WO2009149812A1

WO2009149812A1 - Rotary milling with special start-up strategy

Info

Publication number: WO2009149812A1
Application number: PCT/EP2009/003551
Authority: WO
Inventors: Bernd Faigle; Helmut Glocar
Original assignee: Gebr. Heller Maschinenfabrik Gmbh
Priority date: 2008-06-12
Filing date: 2009-05-19
Publication date: 2009-12-17
Also published as: DE102008027941B4; DE102008027941A1

Abstract

During a starting cut, i.e. at the start of the rotary milling operation, the process according to the invention for the rotary milling of round portions of workpieces uses a special plunging strategy. The movement takes place neither purely tangentially (radially in relation to the rotary milling tool) nor purely axially (radially in relation to the workpiece). Instead, a combination is chosen, between a radial and axial advancing movement (as viewed from the tool) and a tangential and radial advancing movement (as viewed from the workpiece). This produces a plunging path (12) which is inclined at an angle α of a few degrees with respect to the tangent to the workpiece surface. Advantageous conditions are obtained when the workpiece is first contacted shortly after the cutting edge corner in the region of the external diameter of the tool or in the radius runout of the cutting edge. The process yields a long tool life together with high processing quality and precision.

Description

Turning milling with special approach strategy

The invention relates to a method for the rotary milling of round sections of workpieces, such as in particular crank pins and / or journals of crankshafts or non-circular round workpiece sections, such as cams of camshafts or other in Drehfräsverfahren accessible surfaces. The invention also relates to a machine tool, e.g. is set up by suitable control software or other measures for carrying out the method.

In principle, it is known to machine round workpiece surfaces, such as main bearing surfaces or crank pins of crankshafts, in the rotary milling process. For example, AT 286067 C deals with such a milling method. To carry out the method, a shell end mill which has both end cutting edges and peripheral cutting edges is used. The axis of rotation of the shell end mill is set with a defined eccentricity radially to the axis of rotation of the workpiece. The rotary milling process is used both for pre-cutting and for finish-cutting. When pre-cutting the eccentricity is set differently than when finishing cutting. This ensures that the pre-cutting is carried out mainly with the peripheral cutting edges, while the end cutting edges are used for finishing.

From DE 10 2006 024 715 Al a method is also available for machining bearing seats of main and lifting Storage of crankshafts, which is designed as Drehfräsverfahren and includes both a pre-cut Drehfrässchritt and a finish cut Drehfrässchnitt. The rotary milling process described there works with an axial offset between the axis of rotation of the workpiece and the axis of rotation of the tool. This misalignment is called eccentricity. It is constant, including the phase of dipping and extending the tool. During the rotary milling, no feed movement takes place transversely to a longitudinal axis of the end mill.

This concept of radial (with respect to the workpiece) radial immersion of the tool causes a relatively sudden start of the machining process, which can lead to problems.

A much gentler start of the machining process allows the rotary milling process according to WO 97/32680. Here, the rotary milling tool is brought on a tangential path without axial feed movement to the workpiece. The rotary milling tool first comes with its Eckschneidkante with the workpiece in engagement. The bleed is soft. However, the tool wear for the trimming operation is concentrated on the corner cutting edge. The corner cutting edge makes a very small cutting edge area whose length is only 0.05 to 0.25 mm. This results in a very high local wear. In addition, the cutting speed at the corner cutting edge is maximum, resulting in a high cutting wear. The wear can gradually continue into this front cutting edge, which can lead to significant quality problems and service life problems. On this basis, it is an object of the invention to specify how to produce workpieces in high quality and with high tool life in the rotary milling.

This object is achieved by the method according to claim 1 and by means of a corresponding machine tool or control software:

The method according to the invention provides, in particular, a service life or stand-up-optimal starting strategy. It takes into account the retraction of the tool into the workpiece and the wear behavior of the tool. The method is particularly advantageous in the machining of hardened workpieces. It is suitable for labile workpieces, such as Crankshafts, and proves to be particularly stable process.

