2181913 Product Design and Value Engineering-Notes PDF-Unit-2 PDF

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In this documents, you will get an easy explanation to solve Product Design and Value Engineering problems with examples. The content of the notes is very easy to understand and really helps to increase your Product Design and Value Engineering proficiency. All the chapters are filtered in a good ma...

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2 Product Design for Manufacturing and Assembly

Course Contents 2.1 Introduction 2.2

Design for Manufacturing and Assembly

2.3

Design for Maintainability

2.4

Design for Environment

2.5

Design for Safety

2.6

Legal Factors and social issues

2.7

Engineering Ethics & Issues Of Society Related To Design Of Products

2.8

Vision & Illumination design : climate, noise & vibration

2.9

Product costing

2. Product Design for Manufacturing & Assembly

Product Design and Value Engineering (2181913)

2.1 Introduction o As the process of Product Development and Design is how conceived, products must meet a broad series of optimization requirements, generically denominated ‘X’. Design of various factors, such as manufacture, assembly, environment, etc., is defined as DfX and aims to optimize design, manufacture, and support, through the effective feedback of the ‘Xs” within the design domain knowledge, in order to incorporate it during the design stages, X in DfX stands for manufacturability, inspect ability, recyclability, etc. These words are made up of two parts: life cycle business process (x) and performance measures (bility), that is

o X=x + bility o For example, “x=total” and “bility=quality” in “design for total quality”; “x=whole life” and “bility=costs” in “design for whole – life costs”; “x=assembly” and “bility=cost” in “design for assembly cost”, and so on. On another hand, “design” in DfX is interpreted as concurrent design of products and associated processes and systems. o The proliferation and expansion of “Xs” has led to a string of new terms such as design for Manufacturability, design for Quality, Design for Recyclability, etc. Design for X has been devised as an umbrella for these terms. Most of them are closely related and decisions made on any one of them may affect the other “Xs” in the final product performance. o DFMA (Design for Manufacturing and Assembling) is the integration of the separate but highly interrelated issues of assembly and manufacturing processes. It aims to help companies make the fullest use of the manufacturing processes that exist, while keeping the number of parts in an assembly to a minimum. First, Design For Assembly (DFA) is conducted, leading to a simplification of the product structure. Then, early cost estimates for the parts are obtained, for both the original designed and the new design, in order to make trade-off decisions. During this process the best materials and process for the various parts are considered. Once the materials and processes have been selected, a more thorough analysis for Design for Manufacture (DFM) can be carried out for the detail design of the parts.

2.2 Design For Manufacturing And Assembly o Design for Manufacturing (DFM) and design for assembly (DFA) are the integration of product design and process planning into one common activity. The goal is to design a product that is easily and economically manufactured. The importance of designing for manufacturing is underlined by the fact that about 70% of manufacturing costs of a product (cost of materials, processing, and assembly) are determined by design decisions, with production decisions (such as process planning or machine tool selection) responsible for only 20%.

Product Design and Value Engineering (2181913)

2.Product Design for Manufacturing & Assembly

o The heart of any design for manufacturing system is a group of design principles or guidelines that are structured to help the designer reduce the cost and difficulty of manufacturing an item. o The following is a listing of these rules:

➢ Reduce the total number of parts − The reduction of the number of parts in a product is probably the best opportunity for reducing manufacturing costs. Less parts implies less purchases, inventory, handling, processing time, development time, equipment, engineering time, assembly difficulty, service inspection, testing, etc. In general, it reduces the level of intensity of all activities related to the product during its entire life. A part that does not need to have relative motion with respect to other parts, does not have to be made of a different material, or that would make the assembly or service of other parts extremely difficult or impossible, is an excellent target for elimination. Some approaches to part-count reduction are based on the use of one-piece structures and selection of manufacturing processes such as injection molding, extrusion, precision castings, and powder metallurgy, among others.

