Metallics i MachininG
GettinG creative with
been to apply this principle by designing
a flank wear land suitably as a primary
relief.
Correctly applied, the primary
relief land acts a buffer, breaking up
any growing deflection amplitude and
thereby controlling chip thickness and
radial cutting forces. With the new
patented Sandvik Coromant design, as
the insert deflects from the workpiece,
Pocket milling: The CoroMill 790 makes light work of aluminium machining
the land makes momentary contact
with the arising machined curvature
of the component as it reflexes, thus than aluminium’s low melting point of
countering any amplitude growth during 625°C before encountering excessive
the course of machining. This ensures a wear and loss of strength at the cutting
constant steadying effect as part of the edge. However, a frequent problem of
cutting action. The short, occasional machining at high speeds is the need to be higher and more extended, it
contact between the primary relief for high machine power, leading to a provided a prolonged and advantageous
land and workpiece is slight enough to sometimes disadvantageous ratio of entry effect - reducing the shock effect
have no effect on performance, wear material removed per power unit. For substantially and leading to minimised
development or burr formation. this reason, any reduction by the tool in mismatch on the radially milled face of
power requirement is of great advantage. the component. Furthermore, the axial
The balance of power From a tooling perspective, tangential cutting force is also lowered considerably,
Larger diameters do not require the same cutting forces have a decisive influence which means that the pressure exerted
dampening and feed rate also ceases to on power requirement. Lowering the by the tool on the machined surface
be a major influential factor, with the power needed per volume of material under the tool is less.
magnitude of the radial cutting forces removed has a positive influence on
only varying slightly between feeds for aluminium milling applications, either Out and away
the cutter (typically 0.25mm and 0.35mm in the form of higher productivity per In addition, the new chip forming
per tooth). Typically, for a 25mm endmill, operation or on the demand for machine geometry on the rake face of the insert
the land can be 0.1mm wide and angled capability. has been deepened to reduce cutting
at 1° to follow the curved cutting edge As well as determining the ease of forces and to optimise the formation
precisely between certain points, with a cut, the rake angle also affects tangential of the chip and the way it is ejected
rake of 20° for aluminium. cutting force. By making this angle larger, from the insert pocket – out and away
Cemented carbide inserts can the CoroMill 790 design gives a more from the cutting zone and workpiece
withstand far higher temperatures positive insert and aligns it with the surface. The new geometry has also led
rest of the insert geometry, resulting in to a smaller contact area between insert
minimised cutting forces. and chip, which means less friction
and better cutting action. Additionally,
Easy entry it means that the new insert has the
To counter the generation of sudden capacity for a larger depth of cut.
rises in cutting forces, the entry of the In spite of the insert cutting edge
cutting edge into the material needs to seemingly being weakened by a sharper
be as gradual as possible when milling, edge and deeper chip forming geometry,
as this will affect the rate of growth, the stress levels are no higher than in
magnitude and direction of radial cutting comparatively less sharp cutting edges. A
forces. Consequently it will also affect more systematic approach, sophisticated
tool deflection and the amplitude of any calculations, simulations and testing
form errors on the workpiece. have all led to a more intelligent insert
Sandvik Coromant’s engineers have structure that not only performs better
found that by designing the edge of but is equally secure. y
Cuts like a knife: The CoroMill 790 Endmill arbor
the new CoroMill 790 insert geometry www.sandvik.coromant.com
aeroSPaceManUFactUring | noveMber 2009 11
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36