Method and machining tool for producing helically profiled workpieces

For producing hectically profiled workpieces (1) the helical profile (2) is first of all prefabricated by a milling treatment and is then finished by a grinding treatment of the profile surface. To achieve optimum machining qualities in an economic way, the grinding treatment is performed with a grinding tool (6, 12) adapted to the milling tool (3, 9) for the milling treatment in terms of shape, size, position of the axis of rotation and cutter arrangement.

FIELD OF THE INVENTION
 This invention relates to a method of producing hectically profiled
 workpieces, according to which first of all the helical profile is
 prefabricated by a milling treatment and is then finished by a grinding
 treatment of the profile surface, as well as to a machining tool for
 performing this method.
 DESCRIPTION OF THE PRIOR ART
 Hectically profiled workpieces substantially include worm gears, threaded
 spindles, worm conveyors, screws for producing plastic materials, pump and
 compressor rotors and the like, where the helical profile of these
 workpieces must be produced with high accuracy and perfect surface
 quality. By means of a milling treatment the helical profile can be
 prefabricated economically, but milling provides a profile surface of
 mostly insufficient quality, so that a subsequent grinding treatment is
 required.
 In various cases, grinding into the solid material, referred to as deep
 grinding, might provide for a fabrication of profiles without additional
 fine grinding, which deep grinding is, however, rather time-consuming and
 involves quite restricted machining depths. There is also produced
 grinding sludge which is difficult to dispose of, and due to the high
 thermal load hardening cracks may occur.
 For finishing the prefabricated helical profiles there is frequently
 performed a grinding treatment by means of belt grinding due to the low
 machining depth, for which purpose two different machine tools, namely a
 milling machine and a belt grinding machine, are required. But when the
 helical profile is provided with a wear-resistant layer, which due to its
 surface roughness must be regrouped, this reminding must be effected with
 a grinding disk, as the wear-resistant layer is too hard for belt
 grinding. Such grinding disk does, however, not forgive any feed-related
 deviations with respect to the milled surface, which in the case of
 reminding leads to the risk of a local straight-through grinding of the
 wear-resistant layer.
 It is therefore the object underlying the invention to provide a method as
 described above, which in an economic way ensures a fabrication of helical
 profiles of perfect surface quality. There should also be created a
 grinding tool optimally suited for performing this method.
 SUMMARY OF THE INVENTION
 This object is solved by the invention in that the grinding treatment is
 performed by means of a grinding tool adapted to the milling tool for the
 milling treatment in terms of shape, size, position of the axis of
 rotation and cutter arrangement. By means of this both simple and elegant
 measure the advantages of the milling treatment, such as great chip
 removal and fast machining operation as well as the lack of a problematic
 grinding sludge, can be optimally combined with the advantages of grinding
 by means of a hard grinding disk, such as achieving a very smooth surface
 with constant grinding depth, where due to the similarity of the tool
 design for the milling treatment on the one hand and the grinding
 treatment on the other hand identical machining conditions are obtained
 both for milling and for grinding, and the grinding treatment can exactly
 be adapted to the preceding milling treatment, which leads to optimum
 surface qualities.
 To be able to utilize fluidized-bed milling as the fastest of the machining
 operations for prefabricating profiles, the fabrication of profiles is
 effected by fluidized-bed milling and the finishing of profiles is
 effected by an adapted fluidized-bed grinding, so that the surface
 produced by the grinding operation is also exactly adapted to the surface
 produced by the milling operation. Such surface adaptation could not be
 achieved by means of a usual peripheral grinding operation, because the
 surface achieved by fluidized-bed grinding follows quite specific stock
 utilization rules, which can only be observed by a tool equipped with
 inwardly directed cutting edges.
 Since due to the similarity of milling tool and grinding tool the condition
 is satisfied that prefabrication and finishing of the helical profile must
 be performed in a similar way, the milling and grinding treatments can be
 performed in accordance with the invention during a uniform clamping of
 the workpiece in a machine tool, where it is basically possible to perform
 the milling and grinding treatments with tools fitted with cutting edges
 at their end faces, on their outer periphery or on their inner periphery.
 Known grinding tools have a main body rotatable about a tool axis, which on
 its periphery accommodates an annular grinding body. When there is
 provided a disk-shaped main body with a grinding body attached at the
 outer periphery, there can be provided a grinding tool adapted to a
 peripheral milling cutter. When the annular main body is equipped with the
 grinding body at its inner periphery, there is obtained a grinding tool
 comparable to a fluidized-bed tool which can be used for fluidized-bed
 grinding upon fluidized-bed milling. The cross-section of the grinding
 body will each be adapted to the cutting contour determined by the cutting
 edges of the fluidized-bed milling cutter, so as to ensure mutually
 adapted machining conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 To be able to economically produce a cylindrical or conical workpiece 1
 with a helical profile 2, the helical profile 2 is first of all
 prefabricated by a milling treatment and is then finished by a grinding
 treatment of the profile surface.
 As is illustrated in FIGS. 1 and 2, the milling treatment is effected by
 means of a peripheral milling cutter 3, which includes a disk-shaped main
 body 4 rotating about the axis A and having radially outwardly directed
 knives 5, where the tool axis A lies in a plane that is parallel to the
 workpiece axis W. For the subsequent finishing an external grinding tool 6
 is used, which is adapted to the peripheral milling cutter 3 in terms of
 shape, size, position of the axis of rotation and cutter arrangement and
 accordingly has a disk-shaped main body 7 which rotates about the tool
 axis A and includes an annular grinding body 8 seated at the outer
 periphery, where the cross-section of the grinding body 8 corresponds to
 the cutting contour of the knife 5.
 As is indicated in FIGS. 3 and 4, prefabricating the helical profile 2 may
 also be effected by means of a fluidized-bed milling cutter 9, which
 includes an annular main body 10 rotating about the tool axis A and having
 radially inwardly directed knives 11. The subsequent finishing is then
 correspondingly performed with a fluidized-bed grinding tool 12, which
 includes an annular main body 13 rotating about the tool axis A and a
 grinding body 14 disposed at the inner periphery, where the cross-section
 of the grinding body 14 in turn is adapted to the cutting contour of the
 knife 11.
 Since the milling and grinding tools are adapted to each other in terms of
 shape, size, position of the axis of rotation and cutter arrangement, the
 milling and grinding treatments for producing the helical profile can be
 performed on one and the same machine tool, where the machining conditions
 necessarily are the same, so that optimum machining qualities can be
 achieved.