The method according to the invention introduces a combination of tangential and axial start-up or plunge strategy for the beginning of the cutting process and combines the advantages of axial and radial immersion while eliminating the specific disadvantages. Unlike in the case of axial immersion, the method according to the invention begins with relatively short engagement lengths, ie relatively short end cutting edge sections. However, unlike the radial approach, corner cutting edge wear is minimized. The superposition of axial and radial plunge motion resulting from the continuous reduction in eccentricity during the plunge operation provides a plunge angle α which may be set to, for example, 3 °. A very advantageous constellation is given when the first workpiece contact in the vicinity of the cutting edge or takes place in the outlet of the cutting radius. Over the Einfahrweg a maximum distribution of the Abtragvolumens is achieved over the front cutting edge. Alternatively, it is possible to intentionally concentrate the removal volume in the immersion lawn on certain cutting edge areas in order to have a wear stock for the subsequent round milling in order to obtain an increased economy of the tools.

The erf indungsgemaße method allows the achievement of very high roundness accuracies on labile workpieces, such as crankshafts. The transition from immersion in the round milling is very soft. This is especially true if the immersion process over a workpiece rotation angle from 5 °, preferably of large 15 °. The feed vector during the immersion turf approaches the feed vector in the case of round milling, which, similar to the tangential immersion turf, results in significantly improved roundness accuracies. However, the high corner cutting edge wear of tangential immersion is not accepted. The closer the angular position and the amount of the immersion feed vector to the rotary feed vector are, the lower is the loss of accuracy in the transition from the immersion turf to the round tapping. Moreover, it is possible to smooth this transition, d. H . smoothly.

The erfmdungsgemaße immersion protects the corner cutting edge and prevents in particular a proceeding from the corner cutting edge in the end cutting edge progressing excessive wear. Thus, the erf indungsgemaße method provides in particular because of the distribution of wear during the immersion turf on larger parts of the end cutting edge increased stall quantity and ultimately for a lot of number of workpieces improved accuracy. The corner cutting edge can remain disengaged when immersed. This applies to immersion angle α between 0, 1 ° and 10 °. The best dip angle α depends on the plant

- A - Stuck diameter, the allowance, the tool diameter, the cutting edge rounding, the eccentricity oa

The constant changing of the eccentricity is not only advantageous for immersion turf but also makes sense at the end of the round milling process. The extension and retraction of the tool is advantageously carried out with continuous variable eccentricity.

Advantageously, the workpiece rotation angle during retraction (immersion movement) can be more than 15 °. The result is a bleed feed vector that is similar to the round feed vector. It is thereby avoided otherwise resulting in radial immersion point of discontinuity in the transition from immersion in the round. This reduces the control engineering influences of the feed axes involved, which otherwise influence the workpiece stuck accuracy.

In the invention, an improved distribution of the cutting volume over the end cutting edge of the tool is achieved.

The inventive method is particularly suitable for use on solid carbide fibers. It can also be used in processes where the round tilling is done with very little eccentricity. For example, to edit a crank pin in one operation on the entire pin width. The tool cutting edge extends from the outer cutting edge to the center of rotation to enable this.

It is advantageous during the dipping movement to change the tool speed and / or the workpiece speed. For example, the tool speed may be lower at the beginning of the immersion turf and continuously increased to round nose speed until the end of the dipping motion. This relieves the radially outer end cutting edge portion of the tool. Alternatively, you can At very unstable workpieces a damped intervention at the beginning of the immersion movement can be achieved by the fact that the cutting speed at the beginning of the immersion process is selected to be higher.

A similar dampening effect is achieved by selecting the workpiece stoke speed lower at the beginning of the dip and increasing it to the round mill workpiece speed during the dip.

The insertion angle α is preferably selected such that the first workpiece contact takes place in the immediate vicinity of the cutting edges in the region of the tool outer diameter or in the outlet of the cutting radius. In the case of concave cutting edge formation, as used, for example, for spherical bearing seats, the insertion angle α can be correspondingly adjusted in order to advantageously place the first workpiece contact on the front cutting edge of the tool.

A special form of crankshaft machining is the processing of Olbundflachen. The inventive method can be used so that one or both Olbundflachen be processed over one or more Werkstuckumdrehungen with the immersion movement and simultaneously rotating workpiece. In the sequential processing of Olbundflachen can be selected as Frasverfahren a synchronous milling, which is preferred in labile workpieces. Alternatively, the reverse milling can be selected.

