12.05.07
Casting the Future
Today's casting providers offer improved technology, stronger materials and cost savings.
Jennifer Whitney
Editor
In an especially heartwarming episode of the iconic television series Little House on the Prairie, young, spunky Laura Ingalls and her schoolmates were not about to let the bickering adults of Walnut Grove compromise the town’s need for a new church bell. Working with a kind craftsman, the children and he devised their own plan to get the bell made, unbeknownst to the adults. Sneaking around town, they gathered anything they could find that was made of metal—cow bells, lunch pails and even beloved toys and figurines. Once they had found enough metal items (no easy feat in the poor farming community), the children watched as the craftsman melted all these belongings and poured the molten liquid metal into a mold to form the new bell. Beaming with pride when they presented the finished bell to the church parishioners, the children taught the adults a lesson in working together (not to mention sacrificing physical possessions) to reach a common goal for the greater good of the community.
While this show of faith and tenacity was at the heart of that episode, viewers probably didn’t realize that, during the scene in which the bell was being made, they also were watching one of the oldest manufacturing processes in action. Casting, the ancient art of making a shell mold and filling it with metal to produce a perfectly formed part, has long been used in a wide variety of industries—and orthopedic manufacturing is no exception. Although the basic process hasn’t changed much over centuries of use, modern-day technology has made it possible for manufacturers to enhance certain steps in the process to produce many of the hips, knees and other implants and surgical instrumentation on the market today.
Shown is an investment casting mold about five minutes after it had been cast. Photo courtesy of Cencast Corp. |
Today’s casting techniques typically involve the use of a pattern made of wax materials. The pattern often is injection molded, with wax injected into the cavity. After the wax solidifies, the pattern is invested (ie, coated) with other, refractory materials, such as ceramic particulates. The first coat, for example, may be made from very fine particulates that stick to the wax surface, recreating the detail of the part to be made from the cast. Next, progressively coarser particulates are used for additional coats. At this point, the shell is made. Once the shell is set, the wax is removed from the mold with a steam autoclave (or another method), and the ceramic shell is fired—this is known as the “burn-out” process. The purpose is to strengthen the ceramic and vaporize whatever remains in the shell. What remains is a shell containing a cavity that looks like the final part desired. Metal is poured into the cavity and, once it solidifies, the shell is knocked open to reveal a new part.
As industry professionals know, modern medical devices tend to be quite complex, with one part often having various surfaces and shapes. As competition grows in the orthopedic market, many OEMs are designing implants and instrumentation with increasingly detailed features as a way of differentiating their products. Casting techniques can be a cost-effective option for achieving these intricate details.
“As old as casting is, there’s still a reason it’s used. The real advantage in shell investment casting is the incredible detail that forging can’t produce,” said Jim McGeeney, medical business unit manager for FS Precision Tech Co., LLC, a Rancho Dominguez, CA-based division of Fu Sheng USA.
Although many products in the orthopedic market are machined or forged (or a combination of both), casting can offer significant cost savings by wasting less material and gaining a more precisely built part with one process. Converting to casting, therefore, can help OEMs stay competitive in a price-sensitive market.
Although and ancient art, the casting process is used for a wide range of modern orthopedic implants and surgical instrumentation. Photo courtesy of Sandvik Medical Solutions. |
Sandvik similarly has been re-evaluating customers’ needs by identifying optimal solutions for challenging products. “We are continually looking to reduce or eliminate process variation at all stages of the operation and so have invested in a number of initiatives to enhance the repeatability of the process,” Seymour said. “We have used our knowledge of other markets to introduce alternative methods of manufacture, which ultimately reduce the total manufacturing costs for our customers.”
For one project, the company developed a method of manufacturing a single-piece hollow hip head. In the past, Seymour said, the head would be manufactured either by assembling two components and electron beam welding the joint to ensure sealing or the head would be lightened with deep cut-outs. However, repeatability and cost were concerns. The single-piece hollow head addressed those problems.
“Firstly, there are no deep cut-outs, and second, it reduces the number of components by half and eliminates three post-cast operations—machining, press fit assembly and electron beam welding,” Seymour explained. “It also significantly reduces the quality paperwork for traceability purposes…all of which reduces the overall costs incurred by our customers.”
Material Matters: Improvements Abound
In machining, raw materials typically are turned or milled to create a device. If you machine a knee implant, for example, a four-inch cylindrical bar might be cut and chipped at until the desired part is achieved. The problem is, there is a high propensity for wasted material using machining or forging to achieve the part. Providers of casting services said their own process often is more cost effective because it helps conserve materials.
“As the price of materials rises, casting is able to help mitigate the increase through less waste when products are made. Materials prices are increasing and for our OEMs to be more competitive in the market, a lot of these folks are looking at casting to take cost out,” said Tim Hall, vice president of sales and marketing for Cencast Corp. in Mollala, OR.
As such, Cencast has helped keep costs reasonable by implementing Lean manufacturing concepts in its operation. “We’ve incorporated the theories of constraint, Kaizen and Six Sigma to our organization that continually help keep our overhead lower and process more competitive,” Hall noted.
In addition, Cencast has recognized that the industry’s livelihood competes with the fact that forging and machining often enable OEMs to create products with higher-strength materials than casting currently offers and, thus, has been developing its own higher-strength materials in its in-house metallurgical laboratory.
“We’re pushing for enhanced properties for materials, which we’re very close to,” Hall said, adding that such fortified materials most likely will be available to OEM customers within the next six months.
