DESIGN FOR MANUFACTURABILITY

by Dr. David M. Anderson, P.E., CMC
www.design4manufacturability.com
Copyright © 2000 by David M. Anderson

	Design for manufacturability is the process of proactively designing products to (1) optimize all the manufacturing functions: fabrication, assembly, test, procurement, shipping, delivery, service, and repair, and (2) assure the best cost, quality, reliability, regulatory compliance, safety, time-to-market, and customer satisfaction.

	DFM is a proven design methodology that works for any size company. Early consideration of manufacturing issues shortens product development time, minimizes development cost, and ensures a smooth transition into production for quick time to market. 

	Quality can be designed in with optimal part selection and proper integration of parts, for minimum interaction problems. By considering the cumulative effect of part quality on product quality, designers are encouraged to carefully specify part quality.

	Many costs are reduced, since products can be quickly assembled from fewer parts. Thus, products are easier to build and assemble, in less time, with better quality. Parts are designed for ease of fabrication and commonality with other designs. DFM encourages standardization of parts, maximum use of purchased parts, modular design, and standard design features. Designers will save time and money by not having to "re-invent the wheel." The result is a broader product line that is responsive to customer needs.  Click here for article on standardization.

	Companies that have applied DFM have realized substantial benefits. Costs and time-to-market are often cut in half with significant improvements in quality, reliability, serviceability, product line breadth, delivery, customer acceptance and, in general, competitive posture

Designing Products for Manufacturability

In order to design for manufacturability, everyone in product development team needs to:

   C	In general, understand how products are manufactured through experience in manufacturing, training, rules/guidelines, and/or multi-functional design teams with manufacturing participation.

   C	Specifically, design for the processes to be used to build the product you are designing: If products will be built by standard processes, design teams must understand them and design for them.  If processes are new, then design teams must concurrently design the new processes as they design the product.

The Bad Old Days

	Before DFM, the motto was “I designed it; you build it!”  Design engineers worked alone or only in the company of other design engineers in “The Engineering Department.”  Designs were then thrown over the wall leaving manufacturing people with the dilemma of either objecting (but its to late to change the design!) or struggling to launch a product that was not designed for manufacturability.  Often this delayed the both the product launch and the time to ramp up to full production, which is the only meaningful measure of time-to-market.

The Good New Days of Product Development Teams

	One way that manufacturability can be assured is by developing products in multi-functional teams with early and active participation from Manufacturing, Marketing (and even customers), Finance, Industrial Designers, Quality, Service, Purchasing, Vendors, Regulation Compliance specialists, Lawyers, and factory works.  The team works together to not only design for functionality, but also to optimize cost, delivery, quality, reliability, ease of assembly, testability, ease of service, shipping, human factors, styling, safety, customization, expandability, and various regulatory and environmental compliance.

The Importance of Early Concept & Product Architecture Decisions
    
By the time a product has been designed, only 8% of the total product budget has been spent.  By that time, the design has determined 80% of the cost of the product!  See graph from the book, Design for Manufacturability, Optimizing Cost, Quality, and Time-to-Market.1   The design determines the manufacturability which determines a significant part of the introduction and production cost (the 80%) of the product.  Once this cost is locked in, it is difficult for manufacturing to remove it.  Note that the concept or architecture alone determines 60% of the cost!
	
Off-the-shelf Parts

	Paradoxically, one of the first decisions the team has to make is the optimal use of off-the-shelf parts.  In many cases, the architecture may have to literally be designed around the off-the-shelf components, but this can provide substantial benefits to the product and the product development process:

	Off-the-shelf parts are less expensive to design considering the cost of design, documentation, prototyping, testing, the overhead cost of purchasing all the constituent parts, and the cost of non-core-competency manufacturing.  Off-the-shelf parts save time considering the time to design, document, administer, and build, test, and fix prototype parts.

	Suppliers of off-the-shelf parts are more efficient at their specialty, because they are more experienced on their products, continuously improve quality, have proven track records on reliability, design parts better for DFM, dedicate production facilities, produce parts at lower cost, offer standardized parts, and sometimes pick up warrantee/service costs.

	Finally, off-the-shelf part utilization helps internal resources focus on their real missions: designing products and building products

Some Key DFM Guidelines

A1)	Understand manufacturing problems/issues of current/past products

In order to learn from the past and not repeat old mistakes, it is important to understand all problems and issues with current and past products with respect to manufacturability, introduction into production, quality, repairability, serviceability, regulatory test performance, and so forth.  This is especially true if previous engineering is being “leveraged” into new designs.

A2)	Design for easy fabrication, processing, and assembly

Designing for easy parts fabrication, material processing, and product assembly is a primary design consideration.  Even if labor “cost” is reported to be a small percentage of the selling price, problems in fabrication, processing, and assembly can generate enormous costs, cause production delays, and demand the time of precious resources.

 P1)	Adhere to specific process design guidelines.

It is very important to use specific design guidelines for parts to be produced by specific processes such as welding, casting, forging, extruding, forming, stamping, turning, milling, grinding, powdered metallurgy (sintering), plastic molding, etc.  Some reference books are available that give a summary of design guidelines for many specific processes.  Many specialized books are available devoted to single processes.

 P2)	Avoid right/left hand parts.

