Metal working – Plural diverse manufacturing apparatus including means for... – Type of machine
Reexamination Certificate
1997-12-02
2002-04-23
Briggs, William (Department: 3722)
Metal working
Plural diverse manufacturing apparatus including means for...
Type of machine
C029S006010, C029S888080, C082S106000, C409S132000, C409S190000
Reexamination Certificate
active
06374472
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for the metal-cutting machining of cylindrical shapes, in particular of eccentrically mounted cylindrical shapes on a workpiece rotatable about its longitudinal axis, in particular of crank pins by means of a rotatably drivable tool wherein a finished shape is produced such that it either because of sufficiently good surface finish has the final dimensions or that it is oversize for carrying out a finish machining such as grinding or polishing, as well as to an apparatus for carrying out the method and the cutting insert formed therefor.
BACKGROUND OF THE INVENTION
According to the known method crankshaft pins are machined by lathing or rotary lathing with the crankshaft eccentrically mounted so as to produce a purely rotary movement about the crankpin axis. With this mounting, machining of the cheeks is also possible but this type of machining has shown itself to be trouble-prone, in particular the chucks for eccentric mounting of the crankshaft are expensive. In addition the machining by lathing with a tool is done such that in a single operation a finished shape is produced that only needs in the region of the pin a finish machining by grinding. With this machining a different tool must be used for each different crank.
According to the method of the prior art, tool carriers are used with several cutting-insert types used on the tool carrier. By means of this tool carrier the cheeks and undercuts to both sides of the shape and the entire length of the pin are finished in one cutting operation. Thus a tool carrier is needed for each finished shape. According to a special goal of the method in a first step the cheeks are machined and in a second machining step the pins are machined to produce the pin diameter and the undercuts.
According to a second known method the crankshaft is clamped and machined with an inside miller that is moved in an orbit about the crank pin. Disadvantages of this machining are large movements and large moved masses so that high-speed machining is not possible.
A milling head for producing a bearing shape on a crank shaft in one step is known from German 3,824,348. The suggested milling head of the disk or collar type for machining crankshafts which have as surfaces to be machined by milling a cylindrical surface extending parallel to the milling-head axis and preferably merging via a rotation-symmetrical groove into a surface nearly perpendicular to the axis, with on the outside or inside cutter periphery of the milling head sets of indexable cutting plates secured in holders, is so constructed that several sets of index-able cutting plates are arranged uniformly around the cutter periphery of the milling head, that each set of indexable cutting plates fully covers the central shape of the surface of the work-piece to be machined and that at least one indexable cutting plate is provided inside one set of indexable cutting plates for each surface to be individually machined, and is so fitted with special indexable cutting plates that all the surfaces can be simultaneously machined.
An indexable cutting plate which has a polygonal flat body with at least one main cutting edge, a cutting edge, and a free face, is known from German 4,400,570.
Also known is so-called high-speed milling, that is a metal-cutting machine with a miller (outside miller) that works
a) with a high cutting speed of more than 160 m/min,
b) with a thin chip thickness in the region of 0.15 mm, preferably in the region of 0.05 mm to 0.1 mm, and
c) with a reduced cutting-arc length.
The term cutting-art length refers to the length of the tool carrier engaged with the corresponding cutting insert relative to its overall circumference.
High-speed milling produces such a good surface quality that pretreating or additional treatments before heat treatment as a separate step can be completely eliminated. In addition this type of milling, although ideal because of its shortened machining time and better surface quality, is not used to date with the machining of cylindrical shapes, in particular crankshafts because with the known tools
a) as a result of the considerable chip thickness and the relatively small engaging cutters at any time because of the very varied force distribution, considerable vibration is produced,
b) the use of indexable cutting plates with negative cutting angle leads to high machining temperatures, and
c) the high machining speed produces such rapid tool wear that tight tolerances along the pin cannot be guaranteed, so that as a result the indexable cutting plates must be changed often which effectively negates the advantages of high-speed milling.
OBJECT OF THE INVENTION
Starting with the state of the art it is an object of the invention to improve the metal-cutting machining of cylindrical shapes, in particular crankshaft pins, so that while keeping or improving the surface quality and while keeping or improving the dimensional accuracy one achieves a reduction in the machining time so that at the same time the overall efficiency is increased.
SUMMARY OF THE INVENTION
This object is achieved according to the invention by a method of metal-cutting machining of a cylindrical shape in a workpiece that comprises the steps of:
continuously rotating a workpiece about a workpiece axis;
continuously rotating about a tool axis offset from the workpiece axis a tool having a periphery provided with a plurality of cutting inserts; and
bringing the inserts into radial engagement with the workpiece while orienting at least one part of each cutting insert as it contacts the workpiece relative to at an effective cutting angle between −5° and +15° or a positive axial angle.
The inventive method is a machining system which is particularly suitable for the metal-cutting machining of eccentrically mounted cylindrical shapes, in particular crankshaft pins, with a centrally mounted workpiece. Thus both the difficult-to-finish pins as well as the main journals can be finished on the same apparatus or with serial or parallel arrangement of several apparatuses on the same apparatuses.
The production of the finished shape that has the desired finished dimension or is slightly oversize so that it can be reduced by grinding or polishing by means of tools that are equipped with adjacent cutting inserts or that are simultaneously engaged with the workpiece is called cut distribution. This covers for example the separation of the machining of the cheeks of a crankshaft and the machining of the undercuts and the pins of a crankshaft or the production of half a crankshaft-cheek shape with an undercut and a diameter part with a first tool and the production of a second undercut and the remaining diameter part with a second tool. By such a separation or machining with separate tools it is possible to vary the pin length within certain limits, that is even produce pins of different length with a right and a left tool and/or to correct changes in the pin length as a result of tool wear by adjustment with an NC controller.
The machining is carried out in that each tool is driven with constant or variable high speed so that high-speed machining is used. Preferably the variable speed is changed linearly in steps. As a result the advantages of high-speed milling can be achieved even when machining a crankshaft, namely increasing the surface quality, increasing the dimensional accuracy, and reduction of the machining time. For the use of high-speed milling it was necessary to overcome different disadvantages and problems. Thus the use of the already known cutting inserts in existing tools in known apparatus was not possible as they resulted in excessive forces and too much warming for the tools. With flexible crank shafts there is in some cases a great tendency to vibrate. This can be countered in that at least two millers are used. By such division several advantages are obtained. While the use of a single tool creates axial and radial forces which produce forces which can result in considerable vibration, the division can be set such th
Gesell Reinhold
Heinloth Markus
Ramold Klaus
Stallwitz Erwin
Briggs William
Dubno Herbert
Widia GmbH
Wilford Andrew
LandOfFree
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