Programmable Automation Technologies. Daniel Kandray
The concept of productivity will be introduced, and the last few sections will address reasons for automation, corresponding benefits of it, and ways automation can be implemented.
1.2.1 Manufacturing overview
Manufacturing, regardless of the industry under consideration, is a conversion process. Some form of raw material is brought into a manufacturing facility and converted into a more useful finished product. The conversion is accomplished by applying a series of manufacturing steps, or manufacturing processes, to the raw material. Manufacturing processes alter the raw material’s shape, appearance, physical and mechanical properties, and/or assemble it with other components into a desired finished product. This is achieved through the use of equipment, tools, and supplies combined with the application of labor, time, and energy.
The way that manufacturing operations are organized within the facility defines plant layout. The term “manufacturing system” of the facility refers to the plant layout and worker execution of the operations. The manufacturing system used is determined by the product(s) characteristics. Figure 1-0 shows the plant layout of an imaginary facility, the XYZ Company. XYZ Company manufactures widgets. As the layout indicates, bar stock is processed into a widget through a series of manufacturing processes, which include sawing, turning, milling, and painting. Each manufacturing process executes a systematic sequence of operations called a program of instructions. When a program of instructions is complete for one manufacturing process, the product is routed to the next process.
Figure 1-0 XYZ Company plant layout
Note that the factory must perform operations in addition to manufacturing processes to create the product. The product must be moved between the manufacturing processes. It must also be inspected at some point to ensure that it satisfies the customer’s requirement. Additionally, someone must optimize the processes, schedule the operations, monitor labor usage, schedule maintenance, coordinate material handling, control inventory, and make sure the product is shipped on time. These activities do not contribute to the conversion process of the product per se. However, they are critically important to the manufacture of the product. The manufacturing processes and other activities combined are called manufacturing operations. Typical manufacturing operations found in factories include:
• Manufacturing processes
• Material handling
• Quality control
• Manufacturing support.
Each manufacturing process is designed to accomplish a very specific raw material conversion step. Thus, the number of manufacturing processes and the way they are organized within the facility are determined by the product(s) made. Manufacturing processes might include shaping processes such as molding or machining, property-enhancing processes such as the heat treating of steel, surface processes such as cleaning, coating, or painting, and various types of assembly processes. Assembly processes can be permanent, as in the case of welding, soldering, brazing, or adhesive bonding. However, some assembly processes are considered semi-permanent. Semi-permanent assembly processes typically include various types of mechanical joining, such as what is accomplished with the use of threaded fasteners, rivets, and expansion fits. All manufacturing processes are said to add value to the product; but, the other three operations—material handling, quality control, and manufacturing support—do not add value and are often the first targets for automation.
The way manufacturing operations are organized within a facility defines its plant layout. The term “manufacturing system” refers to both plant layout and worker execution of operations.
1.2.2 Defining the product
A given manufacturing facility may turn out only one product, a variety of models of one product, or many different products. Products may be as simple as a paper clip or as complex as a photocopier. Additionally, the facility might make only one product per year, or it might turn out millions of products. A product is either continuous, such as a liquid like gasoline, or it is discrete, like an automobile. (This text focuses on programmable automation of manufacturing processes and systems for discrete products only; continuous product manufacturing processes and systems will not be addressed.) Taken together, these distinctions make up the product definition and are naturally related to the manufacturing system(s) used within the facility.
The choice of manufacturing system employed for a discrete product is a function of the manufacturing 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