Process Planning and Concurrent Engineering PDF

Chapter 24 Process Planning and Concurrent Engineering Chapter Contents 24.1 Process Planning 24.1.1 Process Planning for Parts 24.1.2 Process Planning for Assemblies 24.1.3 Make or Buy Decision 2...

Chapter 24 Process Planning and Concurrent Engineering Chapter Contents 24.1 Process Planning 24.1.1 Process Planning for Parts 24.1.2 Process Planning for Assemblies 24.1.3 Make or Buy Decision 24.2 Computer-Aided Process Planning 24.2.1 Retrieval CAPP Systems 24.2.2 Generative CAPP Systems 24.3 Concurrent Engineering and Design for Manufacturing 24.3.1 Design for Manufacturing and Assembly 24.3.2 Other Concurrent Engineering Objectives 24.4 Advanced Manufacturing Planning The product design is the plan for the product and its components and subassemblies. A manufacturing plan is needed to convert the product design into a physical entity. The activity of developing such a plan is called process planning. It is the bridge between product design and manufacturing. Process planning involves determining the sequence of processing and assembly steps that must be accomplished to make the product. In the present chapter, process planning and several related topics are examined. At the outset, a distinction should be made between process planning and produc- tion planning, which is covered in the following chapter. Process planning is concerned with the technical details: the engineering and technological issues of how to make the product and its parts. What types of equipment and tooling are required to fabricate the 703 704 Chap. 24 / Process Planning and Concurrent Engineering parts and assemble the product? Production planning is concerned with the logistics is- sues of making the product: ordering the materials and obtaining the resources required to make the product in sufficient quantities to satisfy demand. 24.1 Process Planning Process planning consists of determining the most appropriate manufacturing and assem- bly processes and the sequence in which they should be accomplished to produce a given part or product according to specifications set forth in the product design documentation. The scope and variety of processes that can be planned are generally limited by the avail- able processing equipment and technological capabilities of the company or plant. Parts that cannot be made internally must be purchased from outside vendors. The choice of processes is also limited by the details of the product design, as discussed in Section 24.3.1. Process planning is usually accomplished by manufacturing engineers (other titles in- clude industrial engineers, production engineers, and process engineers). They must be famil- iar with the particular manufacturing processes available in the factory and be able to interpret engineering drawings. Based on the planner’s knowledge, skill, and experience, the processing steps are developed in the most logical sequence to make each part. Following is a list of the many decisions and details usually included within the scope of process planning , : Interpretation of design drawings. First, the planner must analyze the part or prod- uct design (materials, dimensions, tolerances, surface finishes, etc.). Choice of processes and sequence. The process planner must select which processes and their sequence are required, and prepare a brief description of all processing steps. Choice of equipment. In general, process planners must develop plans that utilize existing equipment in the plant. Otherwise, the company must purchase the compo- nent or invest in new equipment. Choice of tools, dies, molds, fixtures, and gages. The process planner must decide what tooling is required for each processing step. The actual design and fabrication of these tools is usually delegated to a tool design department and tool room, or an outside vendor specializing in that type of tooling. Analysis of methods. Workplace layout, small tools, hoists for lifting heavy parts, even in some cases hand and body motions must be specified for manual operations. The industrial engineering department is usually responsible for this area. Setting of work standards. Work measurement techniques are used to set time stan- dards for each operation. Choice of cutting tools and cutting conditions. These must be specified for machining operations, often with reference to standard handbook recommendations. Similar decisions about process and equipment settings must be made for processes other than machining. 24.1.1 Process Planning for Parts For individual parts, the processing sequence is documented on a form called a route sheet (some companies call it an operation sheet). Just as engineering drawings are used to specify the product design, route sheets are used to specify the process plan. They are counterparts, one for product design, the other for manufacturing. A typical route Sec. 24.1 / Process Planning 705 Route Sheet XYZ Machine Shop, Inc. Part no. Part name Planner Checked by: Date Page 081099 Shaft, generator MPGroover N. Needed 08/12/XX 1/1 Material Stock size Comments: 1050 H18 Al 60 mm diam., 206 mm length No. Operation description Dept Machine Tooling Setup Std. 10 Face end (approx. 3 mm). Rough turn to Lathe L45 G0810 1.0 hr 5.2 min 52.00 mm diam. Finish turn to 50.00 mm diam. Face and turn shoulder to 42.00 mm diam. and 15.00 mm length. 20 Reverse end. Face end to 200.00 mm Lathe L45 G0810 0.7 hr 3.0 min length. Rough turn to 52.00 mm diam. Finish turn to 50.00 mm diam. 30 Drill 4 radial holes 7.50 mm diam. Drill D09 J555 0.5 hr 3.2 min 40 Mill 6.5 mm deep x 5.00 mm wide slot. Mill M32 F662 0.7 hr 6.2 min 50 Mill 10.00 mm wide flat, opposite side. Mill M13 F630 1.5 hr 4.8 min Figure 24.1 Typical route sheet for specifying the process plan. sheet, illustrated in Figure 24.1, includes the following information: (1) all operations to be performed on the work part, listed in the order in which they should be performed; (2) a brief description of each operation indicating the processing to be accomplished, with references to dimensions and tolerances on the part drawing; (3) the specific machines on which the work is to be done; and (4) any special tooling, such as dies, molds, cutting tools, jigs or fixtures, and gages. Some companies also include setup times, cycle time standards, and other data. It is called a route sheet because the processing sequence de- fines the route that the part must follow in the factory. Decisions on processes to fabricate a given part are based largely on the starting material for the part. This starting material is selected by the product designer. Once