METHOD FOR MANUFACTURING A ROTOR FOR A SCREW SPINDLE PUMP; MACHINING MACHINE FOR IT

Description

[0001] The invention relates to a method for producing a rotor for a screw pump, according to the preamble of claim 1. Furthermore, the invention relates to a machining machine for producing a rotor for a screw pump, according to the preamble of claim 12.

[0002] It is known to manufacture rotors for screw pumps by milling helical profiles into a workpiece. The final finishing of the helical profile, in particular, represents a time-consuming process step, as the final geometry is achieved through numerous complex milling processes.

[0003] EP 1 402 982 A1 discloses a time-consuming method which proposes rough machining by a milling tool and subsequent finishing by a plate-shaped cutting tool in order to introduce helical grooves into a component.

[0004] WO 2011 / 096274 A1 also describes a time-consuming method for producing a rotor for a screw pump, in which the workpiece is rotated about the longitudinal axis and a cutting tool is moved in a controlled manner to form the screw rotors.

[0005] The invention therefore addresses the problem of providing a method that eliminates the described disadvantages and enables simple and rapid production of a rotor for a screw pump. Furthermore, a device is to be provided that enables simple and rapid production of a rotor for a screw pump.

[0006] According to the invention, this problem is solved by a method having the features of patent claim 1 and a machining machine according to claim 12.

[0007] According to the invention, the rotor is manufactured by turning. This enables simple and rapid production of the helical profiling of the rotor. This is achieved in particular by fastening the provided, prefabricated workpiece, which is at least partially cylindrical, so as to be rotatable about its longitudinal axis, e.g. in a computer-controlled metal-cutting machine of a conventional type that is equipped with a suitable cutting tool for the manufacturing process. The workpiece is then rotated about its longitudinal axis in a defined manner while controlling the movement of the cutting tool, with the cutting tool being continuously moved in a machining direction parallel to the longitudinal axis of the workpiece during a cutting process. The current position of the cutting tool in the machining direction is a predetermined function of the current angle of rotation of the workpiece about its longitudinal axis.Such cutting processes are performed multiple times to create the helical profile. This creates the final rotor geometry, especially the helical profile.

[0008] For example, in each cutting operation, the current position of the cutting tool along the longitudinal axis is controlled proportionally to the angle of rotation. This results in a helical trajectory of the cutting tool relative to the workpiece. During each cutting operation, the cutting tool is therefore moved according to the invention at a constant radial distance from the longitudinal axis, i.e. the axis of rotation of the workpiece. From cutting operation to cutting operation, the diameter and position of the helical trajectory (in the longitudinal direction of the workpiece) can then be expediently varied in order to gradually develop the helical profile with an exact contour of the screw flanks. It is of key importance that the angle of rotation is precisely controlled during the rotational movement of the workpiece and assumes defined values ​​across the individual cutting operations.This is the only way to ensure that the helix trajectories traversed in the various cutting processes each have a defined position relative to one another. In this respect, the method according to the invention differs particularly from conventional turning methods, in which the workpiece is continuously rotated (e.g., at a constant speed) while the cutting tool is advanced in the axial and radial directions to create a desired contour. Such a conventional method does not enable the previously described precise contouring according to the invention in several successive cutting processes. Accordingly, conventional turning methods cannot achieve the precision required to produce the screw flanks of a screw spindle pump.

[0009] According to the invention, in particular, the angular position of the helical profile on the rotor shaft can be precisely defined. This allows multiple helical profiles to be provided on a monolithic workpiece, their angular positions being coordinated with one another. The precise specification of the angular positions of the helical profiles relative to one another ensures that two opposing helical profiles on a workpiece are aligned with the correct angle relative to one another with the utmost precision. This is an important prerequisite for the rotors of a twin-screw pump, for example, to mesh without collision.

[0010] The cut made by the cutting tool into the prefabricated workpiece during the cutting process enables particularly simple and rapid finishing of the rotor's helical profile. The rotation of the workpiece around its longitudinal axis provides the cutting movement, while the cutting tool performs a feed movement synchronized with the rotational movement as described above, thus forming the final geometry of the helical profile.

[0011] According to the invention, a rotatable milling tool, preferably with at least two cutting teeth, is provided prior to the provision of the cutting tool. The movement of the rotating milling tool relative to the workpiece is controlled so that a milling operation is performed by the milling tool, whereby the helical profiling is (initially roughly) prefabricated by milling into the workpiece. This prefabrication of the helical profiling allows material to be milled off the workpiece very quickly and effectively. The cutting tool is subsequently used according to the invention for the precise finishing of the helical profiling by turning.