	Avoid designing mirror image (right or left hand) parts.  Design the product so the same part can function in both right or left hand modes.  If identical parts can not perform both functions, add features to both right and left hand parts to make them the same.

Another way of saying this is to use "paired" parts instead of right and left hand parts.  Purchasing of paired parts (plus all the internal material supply functions) is for twice the quantity and half the number of types of parts.  This can have a significant impact with many paired parts at high volume.

At one time or another, everyone has opened a brief case or suit case upside down because the top looks like the bottom.  The reason for this is that top and bottom are identical parts used in pairs.

 P3)	Design parts with symmetry.

Design each part to be symmetrical from every "view" (in a drafting sense) so that the part does not have to be oriented for assembly.  In manual assembly, symmetrical parts can not be installed backwards, a major potential quality problem associated with manual assembly.  In automatic assembly, symmetrical parts do not require special sensors or mechanisms to orient them correctly.  The extra cost of making the part symmetrical (the extra holes or whatever other feature is necessary) will probably be saved many times over by not having to develop complex orienting mechanisms and by avoiding quality problems.

It is a little know fact that in felt-tipped pens, the felt is pointed on both ends so that automatic assembly machines do not have to orient the felt.    

 P4)	If part symmetry is not possible, make parts very asymmetrical.

	The best part for assembly is one that is symmetrical in all views.  The worst part is one that is slightly asymmetrical which may be installed wrong because the worker or robot could not notice the asymmetry.  Or worse, the part may be forced in the wrong orientation by a worker (that thinks the tolerance is wrong) or by a robot (that does not know any better).

So, if symmetry can not be achieved, make the parts very asymmetrical.  Then workers will less likely install the part backward because it will not fit backward.  Automation machinery may be able to orient the part with less expensive sensors and intelligence.

In fact, very asymmetrical parts may even be able to be oriented by simple stationary guides over conveyor belts.

P5)	Design for fixturing.

Understand the manufacturing process well enough to be able to design parts and dimension them for fixturing.  Parts designed for automation or mechanization need registration features for fixturing.  Machine tools, assembly stations, automatic transfers and automatic assembly equipment need to be able to grip or fixture the part in a known position for subsequent operations.  This requires registration locations on which the part will be gripped or fixtured while part is being transferred, machined, processed or assembled.  

P6)	Minimize tooling complexity by concurrently designing tooling.

Use concurrent engineering of parts and tooling to minimize tooling complexity, cost, delivery leadtime and maximize throughput, quality and flexibility.

P8)	Specify optimal tolerances for a Robust Design.

Design of Experiments can be used to determine the effect of variations in all tolerances on part or system quality.  The result is that all tolerances can be optimized to provide a robust design to provide high quality at low cost.

P9)	Specify quality parts from reliable sources.

The “rule of ten” specifies that it costs 10 times more to find and repair a defect at the next stage of assembly.  Thus, it costs 10 times more cost to find a part defect at a sub-assembly; 10 times more to find a sub-assembly defect at final assembly; 10 times more in the distribution channel; and so forth.  All parts must have reliable sources that can deliver consistent quality over time in the volumes required.

	The Rule of 10

	Level of completion		Cost to find & repair defect

the part itself	X
at sub-assembly	10 X
at final assembly	100 X
at the dealer/distributer	1,000 X
at the customer	10,000 X

P10)	Minimize Setups.  For machined parts, ensure accuracy by designing parts and fixturing so all key dimensions are all cut in the same setup (chucking). Removing the part to re-position for subsequent cutting lowers accuracy relative to cuts made in the original position.  Single setup machining is less expensive too.

P11)	Minimize Cutting Tools.  For machined parts, minimize cost by designing parts to be machined with the minimum number of cutting tools.  For CNC “hog out” material removal, specify radii that match the preferred cutting tools (avoid arbitrary decisions). Keep tool variety within the capability of the tool changer.

P12)	Understand tolerance step functions and specify tolerances wisely.  The type of process depends on the tolerance.  Each process has its practical "limit" to how close a tolerance could be held for a given skill level on the production line.  If the tolerance is tighter than the limit, the next most precise (and expensive) process must be used.  Designers must understand these "step functions" and know the tolerance limit for each process.

The Importance of Good Product Development
	
   C	Good product development is a potent competitive advantage.  

   C	Product design establishes the feature set, how well the features work, and, hence, the marketability of the product.  

   C	The design determines 80% of the cost and has significant influence on quality, reliability and serviceability.  

   C	The product development process determines how quickly a new product can be introduced into the market place.  

   C	The product design determines how easily the product is manufactured and how easy it will be to introduce manufacturing improvements like just-in-time and flexible manufacturing.  

   C	The immense cost saving potential of good product design is even becoming a viable  alternative to automation and off-shore manufacturing.

   C	True concurrent engineering of versatile product families and flexible processes determines how well companies will handle product variety and benefit from Spontaneous Build-to-Order and Mass Customization.2

Endnotes/References

1. Design for Manufacturability, Optimizing Cost, Quality and Time-to-Market, by Dr. David M. Anderson, Copyright 1990, CIM Press, Lafayette, California; (805) 924-0200.

2. Agile Product Development for Mass Customization, by Dr. David M. Anderson, published by McGraw-Hill in 1997.