Design for Manufacturing Handbook: Optimizing Product Design & Manufacturing, Summaries of International Business

Download Design for Manufacturing Handbook: Optimizing Product Design & Manufacturing and more Summaries International Business in PDF only on Docsity! Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 Paper 220, IT 302 Developing a Design for Manufacturing Handbook Mohsen Hamidi, Kambiz Farahmand Department of Industrial and Manufacturing Engineering North Dakota State University mohsen.hamidi@ndsu.edu, Kambiz.Farahmand@ndsu.edu Abstract Understanding design for manufacturability is paramount, especially when design requirements exceed technology or manufacturing capability. More and more companies who are outsourcing design are facing this problem, where engineering designs have to be modified to match technology or process capability. Companies are left with the dilemma of how to communicate their capabilities to designers. One approach in communicating manufacturing capabilities to designers is to develop design for manufacturing (DFM) and design for assembly (DFA) handbooks. In this paper, a comprehensive handbook of DFM, developed for a manufacturing company, is presented. The handbook was designed and developed for the purpose of providing a common language between the designers and the manufacturing engineers. It includes: process capabilities and specifications, machinery and tooling capabilities in various manufacturing modules, guidelines for helping the designers understand the manufacturing challenges presented as a result of not well thought out design, and the various design examples or shortcuts that would enable the manufacturing of parts and products efficiently and at lower cost, faster time, and best quality approach. The procedures followed include: visiting workshops and interviewing operators and supervisors; gathering data documentation; discussing issues with engineers, managers, and operators; and making recommendations. The technology/design capability handbook serves as a venue for communication between the design and manufacturing engineers and helps bridge the gap that exists in understanding challenges and capabilities for a better and more efficient operation company-wide. Key words: Design for Manufacturing (DFM), Design for Assembly (DFA) Introduction to Design for Manufacturing (DFM) Design for manufacturability is the process of proactively designing products to (1) optimize all the manufacturing functions: fabrication, assembly, test, procurement, shipping, delivery, service, and repair, and (2) assure the best cost, quality, reliability, regulatory compliance, safety, time-to-market, and customer satisfaction [1]. One of the pillars of DFM knowledge- base is concurrent engineering [2]. Concurrent engineering is the practice of concurrently developing products and their manufacturing processes [1]. For example, if existing processes are to be utilized, then the product must be designed for these processes; if new processes are to be utilized, then the product and the process must be developed concurrently [1] to ensure manufacturability. The concurrent engineering approach is intended to cause Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 the developers and designers, from the outset, to consider all elements of the product lifecycle, from concept through disposal, including fabrication, testing, packaging, and delivery in addition to quality, cost, schedule, and user requirements [2]. DFM and DFA approaches are valuable tools in adopting and implementing concurrent engineering [2]. Their philosophy is based on using manufacturing or assembly as a design constraint, thus taking downstream processes like manufacturing and assembly into full consideration during the early design phase of the product [2]. Decisions made during the early conceptual stages of design have a great effect on subsequent stages [3]. In fact, more than 70 percent of the manufacturing cost of a product is determined at this conceptual stage, yet manufacturing is not involved [3]. Early consideration of manufacturing issues shortens product development time, minimizes development cost, and ensures a smooth transition into production for quick time-to-market [1]. Companies that have applied DFM have realized substantial benefits [1]. Costs and time- to-market are often cut in half with significant improvements in quality, reliability, serviceability, product line breadth, delivery, customer acceptance, and, in general, competitive posture [1]. Understanding design for manufacturability is paramount especially when design requirements exceed technology or manufacturing capability. More and more companies who are outsourcing design are facing this problem, where engineering designs have to be modified to match technology or process capability. Companies are left with the dilemma of how to communicate their capabilities to designers. One approach in communicating manufacturing capabilities to designers is to develop DFM and DFA handbooks. In this paper, a comprehensive DFM handbook developed for a manufacturing company is presented. Design for Manufacturing (DFM) Handbook To produce modern and up-to-date products, the company designs new products and parts, as well as makes modifications to exiting products and parts. Design or design changes are done in two ways: 1) by the company personnel