CHARACTERIZATION OF THE THERMAL PROCESS OF CNC MACHINES AND A STORAGE MEDIUM

Abstract

Procedure, comprehensive: Mounting an artifact (10) with a bore (14) on a CNC machine (212); determining a first position of the artifact bore (14) relative to the CNC machine (212) at a temperature T1 and a second position of the artifact bore (14) relative to the CNC machine (212) at a temperature T2, which is higher than T1; and calculating a deviation of the second position from the first position in order to determine a thermal stability of the CNC machine (212).

Description

TECHNICAL AREA

[0001] The present disclosure relates to methods for characterizing the thermal behavior of CNC machines. BACKGROUND

[0002] CNC machining (Computer Numerical Control) is widely used in the production of a variety of manufactured components, including in the automotive industry. CNC machining centers experience temperature changes during operation, which can lead to reduced machining accuracy due to the thermal expansion of various components within the machine. These temperature changes can be caused by a number of factors, including machine warm-up, heat generated by the machine components, and changes in ambient temperature. Thermal expansion can cause the relative position between the workpiece and the tool to deviate by up to 70 µm from the commanded position.In applications requiring highly controlled tolerances, such errors due to thermal expansion can be unacceptable. To address this problem, CNC machine manufacturers have implemented various approaches to counter thermal drift. One approach is thermal compensation, which may involve sensing the temperature of one or more machine components and applying pre-calibrated algorithms to adjust the commanded position of the workpiece and / or tool to compensate for thermal expansion. The task is to provide a method for determining the thermal stability of a CNC machine. SUMMARY

[0003] This problem is solved by a method having the features of claim 1. The problem is further solved by a method having the features of claim 9 and by a computer-readable storage medium having the features of claim 20.

[0004] In at least one embodiment, a method is provided, including mounting an artifact with a bore on a CNC machine and determining a first position of the artifact bore relative to the CNC machine at a temperature T1 and a second position of the artifact bore relative to the CNC machine at a temperature T2, which is higher than T1. The method can further include calculating a deviation of the second position from the first position in order to determine the thermal stability of the CNC machine.

[0005] The method can include operating the CNC machine to increase the temperature from T1 to T2. The CNC machine can include a spindle and probe, and the determination step can include determining the first and second positions of the artifact bore relative to the spindle and probe. In one embodiment, the method includes measuring the temperature at one or more positions on the CNC machine. A CNC machine thermal compensation mechanism can be activated prior to determining the second position. The step of determining the second position can be performed with the CNC machine thermal compensation mechanism activated and with the thermal compensation mechanism deactivated, and the computation step can include calculating the deviation of the second position from the first position with the thermal compensation mechanism activated and deactivated.

[0006] In one embodiment, the artifact comprises at least two bores, and the determination step comprises determining a first position of each artifact bore relative to the CNC machine at a temperature T1 and a second position of each artifact bore relative to the CNC machine at a temperature T2, and the calculation step comprises calculating a deviation of the second position of each artifact bore from the first position of each artifact bore. In a further embodiment, the determination step further comprises determining a position of the artifact bore relative to the CNC machine at a plurality of temperatures higher than T1, and the calculation step comprises calculating a deviation of the position at each of the plurality of temperatures from the first position.

[0007] In at least one embodiment, a method is provided which includes mounting an artifact with a bore on a CNC machine and performing a test cycle. The test cycle may include checking the artifact's bore to determine its position relative to the CNC machine and performing a dry cycle comprising one or more CNC machining operations. The method may further include calculating any deviation of the bore position from a reference position between the bore and the CNC machine.

[0008] The method can include repeating the test cycle one or more times and calculating the deviation of the bore position from a reference position between the bore and the CNC machine for each test cycle. In one embodiment, the temperature of at least one position on the CNC machine is monitored, and the temperature of that position at a second time point t2 is compared with the temperature at a first time point t1. If the difference between the temperature at t2 and the temperature at t1 is greater than a predetermined value, an additional test cycle can be performed. In another embodiment, the test cycles are repeated for at least a minimum time and up to a maximum time, regardless of the difference between the temperatures at t2 and t1. The method can include comparing the deviation with a predetermined tolerance.

[0009] In one embodiment, the dry cycle includes a drilling or milling process. The dry cycle may also include one or more tool changes, rapid traverse, A / B indexing, and spindle speed / feed adjustments. The predetermined temperature can be in the range of 0.5 to 5.0 °C. The CNC machine may be at ambient temperature prior to an initial test cycle. In one embodiment, the probing step is performed with the temperature control mechanism both switched off and switched on.

