Factory and Equipment Layouts

The layout of the factory and the equipment within it can have a major impact on manufacturing efficiency and costs. Vonderembse and White (1991c) cite a rather extreme example, which, although not related to the food industry, clearly illustrates the importance of this aspect of the design. The example compares vehicle-manufacturing plants operated by Jeep and Honda. Table 6.3lists the principal features of these two facilities and illustrates the benefits of a modern custom-built plant.

Possible layouts are best evaluated using computer-aided layout packages, such as CRAFT, ALDEP and COFAD, which can be used to explore a large number of options at relatively low cost. These packages can be used not only to explore different equipment layouts but also to optimize the routing of service ducts, drainage channels, etc. The designs will also need to consider the movement of people, materials, and equipment within the factory that could give rise to food-safety risks associated with cross-contamination. Discrete-event simulation (DES) packages, also discussed in Chap.10, are very useful in modeling material flows and identifying potential bottlenecks in the process.

The following example illustrates a commonly employed technique that could be used for designing the layout of a food factory. Consider a frozen pizza factory. Like many food manufacturing operations, this will have an essentially linear flow layout consisting of the following processing steps (these have been somewhat simplified in order to clarify the example):

1. Flour receiving and bulk storage

2. Other raw materials receiving and storage

3. Pizza base preparation (dough mixing, forming, and baking) 4. Pizza base storage

5. Preparation of toppings 6. Spreading topping on base

7. Chilling and freezing the assembled pizza 8. Packaging and palletizing

9. Frozen storage of packed frozen pizzas

Table 6.3 Comparison of two vehicle-manufacturing plants (Adapted from Vonderembse and White1991c)

Feature Jeep Honda

Age of plant Built early 1900s Built around 1981

Floor space 5 million ft²(approximately

465,000 m²) to the end of the assembly line

JIT delivery of components No Yes

Production (vehicles/day) 750 875

No. of assembly workers 5,400 2,400

Productivity (vehicles per worker per day)

0.139 0.365

In order to produce an acceptable factory layout design, it is first necessary to consider the required proximity between the above processing steps (or departments as they are commonly referred to in Industrial and Operations Management terminology). These are defined by the following “closeness” indices:A is absolutely necessary, E is especially important, I is important, O is ordinary, U is unimportant, and X is undesirable.

It is first necessary to construct an activity relationship matrix, as shown in Fig. 6.4, which illustrates the required closeness of each of the departments listed above. For example, there is no need for Dept (1), “flour receiving and bulk storage,” to be situated close to Depts (2) and (4)–(9).

However, it should be reasonably close to Dept (3), “other raw materials receiving and storage.”

Likewise, it is absolutely necessary that Dept (3), “pizza base preparation,” be situated close to Dept (4), “pizza base storage,” and especially important that it be sited close to Dept (5), “preparation of toppings.” All other spatial relationships for Dept (3) are unimportant.

Having defined the relationship matrix, the following procedure is adopted. The individual steps described below are illustrated in Fig.6.5.

1. Select the first department; this will be placed at the center of the layout. The processing step with the greatest number of A relationships is selected. If more than one department has the same number ofA relationships, a series of tie-breaking steps are then undertaken as follows. Among the tied steps, the one having the greatest number ofE relationships is selected. If this fails, the numbers of I relationships are taken into consideration. If this does not break the tie, the department having the fewest number of X relationships is selected. Finally, if there is still a tie, one of the candidates is selected at random.

In the example illustrated in Fig. 6.4, Depts (2)–(8) each have a single A relationship. It is therefore necessary to take the E relationships into account. Depts (3) and (4) are the only processing steps to have an E relationship and are consequently the only ones to remain in contention. Neither is associated with an I or an X relationship. Dept (4) is then selected at random.

2. The second department is then selected. This should have an A relationship with the first department selected and should have the maximum number ofA relationships with the remaining departments. If there is a tie, the tie-breaking procedure described above should be employed.

In the example, only Depts (3) and (5) have anA relationship with Dept (4). Both Depts (3) and (5) have a singleA relationship with an unselected department: Dept (2) in the case of Dept (3)

(9) (8) (7) (6) (5) (4) (3) (2) (1)

and Dept (6) in the case of Dept (5). As Dept (5) has anI relationship with Dept (7), it is selected in preference to Dept (3) and placed in the layout adjacent to Dept (4).

