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Designfor

Assembly

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Design For Assembly NTTF

Objective of this Presentation:•Gain an overview of the importance of DFX

•Learn the Guidelines for Design For Assembly

•Understand Case Studies

•Ability to analyze design efficiency of a given product of everyday use, individually

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Design For Assembly NTTF

WHO CASTS THE BI GGEST SHADOWON PRODUCT COST?

% Cost Due toSTAGE Product

Design Labor OverHeads Material

DESIGN &DEVELOPMENTPRODUCTI ON

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Design For Assembly NTTF

WHO CASTS THE BI GGEST SHADOWON PRODUCT COST?

% Cost Due toSTAGE Product

Design Labor OverHeads Material

DESI GN &DEVELOPMENT

5 15 30 50

PRODUCTION 70 5 5 20

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Design For Assembly NTTFProduction Stage

Design & Development Stage

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P

DC

A

On importance of Planning…

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Plan Do Check Act

Linear PDCA Cycle as Time Line

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PLAN EXECUTION

Time Line For any Project

? ?

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PLAN EXECUTION

10% 90%

Time Line For Action

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PLAN EXECUTION

10% 90%

Time Line For Action

PLAN EXECUTION

20% 60%

20% Saving in Time

Explanation?

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Design For Assembly NTTF

ConceptDesignSansDFMA

Detailed DesignPrototyping

&Design Changes

10% 40% 50%

Timeline for a Project

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Design For Assembly NTTF

ConceptDesignSansDFMA

Detailed DesignPrototyping

&Design Changes

10% 40% 50%

ConceptDesignwith

DFMA

20% 20%

Timeline for a Project

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Design For Assembly NTTF

ConceptDesignSansDFMA

Detailed DesignPrototyping

&Design Changes

10% 40% 50%

ConceptDesignwith

DFMA

DetailedDesign

Prototyping&

Design Changes20% 30% 30% 20%

Effect of Applying DFMA on New Product Development

20%

Timeline for a Project

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Design For Assembly NTTF

How does DFMA work?•Simplification of product

•Reduce the number of separate parts

•Reduce part count

•Three basic criteria to examine every part?

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Use the following guideline questions to evaluate the feasibility of combining parts:1. When the product is being used, does the part move with respect to mating parts?2. Must adjacent parts be made of different materials?3. If parts were combined, would assembly of other parts or field service be made more difficult or unfeasible?

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If the answer to any of the preceding questions is “Yes,” then it is probably not feasible to eliminate the part, but if the answer to all is “No,” the part is a good candidate to be combined with others.

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Design For Assembly NTTF

Drive Motor Assembly

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AFTER DFA

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AFTER DFA

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7 4 46

Candidates for elimination

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AFTER DFA

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BEFORE DFA AFTER DFA

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DFA DFM??

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Design for Assembly NTTF

1. Combine parts. Integrate the functions of several parts into one. For example:1.1 Incorporate hinges. Hinges can be incorporated in many plastics parts if theplastic material is flexible and the wall section is thin. This eliminates the need for a two- or three-part hinge and the fasteners required to attach it to two other parts. Many storage containers for consumer products are made with integral hinges. Both injection molding and thermoforming permit this design approach.

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Figure 7.1.1 illustrates a typical example, a container for a spare key, whose lid is held with a "living hinge" of the same material as the container and lid.

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1.2. Use integral springs. Springs can be incorporated in metal and plastic partsand sometimes those made of other materials such as fiber. The result is a simpler, faster assembly. Separate springs are often troublesome from a handling standpoint because they can tangle easily and because their flexibility makes them difficult to handle and insert in the assembly. The integral spring, therefore, provides very significant assembly advantages.

Design for Assembly NTTF

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Comment on this design of assembly

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1.3. Use snap fits. Replace screw-type and other separate fasteners with integral snap-fit elements, tabs, or catches. An example is shown in Fig. 7.1.3. It illustrates the kind of element which, when incorporated in a plastic or sheet metalpart, snaps into place in an undercut in the mating part to hold the two together.

Figure 7.1.3 shows a number of snap-fit assemblies of metal parts.

Design for Assembly NTTF

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???

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1.4. Incorporate guides, bearings, covers, etc. With some manufacturing processes, these elements can be incorporated in the basic part with a tremendous reduction in the number of components. Many plastic materials have natural lubricitythat makes them quite suitable for applications involving bearing surfaces, particularly if the velocity and pressure involved are low.

Design for Assembly NTTF

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For more demanding applications where bearings, slides, cranks, etc., are needed, powder-metal parts can be made with sufficient precision for these functions.

They also can be made with porosity so that lubricating oil is retained in the part itself.

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1.5. Put electrical and electronic components in one location, and consolidate components as much as possible. For example, one combination printed circuit board is preferable to several in separate locations; a light switch and ventilation switch on the same mounting plate is preferable to locating them separately,each with its own mounting hardware.

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DFA: The best assembly is usually the one that has the fewest parts and the least costly type of fastening (consistent, of course, with the functional requirements of the product). In the long run, the lowest-cost assembly is the one that minimizes the total costs for parts, assembly labor, finishing, tool amortization, and product service and warranties.Most of the design suggestions that follow are applicable to assemblies fastened by the purely mechanical methods mentioned above and to those welded, soldered, brazed, and bonded as well.

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Design for Assembly NTTF

Some processes allow very complex parts that result when separate parts are combined into one. Injection molding, die casting, and investment casting are examples.With these processes, a complex part, as would result from the combination of severalsimpler parts, primarily requires only a more complex mold or die. The extra complexity adds only marginally to the cost of the part made by the tooling.

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Some other specific guidelines for combining parts are the following:1. Use bent tabs or crimped sections instead of separate fasteners to hold several partstogether. (See Fig. 7.1.4.)

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Comment from DFA viewpoint?

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2. Use combined fasteners, i.e., those with integral washers.

Design for Assembly NTTF

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3. Instead of using nuts or threaded holes in mating parts, use self-tapping screws.This eliminates costly machining operations otherwise needed to provide a precision hole with internal screw threads.

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Design for Assembly NTTF

4. Use cast or molded-in identification instead of attached labels. Such identification is more reliable because it is more permanent. It completely eliminates the costs involved in purchasing, stocking, and affixing a separate label.

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Design for Assembly NTTF

5. Use integral locators, hooks, or lips to replace some of the fasteners holding one part to another. (See Fig. 7.1.5 for an example.)

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Comment on this assembly design

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6. Press fits, integral tabs, or rivets sometimes can be used to replace threaded or other fasteners that may be more complex.

Press fits with flexible or grooved components are normally less expensive and as effective as precision-machined parts.

Spring Dowel

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What can be this mechanism?

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Poka-Yoke Solution?

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Your comment on DFA?

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Self …….. Design?

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How to calculate optimum length?

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If upsetting over thinner / weaker material is unavoidable ….?

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Interpret

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Limits & Fits

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Auto Hopper Feed

Auto Hopper Feed

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DFA ASSIGNMENT :Please take up an assembly of your choice (Toys / low cost consumer items like a calling bell, stapler, document punching machine…..) & make an DFA analysis ‘before’ & ‘after,’ resulting in proposals for improving design efficiency. This is an individual exercise.