Processes for roughing or rough turning with optimized process parameters

Abstract

Method for roughing or rough turning a workpiece (1) with a milling or turning tool, in which a material volume (2) is removed from the workpiece (1) in several successive layers along a feed axis, each having a layer thickness, with the tool, wherein the tool for removing each layer is guided on a toolpath (3, 5) lying in a working plane with process parameters that include at least a cutting depth, a engagement width, a cutting speed and a feed rate, characterized by that the layer thicknesses for each of the layers and the resulting toolpaths for the removal of each layer are determined in advance using an algorithm such that, compared to machining with identical layer thicknesses for the entire roughing operation, an increased, averaged material removal rate and / or reduced tool wear is achieved when removing the material removal rate (2), and the process parameters for the removal of each layer are set so that the layers are removed with the determined layer thicknesses.

Description

Technical application area and state of the art

[0001] The present invention relates to a method for roughing or rough turning a workpiece with a milling or turning tool, in which a material volume is removed from the workpiece in several successive layers along a feed axis with the tool, wherein the tool is guided for the removal of each layer on a toolpath lying in the working plane with process parameters that provide at least one cutting depth (A p ), an intervention width (A e ), a feed rate (f) and a cutting speed (V) c ) include.

[0002] In milling or turning operations for the production of components with defined geometries, the machining of a workpiece is generally carried out in several machining steps. For example, a two-stage machining process, divided into roughing and finishing, is frequently used for milling. The most common roughing toolpath is Z-axis roughing, in which the volume to be removed is extracted in several successive layers, each with a constant depth of cut. The thicknesses of the individual layers are thus identical. Most CAM programs used for path planning employ constant depths of cut, constant widths of cut, and corresponding constant values ​​for spindle speed and feed rate when guiding the tool.

[0003] The manufacturing costs of a component from a workpiece depend, among other things, on the time required to machine the workpiece. For roughing operations such as milling or turning, this machining time depends on process parameters such as cutting speed, feed rate, depth of cut, and width of cut.

[0004] From DE 11 2011 103 603 T5, a method for machining a workpiece with a rotating cutting tool is known, in which the cutting width is calculated according to a specification before machining, thereby achieving high machining efficiency. The other process parameters, such as the depth of cut, are then adjusted to the selected cutting width.

[0005] A method according to the preamble of claim 1 is known from DE 10 2022 104 111 B3.

[0006] WO 2021 / 197 708 A1 deals with the subsequent manual adjustment of a path program created in a CNC programming language. The operator receives feedback on how the manual changes he makes to machining parameters, compared to the CNC path program, affect productivity.

[0007] US Patent 2013 / 0218319A1 discloses a control system for moving a cutting tool relative to a rotating workpiece. Two different machining directions are selected, with one machining direction producing a different cutting depth than the other.

[0008] US Patent 2022 / 0147011A1 deals with the generation of control command data for a CNC lathe to perform a turning operation using a turning tool. The layer thickness for the outermost layer to be removed is chosen to be smaller than the layer thickness for the subsequent layers.

[0009] The object of the present invention is to provide a method for roughing or rough turning a workpiece with a milling or turning tool, which can reduce the costs of machining the workpiece. Description of the invention

[0010] The problem is solved by the method according to claim 1. Advantageous embodiments of the method are the subject of the dependent claims or can be found in the following description and the exemplary embodiment.

[0011] In the proposed method, a material volume is removed from the workpiece in a known manner in several successive layers along a feed axis, each layer having a constant thickness. The tool is guided along a toolpath in the working plane for the removal of each layer, with process parameters that include at least the depth of cut (corresponding to the respective layer thickness), the engagement width, the feed rate, and the cutting speed.The proposed method is characterized by the fact that the layer thicknesses for each of the layers and the resulting toolpaths for the removal of each layer are determined in advance using an algorithm in such a way that an increased material removal rate (Q) is achieved compared to machining with identical layer thicknesses for all layers for the entire roughing or rough turning operation, and / or a reduced tool wear is achieved compared to machining with identical layer thicknesses for all layers when removing the material removal rate.The algorithm preferably determines the layer thicknesses based on predefined relationships between the process parameters for the tool (and the material to be removed), between the process parameters and the material removal rate, and / or tool wear, and / or preferably based on a predefined residual stock allowance, particularly for surfaces not located in the working plane. The residual stock allowance is determined and appropriately selected by the user. Tool wear is typically defined as the tool's service life, usually expressed as its uptime, for example, in meters or minutes.

[0012] The process parameters for removing each layer with the corresponding determined layer thickness are then selected based on the respective determined layer thickness, preferably using the relationships specified for the tool. The layer thickness directly determines the depth of cut. Layer thickness and depth of cut are therefore equivalent in the proposed method. The other parameters corresponding to this depth of cut—width of cut, cutting speed, feed rate, and cutting velocity—are then set accordingly. This is preferably done using the relationships specified for the tool. The information for this, i.e., the appropriate combination of the individual parameters or the relationships specified for the tool, is usually provided by the tool manufacturer but can also be determined through testing.These relationships can be presented in various forms, such as a table or other representation, from which the appropriate combination of process parameters for the tool, as well as the material removal rate and / or tool wear, can be derived. In the proposed machining process, material removal then occurs with the determined layer thicknesses and the resulting process parameters. As mentioned above, the material removal rate is typically a value provided by the manufacturer in the representation above for the different combinations of process parameters. This also applies to tool wear, which is usually provided as a value for tool life (or service life) depending on the corresponding process parameters.