[0010] In at least one embodiment, a non-transient, computer-readable storage medium can be provided. This non-transient, computer-readable storage medium can store instructions for evaluating the effectiveness of a CNC machine's thermal compensation mechanism. When executed by a computer, the instructions can cause the computer to perform the following functions: receiving information from a CNC machine about the first position of an artifact bore relative to the CNC machine at a temperature T1 and a second position of the artifact bore relative to the CNC machine at a temperature T2 higher than T1, and calculating the deviation of the second position from the first position to determine the effectiveness of the CNC machine's thermal compensation mechanism. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a perspective view of an artifact used to analyze the thermal behavior of CNC machines, according to one embodiment; Fig. 2 is a top view of an artifact attached to a parts table, according to one embodiment; Fig. 3 is a side view of an artifact attached to a parts table, according to one embodiment; Fig. Figure 4 is another side view of the artifact from Fig. 3, wherein the parts table is rotated by 180 degrees; Fig. 5 is an algorithm for characterizing the thermal behavior of CNC machines according to one embodiment; Fig. Figure 6 is a simplified schematic representation of a computer system that can be used to implement the algorithm from Fig. 5 to be carried out according to one embodiment; Fig. Figure 7 is an example of temperature test data showing the temperature change of a CNC machine bed and a CNC machine spindle over time; Fig. Figure 8 is an example of linear deviation test data for a bore in the X, Y and Z directions with thermal compensation switched off and switched on; Fig. Figure 9 is an example of linear deviation test data for another bore in the X, Y, and Z directions with thermal compensation switched off and on; and Fig. Figure 10 is an example of linear deviation test data for six bores in the X direction with thermal compensation enabled. DETAILED DESCRIPTION

[0011] As necessary, detailed embodiments of the present invention are disclosed; however, it should be understood that the disclosed embodiments are merely exemplary of the invention, which can be implemented in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or reduced in size to show details of certain components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art how they may use the present invention in different ways.

[0012] A wide variety of machining operations can be performed using CNC machines. For example, milling machines, lathes, drilling machines, electrical discharge machining (EDM) machines, routers, cutters (e.g., water, plasma, laser, etc.), grinding machines, welding machines, punching machines, painting machines, and others can all be designed as CNC machines. The operating principles of CNC machines are familiar to the average professional in the field and will not be explained in detail here. Generally, CNC machines include a worktable that moves along the X and Y axes and a tool spindle that moves along the Z axis. The workpiece is mounted on the worktable, and the operation is performed by moving the workpiece along the X and Y directions and the tool along the Z direction. Alternatively, the workpiece can be held stationary, and the tool can be moved along the X, Y, and Z directions.More advanced CNC machines can also include rotations around one or more axes using a combination of rotary tables and / or pivots.

[0013] Generally, CNC machines comprise numerous components, such as a spindle, ball screw, indexing table, pivot, machine stand, bed, fixture, and others. These components may each have their own geometry and may be made from different materials. Consequently, due to differences in size and shape and / or differences in thermal expansion properties (e.g., CTEs), the components may react differently to temperature changes. In an attempt to compensate for the thermal expansion or thermal drift of machine components, CNC machine suppliers have developed algorithms that use temperature data acquired from one or more locations on the machine to adjust the commanded position of the tool and / or workpiece, ensuring precise relative positioning.Thermal compensation can also include the use of various temperature control mechanisms. For example, a CNC machine may include air or liquid cooling, fans, heat sinks, or other mechanisms for heat removal or other temperature control.

[0014] However, thermal compensation may not accurately correct the thermal expansion of the CNC machine for several reasons. One possibility is that the calculations performed by the algorithm are inaccurate. The algorithm may receive the correct inputs (e.g., temperature data), but it fails to make the correct adjustments to the commanded position of the tool and / or workpiece, resulting in a deviation that exceeds an acceptable tolerance. These inaccuracies could be caused by incorrect calculations, faulty material property data, incorrect material selection, or other sources of error. Another possibility is that the inputs for the algorithm are incorrect. For example, the temperature data may be inaccurate, there may be too few temperature sensors, the sensors may be positioned incorrectly, or there may be other complications with the input data.Another potential problem is that the temperature control mechanisms are ineffective. The algorithm may require air or liquid cooling of a component or area within the machine to reduce the temperature, but the cooling may be insufficient (or too effective), or the temperature control device may malfunction.

[0015] A failure of the thermal compensation mechanism(s) can occur in one or more dimensions. For example, the position of all three axes (X, Y, Z) may be inaccurate, or only one or two may be. Furthermore, if more than three axes are present, such as in a 5-axis machine, the positioning may be accurate in the X, Y, and Z directions for certain orientations, but not in others. Additionally, problems may only occur at specific temperatures or temperature ranges. Consequently, detecting when a thermal compensation system is malfunctioning can be challenging.

[0016] The need for highly controlled tolerances in CNC machining is growing, and the thermal performance of the CNC machine is a crucial factor in achieving tight tolerances. Buyers of CNC machines would benefit from a method for characterizing the thermal behavior of CNC machines to ensure that the machines maintain their target tolerances. With reference to Fig. References 1 to 5 disclose methods for characterizing the thermal behavior of CNC machines and analyzing the effectiveness of their thermal compensation mechanisms. These methods enable the thermal compensation mechanisms of a CNC machine to be tested to confirm that the thermal compensation functions correctly under varying conditions and that the required tolerances are maintained. If it is found that the thermal compensation is not functioning correctly, the methods can assist in diagnosing and correcting the problem(s).

