CZ2017403A3 - A method of speed and feed control of machine tools and a device for performing this method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the speed and displacement of machine tools having at least two linear axes and / or at least one rotary axis using at least one rotary tool with a circular cutting edge. In each toolpath block, the current cutter diameter of the tool is determined, at which tool and workpiece contact occurs and the tool speed is determined to maintain the desired cutting speed, and the resulting speed is specified in the respective toolpath block to determine the prescribed speed and the feed rate for maintaining the desired feed per tooth and / or feed per revolution. The resulting feed rate is entered in the corresponding NC program block for CNC machine tool control. The invention further relates to an apparatus for carrying out this method comprising a control system (6) of a manufacturing machine to which a file (5) is connected with an NC program generated in the postprocessor (4) coupled to the set (3) of the CL-data of the CAM system (2), wherein at least a part of the speed control device (1) is connected to one part of the machine tool control system (6), the NC program file (5), the post processor (4) and the CAM system (2) and feed rate.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method for controlling revolutions and feed rates when creating and handling NC programs for controlling CNC machines, particularly for machining. By adjusting the speed and feed speed of the tool, the control and drive units of the machine are acted upon to achieve a constant course of the desired cutting speed during machining while maintaining the desired feed rate to the tool tooth. This speed and feed rate control will ensure that the technological parameters are maintained to achieve the expected surface quality parameters of the workpiece and to achieve an efficient and productive machining process by reducing production time compared to the current state.

BACKGROUND OF THE INVENTION

In technical practice, there are several possibilities of controlling feed rates and tool speeds during machining. Continuous tool revolutions have so far been implemented only for turning operations to maintain a constant cutting speed when turning a contour with a changing coordinate from the workpiece rotation axis. With this option, a more productive turning is then achieved, since the feed rate in the cut is also increased in proportion to the speed increase, so as to maintain the feed per tooth or cutting edge. feed per revolution. In milling, no continuous speed control method has been used to achieve a constant cutting speed. So far, the cutting speed and hence the tool speed has been adjusted in a one-time proportion to the combination of the cutting tool, the material being machined and the machine, and adjusting the speed to each other according to the rigidity of the machine-tool-workpiece-jig system. The feed rate control during milling is still solved in two principal ways. The first assumption is that the control uses a machine control function that uses spatial coordinate transformations (Tool Center Point function), and the control system interpolates sufficient path points between two successive toolpath points to meet the linear path condition between two successive toolpath points. In this case, the control system <««

performs the transformation of the coordinates from the workpiece coordinate system to the machine coordinate system according to the type of configuration of the rotary axes of the machine tool. The second assumption is that Tool Center Point is not or cannot be used in multi-axis machining. Thereafter, the control does not perform the coordinate transformation as the coordinate transformation is pre-prepared by the post processor. At the same time, when using the machine control function for spatial coordinate transformation, the feed rate between the tool and the workpiece is usually corrected so that the feed rate specified by the technologist at the tool reference point is maintained. However, without using the coordinate transformation function, the control system does not correct the feed rate during multi-axis machining and the feed rate specified by the technologist is not maintained. For these cases, there is already a solution for a tool path compensation method of a multiaxial computer-controlled machine tool described in patent CZ 306228, which also solves feed rate control in these cases. There are also solutions to control feed rates in machine tool control systems or available software solutions - CAM systems and their superstructures, but only to control feed rates so that the tool does not overload due to the increase in material removal at a given point in the toolpath. However, no current solution offers control, let alone continuous control, of tool speed to achieve a constant cutting speed when milling with tools that have a circular cutting edge, such as spherical or toroidal cutters and their modifications, and there is no solution speed control and for these tools the continuous feed rate control was designed to achieve a constant feed rate per tooth - blade and thus achieve efficient and productive machining. At present, machining with these tools is unproductive, because at the point of contact of the tool and the workpiece along the radius of the tool, the cutting speed prescribed by the technologist is not adhered to, and thus the feed rate is not effectively controlled and the tool can be overloaded or on the contrary, unloaded in terms of failure to adhere to the feed - tooth.

SUMMARY OF THE INVENTION

The above mentioned drawbacks are largely eliminated by continuously controlling the tool speed to maintain a constant cutting speed. At the same time, when the tool speed is changed, the feed rate is controlled so that the specified feed rate per tooth is maintained.

