Adjustable Grind: Medical Manufacturing

Courtesy of ANCA

Because multiaxis tool and cutter machines can grind complex contours using CAD/CAM software, many shops use the machines to produce medical parts, such as this component of an artificial knee.

More flexible grinding machines allow part manufacturers and toolmakers to fine-tune their production processes.

The days of long production runs of identical parts are essentially over in the U.S.; staying competitive today requires manufacturers to produce smaller lot sizes of different parts and part families in a just-in-time fashion. Flexibility—the ability to quickly change processes and efficiently meet changing demand—is a key manufacturing capability.

Grinding has long been considered a deliberate (slow) and dedicated process. In response to global manufacturing trends, however, grinding machine builders are focusing on flexibility as they tailor their equipment to meet the needs of widely differing end users.

Production Changes

Hans Ueltschi, vice president for the cylindrical division of United Grinding Technologies Inc., Miamisburg, Ohio, said the trend towards smaller production runs even includes automakers. “Formerly, they ran several thousand parts a day, and now they may be running lots of a few hundred,” he said.

In that scenario, the differences between lots often involve different details within a family of parts, such as altered dimensions or profiles on a family of shafts.

To quickly change from one part to another, a production grinder can be fitted with flexibility-enhancing options, such as a high-speed spindle for peel grinding. Peel grinding is, in some respects, like turning. Instead of dressing a grinding wheel with a specific profile and plunging it into the part, the peel grinding method uses a smaller, narrower, generically shaped wheel that moves in a traverse path across the part, like a lathe tool, according to programmed CNC movements.

“Peel grinding allows us to do more different shapes with the same type of wheel,” Ueltschi said. “If the shape of the part changes, it is just a matter of changing the program. We don’t have to change the wheel from part to part.”

For example, the Studer S22 production grinder produces various shafts for different transmission models without changing wheels, or it can grind a series of different carbide punches for the can die industry. With the high-speed spindle option, peripheral wheel speeds up to 140 m/sec. are possible. In high-speed operation, diamond wheels grind carbide and CBN wheels grind steel.

Another approach to flexibility addresses a job shop scenario involving small runs of different parts. In those cases, a grinder with multiple spindles enables a shop to grind a variety of part features without retooling the machine for each new part, according to Ueltschi. “It’s not just adding a wheel, but doing it in a way that minimizes interference,” he said. “Sometimes when you have multiple wheels, you reduce the work envelope of a machine.”

Courtesy of United Grinding

The wheelhead of the Studer S33 universal grinder has two motor spindles for external grinding as well as an internal grinding attachment. Coupled with manual or automatic swivel capabilities, the wheel arrangement allows users to grind multiple features in one clamping.

Studer designed the wheelhead of the S33 universal grinder to minimize interference. The wheelhead has two motor spindles for external grinding and an internal grinding attachment. Manual or automatic swivel capabilities permit external and internal grinding in one setup. The arrangement, Ueltschi said, “gives the most flexibility in many scenarios. This wheel arrangement allows the user to do more features in one clamping.”

The grinder also can be fitted with a smartLoad automated workhandling system from Studer. The system’s part-gripping elements can quickly be reconfigured to handle different parts. While retooling the loader on production-focused machines can take from several hours to several days, the process reportedly takes minutes on the universal machine.

Axes and Software

Grinding machines with increased flexibility are also allowing shops to enter new markets. “It comes down to having the axes and software,” said Russell Riddiford, president of ANCA Inc., Wixom, Mich. The growing market for medical tools and components is a prime example. In the past, Riddiford noted, machines that ground medical parts and surgical reamers and drills were designed specifically for those tasks.

“Years ago, you wouldn’t think of a CNC tool and cutter grinder making a hip rasp. It would be a special-purpose grinding machine,” he said. Now, because multiaxis tool and cutter grinders using CAD/CAM software can produce complex contours, many shops are acquiring tool and cutter grinders to produce medical parts (see photo on page 43).

Riddiford said a major factor influencing that trend is the move by many medical part designers to standardize on the Siemens PLM NX CAD modeling package. “The medical companies will provide a model, which has parameters of the shape they want manufactured,” he said. “Companies like ours will pass that NX model through a converting tool to create ANCA control language or other CNC language, and then that generates the software paths for what you want to grind.”

The main driver for adapting standard machines to grind special parts, Riddiford said, is shops don’t want to invest in a special-purpose machine dedicated to grinding just one part. “That part may not be around after a period of time,” he said. “Buying a multiaxis CNC tool and cutter grinder with optional software that can do these rasps and cutters is a much better investment, because if that work goes away, you have the software on the machine to do something else. Or you can just convert it back to a tool and cutter grinder to cut endmills.”

Riddiford cautioned that flexibility alone does not guarantee success. “Getting into medical can be challenging as well as financially lucrative. The demand for part quality and sophistication is extremely high, and not everyone who makes a cutting tool will be able to go through the required approval process to get certified as a supplier,” he said.

Automation is helping manufacturers further expand the flexibility of their grinding machines. Riddiford described the TXcell that ANCA presented at IMTS 2010. The system consists of an ANCA TX7+ tool grinder mated with a Fanuc robot. The robot changes grinding wheel packs and also loads/unloads parts. In a medical application, a knee prosthesis can be ground in the machine, polished with a buffing unit in the machine’s toolchanger, then moved by the robot to a laser etching machine outside the machine for addition of a part number. Such a cell, Riddiford said, allows a shop to accomplish on one machine what once took two or more machines.

High-Volume Strategies

Even the heavy-duty, traditionally high-volume side of grinding operations can benefit from flexibility. Cinetic Landis Corp., Hagerstown, Md., produces grinding machines engineered for finishing shafts 0.5m and longer. Dwight Myers, director of business development, said the company’s machines combine high volume and high precision with flexibility. He said while one machine user may run one shaft “forever,” another may grind “one or two in a row, then changeover very quickly.”

No matter the part volume, he said, “the customers we are targeting traditionally grind a shaft in more than one grinding operation and more than one fixturing. Our target is to accomplish more than one, or, in some cases, all of those grinding operations in one machine, and optimally in one fixture.”