[0012] An advantageous embodiment is that a turning tool is provided before the cutting tool or before the milling tool is provided, wherein the movement of the turning tool is controlled relative to the workpiece so that a turning cutting process is carried out by the turning tool, whereby cylindrical sections (including the rotor shaft) are prefabricated by turning the workpiece. An undercut is preferably introduced between the cylindrical sections in order to be able to better reach and machine the cylindrical sections later with the cutting tool. By prefabricating the cylindrical sections, material can be removed from the workpiece very quickly and effectively, so that the time until the final production of the helical profiling can be significantly reduced with the cutting tool according to the invention.

[0013] Another advantageous embodiment is that at the end of a cutting process, the cutting tool is initially moved back past the helical profiles along the longitudinal axis of the workpiece in a positioning process, counter to the machining direction. The cutting tool is then brought into engagement with the helical profiles again at an initial position predetermined in terms of the angle of rotation of the workpiece about the longitudinal axis, the radial distance from the longitudinal axis and the position in the machining direction. The next cutting process is then carried out from this initial position. The cutting process and the positioning process are expediently repeated several times. The trajectory of the cutting tool, i.e. the functional relationship between the angle of rotation of the workpiece about its longitudinal axis and the position of the cutting tool in the machining direction, remains unchanged in each case.However, the initial position of the cutting tool changes from cutting operation to cutting operation - at least in terms of the radial distance from the longitudinal axis and the position in the machining direction - in order to precisely produce the specified contour of the flanks of the helical profile.

[0014] A preferred embodiment of the method according to the invention provides that the cutting process and the positioning process are repeated until the helical profiling has achieved a shape that deviates from the final shape of the rotor due to an excess, wherein the workpiece is hardened in the excess shape and then the excess is cut away in further repeated cutting and positioning processes until the helical profiling has achieved the final shape of the rotor. The production of the rotor, in particular the helical profiling, from the workpiece can be carried out particularly easily if the workpiece is made of as yet unhardened material. This makes it very easy to achieve a shape that deviates from the final shape of the rotor due to an excess. During hardening, the workpiece can warp to a certain extent, which is taken into account by the excess.The oversize should be selected so that, after hardening the workpiece, the oversize can be removed in subsequent cutting and positioning processes until the final shape of the workpiece is achieved. It is advantageous to minimize the oversize, as the cutting processes into the hardened material lead to high stress and wear on the cutting tool and should therefore be reduced to a minimum.

[0015] According to the invention, the cut made by the cutting tool during the cutting process has a cutting direction that runs perpendicular to the machining direction. This design provides simple kinematics, allowing the helical profile to be produced particularly easily.

[0016] Another advantageous feature is that the cutting tool plunges into a prefabricated profile during the cutting process. Plunging the cutting tool into a prefabricated profile (e.g., roughly by milling) enables efficient production of the final geometry of the helical profile, particularly in the area of ​​the profile flanks. The threads of the screw spindles, i.e., the delivery chambers of the corresponding screw spindle pump, are therefore not completely manufactured by turning. The turning process according to the invention is used only to create the precise flank contour.

[0017] By means of the method according to the invention, the workpiece, i.e. the rotor, can be formed with at least one section with helical profiling (screw package) and with essentially cylindrical shaft sections. The cylindrical shaft sections serve to mount the rotor in the housing of a screw spindle pump and for connection to a drive, as is usual with screw spindle pumps known from the prior art. Advantageously, the rotor can be formed with at least two sections with helical profiling, wherein the helical profilings are oppositely directed. This corresponds to the design in twin-screw spindle pumps, in which the screws of two rotors mesh with each other and thus form delivery chambers between them, which deliver a fluid from two external suction chambers into an internal pressure chamber. It is particularly advantageous that the sections with helical profiling, i.e.the screw packages can be formed integrally, ie monolithically, with the shaft sections by the method according to the invention.