➢ Develop a modular design − The use of modules in product design simplifies manufacturing activities such as inspection, testing, assembly, purchasing, redesign, maintenance, service, and so on. One reason is that modules add versatility to product update in the redesign process, help run tests before the final assembly is put together, and allow the use of standard components to minimize product variations. However, the connection can be a limiting factor when applying this rule.

➢ Use of standard components − Standard components are less expensive than custom-made items. The high availability of these components reduces product lead times. Also, their reliability factors are well ascertained. Furthermore, the use of standard components refers to the production pressure to the supplier, relieving in part the manufacture’s concern of meeting production schedules.

➢ Design parts to be multi-functional − Multi-functional parts reduce the total number of parts in a design, thus, obtaining the benefits given in rule 1. Some examples are a part to act as both an electric conductor and as a structural member, or as a heat dissipating element and as a structural member. Also, there can be elements that besides their principal function have guiding, aligning, or self-fixturing features to facilitate assembly, and/or reflective surfaces to facilitate inspection, etc.

➢ Design parts for multi-use − In a manufacturing firm, different products can share parts that have been designed for multi-use. These parts can have the same or different functions when used in different

2. Product Design for Manufacturing & Assembly

Product Design and Value Engineering (2181913)

products. In order to do this, it is necessary to identify the parts that are suitable for multi-use. For example, all the parts used in the firm (purchased or made) can be sorted into two groups: the first containing all the parts that are used commonly in all products. Then, part families are created by defining categories of similar parts in each group. The goal is to minimize the number of categories, the variations within the categories, and the number of design features within each variation. The result is a set of standard part families from which multi-use parts are created. After organizing all the parts into part families, the manufacturing processes are standardized for each part family. The production of a specific part belonging to a given part family would follow the manufacturing routing that has been setup for its family, skipping the operations that are not required for it. Furthermore, in design changes to existing products and especially in new product designs, the standard multi-use components should be used.

➢ Design for ease of fabrication − Select the optimum combination between the material and fabrication process to minimize the overall manufacturing cost. In general, final operations such as painting, polishing, finish machining, etc. should be avoided. Excessive tolerance, surface-finish requirement, and so on are commonly found problems that result in higher than necessary production cost.

➢ Avoid separate fasteners − The use of fasteners increases the cost of manufacturing a part due to the handling and feeding operations that have to be performed. Besides the high cost of the equipment required for them, these operations are not 100% successful, so they contribute to reducing the overall manufacturing efficiency. In general, fasteners should be avoided and replaced, for example, by using tabs or snap fits. If fasteners have to be used, then some guides should be followed for selecting them. Minimize the number, size, and variation used; also, utilize standard components whenever possible. − Avoid screws that are too long, or too short, separate washers, tapped holes, and round heads and flatheads (not good for vacuum pickup). Self-tapping and chamfered screws are preferred because they improve placement success. Screws with vertical side heads should be selected vacuum pickup.

➢ Minimize assembly directions − All parts should be assembled from one direction. If possible, the best way to add parts is from above, in a vertical direction, parallel to the gravitational direction (downward). In this way, the effects of gravity help the assembly process, contrary to having to compensate for its effect when other directions are chosen.

➢ Maximize compliance − Errors can occur during insertion operations due to variations in part dimensions or on the accuracy of the positioning device used. This faulty behavior can cause damage to the part and/or to the equipment. For this reason, it is necessary to include compliance

Product Design and Value Engineering (2181913)

2.Product Design for Manufacturing & Assembly

in the part design and in the assembly process. Examples of part built-in compliance features include tapers or chamfers and moderate radius sizes to facilitate insertion, and nonfunctional external elements to help detect hidden features. For the assembly process, selection of a rigid-base part, tactile sensing capabilities, and vision systems are example of compliance. A simple solution is to use high-quality parts with designed-in compliance, a rigid-base part, and selective compliance in the assembly tool.

