Pneumatic and electrical actuators used in harmony

MacGregor Welding Systems has designed and built an automated assembly system to fabricate miniature sensor modules for use in analyser equipment. Individual component parts are assembled completely automatically – a process that involves the precision welding of metallic connector ribbons onto small pins. The system makes extensive use of Festo electrical and pneumatic actuators, including two electrical mini slide units with matching controllers, which are fed with position feedback data to ensure high-accuracy assembly and precision micro welding.

MacGregor Welding Systems designs and manufactures a wide range of micro resistance and pulsed micro arc equipment for use in diverse industrial manufacturing applications. Founded in the late 1970s, the company initially concentrated on the development and manufacture of pulsed micro arc welding torches and precision resistance welding heads and power supplies. These are typically used by customers in the medical, aerospace and automotive industries to perform high-reliability joining and interconnection of electronic components and sub-assemblies.

In recent years, MacGregor Welding Systems has expanded the systems engineering side of its business significantly, and today produces a considerable number of application- and customer-specific assembly machines. Most recently, the company has seen a dramatic increase in systems sales following the recent introduction of RoHS legislation, which has created an upsurge of interest in micro joining techniques as the electronic industry moves to lead-free components and manufacturing processes.

Sensor assembly machine

The multi-stage sensor assembly process in the latest machine includes the fitting and lubrication of O-rings and final moulding insertion – as well as welding two strips of metallic ribbons onto a pair of small pins on the sensor module, and onto a connector block. The company chose to base the machine predominantly on Festo pneumatic and electrical actuators, using SLTE electrical mini slides and associated SFC-DC motor controllers for two of the most demanding parts of the system, which require exceptionally high positional accuracy.

Graham MacGregor, Managing Director of MacGregor Welding Systems, comments: "We elected to use Festo SLTE mini slides primarily because they provide a complete, ready-to-run positioning solution. The slides incorporate their own miniature motors, which simplifies system integration and makes them very cost-effective, and the supplied control software is extremely easy to use." One of the mini slides is associated with the initial product assembly stages, the other with the welding stage.

The welding process uses a technique known as micro resistance welding, which involves passing a short-duration, high-current pulse through the materials to be joined, while accurately controlling the applied force. The welding head module provides up to 10mm of dynamic movement and is driven into position by the SLTE mini slide; a compression transducer provides feedback to the control system, which triggers the welding power supply to deliver a pulse of current when the weld electrodes are in the correct position. The weld head can accommodate a force in the range 2-70 N and the current pulse – up to 1000A – is typically limited to 5-50ms. The welding process involves far less thermal energy than a conventional solder joint, making it suitable for heat-sensitive components, and it provides a much faster means of securing consistent, high-integrity electrical connections.

The automated assembly machine was recently installed at the customer's premises, where it is currently undergoing evaluation prior to production ramp-up. It is understood to be performing impeccably and the customer is said to be delighted that a system with such a small footprint can provide the high throughput that is being achieved. Indeed, the customer is so pleased that an order has been placed for a second machine.

About MacGregor Welding Systems

MacGregor Welding Systems is a world leader in the design and manufacture of precision micro joining equipment. The company's products include DC micro resistance welding equipment, linear DC welding power supplies, pulsed-arc micro Tig welding machines, micro welding machines for automated production, micro weld heads, and Droplet Deposition Equipment. MacGregor Welding Systems is ISO 9001:2000 approved and the business offers a full design, build and installation service. For more information, visit www.macgregorsystems.com.