The method according to the invention can be used both for the preliminary cut (radial allowance approx. 0.15 mm) and for the finish cut (radial allowance approx. 0.1 mm) for finishing machining (finishing) of crankshafts. The round milling is carried out after performing the dipping process preferably over a workpiece rotation angle of at least 360 °. The Rundfrasen can over a or several revolutions. Preferably, it is limited to a few, for example two revolutions.

The direction of rotation of the workpiece can be chosen so that the eccentricity at the beginning of the immersion process is positive or negative. Preferably, it is positive, i. the axis of rotation of the workpiece is offset in the direction of rotation of the tool against the axis of rotation of the workpiece.

The method according to the invention can also be used in particular where different hard areas are to be removed on a workpiece, for example on hardened crankshaft bearing seats. There, typical hard-soft transitions with different cutting conditions are present at the edge of the bearing seat. The insertion angle α can be selected here in such a way that the wear in the outer diameter range and the wear in the front edge area are adjusted.

The inventive method is suitable for both crankshaft bearing seats or crank pin with undercut as well as without undercut. If there is no undercut, particularly small corner radii are provided at the corner cutting edges of the tool. By protecting the corner cutting edge, the inventive Frasverfahren is particularly suitable for such application trap.

Although a very high quality of the workpieces is achieved with the method according to the invention, changes in the range of oil passage bores, for example, generally change over the lower removal forces. These cause flaws in the machined cylindrical surface on labile workpieces. For this purpose, angle-dependent shape corrections can be provided empirically, which under certain circumstances can also be used depending on the tool life. Such form errors can also be detected in the process or as a post-process measurement and corrected accordingly. The inventive method is applicable in connection with indexable cutters Bestuckten milling. Preferably, however, a carbide is provided head. The use of mounted CBN cutting edges is possible. The usual cutting speeds for high-speed milling can be used. Preferably, the cutter has a plurality of cutting edges. The same tool can be used for the precut and the finish cut. For example, the preliminary cutting operations and then the finish cutting operations with high-precision tools can first be carried out on all cylinder surfaces of a crankshaft to be machined. Different cutting parameters can be used for the pre-cut and the finished cut. To reduce the variety of tools, all pre-cutting operations with the same tool diameter can be performed. An internal tool cooling can be provided.

Further details of advantageous embodiments of the invention will become apparent from the following description, the drawings or claims. The invention will be described in the description with reference to a method according to the invention. However, the invention equally extends to an apparatus for implementing the method, i. on appropriate machine tools in which the method is implemented, as well as software that realizes the process. Show it:

Fig. 1 is a crankshaft during rotary cutting in a schematic overall view.

Fig. 2, the crankshaft in the rotary cutting, in a sectional view in a schematic and highly simplified representation.

Fig. 3, the crankshaft and the rotary cutting tool just before the start of a dipping or bleeding process, in a highly schematic representation. Fig. 4 shows a detail of Figure 3, in an enlarged view.

Fig. 5 the gate operation, in a schematic representation.

6 shows a detail from FIG. 5.

Fig. 7 shows the end of the bleed or dipping process, in a highly schematic representation.

8 shows a detail from FIG. 7.

Fig. 9 engagement surfaces on a crank pin, in various stages of the immersion process.

10 to 12 an alternative possibility for performing the immersion process, in a schematic representation.

FIG. 1 illustrates a rotary milling process with a tool 1 on a main bearing surface 2 of a crankshaft 3. The lathe tool 1 is preferably a solid carbide tool which has at least one end cutting edge 4. Preferably, it may have a plurality of end cutting edges, each extending from the radially outer end to the center, which is located at a tool axis of rotation 5. The rotary cutting tool 1 may also have one or more peripheral cutting edges 6, which meets with the front cutting edge 4 at a cutting corner 7. The cutting corner 7 can have a very small corner radius, for example in the range of a few tenths of a millimeter.

The machining of the crankshaft 2 takes place when the rotary cutting tool 1 rotates under a right-angled relationship between the tool rotation axis 5 and the workpiece rotation axis 8, which here is the axis of symmetry of the main bearing surface 2.

