WO2007031337A1

WO2007031337A1 - Method and device for machining workpieces

Info

Publication number: WO2007031337A1
Application number: PCT/EP2006/009018
Authority: WO
Inventors: Wolfgang Hintze; Carsten Möller; Frank Eglins
Original assignee: Tutech Innovation Gmbh; Technische Universität Hamburg-Harburg
Priority date: 2005-09-16
Filing date: 2006-09-15
Publication date: 2007-03-22
Also published as: DE102005045143A1

Abstract

The invention relates to a method for machining workpieces using a tool with at least one cutting edge, which comprises a cutting face and a relief face, which forms a relief angle with the workpiece along the cutting edge during the machining process. A first section of the relief angle diminishes as a result of wear during machining. The invention is characterised in that a relative displacement takes place between the tool and the workpiece, said displacement being superposed on the feed and/or cutting displacement and increasing the first section of the relief angle.

Description

Method and device for machining workpieces

The present invention relates to a method and apparatus for machining workpieces with a tool having at least one cutting edge. An open space adjoins the cutting edge, which encloses a clearance angle along the cutting edge with the workpiece surface. Also defined for the tool is a rake face that includes a rake angle along the cutting edge with an imaginary perpendicular to the workpiece surface.

While there is only a small, caused by elastic deformation contact with cutting edge between the tool free surface and work, increases with increasing cutting wear, the contact surface between the tool and workpiece, whereby the friction increases and the cutting force, in particular the pressure, resulting from passive and Feed force, and the cutting temperature rise. Increasing cutting forces and temperatures have a detrimental effect on the workpiece quality, in particular on the dimensional and dimensional stability, the material surface quality and the workpiece edge zone. Increasing cutting forces and temperatures limit tool life. As a result, it is necessary to use a new working cutting edge.

In general, methods are known for the machining, which are characterized by a variable feed. In the known methods, the variation of the feed or the engagement takes place up to the value zero or to a value close to zero, in order to favor a chip breaking. For example, turning with a periodically moving tool is known. Here, the cutting speed is modulated with the target, the contact between the cutting edge and the workpiece, ie to significantly reduce or interrupt the engagement of the cutting edge to promote chip breaking.

From DE 197 16 251 it is known for the machining, to choose a large clearance angle to achieve longer life for the tool.

From DE 103 93 255 T5 a tool holder is known whose critical angle, such as the clearance angle and / or the setting angle, is determined by a CNC control for each section of the geometry of the tool targeted. In order to approach the newly determined position of the tool holder, it is adjusted synchronously with the movement of one of the three linear movement axes. It is also proposed to adjust the clearance angle of the cutting tool with respect to a geometry of the workpiece.

From JP 2003-311512 a tool holder is known, which allows to change an angular position of the cutting tool to cut threads of different pitch.

From Annais of the C.I.R.P., Vol. XV, pages 457-461 it is known to periodically vary the feed motion of a soft material to reduce the chip thickness to zero. For the periodically varying feed results in a reduced surface roughness.

From Z. Klim et al. in WEAR 195 (1996) pages 206 - 213, it is known that the tool life significantly improved in the roughing of tough, corrosion-resistant and high-temperature resistant metal alloys with variable feed. It was found that the mean service life was 20 to 43% extended if a variable feed is used instead of a constant feed.

The invention is based on the object for the machining, for example, turning, planing or bumping, milling, drilling, broaching or chipping, to improve the service life of the tool with simple dimensions, without degrading the quality of processing.

The above object is achieved by a method having the features of claims 1 and 12. Also, the above object is achieved by a device having the features of claim 15. Advantageous embodiments form the subject of the dependent claims.

The inventive method for machining workpieces uses a tool with at least one cutting edge, which has a rake face and an open face. The free surface forms along the cutting edge during machining a clearance angle with the workpiece surface. According to the invention, the clearance angle is increased over time. In the definition of the clearance angle is turned off on the clearance angle of the already mentioned contact surface. This contact surface is also referred to below as the first section. The clearance angle change is particularly useful in such Zerspanvorgängen useful in which wear marks on the free surface limit the quality of the Zerspanprozesses, the workpiece quality or tool life. The change in the clearance angle takes place in the method according to the invention such that when the free surface forms a wear mark, in the area no longer the original clearance angle is present, but due to wear a reduced free angle is present, by changing the free winkeis the cutting edge of the clearance angle in the area the wear mark, ie in the first section, is increased. If one considers the clearance angle not in sections, but point by point, so in the inventive change of the clearance angle, the blade is adjusted so that at all points of the active cutting length (first section) of the clearance angle increases or remains at least constant.

The change of the clearance angle according to the invention counteracts the rake angle so that a rake angle change of opposite sign occurs. If one now considers the case of a clearance angle increase for compensation of the free surface wear, the result is a reduction of the rake angle by the same amount. This rake angle leads to an increase in cutting temperature and cutting force. The invention is based on the finding that this disadvantageous effect is not significant in comparison to the positive effect caused by the oppositely equal increase in the free angle. Thus, it has been found that a clearance angle change dominates the behavior of the chip action as compared to the effects of the rake angle change. This effect is independent of whether or not the effective rake angle increases as a result of scumming due to wear.

