Smart design: Turning Performance

The design for manufacturability process can help designers understand how their parts will actually be machined. The challenge for machine shops that offer DFM services is to convince their customers to use it.

DFM means designing a product, part or assembly so the piece is easy to manufacture and manufacturing costs are reduced compared to a non-DFM part design. DFM allows potential problems to be fixed in the design phase, which is the least expensive place to fix them.

Courtesy of Pro CNC

Paul Van Metre (left), president of Pro CNC, and Estimator Andrew Miller discuss a part designed by the shop via design for manufacturability.

DFM takes into account every aspect of a product’s design and manufacturing, including the workpiece material, time to production, machining methods and overall cost. The machine shops interviewed for this article offer DFM design reviews for customers based on their manufacturing experience and software tools such as GeoMagic Design, Creo Elements/Pro, Autodesk AutoCAD, Autodesk Inventor, Dassault Systèmes’ SolidWorks or Siemens’ Solid Edge for DFM.

DFM is not a new process for CAD/CAM programmers and machinists. It has been around as long as CAD, but it is only starting to become popular as more sophisticated clients of machine shops learn the advantage of consulting with shops on the manufacturability of their designs to avoid costly changes later in the process.

“Our large customers utilize our [DFM processes] frequently,” said Larry Harrison, vice president of engineering at EMC Precision Machining, a machining business with shops in Elyria, Ohio, and Sheridan, Ind. “We make sure we have contacts with their design and engineering departments so we can be on the front end of their designs.” Smaller customers tend not to be as interested in the service, he added.

In addition to consulting with customers on part design, EMC uses DFM to develop, design and prototype some parts for customers. Harrison said: “At times, we even have their engineers come in so they can make changes while we’re preparing to manufacture parts, especially on small- volume part runs. They can then make changes here or back at their office. Our key customers are always talking to us about the design of their new projects.”

Like EMC, Cohagan Engineering Inc. offers DFM services. “Usually, the relationship starts with an initial conversation to nail down exactly what the client is looking for and the best material to work with. Then we create a few hand sketches, get approval and submit an initial CAD design,” said Brent Cohagan, president of the West Palm Beach, Fla., shop. His company offers design review, design collaboration and turnkey part design, mostly for customers in the aerospace and military industries. “The whole time we’re thinking in terms of DFM because we want to design and create it as economically and efficiently as possible. That can sometimes hurt us because they can then take our design and go to any other shop for production, but that’s a risk you take hoping to get that larger run down the road.”

After a customer approves the initial CAD design, the shop makes some minor changes. Then, the customer approves the prototype and production begins.

Cohagan and Traver Maselli, a vice president at the shop, perform the company’s DFM consultations, which sometimes include a licensed professional engineer for verification. Certain customers, such as large corporate customers with large engineering staffs that design their own parts, do not usually ask for DFM services, but they will accept feedback if there is something they’ve overlooked. Usually, it’s the single-designer CAD shops that ask for DFM services. Cohagan charges a flat rate of $60 an hour for its services, no matter if the time is spent in doing DFM, machining or performing other services.

EMC Precision’s Harrison also does not charge anything beyond the normal hourly shop rate for DFM. “It’s a marketing tool and a partnership with our customers,” he said.

Cohagan said the way most of his customers come around to using DFM is by learning first-hand the advantage of eliminating errors during design rather than in production.

“Usually, someone sends you an RFQ, you quote them the number and they ask ‘why does it cost $1,500?’ ” After Cohagan explains that applying DFM can help reduce manufacturing costs, the customer typically gets on board with the process. “We can get those design changes early on, which reduces the cost, and [the customer] can be brought into the design review process,” he said.

Mars and Venus

One of the hurdles to overcome in getting part and product designers to utilize DFM is the lack of communication between designers and shop owners. Achieving common ground on how to design a product, determining the desired result and how to get there can cause frustration and missed opportunities on both sides.

“The younger folks coming into the industry as engineers and designers know only about the software and not about how the parts are produced,” Cohagan said. “We call them software jockeys. They can draw the most awesome CAD designs, but when it comes to making the part, it’s almost impossible for us to machine.

Courtesy of Cohagan Engineering

Cohagan Engineering designed and manufactured this aerospace bezel. The shop worked with the customer’s engineering design team, applying DFM methods to reduce manufacturing costs and lead times. The old design consumed 80 minutes of machining time, for a cost of $88 each, while the new design (shown above and below) consumes just 25 minutes of machining time, for a cost of $33 each. Pictured is the front (above) and back (below) of the redesigned part, in which Cohagan Engineering removed sharp inside corners and all inside radii under 0.015″ and changed a number of ±0.001″ tolerance requirements to ±0.015″, which were acceptable. In addition, the overall size was 0.015″ to 0.020″ larger than standard bar stock sizes. Cohagan Engineering reduced the part length and width to use standard stock and significantly reduced material costs.

“It’s very difficult to find skilled workers who know both manufacturing processes and CAD software,” he continued. “We try to find people that have backgrounds as hands-on mechanical engineers or machinists and also have CAD experience, rather than someone who is, say, SolidWorks-certified but lacks experience in manufacturing. Southern Florida has a large freelance CAD marketplace where people work out of their homes with one seat of software and a computer. When the CAD files they make get moved to us, we often ask, ‘what is this?’ ” he said about the files, which often have multiple errors that makes manufacturing difficult or impossible.

Paul Van Metre, president of Pro CNC Inc., Bellingham, Wash., approaches this problem by taking on the role of DFM educator as well as CNC machinist. Before starting Pro CNC in 1997, Van Metre was a CAD manager for a bicycle manufacturer and a machinist for a motorcycle manufacturer. His shop mainly serves the aerospace industry.

For the last 3 years, Van Metre has produced a DFM e-newsletter, Pro Tips. To date, he has published 40 issues and his subscriber base has grown to nearly 1,500 engineers. The newsletter has led to the shop offering live classes on DFM for clients and prospective clients.