Learning Objectives
9s-1: Employ tools for process selection, analysis, and design.
One of the simplest tools used to compare and select processes is a cost–volume, or breakeven, analysis. To use this tool to make process selection decisions, we calculate the total costs of the processes we’re considering for various production volumes. We then plot on a two-dimensional graph the total cost lines for each process and choose the one that has the lowest cost for the number of units we expect to produce.
Several tools can be used to analyze and understand a process’s complexities so as to design or redesign it. The tools include assembly drawings, assembly charts, route sheets, process mapping, value stream mapping (VSM), and process simulation. Although an assembly drawing is an enlarged view of a product that shows all of its parts and subassemblies, an assembly chart maps how a product’s parts go together and the order in which they are assembled. A route sheet is a document that describes the sequence of different operations, places, or people involved in a process. The sheet helps organize work orders by tracking the parts for products and the status of jobs during their scheduling, production, and quality control phases. A process chart graphically shows all activities related to a process, including its inputs and outputs, decision points such as approvals and exceptions, and any cross-functional relationships. All steps in the process are identified. Value stream mapping (VSM) is a process-mapping technique used to analyze and design the flow of materials and information across multiple processes. Beginning with the customer, VSM examines all processes, including the organization’s supply chain, to determine where value is added or not added across the system. Process simulation provides a dynamic view of the process. Using computers, multiple inputs, work centers, and processing techniques can help operations manager look at the variability of a process under different conditions.
Although many of the process analysis tools we have discussed can also be used to analyze service processes, a very useful tool for analyzing services is a service blueprint. Service blueprints are especially useful for analyzing service processes that have high service content such as the intensive customer interaction observed in luxury hotels.
9s-2: Describe and use the techniques for designing process and product layouts.
In process layouts, the process facilities are shared by a wide variety of different products. Consequently, the relative positioning of the various departments is a compromise. A good process layout minimizes the materials handling or transportation costs or employee and customer traveling or waiting time. The most common way to design a process layout for a manufacturing facility is to arrange departments or work centers so that the total cost of materials handling is minimized. This can be accomplished by reducing the number of nonadjacent moves between the most frequently interacting departments.
When quantitative data are not readily available, qualitative criteria, such as the best judgment of a firm’s managers, can be used to design a process layout. The relationship rating technique developed by Richard Muther is a method used to design new layouts or change old ones based on qualitative criteria. Managers rate the best locations for departments relative to one another, and the information is displayed in a grid known as Muther’s grid.
In a product layout, machines or work centers are arranged based on a predetermined sequence of operations for the product. The goals are to achieve high levels of efficiency and capacity utilization while ensuring that the product flows smoothly through the line with no bottlenecks. The technique of line balancing is used to achieve these goals. Line balancing involves assigning production tasks so that the time required to complete them is approximately equal across workstations. This prevents some workstations from having to wait on others to finish their work on products traveling down the line.
Whenever there is idle time between workstations, a line is said to be unbalanced, and bottlenecks occur. Line balancing also helps minimize the number of workstations a firm needs.
As real-life layout problems are typically large, arriving at an optimal solution to such problems is nearly impossible. Hence, heuristic approaches are used to generate solutions that are not necessarily optimal but are satisfactory. Many commercially available computer packages such as CRAFT, CORELAP, and ALDEP can be used to reduce the effort required to solve large-scale process layout problems. Nevertheless, these programs also rely to a great extent on heuristic approaches. Large line balancing problems for product layouts can be solved quickly using IBM’s COMSOAL or GE’s ASYBL. These computer programs, however, do not guarantee optimal solutions.