the bottleneck time The throughput time is the total time through the longest path in the system, assuming no waiting

Capacity Analysis Wrap 37.5 sec Order 30 sec Bread Fill Toast 15 sec 20 sec 40 sec Toast work station has the longest processing time – 40 seconds The two lines each deliver a sandwich every 40 seconds so the process time of the combined lines is 40/2 = 20 seconds At 37.5 seconds, wrapping and delivery has the longest processing time and is the bottleneck Capacity per hour is 3,600 seconds/37.5 seconds/sandwich = 96 sandwiches per hour Throughput time is 30 + 15 + 20 + 40 + 37.5 = 142.5 seconds © 2011 Pearson Education, Inc. publishing as Prentice Hall

Bottleneck Management Release work orders to the system at the pace set by the bottleneck Lost time at the bottleneck represents lost time for the whole system Increasing the capacity of a non-bottleneck station is a mirage Increasing the capacity of a bottleneck increases the capacity of the whole system Effective capacity at a station is increased by decreasing the process time.

Theory of Constraints Five-step process for recognizing and managing limitations Step 1: Identify the constraint Step 2: Develop a plan for overcoming the constraints Step 3: Focus resources on accomplishing Step 2 Step 4: Reduce the effects of constraints by offloading work or expanding capability Step 5: Once overcome, go back to Step 1 and find new constraints