AVAILABLE TOOLS AND METHODS FOR DFMA

Infinite tools and methodologies may be used to accomplish the goal of a DFMA program. However, all of them fall into two categories: (a) approach alternatives and (b) mechanics. Some of the most important ones are listed below:

Approach alternatives:

Ongoing program/project manager approach
Manufacturing engineering sign-off approach
Design engineering use simulation software package approach
Simultaneous engineering approach
Concurrent engineering approach
Integrator approach

Mechanics:

Quality function development (QFD)
Design of experiments (DOE)
Potential failure mode and effects analysis (FMEA)
Value engineering and value analysis (VE/VA)
Group technology (GT)
Geometric dimensioning and tolerancing (GD&T)
Dimensional assembly analysis (DAA)
Process capability study (C _pk , P _pk , C _p , C _r , ppm indices)
Just-in-time (JIT)
Qualitative assembly analysis (QAA)

COOKBOOKS FOR DFM/DFA

There are no cookbooks for DFMA. However, three organized instruction manuals may be close to most engineers ' terms of guidelines. They are:

Mitsubishi method
U-MASS method
MIL-HDB-727 design guidance for producibility

All of the above methods utilize the principles of Taylor's motion economy, which have been proven to be quite helpful, especially in the DFA area. We identify some of these principles here that may be profitably applied to shop and office work alike. Although not all are applicable to every operation, they do form a basis or a code for improving efficiency and reducing fatigue in manual work:

Smooth continuous curved motions of the hands are preferable to straight-line motions involving sudden and sharp changes in direction.
Ballistic movements are faster, easier, and more accurate than restricted (fixation) or "controlled" movements.
Work should be arranged to permit easy and natural rhythm wherever possible.

Use of the Human Body

The two hands should begin as well as complete their motions at the same time.
The two hands should not be idle at the same time except during rest periods.
Motions of the arms should be made in opposite and symmetrical directions and should be made simultaneously .
Hand and body motions should be confined to the lowest classification with which it is possible to perform the work satisfactorily.
Momentum should be employed to assist the worker wherever possible, and it should be reduced to a minimum if it must be overcome by muscular effort.
Eye fixations should be as few and as close together as possible.

Arrangement of the Work Place

There should be a definite and fixed place for all tools and materials.
Tools, materials, and controls should be located close to the point of use.
Gravity feed bins and containers should be used to deliver material close to the point of use.
Drop deliveries should be used wherever possible.
Materials and tools should be located to permit the best sequence of motions.
Provisions should be made for adequate conditions for seeing. Good illumination is the first requirement for satisfactory visual perception.
The height of the work place and the chair should preferably be arranged so that alternate sitting and standing at work are easily possible.
A chair of the type and height to permit good posture should be provided for every worker.

Design of Tools and Equipment

The hands should be relieved of all work that can be done more advantageously by a jig, a fixture, or a foot -operated device.
Two or more tools should be combined wherever possible.
Tools and materials should be pre-positioned whenever possible.
Where each finger performs some specific movement, such as in typewriting, the load should be distributed in accordance with the inherent capacities of the fingers.
Levers, crossbars, and hand wheels should be located in such positions that the operator can manipulate them with the least change in body position and with the greatest mechanical advantage.

MITSUBISHI METHOD

The Mitsubishi method was developed and fine- tuned by Japanese engineers in Mitsubishi's Kobe shipyard. The primary principle is the combination of QFD and Taylor's motion economy. The Mitsubishi method is very popular in Japan's heavy industries, i.e., shipbuilding industry, steel industry, and heavy equipment industry. There is also evidence of some application of this method in Japan's automotive, motorcycle, and office equipment industries. More efforts are needed to promote and share these techniques, and some effort is needed to fine-tune the Mitsubishi method and make it practical to fit U.S. manufacturing companies' cultures and traditions.

