Making it manufacturable: Medical Manufacturing

New tools help parts makers design for manufacturability, which reduces machining costs and improves part quality.

Any veteran machinist has stories of laughable part designs. Parts with impossibly deep hole callouts, dead-sharp internal corners and grooves wider than the Grand Canyon. Design engineers love to dream up impossible-to-cut part geometries. It might sound harsh, but those engineers sometimes learn the hard way how not to design machined products.

In his book “Design for Manufacturability and Concurrent Engineering,” David M. Anderson, fellow at the American Society of Mechanical Engineers, wrote, “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 to (2) assure the best cost, quality, reliability, regulatory compliance, safety, time to market and customer satisfaction.”

Courtesy of Boothroyd Dewhurst

This new air-duct butterfly-valve assembly, designed with DFM software tools, is manufactured from round aluminum stock with a near-net diameter and has a seal design with wide tolerances, reasonable surface finishes and an angled seating arrangement. These features allow for an easier insertion process than was used in the original valve.

That’s a mouthful. What it means depends on whom you ask. Engineering, cost accounting, logistics and quality departments each have their own version of the truth. To the people in the shop, it’s simple. Design for manufacturability (DFM) means making parts easier and faster to machine and, therefore, more profitable.

Anderson suggests a number of no-brainer techniques: design parts that can be made in a single operation, avoid interrupted cuts and complex part geometries, specify reasonable tolerances and surface finishes, understand workholding principles and design features that can be cut with standard tools. Sounds great, but how does one learn how to design a more machinable mousetrap without first spending years in the shop?

Courtesy of Boothroyd Dewhurst

Figure 1. DFM concurrent costing for an 8 ” Torpedo carpenter’s level. All costs are relational.

DFM software is part of that answer. Brian Rapoza, R&D manager at Boothroyd Dewhurst Inc., Wakefield, R.I., explained how his company’s software helps designers estimate the costs associated with decisions made during the part design process and identify the potential for reduced cost and improved quality.

A typical example of this can be found in a large mechanical assembly. Boothroyd Dewhurst’s Design for Manufacturing and Assembly (DFMA) software analyzes the components used and looks for opportunities to combine them. “Rather than make a large number of simple, single-function parts, the software might recommend a multifunctional part in their place.”

But how is one big monster part better than a bunch of small ones? “It might be more difficult to machine than a single part, but in the end it could be less expensive because you gain higher throughput,” Rapoza said. “You have to evaluate the trade-offs, comparing production volumes and tooling costs, but this approach is usually cost-effective.”

Rapoza explained that the software works by presenting the user with a series of questions, such as potential part volume and projected surface area. “From this, we can estimate the time for each manufacturing process and, therefore, derive the cost to make the part as well as the tooling,” he said. “By identifying the major cost drivers in a part design, we can determine the most economical way to make that part.”

Courtesy of Boothroyd Dewhurst

A simplified CAD rendering of the level. Aztalan Engineering used DFM Concurrent Costing software to compare manufacturing processes and select the best one.

Courtesy of Boothroyd Dewhurst

An extruded aluminum billet for the carpenter’s level is fixtured for machining. DFM analysis led to the elimination of this intermediate machining operation.

A recent case study by Boothroyd Dewhurst stated machine shop Aztalan Engineering Inc., Lake Mills, Wis., saved 25 percent when producing 8 ” Torpedo-brand carpenter’s levels (see Figure 1 above, CAD rendering and photo above, and chart below). DFMA analyzed the customer’s CAD models for opportunities to improve part design, ultimately leading to more competitive prices and greater machinability. DFMA also plays an integral part of engineering design review at Aztalan, as well as procurement and process control. “It’s central to a lot of what we do,” said General Manager Jim Hale.

A 2011 report by Boothroyd Dewhurst about aerospace supplier ITT Aerospace Controls Inc., Valencia, Calif., outlines how DFMA revamped a 30-year-old air-exchange valve design. By reducing the number of components, simplifying the assembly process and creating a valve body design that could be machined in a single operation, ITT Aerospace reduced costs 76 percent.

Boothroyd Dewhurst boasts a large customer list, including Pratt and Whitney, GE and Whirlpool. During Boothroyd Dewhurst’s 2012 International Forum on Design for Manufacture and Assembly, Westinghouse Electric said it reduced the number of components in its Spider nuclear fuel assembly from 41 to two using DFMA and value engineering, a method of improving the value of manufactured products.

Find It Early

Another popular DFM tool is DFMPro from Geometric Ltd., Mumbai, India. Product Manager Rahul Rajadhyaksha stressed that his company’s software is different than other “pure-costing” DFM solutions. “DFMPro is built for design engineers, wherein they can identify and resolve problems right at the design stage,” he said. “These problems may be related not only to cost but also to quality, schedule, standardization and other issues.”

To this end, according Rajadhyaksha, DFMPro encourages the use of design best practices through a series of internal rules. “There are more than 100 built-in checks for manufacturability within the package,” he said. “This allows best practices and learning from downstream costing operations to be leveraged and then validated upstream during the design process. It makes life easy for design engineers; with just a click of a button, they can validate the design. DFMPro not only identifies potential problems but also suggests cost-effective alternatives.”

Those best-practice checks guard against the same design mistakes that get designers kicked out of the shop, such as sharp internal corners, narrow slots and extreme length-to-diameter ratios. And because DFMPro integrates with popular CAD platforms, design flaws can be rooted out before they hit paper.

Teach Them Well

So, all a company needs to design good parts is DFM software, right? Not so fast. “While software tools are part of the solution, more is needed for an effective DFM approach,” said Ken Crow, president of DRM Associates, a product development and consulting firm in Palos Verdes, Calif. DRM offers a holistic approach to improved product design, one focused on training, organization and communication. DFM software is only one of many tools in that toolbox.

Crow noted DFM is a hot button these days. With the poor economy and overseas competition, companies are under increased pressure to bring products to market quickly and at reduced cost. “We do a number of things to help our customers,” he said. “Some are only looking for DFM training, while others need more comprehensive help to put a DFM initiative in place. But all are looking to reduce costs.”

Courtesy of Boothroyd Dewhurst