Advances in machine tooling technology has enabled high feed milling (HFM) to be used in a larger range of applications. Tapio Alatalo* writes.
THE main advantages of High Feed Milling (HFM) are well known – if the feed rate can be raised without changing the width or depth of cut, the rate of metal removal will increase.
A substantial rise in feed rate must be accompanied by a corresponding reduction in depth of cut – but even in this scenario, the net increase in metal removal can be more than 300%.
The extreme stability of the latest generation HFM tools offer this and more. Machining quality is greatly improved and components can often be machined to near-net shapes during roughing operations, making it possible to go straight to semi-finishing or even to omit the semi-finishing stage.
Implementing a HFM strategy is usually a very straightforward process that can be handled by the operator.
Apart from installing the new tooling, the only change that needs be made to an established CNC program is to raise the feed rate – a simple operation as long as the machine has the capacity to handle the higher rate.
The toolpath remains unchanged and requires no time-consuming reprogramming.
With a light depth of cut, a high feed rate is essential to avoid rubbing of the workpiece.
Seco Tools’ approach is to use radiused inserts that generate a small lead angle. The idea is to have a low setting angle and push the cutter hard to achieve the correct average chip thickness.
The insert’s cutting-zone geometry is crucial to stability, therefore cutting edges with very large radii – typically 8 to 16 mm – better ensure that the cutting forces are always in the axial direction.
Another vital factor in obtaining the full benefits of HFM is the machine itself, which must be capable of delivering the potential performance of the tools.
The machine should ideally have ample power, feed-rate capabilities approaching 10,000 mm/min, rigid machine platforms that can handle abrupt changes in multi-directional forces, adaptive controls with high-speed look-ahead features and good chip evacuation.
Fitting the mold
There are many documented cases that highlight the significant productivity increases that can be achieved with HFM tools.
A US company, Northeast Tire Mold, radically reduced the time needed for a multiple plunging operation using High Feed Milling tools.
The workpiece was a 1500-mm-diameter toroidal container in 1020 steel used to hold the individual sections of the mould together, and the operation involved creating nine pockets 50 mm deep and 75 mm wide. A Seco R217.21 high feed tool was recommended for the job and was used on an Alzmetall four-axis CNC machining centre.
Within an hour of start-up this was successfully taken to its maximum capacity of 42 hp (31 kW) and 7,200 rev/min and the time taken to complete the operation was reduced from 6 hours to just 34 minutes.
A more unusual application was the machining of the keel for the Swedish yacht that competed in the 2007 America’s Cup. The material was Weldox 700, a strong, tough structural sheet, and the operation was similar to copy milling.
The engineering company RydVerken used Seco R217.21 milling cutters, which were run at 6,000 mm/min table feed and a cutting speed of 160 m/min with a 0.8 mm depth of cut and a cutting width of 25 mm. The inserts were engaged for 60 minutes and could have remained engaged for a further hour.
Process stability was excellent despite the relatively long overhang, and machining time was reduced by 50% compared to the previous milling cutter.
Tapio Alatalo* is a product specialist at Seco Tools. For more information about the company phone 1300 557 326 or visit the website at www.secotools.com.
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