➢ Minimize handling − Handling consists of positioning, orienting, and fixing a part or component. To facilitate orientation, symmetrical parts should be used whenever possible. If it is not possible, then the asymmetry must be exaggerated to avoid failures. Use external guiding features to help the orientation of a part. The subsequent operations should be designed so that the orientation of the part is maintained. Also, magazines, tube feeders, part strips, and so on, should be used to keep this orientation between operations. Avoid using flexible parts - use slave circuit boards instead. If cables have to be used, then include a dummy connector to plug the cable (robotic assembly) so that it can be located easily. When designing the product, try to minimize the flow of material waste, parts, and so on, in the manufacturing operation; also, take packaging into account, select appropriate and safe packaging for the product.

2.3 Design For Maintainability o Maintainability is the degree to which a product allows safe, quick and easy replacement of its component parts. It is embodied in the design of the product. A lack of maintainability will be evident as high product maintenance costs, long out-of service times, and possible injuries to maintenance engineers. One measure of maintainability is Time to Repair (TTR, also known as ‘turn-around time’). o Two kinds of maintenance activity can be identified for any product: 1. Preventative maintenance 2. Remedial maintenance (repair) 1. Preventative maintenance − For example replacing engine spark plugs every 30,000 km, or changing the oil filter. Preventative maintenance requires the replacement of parts that are still working but are expected to fail soon. It is also undertaken where degradation of a component endangers components elsewhere in the product. For example an old oil filter may cause serious engine damage by starving bearings of oil, or allowing abrasive metal sludge into clean areas. 2. Remedial maintenance (repair) − Fitting a new vehicle starter motor where the existing motor has burned out. Remedial maintenance is performed after the product has failed. o If the anticipated life of a component is known, failure can be avoided by scheduled replacement. In certain instances, wholesale preventative maintenance is cheaper than piecemeal remedial maintenance. For example, replacing all the fluorescent lights in an

2. Product Design for Manufacturing & Assembly

Product Design and Value Engineering (2181913)

office once a year can be cheaper than replacing lights individually as they fail, because labor is used more efficiently.

➢ Modularity and Lines of Repair: − A further consideration is where the components are to be replaced. This could be at the point of use, at a repair depot, or at the point of manufacture. Car maintenance enthusiasts will replace spark plugs at the point of use (their home). Most people will have them replaced at a repair depot (their local dealer or garage). It would clearly be costly and inconvenient if the car had to be returned to the manufacturer for replacement of spark plugs. − These geographical points of repair are often referred to as ‘lines of maintenance’ as follows: 1. 1st line maintenance − It occurs at the point of use. It could be at home, wherever a vehicle breaks down, on the tarmac in the case of an aircraft, or at the coalface in the case of mining equipment. It is appropriate to the replacement of small modular items that require a minimum kit of tools and can be replaced within minutes. 2. 2nd line maintenance − It occurs at a nearby maintenance depot. This could be railway workshops, a car dealer, or your local domestic appliance service centre. It is appropriate where an extended toolkit or special skills and processes are required, where adjustments must be made, where special handling is required, where the time to repair may be lengthy, where reassembly is complex, or where protection against the weather is important. 3. 3rd line maintenance − It is undertaken by the manufacturer. It is rare for volume products to be returned to the manufacturer for repair, but does happen in the case of bespoke equipment or where the repair process requires skills and equipment beyond those available at the local service centre. Examples would be aircraft rewiring or engine rebuilds, and specialist equipment servicing and repair. For volume products, 3rd line maintenance is not usually economically viable. − This raises the issue of modularity. If the toolkit at 1st line is limited in size, then it may be more convenient to replace not the failed component, but the entire module in which the failed component is fitted. For example, a public address system consisting of separate mixer, CD player, amplifier and loudspeakers is modular. The amplifier module can be replaced at 1st line without the need to disturb other modules, and no special tools are required. The failed amplifier can then be sent to 2 nd or 3rd line for repair while the replacement is in use. − Modularity improves maintainability, but carries cost penalties. This is one reason why consumer electronics manufacturers are moving away from separate modules towards ‘all in one’ entertainment systems. There are also weight penalties to consider – modularity adds mass -a potential headache for aircraft manufacturers. Software can also

Product Design and Value Engineering (2181913)

2.Product Design for Manufacturing & Assembly

be made modular. A typical approach is that of ‘structured programming’, where the main programme consists solely of a list of ‘go to subroutine’ commands, each command pointing to a self-contained sub-routine or ‘module’.