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By adhering to the prescribed feed per tooth value, machining thus becomes efficient and productive, unlike the current state where these parameters were not controlled and the feed rate was thus unnecessarily low, thereby increasing production times. The current value of the cutting speed in a given machining step is calculated from the current radius of rotation with respect to the machine spindle axis, the actual radius of rotation being determined by the tool's contact point with the workpiece. The current point of contact of the tool and the workpiece within the circular cutting portion of the tool moves during machining, thus changing the current rotation radius at which the cutting speed vector is located. It is therefore necessary to adequately control the speed of the tool. The point of contact of the tool with the workpiece is calculated from the position and orientation information of the tool relative to the workpiece, taking into account the actual tool profile for the calculation. Thanks to the detected tool-to-workpiece contact point, the current rotation radius at which the cutting speed vector - the distance from the axis of rotation to the material being cut - the tool-workpiece contact point is located - is calculated. To maintain a constant cutting speed at a given point in the toolpath, it is necessary to calculate the required tool speed according to the calculated rotation radius of the cutting speed vector, since the cutting speed is the product of the speed, twice the rotation radius and the Ludolf number. In particular, feed rate programming in units, defined as path increment per unit of time, is used to determine the tool movement speed. Technologically, however, it is necessary to maintain the feed per tooth - cutting edge, which is defined as the path increment per tool revolution divided by the number of teeth - cutting edges. Feed per tooth - cutting edge is determined from the knowledge of cutting and machined material, tool cutting geometry and axial and radial depth of cut. The feed rate is then calculated as the product of the rotational speed and feed rate and the number of tool edges. It follows from this calculation relationship that in order to maintain the technologically desired feed per tooth, when changing the tool speed, in accordance with the above-mentioned speed control principle to maintain a constant cutting speed, it is necessary to calculate the actual value of the required feed speed at that tool path. This process of speed and feed rate control keeps basic technological conditions for cutting tools, especially spherical, toroidal, conical with spherical end of the cutting part or other special tools with radius, namely cutting speed and feed per tooth.

Thanks to adherence to the mentioned technological conditions, the achievement of the expected tool life of the cutting edge during machining, the expected quality of the machined

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“**« 44 »lil itilil surface and of course the production time is greatly saved compared to the original state, when these technological parameters are not continuously controlled. For spherical tools, when this calculation of the cutting conditions is applied at the point where the tool axis intersects the spherical surface, the value of the tool speed may increase excessively due to the zero rotation speed of the cutting speed vector. Therefore, the calculation procedure must be specifically adjusted to avoid generating speed values that exceed the available machine spindle speed limits, given these possible situations that may occur in the region close to the point of intersection of the tool axis rotation axis. Therefore, the calculation procedure is adjusted so that the spindle speed limit values are reached at the same time, and if they should be exceeded in the continuous speed control, the speed values are generated so that the speed increases only up to the speed limit. machine spindles or tool assemblies.

This process of continuous control of technological parameters can be applied to any type of milling operations where spherical, tapered, toroidal or other special tools with radius are used, eg for three-axis operations, multi-axis continuously controlled operations, or multi-axis operations where only In principle, it is possible to incorporate this process of continuous control of technological parameters either directly into the function in the CAM system or into the function in the postprocessor, or it can be implemented directly into the control system of the machine, possibly using a combination of the above. The technical solution also includes the possibility of calculating the actual rotation radius considering the allowance on the machined surface, whereby the area of contact of the tool and the material is considered and due to these detected conditions the speed is controlled so as to maintain the desired cutting speed. speed so that the feed to the tooth is again maintained.

Due to the fact that during machining operations there is still material remaining on the workpiece surface after the previous machining operation - allowance, the above procedure is also applied when calculating the current radius of rotation not only for the point contact of the tool with the workpiece, but also in the case of curve contact. In this case, the curve contact results from the cutting edge of the tool and the workpiece material at a depth given by the remaining material after the previous machining operation. The calculation of the current rotation radius is based on the knowledge of this curve and the subsequent • 4

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Clarification of the figures in the drawings

The invention will be described in more detail with reference to the accompanying drawings, in which: FIG. 1 shows the material to be machined and three variants of the use of tools. In FIG. 2 to FIG. 9, block diagrams showing the possibilities for carrying out the technical solution are shown.

DETAILED DESCRIPTION OF THE INVENTION

The principle of the invention is illustrated in greater detail in FIG. 1. The material to be machined 13 is indicated by a black line and hatching, and three of the possible variants of tooling are indicated. These are spherical cutters 11, the left cutter 11 being indicated in a general inclined position relative to the material 13 and a toroidal cutter 12. The current contact point 14 of the tool with the material to be machined 13. The current rotation radius for the speed calculation is indicated by dimension W. a tangent 15 to the surface of the machined material 13 at the point of contact with the tool and the normal vector 16 indicated at this point. The radius 17 of the ball end mills 11, the diameter 19 of the toroidal milling cutter 12 and the corner radius 18, i.e. the radius of the tip of the cutting edge, the toroidal milling cutter 12 are further indicated. keeping the feed on the tooth.