the material has been specified, the range of possible processing operations is reduced con- siderably. The product designer’s decisions on starting material are based primarily on functional requirements, although economics and ease of manufacture also play a role in the selection. A typical processing sequence to fabricate an individual part consists of (1) a basic process, (2) secondary processes, (3) property-enhancing operations, and (4) finishing operations. The sequence is shown in Figure 24.2. A basic process determines the start- ing geometry of the work part. Metal casting, plastic molding, and rolling of sheet metal are examples of basic processes. The starting geometry must often be refined by second- ary processes, operations that transform the starting geometry into the final geometry (or close to the final geometry). The secondary processes that might be used are closely correlated to the basic process that provides the starting geometry. When sand casting is the basic process, machining operations are generally the secondary processes. When a rolling mill produces sheet metal, stamping operations such as punching and bending are the secondary processes. When plastic injection molding is the basic process, secondary operations are often unnecessary, because most of the geometric features that would oth- erwise require machining can be created by the molding operation. Plastic molding and 706 Chap. 24 / Process Planning and Concurrent Engineering Property-enhancing processes not always required Starting Basic Secondary Property-enhancing Finishing Finished raw material process processes processes operations part Additional secondary processes sometimes required following property enhancement Figure 24.2 Typical sequence of processes required in part fabrication. other operations that require no subsequent secondary processing are called net shape processes. Operations that require some minimal secondary processing, usually machin- ing, are referred to as near net shape processes. Some impression die forgings are in this category. These parts can often be shaped in the forging operation (basic process) so that minimal machining (secondary processing) is required. Once the geometry has been established, the next step for some parts is to improve their mechanical and physical properties. Property-enhancing operations do not alter the geometry of the part, only the physical properties; heat-treating operations on metal parts are the most common type. Similar heating treatments are performed on glass to produce tempered glass. For most manufactured parts, these property-enhancing operations are not required in the processing sequence, as indicated by the alternative arrow path in Figure 24.2. Finally, finishing operations usually provide a coating on the work part (or assem- bly) surface; examples include electroplating, thin film deposition processes, and painting. The purpose of the coating is to enhance appearance, change color, or protect the surface from corrosion, abrasion, and other damage. Finishing operations are not required on many parts; for example, plastic moldings rarely require finishing. When finishing is re- quired, it is usually the final step in the processing sequence. Table 24.1 presents some typical processing sequences for common engineer- ing materials used in manufacturing. In most cases, parts and materials arriving at the ­factory have completed their basic process. Thus, the first operation in the process plan ­follows the basic process that has provided the starting geometry of the part. For example, ­machined parts begin as bar stock or castings or forgings, which are purchased from out- side vendors. The process plan begins with the machining operations in the company’s own plant. Stampings begin as sheet metal coils or strips bought from the rolling mill. These raw materials are supplied from outside sources so that the secondary processes, property-enhancing operations, and finishing operations can be performed in the com- pany’s own factory. A detailed description of each operation is filed in the particular production depart- ment office where the operation is performed. It lists specific details of the operation, such as cutting conditions and tooling (if the operation is machining) and other instructions that may be useful to the machine operator. Sketches of the machine setup are often included with the description (“a picture is worth a thousand words”). Lean production, specifically the Toyota Production System, emphasizes the use of drawings and illustrations as com- munication aids (Section 26.4.2). Sec. 24.1 / Process Planning 707 Table 24.1   Some Typical Process Sequences Basic Process Secondary Property-enhancing Finishing (Material Form) Processes (Final Shape) Process Process Sand casting (sand casting) Machining (machined part) Optional Painting Die casting (die casting) Net shape (die casting) Optional Painting Casting of glass (glass ingot) Pressing, blow molding (glassware) Heat treatment None Injection molding (molded part) Net shape (plastic molding) None None Rolling (sheet metal) Blanking, punching, bending, None Plating forming (stamping) Rolling (sheet metal) Deep drawing (stamping) None Plating Forging (forging) Machining (machined part) None Painting Bar drawing (bar stock) Machining, grinding (machined part) Heat treatment Plating Extrusion of aluminum Cutoff (extruded part) None Anodizing (extrudate) Atomize (metal powders) Press (PM part) Sinter Paint Comminution (ceramic powders) Press (ceramic ware) Sinter Glaze Ingot pulling (silicon boule) Sawing and grinding (silicon wafer) None Cleaning Sawing and grinding (silicon Oxidation, CVD, PVD, etching (inte- None Coating wafer) grated circuits) 24.1.2 Process Planning for Assemblies The type of assembly method used for a given product depends on factors such as (1) the anticipated production quantities; (2) complexity of the assembled product, for example, the number of distinct components; and (3) assembly processes used, for example, mechanical assembly versus welding. For a product that is to be made in relatively small quantities, as- sembly is generally accomplished at individual workstations where one worker or a team of workers perform all of the assembly tasks. For complex products made in medium and high quantities, assembly is usually performed on manual assembly lines (Chapter 15). For simple products of a dozen or so components, to be made in large quantities, automated assembly systems may be appropriate. In any case, there is a precedence order in which the work must be accomplished, an