[0013] In one embodiment of the proposed method, the layer thicknesses are determined solely with the aim of increasing, preferably maximizing, the average material removal rate. This aims for the shortest possible machining time, thereby reducing machining costs. In another embodiment, the algorithm determines the layer thicknesses solely with the aim of reducing tool wear, preferably minimizing tool wear, thereby reducing tool costs and thus also machining costs. Both aspects can also be combined to minimize machining costs. In principle, the algorithm can also determine the appropriate layer thicknesses based on a predefined weighting of both aspects or objectives.

[0014] In all cases, non-cutting tool movements are preferably also taken into account, such as connections, approaches, entry and ramp movements. The algorithm determines the individual layer thicknesses in such a way that, compared to machining with identical layer thicknesses for each layer, a shorter overall machining time, and in particular a minimum machining time, is achieved for removing the material volume.

[0015] In the proposed method, the algorithm must simulate the toolpaths for each layer and between the layers in order to determine the desired result.

[0016] The toolpath along which the tool is guided in the proposed method is therefore a toolpath lying in the work plane with variable process parameters. These process parameters are, of course, determined based on stable cutting conditions for each work plane. In one alternative method, these parameters are selected to achieve the highest possible material removal rate while maintaining favorable cutting conditions. Alternatively, the parameters can be selected to minimize tool wear. Both conditions can also be combined. Depending on the alternative chosen, the proposed method thus reduces machining time and machining costs.

[0017] The proposed method is suitable both for the initial machining phase of roughing or rough turning, in which a volume of material is removed from a typically unmachined workpiece, and for a possible second machining phase, also involving roughing, in which any remaining steps on surfaces that are not parallel or orthogonal to the working plane are reduced layer by layer. The algorithm can, of course, also take into account a combination of both machining phases when determining or optimizing layer thicknesses.

[0018] The algorithm used can operate in various ways, for example, based on discrete values ​​for the respective layer thicknesses with corresponding thickness increments from layer thickness to layer thickness, or based on continuous values ​​or functions. Determining the appropriate layer thicknesses or layer thickness combinations can be done, for example, by simple trial and error (brute force) or by minimizing a cost function. The use of artificial intelligence or other suitable algorithms is also possible, of course. Brief description of the drawings

[0019] The proposed method is explained in more detail below using exemplary embodiments in conjunction with the drawings. These show: Fig. 1 a schematic representation of a workpiece with three different material removal volumes, which were removed according to the prior art; Fig. 2. An example of the proposed procedure; Fig. 3 a schematic representation of an exemplary removal of a removal volume according to the proposed method; Fig. 4 the example of the Fig. 3, in which additional connecting paths of the tool are shown; Fig. 5 a representation of the removal according to Fig. 3, which also shows the paths for removing remaining steps; and Fig. 6 An exemplary representation of the stages remaining after the first machining phase, which can also be removed by roughing in a second machining phase. Ways to implement the invention

[0020] The proposed method is explained in more detail below using the example of milling a workpiece. In conventional machining, identical process parameters for the depth of cut, the width of cut, and the cutting speed or spindle speed are generally selected for removing a material volume 2 from a workpiece 1. Fig. Figure 1 shows an example of the removal of three different material volumes 2, where the first material volume is removed in three layers, the second in two layers, and the third in one layer, each with an identical layer thickness. The corresponding toolpaths 3 for the material removal process are shown in the Fig. 1 also shown.

[0021] The proposed method aims to reduce the machining costs for a workpiece compared to a conventional approach. This is achieved using a suitable algorithm that appropriately determines the layer thicknesses for each layer to be removed according to one or more predefined conditions. The different layer thicknesses determine the different cutting depths (A). p The other process parameters are then adjusted to the selected cutting depth – preferably based on a relationship predefined for the tool. These parameters include the cutting or engagement width (A). e ), the feed rate (f) and the cutting speed (V) c ).

[0022] The inventive procedure is exemplified by the flowchart of the Fig. Figure 2 illustrates this process. First, a workpiece or workpiece area is defined from which a volume of a specified geometry is to be removed. Then, the geometry of the removed volume is defined or specified. This data, along with predefined relationships between process parameters and material removal rate and / or tool wear, is fed into an algorithm. The information about the tool and the corresponding relationships is generally provided by the manufacturer and includes at least different depths of cut and their associated widths of engagement, feed rates, and cutting speeds, or other parameters from which these can be calculated. This data can be provided, for example, in a suitable database and can include both discrete and continuous data. The following table provides examples of such data. Cutting depth A p [mm] Intervention width A e [mm] Vorschub f[mm / min] Cutting speed V c [m / min] Time span volume Q[cm³] 3 / min] 2 13,8 2544 206 70 4 10,2 3069 248 125 6 5,3 3325 286 106 8 5,3 3325 286 141 10 5,3 3325 286 176 12 4,1 3134 291 154

