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As part of a GBP1m investment over the last four years, Cajero has been investing in machine tools supplied by Korber Schleifring UK to manufacture high-quality products.

Tool development and design – plus the necessary ultra-accurate tool grinding capability – is a continuous challenge, said Phil Harding, managing director of specialist tooling developer Cajero.

Cajero has had to meet this demand consistently to satisfy customer activity within the aerospace industry, particularly with clients whose constant quest is to harness the advantages of composites and who ‘invent’ new materials.

‘This has meant that almost 40 per cent of our business revolves around tool development projects,’ said Harding.

‘A prime example is the increase of hybrid composite stacks containing titanium and aluminium, as well as new honeycomb structures incorporating different grades of resin and applications,’ he added.

The advent of hybrid composites necessitates the avoidance of heat generation by the tool to prevent the resins melting, which would lead to material voids and de-lamination.

Tools for honeycomb materials have to be ultra sharp in order to cut rather that bend or deform the workpieces.

Component designers are also pressing for higher orders of surface finish and improved positional accuracy in composites and the industry is attempting to drive down costs.

Cajero’s position is equally maintained by its use of CAD (Solidworks) and ultra-precision tool grinding – technologies that effectively turn ideas and concepts into reality.

Playing the key role in this respect at the Isle of Sheppey, Kent site is a trio of Walter Helitronic Power multi-axis CNC tool grinders and a Walter Helicheck four-axis, non-contact measuring centre, all supplied by Korber Schleifring UK.

In deciding to purchase Walter tool grinders – the latest in February 2008 and the Walter Helicheck in 2007 – absolute rigidity from the machine’s cast-iron base and gantry design was the priority if Cajero was to attain the required quality of tool grind and inspection.

The machines provide high-precision positioning and repeatability to ensure the multiplicity of angles and ultra-sharp cutting edges are produced for some of the laminate materials such as Kevlar with its ‘fluffy’ internal structure and honeycombs.

Software was also high on the agenda and Harding is convinced that the Helitronic Power’s Tool Studio with integral live 3D simulation package, which enables grinding cycles to be verified and optimised for process, operational sequences and most appropriate tool paths for the (up to) six individual grinding wheels that can be carried on the twin-spindle grinding head.

This facility allows Cajero’s operators to kit the machines for single-cycle, multi-wheel applications.

‘In developing tool geometries, we can model and test cycles on screen, and if the system says the process is viable then we are totally confident we can perform the grind,’ said Harding.

Following grinding, Cajero can test and trial tools on a special high-speed spindle vertical machining centre, but quite often its partnership agreements with customers means a tool has to be put through its paces at the customer plant on either specially developed or production machines.

In many of these cases, Cajero technicians are sent along to advise on the set-up and to witness the event first hand.

In turn, this means Cajero also has to advise on production data such as speeds, feeds, depths of cut and step overs.

‘Our guys can be working with the very latest technology machine tools or a 20-year-old workhorse,’ said Harding.

‘Some of our tools for honeycomb, for instance, are like razorblades running at 30,000revs/min – and that’s a very challenging application and tool grind,’ he added.

The Walter Helitronics are also used to grind ultrasonic knives for tape laying machines that cut glass fibre, Kevlar and carbon fibre as well as for contouring and bevelling complex shapes from aluminium and honeycomb.

‘High levels of consistent edge that form in the grind are so important if we are to achieve the right cutting performance,’ said Harding.

The Helitronics are also called upon to grind and regrind button bit drilling tools for rock mining (70 per cent being shipped to the US, Scandinavia and Russia), an industry that has similar technology requirements in terms of tooling performance and quality levels.

The multi-insert tools have to be produced to a tolerance of five microns with very precise geometry.

Traceability is high on Cajero’s quality standards.

The company selects direct from the manufacturer the appropriate grade of carbide.

‘Consistency under cut from tool to tool and batch to batch is paramount, and, when ground, cutters have to be symmetrical and their flutes balanced in perfect relationship,’ said Harding.

Tool material is bought in as rod between 1.5mm and 30mm diameter, cut to length, centreless ground to the precise size before being loaded to the Walter Helitronics for flute, form and geometry grind in a single cycle.

Batch sizes vary between five for initial trials or prototypes to 2,000 and Cajero will only re-grind tools it has produced.

Cajero’s latest Helitronic Power is fitted with a disc-loader pallet system that can accept 40, 56 or 90 tools for processing in a fully automatic cycle.

In these situations, however, someone is always present over the two-shift working patterns due to the high levels of grind being pursued.

Controlled by Fanuc 310i, the machine incorporates adaptive control to adjust the feed rate according to cut requirements, as well as Heli-Probe tool datuming.

With Cajero able to provide customers with a full tooling package, it regularly makes trips into uncharted tool design territory – and it is here that the Walter Helicheck CNC measuring centre is regarded as vital.

In a single chucking, the Helicheck can check rake and helix angles, lead and relief angle and automatically scan the tool profile.

Some tools are 100 per cent checked due to their complexity of form or strict geometric requirements and the machine can provide a fully detailed report within a few minutes.

Even taking into account the high levels of precision that Cajero works to, less than one per cent of tools are out of specification, which Phil Harding said is due to the combination of people skills and the excellent repeatability of the Walter machines.

Koerber Schleifring

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