TECHNOLOGY | VIEWPOINT
“Dry machining is popular in machining aluminium alloys”
Gautam K Ahuja, Managing Director, Dormer Tools India
What are the latest developments in the tooling industry to meet the challenging requirements in machining difficult-to-machine materials? To meet the challenging requirement of the difficult-to-machine materials (DTMM), there is a complete range of rotating as well as indexable tools avaliable. For turning applications, Pramet’s new SF, SM, SF2 and SF3 positive inserts provide a secure and dependable option in high temperature alloys. The sharp cutting edges promote low cutting forces which, in turn, prevent work hardening and ensure a quality surface finish. The PVD coated T6310 grade features a special sintering process, which enhances cutting edge reliability and strength. Its new substrate with intermediate cobalt content provides additional hardness and increased abrasion resistance to offer greater reliability and prolonged tool life. The grade’s triple coating provides durability for higher cutting speeds used when machining stainless steel, heat-treated and hardened materials. In milling, the M6330 grade has been developed specifically to achieve longer cutting edge durability and reliability in a range of difficult-to-machine materials (DTMM) with and without coolant. This is suited to adverse cutting conditions, including interrupted cutting. It also promotes greater operational reliability and tool life, with a high resistance to heat-related cracks. This is due to improved abrasion resistance from a new substrate and PVD coating. In tapping, solid carbide taps for machining hardened steels and other difficult-tomachine materials are available. Offering performance and productivity, the taps are recommended for machining hardened materials up to 63 HRc, providing high wear resistance and long tool life even at high speeds. What role does tooling play in the context of machining composite materials that requires different mechanism of material removal? In the use of carbon fibre-reinforced plastics (CFRP), it is often necessary to machine the components, for example, to make holes, trim the edges, etc, but the cutting of CFRP is often made difficult by delamination of the composites and by the short tool life. The process of machining CFRP consists of a series of fractures, each creating a chip. During machining of unidirectional CFRP perpendicular to the fibres, the surface is destroyed and cracks are formed. If the CFRP is machined parallel to the fibres, the surface is smoother, and the cracks reach only one or two fibre diameters into the composite. During machining of unidirectional CFRP parallel to the fibres, the horizontal cutting force (parallel to the fibres and the cutting direction) is determined by the cutting depth and the rake angle, while the vertical cutting force is determined by the relief angle and the wear of the tool. We can use tungsten carbide, ceramics and even CBN to machine CFRP, but we need to keep the cutting speeds low to about 50 m/min. What are the trends in dry machining? What would be your recommendations to get the most out of the tooling operation, while dry machining? In the machining of aluminium alloys instead of dry machining, Minimum Quantity Lubrication (MQL) is used. This consists of a small quantity of lubricant mixed with compressed air, which after coming into contact with the hot metal, becomes vapour. This is very effective in cooling the tool and component, and there are tremendous savings on the cutting oil used. For dry machining of steel, it is only possible to do in small components, with low depths of cut so that the workpiece does not heat up. Also, for finishing with close tolerances, we need to be careful about the bore size, which may reduce after cooling. Another precaution to be taken is that the hot chips will corrode the bed of the machine, and they should be cleared and put on the conveyor belt with minimum time lag. Due to these reasons, dry machining or MQL is only popular in the machining of aluminium alloys and not for steel.
EM | Nov 2016
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