A method and device for shrink-fitting a tool shank into a sleeve portion of a tool holder to protect it from overheating, and for removing a tool shank from the sleeve portion.

Abstract

The present invention provides a method and device for shrink-fitting a tool shank into a sleeve portion of a tool holder to protect it from overheating, and for removing the tool shank from the sleeve portion. [Solution] A method for operating a shrink-fit device having an induction coil for heating the sleeve portion of a tool holder while avoiding temperatures harmful to the sleeve portion is provided, wherein several different characteristic variables of the induction process that change during heating, particularly when the sleeve portion reaches a critical temperature, are monitored, and if at least one of the characteristic variables exceeds a predefined limit, the heating of the sleeve is terminated.

Description

Background Art

[0001] The shrink fit chuck has established a firm position in the market over many years as a tool holder that also meets high machining requirements.

[0002] An important component of any shrink fit chuck is its sleeve part, which keeps each tool shank in a press-fitted state during operation. This is because the sleeve part has an inner diameter that is smaller than the outer diameter of the tool shank to be clamped at room temperature.

[0003] Press-fitting is brought about during the process of clamping the tool shank. To do this, the sleeve part is induction heated. As a result, the sleeve part expands to such an extent that its inner diameter becomes temporarily larger than the outer diameter of the tool shank to be clamped. Then, this tool shank is inserted into the sleeve part, and after they cool down together again, it is held in a press-fitted state by a large force by the sleeve part.

[0004] The tool shank is removed from the shrink fit state again in reverse order. However, it is necessary to wait for an appropriate period of time so that the sleeve part can be easily pulled out. Specifically, it is the time when the sleeve part is already very hot and fully expanded, but not so much heat has flowed from the sleeve part into the tool shank yet, and the tool shank has not started to increase in temperature so much either.

[0005] The corresponding shrink fit device is known, for example, from (Patent Document 1).

[0006] Such shrink-fit devices carry some risk of failure, particularly during removal from the shrink-fit state. In some cases, the operator of the shrink-fit device may miss the proper timing to withdraw the tool shank and realize that the tool shank is not moving. If the operator mistakenly believes that the sleeve portion is still not hot enough, they may continue to heat the sleeve portion, and thus the sleeve portion may overheat and be damaged relatively rapidly.

[0007] Generally, to avoid overheating, appropriate shrinkage parameters must be set before the start of the shrink-fit process, depending on the sleeve portion being heated. These shrinkage parameters also include limits on the maximum heating of the shrink-fit chuck or its sleeve portion. This is complex and prone to problems.

[0008] Therefore, in many situations, a shrink-fit chuck, and thus its automatic identification of the sleeve portion, is used, and the shrinkage parameters are automatically set according to the identified sleeve portion.

[0009] This works fine if the shrink-fit chucks are properly marked, for example, by a label or data chip. However, problems arise when shrink-fit chucks are used from suppliers whose data is still not stored in a database accessible to the shrink-fitting machine or shrink-fitting equipment, as these chucks are not (still) "chip-marked".

[0010] Measuring the surface temperature of the sleeve portion has already been considered to avoid dependence on this point. However, this does not yield a satisfactory solution. This is because it is a highly dynamic heating process due to the skin effect, and within that range, the pure surface temperature may actually already be supercritical well before reaching the critical temperature at deeper locations inside the sleeve. Furthermore, such a sensor system is expensive and complex. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] German Patent Application Publication No. 19915412 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention is based on the objective of identifying a highly reliable operational method that can limit the heating of the sleeve portion of a shrink-fit chuck, thereby preventing overheating of the sleeve portion. [Means for solving the problem]

[0013] According to the present invention, in order to solve this problem, a novel method is proposed for operating a shrink-fit device having an induction coil, the method of heating the sleeve portion of the tool holder while avoiding the critical temperature of the sleeve portion.

