Manufacturing News

There is an angle to facemilling

Milling a flat face is one of the most straight-forward of machining operations but as Christer Richt* explains, selecting the right cutter is the key to successful milling operations.

MOST facemilling operations involve depths of cut less than 4mm, while nearly half as many operations involve 4 – 10mm leaving the rest to heavy duty depths of 10 – 18 mm. The size and power of the machine tool is most often the limiting factor that has to be addressed, often through the choice of cutter diameter.

But another consideration is the required versatility of the tool: should the cutter perform facemilling, square-shoulder facemilling or even act as an endmill?

This is often the case when there is a lack of tool-magazine positions in machining centres or in multi-task machinery. But this operational versatility comes at a price: performance.

The entering angle of a facemilling cutter is the initial deciding characteristic that determines much of the tool capability. This is the angle of the main cutting edge to the workpiece top-face. The choice is between 90 – 10°.

Usually 90° is the entering angle for square shoulder facemilling. Axial cutting forces are minimised. The main disadvantage of a 90° cutter is the thick chip and the limiting effect this has on the feed rate so as not to overload the cutting edge.

An interesting development for square shoulder milling is the capacity for lighter, really accurate cuts that can utilise smaller machines for high finishing in one pass.

High feed milling

A 10° entering angle is ideal for high-feed milling and plunging. A small entering angle with square inserts provides a considerable amount of chip-thinning but has a very limited depth-of-cut capacity.

This means that feed rates can be high and that it is also ideal to be fed axially, as a plunge-milling cutter and as such suitable for long tool reaches.

Most of the cutting forces are directed axially into the spindle but this also means pressure against the component face being machined.

The 10° facemill is a versatile roughing tool with high metal removal rate for machining, faces, shoulders and cavities.

The round-insert cutter does not have one entering angle as the angle varies from zero to what the depth of cut determines as the maximum angle.

The round cutting edge provides the strongest edge for the general area of facemilling, profiling and with generous chip-thinning effect for high feeds making it also suitable for demanding materials such as super alloys. This is a roughing to semi-finishing cutter with high operational versatility.

General purpose milling

The most suitable entering angle for general-purpose facemills is 45°.

This is because of the advantageous balance of cutting forces and the chip-thinning effect of the long cutting edge that the inclination gives. This means good machining stability as well as the capability for high feed rates resulting in shorter machining times.

The 45° cutter is the dominant all-round tool for milling flat faces in all types of materials. It is capable of roughing at relatively large depths of cut to mirror-finishing using cemented carbide, ceramic, polychrystaline diamond or cubic boron nitride indexable inserts in most types of workpiece materials.

When it comes to the general purpose 45° facemill, a recent new development involves boosting feed rates with a new soft cutting action.

Especially of interest is the added capability of facemilling for smaller machines as well as higher utilisation possibilities of machining centres generally and of large milling machines.

The development of unique double-sided, square inserts has been possible through the design of new insert geometries and specially-designed precision insert-seats in the cutter body.

The cutter needs minimal power requirements, and is capable of high table feeds, for normal to demanding cuts, with depths of cut to 6mm.

Heavy duty milling

The 60° entering angle is ideal for heavy duty milling, combining depth-of-cut with high feed rate capability.

The limitation of the 45° facemill is that of depth-of-cut capability – normally 10mm. To achieve even larger depths, as needed for satisfactory productivity with one-pass cuts in heavy duty facemilling, the entering angle is raised to 60°.

The entering angle then maintains a satisfactory chip-thinning effect for high feed rates combined with balanced cutting forces and enough room axially for generous parrallel lands to generate good surface finish.

New heavy-duty facemill design, with a 60° entering angle, combines a depth of cut capacity of 18mm combined with a high feed rate capability. Typical operations include roughing large material-blanks, structures and castings.

Being intended for really tough machining conditions, this new concept is based on a cassette solution for seating and clamping square inserts.

Apart from very secure clamping, this provides easy and quick insert indexing and, if an insert seat is worn or damaged, of the cassette itself.

Close pitch machining

A 65° facemill specialises in close-pitch alternatives. Designed for strength and cost effectiveness, this cutter concept combines a relatively large depth-of-cut capability with the economy of multi-edge inserts.

This is a facemill primarily intended for cast-iron machining that forms a competitive solution for more demanding steel facemilling, especially when high-volume machining is involved. A large number of teeth per cutter, in the form of thick, double-sided inserts, having eight true cutting edges can rough or finish surfaces such as forged or cast components.

*Christer Richt is technical editorial manager at Sandvik Coromant, 1300 360 938, www.coromant.sandvik.com/au.

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