[0018] Furthermore, the invention relates to a machining center for producing a rotor for a screw pump, comprising a computer-aided numerical control. This can be, for example, a commercially available 5-axis automatic machine. According to the invention, the machining center is configured to carry out the method described above by programming the computer-aided numerical control with control data. The control data determine the rotational movement of the workpiece about the longitudinal axis in accordance with rotation angles, as well as the movement of the cutting tool in the machining direction parallel to the longitudinal axis of the workpiece, in such a way that the control data for a sequence of cutting processes comprise assignments of current positions of the cutting tool in the machining direction to rotation angles of the workpiece about the longitudinal axis.This simply means that, in other words, the axis of rotation during the turning process is an axis of the processing machine controlled by the computer-aided numerical control, so that the trajectory of the cutting tool during the turning process is defined in relation to the circumferential direction of the workpiece. Accordingly, by turning, the rotor with a helical profile is manufactured as a non-rotationally symmetrical workpiece with the highest precision. The control data further expediently includes initial position data, which define the initial angle of rotation of the workpiece around the longitudinal axis, the radial distance of the cutting tool from the longitudinal axis, and the initial position of the cutting tool in the machining direction for the sequence of cutting processes.Based on this control data, the helical profiling can be machined in several cutting processes, whereby the same rotary movement around the longitudinal axis of the workpiece and the synchronous movement of the cutting tool are always carried out, whereby only the distance from the rotary axis, i.e. the radius of the generated helix, and the position of the helix in the machining direction are varied from cutting process to cutting process in order to obtain the desired flank contour of the screw profiling.

[0019] Further features, details, and advantages of the invention will become apparent from the following description and the drawings. Embodiments of the invention are illustrated purely schematically in the following drawings and are described in more detail below. Corresponding objects or elements are provided with the same reference numerals in all figures. They show: Figure 1 schematic representation of a workpiece for a rotor; Figure 2 schematic detailed view of a workpiece for a rotor.

[0020] In Figure 1 Denoted by the reference numeral 1, a workpiece 1 for a rotor of a screw pump produced according to the invention is shown schematically. The representation according to Figure 1 shows a workpiece 1 from which a rotor for a screw pump is being manufactured. The rotor's production is already at an advanced stage, so that two helical profiles can be seen, from the beginning 10 to the end 11 and from the beginning 12 to the end 13, cut out of two cylindrical sections. These cylindrical sections have a larger diameter than the rotor shaft 14 or the hub 9. A relief groove 2 is located between the cylindrical sections.

[0021] The Figure 1 and 2The cutting tool 5 shown engages with the flank 6 of the helical profile 12, 13 and machines it to produce the final geometry. For the cutting process shown here, the workpiece 1 is rotated about its longitudinal axis Z1, wherein the movement of the cutting tool 5 parallel to the longitudinal axis Z1 is synchronized with the rotational movement of the workpiece 1 about the longitudinal axis Z1, as described above. As a result, the cutting tool 5 shown can produce the helical profile 12, 13, in particular the complex geometry of the helical flanks, precisely and quickly by cuts into the workpiece 1. Because the current position of the cutting tool 5 in the machining direction z2 is a predetermined function of the current angle of rotation of the workpiece 1 about the longitudinal axis Z1, among other things, the angular position of the helical profile 12, 13 on the shaft 14 can be determined.This allows the two counter-rotating helical profiles 10, 11, 12, 13 to be aligned at the correct angle to one another, and they can mesh collision-free with another rotor of a twin-screw pump. During the cutting process, the cutting tool 5 moves in the machining direction z2 shown along the longitudinal axis Z1 of the workpiece. During a cutting process, the radial distance of the cutting tool 5 to the longitudinal axis Z1 of the workpiece 1 is kept constant, so that no infeed occurs in the machining direction x2 shown. The position of the cutting tool 5 in the machining direction y2 is also not changed during a cutting process. In the diagram shown in . Figure 1In the position shown, the cutting tool 5 is almost at the end of a cutting process. After it came into engagement with the helical profiling at the beginning 12 of the profiling, it has been displaced parallel to the longitudinal axis Z1 of the workpiece 1 in the machining direction z2 during the cutting process. At the end 13 of the profiling, the cutting process shown here ends and the cutting tool 5 is retracted in a positioning process from the longitudinal axis Z1 of the workpiece 1 against the machining direction x2. This allows the tool to be moved against the machining direction z2 along the longitudinal axis Z1 of the workpiece 1 past the already visible helical profiling 12, 13.Having reached the start 12 of the helical profiling, the cutting tool 5 is moved in the positioning process in the machining direction x2 to the longitudinal axis Z1 of the workpiece 1 until the cutting tool 5 engages with the helical profiling 12 again at a predetermined starting position for a new cutting process in order to carry out a new cutting process from the beginning. The individually predetermined starting position for each cutting process is planned for the individual cutting processes depending on the desired contour of the helical profiling 12, 13 and is achieved by infeeds in the machining direction x2 and in the machining direction z2. In addition, the angular position, i.e. the angle of rotation of the workpiece 1, is set in the starting position so that the desired contour is precisely produced in a number of cutting processes.This means that the continuous rotary movement of the workpiece 1 is interrupted after each cutting process and the workpiece 1 is adjusted to the respective new starting position in terms of the angle of rotation in or against the direction of rotation previously used during the cutting process, before the workpiece 1 is again rotated about its longitudinal axis during the next cutting process. As a rule, no infeed takes place in the machining direction y2 and the tool 5 moves in a plane through which the longitudinal axis Z1 of the workpiece 1 also passes. The cut made by the cutting tool 5 in the cutting process has a cutting direction opposite to the drawn machining direction y2, which runs perpendicular to the drawn machining direction z2. As in . Figure 1 As can be seen, the cutting tool 5 plunges into the roughly prefabricated profile 12, 13 (e.g. by milling) during the cutting process.

