Manufacturing Work Cell Optimization: Design, Layout and Analysis

There are several approaches to work cell optimization, design, and layout. You could use the U-shaped work cell layout, a T-shaped layout, or a floating design such as an S-shaped or Z-shaped layout. All of these options adopt simple rules with regards to work station setup; 1) focus on minimizing transit times between individual work stations within the cell, 2) simplify how work moves from one station and one cell to the next, and 3) make sure the layout is functional by providing operators with the ability to manage, work and oversee more than one work station.

We’ll review how you can use a simple analysis to determine productivity rates in individual stations, the total output from a cell, and then we'll review the various designs that follow these three aforementioned criteria.

Calculating Productivity Rates in Work Stations & Work Cells

Before venturing into the individual cell designs, it’s important to define how you determine the individual productivity rates emerging from each station within a work cell. I adopt this strategy because it forces companies to witness production in person. While some companies determine their productivity rates by comparing production volumes from a given day, week, and month to the next, this approach instead focuses on the actual rates emerging in each location and most importantly, it provides the root causes of downtime and lost time.

First, determine available work time by taking the eight-hour shift and removing time for lunch and breaks. Second, track lost time emerging from the workstation by identifying the causes of work stoppages. This will provide you with the available work time. Third, determine productivity rates within the station by dividing the amount of actual work time (step 2) from the available work time (step 1). Backtrack cycle times to determine work station output. Finally, multiply that output by the number of workstations in the cell. Here are the five steps followed by a simple example.

1. Determine Available Work Time
2. Track Lost Time
3. Determine Productivity Rate
4. Backtrack Cycle Times
5. Determine Work Cell Output

An Example of Productivity Rate Analysis

Let’s assume you have an eight-hour work shift which includes a one-hour lunch and two 15 minute breaks; one in the morning and one in the afternoon. The total available work time is 6 & ½ hours, which equates to 390 minutes of available work time. Next, you’ll account for work stoppages. In our example, we’ll assume 135 minutes of work stoppages have occurred throughout the eight-hour shift. The amount of actual work time is 390 minutes minus the 135 minutes, or 255 minutes. The productivity rate is 255 divided by 390, or 65%. The cycle time is 5 minutes per unit. This means the works station produced 51 units in total; 255 minutes divided by the 5 minute cycle time. You have four workstations in the cell, so your output is 204 units.

 

 

Work Cell Design:

Again, there are three essentials to maximizing work cell optimization in design and layout. These three are summarized below:

1. Minimize Transit Times: Between adjacent work stations and work cells
2. Simplify Work Flow: Provide an easily accessible entrance and exit point
3. Functionality: Make sure workspace is free, clear of obstructions, and spacious

Avoid trying to maximize space in a given production work cell by placing workstations too close to one another. Give your operators enough room to maneuver and don’t inhibit their ability to move semi-finished goods from one chain to the next. The idea is to minimize transit times between stations and cells. 

U-Cell Design

• Simple path distinguished from entry to exit points
• Operators can access multiple workstations
• Free access of semi-finished work from one station to the next
• Operators own entire workflow – from entry to exit point

T-Cell Design

• Ideal for semi-finished product that requires two or more sources of raw materials
• Ideal for cross-function manufacturing where multiple product lines can be worked on simultaneously.
• Easy designation of entry and exit points

S-Shaped or Z-Shaped Cell Design

• Ideal for working in and around obstructions
• Focus points (A & B) allows for easy access to either work station: between stations #1 & #2 as well as between stations #3 & #4

 

 

The above video is from the post: Cycle Time Tracking & Variance Analysis in Excel for Small Manufacturers. It explains how to track the cycle times emerging from individual work cells within work stations. It includes an excel sheet that graphs these times so you can isolate the causes of high cycle times, work stoppages, and downtime.

Remember, workstations and cells need to be near one another, but not so close that it slows down how semi-finished and finished parts move from one station and cell to the next.  Operators need clear, open areas with which to operate machinery and equipment. Functional workspaces are essential as is a flexible workforce that can handle multiple roles and responsibilities. Avoid the temptation to maximize space to the detriment of the workflow. Use multiple layouts around structures, obstructions, and machinery.

Finally, track the productivity rates emerging from individual work stations and then backtrack cycle times to define production volumes within those stations and the entire work cell. If need be, you can use these to measure the production throughput from each cell.