Originally Published MPMN July/August 2002

EQUIPMENT NEWS: Machining Equipment

Suppliers Tout Advances in Precision, Productivity

Ultrasonic equipment introduced for machining ceramics, silicone

Norbert Sparrow

Suppliers of machining equipment for medical device applications are redoubling efforts to increase throughput without sacrificing accuracy or reliability. Equipment makers have developed a variety of technologies to achieve this goal. One firm is introducing ultrasonic machining equipment to the U.S. market, claiming that it is a productivity-boosting tool for the precise machining of ceramic, silicone, and glass materials. Another supplier has designed a grinding machine for the production of medical drills that replaces a four-step operation with a simultaneous process. These developments and related machining equipment news are covered in this section.

Linear-drive technology, ultrasound machining showcased

Specializing in the design and manufacture of metal-cutting machine tools, a company will present its range of linear-drive equipment at the International Manufacturing Technology Show in Chicago on September 4–11. Linear-drive technology substantially boosts machine productivity compared with that of equipment with conventional drives, according to DMG America. The firm will exhibit its newest generation of machining centers at the event and introduce its ultrasonic machining equipment.

A compact vertical machining center with a spindle that revolves at 12,000 rpm, a spiral chip conveyor, and a machine-bed flush mechanism will be displayed at the company stand. The firm will also showcase its new multispindle machines available with CNC-driven synchronous motors or ball-screw spindles. The multispindle machines are suited for processing 0.12–2.16-in.-diam parts.

In addition, the firm will present its ultrasonic machines in the United States for the first time. Designed to machine materials such as ceramics, glass, graphite, and precious stones, the DMS 35/50 line is said to represent a five-fold increase in productivity compared with other technologies. It achieves a surface roughness of <0.2 µm Ra. Ultrasonic equipment is suited for the precise machining of complex geometries and miniature products.

Grinding machine slashes cycle times

A recently developed rotary-transfer grinding machine for the production of medical drills reportedly achieves dramatic reductions in cycle time compared with conventional equipment. Disposable 315-mm-long drills ranging in diameter from 1 to 8 mm can be machined in as fast as 45 seconds, with most changeovers taking no more than 45 minutes, according to Monnier + Zahner Ltd.

Traditional five- and six-axis grinding machines require four operations to machine helicoidal drills: grinding the groove, grinding the back, start-grinding the centering point, and relief-grinding the cutting edge. The M 648 has four modular machining stations in a star shape and a loading station, enabling the four grinding operations and loading and unloading sequence to be done simultaneously.

The Swiss firm supplies about 35 machines to the medical market each year, as well as 15 to 20 machine tools. Thread-milling and thread-whirling machines for bone screws, milling machines for the production of self-cutting flutes, eight-spindle production centers for bone plates, and honing units for hip joints have been developed by the company.

Single-spindle units machine medical products with one setup

A supplier of equipment that combines the speed and productivity of cam-style Swiss-type screw machines and the flexibility and precision of CNC equipment has redesigned some of its larger machines. The DECO 20a and 26a machines, supplied by Tornos Technologies U.S. Corp., have a new cabinet design and a pocket door that permits access to the work area from the top or bottom of the unit. In addition, a window just above the control unit puts the main spindle within easy reach and facilitates collet and guide-bushing changes.

Mechanical enhancements include a larger coolant tank, which now holds an additional 20 L of fluid, and fewer moving parts in the gripper and basin to limit positioning adjustments.

The accompanying software also has been upgraded. Accelerated program generation and data transfer, and more automated functions such as tool-collision monitoring and a geometry help screen are among the improvements.

The DECO 20a and 26a are available with up to 12 axes. The 20a has a 10,000-rpm spindle speed powered by a 5.5-kW motor, while the 26a machine attains speeds of 8000 rpm with a 7.5-kW motor. Both can be equipped with integrated bar loaders.

Tornos machines are routinely used for the machining of medical and dental implants and bone screws.

Drilling machine minimizes bore run-out

Specifically developed for medical device applications, a gun-type drilling machine practically eliminates bore run-out by rotating the tool and the workpiece in opposite directions. Drill depths that are more than 60x the diameter of the hole can be achieved. The drilling machines from TBT Automotive Div. ensure precise and reliable drilling even with difficult-to-machine materials such as titanium and stainless-steel alloys, according to the firm.

A high-pressure coolant system removes chips from holes as small as 0.032 in. diam. The coolant flows through the cutting tool at pressures up to 2500 psi, flushing out the chips, which flow with the coolant along the side of the tool and out of the bore.

During machining operations, the special drills a have burnishing effect on the bore surface. A surface with a roughness of better than 0.2-µm Ra can be achieved. Process monitoring systems prevent even small-diameter tools from breaking.

Machine is suited for finishing hip joints

A microfinishing machine is designed to correct surface imperfections and to impart a mirror finish to hip joints and other spherical surfaces. The SPH 150 machine from Nagel Precision Inc. has a four-position automatic tool changer that enables rough, semifinish, finish, and final-gloss finishing operations to be performed with a single chucking of the part. An automatic stone-dressing device ensures that the wheel contact area is narrow and constant to prevent distortion to the workpiece. An in-process size-control system maintains tolerances down to the micron level. The machine can be equipped with multiple spindles and automatic loading and unloading units to accommodate a range of production requirements.

Noncontact winding-angle detection improves process control

The use of a machine-vision system reportedly has improved the control accuracy of a company's line of coil winders by a factor of 100 compared with previous models. "This new winder has improved all process control variables to help device manufacturers make more consistent products with less waste," says Dale Henson, principal engineer and president of Engineering By Design. The machine's primary function is the production of coil stents and catheters, but it is suitable for a range of small-coil manufacturing operations.

Previous machine designs measured winding angles by feeding wire through a mechanical arm with an angle sensor. When measuring smaller wires, however, the sensor arm was prone to changing the wind angle as it came into contact with the wire. Deviations of as much as 2° were not uncommon. By integrating a noncontact machine-vision system, the new design attains wind-angle detection within 0.02°. "Maintaining a steady tension of 0.2 g and a wind angle of 0.1° makes it possible to produce a coil with 0.0004-in.-diam platinum wire," notes Henson.

In addition to enhanced process control, the Double Vision coil winder has a number of other built-in features to improve productivity. It offers menu-selectable variable, fixed-pitch, and tight-pitch winding capability with automatic mandrel and filament tensioning. Closed-loop tension and slack control enables winding speeds up to 6000 rpm., and by stacking two independent machines on one frame, the company has doubled the production capabilities without requiring additional floor space.

Digital drive boosts machining performance

A vertical high-speed center for machining graphite and metals is equipped with digital-drive technology to enhance performance even when working on complex 3-D projects. The BMC 12 TNC, which was recently introduced by Mikron Bostomatic Corp., also offers higher speeds and tighter tolerances than previous models and enhanced surface finishes.

A sealed cabinet and an integrated extraction system with a suction frame that efficiently removes dust from the point of machining make the equipment suitable for graphite machining. The use of linear guides and high-precision ball screws ensures accurate positioning and high stiffness, which are necessary to achieve the high feed rates and accelerations required to machine graphite.

Liquid-cooled spindle motors with hybrid ceramic bearings attain speeds up to 30,000 rpm. A permanently sealed grease-lubrication system prevents oil dripping from the spindle head, and a standard oil-mist lubrication system minimizes lubricant consumption while eliminating the handling and disposal of coolant emulsions.

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