Fine machining of large bores

Posted on 20 Mar 2017 and read 715 times
Fine machining of large boresTo simplify the fine machining of bores with large diameters, Rugby-based Mapal Ltd ( has developed its HPR400 reaming tool, which features high-accuracy inserts.

According to the company, this means that tool quantities and the time required for tool setting can be reduced.

The fine machining of large tight-tolerance bores traditionally sees machine shops using multi-edged reaming tools, as these are both fast and less sensitive to interrupted cuts, but the reconditioning of reamers with fixed
inserts is a complex process.

By incorporating high-accuracy insert seats on the HPR400, customers can replace inserts instantly, using a torque wrench. Incorrect insert mounting is eliminated, as only one mounting position is possible — and the inserts can be fitted in any pocket.

As a result, no setting is required, and there is no need to send tools away for reconditioning. The quantity of tools will also be minimised as tool bodies do not need to be reconditioned.

Furthermore, the HPR400 has an internal coolant supply that directs coolant directly to the cutting edge. Another design feature is unequal spacing of the insert seats, which is said to ensure a quiet and smooth cutting process.

Available in diameters from 50 to 315mm, the HPR400 is offered with either an HSK interface or Mapal’s own module adapter. The reamers can be applied to almost any workpiece material, as inserts are available in a variety of grades and geometries.

Mapal can provide indexable carbide inserts with or without a CVD coating; there are also cermet inserts and inserts tipped with PCD or PcBN.

For reaming cast iron, Mapal has developed the wear-resistant HC419 insert grade with a CVD coating. The company says that this combination is already proving successful at a number of automotive manufacturers, producing everything from brake callipers and swivel bearings to gearbox housings.

One automotive customer is machining the main bore in a differential housing made from GJS400. With a diameter of 150mm, an HPR400 with eight inserts is obtaining a tolerance level of IT7 and an average surface roughness of 1.35Ra when running at a cutting speed of 160m/min with a feed of 1.6mm.

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