example of which is shown in Table 15.4. The precedence requirements are sometimes portrayed graphically on a precedence diagram, as in Figure 15.5. Process planning for assembly involves development of assembly instructions similar to the list of work elements in Table 15.4, but in more detail. For high production on an as- sembly line, process planning consists of allocating work elements to the individual stations of the line, a procedure called line balancing (Section 15.2.3). As in process planning for in- dividual components, any tools and fixtures required to accomplish an assembly task must be determined, designed, and built, and the workstation arrangement must be laid out. 24.1.3 Make or Buy Decision An important question that arises in process planning is whether a given part should be produced in the company’s own factory or purchased from an outside vendor. If the com- pany does not possess the equipment or expertise in the particular manufacturing pro- cesses required to make the part, then the answer is obvious: The part must be purchased because there is no internal alternative. However, in many cases, the part could either be 708 Chap. 24 / Process Planning and Concurrent Engineering made internally using existing equipment or purchased externally from a vendor that pos- sesses similar manufacturing capability. In discussing the make or buy decision, it should be recognized at the outset that nearly all manufacturers buy their raw materials from suppliers. A machine shop pur- chases its starting bar stock from a metals distributor and its sand castings from a foundry. A plastic molding plant buys its molding compound from a chemical company. A stamping plant purchases sheet metal either from a distributor or rolling mill. Very few companies are vertically integrated in their production operations all the way from raw materials to finished product. Given that a manufacturing company purchases some of its starting ma- terials, it seems reasonable for the company to consider purchasing at least some of the parts that would otherwise be produced in its own plant. It is probably appropriate to ask the make or buy question for every component that is used by the company. A number of factors enter into the make or buy decision. A list of the factors and issues that affect the decision is compiled in Table 24.2. Cost is usually the most important factor in determining whether to produce the part or purchase it. If an outside vendor is more proficient than the company’s own plant in the manufacturing processes used to make the part, then the internal production cost is likely to be greater than the purchase price even after the vendor has included a profit. However, if the decision to purchase results in idle equipment and labor in the company’s own plant, then the apparent advan- tage of purchasing the part may be lost. Consider the following example. Table 24.2   Factors in the Make or Buy Decision Factor Explanation and Effect on Make/Buy Decision How do part costs This must be considered the most important factor in the make or buy decision. compare? However, the cost comparison is not always clear, as Example 24.1 illustrates. Is the process available If the equipment and technical expertise for a given process are not available in-house? internally, then purchasing is the obvious decision. Vendors usually become very proficient in certain processes, which often makes them cost competi- tive in external–internal comparisons. However, there may be long-term cost implications for the company if it does not develop technological expertise in certain processes that are important for the types of products it makes. What is the total production As the total number of units required over the life of the product increases, this quantity and anticipated tends to favor the make decision. Lower quantities favor the buy decision. product life? Longer product life tends to favor the make decision. Is the component a Standard catalog items (e.g., hardware items such as bolts, screws, nuts, and standard item? other commodity items) are produced economically by suppliers special- izing in those products. Cost comparisons almost always favor a purchase decision on these standard parts. Is the supplier reliable? A vendor that misses a delivery on a critical component can cause a shut- down at the company’s final assembly plant. Suppliers with proven delivery and quality records are favored over suppliers with lesser records. Is the company’s plant In peak demand periods, the company may be forced to augment its own already operating at full plant capacity by purchasing a portion of the required production from capacity? ­outside vendors. Does the company need Companies sometimes purchase parts from outside vendors to maintain an alternative supply an alternative source to their own production plants. This is an attempt source? to ­ensure an uninterrupted supply of parts, for example, as a safeguard against a wildcat strike at the company’s parts production plant. Source: Based on Groover and other sources. Sec. 24.2 / Computer-Aided Process Planning 709 Example 24.1 Make or Buy Cost Decision The quoted price for a certain part is $20.00 per unit for 100 units. The part can be produced in the company’s own plant for $28.00. The cost components of making the part are as follows: Unit raw material cost = $8.00 per unit Direct labor cost = $6.00 per unit Labor overhead at 150% = $9.00 per unit Equipment fixed cost = $5.00 per unit Total = $28.00 per unit Should the part be bought or made in-house? Solution: Although the vendor’s quote seems to favor a buy decision, consider the possible impact on plant operations if the quote is accepted. Equipment fixed cost of $5.00 is an allocated cost based on an investment that was already made. If the equipment designated for this job is not utilized because of a decision to purchase the part, then the fixed cost continues even if the equipment stands idle. In the same way, the labor overhead cost of $9.00 consists of factory space, utility, and labor costs that remain even if the part is purchased. In addition, there are the costs of purchasing and receiving inspection. By this reasoning, a buy decision is not a good decision because it might cost the company $20.00 + $5.00 + $9.00 = $34.00 per unit (not including purchasing and receiving inspection) if it results in idle time on the machine that would have been used to produce the part. On the other hand, if the equipment in question can be used to produce other parts for which the in-house costs are less than the corresponding outside quotes, then a buy decision is a good decision. Make or buy decisions are not often as straightforward as in this example. Other factors listed in Table 24.2 also affect the decision. A trend in recent years, especially in the auto- mobile industry, is for companies to stress the importance of building close relationships with parts suppliers. 