sergio antonio salvi, design for manufacturing (lecture extract)

DESIGN FOR MANUFACTURING (DFM)

Sergio Antonio Salvi

PRODUCT DEVELOPMENT

DESIGN FOR MANUFACTURING

DFM concept

The Design for Manufacturing (DFM, also called “… for manufacturability”; cf. Boothroyd, Dewhurst), is a methodology that extends the recommendations of Design for Assembly (DFA), an engineering design approach developed in the eighties.

DFM and DFA come from the need to “drive cost”: design a product so that it is easily manufactured and assembled, means to save money.

In the field of the so called “design sciences” (born in Europe in the sixties), this innovation has also generated the concept “Design for X” (DFX, cf. Ulrich, Eppinger, 2000), in which the “parameter X” represents the problem that must be solved; in other words, the “main direction” the product development must follow (nowadays, for example, Design for X can be “declined” into “Design for Cost”, “Design for competitiveness” etc.).

PRODUCT DEVELOPMENT



“Input” and “output” flows in a productive system

PRODUCT DEVELOPMENT


RAW MATERIALSAND SEMIFINISHED

MATERIALS

ENERGY

WASTE

FINISHED ORSEMIFINISHEDPRODUCTS

informaz. services manpower(labour)

toolsexternal

“standardcomponents”

equipments

PRODUCTIVESYSTEM

informat.

MANUFACTURING COST

ASSEMBLINGCOMPONENTS GENERAL COSTS

internal(“already made”)

external(“to buy”)

to design(“to make”)

standard

row materials

process

tools

process

tools

labour

labour

support

indirect allocations


product manufacturing cost elements

PRODUCT DEVELOPMENT


MANUFACTURING COST

ASSEMBLINGCOMPONENTS GENERAL COSTS

internal(“already made”)

external(“to buy”)

to design(“to make”)

standard

row materials

process

tools

process

tools

labour

labour

support

indirect allocations


DFM principles

Referring to design development strategies, DFM, as mentioned, happens to be the most important methodology, due to its direct influence over production’s costs. It contemplates the following stages (cf. Ulrich, Eppinger, 2000):

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■ 1. production cost estimate;

■ 2.1 components cost reduction;

■ 2.2 assembly cost reduction (cf. DFA, design for assembly);

■ 2.3 production support cost reduction;

■ 3. evaluation of DFM decisions impact over other factors;

■ 4. production cost recalculation.

PRODUCT DEVELOPMENT



DFM flows

(→□)

1. production costestimate

briefing

4. production costrecalculation

2.2 assembly costreduction

3. evaluation of DFMdecisions impact

2.1 components costreduction

2.3 productionsupport cost red.

yesproject development

nofair?PRODUCT

DEVELOPMENT



2.1 components cost reduction: ”NETSHAPE” MANUFACTURING

■ “Net-shape” manufacturing (in a completely definitive way) previews the use of construction processes able to a functional integration of the manufacture goods through its production in only one stage.

■ Components reduction, which is determined by the net-shape processes choice, avoids to resort to different technologies and therefore to materials and to unlike parts management, reducing at the same time costs of assembly.

■ Technologies that mostly satisfy this principle are those using moulds, injection moulding and die casting for first.

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PRODUCT DEVELOPMENT



2.1 components cost reduction: ”NETSHAPE” MANUFACTURING

PRODUCT DEVELOPMENT



2.1 components cost reduction: CHOICE OF THE ECONOMICAL SCALE

■ Usually manufacture cost decreases with the increase of production volume. This happens because the “fixed costs” are divided from the produced units (“amortization”) and, together, “variable costs” decrease due to the fact that the company can justify the access to a bigger scale economy (for example, buy the material at a lower cost).

■ In a productive system fixed costs are represented, for instance, from manufacturing equipment (“set up” operations and, in the most typical case, tools design and construction: cuttings, moulds and so on).

■ Variable costs (variable along with the production!) are instead traceable to: materials, machine-hours and so on.

■ In other words: to produce few units it is convenient to have available processes at low fixed costs and high variable costs; on the contrary for what concerns high productions.

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2.1 components cost reduction: CHOICE OF THE ECONOMICAL SCALE

produced units

total cost

machine toolmachining

injectionmoulding

mould cost

set up cost

equality point

PRODUCT DEVELOPMENT



2.1 components cost reduction: STANDARDIZING COMPONENTS

■ The use of standard components in the industrially produced object is fundamental. Their use means you don’t have to be in charge of their design (or redesign them) and to produce them (or produce them again). In the historic scenery of productions oriented towards design there are even some objects, called “ready-made”, which were almost integrally built resorting to parts already in the market.

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■ External standard components, parts that can be acquired “through a catalogue”, are produced by specialised suppliers and traded at a restrained cost, justified by their high production. Besides, for the same reason, their quality is medium-high. Examples of this category are the mechanical union elements (screws, and so on) and some electrical devices (engines, cables and so on).

■ Unfortunately, often some parts don’t interest this kind of market, but now and then, a company may decide to design and produce internal standard components, able to satisfy the needs of products frequently based on the same platform (wheel rims in cars, toners cartridges and so on).


2.1 components cost reduction: STANDARDIZING COMPONENTS (“Mezzadro” by A. and P. Castiglioni; seat was first applied to an agricultural vehicle)

PRODUCT DEVELOPMENT AND MANUFACTURING TECHNOLOGIES



2.1 components cost reduction: “BLACK BOX” METHOD

■ “Black box” components acquisition method has origin in the Japanese automotive industry experience (cf. Clark, Fujimoto, 1991). It was found out that giving only target specifications to supplier (the product requirements asked for), without an executive project, generated a process of cost reduction and of quality increase.

■ This methodology is obviously sustainable when the interaction with product arquitecture and its components, assembly interface (and so on) are communicated precisely. Consider also the importance of putting in competition a series of suppliers.

■ The advantages are significant: an activity of research and development at zero costs is set up, there is no need for an internal design of parts, as a consequence the company is partially taken off responsibility.

PRODUCT DEVELOPMENT AND MANUFACTURING TECHNOLOGIES


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