[0014] According to the present invention, this method is characterized by monitoring several characteristic variables of the induction process (during heating). Such characteristic variables are those that change during heating, particularly as the sleeve portion approaches a critical value. If at least one of the monitored characteristic variables exceeds a predefined limit ("switch-off limit") relating thereto, heating of the sleeve is terminated.

[0015] The procedure according to the present invention, which uses multiple characteristic variables, significantly increases the guarantee that the sleeve portion does not overheat. Various characteristic values ​​can be combined with each other in terms of number and type as needed, thereby covering all uncertainties.

[0016] The present invention is particularly based on the finding that the sleeve portion strongly influences the behavior of the induction coil depending on its temperature, and therefore, by using several electrical characteristic variables of the induction process, it is possible to immediately identify changes in the characteristics of the target characteristic variable when they are observed, especially when the sleeve portion is about to reach a critical temperature.

[0017] It is also possible to utilize the fact that the magnetic behavior, particularly the permeability of the sleeve portion introduced into the induction coil, and therefore the inductance of the entire system, changes with the rising temperature of the sleeve portion. This effect becomes more pronounced as the temperature of the sleeve portion approaches the Curie point. Nevertheless, the first usable effect can sometimes be seen even near the normal switch-off temperature for shrink-fit chucks at around 350°C, and thus further limits on the characteristic variables can be defined.

[0018] However, in the temperature range up to 350°C, the dominant factor is the change in the overall electrical properties of the system.

[0019] Given this background, it should be noted that, according to the present invention, the term "characteristic variable" includes both characteristic variables that are mainly affected by magnetism, such as the inductance of an induction coil, and characteristic variables that are mainly affected by electricity, such as electrical resistance, current, or voltage, as well as external factors such as heating time, i.e., the duration of the induction process.

[0020] Otherwise, the characteristic variables of an inductive process may be directly measurable, such as instantaneous active current, voltage, and heating time, or they may be given by one or more different measurements obtained by calculation.

[0021] This invention represents a significant step toward the goal of enabling the safe shrink-fitting and removal of shrink-fit chucks for which specific characteristic data (characteristic data that defines how strongly and for how long the sleeve portion can be heated by the induction coil, even before the start of shrink-fitting or before removal from the shrink-fitted state) is unavailable.

[0022] The characteristic variables used in connection with the present invention have the advantage that they occur and can be observed almost or substantially independently of the size and exact geometry of the shrink fit chuck currently being handled in the shrink fitting device, and are based on the effects observed.

[0023] Furthermore, the characteristic variables generally exhibit different sensitivities, i.e., the characteristic variables react at different rates, for example, in a specific temperature range, and thus the above-mentioned safety can be ensured only by combining a plurality of characteristic variables.

[0024] This is a decisive step towards a completely autonomous identification of the time when the heating of the sleeve part of the shrink fit chuck must be terminated.

[0025] Combining the method according to the present invention with the problem of initial automatic identification of the shrink fit chuck is particularly suitable. The initial automatic identification is, for example, by an initial electrical test pulse to the shrink fit chuck, which provides characteristic feedback that can completely identify the shrink fit chuck in question or at least draw conclusions about its mass, and / or geometry, and / or dimensions. The method according to the present invention can be further ensured using such test pulses.

[0026] This approach will surely be useful in all cases where shrink fit chucks are shrink fitted for which exact data that can be read by the shrink fitting device to adjust the shrink parameters is not available.

[0027] In this way, i.e., by evaluating the aforementioned (initial electrical) test pulse (or alternatively by explicit prior knowledge), for example, a specific time until a specified (coil or effective) current is reached, information about the geometry and dimensions of the target shrink-fit chuck, such as the length of the shrink-fit chuck, is obtained. This information can, in some cases, be further used to define the (shrink-fit chuck's) specific switch-off limit values for the monitored characteristic variables, respectively, for each case or for the target shrink-fit chuck. For example, for a very short shrink-fit chuck, if a first switch-off limit value is defined for the characteristic variable "magnitude of the instantaneous effective current" (for preferred options, see below), for a long shrink-fit chuck (of the same diameter or a similar diameter), a second different switch-off limit value can be defined for the characteristic variable "magnitude of the instantaneous effective current".