In a preferred embodiment, the clearance angle is changed while the blade is engaged with the workpiece. Particularly preferred is a continuous change of the clearance angle is used when long cutting paths are to be processed without interruption, such as when working on rollers.

Appropriately, a relative movement between the tool and workpiece is defined when changing the clearance angle, which is superimposed on the feed and / or cutting movement. The relative movement can be superimposed depending on the type of machining as translational and / or rotational movement. For this purpose it is possible to change the position on the tool side and / or on the workpiece side.

In the preferred embodiment of the method, the change of the clearance angle is effected by a change in the position and / or the orientation between the workpiece free surface and the tangent, which bears against the contact point of the workpiece. When shooting curved surfaces, for example, the free-angle change is achieved by a translational and / or rotational movement. In one embodiment of the invention, the cutting edge is machined in external machining, i. in the processing of convex curved surfaces, in the circumferential direction of the workpiece in the cutting direction forward or in the internal machining, i. the processing of concave curved surfaces, in the circumferential direction of the workpiece counter to the cutting direction, ie backward, translationally adjusted. Such an adjustment can be realized for example by a Y-axis, which is preferably arranged at a distance from the workpiece rotation axis C. When machining flat surfaces, such as by turning, planing, bumping and scraping, the change of the clearance angle can be achieved by a rotational movement, as well as in planing, bumping or scraping of curved surfaces.

Due to the change of the clearance angle occurs during the machining of the workpiece to dimensional and shape deviations, which is why a compensation movement in at least one further feed axis is required.

In one embodiment of the method according to the invention, the clearance angle can also be changed between two processing sections. Wherein the two processing sections can be formed by the machining of two workpieces and / or by the processing of two contour elements on one or more workpieces. In the method according to the invention, the clearance angle in the first section is increased in order to compensate for a wear-related decrease in the clearance angle. In this case, the decrease of the clearance angle can be partially compensated by the wear by the inventive adjustment of the clearance angle in the first section. Based on the first adjustment, the further adjustment operations of the tool are made such that the length of the first section preferably does not change in these.

In the method according to the invention, the adjustment of the clearance angle preferably takes place in two independent directions.

The object of the invention is also achieved by a method having the features of claim 12.

The inventive method according to claim 12 relates to the sizing of a workpiece made of a hard and / or brittle and / or abrasive material with a tool having at least one cutting edge. The group of these materials include, for example, hardened steel materials (from 47 HRC) or cast iron materials or brass or aluminum alloys with higher silicon content or magnesium alloys or fiber and / or particle-reinforced, preferably ceramic reinforced materials. According to the invention, the engagement of the tool in the working plane is changed during the working process. A work process can also include the machining of several workpieces or workpiece contour elements, each with individual Zerspanvorgängen. The work plane is spanned by the cutting and feed directions. Preferably, the work operation or the feed operation is changed. The work operation defines the size of the tool's engagement, measured in the working plane and vertically to the feed direction. In particular, when milling and planing and bumping the work intervention is of central importance. The feed engagement defines the amount of engagement of the tool in the feed direction and is particularly important in turning and milling and drilling and rubbing. Important for an effective use of the tool during finishing is that there is the largest possible average engagement of the tool. In the invention, it was recognized that an improvement in the surface quality can be achieved with the greatest possible effectiveness by a variation of the intervention. Finishing is a machining operation under conditions that achieve the desired dimensional and shape accuracy as well as surface quality or roughness on the workpiece. The focus here is on the quality of the workpiece, with the proviso of producing as large a workpiece surface as possible per unit time, and not the maximum possible technically possible per unit time of workpiece volume dispensed with the given pairing of material and cutting material.

The change in the engagement makes it possible to avoid periodic profile peaks forming on the workpiece surface with increasing cutting path and increasing cutting time. As a result of the changed engagement, there are fewer wear notches and less chipping on the cutting edge, which results in significantly lower workpiece roughness. In this embodiment of the invention, too, the crucial idea is that although the kinematically induced theoretical roughness is increased by the change in engagement, an improved workpiece surface is nevertheless achieved, since the influence of the shearknellability on the workpiece surface quality is dominated by the influence of the theoretical roughness ,

In the method according to claim 12 according to the invention, the intervention starts from a base value for the intervention and is performed within a predetermined interval. valls varies. In the method, the tool remains in engagement with the workpiece. The engagement is erfϊndungsgemäß kept always greater than zero. The variation of the Vorschubeingriffes or work intervention takes place in such a way that the value in a predetermined interval continuously or discontinuously fluctuates around an average and is always greater than zero. The variation around the mean value can be realized in various forms, such as in the form of a vibration with a certain amplitude and frequency, in the form of a time- or location-dependent linear growth and decreasing the Vorschubeingriffes or the labor intervention or in the form of a constant value to the Advance intervention or the work intervention gradually increased and lowered accordingly. It follows that the advancing engagement or engagement is always greater than zero, ie, that the process has a substantially higher productivity over existing processes in which chip removal must be accomplished by decreasing the advancing engagement or the zero operation. In this embodiment of the invention, in turn, the clearance angle can be varied according to one of the above features.