➢ General Rules - Design for Maintainability − Maintainability is created during the design process. It cannot be added later. − Establish the maintenance philosophy in terms of ‘repair versus disposal’ of the product or components. Do this before starting any design work. − Consider where maintenance will take place (1st. 2nd or 3rd line). − Consult the maintenance engineer during the design phase and agree upon a set of documents to be handed over to the maintenance people. − Keep it simple. Complex arrangements are usually harder to maintain. − Make it testable. Reactive (fault finding) tests often reveal latent problems that will become faults in the near future. Include diagnostic test points in electrical circuits. Include mechanisms that provide early warning of impending failure. − Design reliability into items that are difficult to maintain (such as components deep within an engine), to reduce the need for maintenance access. − Reduce maintenance frequency overall by ruggedizing and over-specifying components to withstand occasional overload. − Provide warning labels where a maintenance engineer may be exposed to danger. For example on hot or heavy items or where there is stored mechanical or electrical energy. − Provide maintenance instructions and information panels if the routine is difficult to remember, and fix them as close to the point of maintenance as possible. − Design equipment to fail-safe so that risk of injury to maintenance engineers is reduced. − Avoid the requirement for special tools.

➢ Rules Concerning Modules − Wherever 2 components are joined is a potential future maintenance point. The method of joining should reflect the likely frequency of replacement. − Modularize where appropriate. − It should not be necessary to disturb a healthy unit in order to replace a faulty unit. − Do not use permanent fastening techniques (adhesive fastening, riveting or welding) where separation of components will be required for maintenance. − Where any one of a number of acceptable alternative components can be used, design the interface to allow any of the viable alternatives to be fitted. − Where only one unique component should be fitted, design the interface to defeat the attempted installation of unacceptable alternatives. − Where component orientation is important, use a unique pattern of fixing points, or add locating pins or baffles to prevent wrong orientation during assembly. Design every interface so that parts can only be fitted the correct way round. − Adopt structured programming for software code. − Build self-test and diagnostic routines into complex data-oriented products and systems.

2. Product Design for Manufacturing & Assembly

Product Design and Value Engineering (2181913)

➢ Handling and Access Rules − Adjustment should not require the removal of components to access the adjustment point, the exception being where an entire module is easily removed for adjustment on the workbench. − ‘Access’ means enough space for the component, tools, hand, arm, and possibly head or head and body of the maintenance engineer. − Where a tool is required to remove a component, there must be access for the tool and the engineer’s hand, in normal grasp. Where tool access may be restricted, as a last resort add tool guides to steer the tool into a mating position. − Consider reducing the number of fasteners used by ‘hooking’ modules into position and fastening at one edge only (but beware vibration risk). − Design access holes and spaces for the full range of human body shapes and limb sizes, not just the average. − It must be possible to see the maintenance point while hand and arm are manipulating components, tools and fasteners. Access hatches must allow for this, and must not restrict the opening to that required to accommodate hand or arm only. − Access hatch covers and doors should open through 180 degrees and have a fasten-back clip, or be wholly removable. Doors that open to 90 degrees cause obstruction. − The most comfortable working height is between waist and chest height. For more difficult modules, allow them to be removed to a workbench. − Units with the lowest life expectancy should be the easiest to access, and components requiring frequent routine maintenance should be at the outer edge of the pro...