Forging a Better Product With an Age-old Process

Incremental advancements have helped the forging process remain effective

EdKensikAssociateEditor

Forging dates back to more than 6,000 years ago, and this method of applying compressive force to heated metal in a die has changed little, despite some technological advances and the development of more sophisticated software to run forging equipment. And it’s still a preferred way for producing strong, high-quality orthopedic im­plants.

While forging technology remains largely un­changed, contract manufacturers and OEMs continue to make forging their preferred choice of manufacturing for some products because of its decreased machining time, cost effectiveness and product quality. Over the years, in fact, forging has become even more popular as a result of some advances. Along with reduced machining time, a more efficient use of raw materials has also increased the popularity of forging.

“Forging is becoming more acceptable because of some of the technology improvements,” said Nip Singh, a consulting partner and CEO of Cleveland-based S&A Consulting Group. “It used to require a lot more machining. Now, it requires much less machining, be it titanium or cobalt for a near net shape forging.”

While there have been numerous incremental advances in forging methods, the goal has always remained constant: forge a component that helps make implants behave more like natural disks and tendons in the spine.

“Even with the introduction of high-speed machining centers, forging has been able to maintain its popularity due to several advancements,” said John Romano, assistant forge department manager for Wilmington, MA-based Accellent. Specifically, he pointed to software improvements that have played a big part in bolstering that popularity. “There are several forms of forging software on the market that has increased the efficiency and quality of the forging process.”

These and other technological advances have allowed forging houses to decrease time to market for new product lines while also raising quality and manufacturing efficiency, Romano said. At the same time, he added, production costs have decreased.

Materials Forged

Depending on the process, titanium and cobalt chrome are typically the preferred materials in forging plants. For instance, tibial components and hip stems often use titanium, while cobalt chrome is usually found in knee femoral components. Overall, cobalt-based materials remain dominant in hip and knee implants, Singh said. Some companies, though, might be moving away from titanium because of increasing costs, but Singh said that forged titanium offers a great advantage because it is light weight compared with cobalt. The challenge, though, is titanium is more difficult to shape through forging, Singh said.

“Titanium is a more reactive material compared with steel or cobalt-based,” he added.

According to Steve Yopko, U.S. sales director for Solinger, Germany-based Friederich Daniels, most hip and knee forgings are made from titanium or cobalt while most spinal implants are machined from stainless steel or titanium, which results in a better x-ray or MRI scan.

Joe Zuzula, director of sales, marketing and quality for Holt, MI-based Stealth Medical Technologies, added that the key benefit to forging is materials reduction, imparting better physical and mechanical properties and the ability to make complex shapes.

“The advantage of using forging over other [methods] such as a casting is that there are greater mechanical properties such as tensile strength and hardness,” added Zuzula. “Most of the large joint reconstruction implants are made from forgings. These include femoral stems, acetabular cups, femoral knee components, tibial trays, ankles, hemural stems, etc. More recently, spinal components have been forged.”

He added that materials such as zirconium are being forged along with other derivatives of titanium and cobalt chrome.

Auda added that one of titanium’s benefits is its somewhat porous characteristic, which enhances adherence to the bone. Additionally, it has similar properties to bone material. He added that cobalt chrome is more applicable to hip stems and tibial trays.Cobalt chrome has the added property of polishability and gives ball caps and some tibial surfaces a mirror-like finish. Of course the ultimate goal of using any of these materials in the forging process is to achieve the lightest and strongest implant possible.

Types of Forging

Two of the more popular types of forging is drop forging and near net shape forgings, which are favored over press forging and hammer forging.

“Drop hammers still basically perform the same function today as they always did, depending on the type of hammers used. The biggest impact is controlled, repetitive blow intensity and quicker, more reliable forms of heating alloy,” said Robert Kervick, president of KomTeK Technologies, which offers precision closed die forging and investment casting to the medical industry.

Greg Auda, director of marketing for Accellent, added that near net shape forging has become the industry standard today.

“This results in shorter cycle time to machine a finished part and ultimately a lower cost,” he added.

Kervick said that forging methods have not changed much over the years despite today’s sophisticated manufacturing environment. What has changed is the requirements and expectations of orthopedic manufacturers.

“The demands for tighter tolerances has forced the forging industry to refine their processes by removing process variation and adding better controls,” said Zuzula, whose company is a near net titanium and chromium cobalt forging company that specializes in implants.