[0028] Design options The preferred electrical characteristic variable used is the magnitude of the instantaneous effective current. After the start of heating, heating is terminated when the instantaneous effective current changes, particularly decreases, by a specific amount.

[0029] The inventor has recognized here that the following relationship can be well utilized.

[0030] The higher the temperature of the sleeve part, the greater the mutual inductance that opposes the induction coil used for heating. As a result, the instantaneous effective current induced by the induction coil decreases. This means that it is possible to conclude that there is still no risk that the sleeve part reaches the critical temperature, provided that the instantaneous effective current has not yet decreased by a specific amount.

[0031] Another or additional option is to use the instantaneous change in the effective current as a characteristic. For example, heating can be terminated when the effective current no longer changes by a specific minimum amount or specifically when the effective current changes again (by a specific (minimum) amount).

[0032] Here, the inventors have observed that as the temperature rises, the instantaneous active current initially continues to decrease, but when the sleeve portion is about to reach its critical temperature, the rate at which the active current decreases slows down significantly.

[0033] Another or additional option is to use the second derivative of the instantaneous active current with respect to time as a characteristic. As the sleeve portion approaches its critical temperature, the second derivative of the instantaneous active current with respect to time approaches zero.

[0034] Another or additional option is to use the heating time (from the start of heating) as a characteristic variable. Thus, the corresponding limit defines the maximum heating time (after which the heating process is terminated or the heating is switched off).

[0035] Furthermore, the instantaneous inductance of the entire system, including the induction coil and shrink-fit chuck, can also be used as a characteristic variable. For example, this instantaneous inductance can be determined by a test signal during continuous heating, and these values ​​can be controlled against limit values.

[0036] Furthermore, even if the approximate size of the shrink-fit chuck is initially determined by an electrical pulse, and therefore information on the total electrical active energy that can be applied is available before the sleeve portion reaches its critical temperature, the current that has flowed since the start of heating, particularly the coil current, and / or the integral of the active current that has flowed since the start with respect to time can also be used as a characteristic value.

[0037] In particular, it has been demonstrated that using mathematical methods, such as Kalman filters, to predict the profile of characteristic variables is advantageous. [Brief explanation of the drawing]

[0038] [Figure 1] An induction coil unit according to one embodiment of the present invention is shown in a central longitudinal section view. [Figure 2] A circuit diagram of a circuit for supplying power to an induction coil, which may be used to realize the present invention, is shown. [Figure 3] The following shows a selection of characteristic variables that may be used in accordance with the present invention. [Modes for carrying out the invention]

[0039] Ideally, the method according to the present invention is prepared by a learning process not shown in the figures herein. For this purpose, shrink-fit chucks having sleeve portions of various sizes and thicknesses are used.

[0040] Typically, it is preferable to first apply a test pulse, generated by briefly energizing an induction coil, to each sleeve portion of these shrink-fit chucks. The sleeve portion resists the test pulse with a larger or smaller mutual inductance depending on its size and thickness. From this, fairly reliable conclusions can be drawn regarding the dimensions of the sleeve portion and the expected behavior of the sleeve portion during induction heating.

[0041] This makes it possible to check the validity of the instantaneous values ​​currently shown by the characteristic variables of the induction coil used to evaluate the switch-off point, and thus facilitates safe switch-off according to the present invention.

[0042] In many cases, it is particularly preferable to design the method according to the present invention in a self-learning manner. For this purpose, in existing shrink-fit devices, it is recommended to measure and store the characteristic values ​​of the induction coil used to later evaluate when the switch-off is performed for each shrink-fit process, and to evaluate them in relation to the shrink-fit process.

[0043] This is particularly useful with fully manually operated shrink-fit devices, because it allows for recording operator actions or determining / recording / checking operator feedback regarding the shrink-fit process.