The process is based on the following principles:

The Mitsubishi method focuses on the product design's reflection of the customer's desires and tastes. Thus, marketing people, design engineers, and manufacturing staff must work together from the time a product is first conceived.
The Mitsubishi method is a kind of conceptual map that provides the means for inter-functional planning and communications. People with different problems and responsibilities can thrash out design priority while referring to patterns of evidence on the house's grid.
The method involves 12 steps for each part in design/manufacturing, as follows :
1. Customer attributes (CA) analysis ” also called voice of customer (VOC) evaluation ” is performed.
2. Relative-importance weights of CA are determined.
3. Data is collected on customer evaluations of competitive products.
4. Engineering characteristics tell how to change the product.
5. Relationship matrix shows how engineering decisions affect customer perceptions.
6. Objective measures evaluate competitive products.
7. Roof matrix facilitates engineering creativity.
8. QFD is finalized.
9. Parts development is based on manufacturing process planning and handling planning (i.e., start the basic manufacturing process with materials in liquid state, feeding raw materials with elevator feeder, handling the wip with center board hopper, and continuing the forthcoming sequential operation with carousel assembly machine).
10. Manufacturing process and handling operation are based on the principles of motion economy.
11. Process planning is guided by parts/component characteristics, which are based on engineering characteristics, and the latter are based on customer attributes (compare to step #9).
12. Integrator coordinates/controls the project.
Analysis procedure.
Continuing improvement:

Voice of customer, design alternative, and process alternative continue to interface with each other. It is a dynamical situation ” no ending improvement.

Software package.

Table 5.1 shows an example of customer attributes (Cas) and bundles of CAs for a car door. An example of relative importance weights of customer attributes is shown in Table 5.2. An example of customer evaluations of competitive products is shown in Table 5.3.

Table 5.1: Customer Attributes for a Car Door
Primary	Secondary	Tertiary
	Easy to open and close	Easy to close from outside Stays open on a hill Easy to open from outside Does not kick back Easy to close from inside Easy to open from inside
Good operation and use	Isolation	Does not leak in rain No road noise Does not leak in car wash No wind noise Does not drip water or snow when open Does not rattle
	Arm rest	Soft, comfortable In right position
	Interior trim	Material will not fade Attractive (non-plastic look)
Good appearance	Clean	Easy to clean No grease from door
Good appearance	Fit	Uniform gaps between matching panels

Table 5.2: Relative Importance of Weights
Bundles	Customer Attributes	Relative Importance
Easy to open and close door	Easy to close from outside	7
Easy to open and close door	Stays open on a hill	5
Isolation	Does not leak in rain	3
	No road noise	2
	A complete list totals	100%

Table 5.3: Customer's Evaluations of Competitive Products
Bundles	Customer Attributes	Relative Importance	Customer Perceptions
Easy to open and close door	Easy to close from outside	7	Worst				Best
Easy to open and close door	Stays open on a hill	5	1	2	3	4	5
Isolation	Does not leak in rain	3	Worst				Best
	No road noise	2	1	2	3	4	5
	A complete list totals	100%	Comparison is based on individual attributes as compared to: Our car door Competitor A's Competitor B's And so on...

U-MASS METHOD

The U-MASS method is named for the University of Massachusetts, where it was developed by two professors, Geoffrey Boothroyd and Peter Dewhurst, and their graduate students. It is the most common DFM/DFA approach used in the U.S. The primary principle is the conventional motion and time study, while keeping in mind the component counts and motion economy.

This method is heavily promoted in academic communities or institute- related manufacturing companies located in the New England area, such as Digital Equipment Corp. and Westinghouse Electric Company. Other companies are using it as well, such as Ford Motor Co., DaimlerChrysler, and many others. Its appeal seems to be the availability of the software that may be purchased from Boothroyd and Dewhurst. (Some practitioners find the software very time-consuming in design efficiency calculation and believe that more work is needed to fine tune its efficiency, as well as make it more user friendly.) The process is based on the following principles:

Determine the theoretical minimum part count by applying minimum part criteria.
Estimate actual assembly time using DFA database.
Determine DFA Index by comparing actual assembly time with theoretical minimum assembly time.
Identify assembly difficulties and candidates for elimination that may lead to manufacturing and quality problems.

MIL-HDBK-727

This method was developed by the U.S. Army material command and published by the naval publications and forms center. The first edition was published in 1971, and the latest revision was published in April 1984. The primary principle is Taylor's motion economy and some other design tools, i.e., DOE. This method is not too popular. Not many people know about it, and it is not used very much outside of the military. Some updates and revisions are needed to make it more practical to general manufacturing companies.