ME 349

ME 349

Design for Manufacturability (DFM)

"The key objective in any design for manufacturing

effort is to achieve simplicity ... There are many

things which are ... valid measures of simplicity ...

First is the number of parts. Second is assembly

time. You cannot assemble something in a very short

time if it's complex. Third is the number of

processes employed (And last) ... is the complexity

of the process ..."

Fred Schwager, DFM expert

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What is DFM?

DFM is an approach followed during the design

process that has the aim of improving

manufacturing productivity.

In a “for profit” endeavor:

productivity = profit

Objective is to reduce cost

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DFM is a tool

Estimation of part and tooling costs based upon:

Monolithic versus “built-up” geometry

Type(s) of material(s) used

Type(s) of process(es) used

Part size

Part complexity

Supplier operating cost

DFM Concurrent Costing software (CAE)

Manufacturing Cost Estimate Tool

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DFM Use

Do you, or the customer, have requirements on who

or where the product is manufactured?

Designers should keep up to date with available;

• Manufacturing processes (and assembly methods)

• Each has advantages and limitations

• Materials

• Unique properties that can be exploited in design?

• What manufacturing processes can shape a material?

• Components

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DFM

DFM is often divided into two subdivisions

DFP - Design for the Process

• Ease of fabrication

DFQ - Design for Quality

• Accuracy of features

DFM is intended to be used in conjunction with the

Design for Assembly (DFA) process.

These subdivisions overlap and sometimes

contradict

There always exists an element of trade-off in

applying DFM principles

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Common Rules of DFM

Simplify part geometry

• Minimizes the chances of a defective part

• Reduces the total cost of fabrication

Utilize common parts and materials across

product line

• Reduces component costs

• facilitates design activities

• minimizes the amount of inventory in the system

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Common Rules of DFM

Design modular products

Facilitates assembly with building block components

and subassemblies.

Design verifiability into the product and its

components

Eases testing and/or inspecting (non value added)

Increase part symmetry

Avoid unnecessary (non-functional) features

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Common Rules of DFM

Design for ease of fabrication (e.g., machining)

Avoid designs requiring sharp corners or points

• The required cutting tools break more easily

• Another process may be required: e.g., EDM, broaching, etc.

Do not to use walls and webs that are too thin

• These features can cause a part to distort during the machining

process.

Do not include pockets and holes that are too deep

• greater than 5:1 diameter to depth

Avoid tapers and contours unless required for part

functionality.

Place machined features in the same plane or same

diametric access if possible.

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Common Rules of DFM

Avoid impossible or difficult to machine features

No Yes No Yes

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Common Rules of DFM

Avoid impossible or difficult to machine features

No! No! Possible

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Common Rules of DFM

Use the widest possible

tolerances that ensure

function and assembly

Be aware of tolerance

stack-up which will

occur in assembly

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Common Rules of DFM

Design in the middle of a processes' tolerance

range

This allows you to avoid tight tolerances beyond the

natural capability of the manufacturing processes

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Tolerances Related to

Machining Processes

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Specify

surface

qualities

(roughness)

based upon

standard

practices

Design for adequate Surface Quality

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Common Rules of DFM

Consider the surfaces required for…

fixturing and clamping during fabrication,

inspection reference (datum features and targets)

Design parts for orientation and handling

Parts should be designed with surfaces so that they

can be easily grasped, positioned and fastened by

either a human or machine.

• Minimizes unnecessary manual effort

• Facilitates automation

• Avoid ambiguity in orienting and merging parts

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Common Rules of DFM

Surfaces to be machined must be accessible

when workpiece is fixtured

During machining, the tool and toolholder must not

interfere with remaining surfaces of workpiece

Avoid the requirement of part reorientation during

fabrication

Non-value added operations (time consuming)

Increase tolerances

Multi-axis and multi-function machine tools may

allow some relaxation of this restriction

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Common Rules of DFM

For example, provide relief to allow room

for thread cutting tool.

No Yes

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Common Rules of DFM

Design parts with multiple functions and uses

For example, combine mounting points into the

design of functional components.

Easier to make multiple parts of the same design

Use common parts across product lines

Make sure a dialogue is maintained between

designers, engineers, manufacturers and any

other individuals who play a part in determining

final product costs, especially during early stages

of design.

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Common Rules of DFM

Additionally…

Remember that the prototype may be

manufactured with different processes than will be

used for mass production

Shape parts and products for ease of packaging

Product/part should fit into standard packaging

cartons

Facilitates automation and shipment to customer

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DFM Examples A part where mating

surfaces need to be ground

Flatness

Positional accuracy

Surface roughness

Redesign is performed

Reduce area to be ground

Design all surfaces to be

ground in the same, or

parallel, planes

How was the net shape of

this part made?

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References

G. Boothroyd, P. Dewhurst, W. Knight, Product

Design for Manufacture and Assembly, 2002,

Dekker Publishing

J.T. Black and R.A. Kohser, DeGarmo’s Materials

& Processes in Manufacturing, 10th Edition, 2008,

Wiley.

M.P. Groover, Introduction to Manufacturing

Processes, 2012, Wiley.