24.2 Computer-Aided Process Planning Problems arise when process planning is accomplished manually. Different process plan- ners have different experiences, skills, and knowledge of the available processes in the plant. This means that the process plan for a given part depends on the process planner who developed it. A different planner would likely plan the routing differently. This leads to variations and inconsistencies in the process plans in the plant. Another problem is that the shop-trained people who are familiar with the details of machining and other processes are gradually retiring and will be unavailable in the future to do process plan- ning. As a result of these issues, manufacturing firms are interested in automating the task of process planning using computer-aided process planning (CAPP). The benefits derived from CAPP include the following: 710 Chap. 24 / Process Planning and Concurrent Engineering Process rationalization and standardization. Automated process planning leads to more logical and consistent process plans than manual process planning. Standard plans tend to result in lower manufacturing costs and higher product quality. Increased productivity of process planners. The systematic approach and the availabil- ity of standard process plans in the data files permit more work to be accomplished by the process planners. Reduced lead time for process planning. Process planners working with a CAPP sys- tem can provide route sheets in a shorter lead time compared to manual preparation. Improved legibility. Computer-prepared route sheets are neater and easier to read than manually prepared route sheets. Incorporation of other application programs. The CAPP program can be interfaced with other application programs, such as cost estimation and work standards. Computer-aided process planning systems are designed around two approaches: (1) retrieval CAPP systems and (2) generative CAPP systems. Some CAPP systems combine the two approaches in what is known as semi-generative CAPP. 24.2.1 Retrieval CAPP Systems A retrieval CAPP system, also called a variant CAPP system, is based on the principles of group technology (GT) and parts classification and coding (Chapter 18). In this form of CAPP, a standard process plan (route sheet) is stored in computer files for each part code number. The standard route sheets are based on current part routings in use in the factory or on an ideal process plan that has been prepared for each family. Developing a database of these process plans requires substantial effort. A retrieval CAPP system operates as illustrated in Figure 24.3. Before the system can be used for process planning, a significant amount of information must be compiled and entered into the CAPP data files. This is what Chang et al. refer to as the preparatory phase ,. It consists of (1) selecting an appropriate classification and coding scheme for the company, (2) forming part families for the parts produced by the company, and (3) preparing standard process plans for the part families. Steps (2) and (3) are ongoing as new parts are designed and added to the company’s design database. After the preparatory phase has been completed, the system is ready for use. For a new component for which the process plan is to be determined, the first step is to derive the GT code number for the part. With this code number, the user searches the part family file to determine if a standard route sheet exists for the given part code. If the file contains a process plan for the part, it is retrieved (hence, the word “retrieval” for this CAPP system) and displayed for the user. The standard process plan is exam- ined to determine whether any modifications are necessary. It might be that although the new part has the same code number, there are minor differences in the processes required to make it. The user edits the standard plan accordingly. This capacity to alter an existing process plan is what gives the retrieval system its alternative name, “vari- ant” CAPP system. If the file does not contain a standard process plan for the given code number, the user may search the computer file for a similar or related code number for which a stan- dard route sheet does exist. Either by editing an existing process plan or by starting from scratch, the user prepares the route sheet for the new part. This route sheet becomes the standard process plan for the new part code number. Sec. 24.2 / Computer-Aided Process Planning 711 New part design Derive GT code number for part Preparatory stage Search part Select coding family file for Part family file system and form GT code number part families Retrieve standard Prepare standard Standard process process plan process plans for plan file part families Edit existing plan or write new plan Process plan Other application formatter programs Process plan (route sheet) Figure 24.3 General procedure for using one of the r­ etrieval CAPP systems. The process planning session concludes with the process plan formatter, which prints out the route sheet in the proper format. The formatter may call other application programs into use, for example, to determine machining conditions for the various ma- chine tool operations in the sequence, to calculate standard times for the operations (e.g., for direct labor incentives), or to compute cost estimates for the operations. 24.2.2 Generative CAPP Systems Generative CAPP systems represent an alternative approach to automated process plan- ning. Instead of retrieving and editing an existing plan contained in a computer database, a generative system creates the process plan based on logical procedures similar to those used by a human planner. In a fully generative CAPP system, the process sequence is planned without human assistance and without a set of predefined standard plans. Designing a generative CAPP system is usually considered part of the field of ex- pert systems, a branch of artificial intelligence. An expert system is a computer pro- gram that is capable of solving complex problems that normally can only be solved by a human with years of education and experience. Process planning fits within the scope of this definition. 