Electropolishing is an electrochemical process that is almost the opposite of plating. While plating deposits metal on a surface, electropolishing smoothes and polishes the surfaces of metal parts by the controlled removal of microscopic amounts of material.
Frequently used for components that must have a very smooth and lustrous finish, such as surgical instruments, the process is most often applied to stainless steels, especially the commonly used 300- and 400-series materials. It can be controlled to remove metal within ±0.0001 inch and— depending on process time, temperature, current, bath composition and part surface condition before processing—can produce a range of finishes from satin to mirror bright.
None of this is news to Earl Kline, president of Warsaw Electropolishing (Warsaw, IN). Kline has worked in the finishing industry for more than 36 years, first at a plating shop and then in his own business since 1992.
“Having worked at a plating shop for 23 years before starting my own company, I was familiar with the ‘feast or famine’ aspect of the business,” Kline says. “And that’s what we see here. There are very few times that things are just going along at an ideal pace.”
The Medical Market
One thing that helps mitigate the ups and downs of the metal finishing business for Warsaw Electropolishing is its location in the hub of orthopedic implant technology. The small northern Indiana town is home to companies that control the vast majority of the market for artificial hips, knees and other orthopedic devices. While not entirely immune from the current downturn, Warsaw Electropolishing’s medical-related business is still relatively steady compared with other industry segments the company serves, according to Kline.
“About 60% of our business is medical-related,” he says. “We do work directly for some of the big implant companies. We also do work for suppliers who make parts for them.”
As the company name implies, Warsaw Electropolishing has found its niche in non-plated electrochemical surface treatments for stainless steels and titanium alloys. “We do strictly electropolishing and passivating,” Kline says. “The electropolishing part of the business is only for stainless steels. We also passivate some titanium and stainless using nitric and citric acid passivation.”
Most of the medical components the company processes are surgical tools and toolholders. “We electropolish drill bits, rasps and other tools that have contact with the bone during surgery,” Kline explains.
Being a family-owned shop—son Duane is the company’s production manager—Warsaw Electropolishing’s jobs tend toward relatively low-volume specialty work as opposed to high-volume jobs. “Lot sizes vary quite a bit, but the average job is probably in the 100–125 piece range,” Kline says.
According to Kline, his company’s medical customers are looking for a couple of benefits from electropolishing. “The parts we process are either to size or for appearance,” he says. “Sometimes the customer has an oversize part and wants the part taken down to a certain size. That’s pretty straightforward. You just have to make sure you don’t take the parts out of spec.
“The other main thing is appearance,” he continues. “Surface finish is not such a big deal for many jobs, although sometimes it is important.
“It’s often called out on the blueprint, but sometimes the requirement doesn’t really correspond to any function of the part. So we talk with customers about what they really expect in terms of surface finish.”
Part surface finish after electropolishing also depends on the condition of parts when they come in, Kline says. “If the surface finish of as-received parts is around 20 μin Ra, electropolishing should improve it. But if it’s more like 1 or 2 μin Ra, electropolishing may actually increase it.
“The bottom line is, there just aren’t a lot of written specifications for electropolishing. So we talk with customers to see what they’re really expecting from our process.” When surface finish is important, Warsaw Electropolishing uses an optical comparator to visually check parts, he adds.
According to Kline, the passivation part of his company’s business is a bit more clear cut, at least in terms of specifications. “There are all kinds of specs for passivating,” he says. “We run jobs to various general industrial specs—AES, ASTM and AMS-QQ-P—and to customer specifications, which are usually pretty explicit about what they’resteps need to be followed.
The company’s titanium passivation experience consists of processing commercially pure titanium and a couple of aluminum-vanadium alloys most commonly associated with aerospace applications. But nearly all the titanium parts are for medical applications, Kline says.
The EP Process
The electropolishing portion of Warsaw Electropolishing’s work consists mainly of processing 300- and 400-series stainless materials and cobalt-chrome alloys. Kline says the specific alloy being electropolished makes a difference in processing and handling. “The 300-series stainless steels are relatively forgiving, while some of the 400-series materials are very sensitive to, for example, being left in the tank with no current applied,” he says. “Some sensitive materials, you can’t even keep them in the rinse water too long.”
Warsaw Electropolishing generates a routing sheet detailing all needed process steps and processing conditions for every job. “The first time a job comes in, especially if there’s a visual aspect to it, we develop a process to make sure the customer gets what they want,” Kline says. “When the job comes in again, we can pull up the router and follow the procedure through the shop.”
Being precision components bound for use in operating rooms around the world, practically every medical part at Warsaw Electropolishing is subjected to an aqueous ultrasonic cleaning process and spray rinsing. Depending on the material, some parts are also dried before heading to the electropolishing tanks.
“After electropolishing we rinse, and some parts require immersion in nitric acid or another solution after electropolishing,” Kline explains. “If parts need passivation we do that, then check the components to specifications before packing and shipping.”
Temperature in the electropolishing tank is 145°F, and parts remain in the tank for a few seconds to a few minutes depending on size and specifications. The company mixes its own proprietary blend of electropolishing chemicals. “By doing that ourselves, we know exactly what’s in it, and we’ve had pretty good success with that approach,” Kline explains.
For racking, the company usually buys rack components and assembles them in-house. “Occasionally we have a special rack made, but practically all our jobs can be run using a ready-made rack or a rack made with components we purchase,” Kline says.
Some of the jobs in the shop on this day include a vibratory bowl for part handling and orientation, surgical drill bits less than ¼ inch in diameter and stainless steel exhaust pipes for marine engines.
“We run quite a few of the bowls, and some of them are 18–24 inches in diameter,” Kline says. “That’s another segment of our business that’s going pretty well right now—vibratory bowls for pharmaceutical or food processing equipment.
Drill bits are produced from Type 316 stainless steel. “For the drill bits, the flutes and other parts of the drill need to be nice and clean,” he continues. “Electropolishing is really a good way to clean parts.”
Warsaw Electropolishing also processes several sizes and configurations of the exhaust pipes, which are first electropolished and then passivated.
Quality and Environmental Control
Warsaw Electropolishing is in the midst of preparing for ISO 9001 registration, so the company is busy documenting its processes and procedures. For electropolishing process control, workers monitor bath temperature and concentration on a regular basis—a least daily—and make required additions on a regular schedule.
Shop workers also wear plastic gloves when handling parts to avoid fingerprinting. “If customers are visiting, they can handle their own parts without gloves, but even then we’ve sometimes told them to stop,” Kline says. “We just don’t want a fingerprint to be part of a problem, and if there are fingerprints on a part they’re not ours.”
After processing, parts are inspected visually and using standard calipers and micrometers to verify dimensions. “We try not to make inspection more complicated than it needs to be,” Kline says. “We generally work to tolerances in the thousandths, but some jobs require tolerances within a couple ten-thousandths.”
Some customers visit the shop to perform quality audits and others send in a third-party auditor, Kline explains. “And, every medical job requires a certification that tells them exactly what we did and how we did it,” he adds. “Our customers keep those on file so that when they’re audited for ISO or by one of their customers, they have that documentation.”
On the environmental front, the company discharges no wastewater. “With multiple counterflowed rinses, we keep water use to a minimum,” Kline says. “The final rinse is deionized water, and since it’s counterflowed all the other rinse water comes from that. Eventually we neutralize and evaporate the water, and what’s left is hauled away a couple times a year."