As FIG. 2 shows, however, the tool rotation axis 5 and the workpiece rotation axis do not necessarily intersect. An eccentricity 9 can be provided, which is to be measured as the distance between the tool rotation axis 5 and the workpiece rotation axis 8. The eccentricity 9 is illustrated in Figures 2 and 3 and 5 and 7. To carry out the Runddrehfrasvorgang the eccentricity 9 is usually close to zero to keep the rotary cutting tool 1 with its entire diameter with the main bearing surface 2 in engagement. The eccentricity 9 is kept constant in the Runddrehfrasvorgang. Likewise, the axial distance between the end cutting edge 4 and the Werkstuckdrehachse 8 does not change normally. An angle-dependent change of the distance is however possible for the execution of shape corrections or also when processing non-circular workpieces.

The rotary cutting process according to the invention is characterized by measures taken specifically that relate to the beginning of the rotary milling process. This beginning is also called "immersion", It contains a feed movement of the rotary cutting tool 1. This infeed movement is a relative movement between the rotary cutting tool 1 and the crankshaft 3 or another workpiece The delivery process comprises all processes from the first contact between the rotary cutting tool 1 and the main bearing surface 2 to the end of this relative movement The delivery process is understood to be synonymous with the dipping process For the explanation of the delivery process, reference is made to FIGS.

Figure 3 illustrates the relative position of the workpiece or the main bearing surface 2 and the rotary cutting tool 1 before both engage with each other. The eccentricity 9, which is to be measured at right angles to the tool rotational axis 5 and also at right angles to the workpiece rotational axis 8, has a first relatively large value. Preferably, this is at most slightly larger than the radius 10 of the rotary cutting tool 1. For clarification of the overall situation illustrated in FIG. 3, reference is made to FIG. This shows a section around the cutting edge 7 around. As can be seen, the cutting edge 7 is located in the vicinity of an imaginary line 11, which is registered parallel to the tool rotation axis 5 in FIG.

The now running feed follows a dashed line in Figure 4 line 12. The line 12 includes the radial direction to the tool axis of rotation 5 an acute angle α of, for example, 3 °. The radial direction coincides in Figure 4 with the direction of the end cutting edge and the movement on the line 12 comes about by a superposition of two movements namely an axial movement of the rotary milling tool 1 and a radial movement of the same. The radial component of the movement leads to a reduction of the eccentricity 9, as can be seen in Figure 5. This leads to a first contact between the cutting edge 4 and the Aufmaßkontur 13 of the workpiece, as illustrated in Figure 6, at a lying at the line 11 point 14th As can be seen, the end cutting edge 4 touches the workpiece, ie the gauge contour 13, for the first time at a location adjacent to the cutting corner 7.

As this contact takes place, the workpiece, i. here the main bearing surface 2, in a the dipping movement opposing movement. For example, the plunging movement according to FIGS. 3, 5 and 7 takes place from right to left, while the rotary movement is clockwise (clockwise).

During the further immersion movement, the rotary lathe tool 1 continues to follow the path 12, whereby the eccentricity 9 is further reduced, for example, to the low value illustrated in FIG. 7, or also becomes zero or slightly positive. At the same time, the distance between the front cutting edge 4 and the workpiece rotation axis 8 is further reduced. As FIG. 8 shows, the front cutting edge 4 thereby comes to the dashed contour contour 15 shown in FIG. 8, which lies somewhat below the gauge contour 13. Calculated from the first contact between the (fast) rotating lathe tool 1 and the gauge contour 13 and the achievement of the low eccentricity 9 shown in Figures 7 and 8, the workpiece, i. the main bearing surface 2 preferably at an angle of about 15 °. The immersion angle oc amounts to 0.1 ° to 10 °, preferably 1 ° to 3 °. It can be constant or variable along the path 12. Towards the end of the immersion movement, the axial movement of the rotary cutting tool 1 can be stopped gently. Simultaneously or shortly thereafter, the radial movement of the rotary cutting tool 1, which causes the reduction of the eccentricity 9, can be stopped gently. As a result, the bleed feed vector passes smoothly into the round feed vector.