712 Chap. 24 / Process Planning and Concurrent Engineering There are several necessary ingredients in a fully generative process planning sys- tem. First, the technical knowledge of manufacturing and the logic used by successful process planners must be captured and coded into a computer program. In an expert sys- tem applied to process planning, the knowledge and logic of the human process planners is incorporated into a so-called knowledge base. The generative CAPP system then uses that knowledge base to solve process planning problems (i.e., create route sheets). The second ingredient in generative process planning is a computer-compatible de- scription of the part to be produced. This description contains all of the pertinent data and information needed to plan the process sequence. Two possible ways of providing this description are (1) the geometric model of the part that is developed on a CAD system during product design and (2) a GT code number of the part that defines the part features in significant detail. The third ingredient in a generative CAPP system is the capability to apply the ­process knowledge and planning logic contained in the knowledge base to a given part description. In other words, the CAPP system uses its knowledge base to solve a specific problem—planning the process for a new part. This problem-solving procedure is referred to as the inference engine in the terminology of expert systems. By using its knowledge base and inference engine, the CAPP system synthesizes a new process plan from scratch for each new part it is presented. 24.3 Concurrent Engineering and Design for Manufacturing Concurrent engineering is an approach used in product development in which the functions of design engineering, manufacturing engineering, and other departments are integrated to reduce the elapsed time required to bring a new product to market. In the traditional approach to launching a new product, the two functions of design engineering and manu- facturing engineering tend to be separated and sequential, as illustrated in Figure 24.4(a). The product design department develops the new design, sometimes without much consid- eration given to the manufacturing capabilities of the company. There is little opportunity for manufacturing engineers to offer advice on how the design might be altered to make it more manufacturable. It is as if a wall exists between design and manufacturing. When the design engineering department completes the design, it tosses the drawings and specifica- tions over the wall, and only then does process planning begin. By contrast, in a company that practices concurrent engineering, the manufacturing engineering department becomes involved in the product development cycle early on, pro- viding advice on how the product and its components can be designed to facilitate manufac- ture and assembly. It also proceeds with the early stages of manufacturing planning for the product. This concurrent engineering approach is pictured in Figure 24.4(b). The product development cycle also involves quality engineering, the manufacturing departments, field service, vendors supplying critical components, and in some cases the customers who will use the product. All of these groups can make contributions during product development to improve not only the new product’s function and performance, but also its produce- ability, inspectability, testability, serviceability, and maintainability. Through early involve- ment, as opposed to reviewing the final product design after it is too late to conveniently make any changes, the duration of the product development cycle is substantially reduced. Concurrent engineering includes several elements: (1) design for manufacturing and assembly, (2) design for quality, (3) design for cost, and (4) design for life cycle. In addition, certain enabling technologies such as rapid prototyping, virtual prototyping, and organiza- tional changes are required to facilitate the concurrent engineering approach in a company. Sec. 24.3 / Concurrent Engineering and Design for Manufacturing 713 The "wall" between design and manufacturing Manufacturing engineering Production and Product design and process planning assembly Product launch time, traditional design/manufacturing cycle (a) Difference in product launch time Sales and Quality marketing engineering Vendors Product design Manufacturing engineering Production and and process planning assembly Product launch time, concurrent engineering (b) Figure 24.4 (a) Traditional product development cycle and (b) product development using concurrent engineering. 24.3.1 Design for Manufacturing and Assembly It has been estimated that about 70% of the life cycle cost of a product is determined by basic decisions made during product design. These design decisions include the choice of part material, part geometry, tolerances, surface finish, how parts are organized into subassem- blies, and the assembly methods to be used. Once these decisions are made, the potential to reduce the manufacturing cost of the product is limited. For example, if the product designer decides that a part is to be made of an aluminum sand casting but the part possesses features that can be achieved only by machining (such as threaded holes and close tolerances), the manufacturing engineer has no alternative except to plan a process sequence that starts with sand casting followed by the sequence of machining operations needed to achieve the speci- fied features. In this example, a better decision might be to use a plastic molded part that can be made in a single step. It is important for the manufacturing engineer to have the oppor- tunity to advise the design engineer as the product design is evolving, to favorably influence the manufacturability of the product. Terms used to describe such attempts to favorably influence the manufacturability of a new product are design for manufacturing (DFM) and design for assembly (DFA). Of course, DFM and DFA are inextricably linked, so the term design for manufacturing and 714 Chap. 24 / Process Planning and Concurrent Engineering assembly (DFM/A) is used here. It involves the systematic consideration of manufactur- ability and assemblability in the development of a new product design. This includes (1) organizational changes and (2) design principles and guidelines. Organizational Changes in DFM/A. Effective implementation of DFM/A in- volves making changes in a company’s organizational structure, either formally or infor- mally, so that closer interaction and better communication occurs between design and manufacturing personnel. This can be accomplished in several ways: (1) by creating proj- ect teams consisting of product designers, manufacturing