Integrity assured!

Citation

(2005), "Integrity assured!", Aircraft Engineering and Aerospace Technology, Vol. 77 No. 1. https://doi.org/10.1108/aeat.2005.12777aab.002

Integrity assured!

Integrity assured!

Keywords: Aerospace industry, Production engineering

By dramatically reducing the creation of the recast layer in wire EDM operations – Charmilles' CleanCut digital generator opens up new opportunities for aerospace applications.

Charmilles, the EDM specialist and part of Agie Charmilles, is reported to have virtually eliminated the creation of the recast layer produced during the wire EDM process – thereby ensuring better structural and/or surface integrity of the workpiece – with its new CleanCut generator.

This development will assist in the wider acceptance of EDM as a viable process in the manufacture of certain components (aerospace, medical) where, in the past, the creation of the recast layer raised some question marks about the metallurgical integrity of the EDM machined part. It will also negate the need for secondary and time- consuming (hence unprofitable) operations to remove the layer.

An inherent by-product of the EDM process is creation of the recast layer (white layer).

When wire is brought into close proximity to a workpiece, but still separated by a die-electric fluid, and a voltage is applied between the two – a spark will be created and will jump between them. The thermal energy contained within this spark will melt a small volume of both the wire and the workpiece and the die-electric will flush away the resultant debris. This sequence of spark-melt-flush, spark- melt-flush, etc. occurs many thousands of times per second.

However, after a spark has removed some material and has been switched off – not all of the eroded material will have been flushed away. A minute quantity of molten material will be drawn back onto the workpiece due to surface tension and cooling effects. This molten material will then solidify back onto the cooler surface as a highly-carbonaceous layer – the recast layer.

Immediately below the recast layer is the heat affected zone (HAZ) which is partially affected by the heat and temperatures created during the EDM process. The thickness of the recast layer and the depth of the HAZ depend on the current and frequencies used during machining as well as the heat absorption characteristics of the material being machined.

Charmilles' CleanCut generator, available on its Robofil 240 and 440 cc wire machines, reduces the creation of the recast layer across a wide range of materials, e.g. – steel, tungsten carbide, titanium, polycrystalline diamond (PCD) etc. – and therefore opens up significant opportunities in a number of sectors including aerospace, medical and cutting tool manufacture.

The generator produces uniquely- formed, high-intensity sparks that optimise erosion performance, produce fast cutting speeds (400 mm²/min) and control electrolytic effects.

With the CleanCut generator – perfectly calibrated sparks are created which create an extremely thin recast layer during roughing operations that virtually disappears after two finishing passes. Because surface hardness is not modified by the process – these cutting tools have a longer working life.

Short, high-intensity sparks eliminate micro-cracking and reduce the electrolytic effect. Cobalt used as a binder is not depleted during the EDM process ensuring maximum tool life.

The CleanCut generator claims to eliminate pollution of the titanium work surface caused by copper or zinc particles and does not lead to surface oxidation which creates a blue tinge to the titanium.

Elimination of electrolytic effects and perfectly-calibrated sparks produced by the CleanCut generator reportedly ensure sharp, solid and durable cutting edges to be created for cutting tools, extrusion dies, form tools, etc.

For further details contact: Agie Charmilles Ltd. Tel: +44 (0) 2476 538666; Fax: +44 (0) 2476 530023; E-mail: info@agie-charmilles.co.uk; Web site: www.agie-charmilles.com