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DFMA to RP, ASAP PUBLIC ACCESS

Design for Manufacture and Rapid Prototyping Both Seek the Same Size Prize: A Better Product Made Faster.

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Mechanical Engineering 121(09), 72-74 (Sep 01, 1999) (3 pages) doi:10.1115/1.1999-SEP-5

Manufacturing companies are turning increasingly to rapid prototyping (RP) to perform pre-assembly testing and improve the quality of the final product. Manufacturers also have begun to complement their RP practices using design for manufacture and assembly methodology. Design for assembly lowers the complexity of products through parts reduction and enables manufacturers to quantify assembly times and costs. Users are prompted to consider each part and decide if it must be separate from others in the assembly, leading to systematic simplification of design. The four approaches by which design for manufacturer (DFMA) software analyzes product configurations incorporate design for assembly, design for manufacture, design for service, and design for environment. Using design for assembly can reduce the number of parts in the product, but can increase the complexity of the parts that remain. Rapid prototyping combined with DFMA tools not only can determine if a product will perform its desired functions. According to an expert, when early manufacturing process planning is performed using DFMA and RP, it is synergistic.

Before a royal meal, the kings of old would have tasters eat first to test the food. If the taster lived, It was assumed the king would survive the meal as well. While clearly more advanced methods of testing are available today, this, in theory, is what manufacturers do to ensure not only that the customer survives the product, but that the product survives the customer.

Manufacturers endeavor to produce the best products possible to compete strategically in a given market. Companies have turned increasingly to rapid prototyping to perform pre-assembly testing and improve the quality of the final product. Manufacturers also have begun to complement their RP practices by the use of design for manufacture and assembly methodology.

The concept of DFMA was developed in 1980 by Geoffrey Boothroyd and Peter Dewhurst, professors of industrial and manufacturing engineering at the University of Rhode Island in Kingston. The following year, they founded Boothroyd Dewhurst Inc. to market proprietary DFMA packages. Although other software packages have addressed parts of what DFMA provides, Boothroyd Dewhurst claims its package is unique in combining four approaches to product development and is a nationally recognized standard.

The four approaches by which DFMA software analyzes product configurations incorporate design for assembly, design for manufacture, design for service, and design for environment.

Design for assembly lowers the complexity of products through parts reduction-that is, elimination or consolidation- and enables manufacturers to quantify assembly times and costs. Users are prompted to consider each part and decide if it must be separate from others in the assembly, leading to systematic simplification of design.

Design for manufacture provides cost estimates for the manufacture of individual parts. This allows users to make tradeoff decisions between process and assembly costs and optirnized part designs. It also lets users choose work materials and machine tools from editable libraries. In addition, it imposes power and speed, and makes corrections in tooling approaches.

Design for service supplies a method of designing products for efficient maintenance and repair. It establishes a disassembly sequence to service an item, identifies items that must be discarded or replaced for specific service tasks, assesses the degree of difficulty when servicing specific items, and generates a reassembly sequence and time estimate.

Design for environment helps to quantify design in terms of cost and environmental impact, ensuring that products can be disposed of responsibly at the end of their use. It provides assessments on financial returns and environn1ental impact.

Boothroyd Dewhurst brought together a panel of four industry experts at a forum held in Newport, R.I., this sunU11er, to discuss the interoperability of DFMA and RP.

"Both techniques [DFMA and RP] are used early in and throughout the design cycle, and are applied at the same time," said Brent Stucker, assistant professor of industrial and manufacturing engineering at the University of Rhode Island. "They are both ways of going about the same thing, so, consequently, they are more easily integrated."

Using DFMA software, a machine tool path is verified and generated to fabricate a prototype door and ensure that the part will be produced to the CAD database geometry in the CNC machining center.

He said that not only do both approaches lead toward more robust designs for manufacture, assembly, and product use, but both enable critical changes to be made before expensive tooling has to be applied to the manufacturing process.

Many feel that concurrent use of DFMA software and Rapid Prototyping facilitates more detailed product testing to increase its overall quality.

Grahic Jump LocationMany feel that concurrent use of DFMA software and Rapid Prototyping facilitates more detailed product testing to increase its overall quality.

"Using both techniques in an integrated fashion can only be helpful because rapid pro to typing eliminates some of the design and geometry constraints left by the software, and the DFMA software provides quantification and cost analysis that RP does not," Stucker continued.