engineers, and other specialties (e.g., quality engineers, material scientists) to develop the new product design; (2) by requiring design engineers to spend some career time in manufacturing to witness first- hand how manufacturability and assemblability are impacted by a product’s design; and (3) by assigning manufacturing engineers to the product design department on either a temporary or full-time basis to serve as producibility consultants. Design Principles and Guidelines. DFM/A also relies on the use of design prin- ciples and guidelines to maximize manufacturability and assemblability. Some of these are universal design guidelines that can be applied to nearly any product design situation, such as those presented in Table 24.3. In other cases, there are design principles that apply to specific processes, for example, the use of drafts or tapers in casted and molded parts to facilitate removal of the part from the mold. These process-specific guidelines are covered in texts on manufacturing processes, such as you will find in reference. The guidelines sometimes conflict with one another. For example, one of the guide- lines in Table 24.3 is to “simplify part geometry; avoid unnecessary features.” But an- other guideline in the same table states that “special geometric features must sometimes be added to components” to design the product for foolproof assembly. And it may also be desirable to combine features of several assembled parts into one component to mini- mize the number of parts in the product. In these instances, a suitable compromise must be found between design for part manufacture and design for assembly. 24.3.2 Other Concurrent Engineering Objectives To complete the coverage of concurrent engineering, other design objectives are briefly described: design for quality, cost, and life cycle. Design for Quality. It might be argued that DFM/A is the most important compo- nent of concurrent engineering because it has the potential for the greatest impact on product cost and development time. However, the importance of quality in international competition cannot be minimized. High quality does not just happen. Procedures for achieving it must be devised during product design and process planning. Design for quality (DFQ) refers to the principles and procedures employed to ensure that the highest possible quality is designed into the product. The general objectives of DFQ are : (1) to design the product to meet or exceed customer requirements; (2) to design the product to be “robust,” in the sense of Taguchi (Section 20.6.1), that is, to design the product so that its function and performance are relatively insensitive to variations in manufacturing and subsequent application; and (3) to continuously improve the performance, functionality, reliability, safety, and other qual- ity aspects of the product to provide superior value to the customer. The discussion of quality in Part V is certainly consistent with design for quality, but the emphasis in those chapters was directed more at the operational aspects of quality during production. Sec. 24.3 / Concurrent Engineering and Design for Manufacturing 715 Table 24.3   General Principles and Guidelines in DFM/A Guideline Interpretation and Advantages Minimize number of Reduced assembly costs. components Greater reliability in final product. Easier disassembly in maintenance and field service. Automation is often easier with reduced part count. Reduced work-in-process and inventory control problems. Fewer parts to purchase; reduced ordering costs. Use standard commercially Reduced design effort. Fewer part numbers. available components Better inventory control possible. Avoids design of custom-engineered components. Quantity discounts are possible. Use common parts across Group technology (Chapter 18) can be applied. product lines Quantity discounts are possible. Permits development of manufacturing cells. Design for ease of part Use net shape and near-net shape processes where possible. fabrication Simplify part geometry; avoid unnecessary features. Avoid making surface smoother than necessary since additional processing may be needed. Design parts with tolerances Avoid tolerances less than process capability (Section 20.3.2). Specify that are within process bilateral tolerances. capability Otherwise, additional processing or sortation and scrap are required. Design the product to be Assembly should be unambiguous. Components should be designed foolproof during assembly so they can be assembled only one way. Special geometric features must sometimes be added to components. Minimize flexible components These include components made of rubber, belts, gaskets, electrical cables, etc. Flexible components are generally more difficult to handle. Design for ease of assembly Include part features such as chamfers and tapers on mating parts. Use base part to which other components are added. Use modular design (see following guideline). Design assembly for addition of components from one direction, usually vertically; in mass production this rule can be violated because fixed automation can be designed for multiple direction assembly. Avoid threaded fasteners (screws, bolts, nuts) where possible, especially when automated assembly is used; use fast assembly techniques such as snap fits and adhesive bonding. Minimize number of distinct fasteners. Use modular design Each subassembly should consists of 5–15 parts. Easier maintenance and field service. Facilitates automated (and manual) assembly. Reduces inventory requirements. Reduces final assembly time. Shape parts and products for ease Compatible with automated packaging equipment. of packaging Facilitates shipment to customer. Can use standard packaging cartons. Eliminate or reduce adjustments Many assembled products require adjustments and calibrations. During product design, the need for adjustments and calibrations should be minimized because they are often time consuming in assembly. Source: Groover. 