The object of the invention is also achieved by a device according to claim 16 for machining workpieces with a tool carrier with at least one tool. The tool has at least one cutting edge, which has a rake face and an open face, wherein the free face along the cutting edge during machining encloses a clearance angle with the workpiece surface. According to the invention, means are provided for adjusting a relative position of the workpiece and the tool in such a way that the clearance angle increases in a first section in which the clearance angle decreases as a result of wear during machining. According to the invention, the enlargement of the clearance angle in the first section is effected by a rotation and / or displacement / translational movement of the tool carrier. Adjust in a preferred embodiment the means the clearance angle while the cutting edge is engaged with the workpiece. The adjustment of the tool carrier can be done via a toothing, an NC axis, a torque motor and / or a clutch. Preferably, the adjusting movement of the tool carrier is superimposed on at least one further movement about a translational and / or rotational axis.

The invention will be explained in more detail with reference to exemplary embodiments.

It shows:

1 shows the cutting force above the cutting path,

2 shows a variation of the clearance angle in a schematic view,

3 shows a variation of the clearance angle in a schematic view,

FIGS. 4a-d show in schematic views the wear mark widths,

5 shows an example of an increased clearance angle in the surface-generating region for inner longitudinal rotation,

6 is a block diagram for controlling a continuous clearance angle change,

FIGS. 7 a-f the clearance angle increase when rotating cylinder and plane surfaces of a shaft or annular component, FIGS. FIGS. 8a-b show, in a schematic representation from the front and from the side, a recess during longitudinal turning with round cutting plates with a variation of the clearance angle, FIG.

9 shows the course of the cutting force over the cutting path,

10 shows the maximum wear mark width over the cutting path,

Fig. 11 for the variation of the engagement, the development of roughness over the

cutting path

12 is a schematic representation of the intervention with a constant or inventively variable feed advance,

13 shows a surface with a continuous variation of the working engagement along the cutting path,

FIG. 14 measurement results for three different clearance angles, FIG.

FIG. 15 measurement results for a variation of the working engagement, FIG.

16 the enlargement of the clearance angle on convexly curved peripheral surfaces,

17 shows the enlargement of the clearance angle in a machine having a rotation axis B, which is arranged skewed to a Z axis, and Fig. 18 shows the adjustment of a tool turret to change the

Clearance angle.

1 shows the schematic course of cutting force and / or temperature for the method 10 according to the invention in comparison with the prior art 12. The prior art curve 12 increases above the cutting time or the cutting path due to the wear-related reduction of the clearance angle ct _\ up to the wear limit 14 continuously, whereby the service life or the tool life is achieved. Also, according to the invention, the cutting force and / or temperature increases continuously as a result of the wear-related reduction of the clearance angle Cu ₁ up to the defined wear limit. Then a new clearance angle α ₂ >

adjusted, which abruptly the cutting force and / or temperature drops. In view of the resulting smaller rake angle, the cutting force and / or temperature reaches only approximately the level of the working cutting edge. After the cutting force and / or temperature has again reached the defined wear limit, another clearance angle α ₃ > α ₂ can be set. This process can be repeated until there is no sufficient reduction in cutting force and / or temperature. Due to the method according to the invention, a significant increase in the endurance or the service life compared to the prior art can be achieved.

The qualitative profile of the maximum wear mark widths for the method according to the invention is shown in FIG. 10 in comparison with a known method. In the conventional method, the wear curve 16 is characterized by a turning point 18, after which it increases progressively. For reasons of reject avoidance and process reliability, the wear limit 20 is established and the tool life or tool life is obtained. According to the invention, the tool cutting edge is only until about the inflection point of the wear curve and then increased the clearance angle of a _\ to α ₂ and later to α ₃ . This procedure is repeated until other service life criteria, eg the permissible surface roughness, have been reached. With the method, an increase of the endurance or the service life is achieved compared to the conventional method.

Another possible embodiment of the method according to the invention is shown in FIG. 9. In this variant of the method, the clearance angle is slightly increased in each case after short individual cutting paths or individual cutting times, whereby the cutting force and / or temperature decreases. By periodically repeating the process, not only an extension of the service life or the endurance can be achieved, but alternatively can be achieved while maintaining the life or the endurance, which are achieved in the prior art, reduce the cutting force or temperature, i. significantly improve workpiece quality or process reliability. This may be useful, for example, in finishing finishing of hardened workpieces on combined turning / grinding machines to reduce grinding allowance.

