Machining method for manufacturing dental objects - Patent application

Abstract

To carry out machining more efficiently.SOLUTION: The present invention relates to a machining method comprising the steps of: (S101) providing a data set (101) for the milling process in which at least one process parameter (103) for machining a workpiece is specified; (S102) simulating machining force on the workpiece based on the data set; and (S103) adjusting the process parameter (103) for machining until a predetermined maximum value for the machining force is reached or a predetermined minimum value is maintained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a machining method for manufacturing dental objects, a computer program for the machining method, and a machining device for manufacturing workpieces. [Background technology]

[0002] Currently, milling templates, which describe the tool path and associated process parameters for the milling process, such as feed rate or spindle speed, are designed for the worst-case scenario. In reality, this occurs less than 10 percent of the time. Therefore, efficiency improvements of over 90 percent can be realized in these processes. Therefore, current milling templates are slow.

[0003] The approach of simulating machining through models is resource intensive. Also, these models do not take into account the dynamic behavior and control of the equipment. Therefore, they are not suitable for widespread use and do not have the possibility to determine the machining forces that occur. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to carry out the machining method more efficiently.

[0005] This technical object is solved by the subject matter of the independent claims. Technically advantageous embodiments are the subject matter of the dependent claims, the description and the drawings. [Means for solving the problem]

[0006] According to a first aspect, this technical object is solved by a machining method for manufacturing dental objects, the machining method comprising the steps of: providing a data set for a milling process, in which at least one process parameter for machining a workpiece is specified; simulating a machining force on the workpiece based on the data set; and adjusting the process parameters for machining until a predetermined maximum value of the machining force is reached or a predetermined minimum value is maintained. The vector machining force can be simulated in one, two, or three spatial directions. This machining method achieves the technical advantages of being able to manufacture workpieces faster, more efficiently, and more robustly. Furthermore, longer tool life and less wear on the machining equipment are achieved.

[0007] This allows the work area to be identified before the machining equipment starts machining. The machining file can be efficiently and optimally designed, optimizing quality, machining speed, and wear. Additionally, the manufacturing accuracy and surface quality of the workpiece can be optimized. Peak forces during machining can be avoided, protecting the milling spindle, the tool, and the entire machining equipment. Furthermore, smaller, cheaper machining equipment can be used with the same performance as larger, conventional equipment.

[0008] In a technically advantageous embodiment of the machining method, the adjusted process parameters are stored in at least one data set. Generally, the process parameters can also be stored in several data sets. This provides the technical advantage that, for example, the process parameters can be easily transferred together.

[0009] In a further technically advantageous embodiment of the machining method, the machining forces are simulated based on a digital twin of the machining device and / or the workpiece, which has the technical effect, for example, that the machining forces can be accurately calculated.

[0010] In a further technically advantageous embodiment of the machining method, the machining forces are simulated based on a tool path for machining the workpiece, where machine dynamics may be involved or taken into account, which has the technical advantage that, for example, machining forces can be calculated for each movement of the milling head.

[0011] In a further technically advantageous embodiment of the machining method, the data for the tool path are specified in a data set. This has the technical advantage that, for example, the tool path data and the process parameters can be transmitted together. The transfer and the start of the machining method can take place before the simulation is finished.

[0012] In a further technically advantageous embodiment of the machining method, the tool path is adjusted until a predetermined maximum value of the machining force is reached and / or until a predetermined minimum value is maintained, which achieves the technical advantage of obtaining a tool path that can be machined quickly, for example.

[0013] In a further technically advantageous embodiment of the machining method, the machining force on the workpiece is calculated based on the acceleration, feed rate, and / or machining volume per time, which achieves the technical advantage that the machining force can be accurately calculated, for example.

[0014] In a further technically advantageous embodiment of the machining method, the simulation is performed based on a linear relationship between the process parameters and the machining forces, which achieves the technical advantage that the simulation can be calculated quickly and in few steps, for example.

[0015] In a further technically advantageous embodiment of the machining method, the simulation of the machining forces is performed during the machining of the workpiece, thereby achieving the technical advantage that for example the tool can mill with improved parameters in real time.