3. The third department to be incorporated into the layout should have the highest combined relationship with the two departments already selected. The following hierarchy is employed:

AA, AE, AI, A*, EE, EI, E*, II, and I*. Here, “*” denotes an O or a U. The selected department is located adjacent to the department(s) with which it has the strongest spatial relationship.

In the example, Depts (3) and (6) have the highest combined relationship,AE, with Depts (4) and (5). Dept (3) is selected arbitrarily and is located adjacent to Dept (4) with which it has theA relationship.

4. The fourth department to be incorporated into the layout should have the highest combined relationship with the three departments already selected. The following hierarchy is employed:

AAA, AAE, AAI, AA*, AEE, AEI, AE*, A**, EEE, EEI, EE*, EII, EI*, E**, III, II*, and I**. Again,

“*” denotes anO or a U. The selected department is located adjacent to the department(s) with which it has the strongest spatial relationship.

Step 1 Step 2 Step 3 Step 4

Fig. 6.5 Steps in the development of the frozen pizza factory layout derived from the activity matrix shown in Fig.6.4

Dept (6) exhibits the highest score in the example (AE*) and is located adjacent to Dept (5) with which it has theA relationship.

5. Subsequent departments are selected in turn using the same logic as outlined above. The results for our example are as follows:

– Dept (7) scoredAI** and was located adjacent to Dept (6).

– Depts (2) and (8) both scoredA****. Dept (2) was chosen arbitrarily and was located adjacent to Dept (3) with which it had theA relationship.

– Dept (8) scored A***** and was located adjacent to Dept (7) with which it had the A relationship.

– Dept (9) scored A****** and was located adjacent to Dept (8) with which it had the A relationship.

– Finally, Dept (1) was selected. It was located adjacent to Dept (3) with which it had a weak (O) spatial relationship.

The final layout depicted in step 9 of Fig. 6.5is one of a number of possibilities that can be formulated on the basis of the relationships depicted in Fig.6.4. In this instance, those tested all yielded broadly comparable results, which are quite similar to the layout of a frozen pizza factory (Fig.6.6) described by Wallin (1997).

In order to convert the schematic layout shown in Fig.6.5into a finalized factory design, it is necessary to specify a number of other factors. Firstly, the floor areas required by each department (process step) must be known; these are largely dictated by the size and layout of the equipment within each department and the manpower space requirements. External facilities such as utility, office and recreational buildings, laboratories, and access roads must also be incorporated into the design.

In many cases, the footprint of a new food factory will be constrained by the area of the land upon which it is built. Although a single-story building is arguably best suited to many food-production processes, it may not be the best option in areas where high land prices prevail or where gravity feed of the raw materials is desirable. Under these conditions, a multistory factory could provide a better solution despite its higher per unit floor area building costs. The following guidelines will aid in the design of an effective factory layout (Wallin1997).

1. The selected equipment layout should minimize the use of floor space. However, sufficient spacing should be allowed between individual items of equipment to permit efficient operation, manual intervention, routine maintenance, and effective materials handling.

Base Mix

Fig. 6.6 Frozen pizza factory layout (Adapted from Wallin (1997))

2. In order to provide as much flexibility as possible to accommodate future changes, internal partitioning, columns, and drains should be kept to a practical minimum and service channels and ducts should be sited with this possibility in mind. Some internal partitioning may, however, be needed to accommodate food-safety requirements (see below). Land earmarked for the future construction of buildings and facilities required for factory expansion is normally grassed over and landscaped until required.

3. A straight-line arrangement with raw materials entering at one end and finished goods leaving at the other is normally the most desirable option. However, this is not always feasible as some processes require large amounts of work in process (WIP) and/or large equipment (e.g., baking ovens, chillers/freezers, and dryers), which would result in excessively long production lines. An example of an approximately linear design, that of a frozen pizza factory, is shown in Fig.6.6.

Note that in this example, spiral chillers and freezers are employed in order to minimize floor space and the length of the line.

4. Food-safety and processing requirements often dictate the need to partition off different areas of the factory. A commonly adopted approach is to separate high-risk from low-risk areas. High-risk operations include the storage of sensitive fresh ingredients, fresh food preparation, and the filling of foods into primary packaging. Secondary and tertiary packaging and the storage of frozen and ambient foods constitute low-risk operations. Typical examples of where to partition the factory include:

– After filling or sealing the product in its primary packaging.

– After cooling in a chilled or frozen food factory (as in the example in Fig.6.6). In such cases, the chiller or freezer can act as the partition.

– After drying in a dehydrated food plant; here the water activity will be too low for microbial growth to occur.

It is also common practice to separate areas requiring different environments.