FIGS. 4 a to d illustrate, irrespective of whether a cylinder or end face is to be machined, the influence of the flank wear during cutting with a defined cutting edge. In the figures, a worn cutting edge 24 with wear mark widths 26 VB ₁ , VBn, VBm is shown in each case in the original position 22, which has contact with the workpiece over the entire free surface wear, resulting inter alia in a high cutting force and / or temperature. By a changed employment 28 of the worn cutting edge to the workpiece 29, a new clearance angle is set (solid line), whereby the cutting force and / or temperature drops. This procedure can be repeated several times. FIG. 4a shows two successive adjustment processes in which the clearance angles d { ₌ θii ₌ αm remain the same. 4b shows the adjustment processes, each with different clearance angles cη _≠ ctu _≠ ctm. In both adjustment processes, the wear mark width VB remains the same in each case.

Fig. 4c shows two successive adjustment operations, in which in each case the same clearance angle a. is set and wear widths increase VBi <VBn <VB _III . Fig. 4d shows the case where the wear mark width decreases VB ₁ > VB _π ≥VBm.

FIG. 2 illustrates, by way of example, a possibility for implementing the clearance angle increase in the surface-producing cutting area for the outer longitudinal turning 30. If the cutting edge is intact and the center is turned, the tool clearance angle is ct _\ (see Fig. 2b). With increasing cutting time or increasing cutting path, a flank wear sets, whereby in the contact area of the effective clearance angle = 0 °. A positive clearance angle is achieved by a translatory tool and / or workpiece displacement in the Y direction and / or by a rotational displacement of the tool about a C ₂ axis 34 by the tool cutting edge is positioned below the center of rotation. A translational displacement can be further realized by the cutting edge is arranged at a distance from a rotation axis and the rotation axis is arranged so that it is not parallel to or identical to the Y-axis. This turns a Freiwin

In the case of internal longitudinal turning 36, an increasing clearance angle in the surface-producing region can be achieved by "setting over center" of the tool cutting edge Fig. 5 shows an exemplary embodiment in which the cutting edge is positioned translationally above the rotational center. Due to a translational and / or rotational displacement of the tool cutting above or below the center of rotation, it comes to the workpiece to form and dimensional deviations that make compensatory movements in at least one further feed axis necessary.

The example of FIG. 3 for external transverse planing 42 illustrates the increase in the free angle in the surface-producing region in the case of flat surfaces. The change of the clearance angle can be carried out only by a rotational movement 44 of the tool and / or workpiece, which is realized in the example shown by an A ₂ axis. The inclination of the tool and / or workpiece ΔA ₂ corresponds to the newly set clearance angle C ^ ₂ . When turning plane surfaces into the workpiece center, ie x = 0 mm, it is absolutely necessary that the deviation of the tool cutting edge from the center of rotation Δy be compensated.

Fig. 7 illustrates the embodiment of the method according to the invention when turning 46 of cylinder and plane surfaces of a typical wave-shaped component 48 or annular component, wherein the free-angle increase takes place at each edge-generating cutting point 50. In the upper drawing, Fig. 7a, the feed direction for the processing of the respective end and cylindrical surfaces is shown. The middle and lower drawing, Fig. 7b and 7c, explains ways in which the free-angle change can take place. The middle illustration shows a rotation of the tool 56, wherein the axis of rotation lies in the XZ plane and has an angle to the Z-axis of 0 ° to 90 °, preferably 30 ° to 60 °. As a result, the clearance angle increases both in the cutting area for machining the end face and in the cutting area for machining the cylindrical surface relative to the feed directions shown in FIG. 7a. The advantage here is that only one additional pivot axis 54 is required. Due to the fact that decreasing rake angle, the maximum possible free-angle increase is limited. Alternatively, the lower illustration, Fig. 7c, shows an embodiment with 2 pivot axes with which the free-angle change for the machining of face and cylinder surface can be performed separately from each other. Taking into account that the cutting edge except the respective cutting point 50 depending on Bearbeitungsaufmaß on a cutting length with the workpiece is engaged, resulting in particular when turning the face shoulder in the direction of the workpiece axis, as shown in Fig. 7a vectorially, contact the cutting edge with a levels and a convexly curved workpiece surface area. The arrangement shown in FIG. 7b with an adjusting axis arranged at an angle as well as a blade spaced therefrom consequently permits an increase of the clearance angle in the entire active cutting area. However, this is only possible with the selected feed direction. If the face shoulder is machined from the small to the large workpiece diameter, ie radially outward (reverse feed direction as in FIG. 7a), a blade contact with a concavely curved workpiece surface and with the selectively flat workpiece surface results due to the chip width on the face shoulder. An equal adjustment of the clearance angle to higher values for the entire active cutting area does not appear possible in this constellation. However, it is possible to realize a free angle increase of workpiece contours with arbitrary rising and falling contours and even on opposite plane surfaces with only one rotary adjustment axis.