in the design department or 2) by designers outside the company. When designers present a design, manufacturing engineers check whether the designed part can be manufactured given the facility’s capabilities or incorporated into the existing production line with minimum interruptions to work or material flow. The manufacturing engineer’s feedback helps designers make the necessary corrections to develop a design for manufacturability. Actually, manufacturing engineers will always have some manufacturability concerns (in terms of technical feasibility, time, cost, and quality) with regard to new engineering designs. In other words, designers, especially designers outside the company or even outside the country, are not always familiar with all the manufacturing capabilities and limitations of the company. As more and more companies outsource their design process overseas, the disconnect between the designers and manufacturers keeps growing. One of the first steps in bridging the gap is the availability of a handbook for the designers. The DFM handbook is an attempt to assist the designers with Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 4. Facilitation employs techniques and combining steps to make work easier to perform. Examples: Visual controls including color coding, marking, or labeling parts to facilitate correct assembly; exaggerated asymmetry to facilitate correct orientation of parts; a staging tray that provides a visual control that all parts were assembled, locating features on parts. 5. Detection involves identifying an error before further processing occurs so that the user can quickly correct the problem. Examples: Sensors in the production process to identify when parts are incorrectly assembled; built-in self-test (BIST) capabilities in products. 6. Mitigation seeks to minimize the effects of errors. Examples: Fuses to prevent overloading circuits resulting from shorts; products designed with low-cost, simple rework procedures when an error is discovered; extra design margin or redundancy in products to compensate for the effects of errors. f. Design for parts orientation and handling. g. Minimize flexible parts and interconnections. h. Design for ease of assembly. i. Design for efficient joining and fastening. j. Design modular products. k. Design for automated production. Manufacturing Processes Identification Each manufacturing process is thoroughly defined in the handbook. As an example, definition and specifications of gas metal arc welding are mentioned below. • Gas Metal Arc Welding (GMAW) The gas metal arc welding process uses an arc between a continuously fed electrode and the weld pool. The weld process uses an externally supplied shielding gas without the application of pressure. • Gas Metal Arc Welding (GMAW) Specifications • It is particularly well-suited to high production and automated applications, as evidenced by its predominant usage of welding robots. • The equipment is more complex and costly and less portable than that of submerged arc welding (SAW). GMAW is more difficult to use in hard-to-reach areas because the welding gun is larger than the SAW electrode holder and the gun must be held closer to the work (1/2” to 3/4”). Processes Capabilities Capabilities of different processes that can perform similar operations are compared in the handbook. Table 1 shows the capabilities of different methods for punching or cutting holes. Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 Table 1: Punching or Cutting Holes Methods Capabilities Method Torching Plasma Punching Laser Machining Minimum Hole Diameter Material Thickness Material Thickness Material Thickness No Minimum Hole Tolerance ± 1.5 mm ± 0.8 mm ± 0.1 mm ± 0.8 mm (Drilling) ± 0.025 mm (Boring) Holes Positioning ± 1.5 mm ± 0.8 mm ± 0.25 mm ± 0.01 mm Process Parameters To help designers understand the relationship between the independent and dependent parameters of each process, the process parameters and their relationships are specified in the handbook. An example of process parameters for vee-die openings is presented here. • Vee-die Opening The recommended vee-die opening for mild steel up to 1/2" thick is eight times the metal thickness. For thicker than 1/2" mild steel, it may be necessary to increase the vee-die opening up to ten times the material thickness to minimize cracking of the material. To determine the vee-opening for a simple 90 degree bend, multiply the metal thickness by eight. The answer is then rounded to the next higher 1/8" figure. For example: 14 ga. (0.075") x 8=0.600". This is rounded to a 5/8" vee opening. Material Utilization Guidelines To maximize material utilization in the cutting process, a section addressing material utilization is included in the handbook. Material costs constitute the majority of a finished part cost. Increasing material utilization leads to cost reduction. Material utilization is the weight ratio of the finished part to the raw material required to produce the part. Table 2 is an example of the real effect of material utilization on annual cost. Table 2: Material Utilization Effect on Cost Average Material Utilization in 2006 Scrap Percentage Annual Material Cost Annual Scrap Waste 65% 35% $25,000,000 $8,750,000 As shown in Table 2, a considerable amount of money could be saved by improving material utilization. To achieve this goal, the following guidelines should be considered in choosing material: Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 1. Try to use commonly used materials with minimum thickness and minimum cost. (A table in which the materials’ thickness, annual usage [sheets or plates per year], and cost per pound are presented is included in the handbook.) 