[0016] In a further technically advantageous embodiment of the machining method, the workpiece is manufactured based on modified process parameters and / or tool paths, which has the technical effect of, for example, allowing the workpiece to be manufactured more efficiently.

[0017] In a further technically advantageous embodiment of the machining method, the spindle current is measured and / or the machining energy is determined during machining of the workpiece. The spindle current correlates with the machining force. Therefore, control can be derived from the spindle current. This also achieves the technical advantage of being able to accurately determine, for example, the machining force.

[0018] In a further technically advantageous embodiment of the machining method, machining is stopped when the spindle current and / or machining energy exceeds a predetermined value, which has the technical effect of preventing, for example, damage to the workpiece or the machining device.

[0019] In a further technically advantageous embodiment of the machining method, the feed rate is slowed down or accelerated if the spindle current and / or the machining energy and / or the machining force exceed or fall below a predetermined value, which achieves the technical advantage that, for example, machining of the workpiece can be optimized.

[0020] According to a second aspect, this technical object is solved by a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the machining method according to the first aspect.

[0021] According to a third aspect, this technical object is solved by a machining device for manufacturing a dental object using a computer program according to the second aspect.

[0022] Examples of embodiments of the invention are illustrated in the drawings and are explained in more detail below.

[0023] The drawings show: [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a block diagram of a machining method according to the present invention; [Figure 2] FIG. 10 is a diagram of generated and simulated machining forces as a function of time according to the present invention. [Figure 3] FIG. 10 is a close-up view of generated and simulated machining forces as a function of time according to the present invention. [Figure 4] 1 is a perspective view of a workpiece in a machining apparatus according to the present invention; [Figure 5] FIG. 2 is a further perspective view of a workpiece according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows a block diagram of a machining method for producing a dental object from a workpiece. The machining method is a manufacturing process that includes turning, drilling, milling, and grinding. For example, the dental object may be a crown, bridge, veneer, abutment, inlay, onlay, splint, or partial or full denture. Generally, the dental object may be any object in the dental field that is manufactured as part of a dental treatment.

[0026] In step S101, a data set 101 for a machining method is provided, in which at least one process parameter 103 for machining a workpiece 105 is specified. The data set 101 may be formed by a numerical control file (NC file). The process parameter may be, for example, a feed rate, an infeed, a path distance, and / or a spindle speed.

[0027] For example, machining energy is calculated based on several factors such as milling volume per time, material dependency, contact area, time, spindle speed, and machining force.

[0028]

number

[0029] Next, in step S102, machining forces on the workpiece 105 are simulated based on the data set. Next, in step S103, process parameters 103 for machining are adjusted until the machining forces reach a predetermined maximum value or remain at a predetermined minimum value. The workpiece can then be manufactured using the adjusted process parameters.

[0030] The machining method may be performed on a machining apparatus 200 that uses a metal-machining method to machine the workpiece 105. The machining apparatus mechanically removes material from the workpiece 105, for example, by a rotating machining tool, to create a desired shape.

[0031] For this purpose, the machining apparatus 200 may include a computer having a processor for executing a corresponding computer program and a digital memory for storing the computer program and other data. The computer program may implement steps S101, S102, and S103 of the machining method. The workpiece 105 may then be milled based on the adjusted process parameters. For example, the workpiece 105 may be a dental object such as a crown, a bridge, a veneer, an abutment, an inlay, or an onlay.

[0032] The generated force F can be calculated using the following formula:

[0033]

number

[0034] The machining energy u is calculated using the following formula:

[0035]

number

[0036] where u is the loop energy in J / mm3, F is the machining force as a space vector in N, vc is the machining speed in m / min, ap is the feed in Z direction in mm, ae is the feed in X direction in mm and Vf is the feed rate in mm / min. Based on these equations, a prediction of the generated machining forces can be made and the adaptation of the process parameters can be calculated.

[0037]

number

[0038]

number

[0039] This machining method allows for the extraction and processing of process parameters from the CAM file, NC file, digital twin, and / or machine at any point in the machining process, thereby allowing predictions of the machining conditions that will occur and for optimal changes to be made to the process parameters.

[0040] To adjust the load, it is possible to adjust only one parameter at a time or all parameters, generally all parameters are adjustable here.