As shown in Figs. 7d to f, the falling face shoulder requires a rotation in the opposite direction (see double arrow) due to the surface normal facing away from the adjustment axis in order to increase the clearance angle on the flat workpiece surface. In this case, there is a distance U _al , U _a2 or U _b1 , U _b2 , which is different from zero, between the engagement region and the rotation axis of the tool. If the shoulder is now moved from small to large Piece diameter, ie processed radially outward (see arrow), which is in contact with the active cutting edge workpiece surface concavely curved. The rotation according to the double arrow leads to the change in height .DELTA.h opposite to the cutting direction, so that the clearance angle increases as intended in the entire active cutting area.

FIGS. 8a and b show a Auskammern by longitudinal rotation with round cutting plates 56, wherein the contour to be produced is wider than the tool cutting edge. For abrasive materials where it is not appropriate due to the rapid flank wear and tear with a cutting the entire cutting path, this is split, wherein alternately from the left and right sides 58, 60 of the contour is rotated towards the center. Depending on the feed direction, the clearance angle for the active tool cutting edge is adjusted in opposite directions. The application also offers the possibility of increasing the tool life and the tool life during the roughing process.

As shown in Fig. 8b, the cutting at a distance U can be positioned from the adjustment axis, on which the cutting movement v _c-facing side. As a result, the vertical position of the cutting edge is reduced by an amount .DELTA.h during rotational adjustment and as a result the clearance angle also increases on the cylindrical outer surface. The smaller the workpiece diameter 2 Γ _WST is the larger there is the free angle increase α and the result for the exemplary arrangement of FIG. 8b is sin α = Δh I r \ ysτ-

In addition to a gradual free-angle change, the clearance angle can also be varied continuously in-process. A control for a continuous clearance angle change is shown in FIG. 6. Input variables 62, which determine the cutting process, are the workpiece material, the cutting material, the cutting geometry and the Cutting parameters. As a disturbance, the tool wear affects the output variables of shape and dimensional accuracy, surface quality, workpiece edge zone and cutting performance. With in-process measured variables 64, such as force and / or torque and / or acceleration and / or strain and / or temperature and / or current and / or power tool wear is determined indirectly. The measured values are compared with the stored nominal values 66, from which the free angle change is calculated by a controller 68 and this is returned by an actuating unit 70 to the machining process. In addition, the controller determines the resulting shape and dimensional deviation and compensates for this by correcting movements of the feed axes.

One application example of the clearance angle change is the turning of sintered cemented carbide. In this case, the tool edge of the high-hardness cutting material obtained at a return angle of C ^ = 8 ° due to the rapid wear increase after about 5 min, the wear limit of VB = 150 microns, Fig. 14. According to the prior art, the service life of the tool cutting edge is reached. By the inventive enlargement of the return angle to O _p = 13.5 ° and then to C ^, = 19 °, it is possible to continue to use the cutting tool. Thus, the service life of the cutting edge was increased to approx. 17.5 minutes. The cutting force according to the method of the invention has a nearly linear course, whereas the pressure force, which is the vectorial addition of the feed and passive force, initially decreases with each increase in clearance angle and then increases again because of the renewed flank wear.

Fig. 12 shows the variation of the feed engagement in the machining. The prior art is characterized by a constant feed engagement, ie an = ^ _f2 ≡ a _ß . In contrast, the erfmdungs- proper method by a variable Vorschubeingriff. The feed of the tool (not shown) is indicated by the arrow 70.

Due to periodic profile peaks of the workpiece surface, with increasing cutting path and increasing cutting time, pronounced wear notches and scars in the surface-generating cutting area, which reduce the workpiece surface quality, occur conventionally. In comparison, the variation of the engagement avoids and reduces periodic profile peaks of the workpiece surface. As a result, lower wear notches and scars occur, which lead to a significantly lower increase in the workpiece roughness, in particular the maximum roughness depth R _t or the average roughness depth R _z or the average roughness value R _a , above the cutting path and the cutting time. Although the kinematic, theoretical roughness (R _theo ) is increased by the method according to the invention, the workpiece surface is improved, since the influence of the shear tolerances on the workpiece surface quality dominates the influence of the theoretical roughness.

Fig. 13 illustrates an embodiment of the invention for varying the working engagement along the cutting path or the cutting operation in comparison with the prior art. According to the prior art, the working engagement remains constant during the cutting path, so that always the same surface-generating cutting area is engaged, whereby this cutting area has pronounced wear notches and scars, and thus the workpiece surface quality decreases rapidly. According to the invention varies during the cutting path of the work, so that the surface-generating cutting area is loaded evenly, so that wear notches and scars are minimized in the cutting area and the workpiece roughness remains almost constant. An application example for varying the work engagement is the Feinstzerspanung by planing, which is shown in Fig. 15. In this process, hardened steel with a hardness of 50 - 54 HRC is machined with a sharp-edged PCBN cutting edge. According to the state of the art, the workpiece surface characteristic values increase significantly over the cutting path or the cutting time. The cutting edge wear has systematic wear notches with a pitch of about 0.01 mm (see Fig. 11) corresponding to the working engagement a _e = 0.01 mm. The variation of the working engagement according to the invention by a defined basic working engagement during machining counteracts the formation of these wear notches. The resulting reduction in tool wear leads to a significant improvement in the surface finish produced. Advantageously, the inventive method also leads to a reduction of Zerspankräfte.