[0022] It is particularly advantageous to initially machine the contour of the helical profile 12, 13 with an oversize. The rotor with the oversize contour is then hardened, and only then is the final contour of the helical profile 12, 13 machined by removing the oversize. It is advisable to keep the oversize as small as possible, since cutting into the hardened material of the helical profile 12, 13 leads to high stress and wear on the cutting tool 5.

[0023] In Figure 1On the left half of workpiece 1, a counter-rotating helical profile from the beginning 10 to the end 11 is also shown in its final geometry. The helical profiles 10, 11 are also created here by cuts of the cutting tool 5, with the individual cutting processes being carried out from the beginning 10 of the helical profile A to the end 11 of the helical profile 11. The undercut 2 between the helical profiles facilitates the view of the cutting tool 5 and the machining of the profiles by the cutting tool 5.The inventive synchronization of the rotational movement of the workpiece 1 with the movement of the cutting tool 5 in the direction z2, namely over the successive different cutting processes, ensures the precise adjustment of the angular position of the course of the helical profiling 10, 11, so that it is formed at the correct angle to the opposite helical profiling 12, 13 on the same workpiece 1.

[0024] The Figure 2 shows a schematic detailed view of the Figure 1illustrated machining situation. Here it can be seen more clearly that the cutting tool 5 has a cutting edge 7, which is preferably a ceramic cutting edge. This cutting edge 7 has a cutting tooth 8 which engages with the flank 6 at the end 13 of the profiling B. Because only a relatively small cutting tooth 8 engages in a single cutting process, a particularly precise contour of the helical profiling can be achieved by repeating cutting and positioning processes. It can also be clearly seen that the helical profiling is formed from thread grooves 3 and thread lands 4. The thread lands 4 have the diameter of the cylindrical sections from which they are formed. The thread grooves 3 have a smaller diameter, which extends to the inner diameter of the hub 9. List of reference symbols

[0025] 1 Workpiece 2 Undercut 3 Thread groove (helical profiling) 4 Thread land (helical profiling) 5 Cutting tool 6 Flanks (helical profiling) 7 Cutting edge 8 Cutting tooth 9 Inner diameter (hub) 10 Start of profiling A 11 End of profiling A 12 Start of profiling B 13 End of profiling B 14 Shaft Z1 Longitudinal axis (workpiece) x2 Machining direction, feed direction (tool) y2 Machining direction opposite to the cutting direction (tool) z2 Machining direction (tool)

Claims

1. Method for manufacturing a rotor for a screw spindle pump with following steps: a) Provision of a prefabricated, at least in sections cylindrical workpiece (1) with a longitudinal axis (Z1) and rotatable fastening of the workpiece (1) about this longitudinal axis (Z1), b) Provision of a rotatable milling tool, c) Motion control of the rotating milling tool relative to the workpiece (1), d) Execution of milling operations by the milling tool and prefabrication of the helical profiling (3, 4) by milling into the workpiece, e) Providing a cutting tool (5), characterized by following steps: f) Rotation of the workpiece (1) about the longitudinal axis (Z1) and movement control of the cutting tool (5), wherein the cutting tool (5) is moved in a machining direction (z2) parallel to the longitudinal axis (Z1) of the workpiece (1), wherein the instantaneous position of the cutting tool (5) in the machining direction (z2) is a predetermined function of the instantaneous angle of rotation of the workpiece (1) about the longitudinal axis (Z1), wherein the cut made by the cutting tool (5) during the cutting process has a cutting direction which is perpendicular to the machining direction (z2), g) multiple execution of cutting operations according to step f) for producing a helical profiling (3, 4) by cutting into the prefabricated workpiece (1), wherein the cutting tool (5) is moved at a constant radial distance from the longitudinal axis (Z1) of the workpiece (1) in each cutting operation, wherein the cutting tool (5) is moved continuously in a cutting operation in the machining direction (z2) parallel to the longitudinal axis (Z1) of the workpiece (1).

