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Businesses & Markets Investment Casting Saves Lives

| Author / Editor: Robert Piterek / Nicole Kareta

The German company Vacucast, a business of Link Holding GmbH, casts implants that are used for joint replacement in operating theaters worldwide. Managing Director Tonguc Sahin guides a group of doctors through his investment foundry and shows them the manufacturing process of these sophisticated products - which can sometimes even save lives.

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With an artificial skullcap made of titanium it was possible to save the life of a seriously injured motorcyclist.
With an artificial skullcap made of titanium it was possible to save the life of a seriously injured motorcyclist.
(Source: gemeinfrei / Pixabay )

Doctor's round at Vacucast in Berlin: Managing Director Tonguc Sahin is welcoming a group of doctors today, all of whom are specialists in the use of so-called endoprostheses and would like to learn more about the production process during a tour of the company. The attending physicians come from all parts of Germany and regularly use the prostheses in the operating theater to replace damaged joints either partially or completely. Today, it is an established, continuously growing business area, with global sales of 43.1 billion US dollars in 2012. Knee and hip endoprostheses, which are also predominantly manufactured by Vacucast, account for more than 40 % of sales. The critical eyes of the doctors are now focused on Sahin, who is passing around a palm-sized bent metal part - an artificial skullcap made of titanium. A counterpart of this implant was used to help a seriously injured motorcyclist. The surgery saved his life.

A Passion for Titanium

Tonguc Sahin, a materials science engineer from the Turkish Mediterranean city of Anamur and living in Germany since 1995, starts his remarks with the beginnings of titanium casting at Vacucast. The material inspired the founders of the company, which was launched in 1974, from the very beginning, even though their intention to cast the material instead of forging was initially met with skepticism. "Everybody wanted to work with this material, which was first used in the military and later in civil aviation," says Sahin. Pros: Light weight combined with excellent strength. "Today we also use the material to produce dynamically resilient artificial hip shafts on our cold-wall vacuum casting machine, which you will see now," he announces. The guests nod their approval. But first Sahin leads the group of doctors down to the production hall to show them the investment casting process right from the start.

Precise Wax Models

Three wax injection molding machines are located in a room measuring about 70 square meters. In the preceding room, several people work on wax models, giving them the finishing touches or combining them to make cast alloys. An employee uses a lamp to check whether the clusters are properly joined. The doctors spread out in the room and look over the workers' shoulders. Some reach for their reading glasses to take a close look at the negatives of the castings.

Then, Sahin takes the floor again and familiarizes the group of doctors with the manufacturing process used here - the lost wax process. He explains that the 3D data sets are used to produce the models in the wax injection molding machines and that Vacucast collaborates with an external mold maker for the production of the injection molds. The company regularly receives the data sets for model production from the headquarters of Vacucast's parent company Link in Hamburg, where 45 development engineers are employed. The family-run medical technology company took over Vacucast from its founder in 1997. The company, which has around 1000 employees, manufactures endoprostheses from cast, forged and now also printed blanks.

Forging or Casting?

"The tolerances of our components are very tight," continues Sahin, looking from doctor to doctor. "They have to be true to size and close to the final contour, because the precise final dimensions have to be as close as possible to the blank." Another general nodding and approving murmur go through the ranks of the assembled doctors. A physician in a coarse brown wool jacket asks an interposed question: What materials are used and what other medical devices are produced here. Sahin counts the product range on his fingers - from thigh prostheses from the pelvis to the knee, artificial hip shafts and knee joints to so-called modular revision shafts consisting of up to three parts and artificial ankle joints. He adds that Vacucast offers hip stems in various lengths and thicknesses and does not forget to mention that intervertebral prostheses also used to be part of the product portfolio.