[0017] With reference to Fig. 1. An artifact 10 is provided which can be used in the disclosed methods. The artifact 10 can have highly precise dimensions and be made of a material with a very low coefficient of thermal expansion (CTE). Any material with a suitably low CTE can be used for the artifact 10 (e.g., less than 10 × 10⁻⁶). -6 m / m K). In one embodiment, the artifact is formed from a rock or mineral, such as granite. The artifact 10 can have any shape, but in at least one embodiment it is a rectangular prism, as in Fig. Figure 1 shows that the artifact 10 can have multiple faces 12. For an artifact 10 that is a rectangular prism, the faces can be designated as front (F), back (B), left (L), right (R), top (T), and bottom (BT). One or more bores 14 can be formed in each face 12. The bores 14 can have high-precision dimensions (e.g., submicron tolerances). For example, if the bores 14 have a circular cross-section, as shown in Figure 1, the bores 14 can be designed to be 12. Fig. As shown in Figure 1, the diameter and / or depth of the bores 14 can be highly precise and remain so over a specific temperature range. High-precision sleeves (not shown) can be inserted into the bores 14 to further support the provision of highly precise dimensions of the artifact. The sleeves can also be made of a low CTE material and can have very high-precision dimensions (e.g., submicron tolerances) that remain precise over a specific temperature range (e.g., thermally qualified precision).

[0018] The front (F), right (R) and top (T) surfaces 12 of artifact 10 are in Fig. Figure 1 shows each face 12 with two holes 14; however, some faces may have zero holes, one hole, or more than two holes. Each hole 14 may be assigned a designation based on the face on which it is located and a number. The in Fig. The six holes 14 shown in Figure 1 can thus be designated F1, F2, R1, R2, T1, and T2, as illustrated. The holes 14 can have any size (e.g., diameter and depth for a cylindrical hole) that corresponds to the size of a milling, drilling, or other machining operation for which the machine is programmed. The holes 14 on each surface 12 can be aligned or randomly arranged. For example, holes F1 and F2 are horizontally aligned, while R1 and R2 have a diagonal spacing or orientation.

[0019] With reference to Fig. 2-4 The artifact 10 can be attached to a parts table 20 of a CNC machine. Although CNC machines can have numerous configurations, Fig. 2-4 described in relation to a 5-axis B-over-A configuration. In this configuration, the parts table 20 can be referred to as the B-table. The B-table can rotate about the Z-axis, as shown in Fig. Figure 2 shows that the artifact can be rotated a full 360 degrees from a starting point (e.g., 0 degrees). The CNC machine can be programmed to rotate the B-table to specific positions, such as 0, 90, 180, and 270 degrees, as shown in Figure 2. Fig. Figure 2 shows the artifact at position B = 270 degrees, and positions 0, 90, and 180 degrees are shown with dashed lines. However, additional or other positions can be used, for example, intervals of 30, 45, or 60 degrees.

[0020] In Fig. 2-4 The spindle is designed to move along the Z-axis, the B-table rotates around the Z-axis, and the B-table can also be rotated around the X-axis by means of a pivot pin (not shown). The angle of rotation around the X-axis can be referred to as the A-position. Fig. 2 is at 90 degrees, which leads to the bores T1 and T2 of the upper surface of artifact 10, which faces the spindle. Fig. In step 3, the B-table is still in position B = 270 degrees, and position A has been changed to 0 degrees. With the B-table rotated around the X-axis, one of the side surfaces 12 now faces the spindle. Therefore, various bores 14 are accessible to the spindle, such as bores R1 and R2. Fig. In step 4, the B-table was rotated to position B at 90 degrees and position A at 180 degrees. As a result, artifact 10 was relative to Fig. 3 is turned upside down, but also rotated around the Z-axis (position B) so that the same surface 14 faces the spindle. Using a combination of positions A and B, the artifact 10 can be rotated so that each surface 12 can face the spindle (except for the surface attached to the parts table 20). This can make each bore 14 of the spindle accessible.

[0021] Artifact 10 can be used to characterize the thermal behavior of a CNC machine, such as a 5-axis machine as described above. This characterization can be used for various purposes, including machine acceptance testing and / or troubleshooting. As described above, CNC machine suppliers often incorporate temperature compensation mechanisms into their machines to correct changes in position due to thermal expansion. The disclosed thermal behavior characterization process can enable a customer or potential customer to evaluate the accuracy and effectiveness of the temperature compensation mechanisms prior to accepting delivery or as a condition of final payment (e.g., machine acceptance testing).The thermal characterization process can also enable CNC machine suppliers to troubleshoot their thermal compensation mechanisms under real-world conditions and in a variety of situations.

[0022] The thermal growth characterization (TGC) process generally comprises a probing routine and a dry cycle, which together form a test cycle. The probe can be inserted into the spindle, replacing the tool. The probing routine may involve inspecting one or more holes (or other positioning features) of an artifact to determine the hole center position (e.g., X and Y coordinates) and / or the hole depth (e.g., Z coordinate). Positions other than the hole center can also be used, such as top / bottom or sides. The position can be a relative position between the hole and the CNC machine (e.g., spindle and probe).By rotating the parts table, for example by adjusting positions A and B as described above, the artifact can be rotated so that every surface of the probe (except the surface attached to the parts table) is exposed. Although every surface of the artifact faces the probe, one, some, or all of the holes on that surface can be probed to determine the position of the hole center and / or depth. The artifact can then be rotated so that a different surface is exposed to the probe, and the measurements can be repeated. This process can be continued until every surface and hole has been probed. If a shorter probing routine is desired, some surfaces and / or holes can be skipped in the probing routine.Furthermore, the number of surfaces and / or bores probed can remain the same for each cycle, or the probing routine can change from cycle to cycle. For example, a full probing routine can be performed for the first and last test cycles, but a shorter probing routine could be performed for some or all of the intermediate test cycles to reduce the overall time of the TGC process.