During the dipping movement, the rotary cutting tool 1 and the workpiece (main bearing surface 2) can rotate at constant speeds. It is also possible to vary at least one of these speeds during the dipping process. For example, the Speed of the rotary cutting tool to minimize the chip thickness initially be increased. Other variations are possible. In the exemplary embodiments described above, the rotary cutting tool 1 follows the linear path 12 during immersion. However, the path can also have a curvature in sections or everywhere. For example, it can be s-shaped curved. For example, a branch of the s-shaped path can smoothly and smoothly connect to the Rundfrasbewegung. In order to achieve this, the feed speed of the linear axes during immersion can be varied.

FIG. 9 schematically illustrates the bleed conditions on the main bearing surface 2. The first contact occurring between the front cutting edges 4 and the main bearing surface 2 leads to a material removal in a small-area first region 16, approximately in the middle of the main bearing surface 2. With continued dipping the area increases and passes through several stages 17, 18 until the engagement surface 19 reaches is, with the Runddrehfrasvorgang over at least one full revolution of the main bearing surface 2 or more revolutions of the same is continued.

The subsequent finishing operation, in which the workpiece and the rotary cutting tool 1 are disengaged, can in turn be done with a path inclined to the tangential direction analogously to the immersion with a constant or path-variable exchange angle. It is possible to move on the path 12 by increasing the eccentricity again from the position of Figure 7 on the position of Figure 5 to the position of Figure 3. Alternatively, however, the radial movement of the immersion process can continue in the same direction and only the axial movement can be reversed. Then the eccentricity reverses when reversing its sign. In the example according to FIGS. 3 to 7, this would be a movement of the rotary cutting tool 1 to the left. Again, a dip angle of a few degrees, for example, 0.1 ° to 10 °, preferably 1 ° to 3 ° find application. The rotational movement of the workpiece can be according to Figure 5 in the clockwise direction or alternatively also in the counterclockwise direction.

The method described above can also be used for all other round surfaces of the crankshaft 3, in particular for its crank pins 20 or for other workpieces.

On the one hand to protect the cutting corner 7 of the rotary cutting tool and on the other hand to use the front cutting edge 4 as possible over the entire length, the lowest possible insertion angle α is selected. It can be determined according to the following formula:

RWS + AFM. RWS a _mm = arcsin, _ -arcsin-

-J (RWZ-RSK EXZ) ² + ² s RWS] (RWZ -RSK-EXZ) ² + RWS ^''

in which :

minimal dip angle

RWS = workpiece radius (without allowance), i. Workpiece target radius

AFM = radial workpiece allowance

RWZ = tool radius

RSK = cutting edge radius of the tool

EXZ = eccentricity in round milling.

The cutting edge radius RSK can be assumed to be zero or less than the actual value if a first workpiece / tool contact is desired in the radius transition from the cutting corner to the end cutting edge 4. Below are three examples that provide good results in terms of machining accuracy and tool life:

Feature Unit Example 1 Example 2 Example 3

RWS [mm] 20 50 25

AFM [mm] 0.1 0.4 0.2 RWZ [mm] 15 12 12

RSK [mm] 0, 02 1 0, 05

EXZ [mm] 2, 5 4, 65 3

Cmin [degrees] 0, 462 6, 780 1, 323

In the exemplary embodiments described above, a purely transverse adjustment of the tool rotation axis 5 in combination with a small feed movement was used to carry out the dipping movement inclined to the tangential direction. If there is no possibility of transverse adjustment, but there is a possibility of inclining the drive axle of the rotary cutting tool 1, the oblique plunge operation described above, also in accordance with FIGS. 10 to 12, can take place by inclining the tool rotational axis 5. FIG. 10 shows the starting position of the rotary cutting tool 1 and the main bearing surface 2. The ratios correspond to FIG. 3. Under continued axial feed of the rotary cutting tool 1, the tool rotational axis 5 can now be inclined such that the eccentricity 9 in accordance with FIG. There may be a first contact between the cutting edge 4 and the main bearing surface 2. The ratios according to FIG. 6, a continued axial feed of the rotary cutting tool 1 combined with a continued increase in the inclination of the tool rotational axis 5, leads to the minimal eccentricity 9 according to FIG. 12 and the engagement ratios according to FIG.