"As rapid prototyping technology matures, DFMA will be more helpful in making its implementation effective." Basically, if RP becomes faster and more precise, in both design and material used, DFMA will better predict the product's function after testing.

According to R. Ian Campbell, a professor of manufacturing engineering and operations management at the University of Nottingham in England, "The conventional use of RP is to produce models, while DFMA is designed to reduce costs, save time, and improve quality. Putting them together takes what happens, or is going to happen, and pulls it forward in the design process by way of simulation."

He said that concurrent use of both approaches allows for more modifications in tooling and design to be made at the earliest possible stage before anything is actually made. That, of course, results in a cost savings.

In many ways, it is similar to what is done in an editorial setting. When all writing, editing, and proofreading are performed before the deadline, it is far less expensive to make changes than it is to do so once the editorial product has reached the press.

"Yes, a customer may still see things from a different perspective, and additional changes may need to be made," Campbell explained, "but the two primary results are that the time scale has been shortened, and more changes early on mean fewer changes later."

Often, prototypes are used to verify DFMA an alysis." Not only does DFMA bring analysis to the conventional manufacturing process, it can also determine what materials are used and what the cost will be to produce a model through RP," he said.

Using the example of a valve and nozzle manufacturer making a new sprinkler, Camp bell said that the company wants to see water coming out of a nozzle rather than just a drawing or CAD model. DFMA analysis can be used to determine what materials and tooling are best suited for this function, and the physical model can be constructed to show that it is easy to assemble and that it works.

"Rapid prototyping furthers the collective brainstorming and design analysis of the DFMA process," said Raymond Bradford, vice president of software at Solid Concepts Inc. in Valencia, Calif. "By using 3-D communication and visualization to communicate DFMA-recommended changes, a wide array of ideas and expertise can contribute to design."

DFMA software can be used to analyze designs for ease of manufacture, assembly, and maintenance, and for environmental impact

Grahic Jump LocationDFMA software can be used to analyze designs for ease of manufacture, assembly, and maintenance, and for environmental impact

Machining and tolerances are areas where the use of DFMA and RP are of particular benefit, according to Bradford. DFMA-specifically, the design for manufacture aspect—can help manufacturers select tool materials, types and dimensions of cuts, and a surface finish. Bradford said that fusing these functions with concurrent machining processes and a physical model are key. "The nice thing about machining this way is that 95 percent of the time we can come up with exactly the right materials," he said.

The use of-DFMA tools brings the entire design team to the table, according to Cordon Lewis, director of manufacturing practices at DaTuM 3D Inc. in Newton, Mass. " It is important to set the expectations of what will be done in the design," he said. "DFMA is critical here in that it's a communications tool."

Using design for assembly can reduce the number of parts in the product, but can increase the complexity of the parts that remain. "You could have a product originally designed with 50 parts, but good use of DFA can lower that number to 20," Lewis said. "Of those 20 parts, three or four are bound to be more complex."

This complexity, said Lewis, is why RP is so important. "If I've now created a very complex part, I want to get it in my hands as soon as possible to begin testing it," he said. "DFA drives part complexity, not product complexity."

Rapid prototyping combined with DFMA tools not only can determine if a product will perform its desired functions, but how well and, often, for how long. It may sound simple, but just because something works, doesn't mean it works as well as it could, or for as long.

"This is why you do DFA," Lewis explained. "some RP materials are robust enough to perform functional testing, but without DFA you can't do life testing."

Stucker added, "Using DFMA and RP together opens up the design constraints and makes major geometry and material changes. This way, it is possible to manufacture highly engineered products smoothly, quickly, and economically."

Campbell further reasoned, "If products are designed using DFMA and RP, they will be easier to make, will have a simpler design, and will be subject to quality testing to ensure a quality end result. Basically, the use of these two architectures brings design and manufacturing together, which not only increases the amount of effort put in to the product, but allows manufacturers and designers the more promising prospect that it was done right."

According to Bradford, "When early manufacturing process planning is performed using DFMA and RP, it is synergistic. By that, I mean that a product's total esthetics and functionality are considered jointly, and result in products constructed with optimal functionality, correct materials, and efficient assembly. This improves the entire product on all fronts."

With all the test capabilities provided by these two methods, the king can eat whatever and whenever he wants.

Copyright © 1999 by ASME
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