Design for manufacturability (also referred to as design for manufacture and assembly—DFMA) centers around a group of common-sense concepts and tech-niques that ensure that a product design can be produced within projected cost.
In this case, manufacturability refers to the company’s ability to produce and test or inspect the product as well as its ability to purchase required materials.
Therefore, supplier capability must also be a consideration. This process focuses on the reduction of manufacturing cost through decreasing labor and material costs. Specifi c techniques include reducing the total number of parts, the number of different parts, the total number of manufacturing operations, and making use of available production capabilities.
Of course, having a good understanding of the true needs of the customer is helpful, as consideration of manufacturing capabilities often turns to a discussion of trade-offs. Therefore, DFM is closely related to value engineering, which is a tech-nique for evaluating the design of a product to assure that the essential functions are provided at a minimal overall cost to the manufacturer or user. In other words, don’t provide “bells and whistles” when the customer doesn’t want bells or whistles.
The bells and whistles will certainly come at a cost. Therefore, a good question to ask is: “Can a design element be eliminated altogether?” Over-designing, in which the product performance exceeds the needs of the customer, also comes at a cost.
The specifi c techniques of DFM will vary based on the product being designed. Typically, ideas are generated as part of a brainstorming exercise involving cross-functional representatives to identify numerous alternatives to specifi c design elements being considered.
Some general questions to prompt meaningful discussion for mechanical design elements are
Can a lesser level of quality be used? For example, can a coarser surface
◾
fi nish be used? Can a lesser fl atness requirement be used?
Can available or preexisting parts be used? Do design libraries exist where
◾
existing parts can be quickly identifi ed for potential use?
108 ◾ Appendix
Can several parts be combined? What would be the impact on
manufactur-◾
ing? Consideration of size and weight must be given.
What number and length of welds is really needed? Can welds be replaced
◾
by bends or mechanical fasteners? Less skilled labor would be required.
What would be the impact on manufacturing?
Can the type of fasteners be standardized? Can almost-like parts be made
◾
the same? Can the number of fasteners be reduced? Avoid two-part fasten-ers. Use captive or snap together fasteners where possible.
Can the design be such that it allows for mistake-proofi ng techniques in
◾
assembly? Can parts be designed so that they can only be assembled or oriented in one way? Will the design lend itself to the use of fi xtures in assembly?
Can the parts be designed to be self-aligning or self-locating?
◾
How will part characteristics be assessed (e.g., inspected, tested)? Can they
◾
make use of available techniques?
Are component dimensions compatible with the standard raw stock from
◾
which they will be made? Can the raw stock be easily purchased?
What grade of material is really required? Can a lesser grade, alloy, etc., be
◾
used without jeopardizing design integrity?
Will the materials being considered require any special handling or machining
◾
processes (e.g., hazardous materials)? What will be the impact on safety, cost?
Can a casting be replaced with plastic components that can be molded,
◾
extruded, or formed? What would be the cost and lead time impact?
What external processes will be required when internal capabilities do not
◾
exist? What will be the impact on cost and lead time?
Can slots, pear-shaped holes, and other techniques be included in the design
◾
to permit use of less precise machining methods and to facilitate assembly?
Can the design be modularized in a way that permits cellular manufacturing
◾
to be effectively used in production? Work balancing is a consideration here.
Ideally, no module should require substantially more time than another.
Can part accessibility and orientation be such that it allows for ease of
◾
manufacturing (e.g., top-down assembly)? Can the number of times a part has to be reoriented during assembly be reduced? How about the impact on machining? Will less complicated machining methods be required?
What impact will the size and weight of components have on material
han-◾
dling in operations? Can less complicated methods be used?
What is the labor required to prepare the fi nished product for
transporta-◾
tion? Can the number of packaging components be reduced? Packaging is a design in and of itself. So, many of the questions previously stated will apply.
