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Ensuring high-productivity and work-piece quality in boring operations

Ensuring high-productivity and work-piece quality in boring operations

Added to MTDCNC by Mills CNC Ltd on 04 June 2014

Mills CNC, the exclusive distributor of Doosan machine tools in the UK and Ireland, has recently conducted successful boring machining trials with tooling partner, Sandvik Coromant, using the company’s Coromant Capto clamping systems and its ‘Silent Tools’ dampened boring bars on a Doosan Puma 700LY machine (a large slant-bed turret lathe with integrated Y-axis and driven tools).

The trial results will be of interest to oil and gas precision component manufacturers, especially those using large length-to-diameter ratio boring bars to machine internal profiles and features on components typically found and used in the sector.

Vibration: the enemy

The internal machining of large diameter holes, deep holes or a combina¬tion of both requires a stable, and often repeatable, machining process.

In addition to taking care of critical elements such as maximum bar diameter; sufficient chip evacuation; positive insert geometry; correct insert shape; small nose radius and sharp cutting edge; special tool features will also need to be consid¬ered to minimise vibration – especially when tight tolerances and fine surface finishes are required.

Boring bars with long over¬hangs can often create vibrations during machining operations. Vibration if left unchecked can affect quality and, in the worst case scenarios, can damage the work-piece. Not good news when machining high-value parts.

To mitigate the effects of vibration, component manufacturers may well consider altering their process parameters (e.g. reducing speeds and feeds, and depths of cut).

But while such a response may help maintain quality it will almost certainly have a negative impact on productivity.

The trial

The Mills : Sandvik Coromant trial was designed to test the productivity and performance benefits of machining a steel test ring using a Coromont Capto ‘quick-change’ C10 clamping system with a C10 10 x D dampened boring bar (Ø100 x 1000mm).

Throughout the eight different trials cutting speeds remained constant (250m/min) but feed rates (0.10 – 0.25mm/rev), and depths of cut (2mm/3mm/4mm) were altered.

The results demonstrated the efficiency of the dampened boring bar solution with no vibrations occurring, even during the higher depth of cut trial, and radial deflection kept to a minimum.

Says Andrew Jack, technical director at Mills CNC:

'Productivity is the number one important issue in remaining competitive.

'The use of a Silent Tool can help customers maintain, or in many cases improve their productivity.

'Silent Tools allow usual cutting speeds and feeds at normal cut depths to be used. The result of which is a secure machining process, high-quality surface finishes, closer tolerances and improved tool life - even when working with boring bars with length to diameter overhang ratios of up to 10 times with Coromant Capto, or up to 14 times with cylindrical shank version tools.'

Coromant Capto: the quick-change advantage

As well as ensuring high work-piece accuracy and high-productivity (due to the avoidance of vibration and maintenance of high cutting data), the Coromant Capto solution also provides manufacturers with a number of other benefits – primarily concerned with speed of set-up, tool change time, turret space availability (owing to the systems’ universal modularity), and repeatability.

The quick-change facility is particularly advantageous when boring bars extend out so far that it is difficult (if not impossible) for other operations to be performed when the bar is in the turret.

The Coromant Capto system enables the bar to be unloaded / re-loaded with excellent repeatability, very quickly and easily, as opposed to 40 minutes on average when other tool holder systems with large, heavy tooling blocks are used.

In addition, with the use of the Coromant Capto coupling, the radial position of the insert is automatically orientated onto the centreline which eliminates any need for manual adjustment by the operator thus resulting in further reduction in machine tool downtime.

Concludes Andrew Jack:

'Our large Doosan Puma lathes are powerful, high-productivity machines. They are used extensively by precision component manufacturers in the oil and gas and power generation sectors (to name but a few).

'The recent trials undertaken with Sandvik Coromant have demonstrated that our machines, when using Coromant Capto clamping systems and dampened boring bars, deliver excellent cutting performance.'

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