Lo # 1 manufacturing process selection design part 1

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LEARNING OUTCOME 1EMC 2033 Manufacturing TechnologyLO # 1: Design factors affecting the selection of manufacturing process.Identify criteria to be considered relative to design for manufacture: a) functionality , b) manufacturing issues , c) handling and assembly 

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DFMA Design for Manufacturing

and Assembly

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DFM Design for Manufacture Concept

• Design for manufacture concerns reducing the cost by reducing the difficulty of making the product.

• Simple Example: Design for manufacture (DFM) at a single part level, involves details such as ensuring that where a pin is to be assembled into a hole that is only slightly larger in diameter, then it is much easier if the end of the pin or the entry to the hole (or both) are chamfered or finished with a radius.

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Design for Manufacture concept DFM• This also applies whether the assembly is carried out manually or automatically. This is a fine tuning process carried out once the product form has been decided.

• Indeed automatic assembly would be very difficult /expensive if neither component of a close fitting pair was chamfered.

• At a more complex level, product DFM tackles the more fundamental problem of deciding on the product structure, material and form.

• Design for assembly (DFA) is an important part of this.

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DFM requires the collaboration of design engineers and manufacturing engineers

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Design for Manufacture Guidelines• Design for manufacture (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 products (cost of material, processing, and assembly) are determined by design decisions.

• Production decisions (machine and tools, processes selection) responsible for 20% of the costs.

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Rules to Reduce Cost and Difficulty• The following are rules or principles for reducing cost and

difficulty of manufacturing an item:1- Reduce the total number of parts.2- Develop a modular design.3- Use of standard components.4- Design parts to be multi-Functional.5- Design parts for multi-use.6- Design for ease of fabrication.7- Avoid separate fasteners.8- Minimize assembly directions.9- Maximize compliance.10- Minimize handling.

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1- Reduce the total number of parts:• This will reduce the manufacturing cost.• Less parts means less purchases, inventory, handling, processing time, equipment, engineering time, assembly difficulty, service inspection and testing.

• Eliminate the use of different materials for parts whenever possible.

• It is recommended to have one-piece structure and selecting of manufacturing process such as injection molding or precision casting method for manufacturing.

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Example less number of parts:

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2- Develop a Modular Design:• “Modularity in design" is an approach that subdivides a system into smaller parts (modules) that can be independently created and then used in different systems to drive multiple functionalities.

• The use of Modules in product design simplifies manufacturing activities such as inspection, testing, assembly, maintenance and so on.

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A computer is actually one of the best examples of modular design, IBM managed to have many modular parts to be used in many assemblies.

The idea is to build computers with easily replaceable parts that use standardized interfaces. This technique allows you to upgrade certain aspects of the computer easily without having to buy another computer altogether.Other examples are car parts, furniture, fridge …etc.

Modular design Example:

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Example of Modular Design (IBM) • Seven different motors are used in the IBM printers each made out of 29 components.

• 3 Modular parts (gears set, collates, and mounting plates) are used in all 7 different motors.

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IBM printer motor case example• Two manufactured parts used as three different assemblies (inner, outer, and center motor case).

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Also Modularize multiple parts into single sub-assemblies

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3- Use of Standard Components:• standards components are less expensive than custom-made ones.

• the availability of these components reduces the lead times.

• these standard components also more reliable.• the use of these standard components will relief the production pressure and shift it to the suppliers of that components.

• Example: standard batteries, tires, bearings, screws, bolts ….

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Standard Components

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4- Design for ease of multi-functional:

•Multi-functional parts will reduce the total number of parts in the design, and will lead to achieving rule #1.

•Example designing the heat sink as structure case too, or electric conductor and structure member.

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5- Design parts to be multi-use:• Different products can share parts that have been designed for multi-uses.

• These parts can have same or different functions when used in different products.• First we need to identify parts that are suitable for multi-use.

• this requires sorting and organizing the parts into “part families”.

• Parts in one families will be produces in same route to avoid unnecessary operations. (example: motors, or pumps)

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6- Design for ease of fabrication:• Select the optimum combination between the material and fabrication process to minimize the overall manufacturing cost.

• Whenever possible skip the final operations such as painting, polishing, finish machining, etc.

• Avoid excessive tolerances, surface-finish requirement, and any higher than necessary finishing processes.

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7- Avoid separate fasteners:• The use of fasteners increases the cost of manufacturing a part due to the handling and feeding operations.

• Fasteners also increases the cost of the equipment required for them, and not always 100% successful, leading to reducing the overall manufacturing efficiency.

• fasteners should be avoided and replaced by using snap fits or self tabs.

• If fasteners must be used, then follow these guides:

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Guides for using Fasteners in designs

1. Minimize the number, size, and variations of the used fasteners.

2. Utilize standard fasteners when possible.3. Avoid too long or too short fasteners.4. Avoid the use of separated washers, tapped

holes, round heads and flat heads ( hard to handle by vacuum pickup)

5. Use self-tapping and chamfered screws.6. Select screws with vertical side heads to easy

pickup by vacuum tools.

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Standardize and less variety bolts

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Use self tapping screws or snap fastner

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Reduce fasteners and place them in free positions

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8- Minimize Assembly directions:• All parts should be assembled from one direction.

• the best way to add parts for assembly is from above, in a vertical direction, to take advantage of gravity direction downwards.

• It is not recommended to use other than the above direction since we need to overcome the gravity effect.

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8B- Assembly from above to use gravity

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8C- Minimize the number of insertion direction

Never require

the assembly

to be turned over.

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Allow assembly in open spaces

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9- Maximize Compliance• Errors can happen during the insertion operations due part dimensions or the accuracy of the positioning machine.

•This might damage the part or the insertion machine.

• Use built-in compliance features such as tapers or chamfers and moderate sizes radius to facilitate insertions.

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Examples of Compliance features

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Parts should be easily oriented

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Set orienting features to avoid errors

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10- Minimize Handling:• Handling consist of positioning, orienting, and fixing a part or component.

• to facilitate orientation, symmetrical parts should be used, or else exaggerated asymmetry used to avoid errors.

• Use external guiding features to help orientation of parts.• if cable to be used use dummy connectors to plug the cables easily.

• finally try to minimize the flow of waste materials and parts.

• take packaging into account and select appropriate safe packaging for the product.

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Parts easily picked up and don’t stick to each other

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Distinguish apparently similar parts

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Think about easy insertion of mating parts

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Summary• Minimizing the number of parts during the assembly of the product is the key concept, a part is required only when:

1. A motion of the part is required.2. Different material is required.3. Assembly of other parts would otherwise be

prevented.In not then the parts do not need to be separate entities and me be combined.

Follow the “KISS” Principle:“Keep It Simple Stupid”

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Watch Video

•Assembly of screws• http://www.youtube.com/watch?v=suMsrcZH-t8 • http://www.youtube.com/watch?NR=1&feature=endscreen

&v=tF4LQMEo4HU