A methodology for Calculating Manufacturing Velocity and Evaluation of a Bucket Brigade System for PDL

MANAGEMENT SCIENCE HONOURS PROJECT 2001

Tsung-Han (Hans) Chang and Darren Pat

PDL Industries Ltd. has the goal of obtaining Class A certification on the 8th of November 2001.One of the Class A requirements is the ability to measure manufacturing velocity. This University of Canterbury Management Science Honours Project has the task of developing a velocity methodology for PDL. The specific project aims are:

1)    Develop a methodology that defines how to measure manufacturing velocity so that PDL can achieve Class A MRP II certification.

2)    Adapt the methodology so that it can be applied outside of manufacturing.

3)    Evaluate the viability of implementing a Bucket Brigade system on PDL’s current assembly line. 

The Velocity Methodology

Graphical Representation of a Process Velocity
 

Manufacturing Velocity Defined

Actual Manufacturing Velocity  (Value Added Time/Total Throughput Time)x100%
= Manufacturing Efficiency 

Value Added Time = The processing time of operations that increase the income to the manufacturer.

Total Throughput Time = Starts counting when materials are checked out of the main store and stops when the finished parts are checked into the main store. (Over business hours only)

Planned Manufacturing Velocity (Planned Value Added Time/Planned Total Throughput Time)x100%

Data for the planned total throughput time and planned value-added time can be gathered from the MRP II database. The planned total throughput time is the planning duration of the operation. The planned value-added time is the sum of the process times stored in the database.

The ability to calculate manufacturing velocity is not enough to acquire the Class A MRP II certification. A comparison is made between the actual and planned velocity for each operation to determine if they are within 5% of each other. The 5% variation is the threshold set by the Oliver Wight organisation. If the variation is greater than 5%, then Class A certification may not be given.

What is a Bucket Brigade Assembly Line?

“Bucket Brigades are a way of coordinating workers who are progressively assembling product along a flow line in which there are fewer workers than stations.It coordinates the worker so that they move to where the work is, and it emphasizes teamwork rather than advanced technology”

Bartholdi & Eisenstein (1995)

We proposed bucket brigades as a way of improving throughput on one of PDL’s assembly lines. Bucket brigades are consistent with Oliver Wight’s ABCD checklist for manufacturing velocity; they are also at the manufacturing forefront at Christchurch outdoor clothing company, Macpac; and bucket brigades remedy the chaotic product flow of the existing assembly line.

7 Machine / 3 Worker Bucket Brigade
7 Machine/3 Worker Bucket Brigade

In the figure above, one can see the linear flow of product between machines. Workers move up and down the assembly line while remaining between the workers either side of them. Machines are positioned in a product flow fashion such that value is added to the product as it moves down the assembly line. There are fewer workers than machines and workers carry items through as many machines as possible until they are blocked. This dynamic movement is a major departure from conventional assembly lines where workers are tied down to operating just one machine. In bucket brigades, workers are required to be multi-skilled so that they can operate a range of machinery.

Simulating Bucket Brigades

To determine the viability of bucket brigades at PDL, we created a Visual Basic Simulation program in Excel to model a 7 machine/3 worker bucket brigade.

Simulation Excel screen shot

Our simulation strongly suggests that two independent bucket brigades, with a total of 6 workers, has 15% greater throughput than PDL’s existing assembly line with 7 workers.