In the invention, the change of the clearance angle is performed by a tool-side and / or workpiece-side movement.

The clearance angle change is gradual or continuous, wherein a stepwise change of the clearance angle is preferably carried out between the machining of successive workpieces and / or between the processing of two contour elements, a continuous change of the clearance angle, preferably during machining.

The clearance angle can be changed according to predetermined cutting times or paths or after a number of machined workpieces by an angular amount based on previously determined empirical values.

Also, the clearance angle during the machining process can be changed continuously at a constant or variable speed, with no detection of measured variables.

Alternatively, the change of the clearance angle can be controlled or regulated stepwise or continuously on the basis of directly or indirectly, in-process or process-intermittently detected measures. For example, the clearance angle and its wear-related change can be measured indirectly on the processing machine on or at the processing machine according to various measurement methods (for example optical or mechanical scanning) directly or else indirectly via the wear mark. Alternatively, a modified clearance angle can be indirectly detected with the aid of in-process measured variables, such as force and / or moment and / or strain and / or acceleration and / or acoustic emission and / or temperature and / or current and / or power. Corresponding correction movements for the clearance angle are carried out via a control loop. In addition, the numerical control calculates a systematic error in the shape and dimensional accuracy of the workpiece, resulting from the change of the clearance angle, and compensates for this by correcting movements of the feed axes.

In finishing, the clearance angle in the contour producing cutting area (i.e., the cutting edge) deserves particular attention, e.g. with regard to the compliance with tolerances and / or the avoidance of thermo-mechanical damage of the workpiece edge zone or of material deposits / fake chip formation on the free surface. Therefore, the clearance angle change is about for this area.

The free angle change can also be carried out preferably for cutting points at which high chip thicknesses are present or the effective clearance angle is low or the temperature is high. This embodiment is advantageous, for example, in the case of roughing and / or for reasons of component or tool rigidity and / or to avoid vibrations in the cutting process and / or to reduce the heat input into the tool.

When working on thermally sensitive materials, e.g. of plastics, can build up due to wear on the tool surface adhesive bonds. These increasingly prevent the dissipation of Zerspanungswärme in the tool. The temperature rises and when the permissible temperature is exceeded, the thermally sensitive material in the edge zone region of the component is damaged. The processes described are reduced or eliminated by the method according to the invention.

When working with thermally sensitive cutting materials such as HSS or diamond, they can abruptly fail as a result of thermal overload if the temperature reaches a permissible limit, especially when the free surface wear increases. This failure, which is known as HSS low-braking, can be counteracted by raising the clearance angle.

Alternatively, the clearance angle change may preferably be made for the cutting area which processes the workpiece contour in the direction of least component rigidity or which points in the direction of lowest tool rigidity, e.g. for slender shafts or long cantilever slender tools (e.g., drill rods) in the radial direction.

When complex workpiece geometries are to be machined, such as gear shafts, brake discs, pistons, tooth flanks, profiled rollers, mold cavities, the engagement conditions change gradually or steadily during machining, and thus the cutting area travels on the cutting edge for which the clearance angle change is to be made. The invention therefore provides methods and devices in order to make free angle changes in different, preferably two independent directions. Also, moving, in particular rotating tools are provided with motor controllable in the angular orientation cutting.

In the case of machining cylinder and plane surfaces, e.g. With rhombic cutting inserts, as is often the case with feed and shaft parts, in one embodiment of the method, the free angle changes are performed depending on the contour more radially or axially, depending on which of the criteria influencing the free angle change priority. In the case of finishing, this may e.g. the clearance angle at each contour-generating cutting area, in the case of roughing the clearance angle of a cutting area of the main cutting to reduce abrasion and / or when working with thermally sensitive cutting materials, such as HSS or diamond, to reduce the heat input into the tool.

In the latter case, the invention can also be used instead of a Standwegverlängerung an improvement in workpiece quality thereby achieve that fluctuations in the quality-determining process parameters (For example, cutting force and / or temperature) are significantly reduced.

The second aspect of the invention relates to the surface quality. The surface quality of the workpiece is determined by the kinematic, ie theoretical roughness of the cutting profile, further by the chipping of the new cutting edge, further by the surface quality of chip and flank surface and by material-related influences, such as built-up edge and breakouts of material particles, Bonding of material removal on the open space. As a result of wear, the cutting edge profile and the pungency of the cutting edge (eg local defects such as chipping, eruptions) as well as the surface quality of the chip and the flank face can change, which influences the surface quality of the workpiece.

The theoretical roughness R _theo is determined by the feed advance a _f and the working engagement a _e . R _t h _eo progressively increases with af or ae, and roughly quadratically with a round cutting profile.

In the finishing process, the influence of the cutting edge roughness ("cut surface roughness") on the surface quality of the workpiece in comparison to the influence of the cutting profile (theoretical roughness) is of considerable importance, for example in that measured workpiece surface characteristics, such as the average roughness R ₂ or the maximum roughness R _{t) is} more than twice to four times the theoretical roughness R _theo - Accordingly, a _f or a _e can be varied within limits without the workpiece surface deteriorating.