[0041] The milling process can be performed in the optimum range, i.e. as quickly as possible and with minimal wear. Adjustments can be made sensorless and / or by measuring the power of the machining spindle with an integrated current sensor. The milling process is pre-optimized for a specific design and then corrected according to the current state of the machining equipment.

[0042] This information can be extracted from the CAM or NC file for any point in the machining method. It is also possible to simulate the milling process using the digital twin, which allows dynamic parameters such as acceleration and feed rate at each point in time to predict the resulting machining state. The digital twin simulation can be performed temporarily before the machining method, but can also be taken into account during the machining method.

[0043] This allows the NC file to be pre-optimized for minimum machining time, minimum tool wear, maximum accuracy and / or maximum surface quality. This can be done in the CAM 20 software and saved in the NC file. This involves communication between the CAM software and the machining equipment (CNC - Computer Numerical Control). This can be achieved in real time. In this process, the CAM software sends data packets to the machining equipment, which can be adjusted accordingly. The adjustments are calculated in the CAM software and executed on the machining equipment.

[0044] The same algorithm can be run on the machining tool, but with the additional training of spindle current as an input variable. Using the current values ​​on the tool and the spindle current, the model can predict the currently occurring forces.

[0045] Figure 2 shows a diagram of the simulated machining forces generated as a function of time for a number of tool paths. Through the process parameters, it is possible to predict the generated machining forces based on the simulation.

[0046] The measured machining forces are shown as line 109. Line 107 shows the machining forces predicted by the algorithm. A linear model (linear regression) is trained using which machining forces can be predicted via process parameters with low computational effort.

[0047] The same algorithm can be run on the machining tool, but with the additional training of spindle current as an input variable. Using the current values ​​on the tool and the spindle current, the model can predict the currently occurring forces. The same algorithm can be run on the machining tool, but with the additional learning of spindle current as an input variable. Using the current values ​​on the machining tool and the spindle current, the model can predict the current forces. This makes it possible to detect unplanned problems and react accordingly. An optimal milling-grinding process can therefore be guaranteed at all times.

[0048] In this case, a small and imbalanced dataset is used to train the model, and predictions are 89-90% accurate.

[0049] Figure 3 shows a close-up of the simulated machining forces generated as a function of time for several tool paths. The deviation between the simulated machining forces 107 (dashed line) and the measured forces 109 (solid line) for the tool paths is small.

[0050] 4 shows a perspective view of a workpiece 105 in a machining apparatus 200 having a milling head 111. Additionally, the associated coordinate system, infeeds in the x and z directions, and feed rate in the y direction are shown.

[0051] For example, the workpiece 105 is manufactured with process parameters of a spindle speed of 50,000 rpm, a path spacing of 0.1 mm, and a feed rate of 2500 mm / min. The objective is to ensure that a constant machining force of 50 N is applied throughout the machining process. The machining is performed, for example, by AI milling.

[0052] There is a direct relationship between the process parameters and the machining forces. Although the relationship is roughly linear, each parameter has a different effect on the machining conditions that occur. These constantly change during the milling process and are never constant.

[0053] 5 shows a further perspective view of the workpiece 105. During machining, for example, three different situations 1, 2, and 3 can exist.

[0054] Situation 1: In this situation, throughput is high at this point.

[0055]

number

[0056]

number

[0057] The load of 83 N exceeds the specified maximum. Therefore, the process parameters are selected to reduce the load to 50 N. One possibility is to adjust the process parameters for the feedstock. Releasing this process parameter and inserting the desired load results in an adjusted new feed rate being used for the equipment within that range to achieve the desired 50 N force. The process parameters for the feed are reduced from 2500 mm / min to 1510 mm / min.

[0058] Situation 2: In this situation, the processing power is low at this time.

[0059]

number

[0060]

number

[0061] A load of 25 N is below a specified minimum. Therefore, a process parameter is selected to increase the load to 50 N. One possibility is to adjust the process parameter for the feed. If this process parameter is left blank and the desired load is inserted, the result is an adjusted new feed rate used for the device within this range to achieve the desired 50 N force. The process parameter for the feed is increased from 2500 mm / min to 4908 mm / min.

