Technology News
Workstation Prevents ESD during
Abrasive-Jet Machining
Abrasive-jet machining has become a helpful tool in medical and electronics manufacture, where it is used for drilling, deburring, beveling, lead cleaning, wire stripping, and coating removal. Unfortunately, the process tends to generate electrostatic charges within work chambers. In fact, abrading with aluminium oxide, silicon carbide, or other powders can result in a static load of 5000 V, giving rise to ESD events that can destroy sensitive devices such as resistors, PCBs, and pacemakers. The Technisch Buro Samoen B.V. (Ridderkerk, Netherlands) has developed a workstation that prevents these electrostatic charges from building up.
R. L. van Ameijde, product manager for the Technisch Buro Samoen, explains that the workstation was originally developed at the request of Medtronic in the Netherlands. For more than 20 years, Medtronic had been using abrading equipment inside closed workstations to produce pacemakers, and ESD was a recurring problem. The company had tried to prevent static buildup through grounding and the use of dissipative materials. Ionization devices, however, could not be used because they were easily damaged by the abrasive powder swirling within the work chamber.
Engineers at the Technisch Buro Samoen were faced with several major obstacles. To begin with, the standard ionization equipment could not be placed within the closed workstation, even if a vacuum system were used to remove the abrasive powder. Also, in the abrasive-jet process, the gap between the nozzle and the workpiece is generally only 1 mm or less, and this close proximity makes ESD events even more likely; ionization would have to reach this very small area to be effective. Moreover, engineers couldn't simply ionize the entire work chamber, because the grounded metal housing would neutralize the positive and negative ions before they could reach the target area. Ionization bars would not be suitable, because the maximum acceptable ion balance of ±250 V could be exceeded, and the continuing flow of ionization could damage critical components even before the actual abrading process began. Only a sharply focused stream of ionized air coming from outside the closed workstation would do the job.
The design team was able to develop an ESD-controlled workstation that met all these stringent requirements. The work chamber is, of course, grounded, but the abrading handpiece and nozzle are grounded separately and interconnected by a 1-MA resistor. Two more ground connections are attached to wrist straps. The metal chamber does not contain any nonconductive parts--even the portholes, ionized-air inlet, and light hood are all constructed from dissipative materials. Any loss of active ions to the metal housing is negligible.
The chamber uses a Simco Top Gun ionizer, which sits on top of the work chamber rather than inside it, at a safe distance from the abrasive powder. The unit generates an inverted-cone-shaped stream of ions at up to 30 V; the ionizing cone starts from an area of about 80 mm in diameter at the top and ends in a focused spot on the bottom plate centered midway between the portholes. The airstream hits the target at an angle of 75°. After passing the workpiece, the ionized air circulates irregularly before being drawn into a Torit VS 550 dust collector and neutralized; the dust collector also prevents the used abrasive powder from traveling in the wrong direction, and therefore needs to be switched on before the abrading unit is switched on.
The jet of ionized air is strong enough to pinpoint the target area without affecting the trajectory of the abrasive powder. For example, an abrasive nozzle operating at 6 bar of pressure would be adequately ionized with a stream of compressed air at 3 bar. In addition, the abrasive-powder jet and the ionizing-air jet can be regulated independently. Differences in ratio are influenced by the position and size of the workpieces and dust-collector capacity. Although the ESD-controlled work chamber was originally developed for use in making pacemakers, van Ameijde expects that it will benefit a wide range of delicate electromedical devices.
Molecular Cold Welding Technology Joins Nonferrous and Ceramic Materials
A molecular cold welding technique produces heliumtight joints with a minimum of electrical and thermal transition resistance. The technology, developed by Telsonic AG (Bronschhofen, Switzerland) can be used to weld nonferrous and precious metals to ceramics. According to the company, the cold welding process is most appropriate for joining aluminium or copper, but also achieves quick welds of dissimilar nonferrous metals. In fact, the technique can generate a heliumtight cold weld between a cap and a container up to 60 mm in diameter in less than 0.05 seconds.
Engineers at Telsonic cite several benefits of the system. For example, the heliumtight welds can help extend the shelf life of chemical products and eliminate the need for additional seals or packaging. The process generates almost no heat, and can therefore be used with heat-sensitive packaging materials and products. The technology can also be used by electronics manufacturers to weld soldering terminals, contacts, or electrical components. The process is easily integrated into automated production lines.
Linear Motors Accept Three-Phase Servo Input
Linear Drives Ltd. (Basildon, Essex, UK) has developed a line of linear motors that are electrically identical to conventional rotary brushless servomotors. As a result, the LD-series motors can be driven by almost any suitably rated three-phase servo amplifier. According to Hugh-Peter Kelly, CEO of Linear Drives and inventor of the tubular linear motor, three-phase operation significantly increases motor performance. In fact, the LD-series motors offer twice the performance of the company's SC-series motors, which were launched only last year. As a result, the motors can potentially be used in applications that were previously thought to be beyond the scope of linear-motor systems. By using their favorite servo controller along with their preferred servo amplifier, customers can enjoy a significant reduction in initial installation costs.
The LD-series motors are similar in appearance to the SC-series motors, according to the company, but are considerably more responsive. Top speeds have been increased thanks to the inherently high drive voltages involved. Short-duty-cycle speeds of up to 8 m/sec are possible, and the overall 100% duty-cycle performance is itself substantially improved. Higher standard thrusts and faster acceleration/deceleration rates combine to provide commensurate increases in both payload and inertia-handling capabilities.
The LD-series motors accommodate travel lengths of up to 2 m and are available with or without the supplier's LDA 310 servo amplifier. Units can be supplied as motor modules or with the motor integrated within a load-bearing axis. The LD-series motors can also be provided in basic component form only, comprising just the thrust rod and motor thrust block, enabling OEMs to integrate the direct-thrust technology into their own mechanisms.
