Computation Section
Subunit Facility Layout
 -CRAFT Method

To create a worksheet for the Traditional Craft option, click that button on the Options dialog. The most convenient way to initialize the layout is with a sequencial layout. Otherwise, click the Leave Blank button.


Sequential Initial Solution

  To illustrate the CRAFT method we start with a sequential layout with the departments sequenced in order of department index as below. The CRAFT method is not limited to this kind of initial solution, but it is convenient since the process is automatic.

Similar to the sequential method, the CRAFT method also investigates departments for switching. Candidates for switching are pairs of departments that have the same area or pairs of departments that are adjacent in the layout. For example, consider the feasible switches that involve department 6 in the layout above. Departments 2 and 8 have the same area, so the pairs (2, 6) and (6, 8) are feasible. Departments that are adjacent to 6 are departments 3, 5, 7, 9 and 10, so the pairs involving these departments and department 6 are feasible.

To evaluate the effect of switching the two departments, the CRAFT method assumes that the centroids of the two departments are switched and computes the resultant cost savings. When the two departments are the same size, this evaluation is accurate. When the departments have different sizes, the centroids of the departments do not exactly switch locations. In this case the evaluation may be not be accurate and a switch that looks promising may actually increase the cost of the layout. The CRAFT method implemented by this add-in terminates if this occurs.

For the example, the best feasible pair is 9 and 10. Since the two departments are different sizes, there are many alternatives for arranging the cells of the smaller sized department 9 into the larger area formerly holding department 10. The program has an algorithm for choosing the arrangement that results in the layout below. Although one might question the logic of this arrangement, it is difficult to program an algorithm that always makes the most reasonable assignment. The user can adjust the assignment of cells by changing cell indices, but this is a manual operation.


The next iteration interchanges departments 2 and 3.


The next iteration interchanges departments 2 and 5. Note that this change causes department 5 to overlap two widths of the formerly sequential layout. Although we started with a sequential layout, the CRAFT method does not consider department widths in its algorithms. We have erased the lines representing aisles, because no aisles are implied by the CRAFT layout.


The program next determines that if the centroids of departments 7 and 8 are switched, the cost of the layout will be reduced. When the switch is actually made, the cost increases. The add-in recovers the solution before the switch and terminates. The summary of the CRAFT process is shown below.


We rearranged some of the cells manually to obtain more regular departments. The results have a lower cost than the final solution obtained by the algorithm. This solution could not have been obtained with the sequential method because department 5 spans two widths of 5 cells each.



Blank Initial Solution

The CRAFT method is not restricted to initial layouts obtained by the sequential method. By choosing Blank on the dialog, a blank layout is presented.

An initial layout is constructed by placing numbers or colors on the layout. One possible initial layout is below.

The blank spaces might represent the actual building shape or unusable portions of the facility. Pressing the Evaluate button, colors the cells and evaluates the layout.

  The iterations of CRAFT are shown by the following series of layouts.


The last switch is hard to see because 3 and 9 are similar shades of blue. The method terminates when a proposed switch of departments 6 and 9 is unsuccessful in improving the solution.

The CRAFT method only uses the cells defined by the initial layout. Thus cells can be designated as unused by simply leaving them blank. The procedure will never use them.

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Operations Management / Industrial Engineering
by Paul A. Jensen
Copyright 2004 - All rights reserved