[0062] Situation 3: In this situation, throughput is again high at this point.

[0063]

number

[0064]

number

[0065] The 70 N load is again above the predetermined maximum. Therefore, the process parameters are selected so that the load is 50 N. One possibility is to adjust the process parameters for the feedstock. If this process parameter is left blank and the desired load is inserted, the result is an adjusted new feed rate within this range, within which the machining will occur to achieve the desired 50 N force. The process parameters for the feed are reduced from 2500 mm / min to 1785 mm / min.

[0066] In these examples, the feed rate is used as the controlled variable. However, other process parameters, such as path spacing and / or spindle speed, can also be varied according to the same principle to achieve the desired load. In this case, control can be stepless. For this purpose, the milling path can be changed in the CAM software. The adjustment is made by simulation in the CAM software or by information in the CAM software for path calculation. The deeper the milling drill penetrates into the workpiece 105, the greater the machining force.

[0067] This analysis can be based on vector machining forces, one-dimensional machining forces, or spindle loads. Vector forces are forces that have a magnitude and a spatial direction, whereas spindle loads are scalar quantities.

[0068] Artificial intelligence-based algorithms can predict various loads not covered by analytical solutions, for example, when the tool lifts out of or penetrates the material, or during the buildup of forces at the start of a machining operation.

[0069] In this way, it is possible to optimize the machining of the workpiece 105 for maximum efficiency without high computational effort and additional costs. The generated machining forces can be predicted using a self-learning algorithm (machine learning algorithm) based on the process parameters and the material of the workpiece 105.

[0070] All the features described and shown in connection with individual embodiments of the invention may also be provided in different combinations in the subject matter of the invention in order to simultaneously realize their advantageous effects.

[0071] All method steps may be performed by an apparatus configured to perform the respective method step. All functions performed by the objective features may be method steps of the method.

[0072] The scope of protection of the invention is given by the claims and is not limited by the features described in the specification or shown in the drawings. [Explanation of symbols]

[0073] 101 datasets 103 Process Parameters 105 workpieces 107 Simulated Forces on Tool Path 109 Tool path measurement force 111 Milling head 200 Machining equipment

Claims

1. 1. A machining method for manufacturing a dental object, comprising: providing (S101) a data set (101) for a milling process, in which at least one process parameter (103) for machining a workpiece (105) is specified; A machining method comprising the steps of: simulating (S102) a machining force on a workpiece (105) based on a data set; and adjusting (S103) process parameters for machining, the simulation being carried out based on a linear relationship between the process parameters and the machining force, until a preset maximum value of the machining force is reached and / or a preset minimum value is maintained.

2. 2. The machining method of claim 1, wherein the adjusted process parameters are stored in at least one data set (101).

3. 2. The machining method of claim 1, wherein the machining forces are simulated based on a digital twin of the machining device (200) and / or the workpiece (105).

4. A machining method as described in claim 1, wherein the machining force is simulated based on a tool path for machining the workpiece (105).

5. The machining method of claim 4 wherein tool path data is specified in the data set.

6. 5. A machining method according to claim 4, wherein the tool path is adjusted until a predetermined maximum value of the machining force is reached and / or until a predetermined minimum value is maintained.

7. 2. The machining method of claim 1, wherein the machining force on the workpiece (105) is calculated based on acceleration, feed rate, and / or machining volume per time.

8. 2. The machining method of claim 1, wherein simulating the machining forces is performed during machining of the workpiece (105).

9. 2. The machining method of claim 1, wherein the workpiece (105) is manufactured based on modified process parameters and / or tool paths.

10. 10. The machining method of claim 9, wherein the spindle current is measured and / or the machining energy is determined during machining of the workpiece (105).

11. 11. A machining method according to claim 10, wherein machining is stopped when the spindle current and / or machining energy exceeds a predetermined value.

12. 12. A machining method according to claim 11, wherein the feed is slowed down or accelerated when the spindle current and / or the machining energy and / or the machining force exceeds or falls below a predetermined value.

13. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the machining method according to any one of claims 1 to 12.

14. A machining device (200) for manufacturing dental objects using a computer program according to claim 13.

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