Yopko added that improved raw materials, the ability to adhere to tighter tolerances and more efficient scheduling are helping forging manufacturers meet customers demands. He added that CAD planning tools have come into the forging process, which help control tolerances and, in turn, make a better finished product.

With clients demanding shorter production times and lower costs, many companies are looking to near net shape forgings. That’s because there is less machining and finish processing involved.

“What better than to forge a part with finished dimensioning,” said Auda. “As technological advances are made in the manufacturing of forging presses and forging software, the forging of near net and net shaped parts is rapidly becoming the process to master.”

Forging Vs. Casting

Because of the strength derived from forged products, this process continues to maintain its lead over casting. And for a number of OEMs, this consideration alone is why they prefer forging over casting.

“The forging process produces a very strong, high-quality product that requires fewer manufacturing steps than casting,” said Dave Waterson, commodity manager, global supply chain of Warsaw, IN-based DePuy, a Johnson & Johnson company. “However, castings are still a strong, acceptable method of manufacturing an implant. It really depends on the given application and design intent.”

However, forging also has its shortcomings. For instance, casting offers greater net shape features and a lower cost in some instances.

“A forging is definitely going to give you the most opportunity to refine that piece of metal and add the highest value, whereas if you really are looking purely at the raw cost you likely will find that a cast is a viable option,” said Doug Slomski, Director of Sales for Bannockburn, IL-based Teleflex Medical OEM business unit. “But again, the durability and function demand on that instrument will be far lower in terms of its form, fit, and function versus the durability and value-added of a forged specialty instrument.”

Singh said that forged products boast better properties than casting, but casting provides superior shaped property. In addition, forging involves fewer steps than casting and is capable of achieving tighter tolerances, resulting in less machining costs.

Forging Challenges

Even as they have cut costs and production times, outsourced manufacturers are still being pressured to raise the bar. Reducing costs further at a time of tight raw material availability—be it titanium or cobalt—poses additional challenges. Further­more, OEMs are asking for shorter lead times along with post-forge processing as some of the value-added services from their forging service providers.

“Usually, the customer’s desire to get quick production turnaround on a short notice is the biggest challenge, especially if there is an industry-wide lead time issues with obtaining raw materials,” said Kervick. “Adoption of lean manufacturing has been critical to allow us to meet these requirements. Quality initiatives are no longer a selling point; it’s expected, as it should be. In some cases, we get much better communication between our customer’s MRP systems and ourselves. Our customers have learned that the greater visibility we have into their production scheduling, the easier we are able to plan and schedule our process to meet those requirements. Direct line-of-sight into their system is the way to go.”

While forging has not changed much over the years, the outsourcing of the process has grown significantly as OEMs continue to focus on core competencies. That’s because service providers are no longer just forging products; in many instances they are offering a full suite of services. At Accellent, orthopedic implants are manufactured to their final form including porous coating and HA coating. At KomTeK, casting is offered in conjunction with forging, which gives the customer flexibility in the their volume mix. Stealth Medical also provides expanded services, including designing, machining, polishing, and porous, plasma and HA coating.

“Instead of supplying a raw forging that has been trimmed, basted and inspected, OEMs want further processing from the supplier before receiving the product,” Kervick continued. “A great deal of what used to be in-house, value-added processing (primarily machining and polishing) has been outsourced, and the forging supplier is being made responsible for upgrading the product. Only the processes that are considered to be critical steps to the OEM are still being completed in-house (i.e. proprietary coatings, final inspections).”

Automation Grows

While skilled craftsmanship is still valued in forging, automation has become the preferred production method. With automation, forged products become much more cost effective.

“Automation also has played a big role in keeping forging in the forefront of manufacturing orthopedic implants,” Ray Rossi, the forge department manager at Accellent, said, adding that the company has two full, automated forging cells that run 24/7.“It adds consistency to the whole process by providing strict controls on all of the variables involved in the forging of a part (i.e. metered lubricant dosing, furnace time and temperature, part placement in the die, etc.). Controlling the input variables translates into controlling the output of a forged part.”

Forging will continue to be the dominant process in the manufacture of many orthopedic implants, and service providers say more incremental improvements will be made to the process. For instance, Yopko said the result will be a more efficient use of raw materials, tighter tolerances and better scheduling that leads to quicker turnaround of products.