2. Try not to choose special sheet sizes (width and length), other than those mentioned in the handbook. 3. Try not to use materials other than plain carbon, grade 50, HSLA, ROPS. 4. Try to increase number of parts available for dynamic nesting per material, as shown in Figure 1. Different parts with different sizes allow for optimal nesting. 5. Try not to use irregular and unusual sized and shaped parts. As shown in Figure 1, these parts increase the gaps between part patterns in nesting and decrease material utilization. 6. Try to design large parts as two smaller parts to be assembled, rather than one single large part. It allows for the simultaneous use of multiple torches (especially on an oxy-fuel machine) as shown in Figure 1. Also, small parts can fill the gaps in a nesting and increase material utilization. However, this is a delicate issue and could vary from operation to operation. Keep in mind that if a part is divided into two smaller parts, a process is needed to join them together. Figure 1: Nesting Example Machinery Specifications and Capabilities For each machine, an identification sheet is prepared. In this sheet, general capabilities and specifications of the machine, material specifications, machine accuracy, and tooling being used by the machine are introduced. Two examples are presented in Figure 2 and Figure 3. Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 cases, 30 degree dies can be selected to obtain true air bending of 90 degree angles. An air bend die is shown in Figure 4. Figure 4: Air Bending Die Design Considerations For each process, general design considerations are provided in the handbook. Some of the design considerations for the arc welding process are listed below. • Arc Welding Design Considerations 1. Use the minimum practical size fillet-weld needed: • Reduces the cost of filler metal and welding. For example, if weld size is increased from 8 mm to 10 mm, the amount of filler metal needed will be doubled. • Minimizes distortion. • Maximizes cell production capacity. 2. Design joints that have good stress transition. Poor Stress Transition Good Stress Transition Figure 5: Stress Transition 3. Ensure welded attachments are not placed in high stress areas that may cause fatigue failures later. 4. Avoid joints that require multiple starts and stops of several welds at the same point. 5. If possible, position welds so that they can be welded in the flat position. • Take into consideration the type of fixtures that will likely be used. Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 • Avoid welding in the vertical and overhead positions, if possible. These will require additional welding skill and increase welding cost due to reduced welding speeds. 6. As it is shown in Figure 6, if Sheet A is to be welded along a line parallel to the edge of Sheet B, the distance of d (the distance between Sheet A and the edge of Sheet B) should be at least equal to d = L + P1 + P2 + T + 3 mm, where L is the weld size, P1 is positioning tolerance, P2 is profile tolerance, and T is sheet tolerance. Figure 6: Minimum Distance Required for Welding For example, if the weld size is 12 mm, Sheet A’s positioning tolerance is ± 1.5 mm, and Sheet B’s tolerance is 2 mm, then d = 12 + 1.5 + 0 + 2 + 3 = 18.5 mm. In Figure 7, a part of an arm is shown. Part A is the arm and Part B is the boss. If the weld size is 10 mm, Part B’s positioning tolerance is ± 1.5 mm, Part A’s profile tolerance is ± 2 mm, and Part B’s profile tolerance is ± 1.5 mm, then the minimum distance between Part B and the edge of Part A should be equal to d = 10 + 1.5 + 2 + 1.5 + 3 = 18 mm. Figure 7: Minimum Distance Required for Welding Sh ee t A Sheet B d A B Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 Quality Control Considerations One quality control consideration is presented as follows: Do not use excessive and unneeded origins or datum in drawings. Having many origins in a given drawing increases the inspection time and decreases precision of dimensioning for quality control purposes. However, for functionality purposes, using some extra origins is inevitable. As shown in Figure 8, there are many dimensions with a few origins. Figure 8: Many Dimensions with a Few Origins Development Process of the Handbook To design and affiliate the handbook, the company’s manufacturing engineering department was in constant communication and collaboration with the developers of the DFM handbook. The task required a thorough understanding of the engineering design process and requirements, along with manufacturing/company limitations. The manager, the advanced manufacturing manager, and manufacturing engineers in different areas (fabrication, machining, welding, painting, quality assurance, and assembly) were involved at all stages of the development process. The approach was to first tackle the five manufacturing areas, including fabrication, welding, machining, painting, and assembly. This included interviewing operators, reviewing the manufacturing process, talking to the manufacturing engineers and supervisors, and