In March this year, Bowyer Engineering — a manufacturer of special-purpose machines and a CNC machining sub-contractor — bought its first magnetic work-holding equipment: an Italian-made component clamping system from Tecnomagnete.

Production manager John McNab says the £4,000 investment paid for itself within the first 12 weeks, significantly reducing the cost of machining steel plates for vehicle exhaust welding rigs, and helping the company to
address the ever increasing demand from its customers for savings.

Called MillTec Grip — and supplied through sole UK agent 1st Machine Tool Accessories, Salisbury (www.1mta.com) — the ‘permanent electro-magnetic’ work-holding arrangement for use on machining centres and milling machines uses a double circuit to generate a uniform clamping force between the workpiece and the magnetic surface, and at the same time between the magnetic system and the machine table.

The brief application of an electrical supply is sufficient to activate and de-activate the circuit. A patented feature of the low-profile frameless clamps is their sealed construction, which features a monolithic all-metal top section into which an array of sacrificial cylindrical-pole extensions is screwed for holding down ferrous workpieces.

Andover-based Bowyer Engineering, a 35-employee company that is celebrating its 70th anniversary this year, is predominantly a supplier to the aerospace sector. It manufactures machines for manipulating and inspecting turbine blades; it also mills and turns components for use in aircraft manufacture. A wide range of exotic materials is machined on a variety of CNC lathes as well as on Bridgeport three-axis vertical machining centres and a Matsuura five-axis model, which was installed in January 2015.

Exhaust fixtures

Bowyer also makes jigs for securing vehicle exhausts during automated arc welding. Until recently, the fixtures were manufactured from multi-component fabrications. These were difficult and time-consuming to mill and drill accurately, due to their complexity and the need to fixture them at compound angles. Furthermore,
a large variety of materials had to be stocked for their production.

Mr McNab subsequently devised a new production method that moved away from machining entire fabrications to milling and drilling steel base plates individually, then assembling them. He decided to standardise on 12mm-thick bright bar, 200mm wide and up to 4m long, which is sawn into billets as required.

Initially, the billets were cut into pieces of different sizes to suit the individual plates. Each piece had to be clamped on its edges in a vice for machining, which meant repositioning it for the second operation of milling the edges. As a result, the production cost was high, prompting Mr McNab to develop a more economical production technique.

He considered clamping a single billet for profiling a nest of variously shaped base plates by milling to depth around their profiles, followed by drilling. While this approach offered distinct benefits, the use of conventional fixturing would still have created a dead zone around the periphery caused by interference with the spindle, reducing the material yield. Moreover, using Bowyer’s zero-point work-holding equipment would have introduced long idle times, as it would have been necessary to attach pull studs to the under-side of each billet to provide security for heavy milling.

Mr McNab says: “Spindles turning means spindles earning,” so he set about finding a quicker method of clamping the billets without compromising the ability to machine components right up to the edge. While at a Matsuura Open House in Coalville last year, where 1st MTA had a stand in the supplier village, he remembered it making a presentation on the Tecnomagnete clamping system and reckoned this might offer a solution, allowing a billet tobe clamped on one face while leaving the other five faces free. A Bridgeport XR1000 three-axis VMC with a 12,000rev/min spindle, through-tool coolant and a 30-tool magazine was allocated to the project.

Flexible solution

So far, the MillTec Grip magnetic clamping system has been used exclusively on this Bridgeport machine, although it could be swapped over to other machining centres on the shopfloor, including the five-axis model. Thirty exhaust welding fixtures can be in build at a time — all of them different — and each can contain up to 100 plates, so the machine is kept busy.

Mr McNab says: “The magnetic work-holding and nesting technique substantially reduces the cost of producing every base plate. We produce the cutter path quickly, using a custom-designed template in EdgeCam that recognises recurring features.

“If the MillTec Grip does not happen to be on the Bridgeport, it is quick to fix it to the table by connecting an electric current, which is then switched off. Securing the steel billet onto the magnetic pole extensions is even faster and extremely secure.

“The magnetic work-holding station is positioned at one end of the machine table, allowing another clamping arrangement to sit alongside it for machining other types of component, resulting in maximum versatility.”

Bowyer also makes welding fixtures and other fixtures for manufacturing different products such as off-road vehicle frames and boiler housings. Its new method of making such jigs will expand business opportunities in this area.

Moreover, the company is already successfully using the magnetic clamping system to streamline production of a range of sub-contract parts for the aerospace, oil and gas, medical and general engineering sectors.

1st MTA provided a high level of technical back-up during initial installation of the Tecnomagnete equipment, advising how best to mount the unit on the machine and position the base plates. Support and advice from the supplier are on-going, since Bowyer frequently encounters different work-holding requirements as it transfers more and more sub-contract machining onto the magnetic clamping system.

In conclusion, Mr McNab says: “The whole project has been a resounding success, from concept to operation. Not only have our work-holding requirements been met, but the solution has exceeded all our expectations.”