716 Chap. 24 / Process Planning and Concurrent Engineering Design for Product Cost. The cost of a product is a major factor in determining its commercial success. Cost affects the price charged for the product and the profit made by the company producing it. Design for product cost (DFC) refers to the efforts of a com- pany to specifically identify how design decisions affect product costs and to develop ways to reduce cost through design. Although the objectives of DFC and DFM/A overlap to some degree, because improved manufacturability usually results in lower cost, the scope of design for product cost extends beyond manufacturing in its pursuit of cost savings. It includes costs of inspection, purchasing, distribution, inventory control, and overhead. Design for Life Cycle. To the customer, the price paid for the product may be a small portion of its total cost when life cycle costs are considered. Design for life cycle refers to the product after it has been manufactured and includes factors ranging from product delivery to product disposal. Other life cycle factors include installability, reli- ability, maintainability, serviceability, and upgradeability. Some customers (e.g., the fed- eral government) include consideration of these costs in their purchasing decisions. The producer of the product is often obliged to offer service contracts that limit customer li- ability for out-of-control maintenance and service costs. In these cases, accurate estimates of these life cycle costs must be included in the total product cost. 24.4 Advanced Manufacturing Planning Advanced manufacturing planning emphasizes planning for the future. It is a corporate- level activity that is distinct from process planning because it is concerned with products being contemplated in the company’s long-term plans (2- to 10-year future), rather than products currently being designed and released. Advanced manufacturing planning in- volves working with sales, marketing, and design engineering to forecast the future prod- ucts that will be introduced and determine what production resources will be needed to make those products. The future products may require manufacturing technologies and facilities not currently available in the firm. In advanced manufacturing planning, the current equipment and facilities are compared with the processing needs of future planned products to determine what new technologies and facilities should be installed. The general planning cycle is portrayed in Figure 24.5. The feedback loop at the top of the diagram is intended to indicate that the firm’s future manufacturing capabilities may motivate new product ideas not previously considered. Activities in advanced manufacturing planning include (1) new technology evaluation, (2) investment project management, (3) facilities planning, and (4) manufacturing research. New Technology Evaluation. One of the reasons a company may consider in- stalling new technologies is because future product lines require processing methods not currently used by the company. To introduce the new products, the company must either implement new processing technologies in-house or purchase the components made by the new technologies from vendors. For strategic reasons, it may be in the company’s interest to implement a new technology internally and develop staff expertise in that tech- nology as a distinctive competitive advantage for the company. The pros and cons must be analyzed, and the technology itself must be evaluated to assess its merits and demerits. A good example of the need for technology evaluation has occurred in the micro- electronics industry, whose history spans only the past several decades. The technology of Sec. 24.4 / Advanced Manufacturing Planning 717 New product ideas Existing Future manufacturing manufacturing capabilities capabilities Advanced New Future manufacturing technologies products planning and facilities New Facilities technology planning evaluation Investment Manufacturing project research management Figure 24.5 Advanced manufacturing planning cycle. microelectronics has progressed very rapidly, driven by the need to include ever-greater numbers of devices in smaller and smaller packages. As each new generation has evolved, alternative technologies have been developed both in the products themselves and in the required processes to fabricate them. It has been necessary for the companies in this ­industry, as well as companies that use their products, to evaluate the alternative tech- nologies and decide which should be adopted. There are other reasons why a company may need to introduce new technologies: (1) quality improvement, (2) productivity improvement, (3) cost reduction, (4) lead time reduc- tion, and (5) modernization and replacement of worn-out facilities with new equipment. A good example of the introduction of a new technology is the CAD/CAM systems that were installed by many companies during the 1980s. Initially, CAD/CAM was introduced to modernize and increase productivity in the drafting function in product design. As CAD/ CAM technology itself evolved and its capabilities expanded to include 3-D geometric mod- eling, design engineers began developing their product designs on these more powerful sys- tems. Engineering analysis programs were written to perform finite-element calculations for complex heat transfer and stress problems. The use of CAD had the effect of increasing design productivity, improving the quality of the design, improving communications, and creating a database for manufacturing. In addition, CAM software was introduced to imple- ment process planning functions such as NC part programming (Section 7.5) and CAPP (Section 24.2), thus reducing transition time from design to production. Investment Project Management. Investments in new technologies or new equipment are generally made one project at a time. The duration of each project may be several months to several years. The management of the project requires a collabo- ration between the finance department that oversees the disbursements, manufacturing engineering that provides technical expertise in the production technology, and other functional areas that may be related to the project. Each project typically includes the 718 Chap. 24 / Process Planning and Concurrent Engineering following sequence of steps: (1) proposal to justify the investment is prepared, (2) man- agement approvals are granted for the investment, (3) vendor quotations are solicited, (4) order is placed to the winning vendor, (5) vendor progress in building the equipment is monitored, (6) any special tooling and supplies are ordered, (7) the equipment is installed and debugged, (8) operators are trained, (9) responsibility for running the equipment is turned over to the operating department. Facilities Planning. When new equipment is installed in an existing plant, the fa- cility must be altered. Floor space must be allocated to the equipment, other equipment may need to be relocated or removed, utilities (power, heat, light, air, etc.) must be con- nected, safety systems must be installed if needed, and various other activities must be accomplished to complete the installation. In some cases, a new plant may be needed to