2. Method according to claim 1, characterized in that the instantaneous position of the cutting tool (5) along the longitudinal axis (Z1) is controlled proportionally to the angle of rotation.

3. Method according to claim 1 or 2, characterized in that following steps are carried out before the cutting tool is provided (method step e) ) or before the milling tool is provided (method step b) ): h) Provide a lathe tool, i) Movement control of the lathe tool relative to the workpiece (1), j) Performing of turning cut operation by the lathe tool and prefabrication of cylindrical sections by turning off the workpiece (1).

4. Method according to any one of the preceding claims, characterized in that the cutting tool (5) is moved back past the helical profiles (3, 4) at the end of a cutting operation in a positioning operation counter to the machining direction (z2) along the longitudinal axis (Z1) of the workpiece (1).

5. Method according to claim 4, characterized in that the cutting tool (5) is brought into engagement with the helical profiling (3, 4) in the positioning process at an initial position predetermined with respect to the angle of rotation of the workpiece about the longitudinal axis (Z1), with respect to the radial distance from the longitudinal axis (Z1) and with respect to the position in the machining direction (z2), in order to carry out a next cutting process.

6. Method according to claim 5, characterized in that the cutting operation and the positioning operation are repeated, wherein the initial position of the cutting tool (5) is varied from repetition to repetition at least with regard to the radial distance from the longitudinal axis (Z1) and with regard to the position in the machining direction (z2), in order in this way to produce a predetermined contour of the flanks of the helical profiling (3, 4).

7. Method according to any one of claims 4 to 6, characterized in that the cutting operation and the positioning operation are repeated until the helical profiling (3, 4) has reached a shape deviating from the final shape of the workpiece (1) by an oversize, wherein the workpiece (1) is hardened in the shape having the oversize and the oversize subsequently being cut away in further repeated cutting and positioning operations until the helical profiling (3, 4) has reached the final shape of the workpiece (1).

8. Method according to any one of claims 1 to 7, characterized in that the cutting tool (5) dips into a prefabricated profiling (3, 4) during the cutting process.

9. Method according to any one of claims 1 to 8, characterized in that the workpiece (1) is formed with at least one section with helical profiling (3, 4) and with substantially cylindrical shaft sections.

10. Method according to claim 9, characterized in that the workpiece (1) is formed with at least two sections with helical profiling (3, 4), wherein the helical profilings are in opposite directions.

11. Method according to claim 9 or 10, characterized in that the sections with helical profiling (3, 4) and the shaft sections are formed in one piece with each other.

12. Cutting processing machine for manufacturing a rotor for a screw spindle pump, having a computer-aided numerical control, characterized in that the machine tool is set up by programming the computer-aided numerical control with control data for carrying out the method according to any one of claims 1 to 11 in such a way that the control data determine the rotary movement of the workpiece (1) about the longitudinal axis (Z1) in accordance with angles of rotation, and the movement of the cutting tool (5) in the machining direction (z2) parallel to the longitudinal axis (Z1) of the workpiece (1), in such a way that the control data for a sequence of cutting operations comprise assignments of instantaneous positions of the cutting tool (5) in the machining direction (z2) to angles of rotation of the workpiece (1) about the longitudinal axis (Z1), wherein the cutting tool (5) is moved at a constant radial distance from the longitudinal axis (Z1) of the workpiece (1) during each cutting operation, wherein the cutting tool (5) is moved continuously in a cutting operation in the machining direction (z2) parallel to the longitudinal axis (Z1) of the workpiece (1).

13. Processing machine according to claim 12, characterized in that the control data further comprise initial position data which, for the sequence of cutting operations, in each case define the initial angle of rotation of the workpiece about the longitudinal axis (Z1), the radial distance of the cutting tool (5) from the longitudinal axis (Z1) and the initial position of the cutting tool (5) in the processing direction (z2).