Local stresses and defects of the cutting edge can have systematic and random causes. Among the systematic causes is the formation of wear notches, caused for example by strongly solidified or elastically rebounding areas of the workpiece edge zone, especially at the ends of the chip cross section. With constant a _f or a _e , constant cutting edge inclination and constant setting angle, the same cutting area always has contact or periodically repeated contact with the solidified or elastically rebounding workpiece surface area. In this case, the said cutting area is responsible for the formation of the cut surface roughness, so that the stresses described above strongly wear-promoting in the sense of deteriorating Affect workpiece surface quality. According to the invention the engagement of the cutting edge is changed tangentially to the workpiece surface produced during the period of use of the tool by relative movements between the tool and the workpiece are superimposed on the feed and / or cutting movements. These lead to a variation of the Vorschubeingriffs or the working engagement or the inclination angle λ. This causes, in particular, the surface-influencing wear notches to be distributed to different cutting areas, whereby a higher workpiece surface quality can be achieved. The variation of the thrust engagement or the working engagement is in the range of ± 5% to ± 60%, preferably ± 10% to ± 30%, the variation of the inclination angle λ is in the range of +/- 30 degrees, preferably +/- 10 degrees , The variation occurs in stages or alternately around a fixed underlying.

The change of the feed engagement or the work operation is performed by a tool side and / or workpiece side movement.

The change of the feed engagement or the working engagement may be made stepwise, wherein a stepwise change is preferably made between the machining of successive workpieces and / or between the machining of two contour elements and / or cutting paths.

In a further embodiment of the invention, the feed intervention or the working intervention is varied after a predetermined number of cutting paths in discrete steps, which lie within a defined interval and are based on previously determined empirical values. In fine planing, for example, the working engagement a _e = 0.008 / 0.01 / 0.012 / 0.01 / 0.008 / 0.01 mm, etc.

Another possible embodiment of the method according to the invention is that the feed advance or the working engagement during the cutting path is changed continuously at a constant or variable speed, wherein there is no detection of measured variables.

An improved workpiece surface quality is achieved when, for example, when turning or milling or Breitschlichtfräsen the condition Vorschubeingriff a _f 'surface-generating Schneckenckenradius r _£ or planing, bumping or milling the condition a _e «r _£ and a _ε « d is met. The surface finish of the workpiece can be improved by wiping and / or indexable inserts with wiper geometries During the cutting time, notch wear occurs in the surface-forming cutting area, which reduces the surface finish and thus limits the cutting edge life Cutting radius in the surface-generating cutting area is significantly larger than the engagement, the formation of a notch wear can be delayed or reduced by a varying intervention.

Also, the inclination of the cutting edge in the surface-generating cutting area can be varied.

Fig. 16 shows a further preferred embodiment for increasing the clearance angle on cylindrical peripheral surfaces, on rising and falling, eg conical or toric contours and on rising and falling plane surfaces using the axes X, Z and the adjustment axis R, wherein the R axis is arranged approximately in the XY plane. The active cutting point of the tool 62 is located at a distance U to the rotation axis R and is in the external machining on the cutting direction facing side, in the internal machining on the side facing away from the cutting direction. This arrangement is suitable for example disk-shaped and wavy workpieces. Also, the R-axis may be inclined relative to the X-axis.

Fig. 17 shows a further embodiment in which an in-machine rotational axis B which is spaced from the Z-axis, i. skewed, is used to adjust the clearance angle when machining annular plane surfaces, e.g. Increase contact surfaces / plan shoulders of waves. In this case, the cutting edge is arranged at a height H which is 0.6 to 0.95 times the inner ring surface radius rwsτmin.

In the case of a tool turret, the clearance angle increase a depends mainly on the ratio between the distance cutting point to the turret rotation axis Γ _R and the workpiece radius Γ _WST . If the distance cutting point to the turret axis of rotation Γ _{R is} significantly greater than the workpiece radius r \ysτ (Γ _R »ΓW _ST ), eg during shaft machining, then the adjustment is preferably carried out by motors with reduction gears and / or torque motors, since these movements can realize 6 _R of a few angular minutes of preferably <0.5 °, especially <0, l °, cf. Fig. 18. The motors with reduction ratios are electric, eg DC motor, three-phase motor and stepper motor, or hydraulically. As an alternative to torque motors, which allow continuous adjustment of the clearance angle due to a high torque, can be used with a motor with reduction, with which preferably discontinuous deliveries are made. Preferably, the adjustment axis is clamped during machining by a brake or shiftable clutch in order to increase the rigidity and to eliminate the game especially in a gear reduction.