produce a new product line or expand production of an existing line. The planning work required to renovate an existing facility or design a new one is carried out by the plant engineering department (or similar title) and is called facilities planning. In the design or redesign of a production facility, manufacturing engineering and plant engineering must work closely to achieve a successful installation. Manufacturing Research and Development. To develop the required manufac- turing technologies, the company may find it necessary to undertake a program of manu- facturing research and development (R&D). Some of this research is done internally; in other cases projects are contracted to university and commercial research laborato- ries specializing in the associated technologies. Manufacturing research can take various forms, including the following: Development of new processing technologies. This R&D activity involves the devel- opment of new processes that have never been used before. Some of the process- ing technologies developed for integrated circuits fabrication fall into this category. Other recent examples include rapid prototyping techniques (Section 23.1.2). Adaptation of existing processing technologies. A manufacturing process may exist that has never been used on the type of products made by the company, yet it is perceived that there is a potential for application. In this case, the company must engage in applied research to customize the process to its needs. Process fine-tuning. This involves research on processes used by the company. The objectives of a given study can be any of the following: (1) improve operating effi- ciency, (2) improve product quality, (3) develop a process model, (4) achieve better control of the process, or (5) determine optimum operating conditions. Software systems development. These are projects involving development of cus- tomized manufacturing-related software for the company. Possible software de- velopment projects might include cost estimation software, parts classification and coding systems, CAPP, customized CAD/CAM application software, production planning and control systems, work-in-process tracking systems, and similar proj- ects. Successful development of a good software package may give the company a competitive advantage. Automation systems development. These projects are similar to the preceding except they deal with hardware or hardware/software combinations. Studies related to the application of industrial robots (Chapter 8) in the company are examples of this kind of research. References 719 Operations research and simulation. Operations research involves the development and application of mathematical models to analyze operational problems. The tech- niques include linear programming, inventory models, queuing theory, and stochastic processes. In many problems, the mathematical models are too complex to be solved in closed form. In these cases, discrete event simulation can be used to study the op- erations. A number of commercial simulation packages are available for this purpose. Manufacturing R&D is applied research. The objective is to develop or adapt a technology or technique that will result in higher profits and a distinctive competitive advantage for the company. References Bakerjian, R., and P. Mitchell, Tool and Manufacturing Engineers Handbook, 4th ed., Volume VI, Design for Manufacturability, Society of Manufacturing Engineers, Dearborn, MI, 1992. Boothroyd, G., P. Dewhurst, and W. Knight, Product Design for Manufacture and Assembly, 3rd ed., CRC Press, Boca Raton, FL, 2010. Chang, T.-C., and R. A. Wysk, An Introduction to Automated Process Planning Systems, Prentice Hall, Inc., Englewood Cliffs, NJ, 1985. Chang, T.-C., R. A. Wysk, and H. P. Wang, Computer-Aided Manufacturing, 3rd ed., Pearson/Prentice Hall, Upper Saddle River, NJ, 2006. Eary, D. F., and G. E. Johnson, Process Engineering for Manufacturing, Prentice Hall, Inc., Englewood Cliffs, NJ, 1962. Felch, R. I., “Make-or-Buy Decisions,” Maynard’s Industrial Engineering Handbook, 4th ed., William K. Hodson (ed.), McGraw-Hill. Inc., New York, 1992, pp. 9.121–9.127. Groover, M. P., “Computer-Aided Process Planning—An Introduction,” Proceedings, Conference on Computer-Aided Process Planning, Provo, UT, October 1984. Groover, M. P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 5th ed., John Wiley & Sons, Inc., Hoboken, NJ, 2013. Groover, M. P., and E. W. Zimmers, Jr., CAD/CAM: Computer-Aided Design and Manufacturing, Prentice Hall, Englewood Cliffs, NJ, 1984. Kamrani, A. K., P. Sferro, and J. Handleman, “Critical Issues in Design and Evaluation of Computer-Aided Process Planning,” Computers & Industrial Engineering, Vol. 29, No. 1–4, 1995, pp. 619–623. Kusiak, A., Editor, Concurrent Engineering, John Wiley & Sons, Inc., New York, 1993. Nevins, J. L., and D. E. Whitney, Editors, Concurrent Design of Products and Processes, McGraw-Hill Publishing Company, New York, 1989. Parsaei, H. R., and W. G. Sullivan, Editors, Concurrent Engineering, Chapman & Hall, London, UK, 1993. Tanner, J. P., Manufacturing Engineering, Marcel Dekker, Inc., New York, 1985. Tompkins, J. A., J. A. White, Y. A. Bozer, and J. M. A. Tanchoco, Facilities Planning, 4th ed., John Wiley & Sons, Inc., Hoboken, NJ, 2010. Wang, H. P., and J. K. LI, Computer-Aided Process Planning, Elsevier, Amsterdam, The Netherlands, 1991. www.npd-solutions.com/capp www.wikipedia.org/wiki/Computer_aided_process_planning 720 Chap. 24 / Process Planning and Concurrent Engineering Review Questions 24.1 What is process planning? 24.2 Name some of the decisions and details that are usually included within the scope of pro- cess planning. 24.3 What is the name of the document that lists the process sequence in process planning? 24.4 A typical process sequence for a manufactured part consists of four types of operations. Name and briefly describe the four types of operations. 24.5 What is a net shape process? 24.6 Name some of the factors that influence the make-or-buy decision. 24.7 Name some of the benefits derived from computer-aided process planning. 24.8 Briefly describe the two basic approaches in computer-aided process planning. 24.9 What is concurrent engineering? 24.10 Design for Manufacturing and Assembly (DFM/A) includes two aspects: (1) organizational changes and (2) design principles and guidelines. Identify two of the organizational changes that might be made in implementing DFM/A. 24.11 Name some of the universal design guidelines in DFM/A. 24.12 Name the four activities often included within the scope of advanced manufacturing planning.