Electrochemical Machining – Elegant Manufacturing for the Future

Story by Callie Patteson

Since the early 2000’s, TURBOCAM Inc. has been pursuing an “elegant” and non-conventional type of manufacturing: Electrochemical Machining.

Often referred to simply as “ECM,” this non-contact machining process is drastically different from conventional manufacturing that mechanically removes material through applying pressure to a sharp tool to directly cut metal.

Rather than slicing away chips, ECM selectively dissolves solid material using electrolysis, which happens in a small gap between the workpiece and a mold (commonly called an electrode or cathode) which generally matches the final intended shape of the workpiece.

The typical process is performed by connecting a power supply to the cathode and workpiece, using saltwater to conduct electrical current through the cathode and workpiece, then pumping the same saltwater across the workpiece to remove the dissolved material, until the contour of the electrode is sunk into the workpiece.

To further understand how this type of shaping works, imagine having a block of wax and a metal tool heated to 500 degrees. If you slowly press the metal tool in towards the block, any wax close to the tool will melt or vaporize. After removing the tool, an impression will be left in the wax, but there is no force being used to change the wax’s shape, just heat acting at a distance from the tool.

Similarly, ECM uses electrical and chemical energy to dissolve the material and change its shape in three dimensions, in contrast to mechanical or thermal machining, casting (solidification constrained by a solid mold) or forging (solid deformation constrained by a solid mold or tool).

ELEGANT MACHINERY 

One of the perks of using ECM is the minimal contact between the metal and machines, explained Jim Cooper, the general manager for TURBOCAM’s Aero-Engine group.

“There [are] no forces, no contact between the tool and the material,” Mr. Cooper said, suggesting that in theory, ECM tools “should last forever.”

This is a massive benefit when looking to stretch machine longevity, as parts in conventional machines need to be regularly replaced, with edges and tools breaking down as they cut metal and other materials with brute force. In ECM, neither a delicate cutting tool nor a flexible final part is subject to forces high enough to deform or break them.

TURBOCAM President Marian Noronha has described ECM as “elegant” and “beautiful.”  “All the processes come together in such a way that you’re not fighting each other and you can produce something of excellence,” he said. “There are other processes…where you’re just cleaning up the mess as you go along.”

ON THE MAP 

Marian first took a class on ECM in 1993. At the time, very few companies were using the technology, mainly due to high costs of entry and necessary knowledge of regulations and chemical systems.

He recalled attending a trade show in Germany, where a competitor had a part on display that had been made by ECM.  “It was just plain gorgeous,” he said.

By 2005, TURBOCAM began actively researching and experimenting with ECM.

It was a risky endeavor, as the technology had a reputation for being dangerous and uncontrolled at the time. The fluids and waste from ECM can contain salts, caustic additives, and a rust-like sludge that must be managed and re-processed to avoid skin and respiratory irritation, and stray salt can rust nearby equipment and materials. With many metals containing chromium, ECM processes produce Hexavalent Chromium (Cr6+), a toxic chemical that is known to cause cancer and other health problems when exposed to over time.

Though much of the technology was once developed in the US, ECM is now relatively rare in the United States, even as advances in process control and filtration enable the few industries to harness its power to make increasingly complex components and features.

“I remember doing a big scribble on my whiteboard and figured out that either we had to buy 45 milling machines for $18 million, or we could try buying an ECM machine and spend about $5 or $7 million and do something risky instead of something that was just plain, big and ugly,” Marian explained.

Over the course of the next several years, TURBOCAM continued to experiment with ECM, building prototype machines, looking for various customer partnerships, as well as working and training with ECM specialists and advisors.

As TURBOCAM engineers researched the technology, they learned early on from Dutch specialists who had used ECM extensively, on how to make precise parts and handle wastes like Chromium 6.  Specifically, they found that there were safe additives which could be put in the electrolyte that would neutralize and solidify the chemical, so that it could be filtered out, compacted, and removed as dry waste.

At this point, TURBOCAM was conventionally manufacturing over 100,000 stainless steel nozzle rings annually for turbochargers. As the engineering team researched ECM and made prototypes, they developed experience that could apply to making vanes from nickel alloys. It wasn’t long before production opportunities arrived.

The company officially started production in 2014 with equipment built internally, as well as a number of customized machines supplied by experienced builders and process specialists. Within one year, TURBOCAM was consistently manufacturing products using ECM for customers like Pratt & Whitney.

It was then that TURBOCAM visibly had an edge over other competitors in the industry, Tim Noronha, General Manager for TURBOCAM’s ECM group said.

“We had a huge competitive edge for the product we did. There are others getting into it…I would be fairly confident that we are improving our advantage faster than other folks are catching up,” he said.

Part of this edge, he explained, is in large part due to meeting experts in the field that have been “key” for TURBOCAM’s progress.

Marian Noronha has touted the success TURBOCAM has had using ECM and overcoming its risks, saying it “put us on the map.”

Currently, the company has 11 ECM machines in production with a few dozen people running multiple shifts in order to keep consistent output.

TURBOCAM has continued to revisit researching the technology to ensure safety and efficiency when using it, particularly with rocket engine parts. As this research is ongoing, ECM is only used for such products when there is no other feasible way to produce it.

CATCHING UP 

While there are many advantages of ECM compared to conventional manufacturing, it is an extremely expensive alternative. Typically, a 5-axis milling machine can be purchased for around $400,000; comparatively, a high-precision ECM machine can be upwards of $1 million.

“You need a high volume, high production opportunity to go after it,” Jim Cooper explained. “But once you do that, it’s a real big competitive advantage for things like cost because you’re not paying for cutters.”

Looking towards the future, TURBOCAM hopes to expand their use of ECM – particularly in the rocketry industry. Marian Noronha explained in recent years, aircraft and rocket engines have been reaching higher temperatures to use fuel in the most efficient and effective way. Because of this, companies have been opting to use heat resistant metals, which are more difficult to cut conventionally.

“Machining has made progress, but ECM is an elegant way of removing the metal instead of brute force. Often the effect of brute force is to create fractures in the metal, which weakens the metal,” he said.

However, relying on ECM for rocketry could take some time to implement as the company’s hands are full keeping up with already massive demand.

At the same time, TURBOCAM is looking to stretch ECM’s traditional capabilities when it comes to developing products.

Tim Noronha said one of his goals with the machining process is to make certain shapes out of various materials that people have never imagined before.

“We want to be using ECM to enable…very feature dense designs in rocketry and energy conversion,” he said. “We want ECM to be safer. We don’t necessarily want it to be simpler. We want it to be safe and predictable.”

While some companies might be hesitant to use ECM due to historical risks, TURBOCAM is positive they have created a safe environment to use it in production, reducing the risks to lower than it would be with conventional manufacturing.