Some general questions and statements to prompt meaningful discussion for electrical design elements include:
Can standard off-the-shelf electrical components be used? These typically
◾
require much less lead time to procure.
Appendix ◾ 109
Will the electrical components selected lend themselves to available
manu-◾
facturing capability, such as surface mount or automated pick and place machines? Can secondary manual assembly be eliminated? Be certain to allow suffi cient clearance for machine insertion.
Align ICs (integrated circuits) and polarized components (e.g., diodes) in the
◾
same direction.
Standardize hole sizes in through-hole boards.
◾
Can standard size circuit boards be used? What will be the impact on
man-◾
ufacturing of any “batching” of printed circuit boards where many smaller boards are made from a single larger board and then cut and/or trimmed?
Can the number of layers of a printed circuit board be reduced, which
typi-◾
cally results in lower cost?
Would application-specifi c integrated circuits (ASICs) be less costly than a
◾
printed circuit board?
Can the number of connections be reduced? Can standard connectors be used?
◾
Can software programming (e.g., burn-in, tuning) of components or the
electri-◾
cal assembly itself simplify the design and, in turn, the manufacturing process?
What will be the impact on testing? Does the design lend itself to available
◾
testing capabilities? How about accessibility to perform required tests?
What is the expected test cycle time? Can the test be modularized? What
◾
in-process testing can be performed to ensure product quality throughout the manufacturing process, rather than relying solely on an end-of-line test?
Perhaps isolating design elements or partitioning techniques will allow for this.
Does the printed circuit board or electronic assembly require a particular
◾
coating or epoxy potting? What is the cure time for coatings being consid-ered? Can cure times be reduced with use of a specifi c coating or by use of elevated temperature cures?
Do the materials being considered for use require any special handling or
◾
manufacturing processes? What impact will there be on safety, cost, waste disposal?
Some general questions to prompt meaningful discussion for software design elements include:
Can software code be used from previous product designs? Can
commer-◾
cially available code be used?
Can hardware functions be replaced with software?
◾
Can testing, adjustments, maintenance, etc. be handled by software?
◾
Are industry software development standards being used?
◾
Can user interface software or hardware be simplifi ed?
◾
Are effi cient software development tools being used to reduce development
◾ cost?
How can the software be tested before being integrated with the hardware
◾
(e.g., simulations)? How can the code be easily debugged and corrected when problems arise?
110 ◾ Appendix
How can upgrades be performed easily? Will modularity in software code
◾
make upgrades easier and less costly?
Are built-in-test or built-in-diagnostic capabilities warranted in the design?
◾
A review of the questions presented reveals that the subject of DFM or DFMA really goes well beyond manufacturing. It also includes testability, reliability, maintainability, safety, and environmental considerations. Some additional ques-tions and statements to be considered (Mascitelli 2004) are:
Can testability be improved by having a single test connection? Is there
suf-◾
fi cient accessibility and clearance to perform required testing?
Can testing be made autonomous with automated alarming or signals to
◾
communicate failures? This will eliminate or at least reduce “machine watch-ing” by production or quality assurance personnel.
Can quick disconnect methods be used to facilitate the testing process (e.g.,
◾
pressure testing)?
Can reliability be improved by avoiding dissimilar metal interfaces? Are
◾
there any other sources of potential corrosion?
Are there any sources of potential wear (e.g., abrasion, mechanical wear,
◾
electromigration)?
Can stresses on components be reduced in some way (e.g., changing part
◾
orientation, reducing thermal loads, balancing mechanical loads)?
Can the number of interconnections be reduced, thereby improving
reliabil-◾
ity over time?
Avoid sharp corners, edges, points, etc. that can potentially injure
assem-◾
blers or users.
Ensure that any components expected to require service in the future are
◾
easily accessible and removable (e.g., fi eld replaceable units).
Ensure visibility of any gauges and the like that require monitoring to
◾
assure proper equipment function.
Access covers should be easy to open and self-supporting.
◾