Gear cutting – milling – or planing – Milling – Including means to infeed rotary cutter toward work
Reexamination Certificate
1999-07-12
2001-11-27
Briggs, William (Department: 3722)
Gear cutting, milling, or planing
Milling
Including means to infeed rotary cutter toward work
C082S106000, C409S200000
Reexamination Certificate
active
06322300
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to milling machines which can be used to machine both eccentric end faces and circumferential faces, e.g. peripheral faces.
A typical workpiece having such faces is a crankshaft, for which reason the following text always refers to a crankshaft, without limiting the possible workpieces to this alone.
For crankshafts, metal-removing machining is known both with external-milling machines and with internal-milling machines, that is to say by means of a milling cutter which annularly surrounds the crankshaft and has inwardly directed teeth. In this case, the axis of rotation of the milling cutter lies parallel to the longitudinal axis of the crankshaft.
In this case, the crankshaft is held at its ends, that is to say on one sides at its end flange and on the other side at its end journal, centrically, that is to say on the centre axis of its centre bearings, in chucks on both sides.
In a known solution, the crankshaft does not move during the machining, and thus the chucks are not driven by a spindle head. For machining of the crankpin journals, the annular internal-milling cutter rotates, on the one hand, about its own centre point in order to generate the cutting speed and, on the other hand, on an orbit about the centre of the crankpin journal to be machined, in order to mill the peripheral face thereof. Web end faces and web circumferential surfaces can also be machined in this manner, as long as the radius of curvature is smaller than the radius of the circuit of the cutting edges of the internal-milling cutter. With the crankshaft stationary, the internal-milling cutter can be displaced in a defined manner in the X- and Y-directions.
The mounting which annularly surrounds the internal-milling cutter is extremely stable, but has a relatively wide extent in the Z-direction, for which reason, for short crankshafts, the simultaneous deployment of two internal-milling cutters axially spaced apart on the same crankshaft can be problematical.
It is also known in that solution to rotate the crankshaft slowly during the machining, that is to say to be able to drive at least one of the chucks in a defined manner by means of a spindle head and to set its rotational position. This realisation of the C-axis for the workpiece makes it possible to dispense with the movement of the tool slide rest in the Y-direction, so that therefore only the tool slide rest for the internal-milling cutter merely comprises a lower slide for movement in the Z-direction and an upper slide for movement in the X-direction.
Furthermore, external-milling machines are known, in which the milling units—in addition to the displaceability in the Z-direction—were displaceable in a defined manner in the X-direction, and the chucks for the crankshaft were held in one or two spindle heads. Realisation of the C-axis on the workpiece meant that the external-milling cutter was guided on in a defined manner in the X-direction during the machining of eccentric surfaces. However, the machining of eccentric surfaces did not entail two or more external-milling units, operating independently of one another, being deployed on the same crankshaft. This was only possible when machining the eccentric surfaces, e.g. the centre-bearing journals.
In the case of the known milling machines, work is carried out with a conventional, negative cutting-edge geometry and cutting speeds on workpieces made of grey cast iron (GGG60-GGG80) of at most 160 m/min. As a result, very high cutting forces are introduced into the workpiece, for which reason it is also necessary as a rule to support the centre of the workpiece by means of steady rests, etc. A further drawback consisted in the fact that a high proportion of the process heat was introduced both into the workpiece, and thus also into the tool, and only a small proportion was dissipated via the chips.
SUMMARY OF THE INVENTION
a) Technical Object
It is therefore the object of the invention to provide a milling machine for machining both eccentric end faces and circumferential faces which, despite a simple design, ensures a short machining time.
b) Solution to the Object
This object is achieved by means of the characterizing features of claim
1
. Advantageous embodiments result from the subclaims.
Owing to the C-axis of the workpiece and the resultant possible defined, but relatively slow rotation of the workpiece of generally less than 60 revolutions/minute, frequently only 15-20 revolutions/minute, it is sufficient that the tool slide rests has to be able to move the tool, generally an external-milling cutter, in a defined manner, in addition to in the Z-direction, only also in the X-direction.
This rotation of the workpiece is so slow that any imbalances of the workpiece which may arise do not have a disadvantageous dynamic effect on the result of the machining.
c) Advantages
The short machining time is achieved due to the fact that, despite the rotation of the workpiece, e.g. of the crankshaft, two tool units can work, independently of one another, on eccentric surfaces whose rotational positions do not coincide, which effect is only possible by means of a machine control system which controls the independent tool slide rests as a function of the position and rotation of the workpiece, it preferably being possible to specify optimisation targets, such as for example the chip thickness or the cutting speed.
In this case, for a specific workpiece it is possible even before machining to calculate, for each instant of the machining, the rotational position, direction of movement and speed of the workpiece, the rotational speed of the milling cutters, the X-position and direction of movement and speed of movement of the milling cutters, etc., and to store these parameters in a working program, for example as a table of settings for various states of the machining, which program can then be executed by the machine control system.
d) Further Configurations
Another possibility consists in taking into account at the same time the current actual position and actual movement of the workpiece during the machining and, as a function of these, controlling the tool slide rests. However, this is considerably more complex in terms of the sensor technology and the control outlay.
Owing to the relatively low rotational speed of the workpiece, slip errors, that is to say deviations between the desired and the actual position, during the movement of the workpiece are relatively low.
In order also to achieve this on the tool side, for example when using a side-milling cutter, the diameter is designed to be larger than would be necessary for the penetration depth for milling the big-end journal of a crankshaft. This enlargement of the side-milling cutter results in a likewise relatively low rotational speed of the milling cutter, so that in addition the rotational speed of the tool can be constantly adjusted with slip errors which are only negligibly low.
For machining a passenger-car crankshaft with a throw of 10-15 cm, the diameter of a side-milling cutter used for this purpose is about 800 mm. This also results in thermal advantages, since a relatively long time is available for cooling between two successive deployments of one and the same cutting edge of the milling cutter.
If suitable cutting materials and cutting-edge geometry are used, cutting speeds of 800 m/min and even significantly more can be achieved, and in addition the machine does not need any cooling lubricant at the machining location, since dry milling is possible, in particular with a positive tool geometry.
Instead of a linear movement of the milling cutter in the X-direction, it is also possible to pivot the milling cutter about an axis parallel to the Z-axis, which is necessary in particular when using a slotting cutter, the axis of rotation of which is arranged perpendicular to the longitudinal axis of the crankshaft. The cutting edges on the front end face of a slotting cutter of this kind machine circumferential faces, that is to say, for example, the peripheral faces of the crankpin jo
Kiefer Herbert
Kohlhase Matthias
Santorius Rolf
Scharpf Paul Dieter
Schreiber Leo
Boehringer Werkzeugmaschinen GmbH
Briggs William
Norris McLaughlin & Marcus P.A.
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