30079_30.pdf

PART 3

MANUFACTURING ENGINEERING

CHAPTER 30

PRODUCT DESIGN FOR

MANUFACTURING AND ASSEMBLY

(DFM&A)

Gordon Lewis

Digital Equipment Corporation

Maynard, Massachusetts

30.1 INTRODUCTION

935

30.2.2 Getting the DFM&A

Process Started 942

30.2.3 The DFM&A Road Map 946

30.2 DESIGN FOR

MANUFACTURING AND

ASSEMBLY

936

30.3 WHY IS DFM&A

IMPORTANT?

30.2.1 What is DFM&A?

937

950

30.1 INTRODUCTION

Major changes in product design practices are occurring in all phases of the new product development

process. These changes will have a significant impact on how all products are designed and the

development of the related manufacturing processes over the next decade. The high rate of technology

changes has created a dynamic situation that has been difficult to control for most organizations.

There are some experts who openly say that if we have no new technology for the next five years,

corporate America might just start to catch up. The key to achieving benchmark time to market, cost,

and quality is in up-front technology, engineering, and design practices that encourage and support

a wide latitude of new product development processes. These processes must capture modern man-

ufacturing technologies, piece parts that are designed for ease of assembly, and parts that can be

fabricated using low-cost manufacturing processes. Optimal new product design occurs when the

designs of machines and of the manufacturing processes that produce those machines are congruent.

The obvious goal of any new product development process is to turn a profit by converting raw

material into finished products. This sounds simple, but it has to be done efficiently and economically.

Many companies do not know how much it costs to manufacture a new product until well after the

production introduction. Rule #1: the product development team must be given a cost target at the

start of the project. We will call this cost the unit manufacturing cost (UMC) target. Rule #3: the

product development team must be held accountable for this target cost. What happened to rule #21

We'll discuss that shortly. In the meantime, we should understand what UMC is.

UMC = BL + MC + TA

where BL = burdened assembly labor rate per hour; this is the direct labor cost of labor, benefits,

and all appropriate overhead cost

MC = material cost; this is the cost of all materials used in the product

TA = tooling amortization; this is the cost of fabrication tools, molds and Assembly Tooling,

divided by the forecast volume build of the product

UMC is the direct burdened assembly labor (direct wages, benefits, and overhead) plus the material

cost. Material cost must include the cost of the transformed material plus piece part packaging plus

duty, freight, and insurance (DIP). Tooling amortization should be included in the UMC target cost

calculation, based on the forecast product life volume.

Mechanical Engineers' Handbook, 2nd ed., Edited by Myer Kutz.

Example UMC Calculation BL + MC + TA

Burdened assembly labor cost calculation (BL)

Labor

BL - ($18.75 + 138%) - $44.06/hr

Wages+Benefits overhead

Burdened assembly labor is made up of the direct wages and benefits paid to the hourly workers,

plus a percentage added for direct overhead and indirect overhead. The overhead added percentage

will change from month to month based on plant expenses.

Material cost calculation (MC)

(Part Cost + Packaging) + DIP + Mat. Acq. Cost =

MC = ($2.45 + $.16) + 12% + 6%

MC = $2.61

+ $.31 + $.15

- $3.07

Material FOB Assm. Plant

Material cost should include the cost of the parts and all necessary packaging. This calculation should

also include a percent adder for duty, freight, and insurance (DPI) and an adder for the acquisition

of the materials (Mat. Acq.). DIP typically is between 4% and 12% and Mat. Acq. typically is in

the range of 6% to 16%. It is important to understand the MC because material is the largest expense

in the UMC target.

Tooling amortization cost calculations (TA)

(Tool Cost) # of parts

TA - TC / PL

TA = $56,000/10,000 = $5.60 per assembly

TC is the cost of tooling and PL is the estimated number of parts expected to be produced on this

tooling. Tooling cost is the total cost of dies and mold used to fabricate the component parts of the

new product. This also should include the cost of plant assembly fixtures and test and quality in-

spection fixtures.

The question is, "How can the product development team quickly and accurately measure UMC

during the many phases of the project?" What is needed is a tool that provides insight into the

product structure and at the same time exposes high-cost areas of the design.

30.2 DESIGN FOR MANUFACTURING AND ASSEMBLY

Designing for Manufacturing and Assembly (DFM&A) is a technique for reducing the cost of a

product by breaking the product down into its simplest components. All members of the design team

can understand the product's assembly sequence and material flow early in the design process.