[0023] This data applies to a specific material group (the material to be removed) for this tool and also includes the material removal rate Q, which is achieved with the corresponding parameters or enables its calculation. Alternatively or additionally, the tool life value, i.e., a measure of tool wear, can also be included in the data. Using this data, the algorithm then determines—for example, iteratively—a sequence of layers with the corresponding layer thicknesses that achieves a minimum total machining time in this example. The type of algorithm used and its operation, for example, using discrete optimization methods, continuous optimization methods, or artificial intelligence, are not specified. The material removal then takes place layer by layer using the process parameters determined by the algorithm in this way.

[0024] Fig. Figure 3 shows an example of a material removal process according to the proposed method, in which the material is removed from the workpiece 1 in two layers with different layer thicknesses. The toolpaths 3 are again shown in the figure. Due to the relationship between cutting depth and engagement width, the toolpaths 3 are spaced differently in the respective working planes.

[0025] In an advantageous embodiment, the movements of the tool required to connect the individual machining paths or at the beginning and end of a machining process are also taken into account to reduce or minimize the machining time. Fig. 4 is a representation based on the processing of Fig. 3, in which these additional toolpaths 4 are also shown. Preferably, these additional toolpaths, on which no machining of the workpiece takes place, are not used in the method according to Fig. 2. This was also taken into account to minimize processing time.

[0026] During the initial roughing operation, steps are created on surfaces that are not parallel or perpendicular to the working plane due to the layer-by-layer material removal, as seen in Fig. 6 are illustrated. The representation of the Fig. 6 is the result of the removal according to Fig. 2. The remaining six stages can be reduced by a subsequent roughing operation, where a smaller residual stock allowance is selected. Machining of the stages is generally performed from bottom to top. This machining, i.e., also a layer-by-layer removal of a corresponding material volume (in the form of a portion of the stages), can also be carried out according to the proposed procedure to minimize machining time, tool wear, or machining costs while maintaining a specific residual stock allowance. It is also possible to have the algorithm consider both the first and this second machining phases as a single, continuous operation. Furthermore, non-cutting movements between these phases, such as connections, approaches, entry, and ramp movements, can be taken into account.

[0027] Fig. Figure 5 shows a representation in which, following the first processing phase according to Fig. 3. The steps were reduced by a second machining phase with the toolpaths shown there. 5. As already mentioned, the algorithm can also be used separately for the two machining phases, preferably using a specific residual stock allowance as a predefined value for both the first and second machining phases.

[0028] Instead of minimizing processing time, the algorithm used in Fig.2. The machining process can also be geared towards minimizing tool wear. The algorithm then selects the layer thicknesses so that, given the geometry of the material removal volume, tool wear is minimized. The algorithm can also be used for a combination of these parameters to minimize the machining costs resulting from the sum of machining time and wear. In this case, a suitable relationship must be defined, which can be derived, for example, from empirical data. Reference symbol list 1 workpiece 2 Removal volume 3 Tool path 4 connecting routes 5 Toolpath of the second machining phase 6 steps

Claims

[1] Method for roughing or rough turning a workpiece (1) with a milling or turning tool, in which a material volume (2) is removed from the workpiece (1) in several successive layers along a feed axis, each having a layer thickness, with the tool, wherein the tool for removing each layer is guided on a toolpath (3, 5) lying in a working plane with process parameters that include at least a cutting depth, a engagement width, a cutting speed and a feed rate, characterized by , that the layer thicknesses for each of the layers and the resulting toolpaths for the removal of each layer are determined in advance using an algorithm such that, compared to machining with identical layer thicknesses for the entire roughing operation, an increased, averaged material removal rate and / or reduced tool wear is achieved when removing the material removal rate (2), and the process parameters for the removal of each layer are set so that the layers are removed with the determined layer thicknesses. [2] Method according to claim 1, characterized by, that the determination of the layer thicknesses is carried out depending on relationships between the process parameters specified for the tool and between the process parameters and the material removal rate and / or the tool wear, and that the process parameters for the removal of each layer are then set according to the relationships between the process parameters specified for the tool. [3] Method according to claim 1 or 2, characterized by that the determination of the layer thicknesses is additionally carried out depending on a predeterminable residual volume that is to be achieved by the removal. [4] Method according to any one of claims 1 to 3, characterized by, that the layer thicknesses are determined by the algorithm in such a way that, taking into account tool movements (4) without intervention in the workpiece (1) required for machining, a shorter machining time for the removal of the material volume (2) is achieved compared to machining with identical layer thicknesses for the entire roughing or rough turning operation. [5] Method according to any one of claims 1 to 4, wherein the roughing or rough turning operation is carried out after a first machining phase in which a first material removal volume was removed layer by layer from the workpiece (1) by roughing or rough turning operation in order to at least partially remove any remaining steps after the first machining phase or this first machining phase as a supplement to the layer by layer removal.

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