To compare the materials, Sahin passes around two hip shafts made of different materials. One is cast from a cobalt-chrome-molybdenum alloy, the other from titanium. "The titanium shaft has a slightly roughened middle section. This enlarges the surface so that the bone cells can attach themselves more easily to the prosthesis," he explains, stroking the rough surface of the casting. This is followed by another question from a doctor with an unmistakable North German accent. He asks whether forged hip shafts are not better than cast ones. "There is a prevailing belief that forged parts are more durable," says Sahin, "but with anatomical, complex shapes, casting is actually easier than forging. This is because the various post-treatments, such as hipping, often allow values far above the required standards to be achieved.

Cable Car for Model Clusters

A further essential step in the lost wax process is the application of a ceramic layer to the wax model. The huge room that the doctors now walk through with Sahin is dominated by a facility that at first glance looks like a cable car for model clusters. As if strung together like a string of pearls, the blue wax arrangements float slowly through the room on a flexible frame. Their destination is the manipulator covered with a protective foil in the middle of the room. A protective fence blocks the way to a pool of white tough liquid and the working robot. This is where the group comes to a stop. "The manipulator is one of two that we use in our 75-man operation here in Berlin-Reinickendorf," Sahin points out. Behind him, the robot is maneuvering a cluster of wax models to the basin filled with ceramic slurry in front of it and gently dips them in. Sahin adds that depending on the application, the cluster is dipped several times. After each dipping, sanding and drying follows before the cluster is dipped again. This is a lengthy process, which means that some castings can cost several hundred euros. "For us, quality is more important than quantity," Sahin explains the production requirements.

"How important is automation for you?" asks a young man with glasses. "It is indispensable in our ceramic coating process," emphasizes Sahin, while the robot is doing its job reliably behind him. "The process runs in three shifts and I can only staff two shifts. The robot covers the third one."

However, given the complexity of some parts, it is not always so easy to automate this process. Vacucast also operates a semi-automatic machine for the wax spraying process, for example. Despite limited possibilities for automation, the company has made a considerable leap in productivity in recent years: "Today, we have slightly fewer production employees than before, but we produce twice as many castings," says Shahin proudly.

On a production area of 5000 square meters, the company currently produces around 200 to 220,000 castings a year. The batch sizes of the approximately 400 permanently produced articles range from two to 144 pieces. To optimize processes, nine million euros have been invested over the past ten years.

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Hot Passion

Then the doctors and Tonguc Sahin reach the inner sanctum of the investment foundry - the casting hall. The doctors are visibly thrilled by the encounter with the fire at the autoclave, where the wax in the dried ceramic molds is melted, and the casting area, where knee joints and hip shafts are poured with cobalt-chrome melt in the burned molds. However, they respectfully keep their distance without Sahin having to ask them to keep the safety distance. "Each mold is cast individually to ensure traceability and quality," emphasizes the Managing Director when the group finally settles down after some technical discussions among themselves. The quality of the Vacucast prostheses must also meet the highest standards beyond Germany's borders. The Link Group has subsidiaries and agencies around the world, so Vacucast prostheses are also sold in China, EU countries such as Sweden, Spain and Italy, and South America - the export share is 85 %. Sahin is one of four managing directors at Link and is thus also responsible for the good reputation of the products around the world. "Our products are Made in Germany and Made in Berlin and can compete on the world market," he tells the assembled medical professionals.

Sophisticated Titanium Casting Process

Then the group finally arrives at the cold-wall vacuum casting machine for titanium, which Sahin had announced at the beginning. The white-painted plant is housed on two levels. A seemingly complex construction of boilers, control cabinets, coiled cables and wiring. On the second level a display in a control room shows a titanium block in a copper crucible inside the melting chamber. A young doctor demonstrates her knowledge of materials technology and is surprised at the use of the copper crucible in the titanium melting process. "You're right," confirms Sahin. "The melting point of titanium is 1605 to 1650, that of copper is only 1084 degrees. So, the crucible wouldn't stand a chance. But, as the name of the plant suggests, it is cooled extremely effectively. This creates a so-called 'skull' at the bottom of the container, which forms a barrier between the titanium melt and the copper crucible.