At almost the same distance, the cutting point to the turret axis of rotation r _R and workpiece radius r \ vsτ (ΓR ~ Γ _WST ), such as the brake disc, or at a Clearly larger workpiece radius Γ _WST compared to the distance cutting point to the turret axis of rotation Γ _R (Γ _R «r _\ vsτ), such as during roll machining, the adjustment of the turret preferably by a motor with a reduction and / or a torque motor and / or To realize a teeth and / or a clutch, since the turret to larger angle increments, ie, multiple degrees to adjust. Preferably, the adjustment by means of gears and / or clutches can be done in discrete steps and outside the cutting engagement.

For predominant or exclusive planar machining, e.g. Brake discs and flanges, for a clearance angle change is preferably to arrange the adjustment at an angle of at most 30 °, more preferably at most 20 ° to the normal of the plane surface, since the effective angle change is achieved only by a rotation of the revolver. On flat surfaces, a maximum clearance angle change occurs when the turret axis of rotation is perpendicular to the surface normal of the workpiece surface at the cutting point.

For planar machining of the clearance angle can be increased with relatively small diameter differences in the use of preferably piercing tools when the rotational movement of the revolver is carried out by a plane normal to the workpiece tangentially arranged axis of rotation. In this case, preferably the height H, which represents the distance of the cutting point to the axis of rotation of the workpiece, should be less than or equal to the minimum workpiece diameter _{rws T.mm.} With a plan grooving, ie the workpiece diameter is constant (Γ _WST = const), the radius position of the cutting edge can be corrected via the axially arranged axis. In this case, the height H is preferably chosen to be H = 0.7... 0.95. R _W sτ.

Claims

Claims:

A method of machining workpieces with a tool having at least one cutting edge having a rake surface and a flank which includes a clearance angle along the cutting edge during machining with the workpiece surface, wherein in a first portion the clearance angle is due to wear during the operation Processing decreases, characterized in that a relative movement between the tool and workpiece takes place, which is superimposed on the feed and / or cutting movement and which increases the clearance angle in the first section.

2. The method according to claim 1, characterized in that the clearance angle is changed while the cutting edge is engaged with the workpiece.

3. The method according to claim 2, characterized in that the clearance angle is changed continuously.

4. The method according to any one of claims 1 to 3, characterized in that the relative movement is translational and / or rotational.

5. The method according to any one of claims 1 to 4, characterized in that the change of the clearance angle on the tool side and / or workpiece side.

6. The method according to claim 1, characterized in that the clearance angle between two processing steps is changed.

7. The method according to claim 6, characterized in that the two processing sections are formed by the machining of two workpieces.

8. The method according to claim 6 or 7, characterized in that the two processing sections are formed by the processing of two contour elements on one or more workpieces.

9. The method according to any one of claims 1 to 8, characterized in that the increase in the clearance angle after a change compensates for a wear-related decrease in the clearance angle partially.

10. The method according to any one of claims 1 to 9, characterized in that the length of the first portion remains the same in the repeated relative movement.

11. The method according to any one of claims 1 to 10, characterized in that the clearance angle is changed in two independent directions.

12. A method of finishing a workpiece from a material difficult to machine with a tool having at least one cutting edge, characterized in that the engagement of the tool is changed in the working plane during the work process, without the tool is disengaged during the Zerspanvorgangs.

13. The method according to claim 12, characterized in that the change of the engagement starts from a base engagement and is varied within a predetermined interval.

14. The method according to claim 12 or 13, characterized in that the variation of the engagement takes place during or between two Zerspanvorgängen.

15. The method according to any one of claims 12 to 14, characterized in that the clearance angle is changed according to one of the methods according to one of claims 1 to 11.

16. An apparatus for machining workpieces with a tool carrier having at least one tool having at least one cutting edge, which has a rake face and a flank, which includes along the cutting edge during machining a clearance angle with the workpiece surface, wherein means are provided to to adjust a relative position of the workpiece and the tool such that the clearance angle increases in a first portion in which the clearance angle decreases due to wear during machining, characterized in that to increase the clearance angle in the first section, a rotational movement and / or displacement / Translational movement of the tool carrier takes place.

17. The apparatus according to claim 16, characterized in that a tool turret is provided as a machine tool carrier, is adjusted by the movement of the clearance angle.

18. The apparatus according to claim 17, characterized in that the tool turret has a toothing and / or a motor with reduction and / or a torque motor and / or a coupling.

19. The apparatus according to claim 18, characterized in that the adjusting movement is realized by a CNC-driven motor with reduction, wherein the angle increments preferably <0.5 °, especially <0.1 °.

20. The apparatus according to claim 17, characterized in that the drive is a torque motor, wherein preferably the distance of the cutting point to the turret axis of _rotation r _{R is} significantly greater than the machinable workpiece radius Γ _WST .

21. The apparatus according to claim 18, characterized in that the motor is clamped with reduction during processing by a brake or shiftable clutch.

22. Device according to one of claims 16 to 21, characterized in that the adjusting axis is arranged skewed to the axis of rotation of the workpiece.

23. Device according to one of claims 17 to 22, characterized in that the movement of the tool turret is superimposed for free angle change by at least one further translational axis and / or rotational axis.