product definition, which encompasses three main factors:
• Product complexity
• Product variety
• Product quantity.
These factors provide the most complete picture of the type of manufacturing system(s) needed to make a product economically.
The level of a product’s complexity is tied to the level of difficulty in the manufacture of that product. In general, product complexity is an indication of whether the product is a small, simple, single component, as is the case with the widget made by the XYZ Company, or a large and complex product, like a nuclear submarine, which has numerous complex individual components. Obviously, the manufacturing systems that would produce these two products would be vastly different. This product complexity is further illustrated in Figure 1-1.
Figure 1-1 Product complexity example
Product variety refers to the number of different product designs, versions, or models to be produced within a facility. If a facility made just a single product, such as a toothbrush, it would use a manufacturing system conducive to efficient production of that one product. Conversely, if the facility were to manufacture, say, hairbrushes in addition to toothbrushes, it might have multiple manufacturing systems or a single system designed to accommodate this product variety.
In addition to this factor, there are different levels of product variety. Soft product variety indicates that product difference within the operation is small. Hard product variety means the products are vastly different. The best way to differentiate soft from hard product variety for assembled products is to consider the number of common parts each product uses. A high percentage of common parts indicates soft product variety, whereas a low percentage points to hard product variety. The case of the toothbrushes and hairbrushes represents hard product variety. Soft product variety might exist in the production of different models or styles of toothbrushes (color, bristle density, and so on). An illustration of this case of hard versus soft product variety is shown in Figure 1-2.
Figure 1-2 Hard versus soft product variety
Product quantity, naturally, specifies the number of products that are to be turned out over a given time period. This is more often referred to as product volume. As will be seen in subsequent sections, high volume product requirements dictate the use of automated high speed manufacturing systems. Low volume manufacturing systems are typically less automated with more worker involvement.
Observe that product definition and manufacturing system are interdependent. High volume manufacturing systems are typically less capable of accommodating product variety. Conversely, manufacturing systems capable of handling a great deal of product variety cannot produce as high a volume. Complex products dictate a complex manufacturing system; simple products will typically be turned out by a relatively simple manufacturing system. Thus, once a manufacturing system is established within the facility it will dictate the type of future products that can be produced, unless, of course, capital is allocated to add other manufacturing systems to the facility.
1.2.3 Manufacturing system
As mentioned already, the manufacturing system is the combination of manufacturing processes and the organization of workers, designed so as to efficiently and effectively create the desired product. There are essentially four standard systems, with numerous variations, that have evolved over time. Each system is geared to produce a fairly specific product definition. The four standard manufacturing systems are:
1. Fixed-position
2. Process
3. Quantity manufacturing system
4. Flow-line.
(Refer to Figure 1-3.) Because of the narrowness of product definition relating to each system, an individual facility may employ one or more of these systems.
Fixed-position manufacturing systems (Figure 1-3(a)) are used for making large, complex products. Because such products are not easily moved, the manufacturing processes are taken to the product; the product remains in a fixed position throughout manufacture. This system produces items that are highly complex, relatively large and immobile, with low volume production requirements, and of soft product variety. Submarines, ships, and large aircraft are examples of products that use this system.
The process manufacturing system is used when product complexity is relatively low and there is hard product variety. Accordingly, production quantities range from low to moderate. This system is also called a job shop system because it can accommodate a wide variety of products or jobs. The manufacturing processes are grouped together according to function or process. Products are routed though the facility to the required manufacturing processes in groups called lots or batches. The size of the lot, or lot size, is the number of products in the group. The use of lots is necessary because of the variety of products the system must accommodate. In a process manufacturing system each manufacturing process to which a product is routed will have to be set up, or prepared, to process that particular product. Consequently, it is economically desirable to run a specific number of products through the process each time it is set up. Some factors that influence lot size include variety of the products made in the facility, setup times, order sizes, and manufacturing lead-time. This system is shown in Figures 1-0 and 1-3(b).
Figure 1-3 Standard manufacturing systems
The quantity and the flow-line manufacturing systems are often combined into one category, called the product manufacturing system. These systems produce mass quantities of products and are thus mass production systems. However, both product complexity and product variety of mass-produced items dictate the division of the product manufacturing system into the quantity and flow-line manufacturing systems.
The quantity manufacturing system is used with low product complexity and hard product variety. These products are produced on a single standard machine, like a plastic injection molding machine with exchangeable tooling. (Refer to Figure 1-3(c).) Other examples of products manufactured with this system include metal stampings and blow molded plastic products, like water bottles.
Flow-line manufacturing is for products with high product complexity and soft product variety. For assembled products, flow-line is more commonly called assembly line manufacturing system. Raw material flows down a line of manufacturing processes, in the end to be converted into a finished product. Henry Ford is often credited with perfecting this system. He produced the Model T using the flow-line manufacturing system to reduce cost so that the average American could afford his automobile. Because of the nature of the flow-line manufacturing system, product variety was essentially nonexistent. All Model T cars had the same body shape and were made in one color. The early flow-line system evolved