[0044] This feedback can be used to draw conclusions regarding the quality of the shrink-fit process. Therefore, artificial intelligence can preferably be used to optimize the shrinkage parameters and switch-off criteria.

[0045] Here, for example, the device operator manually pushes the tool shank toward the tool chuck in the sleeve portion, and then activates the induction coil with the other hand to perform the shrink fit. This action ends as soon as the sleeve portion has expanded sufficiently and the tool shank slides into the tool chuck in the sleeve portion. The device operator then deactivates the induction coil. Removal from the shrink-fitted state is performed in a similar manner. The device operator pulls the tool to be removed from the shrink-fitted state with one hand and activates the induction coil with the other hand, stopping the process as soon as the tool shank can be pulled out of the sleeve portion.

[0046] When numerous characteristic curves are recorded in this manner for the characteristic variables of an induction coil used to evaluate the switch-off point, it becomes possible to identify or verify with great precision the changes typically shown by the characteristic curve of the characteristic variable in question, near or at the point of switch-off.

[0047] When shrink-fitting a shrink-fit chuck, the shrink-fit device measures its temperature profile using an appropriate sensor system, and further optimization options can be realized by optimizing the parameter set using these actual temperature profiles. This can, in particular, preferably be done by artificial intelligence.

[0048] Figure 1 shows the basic structure of an induction coil unit, which is also called a shrink-fit device due to its intended function.

[0049] As shown in Figure 1, the shrink-fitting device provides an induction coil 1 having individual windings 2, with a tool holder 4 inserted in its center, where a retaining shaft H of a tool W, such as a milling cutter, is shrink-fitted into or removed from the sleeve portion HP.

[0050] The operating principles underlying shrink-fit and removal are described in detail in (Patent Document 1). These are incorporated herein by reference into the subject matter of this application.

[0051] The induction coil 1 is provided with a first sheath 3 made of a non-conductive and magnetically permeable material on its outer circumference. Typically, the first sheath 3 consists of ferrite or metal powder or metal sintered material, the individual particles of which are electrically insulated and separated from each other, and thus the whole is substantially magnetically permeable and non-conductive.

[0052] The first sheath 3 is also designed to close off almost the entire circumference in the circumferential direction, that is, to cover most of the circumferential surface of the induction coil 1, so that theoretically, there is no “magnetic gap” left except for insignificant local apertures such as individual and / or small local holes.

[0053] Furthermore, as also shown in Figure 1, in the shrink-fit device 20, the shield made of permeable and nonconductive material does not terminate at the first sheath 3. Rather, the magnetic covers 3a and 3b made of the above material are adjacent to at least one end face, more preferably both end faces, of the first sheath 3 and generally in contact with the first sheath 3. At the end face of the induction coil 1 opposite to the tool holder 4, the magnetic cover 3a is preferably designed as a fully or preferably partially replaceable pole shoe, i.e., as a ring-shaped structure having a central opening that forms a passage 7 for clamping or releasing the tool W.

[0054] On the end face of the induction coil 1 facing the tool holder 4, the magnetic cover 3b is preferably designed as an essentially planar annular disk, which ideally fully engages with the windings of the induction coil 1 and has a central passage for the sleeve portion HP.

[0055] To further improve the shielding, the induction coil 1 and its first sheath 3 are surrounded on their outer circumference by a second sheath 9, as also shown in Figure 1. Specifically, the first sheath 3 and the second sheath 9 are in contact with each other over most or all of their mutually facing circumferential surfaces.

[0056] Figure 2 shows the relevant circuit. This circuit has a resonant circuit SKS (see Figure 2).

[0057] In the resonant circuit SKS, the majority of the required energy oscillates periodically (at high frequency) between the induction coil 1 used for heating the sleeve portion and the capacitor units 14a and 14b. This means that, within each period or periodically, only the energy extracted from the resonant circuit SKS by its heating power and other power losses needs to be fed back. Therefore, the extremely high losses of the conventional design no longer occur.