FS Precision also has been experimenting with combinations of various materials to find optimal alloys that offer high-strength, low-fatigue properties. “We’re not constrained by what’s available on the wrought metal market [ie, bar and sheet material],” McGeeney said. “We can go to our sources and have those materials custom melted for about the same price as a standard alloy.”
In the past decade, “tremendous” advances also have been made in engineered pattern-making materials, McGeeney said. Today’s waxes are more dimensionally stable, which has been a result of keen attention toward the materials used for making patterns.
Furthermore, the shell-making process has benefited from improved technology. “The shell has to duplicate the surface of your part with extreme integrity, but it also must be engineered very carefully so it doesn’t change shape or dimension and still maintain strength when you’re pouring metal into the shell,” McGeeney said. “It has to be engineered so it doesn’t crack during the extreme thermal cycles.”
Casting Providers Strive for Rapid Turnaround
As Orthopedic Design & Technology noted in its September/October issue (see “Ideation ‘ Creation”), rapid prototyping has made a large impact on how quickly OEMs can get a part manufactured. The advent of CAD drawings means casting providers can quickly turn these iterations into a pattern for casting. With lead times being a top consideration in who gets manufacturing contracts today, providers of casting services are focusing on meeting OEM demands for quick turnaround.
“Lead times are a big driving force these days on where the work gets placed. We have reduced lead times through an improved shelling process,” Hall noted. “And through proprietary prototyping processes, we’ve been able to give extremely quick turnaround and net shape.”
Cencast has been working toward improving the tooling process used to create high-resolution patterns for its molds. “From our perspective, we’ve looked at multiple ways of producing this tooling through rapid prototyping or cost-effective molds through various applications,” Hall said. “We can offer traditional tooling, but also we can offer very quick and efficient—and cost-effective—tooling from polymer materials to create a mold,” which are beneficial in short-term runs and in prototyping.
Sandvik also has been honing its Lean manufacturing and other initiatives to benefit customers, which have led to an approximately 30% reduction in lead times. Further development in new product launches and rapid prototyping also have taken place. “If using the traditional method of rapid prototyping waxes, the requirement for greater quantities would result in longer lead times. This is because of the wax build times and the degree of finishing required at the wax stage,” Seymour continued. One way the company has sidestepped the challenges presented at this stage of casting is through the introduction of a rapid tooling machine that can produce a tool capable of running high-quality samples in greater volumes than those recommended for wax rapid prototyping—all within a matter of a few days.
“This service has only just been commissioned and is now ready and waiting for work,” Seymour said. “To date, we have used it to machine successfully for internal projects. This new facility will add to our current level of service and proves to our customers, old and new, that we are committed to meeting their needs.”
Although building a shell for casting can be a time-intensive step, new techniques are coming into play, helping to reduce lead times for customers needing a part made quicker. Developing the perfect technique is tricky, though. If the shell is made too quickly, the properties of the shell could be compromised. On the other hand, if made too slowly, moisture could remain and damage the part. Still, McGeeney said, “You see systems now that can build and dry a shell in a matter of a day.”
Some of the strides made in the shell-dipping process are due to the use of automation and robotics. “Automation is a key to the shell-building process,” McGeeney said. “But, it’s also very difficult to reproduce the hand-dip approach robotically. Most in the industry—us included—use a combination of hand and robotic dipping.” He and other service provides believe the industry will see even more robotics and automation permeate the casting realm over the next few years.
A Healthy Outlook
As the orthopedic market continues to expand, manufacturing operations also are growing to meet demand.
Hall said that, since his three-year-old company has secured large volumes of business since its inception, Cencast is now looking at what other value-added services OEMs are seeking and is taking steps to become a one-stop service provider.
“Shipping costs [among others] have gone up dramatically. If you can take out one or more steps in the supply chain, you stay ahead of the competition,” he noted.
Meanwhile, FS Precision is working with forging providers to create a hybrid forging/casting process. Although the hybrid process is still under development, McGeeney said it eventually could offer potential savings of 20%-30% compared with traditional processes.
The bottom line is that if exceptional customer service is on the table, a win-win situation is involved for casting providers and their customers alike.
“Close collaboration with customers’ design, engineering, procurement and, indeed, sales and marketing teams enables us to fully understand their requirements and, just as importantly, the time to market and cost drivers. Ultimately, this means we can successfully deliver the correct solution utilizing our processes,” noted Bob Bruce, sales and marketing director for Sandvik Medical Solutions. “As market leader in cast orthopedics, we are in a unique position, but one we definitely don’t take for granted. We never rest on our laurels and are always looking to work in collaborative partnerships with our customers to ensure we both succeed and prosper…The cornerstones of our business are technical differentiation, smarter supply solutions, operational excellence and being an agile enterprise. All this we achieve through communication, people performance and service.”
With that type of singular focus, some providers of casting are forecasting double-digit growth for 2008.
“It’s busy, which is wonderful news for us,” said Hall. “The activity level is different because so many medical OEMs are looking for cost-out opportunities, and castings are really the best route for these opportunities.”
It’s true that forging and machining outfits remain a challenging force for providers of casting. In addition, many OEMs still perform their casting operations in-house. However, it’s not of huge concern to those working on the front line of orthopedic manufacturing.
As Hall noted, “I think castings will grow with the market. Machining continues to get better, but so does casting.”