[0023] The probing routine can be performed with the CNC machine's thermal compensation (TC) mechanisms switched on or off. In at least one embodiment, the probing routine is performed once with thermal compensation switched off and then again with thermal compensation switched on (or vice versa). Performing the probing routine with TC switched on or off can provide additional insight into the effectiveness and / or accuracy of the thermal compensation. During the probing routine, thermal compensation can be switched on or off at any desired interval. For example, all holes can be measured with TC switched off, and then the probing routine can be performed again with TC switched on. Alternatively, TC can be switched on and off during the probing of each surface or the probing of each hole. For example, the holes of the top surface (e.g.,T1 and T2) are probed with TC switched off before rotating the artifact and then probed again with TC switched on, so that a different surface is exposed to the probe.

[0024] Before (or after) the probing routine, a dry cycle can be performed by the CNC machine. A dry cycle can include some or all of the normal routines performed by a CNC machine when machining a workpiece. In addition to basic machining processes, such as spindle rotation and table movement, other processes that occur during a machining operation can also be included in the dry cycle. For example, the dry cycle can include tool changes, rapid traverses, A / B indexing, spindle speed / feed adjustments, or other processes. Accordingly, the dry cycle can simulate some or all of the operations that would normally occur within the CNC machining center, but without an installed tool or actual workpiece.

[0025] Prior to the first test cycle, probe calibration or an accuracy procedure may be performed. In one embodiment, a gauge R&R test may be performed prior to the test cycles. Gauge R&R tests (repeatability and reproducibility) are familiar to average professionals in the field and will not be explained in detail. In short, gauge R&R tests measure the level of variability caused by the measurement system itself and compare it to the observed total variability to determine the system's feasibility. Repeatability refers to the variation in measurements taken by a specific person or instrument for the same target and under the same conditions. Reproducibility refers to the variation caused when different operators or instruments measure the same target.The required level of repeatability and reproducibility to pass the Gage R&R test can vary from customer to customer (or supplier to supplier, etc.). For example, some processes may require an R&R of up to 5%, up to 10%, up to 15%, or other values. The probe calibration or accuracy procedure (e.g., Gage R&R) can be performed at a single artifact location, such as A = 90 and B = 0, or it can be performed at multiple artifact locations.

[0026] In at least one embodiment, the TGC process can be initiated by a cold start. A cold start can involve starting the machine after it has been shut down long enough to cool down to ambient conditions (e.g., temperature). Depending on the machine type, size, ambient conditions, and other factors, the required shutdown time to reach ambient conditions can vary. Generally, if the machine remains stationary for 24 hours, ambient temperature will be reached; however, it can take 12, 10, 8, 6 hours, or less. The TGC process can be performed at any ambient temperature of the machine during operation. Accordingly, in at least one embodiment, no enclosure (e.g., tenting) is arranged around the machine, and no external heating or cooling (apart from typical building heating, ventilation, and air conditioning systems) is provided.In another embodiment, however, the ambient temperature can be controlled within a specific range. For example, the ambient temperature can be controlled within 20–30 °C or a sub-range therein, such as 24 ± 2 °C. Generally, adequate preparation for the TGC process can include setting up a CNC machine in the morning or afternoon, allowing the machine to acclimatize, and performing a cold start the following morning.

[0027] When the TGC process is started from a cold start, the CNC machine components can experience a wider temperature range. For example, the CNC machine components start at ambient temperature and can reach a steady temperature during the TGC process. This can allow the TGC process to analyze more temperature and probe position data points than if the process were started on a warmed-up machine. Although there are advantages to starting with a cold start, the TGC process can also be initiated from a non-cold start (e.g., a machine above ambient temperature).

[0028] After the CNC machine has been started and the optional probe calibration or accuracy procedure is complete, the first test cycle can be performed. As described above, the test cycle can include a probing routine followed by a dry cycle (or vice versa). During the probing routine, some or all of the holes in the artifact can be measured with respect to their hole center coordinates (e.g., X, Y, and Z) or any other suitable reference position. The position of the hole center (or other reference point) can be relevant to the CNC machine (e.g., for the spindle and probe). In one embodiment, the probing routine can establish a reference position for each hole during the first cycle, corresponding to the programmed or intended relative position between the hole and the CNC machine.In another embodiment, the reference position for each bore can be known and stored in memory before the first test cycle (e.g., from a previous probing routine). During subsequent test cycles, the relative positions of each bore can be compared to the bore's reference position to determine any deviation from the reference position. The probing routine can include measurements with thermal compensation switched off or on, as described above. Each surface and bore can be probed, or a representative or statistically sufficient number can be probed. The probe measurement data are recorded and stored for each cycle.