[0058] As shown in Figure 2, the power electronics supplying power to the induction coil 1 are supplied at the input side with a commonly available commercial current NST, which is 400V / 50Hz in Europe (three-phase current, 3f) (corresponding values ​​in other countries). As shown in Figure 2, the current taken from the power grid is converted to a DC current by a rectifier G21, which is then smoothed by one or more smoothing capacitors (not shown).

[0059] Furthermore, as shown in Figure 2, this DC current is supplied to the actual resonant circuit SKS.

[0060] The backbone of the resonant circuit SKS is formed by a power semiconductor element 10, a resonant circuit capacitor 14b, and an induction coil 1 used for shrink-fitting and removal from the shrink-fitted state.

[0061] The resonant circuit SKS is controlled or regulated by the control electronic equipment SEK, which is supplied with a DC current from the rectifier G.

[0062] The power semiconductor element 10 is preferably realized by an insulated gate bipolar transistor, or IGBT for short.

[0063] The control electronic device SEK switches the power semiconductor element 10 at a frequency specified by the operating frequency set by the resonant circuit SKS.

[0064] It is important that the resonant circuit SKS does not operate precisely at the resonant state. Here, operation precisely at the resonant state would result in a voltage peak that would cause rapid destruction of the power semiconductor element 10. Instead, the control electronics SEK are designed to operate the power electronics or their resonant circuit SKS within a predefined operating range that is simply close to the system's resonant or natural frequency. Preferably, the resonant circuit is controlled or tuned (by the controller 20) so that 0.9 ≤ cos p ≤ 0.99. Values ​​within the range of 0.95 ≤ cos p ≤ 0.98 are particularly preferred. Here again, this avoids voltage peaks and thus further promotes miniaturization.

[0065] To operate the shrink-fit device 1 in the most automated manner possible while maintaining a certain degree of operational safety, the shrink-fit device is equipped with an automatic heating controller / regulator that enables automated shrink-fit operation. This heating controller / regulator is implemented by a corresponding controller or regulator 20 in the shrink-fit device and is basically based on the analysis of the measured coil current M-SpA, coil voltage M-SpV, and / or input current M-EA, and / or input voltage M-EV or their temporal profiles.

[0066] To measure the coil current (M-SpA), coil voltage (M-SpV), input current (M-EA), and input voltage (M-EV), the circuit is equipped accordingly with current / voltage measuring instruments M-SpA (coil current), M-SpV (coil voltage), or M-EA (input current), or M-EV (input voltage), as also shown in Figure 2, which are installed in the corresponding positions shown in the diagram within the circuit.

[0067] According to the present invention, the following procedure is performed.

[0068] Before heating of the sleeve portion introduced into the induction coil begins, the geometry or outer diameter of the sleeve portion introduced into the induction coil is preferably determined automatically first.

[0069] For this purpose, a test pulse of the induction coil, generated by briefly energizing the induction coil, is first applied to the sleeve portion. The sleeve portion resists the test pulse with a larger or smaller mutual inductance depending on its size and thickness. This method for generating a "fingerprint" of the sleeve portion is known in itself.

[0070] This "fingerprint" is evaluated and compared to the respective mutual inductances stored in the database as a kind of "fingerprint" for other sleeve portions. In many cases, this makes it possible to identify the type of shrink-fit chuck and pre-select and pre-set an appropriate set of parameters, including the shrinkage parameters used, along with the associated overheat protection logic system (i.e., which characteristic values ​​have which limits).

[0071] The procedure according to the present invention (which will be described again in more detail) is then used solely to further ensure that the maximum allowable heating of the sleeve portion is not exceeded. In this case, a very high level of assurance is provided because stored information (characteristic values ​​and their limits) defined for a particular shrink-fit chuck, such as the magnitude of the drop in instantaneous active current and the maximum amount of heating energy that can be supplied overall, can be used.

[0072] If a suitable parameter set cannot be found, the present invention can still be used to perform shrink fitting without having to sacrifice extensive protection against overheating of the sleeve portion.

