Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2000-07-18
2004-02-03
Jordan, Charles T. (Department: 3644)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S888100, C029S558000, C409S132000
Reexamination Certificate
active
06684500
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German Application No. 19749939.2, filed Nov. 11, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention concerns a method of machining workpieces with rotationally symmetrical surfaces, for example unstable workpieces of a complicated shape, with rotationally symmetrical, even eccentric surfaces, and apparatus for such a machining procedure.
Machining is used in this specification broadly, embracing not just chip-cutting machining but also for example water jet cutting, laser cutting, laser hardening, heat treatment and so forth.
A typical representative of such a workpiece is a crankshaft used for reciprocating piston internal combustion engines, reciprocating piston compressors and so forth, or a camshaft for similar uses.
Machining of a crankshaft in the rough condition, that is to say cast or forged, consisting of steel or cast iron, is generally effected by known cutting machining procedures. Crankshafts are most frequently used in an internal combustion engine of a motor vehicle, and are generally produced in very large numbers. Therefore, in terms of selecting the machining method and the machine configuration, the method which has the expectation of the shortest possible machining time for each crankshaft is adopted.
In accordance with the known procedures, the central or main bearings of the crankshaft are machined by means of rotational broaching or turning-rotational broaching, for example as disclosed in German Patent DE 35 23 274 C2 or European Patent EP No 86 108 666, while the crank throw or big-end bearings and is possibly also the crank side cheek faces can be machined by means of external milling, in particular high-speed external milling, for example as disclosed in German Patent DE 196 26 627 A1, or by means of internal milling, also referred to as spinning cutting, or by means of rotary milling, for example as disclosed in German Patent DE 44 46 475.
As an alternative to external milling it, is also possible to use rotary milling. Under some circumstances the respective cutting machining operation takes place when the workpiece is in an already hardened condition. In that respect the terms just used are employed to denote the following:
Rotational Broaching:
Arranged at the periphery of a disk-shaped tool, spaced in the peripheral direction thereof, are rotational broaching cutting edges whose spacing increases relative to the center of the rotational disk-shaped tool. That disk-shaped tool rotates with its axis in parallel relationship beside the axis of the crankshaft and material is removed at the peripheral surface of the crankshaft by the rotational broaching cutting edges being pivoted along the periphery of the crankshaft which is rotating substantially faster (about 1000 rpm). If the rotational broaching cutting edges are all at the same spacing relative to the center of the tool, a feed must be implemented radially with respect to the crankshaft, in the X-direction, between the tool cutting edges. Those procedures can be distributed to a plurality of cutting edges or can be supplemented by sister tools.
Turning-rotational Broaching:
This involves the rotational broaching operation described above, wherein implemented prior thereto is a plunge-cut turning operation which is implemented by means of a cutting edge which is also arranged on the periphery of the disk-shaped tool. Plunge-cut turning is effected by a procedure whereby the disk-shaped tool does not rotate during engagement of the cutting edge, but is only moved radially forwardly towards the workpiece.
External Milling:
In this case also the cutting edges are disposed on the periphery of a disk-shaped tool which is drivable in rotation with an axis parallel to the axis of the workpiece. The cutting speed however results primarily from the rotary movement of the tool while the workpiece only rotates at about 10 rpm until an at least complete rotary movement of the tool has been completed about the rotationally symmetrical surface of the workpiece, which is to be machined.
Particularly when dealing with large oversizes, a number of passes of the tool around the workpiece surface are required, but even if a single pass seems adequate by virtue of the oversize involved, more than one complete rotary pass is often necessary because of the tangential inward and outward movement of the tool.
The disk-shaped tool is equipped with milling teeth over its entire periphery.
The spacing of the cutting edges in the peripheral direction relative to each other can possibly be less than in the case of rotational broaching or turning-rotational broaching, in regard. to which the intention is generally to conclude the machining operation with the one cutting edge before the next cutting edge comes into the condition of engagement into the workpiece.
Disk-shaped Tool:
This generally involves a circular disk. Theoretically however it is also possible to use non-circular disks, for example ellipses and so forth. Preferably however the disks only ever exhibit convexly outwardly curved peripheral contours and in that respect in particular do not have any hard or abrupt steps in the peripheral contour. If there are cavities in the peripheral contour, they are not equipped with cutting edges.
Rotary Milling:
In contrast to external milling, rotary milling is operated with a generally finger-shaped milling cutter whose axis of rotation is in orthogonal relationship with the axis of rotation of the workpiece to be machined. The peripheral surfaces are machined with the one or more end cutting edges of such a finger milling cutter, and the end faces of the workpiece are milled with the cutting edges arranged on the peripheral surface of the finger cutter.
High-speed Milling (Rotary Milling or External Milling):
This milling occurs at a cutting speed of, for example, in the case of steel: over 130 m/min, in particular over 180 m/min, in the case of cast iron: over 150 m/min, in particular over 200 m/min, and in the case of aluminum: over 300 m/min, in particular over 500 m/min. Such cutting speeds are promoted in particular by a positive cutting edge geometry and the appropriate cutting material choice.
This high cutting speed is advantageous because it minimises all the disadvantages of interrupted cutting, which are inherent in the milling system.
In the prior art, machining operations involving turning/rotational broaching/turning-rotational broaching on the one hand and machining by means of external milling or rotary milling, that is to say generally milling, on the other hand, were not used in combination as it was considered to be impractical by virtue of the completely different necessary ranges of rotary speed for the workpiece. While, in the case of turning/rotational broaching/turning-rotational broaching, the cutting speed was primarily attained on the basis of the speed of rotation of the workpiece which is about 1000 rpm for a private automobile crapkshaft, and the disk-shaped tool was pivoted in or rotated only at a speed of less than 30 rpm, the situation is approximately diametrally opposite in the case of external milling/rotary milling, in particular in the case of high-speed milling.
In a corresponding fashion the problems which occur in such machining procedures also arise in completely different areas:
In the case of turning/rotational broaching/turning-rotational broaching, it is not necessary to use the C-axis which involves monitoring the rotational position of the workpiece because of the high speed of rotation of the workpiece. Furthermore, co-ordinated tracking, of the tool in the X-direction is in any case not possible with that speed.
The main difficulties with the high speeds of rotation involved include the area of the clamping force, compensating for unbalance and so forth.
By contrast, with external milling/rotary milling, as inter alia the crank throw or big-end bearings are to be machined hereby, implementation of the C-axis is an absolute necessity. The problems lie
Kohlhase Matthias
Santorius Rolf
Boehringer Werkzeugmaschinen GmbH
Nguyen T.
LandOfFree
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