[0029] After completion of the probing routine, a dry cycle can be performed by the CNC machine. The dry cycle can include any or all of the programmed steps for a CNC machining operation (e.g., milling or drilling), but the tool and workpiece are not included during the dry cycle. The dry cycle can include operations such as tool changes, rapid traverses, A / B indexing, spindle speed / feed adjustments, or other processes. The dry cycle therefore accurately simulates an actual CNC machining operation, resulting in precise temperature changes within the machine. Temperature sensors within the machine, for example, mounted on the machine base, a fixture, the workpiece, the spindle or spindle bearing and motor, the ball screw, the parts table, the pivot, the machine stand, the bed, etc., can measure, record, and store temperature data during the test cycle.Temperature data can be measured and recorded at defined intervals throughout the entire test cycle (manually or programmed), at the start and end of the test cycle, continuously throughout the entire test cycle, or according to any other suitable algorithm. The temperature sensors used to record the temperature data during the test cycle can be the same sensors used by CNC machine temperature compensation mechanisms, or they can be additional sensors added to the machine for the TGC process (or a combination of both).

[0030] The length of the drying cycle can vary based on the type of CNC machine and the type of simulated machining operation. In one embodiment, the drying cycle has a length of 5 to 60 minutes, or any partial range thereof. For example, the drying cycle can last 10 to 50 minutes, 15 to 45 minutes, or 15 to 30 minutes. At the end of the drying cycle, the test cycle can be completed. The temperature data can then be analyzed to determine whether additional test cycles should be performed. In at least one embodiment, if the difference between the maximum and minimum temperatures over a certain period of time is less than a predetermined value, no further test cycles are performed. If the temperature difference exceeds the predetermined value, another test cycle (e.g., a probing routine and a drying cycle) is performed.

[0031] The predetermined value and duration can vary based on the type of CNC machine and the type of simulated machining operation. In one embodiment, the predetermined value is from 0.5 to 5 °C or any sub-range therein. For example, the predetermined value can be from 0.5 to 4 °C, 0.5 to 3.0 °C, or 0.5 to 2.0 °C, including 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, or 4.0 °C. In another embodiment, the duration can be from 0.25 to 2 hours or any sub-range therein. For example, the duration can be 0.5 hours, 1 hour, or 1.5 hours. The duration over which the temperature difference is determined can be a moving time window. For example, if the duration is one hour, for each temperature measurement, the temperature at the time of measurement can be compared to the temperature one hour before the measurement. Alternatively, the temperature differences could be compared at regular intervals.For example, every hour after the start of the first cycle (e.g., if starting at 9:00 AM, check at 10:00 AM, 11:00 AM, at noon, 1:00 PM, etc.).

[0032] In at least one embodiment, a minimum time for the TGC process can be set. Running the TGC process for at least a certain duration can ensure that the CNC machine reaches, or is approximately at, a steady-state temperature. It can also allow for at least a certain number of probing routines and dry cycles to be performed in order to generate sufficient data for analysis. In one embodiment, the minimum runtime for the TGC process can be at least one hour, for example, at least 1, 2, 3, or 4 hours. Accordingly, if the TGC process is executed for a shorter time than the minimum runtime and the temperature difference after a dry cycle is below the predetermined value, the TGC process is not terminated. Instead, additional test cycles can be performed until the minimum runtime is reached.If the TGC process has completed its minimum runtime and the temperature difference is below the predetermined value, the TGC process can be terminated without executing any additional test cycles. If the temperature difference is above the predetermined value, the minimum runtime will have no effect on the TGC process.

[0033] In at least one embodiment, a maximum time can be set for the TGC process. This maximum time can be set so that the TGC process can be completed in a single day, allowing a potential customer to schedule machine acceptance on the same day as the TGC process. The maximum time can also prevent the TGC process from running beyond the shutdown time of the facility where the TGC process is performed, thus eliminating the need for additional personnel monitoring. Additionally, a maximum time can be set that corresponds to the period after which the CNC machine's steady-state temperature should be reached. CNC machines do not typically maintain their temperature indefinitely unless there is a problem or malfunction.The maximum time can therefore be used to stop the TGC process so that the source of the problem can be identified and addressed. In one embodiment, the maximum runtime for the TGC process can be less than or equal to 24 hours. For example, the maximum runtime can be less than or equal to 18 hours, 12 hours, 8 hours, or 6 hours. Accordingly, if the runtime of the TGC process is longer than or exceeds the maximum time, the TGC process can be stopped, even if the temperature difference exceeds the predetermined value. If the runtime of the TGC process is shorter than the maximum time, additional test cycles can be performed (if the temperature difference is above the predetermined value).

[0034] The minimum and maximum times for the TGC process can vary depending on several factors, including the type of CNC machine, probing routine and drying cycle times, ambient temperature, the type and number of operations performed during the drying cycle, and others. Accordingly, the minimum and maximum times may differ from those described above. Furthermore, the minimum and maximum times for the TGC process can be omitted. For example, if it is desirable to perform the TGC process as quickly as possible, the minimum time requirement can be removed so that the process terminates as soon as the temperature difference requirement is met.Similarly, if it is desired to perform an extremely thorough TGC process and time or potential machine problems are not concerns, the maximum time requirement can be removed so that the TGC process continues indefinitely until the temperature difference requirement is met or the process is manually stopped.