[0073] Next, the “response” or fingerprint of the sleeve portion of the chuck to be shrink-fitted is preferably evaluated to the extent from which conclusions can be drawn therefrom regarding the size / mass and / or geometry and / or shape of the sleeve portion, which is itself unknown, and thus the parameter set is “estimated.”

[0074] In this case, a particularly preferred embodiment of the shrink-fit device according to the present invention is equipped such that a maximum heating energy is defined that can be supplied to the sleeve portion before the sleeve portion overheats, and a maximum amount is established by which the instantaneous active current in the sleeve portion (as expected to be seen in the shrink-fit device) can decrease before there is a risk of the sleeve portion overheating.

[0075] Next, the heating process for the sleeve portion begins. The instantaneous active current is measured and adjusted. When the instantaneous active current drops to a range remembered for when a comparable sleeve portion is likely to overheat relative to the fingerprint, the heating process is then terminated or not continued further. If the integral of the instantaneous active current with respect to time becomes very large earlier, and it can be assumed that the sleeve portion from which the fingerprint was first taken is beginning to overheat because the maximum allowable heating energy has already been supplied, the heating process is also terminated or not continued further, regardless of the fact that the instantaneous active current has not yet dropped to the extent that the assumed sleeve portion would actually overheat if it were likely to overheat.

[0076] If the procedure is carried out more safely, in addition to the two characteristic variables already considered, at least one further characteristic variable of the induction process is used and considered, so that the heating process is terminated as soon as only one of these three or more characteristic variables reaches a value in which it can be inferred that the sleeve portion is likely to overheat.

[0077] For further examples of this approach, please refer to Figure 3.

[0078] Curve 100 represents the instantaneous value of the active current plotted over time. It is easy to see that the currently flowing active current decreases significantly over time, that is, as the heating of the sleeve portion increases. This behavior is observed for all sleeve portions, regardless of size, differing only in their magnitude.

[0079] Therefore, the amount by which the instantaneous active current decreases can be used as a characteristic variable to trigger the switch-off. This can be done, at least if the fingerprint of the shrink-fitted sleeve portion identified based on the input can be reasonably inferred from its geometry.

[0080] The first derivative of curve 100 with respect to time is shown by the sloping triangle in curve 100 (see Figure 1, where three sloping triangles are shown). This is an indicator of when the decrease in instantaneous active current flattens or stops completely, such as just before the sleeve portion begins to overheat. This flattening is also shown by all sleeve portions, as it allows for easy detection of the tendency for the tangent to become zero. In general, it is particularly preferable to use the tangent here, as it allows for the observation of flattening regardless of the current mass or geometry of the sleeve portion. Thus, this includes a characteristic value that can be reliably used even when the test pulse mentioned at the beginning cannot generate a reasonably assignable fingerprint of the sleeve portion being shrink-fitted, and therefore it is difficult to estimate how much the magnitude of the instantaneous active current will decrease in a particular case.

[0081] Curve 300 evaluates only the rise in active current. This shows when the active current rises again, which indicates a situation where the temperature is close to or above the critical temperature. This is also a reliable characteristic variable that can be used to determine whether the sleeve portion is likely to overheat, regardless of its size or properties, because if this is the case, curve 300 tends to move towards zero.

[0082] Curve 400 is calculated from curve 100 using a Kalman filter and represents the second derivative of curve 100. This shows how rapidly the slope of curve 100 decreases. The Kalman filter itself is well known. However, in this context, the use of the Kalman filter is novel.

[0083] The Kalman filter is used to estimate system variables that cannot be directly measured while optimally reducing measurement errors. For dynamic variables, a mathematical model can be added to the filter as a quadratic condition to account for the dynamic relationships between system variables.

[0084] This can also be used to very reliably prevent the sleeve from overheating. Using the fingerprint of the unknown sleeve obtained according to the method described at the beginning, conclusions can be drawn about the overall properties of the sleeve, and therefore how much the instantaneous active current drops when the sleeve is about to overheat, and this criterion can be used as a hidden value.

