Material Handling

Chapter 7: LAYOUT Long-range viewpoint and coordinating the facilities plan with the plans of the other organizational units is very important. A facilities layout strategy should emerge from the overall strategic plan. Product, manufacturing, marketing distribution, management, and human resource plans will be impacted by and will impact on the facilities layout. It seems appropriate to ask the following question. Which comes first, the material handling system or the facility layout? Many appear to believe the layout should be designed first and then the material handling system should be developed. Yet, material handling decisions can have a significant impact on the effectiveness of a layout. For example, the following decisions will affect the layout: 1. Centralized versus decentralized storage of work-in-process (WIP), tooling, and, supplies. 2. Fixed path versus variable path handling. 3. The handling unit (unit load) planned for the systems. 4. The degree of automation used in handling. 5. The type of inventory control, physical control, and computer control of materials. 2. Layout Procedures In designing layouts, the procedures can be classified into two main categories: 1. Construction type layout methods basically involve developing a new layout “from scratch”, and 2. Improvement procedures generate layout alternatives based on an existing layout. Apple’s Plant Layout Procedure: 1. Procure the basic data 2. Analyze the basic data 3. Design the productive process 4. Plan the material flow pattern 5. Consider the general material handling plan 6. Calculate equipment requirements 7. Plan individual workstations 8. Select specific material handling equipment 9. Coordinate groups of related operations 10. Design activity interrelationships 11. Determine storage requirements 12. Plan service and auxiliary activities 13. Determine space requirements 14. Allocate activities to total space 15. Consider building types 16. Construct master layout 17. Evaluate, adjust, and check the layout with the appropriate persons 18. Obtain approvals 19. Install the layout 20. Follow up on implementation of the layout Reed’s Plant Layout Procedure: 1. Analyze the product or products to be produced 2. Determine the process required to manufacture the product 3. Prepare layout planning charts 4. Determine workstations 5. Analyze storage area requirements 6. Establish minimum aisle widths 7. Establish office requirements 8. Consider personnel facilities and services 9. Survey plant services 10.Provide for future expansion Reed calls the layout planning chart (figure 8.5) “the most important single phase of the entire layout process”. It incorporates the following: 1. Flow process, including operations, transportation, storage, and inspection 2. Standard times for each operation 3. Machine selection and balance 4. Manpower selection and balance 5. Material handling requirement Figure 8.5. Layout planning chart Muther’s Systematic Layout Planning (SLP) Procedure Figure 8.6. Systematic layout planning (SLP) procedure The systematic layout planning (SLP) procedure uses as its foundation the activity relationship chart (figure 8.7). Based on the input data and an understanding of the roles and relationships between activities, a material flow analysis (from-to-chart) and an activity relationship analysis (activity relationship chart) are performed. From the analyses performed, a relationship diagram is developed (figure 8.8). The next two steps involve the determination of the amount of space to be assigned to each activity. Departmental service and area requirement sheets would be completed for each department. Once the space assignments have been made, space templates are developed for each planning department and the space is “hung on the relationship diagram” to obtain the space relationship diagram (figure 8.9). Based on modifying considerations and practical limitations, a number of layout alternatives are developed (figure 8.10) and evaluated. The preferred alternative is then recommended. Figure 8.8. Relationship chart Figure 8.7. Activity relationship chart Figure 8.9. Space relationship diagram Figure 8.10. Alternative block layouts 8.3. Algorithmic Approaches 8.3. 1. Relationship Diagramming for New Layouts To illustrate the relationship diagramming procedure, consider the information given in table 1. The activity relationship chart for this illustration is shown in figure 8.11. the information in this table is converted into a relationship diagramming worksheet (table 8.2), which will be used as the basis for constructing a relationship diagram and layout. Code Function Area (Square feet) Number of Unit Area Templates 1 Receiving 12000 6 2 3 4 5 6 7 Milling Press Screw machine Assembly Plating Shipping 8000 6000 12000 8000 12000 12000 4 3 6 4 6 6 Table 8.1. Department areas and number of unit area templates Rel. Dept. 1 Dept. 2 Dept. 3 Dept. 4 A E 2 14 2 I 4 56 15 O 35 U 67 16 37 2457 367 Dept. 5 Dept. 6 6 5 Dept. 7 7 6 247 2 5 1 3 3 14 1234 X Table 8.2. Relationship diagramming worksheet Figure 8.11. Activity relationship chart to illustrate a variation of the SLP The steps in constructing a relationship diagram are: Step 1: Select the first department to enter the layout The department with the greatest number of “A” relationship is selected. If a tie exists, the tie-breaking rule is based on the hierarchy of the relationships (greatest number of “E”, “I”, “O”, “U”, “X” relationships will enter respectively). Step 2: Select the second department to enter the layout The second department selected should have an “A” relationship with the first department selected. Additionally, it should have the greatest number of “A” relationships with the other departments not yet selected. Step 3: Select the third department to enter the layout The third department selected should have the highest combined relationships with the two departments