DFM&A tools lead the development team in reducing the number of individual parts that make

up the product and ensure that any additional or remaining parts are easy to handle and insert during

the assembly process. DFM&A encourages the integration of parts and processes, which helps reduce

the amount of assembly labor and cost. DFM&A efforts include programs to minimize the time it

takes for the total product development cycle, manufacturing cycle, and product life-cycle costs.

Additionally, DFM&A design programs promote team cooperation and supplier strategy and business

considerations at an early stage in the product development process.

The DFM&A process is composed of two major components: design for assembly (DFA) and

design for manufacturing (DFM). DFA is the labor side of the product cost. This is the labor needed

to transform the new design into a customer-ready product. DFM is the material and tooling side of

the new product. DFM breaks the parts fabrication process down into its simplest steps, such as the

type of equipment used to produce the part and fabrication cycle time to produce the part, and

calculates a cost for each functional step in the process. The program team should use the DFM tools

to establish the material target cost before the new product design effort starts.

Manufacturing costs are born in the early design phase of the project. Many different studies have

found that as much as 80% of a new product's cost is set in concrete at the first drawing release

phase of the product. Many organizations find it difficult to implement changes to their new product

development process. The old saying applies: "only wet babies want to change, and they do it

screaming and crying." Figure 30.1 is a memo that was actually circulated in a company trying to

implement a DFM&A process. Only the names have been changed.

It is clear from this memo that neither the engineering program manager nor the manufacturing

program manager understood what DFM&A was or how it should be implemented in the new product

development process. It seems that their definition of concurrent engineering is, "Engineering creates

the design and manufacturing is forced to concur with it with little or no input." This is not what

DFM&A is.

Memorandum: Ajax Bowl Corporation

DATE: January 26, 1997

TO: Manufacturing Program Manager, Auto Valve Project

FROM: Engineering Program Manager, Auto Valve Project

RE: Design for Manufacturing & Assembly support for Auto Valve Project

CC: Director, Flush Valve Division

Due to the intricate design constraints placed on the Auto Valve project engineering feels they will

not have the resources to apply the Design for Manufacturing and Assembly process. Additionally,

this program is strongly schedule driven. The budget for the project is already approved as are

other aspects of the program that require it to be on-time in order to achieve the financial goals of

upper management.

In the meeting on Tuesday, engineering set down the guidelines for manufacturing involvement on

the Auto Valve project. This was agreed to by several parties (not manufacturing) at this meeting.

The manufacturing folks wish to be tied early into the Auto Valve design effort:

1. This will allow manufacturing to be familiar with what is coming.

2. Add any ideas or changes that would reduce overall cost or help schedule.

3. Work vendor interface early, manufacturing owns the vendor issues when the product comes to

the plant, anyways.

Engineering folks like the concept of new ideas, but fear:

1. Inputs that get pushed without understanding of all properly weighted constraints.

2. Drag on schedule due to too many people asking to change things.

3. Spending time defending and arguing the design.

PROPOSAL—Turns out this is the way we will do it.

Engineering shall on a few planned occasions address manufacturing inputs through one manu-

facturing person. Most correspondence will be written and meeting time will be minimal. It is un-

derstood that this program is strongly driven by schedule, and many cost reduction efforts are

already built into the design so that the published budget can be met.

The plan for Engineering:

• When drawings are ready, Engineering Program Manager (EPM) will submit them to Manufac-

turing Program Manager (MPM).

• MPM gathers inputs from manufacturing people and submits them back in writting to EPM.

MPM works questions through EPM to minimize any attention units that Engineering would

have to spend.

• EPM submits suggestions to Engineering, for one quick hour of discussion/acceptance/veto.

• EPM submits written response back to MPM and works any Design continues under ENG

direction.

• When a prototype parts arrives, the EPM will allow the MPM to use it in manufacturing

discussions.

• MPM will submit written document back to EPM to describe issues and recommendations.

• Engineering will incorporate any changes that they can handle within the schedule that they see

fit.

Fig. 30.1

30.2.1 What is DFM&A?

DFM&A is not a magic pill. It is a tool that, when used properly, will have a profound effect on the

design philosophy of any product. The main goal of DFM&A is to lower product cost by examining

the product design and structure at the early concept stages of a new product. DFM&A also leads

to improvements in serviceability, reliability, and quality of the end product. It minimizes the total

product cost by targeting assembly time, part cost, and the assembly process in the early stages of

the product development cycle.