[0035] With reference to Fig. Figure 5 shows a flowchart of the TGC process 100 according to one embodiment. In step 102, the TGC process is initiated. In step 104, the CNC machine is cold-started at ambient temperature, and a gauge run-through (Gage-R&R) test is performed on the probe. If the results of the Gage-R&R test are acceptable, a test cycle is performed in step 106. The test cycle comprises a probing step 108 and a dry cycle step 110. During the first test cycle, the probing step 108 can establish a reference point for each hole, as described above. In subsequent test cycles, the probing step 108 can measure the position of each individual hole, which can be relative to the CNC machine. The deviation of each hole position from the reference point can also be calculated. The position, deviation, and temperature data can be recorded and stored during each test cycle 106.

[0036] After the test cycle, a temperature difference calculation is performed at step 112. If the difference between the maximum and minimum temperatures is greater than 1 °C in the last hour (i.e., Tmax - Tmin is not less than 1 °C in the last hour), it is determined that the temperature is not at or near a steady state. If the temperature difference in the last hour is not less than 1 °C, the runtime of the TGC process at step 114 is compared to the maximum runtime of 8 hours. If the TGC process has not been executed for 8 hours or more, another test cycle is performed at step 106. If the TGC process has been running for 8 hours or more, no additional test cycles are performed, and a second gauge R&R test is performed on the probe at step 118.

[0037] If the temperature difference calculation at step 112 determines that the difference between the maximum and minimum temperatures is less than 1 °C in the last hour (i.e., Tmax - Tmin is less than 1 °C in the last hour), the temperature is determined to be at or near steady state. If the temperature difference in the last hour is less than 1 °C, the runtime of the TGC process at step 116 is compared to the minimum runtime of 3 hours. If the TGC process has not run for 3 hours, another test cycle is performed at step 106. If the TGC process has run for 3 hours, no additional test cycles are performed, and a second gauge run-and-reverse (Gage R&R) test is performed on the probe at step 118. After the second Gage R&R test, the TGC process is terminated at step 120.

[0038] The in Fig. The TGC process shown in Figure 5, 100, is an example of a TGC process and is not limiting with respect to the disclosed thermal characterization process. As described above, the parameters, such as the minimum time, maximum time, temperature difference, and temperature difference time period, can vary depending on the CNC machine, the type and length of the probing routine and dry cycle, and other factors. Furthermore, not all steps in process 100 may be required, as described above. For example, the minimum and / or maximum time requirements can be omitted. In addition, the gauge R&R test can be replaced by another probe calibration or accuracy test, or it can be omitted entirely.

[0039] Following a TGC process, temperature, position, and deviation data can be retrieved and analyzed. This data can be used to determine whether the CNC machine's thermal compensation mechanisms are functioning correctly. Depending on the user, customer, or supplier, the acceptable deviation from the probe's reference / intended relative position can vary. For applications requiring very tight tolerances, the acceptable deviation may be small. Conversely, if tight tolerances are not required, the acceptable deviation may be relatively large. Furthermore, the acceptable deviation can change depending on which axis is being analyzed. For example, Z-axis deviation may not be as critical as X- and Y-axis deviations in some applications (or vice versa).In one embodiment, the acceptable deviation in one or all directions may be within 1 to 50 µm, or a subrange therein, such as 5 to 30 µm, 5 to 25 µm, 5 to 15 µm or at about 10 µm.

[0040] The collected deviation data can be used to analyze the effectiveness of the machine's thermal compensation mechanisms, troubleshoot these mechanisms, make a purchase or machine acceptance decision, or for any other purpose. If the thermal compensation functions effectively for the deviation requirements, a customer can accept delivery of the machine, make a payment, or otherwise enter into a purchase agreement. A machine supplier can use the TGC process to perform quality control of the machines and their thermal compensation mechanisms. If it is determined that the thermal compensation mechanisms are not functioning adequately in one or more axes, a customer can refuse delivery or payment, or request the supplier to make the necessary adjustments to meet the deviation requirements.A machine supplier can also use a failed TGC process to resolve problems with thermal compensation mechanisms. For example, the calculations used in the thermal compensation algorithms may be inaccurate, or temperature control mechanisms (e.g., cooling systems, fans, etc.) may not function properly.

[0041] The temperature data recorded during the thermal characterization process can also be useful in assessing the effectiveness of thermal compensation mechanisms or in troubleshooting. For example, if the thermal characterization process runs for the maximum permissible duration, this may indicate a problem with the machine. Generally, CNC machines reach relatively steady-state temperatures within 6-10 hours. Therefore, if the machine runs for 8 hours and the temperature continues to rise, there may be a problem with the machine. For machines that reach a relatively steady-state temperature, the temperature data shows how quickly a steady state is reached and what temperatures the various machine components experience.

[0042] To provide additional context for various aspects of the present disclosure, the following discussion will offer a brief, general description of a suitable computing environment in which the various aspects of the disclosure can be implemented. Although one or more embodiments of the disclosure relate to the general context of computer-executable instructions that can be executed on one or more computers, those skilled in the art will recognize that the subject matter can also be implemented in combination with other program modules and / or as a combination of hardware and software.