A foundryman at the machine is just placing a red-hot ceramic mold in an airtight chamber and then carefully closes the door. "Titanium is a highly reactive metal. It may not come into contact with oxygen, nitrogen or hydrogen - remelting must therefore take place under a vacuum," says Sahin, describing the technically sophisticated process. "I don't need to tell you that titanium prostheses are indispensable for allergy patients. In addition, we have to prepare for more and more younger patients. Arthrosis is already being treated in younger people," he says, sparking a lively exchange among doctors on the way to the next production station.

Master of All Processes

The quality cycle does not end with the casting and removal of the ceramic mold but receives a decisive boost at the end of the production process during hot isostatic pressing. Vacucast has been carrying out this process, known as hipping, since 1985. “It is also known as gas forging because the process takes place in an argon gas atmosphere," explains Sahin. At over 1000 bar pressure and high temperatures, cavities that may have formed during solidification close. This additional refinement of the prostheses is carried out by a truck-sized plant located at the periphery of the production hall. Sahin: "99 % of our processes are in-house, so we are in control of the processes from model to blank."

Before the implants are sent to the Link headquarters in Hamburg for completion by grinding, polishing, sterilization and packaging, they are subjected to heat treatment and extensive quality control measurements by emission spectrometer, fluorescent penetrant crack detection and X-ray testing. The life cycle simulation, which completes the extensive documentation effort for all components manufactured here, also attracts the attention of interested doctors. Clattering noisily in a quality control room, the load bearing capacity of a prosthesis is tested in a dynamic simulator. Vacucast's prostheses are really good, as the test according to the Swedish knee arthroplasty register proves. There, the SP II Lubinus hip endoprosthesis from Link was rated the safest of all available implants with a survival rate of 94.7 % after 16 years. "In Sweden, the model is the most frequently used implant for the cemented hip joint replacement," says Sahin.

A look at Vacucast from the outside: The red brick building has a production area of 5000 square meters. Currently, around 200 to 220,000 castings are produced here each year.
A look at Vacucast from the outside: The red brick building has a production area of 5000 square meters. Currently, around 200 to 220,000 castings are produced here each year.
(Source: Clemens Scholl)

E-mobility Drives Up Cobalt Prices

At the end of the tour, the managing director addresses final questions. The young doctor who already proved her knowledge of materials - as it turns out, an expert in endoprosthetics from a specialist clinic in Saarland - raises her hand. "How is it with you?" she asks. "How did you get to your current position"? Sahin laughs and then reports on his studies to become a mining engineer in Izmir, Turkey, followed by a university education in Germany and his career start as a working student at Vacucast, where he worked his way up from quality manager to foundry manager to managing director. In his private life he is married and has two daughters.

A medical doctor wants to know: "Isn't cobalt also needed on a large scale for batteries in electric cars?” "At the moment, cobalt is used extensively in the manufacture of batteries for e-mobility, among other things. I actually wonder whether the increasing demand for e-cars might one day lead to hospitals no longer being supplied with inexpensive implants," says the managing director, looking to the future. The price per kilogram has temporarily risen from 30 to up to 90 US dollars.

Resilient Industry

Vacucast offers quality Made in Germany thanks to sophisticated system technology and high process reliability. Tonguc Sahin demonstrated this to the doctors during their visit - a visit that did not take place, but which could have looked like this. Sahin regularly guides doctors through the plant but has organized this tour exclusively for Giesserei. His company is well placed to expand its product range in the coming years - for example, to include parts for the mechanical engineering and aviation industries.

But qualified know-how carriers are also essential. Such specialists are sometimes rare - even in the cosmopolitan city of Berlin. Currently, a production manager, engineers and other specialists are needed: "The demand for our products will not decrease", Sahin is convinced, "because the focus is on helping people!”

About Giesserei

(Source: Giesserei)

This article originates from Giesserei, one of the leading German-language specialist magazines for the foundry industry. The main topics are technology, innovation and management with a target group-specific economic section and patent report. Giesserei addresses foundries (iron, steel and malleable foundries, non-ferrous metal foundries and die-casting foundries), foundry plant and machine manufacturers, foundry customers, suppliers and further processing industries. The monthly published magazine was founded 1914.

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