Huge technological advancements that cut costs and meet or exceed quality standards are yielding the smaller, thinner, and more difficult-to-manufacture parts demanded by the lucrative medical market. One good example comes from a builder of Swiss-type machine tools. Another comes from a cutting-edge company that designs, automates, and manufactures exceedingly small and precise medical parts.

Turning Machines Operate in 12 Axes

If you aren't familiar with machine-tool terminology, it helps to know that almost all machines used in meaningful industrial applications are now run by numerical control (NC). And each direction of motion in which the table or tool positionally rotates is called an axis. Years ago, three axes of motion was considered fairly sophisticated. This lets the tool locate at any point in a three-dimensional workspace. Articulating the tool at any angle (much as you can move your wrist in space) requires an additional two axes for rotation, giving a total of five axes of motion.

Initially, typical job shops rarely had machines capable of more than three-axis control. Many were doing only two-axis work. Five-axis machines were found mainly in the aerospace industry or other fields where complex surfaces and intricate features had to be generated.

With advances in the computerization of NC and motion control, five-axis control is now more common. In fact, machines are now being built with more than five axes of motion, and much of the work inspiring this is in the medical field.

Since five axes allow total positioning capability in any specific spatial envelope, it is logical to ask how additional axes are used. Additional axes allow performing more operations on a workpiece with a single setup and without intermediate repositioning or handling. For example, a machine might use several axes in a turning operation, then employ additional axes to position tools for milling and drilling without the part having to be manually repositioned or otherwise handled. Labor savings through elimination of workpiece handling is especially valuable in the medical industry because of increasing pressure to reduce costs associated with machining complex parts.

The 12-axis turning centers built by Tornos Technologies, Brookfield, Conn., (tornos.com) are examples of machines intended for complex operations while reducing setups and handling. The machines are often referred to as Swiss-type lathes. This has to do with how workpieces are gripped and supported rather than the country of origin. Tornos machines can combine standard milling and turning with operations that have only recently been applied to Swiss machines, such as boring, cross milling, drilling, thread whirling, and gundrilling.

An application of the Tornos 12-axis equipment is the machining of dental implants that cannot be produced on conventional NC turning centers. Although standard machines can perform three-axis work, the cutter cannot be offset from the centerline of the part to produce the angular features of the implants.

With the Tornos machine, complex parts up to 16-mm diameter can be produced in a single setup and with all 12 axes operating simultaneously. This application shows that the technological demands for machining surgical screws and various implants are greater than for any other type of industrial or commercial product. In addition to machining complex surfaces, the 12-axis machines provide superior tolerances and high surface finishes, with both rough and finish passes made with one setup.

The numerical control used in Tornos machines is different from that used conventionally. It couples with software that runs on a Windows PC and programs complex parts such as angular implants. Unlike other controls, the Tornos control has a central clock that acts as an “electronic cam“ and also has “virtual“ electronic cams.

The control electronically mimics the action of a conventional cam-operated machine. On a conventional machine, each cam controls one action, such as the motion of a tool, and the camshaft synchronizes the cams to act simultaneously.

In the Tornos NC, the control stores tool paths as data tables. Each axis has its own control chip or “electronic cam“ that stores only its toolpath as a step table, which is a sequence of moves in one or two axes. The clock signal generator reads and executes steps every eight milliseconds. No path calculations are required.

Data tables used comprise one for the axes of toolpaths, another for spindle speed, rotation and stops, and a third for machine functions. Data tables are programmed offline for each part.

The clock synchronizes the reading of the multiple individual toolpaths. Whereas the “cycle“ in a cam-operated machine is limited to the 360° rotation of the cam, there is no limit on the electronic clock. The control reads data tables in parallel, not one at a time, so, for example, the machine can have four tools cutting simultaneously.

High-Powered Engineering for Plastic Parts

Plastic parts are normally thought of as commodity products not necessarily embodying state-of-the-art engineering or manufacturing processes. But nothing could be further from the truth with parts made by Phillips Plastics Corp., Prescott, Wis., (phillipsplastics.com) for the medical industry.

Phillips, working in concert with customers, independent design firms, and its substantial engineering department, applies a wide array of engineering processes, new molding and production technologies, and its proprietary method for injection molding metal parts similar to the way plastic parts are produced.

An integral part of the concurrent engineering done at Phillips is finite-element analysis (FEA), supported by a network of Phillips engineers with expertise in stress analysis. This involves calculating stress, strain, deflections, and temperatures under specified conditions, and it includes static, dynamic, linear, nonlinear, and impact structural analysis. These methods determine exactly the strengths or weaknesses of components.

In the design stage, FEA helps ensure parts will be configured correctly and meet specifications in the first engineering iteration. It also reduces the need for costly revisions of production tooling, allowing products to get to market faster.

For example, as tooling is being designed, Moldflow software simulates the injection-molding process, indicating whether the part design needs tweaking. Properly applied early in the design stage, Moldflow reduces cost, cuts lead times, and helps produce close tolerances.

Mold filling simulations not only show how part geometry affects the molding process, they also reveal what will happen when multiple cavities are placed in a mold. This reduces or eliminates rework and helps in troubleshooting existing molds. Simulations suggest how to optimize molds through the creation of gate and runner systems, and they also predict the flow of injected material, cycle time, shot size, and required clamping force for the injection-molding machine.

Laser Marking: Plastic components often must carry graduations or instructions and warning labels. Laser etching is a high-tech means to burn numbers or letters into the surface of plastic. The laser beam penetrates up to 0.015 in. into the resin for a durable marking that exceeds pad printing or hot-stamping operations.

Unlike pad printing or hot stamping, no new tooling is required to update the graphics. Instead, graphic files are downloaded to the laser-etching machine as needed. An additional benefit is more freedom of design because laser graphics can be applied on more complicated geometries, such as the cylindrical shape of drug-delivery devices. Because laser etching tends to be permanent, the company also uses it for lot coding, which is mandated by certain FDA requirements.

Automated Assembly: Advanced assembly methods play an increasingly important role in manufacturing medical parts. Phillips has an internal automation group that evaluates products to create production automation devices for both low and high-volume runs.

The company also offers full and sub-assembly capabilities in Class 100,000 and 10,000 clean room environments, along with electronic assembly in cellular manufacturing stations. The facilities operate with complete lot traceability and are FDA registered. High-speed robotics and closed-loop processes reduce the possibility of contaminated parts. Automated vision systems also help prevent cosmetic and functional defects.

Metal Injection Molding: The medical field is constantly looking for less invasive procedures that require smaller surgical tools. And small metal implants are being used more frequently. To mass-produce precision small devices to close tolerances, Phillips developed a proprietary micromolding process for making micro-scale metal parts requiring no machining. Micromolding can be used with alloys including nickel steels, stainless steels, and titanium.

The net result is long-lasting implants and surgical tools that are brought to market with short lead times. Parts can be micromolded in sizes from 0.003 in.³ down to 0.0001 in.³ for both plastics and metals. Tolerances can be held to ±0.0005 in. and both undercuts and threads can be molded. Prototypes can produced in three to four weeks.