[0043] In general, program modules comprise routines, programs, components, data structures, etc., which perform specific tasks or implement certain abstract data types. Furthermore, those skilled in the art will recognize that aspects of the methods according to the invention can be carried out with other computer system configurations, including single-processor or multi-processor computer systems, minicomputers, mainframe computers, personal computers, handheld wireless computing devices, microprocessor-based or programmable consumer electronics, and the like, all of which can be operationally coupled with one or more associated devices. Aspects of the disclosure can also be carried out in distributed computing environments in which certain tasks are performed by remote processing devices connected via a communication network.In a distributed computing environment, program modules can be located in both local and remote storage devices.

[0044] The disclosed methods and processes can be carried out by a computer or computers that may be part of a CNC machine (or otherwise in communication with the machine). Alternatively, data can be generated by the CNC machine and transmitted to a computer that is not in communication with the CNC machine. With reference to Fig. Figure 6 shows a simplified schematic representation of a computer system 200, which is used to perform the disclosed functions. The computer system may include a controller 202, such as a processor or microprocessor. It may also include a memory 204 and RAM 206. The computer may have an input 208, such as a mouse, a keyboard, or another interface, and an output 210, such as a display. The computer system can receive information from the CNC machine 212, such as time, temperature, position, deviation, and other information, as described above.

[0045] Computer System 200 is a simplified schematic representation, and it is understood that the computer(s) may comprise any number of microprocessors, integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read-only memory (ROM), electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or other suitable variants thereof), and software, which work together to perform the operation(s) disclosed herein. Additionally, any one or more of the computers may be designed to execute a computer program written in a non-transitory, computer-readable medium, which is programmed to perform any number of functions as disclosed.In general, persistent (non-transient) storage can include all forms of storage that retain data when a computer or other device is turned off. This includes, but is not limited to, hard disk drives, CDs, DVDs, magnetic tapes, solid-state drives, portable USB drives, and any other suitable form of persistent storage.

[0046] An exemplary environment for implementing various aspects of the present disclosure may include a computer comprising a processing unit, system memory, and a system bus. The system bus connects system components, including but not limited to system memory, to the processing unit. The processing unit may be any of the various commercially available processors. Dual microprocessors and other multiprocessor architectures may also be used as the processing unit.

[0047] The system bus can be any of several types of bus structures, which can further connect to a memory bus (with or without memory control), a peripheral bus, and a local bus using a variety of commercially available bus architectures. System memory can include read-only memory (ROM) and / or random-access memory (RAM). A basic input / output system (BIOS) is stored in non-volatile memory, such as ROM, EPROM, or EEPROM, and contains the basic routines that assist in transferring information between components within the computer, such as during startup. RAM can also include high-speed RAM, such as static RAM for temporary data storage.

[0048] A number of program modules can be stored in the drives and in RAM, including an operating system, one or more application programs, other program modules, and program data. All or parts of the operating system, the applications, the modules, and / or the data can also be cached in RAM. It should be noted that the subject matter of this disclosure can be implemented with various commercially available operating systems or combinations of operating systems.

[0049] The computer can operate in a networked environment using logical connections via wired and / or wireless communication with one or more remote computers. The remote computer(s) can be a workstation, server computer, router, personal computer, laptop, personal digital assistant, mobile device, microprocessor-based entertainment device, peer device, or other common network node, and can include many or all of the elements described relative to the computer. The logical connections shown include wired / wireless connectivity to a local area network (LAN) and / or larger networks, such as a wide area network (WAN).Such LAN and WAN network environments are commonplace in offices and businesses, enabling company-wide computer networks, such as intranets, which can all connect to a global communication network, such as the Internet. EXAMPLES

[0050] With reference to Fig. Figures 7-10 show examples of temperature and deviation data obtained using the disclosed TGC processes. Fig. Figure 7 shows temperature data from sensors mounted on the CNC machine bed and the CNC machine spindle. As can be seen in the graph, the spindle temperature rises rapidly from a cold start before increasing at a more gradual rate. In contrast, the bed temperature exhibits a more gradual temperature increase from a cold start. Depending on the minimum runtime, temperature difference, and temperature difference time period, a thermal behavior characterization process could be performed using the temperature data from the sensors. Fig. 7. Continue to perform additional test cycles or it could be stopped due to the slowing of the temperature increase.

[0051] Fig. 8 and Fig. Figure 9 shows test data for two holes in an artifact, hole 1 (B1) and hole 2 (B2). The holes were probed in the X, Y, and Z directions with and without thermal compensation of the CNC machine (referred to as "woc" and "wc" respectively). The acceptable linear deviation for these tests was 10 µm with thermal compensation enabled. As shown in Fig. 8 and Fig. As shown in Figure 9, the Y and Z deviations of both bores remain within 10 µm of their start / reference position with thermal compensation enabled. The Y deviation remains within 10 µm even with thermal compensation disabled, and the Z deviation comes very close to the 10 µm limit with thermal compensation disabled near the end of the test. In contrast, the X deviation of both bores significantly exceeds the acceptable limit of 10 µm with thermal compensation disabled and with it enabled. Accordingly, the TGC process has detected that the X-axis thermal compensation is not working effectively.