already in the layout. The highest possible combine relationships would be an “A” relationship with the both of the departments already selected. (Ranking: AA, AE, AI, A*, EE, EI, E*, II, and I*) Step 4: Determine the fourth department to enter the layout The fourth department selected is based on the same logic as in Step 3. The selection is based on the highest combined relationship with the three departments already in the layout. ( Rankings: AAA, AAE, AAI, AA*, AEE, AEI, AE*, AII, AI*, A**, EEE, EEI, EE*, EII, EI*, E**, III, II*, and I**) Step n: Department n is placed according to the rules described in Steps 3 and 4. Figure 8.12. Relative location of block templates for the example Figure 8.13. Final layout by relationship diagramming technique 8.3.2. Pairwise Exchange Method The majority of layout problems involves the redesign of an existing facility, which is typically triggered by the addition of new machines, changes in product mixes, decisions related to the contraction and expansion of storage areas, or a simple realization that the old layout is no longer adequate for its current needs. We will discuss the layout improvement based on minimizing the total cost of transporting materials among all departments in a facility. We will assume that the distance between departments is rectilinear and is measured form the department centroids. From Department To Department 1 2 3 1 2 3 4 — 10 15 20 — 10 5 — 5 4 — Table 8.3. Material flow matrix Suppose a distance matrix is given as if in table 3. The total cost of existing layout computed as follows: TC1234 = 10(1) + 15(2) + 20(3) + 10(1) + 5(2) + 5(1) = 125 The pairwise exchange method is simply states that for each iteration, all feasible exchanges in the locations of department pairs are evaluated and the pair that results in the largest reduction in total cost is selected. Since all departments areas are assumed to be of equal size, the feasible exchanges are 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. (a) Iteration 0: 1-2-3-4 (b) Iteration 1: 3-2-1-4 (c) Iteration 2: 2-3-1-4 TC2134(1-2) = 10(1) + 15(1) + 20(2) + 10(2) + 5(3) + 5(1) = 105 TC3214(1-3) = 10(1) + 15(2) + 20(1) + 10(1) + 5(2) + 5(3) = 95 TC4231(1-4) = 10(2) + 15(1) + 20(3) + 10(1) + 5(1) + 5(2) = 120 TC1324(2-3) = 10(2) + 15(1) + 20(3) + 10(1) + 5(1) + 5(2) = 120 TC1432(2-4) = 10(3) + 15(2) + 20(1) + 10(1) + 5(2) + 5(1) = 105 TC1243(3-4) = 10(1) + 15(3) + 20(2) + 10(2) + 5(1) + 5(1) = 125 Thus, we select pair 1-3 and perform the exchange in the layout [(b) iteration 1]. For the next iteration, we consider all feasible exchanges: TC3124(1-2) = 10(1) + 15(1) + 20(2) + 10(1) + 5(1) + 5(3) = 95 TC1234(1-3) = 10(1) + 15(2) + 20(3) + 10(1) + 5(2) + 5(1) = 125 TC3241(1-4) = 10(2) + 15(3) + 20(1) + 10(1) + 5(1) + 5(2) = 110 TC2314(2-3) = 10(2) + 15(1) + 20(1) + 10(1) + 5(3) + 5(2) = 90 TC3412(2-4) = 10(1) + 15(2) + 20(1) + 10(3) + 5(2) + 5(2) = 105 TC4213(3-4) = 10(1) + 15(1) + 20(2) + 10(2) + 5(1) + 5(3) = 105 The pair 2-3 selected with a total cost value of 90 [(c) iteration 2]. Continuing on, the third iteration calculations are TC3124(1-2) = 10(1) + 15(2) + 20(1) + 10(1) + 5(2) + 5(3) = 95 TC1324(1-3) = 10(2) + 15(1) + 20(3) + 10(1) + 5(1) + 5(2) = 120 TC3421(1-4) = 10(1) + 15(3) + 20(2) + 10(2) + 5(1) + 5(1) = 125 TC2134(2-3) = 10(1) + 15(1) + 20(2) + 10(2) + 5(3) + 5(1) = 105 TC3142(2-4) = 10(2) + 15(1) + 20(1) + 10(3) + 5(1) + 5(2) = 100 TC4123(3-4) = 10(1) + 15(2) + 20(1) + 10(1) + 5(2) + 5(3) = 95 Since the lowest total cost for this iteration, 95, is worse than the total cost value of 90 in the second iteration, then the procedure is terminated. Thus, the final layout arrangement is 2-3-1-4. 8.3.3. Graph-Based Construction Method Figure 8.14. Adjacency graphs for alternative block layouts Which block plan layout is better? We can score each block plan layout by summing the numerical weights assigned to each arc. On this basis, block plan layout (b) is better than block plan layout (a) with scores 71 and 63, respectively. Thus, finding a maximally weighted block plan layout is equivalent to obtaining an adjacency graph with the maximum sum of arc weights. Observations: (a) The score does not account for distance, nor does it account for relationships other than those between adjacent departments. (b) Dimensional specifications of departments are not considered; the length of common boundaries between adjacent departments are also not considered. (c) The arcs do not intersect; this property of graphs is called planarity. We note that the relationship diagram is usually a nonplanar graph. (d) The score is very sensitive to the assignment of numerical weights in the relationship chart. Figure 8.15. Relationship chart and relationship diagram Figure 8.16. Steps in graph-based procedure Figure 8.17. Block layout from the final adjacency graph 8.3.4 CRAFT Method Suppose the following layout provided as the initial layout to CRAFT. The flow- between and the distance matrix are given as below. (All Cij values are equal to 12) a. Compute the cost of initial layout b. Compute the estimated layout cost assuming that department E and F are changed. Distance from A and B = 3 Distance from A and C = 2.5 Distance from A and D = 5.5 Distance from A and E = 5 Distance from A and F = 8 Distance from B and C = 4.5 Distance from B and D = 2.5 Distance from B and E = 6 Distance from B and F = 5 Distance from C and D = 3 Distance from C and E = 2.5 Distance from C and F = 3 Distance from D and E = 5.5 Distance from D and F = 2.5 Distance from E and F = 3 Total initial layout cost = $1403 Department E and F are changed Suppose the distance matrix given as if in material flow matrix shown below. The total cost of existing layout computed as (TC12345). Use the Pairwise exchange method for all feasible exchanges in locations of department pairs that lead to largest reduction in total cost.

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