[0085] However, for safety reasons, care should also be taken to ensure that a situation in which the instantaneous active current curve is significantly flattened can be identified in a timely manner, even if the absolute value of the instantaneous active current has not actually decreased to the extent expected according to the fingerprint on the sleeve portion.

[0086] The integral of the instantaneous active current with respect to time can also be used as an additional guarantee. This also leads to a switch-off if the other two criteria are not met, since at this point, neither the absolute decrease in the actual active current nor the theoretically supplied heating energy is sufficient to actually predict overheating. [Explanation of Symbols]

[0087] 1. Induction coil 2 windings 3. The first sheath 3a Magnetic cover 3b Magnetic cover 4 Tool Holders 7 aisles 9. The second sheath 10 Power semiconductor devices 14A Capacitor Unit 14b Capacitor Unit 20 controllers G Rectifier H retaining shaft HP sleeve section NST commercial current SEK Control Electronics SKS resonant circuit W tool

Claims

1. A method for operating a shrink-fit device having an induction coil for heating the sleeve portion of a tool holder while avoiding harmful temperatures to the sleeve portion, During heating, several different characteristic variables of the induction process that change, particularly when the sleeve portion reaches a critical temperature, are monitored, and The method is characterized in that the heating of the sleeve is terminated when at least one of the characteristic variables exceeds a predefined limit value.

2. The method according to claim 1, characterized in that one of the characteristic variables is an active current, and heating is terminated when the instantaneous active current decreases by a specific amount after the start of heating.

3. The method according to claim 1 or 2, characterized in that one of the characteristic variables is an instantaneous change in the active current, and heating is terminated when the active current no longer changes by a specific minimum amount.

4. The method according to any one of claims 1 to 3, characterized in that one of the characteristic variables is the instantaneous rate of change of the active current, and heating is terminated when the active current does not change at a specific minimum rate.

5. The method according to any one of claims 1 to 4, characterized in that one of the characteristic variables is the integral of the current that has flowed since the start of heating, in particular the energy from the coil current and / or the instantaneous effective current that has flowed since the start of heating with respect to time.

6. The method according to any one of claims 1 to 5, characterized in that one of the characteristic variables is the heating time since the start of heating.

7. The method according to any one of claims 1 to 6, wherein the instantaneous inductance of the entire system including the induction coil and the shrink-fit chuck is used as the characteristic variable, and in particular the instantaneous inductance is identified by a test signal during continuous heating and controlled against a limit value.

8. The method according to any one of claims 1 to 7, characterized in that one of the characteristic variables is the instantaneous phase angle between the instantaneous active current and the voltage driving it.

9. The method according to any one of claims 1 to 8, characterized in that one of the characteristic variables is the instantaneous inductance of the induction coil.

10. The method according to any one of claims 1 to 9, characterized in that a measurement signal supplied by at least one electrical characteristic variable passes through a digital smoothing filter, preferably a Kalman filter, before it is evaluated.

11. The method according to any one of claims 1 to 10, characterized in that the identification of the shrink-fit chuck or at least the characteristics of the sleeve portion or its mass / thickness and / or size and / or geometry are determined in advance by a test pulse.

12. The method according to any one of claims 1 to 11, characterized in that the parameter set is optimized, in particular using artificial intelligence, based on actual data from the shrink-fit process, especially temperature curves, and / or user feedback and / or user behavior.

13. A shrink-fit device for carrying out the method according to any one of claims 1 to 12, comprising: an induction coil; at least one current and / or voltage detector either in the intermediate circuit and / or in the coil circuit of a frequency converter that serves to supply electrical energy to the coil circuit; and a comparator, wherein the comparator compares at least two characteristic variables of the induction process with specified limits for them, and stops heating the coil or prevents further heating of the coil if the limit is exceeded for at least one characteristic variable.

Images