The life of a product begins with defining a set of product needs, which are then translated into

a set of product concepts. Design engineering takes these product concepts and refines them into a

detailed product design. Considering that from this point the product will most likely be in production

for a number of years, it makes sense to take time out during the design phase to ask, "How should

this design be put together?" Doing so will make the rest of the product life, when the design is

complete and handed off to production and service, much smoother. To be truly successful, the

DFM&A process should start at the early concept development phase of the project. True, it will

take time during the hectic design phase to apply DFM&A, but the benefits easily justify additional

time.

DFM&A is used as a tool by the development team to drive specific assembly benefits and identify

drawbacks of various design alternatives, as measured by characteristics such as total number of

parts, handling and insertion difficulty, and assembly time. DFM&A converts time into money, which

should be the common metric used to compare alternative designs, or redesigns of an existing concept.

The early DFM&A analysis provides the product development team with a baseline to which com-

parisons can be made. This early analysis will help the designer to understand the specific parts or

concepts in the product that require further improvement, by keeping an itemized tally of each part's

effect on the whole assembly. Once a user becomes proficient with a DFM&A tool and the concepts

become second nature, the tool is still an excellent means of solidifying what is by now second

nature to DFA veterans, and helps them present their ideas to the rest of the team in a common

language: cost.

DFM&A is an interactive learning process. It evolves from applying a specific method to a change

in attitude. Analysis is tedious at first, but as the ideas become more familiar and eventually ingrained,

the tool becomes easier to use and leads to questions: questions about the assembly process and

about established methods that have been accepted or existing design solutions that have been

adopted. In the team's quest for optimal design solutions, the DFM&A process will lead to uncharted

ways of doing things. Naturally, then, the environment in which DFA is implemented must be ripe

for challenging pat solutions and making suggestions for new approaches. This environment must

evolve from the top down, from upper management to the engineer. Unfortunately, this is where the

process too often fails.

Figure 30.2 illustrates the ideal process for applying DFM&A. The development of any new

product must go through four major phases before it reaches the marketplace: concept, design, de-

velopment, and production. In the concept phase, product specifications are created and the design

team creates a design layout of the new product. At this point, the first design for assembly analysis

should be completed. This analysis will provide the design team with a theoretical minimum parts

count and pinpoint high-assembly areas in the design.

At this point, the design team needs to review the DFA results and adjust the design layout to

reflect the feedback of this preliminary analysis. The next step is to complete a design for manufac-

turing analysis on each unique part in the product. This will consist of developing a part cost and

tooling cost for each part. It should also include doing a producibility study of each part. Based on

the DFM analysis, the design team needs to make some additional adjustments in the design layout.

At this point, the design team is now ready to start the design phase of the project. The DFM&A

input at this point has developed a preliminary bill of material (BOM) and established a target cost

for all the unique new parts in the design. It has also influenced the product architecture to improve

the sequence of assembly as it flows through the manufacturing process.

The following case study illustrates the key elements in applying DFM&A. Figure 30.3 shows a

product called the motor drive assembly. This design consists of 17 parts and assemblies. Outwardly

it looks as if it can be assembled with little difficulty. The product is made up of two sheet metal

parts and one aluminum machined part. It also has a motor assembly and a sensor, both bought from

an outside supplier. In addition, the motor drive assembly has nine hardware items that provide other

functions—or do they?

At this point, the design looks simple enough. It should take minimal engineering effort to design

and detail the unique parts and develop an assembly drawing. Has a UMC been developed yet? Has

a DFM&A analysis been performed? The DFA analysis will look at each process step, part, and

subassembly used to build the product. It will analyze the time it takes to "get" and "handle" each

part and the time it takes to insert each part in the assembly (see Table 30.1). It will point out areas

where there are difficulties handling, aligning, and securing each and every part and subassembly.

The DFM analysis will establish a cost for each part and estimate the cost of fabrication tooling.

The analysis will also point out high-cost areas in the fabrication process so that changes can be

made.

At this point, the DFA analysis suggested that this design could be built with fewer parts. A

review of Table 30.2, column 5, shows that the design team feels it can eliminate the bushings, stand-

offs, end-plate screws, grommet, cover, and cover screws. Also by replacing the end plate with a

new snap-on plastic cover, they can eliminate the need to turn the (reorientation) assembly over to

install the end plate and two screws. Taking the time to eliminate parts and operations is the most

powerful part of performing a DFA analysis. This is rule #2, which was left out above: DFM&A is

a team sport. Bringing all members of the new product development team together and understanding

the sequence of assembly, handling, and insertion time for each part will allow each team member

to better understand the function of every part.

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