In FIG. Figures 2 to 6 show the basic embodiments of the invention, or the inclusion of the aforementioned optimization functions for controlling the speed and feed rate in the data processing process for controlling a production machine. The following components are shown: speed control and feed rate optimization device 1, CAM system 2, CL data file 3, i.e. CAM system data, postprocessor 4, NC program file 5, control system 6 of a manufacturing machine and apparatus 7 with supporting optimization software. In FIG. 1, a solution is disclosed wherein the speed and feed rate control functions are incorporated into CAM system 2. FIG. 3, there is shown a solution where the speed and feed rate control functions are incorporated into the post processor 4. FIG. Fig. 4 shows a solution where the functions for controlling the speed and feedrate are described. the speeds are incorporated into the control system 6. FIG. 5 shows a solution where; the present speed and feed rate control functions are incorporated into a device 7 with support optimization software that cooperates with the post processor 4. FIG. 6, a solution is shown where the speed and feed rate control functions are incorporated into a separate device 7 with support optimization software that modifies the NC program file 5. Of course, it is also possible to realize the technical solution by dividing the speed and feed rate control functions between the parts of the process, eg in the CAM number 2, post processor 4, control system 6 or device 7. Other possible solutions are shown in Fig. . 8 and FIG. 9. The block diagram also shows the CL data file 3, which is data created in the CAM system.

An example of the solution is the implementation of the speed and feed rate optimization device 1 in the postprocessor 4 for the MCFV 5050 LN machine with the Sinumerik 840D control system 6. In this postprocessor 4, a solution has been implemented where, in the generated NC programs 5, speed and feed rate control are generated using ball cutters 11 and toroidal cutters 12 so as to maintain a constant cutting speed and feed per tooth, ie prescribed technological conditions between the tool and workpiece 13. This makes production more productive, for example, in the so-called swathing operations that are carried out on the machine, which will be demonstrated by the following example.

In the case of a workpiece 13 with a diameter of 63 mm, a spherical cutter 11 with a diameter of 10 mm - a radius of 5 mm with four teeth - blades was selected for the spacing operation. The material of the workpiece 13 was an aluminum alloy EN AW 7075. A cylindrical surface of a 180 ° sector with a width of 15 mm was machined. The depth of cut was set to 0.5 mm, the feed per tooth was 0.04 mm and the scallop, the height of the projections after the spacing was set to 0.002 mm. This machine has a spindle limiting spindle which has a maximum speed of 15,000 rpm for the aluminum alloy machining technology, therefore 6500 rpm and feed speed were selected for a basic test that demonstrates standard constant speed control of non-specified cutting speed. was 1040 mm / min and then the measured machining time was 373 s. When speed and feed rate control was applied in postprocessor 4, the speed was controlled between 6500 rpm and 13,000 rpm during travel and the feed rate was controlled between 1040 mm / min

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-7 to 2080 mm / min, the machining time was 266 s. It is evident that the application of speed and feed rate control functions has saved time by 40%. The machining test confirmed the time savings in relation to the required surface quality.

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Industrial applicability

This method of speed and feed control is applicable to all types of machine tools having at least two linear axes and / or at least one rotary axis. The cutting tool must be either a rotary tool - a milling cutter with semicircular end cutters - a milling cutter with a round end of the cutting part, a milling cutter with a rounding tip - toroidal cutter, tapered cutter with a circular etc., ie any rotary tool with a circular cutting edge. When applying the mentioned speed and feed control, it is possible to ensure that the specified cutting conditions - cutting speed and feed per tooth - are maintained. Adherence to these recommended conditions for a given cutting tool / workpiece combination is important for optimum machining operation, proper operation of the cutting tool and resulting surface finish. By means of this control it is possible at the same time to achieve higher productivity and process economy. The control is applicable to any machining operation with the above-mentioned machines and tools, in which the position of the contact point of the tool, the chip and the workpiece on the cutting edge is changed. The use of the principle is especially suitable for incorporation into postprocessors for generating NC programs for control of CNC machine tools, or the principle can be used in a given step of NC program preparation.

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Claims (5)

A method of speed and feed control in machine tools with at least two linear axes and / or at least one rotary axis, wherein at least one rotary tool with a circular cutting edge is used, characterized in that the current cutting diameter is determined in each tool path block tool where the tool and workpiece come into contact and the tool speed is determined to maintain the desired cutting speed, the resulting speed is specified in the appropriate NC block of the CNC machine tool and / or the specified speed is determined in each tool path block and determined The feed rate is specified in the corresponding block of the NC program for controlling the CNC machine tool. Method according to claim 1, characterized in that the allowance after the previous operation is respected and the required rotational speed to maintain a constant cutting speed is determined to this calculated diameter and the necessary feed rate to maintain the feed per tooth is determined. Device for carrying out the method according to claim 1 or 2, characterized in that it comprises a control system (6) of the production machine to which is connected the file (5) with the NC program generated in the postprocessor (4) connected to the file (3) with CL data from the CAM system (2), wherein at least a portion of the device (1) is selected from one of the manufacturing machine control system (6), the NC program file (5), the post processor (4) and the CAM system (2). 1) to optimize speed and feed rate control. Device according to claim 3, characterized in that a device (7) with supporting optimization software is connected to one part selected between the NC program file (5) and the post processor (4). Device according to claim 3 or 4, characterized in that one part of the speed control and feed rate optimization device (1b) is connected to the control system (6) of the production machine and the other part of the device (1a) is connected to one part of the selected a CAM system (2), a postprocessor (4), and a device (7) with supporting optimization software.