The inventive method for rotary cutting of round sections of workpieces used during cutting, ie at the beginning of the rotary milling process, a special immersion strategy. The movement is neither purely tangential (radial with respect to the lathe tool) nor purely axial (radial with respect to the workpiece). Rather, a superposition between the view of the tool radial and axial or from the perspective of the workpiece tangential and radial feed movement is selected. This results in an immersion path which is inclined at an angle of a few degrees to the tangents of the workpiece surface. Advantageous conditions are when the first workpiece contact occurs shortly after the cutting corner in the area of the tool outer diameter or in the cutting radius outlet. The method provides a long tool ^¬ quantity at high machining quality and precision.

Reference sign:

1 rotary milling tool

2 main storage area

3 crankshaft

4 end cutting edge

5 tool axis of rotation

6 peripheral cutting edge

7 cutting corner

8 workpiece axis of rotation

9 eccentricity

10 radius

11 line

12 way

13 measurement contour

14 place

15 target contour

16 area

17, 18 stadiums

19 engagement surface

20 crank pins

Claims

Claims:

1. A method for the rotary milling of round sections of workpieces, in particular crank pin (20) and / or bearing pin (2) of crankshafts (3), in which:

a rotary milling tool (1) having at least one end cutting edge (4) is rotationally driven about a tool rotation axis (5) having an eccentricity (9) with respect to a workpiece rotation axis (8), and

the rotary milling tool (1) is brought into engagement with the workpiece (3) while continuously reducing the eccentricity (9) by being brought in the direction of the tool axis of rotation (5).

2. The method according to claim 1, characterized in that takes place during the feed movement, the first contact between the rotary milling tool (1) and the workpiece (3) on the end cutting edge (4) of the workpiece (3).

3. The method according to claim 1, characterized in that takes place during the feed movement, the first contact between the rotary milling tool (1) and the workpiece (3) at a radially outer portion of the end cutting edge (14) of the rotary milling tool (1).

4. The method according to claim 3, characterized in that the radially outer cutting edge corner (7) at the first contact between the workpiece (3) and the rotary milling tool (1) remains disengaged.

5. The method according to claim 1, characterized in that during the feed movement, the first contact between the rotary milling tool (1) and the workpiece (3) on such a portion (14) of the end cutting edge

(4) of the rotary milling tool (1) takes place that the end cutting edge (4) over its length provides a largely uniform cutting volume.

6. The method according to claim 1, characterized in that by the superposition of the axial feed movement of the rotary milling tool (1) with the eccentricity reduction movement an effective feed movement is achieved, based on the tool rotation axis (8) both an axial component (y) and a Radial component (x).

7. The method according to claim 6, characterized in that the effective feed movement (V) has a movement direction with the radial direction (x) of the rotary milling tool a plunge angle (α) of 0.1 ° to 45 °, preferably 1 ° to 10 ° , more preferably 1 ° to 3 °.

8. The method according to claim 1, characterized in that the workpiece (3) during the reduction of the Zustellens and reducing the eccentricity (9) performs a rotational movement about its workpiece axis of rotation (8).

9. The method according to claim 8, characterized in that the workpiece (3) in this case by a workpiece rotation angle (β) is at least 5 °, preferably at least 15 °.

10. The method according to claim 1, characterized in that the workpiece is rotated after the end of the Zustellvorgangs in a Rundfräsvorgang at least 360 °.

11. The method according to claim 1, characterized in that the workpiece (3) after completion of the Zustellvorgangs in a round milling at most rotated by 720 °.

12. The method according to claim 1, characterized in that the tool speed and / or the workpiece speed is varied during the Zustellvorgangs.

13. The method according to claim 1, characterized in that during the Zustellvorgangs the feed rate is varied.

14. The method according to claim 1, characterized in that the rotary milling tool (1) under continuous enlargement of the eccentricity (9) by removal in the direction of the tool axis of rotation (6) of the workpiece (3) is disengaged away.

15. Turning milling machine, set up for carrying out the method according to one of claims 1 to 14.

16. Software product for controlling a machine tool for carrying out the method according to at least one of claims 1 to 15.