Machining Critical Features into Stamped Parts Can Be Cost Effective

Producing basic features by stamping, and then incorporating more critical features by computer numerical control (CNC) machining can result in a much lower cost part than a fully machined part. Stamped metal and springs are used in millions of products across the gamut of industries. Experience in how metals move and where they are likely to fail goes a long way to reducing costs and developing solutions. In addition, experienced engineers can increase value and reduce costs by designing tooling with flexible options for change. This is frequently done by adding skip stations in a die for a nominal upfront tool cost where additional cutting or forming can be added if needed.

Value engineering helps customer design parts that are within a tight tolerance and yet very manufacturable and consistent in the long run. It is most effective when the engineer has familiarity with a customer’s product range and can take what they’ve learned in the past and apply it to new products. Firms like Connecticut Spring & Stamping (CSS), Farmington, CT, control all aspects of the part, from prototyping and development to final production. Designing and building both the progressive tooling for the stamping and the fixtures required for the machining process helps in meeting the quality requirements of its customers, especially those in the medical device industry.

Original equipment manufacturers are pushing the envelope to get from concept to production in the fastest possible time. To meet OEMs’ need for this fast pace in the world of metal stamped parts and springs, engineering expertise is taking on an even more important role. Expertise in prototyping parts to test and prove design concepts, suggesting ways to reduce secondary operations to reduce cost, and providing value with engineering consulting expertise, are key engineering skills that ensure the success of projects. Behind it all is a foundation of communications and two-way dialogue that ensures that products meet customer requirements.

In 2004, CSS noticed that more and more customers were looking to get higher-precision parts off a progressive tool, so the company purchased a used Fadal machining center, as shown in Figure 1, and engineered and designed its own fixtures.

Mike Vanadestine, CSS Self Directed Work Team Leader- CNC, explains that the “one-stop shop” process the company uses differentiates them from the traditional CNC machining suppliers. “We have in-house engineering personnel who can aid in any redesign or alterations needed to achieve the functional requirements directed by our customers.” This means that the customer needs to partner with only one vendor. “We are able to take a stamped part and then machine critical features, and this can be done at a considerably lower cost than having to machine the complete component,” says Vanadestine.

As the word spread that CSS could machine stamp parts, the company began to get requests from other customers looking for the same accuracy and finish that the CNC machines were producing, so they started looking at additional machines to keep up with the demand.

In 2009, the stakes were raised higher, as CSS found itself with new medical customers looking for even tighter tolerances than had been achieved before.

Robert Allen, CSS Director of Engineering, Tooling and Metal Form, notes that they were no longer looking at holding ±.003 tolerances, but instead were asked to hold tolerances of ±.0005. To achieve these close tolerances would require a very accurate CNC machine, and, after doing a great deal of research, they settled on the Hyundai Kia VX400. (See Figure 2)

“These machines are significantly more accurate than our first machines and are able to hold tight tolerances all day, every day. We have also taken on a 5-axis machining job using a rotary table and all the machine’s capabilities,” he said.

For example, CSS recently worked with a medical device company that had been purchasing one of its parts as a completely machined tube, but wanted to explore the possibility of moving to a stamped part with machined features. The project was tricky, since the tube has important features that had to be duplicated in a stamped part. A pin has to smoothly ride on a surface to create the torque necessary to grab flesh. Also, there could be no bumps or ridges that might cause the tube to skip or the surgeon to feel tension. Finally, a coined feature was needed where wires c an be attached that made the instrument head articulate.

CSS began to re-design the new tube using 3D solid modeling software (SolidWorks). Working with the customer’s critical features, CSS engineers successfully moved towards changing to a stamped part, and finishing the features using its CNC machining process. The result is a savings of about $6 per part, a great result for the customer, which manufactures about 100,000 of these parts per year.

After gaining experience in CNC machining, the company realized it was extremely time-consuming to load parts in the fixtures, and the loading process was increasing cycle times. So, in 2011, CSS purchased two new Hyundai Kia VX380TD machines, which use a rotary-type table to shuttle parts in and out of the work zone. (See Figure 3)

The operator will no longer be taking fixtures in and out; instead everything is mounted directly to the machine base and is shuttled in. These new machines have the potential of cutting 25 to 30 percent off the company’s current cut times, all the while maintaining tolerance and finish requirements.

This article was written by Mike Vanadestine, Self-Directed Work Team Leader – CNC, and Robert Allen, Director of Engineering, Tooling and Metal Form, for Connecticut Spring & Stamping, Farmington, CT. For more information, Click Here