[0052] Fig. Figure 10 shows test data for the X-axis deviation of six bores (F1, F2, L1, L2, R1, R2) in an artifact. The test data were acquired following a correction of the thermal compensation mechanism of a CNC machine, which was failing to meet an acceptance requirement of 10 µm in the X-direction (as, for example, in Fig. (shown in Figures 7-8). After correcting the thermocompensation mechanism, another TGC process was performed on six bores with thermocompensation enabled to determine if the corrections were sufficient. The X-axis deviation data for each bore are shown, with the data offset having a uniform starting position. As shown in the graph, each of the X-axis deviations is well within the 10 µm limit. In fact, each bore is within 5 µm of the reference position.

[0053] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the description are descriptive and not limiting, and it is understood that various modifications can be made without deviating from the essence and scope of the invention. Furthermore, the features of different implementation embodiments can be combined to form further embodiments of the invention.

Claims

[1] Procedure, encompassing: Mounting an artifact (10) with a bore (14) on a CNC machine (212); determining a first position of the artifact bore (14) relative to the CNC machine (212) at a temperature T1 and a second position of the artifact bore (14) relative to the CNC machine (212) at a temperature T2, which is higher than T1; and calculating a deviation of the second position from the first position in order to determine a thermal stability of the CNC machine (212). [2] Method according to claim 1, further comprising operating the CNC machine (212) to increase the temperature from T1 to T2. [3] Method according to claim 1 or 2, wherein the CNC machine (212) comprises a spindle and probe and the determining step comprises determining a first and second position of the artifact bore (14) relative to the spindle and probe. [4] Method according to any of the preceding claims, further comprising measuring the temperature at one or more positions on the CNC machine (212). [5] Method according to any of the preceding claims, further comprising activating a CNC machine thermocompensation mechanism prior to determining the second position. [6] Method according to one of the preceding claims, wherein the step of determining the second position is performed with the CNC machine thermal compensation mechanism activated and with the thermal compensation mechanism deactivated, and the calculation step comprises calculating a deviation of the second position from the first position with the thermal compensation mechanism activated and deactivated. [7] Method according to any of the preceding claims, wherein the artifact (10) comprises at least two bores (14) and the determination step comprises determining a first position of each artifact bore (14) relative to the CNC machine (212) at a temperature T1 and a second position of each artifact bore (14) relative to the CNC machine (212) at a temperature T2; and the calculation step comprises calculating a deviation of the second position of each artifact bore (14) from the first position of each artifact bore (14). [8] Method according to one of the preceding claims, wherein the determination step further comprises determining a position of the artifact bore (14) relative to the CNC machine (212) at a plurality of temperatures which are higher than T1; and the calculation step comprises calculating a deviation of the position at each of the plurality of temperatures from the first position. [9] Procedures, comprehensive: Mounting an artifact (10) with a bore (14) on a CNC machine (212); performing a test cycle, including: Checking the bore of the artifact (10) to determine its position relative to the CNC machine (212); and Performing a dry cycle, which includes one or more CNC machining processes; and Calculating a deviation of the bore position from a reference position between the bore (14) and the CNC machine (212). [10] Method according to claim 9, further comprising repeating the test cycle one or more times and calculating a deviation of the bore position from a reference position between the bore (14) and the CNC machine (212) for each test cycle. [11] Method according to claim 9 or 10, further comprising monitoring a temperature of at least one position on the CNC machine (212) and comparing a temperature of the at least one position at a second time t2 with a temperature at a first time t1. [12] Method according to claim 11, wherein if the difference between the temperature at t2 and the temperature at t1 is greater than a predetermined value, an additional test cycle is performed. [13] Method according to claim 11, wherein test cycles are repeated for at least a minimum time and up to a maximum time, regardless of any difference between the temperatures at t2 and t1. [14] Method according to any one of claims 9 to 13, further comprising comparing the deviation with a predetermined tolerance. [15] Method according to any one of claims 9 to 14, wherein the dry cycle comprises a drilling or milling process. [16] Method according to any one of claims 9 to 15, wherein the drying cycle further comprises one or more tool changes, rapid traverse, A / B indexing and speed / feed. [17] Method according to any one of claims 12 to 16, wherein the predetermined value is in the range of 0.5 to 5.0 °C. [18] Method according to any one of claims 9 to 17, wherein the probing step is performed with a temperature control mechanism switched off and with a temperature control mechanism switched on. [19] Method according to any one of claims 9 to 18, wherein the CNC machine (212) is at ambient temperature before a first test cycle. [20] Non-transitory computer-readable storage medium which stores instructions for assessing the effectiveness of a CNC machine thermocompensation mechanism which, when executed by a computer, cause the computer to perform the following functions: Receiving information from a CNC machine (212) about a first position of an artifact bore (14) relative to the CNC machine (212) at a temperature T1 and a second position of the artifact bore (14) relative to the CNC machine (212) at a temperature T2 which is higher than T1; and Calculating the deviation of the second position from the first position to determine the effectiveness of the CNC machine's thermocompensation mechanism.

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