Method and device for controlling the temperature of a shrink-fit chuck for tools

Abstract

Method for controlling the temperature of a shrink-fit chuck (10) for tools (16), in which heat energy is supplied to the shrink-fit chuck (10) by means of a heating device (32) with a predetermined time profile in such a way that a tool holding section (12) of the shrink-fit chuck (10) reaches a tool joining dimension after a warm-up opening time elapsed up to an opening time (TO) and remains open for a predetermined holding time (ZH), characterized in that the supply of heat energy is controlled or regulated such that the heat output (Q̇, WL) of the heating device (32) is lower than a maximum initial heat output (WLAM) at a time (T1; T1*;T1**), which is before the opening time (TO) of the shrink chuck (10), is reduced, and the total amount of energy (QV) supplied up to the opening time (TO) of the shrink chuck (10) is chosen to be large enough that the shrink chuck (10) still achieves the tool joining dimension under the influence of the heat energy absorbed and stored by the material of the shrink chuck (10).

Description

The invention relates to a method and a device for controlling the temperature of a shrink-fit chuck for tools, according to the preamble of claim 1 and 7, respectively. Shrink-fit chucks are frequently used in modern manufacturing when it comes to clamping high-performance tools, especially rotary-driven shank tools, with the highest possible centering accuracy. Shrink-fit devices are used to mount and dismount the tool in the chuck. These devices create a positive-locking connection between the tool and the tool holder by heating a clamping section that is undersized relative to the tool shank to a tolerance that allows the tool shank to be inserted. A heating device is used for both the insertion and removal of the tool, and this device can operate based on various physical effects. For example, such heating devices operate inductively or with hot air. Document DE 20 2007 003 045 U1 discloses an inductive heating device for heating and expanding a tool holder for shrinking and unshrinking tools, in which the heating device provides the operator with pre-selectable process parameters for shrinking and unshrinking tools. This allows for consideration of the fact that, for example, less energy is required for shrinking than for unshrinking. Document DE 10 2004 011 747 A1 discloses a method for shrinking a tool, in which, to protect the material during the shrinking process, an actuating force is exerted on the tool from the heating device via a tool gripping device, so that the heating of the shrink chuck can be shortened. To further reduce the working time for shrinking and shrinking, achieve higher throughput, and save energy, document DE 102 31 318 A1 discloses a system that includes a sensor unit with which a characteristic parameter of the tool holder can be detected via at least one contact, whereby the heating power of the heating device can be controlled depending on the characteristic parameter. The characteristic parameter can be used to determine the temperature of the tool holder. The heating device can be switched off when a specific setpoint is reached, and a joining process can be initiated precisely when the setpoint is reached. Finally, document DE 200 23 809 U1 discloses a device for the thermal clamping and unclamping of tools, which enables a largely automated shrinking process. This is achieved by allowing the user to input parameters characterizing the shrinking pair, such as the diameter or diameter range and the material of the tool to be shrunk, via a control panel. Automatic detection of the shrink chuck type is possible, enabling the control of the power drawn from the shrink chuck or its automatic heating via pre-programmed values ​​for heating time and power. However, all known methods for controlling the temperature of a shrink-fit chuck have in common that they place considerable thermal stress on the shrink-fit chuck and – especially during shrinking – also on the tool, thereby limiting the service life of the shrink-fit chuck and / or the shrunk-in tools. The invention is therefore based on the objective of further developing a method for controlling the temperature of a shrink-fit chuck for tools according to the preamble of claim 1 and a device for carrying out this method with the features of the preamble of claim 7 in such a way that, on the one hand, energy is saved and, on the other hand, the service life of the shrink-fit chuck and the tools to be clamped therein is extended. This problem is solved with regard to the method by the features of claim 1 and with regard to the device by the features of claim 7. According to the invention, the total amount of energy supplied to the shrink-fit chuck for expanding the clamping section is reduced to a minimum by selecting it to be just large enough that the shrink-fit chuck, under the influence of the heat energy absorbed and stored by the material of the shrink-fit chuck, still achieves the tool joining dimension. The tool joining dimension can be the tool mounting dimension or the tool removal dimension. The tool joining dimension can therefore be slightly smaller than the outer diameter of the tool shank if an additional external force acts on the tool for shrinking or shrinking. Compared to the conventional method, where the heating power is only reduced once the shrink-fit chuck has already reached the tool-to-tool joining dimension, savings of 10 to 20% in heating power can easily be achieved without noticeably increasing the time until the shrink-fit chuck can be opened. At the same time, the measures according to the invention ensure that the temperature of the shrink-fit chuck after opening rises far less than is currently typical, which significantly reduces the thermal stress on the shrink-fit chuck and / or the tool it holds, thus extending the shrink-fit chuck's service life.Furthermore, the additional advantage arises that the energy savings during heating simultaneously means that the cooling system also has to dissipate less energy after the tool has been joined, with the result that the cooling system can be dimensioned smaller and the cooling process can be completed in a shorter time, thus shortening the overall tool joining and exchange cycle. An optimization of the energy balance is achieved with the features of claim 2 or claim 8. Accordingly, the total amount of energy supplied at the time of opening of the shrink chuck is chosen to be just large enough that the shrink chuck, under the influence of the heat energy absorbed and stored by the material of the shrink chuck, just barely reaches the tool joining dimension. The energy required to be introduced into the shrink-fit insert can be further reduced by supplying, according to claim 3, only enough heat energy from the opening point onward to maintain the open state of the shrink-fit insert. This further development advantageously extends the opening time of the shrink-fit insert with the lowest possible energy input, without subjecting the shrink-fit insert to excessive thermal stress. Various profiles for the temporal progression of the heat input can be used to control the heat output or heat quantity supplied to the shrink-fit chuck. A particularly simple control method is achieved with the further development of claim 4, according to which the heat output is no longer increased after a maximum initial heat output has been reached. This maximum heat output can be at the beginning of the heating control or within the time frame from the switching on of the heating device until the opening time of the shrink-fit chuck. The heat output control is not fixed for all types of heating devices, shrink-fit chucks, or shrink-fit chuck / tool ​​combinations. Instead, the heating control parameters are advantageously determined based on the design and / or dimensions of the shrink-fit chuck, the type of heating device, and / or, if applicable, the dimensions and / or material of the tool or shrink-fit chuck. It has proven advantageous to define these heating control parameters iteratively, for example, by using different heating power curves for both the shrink-fit and shrink-out processes and then iteratively optimizing the heating power to achieve a minimum total energy input.Once an optimal heating power curve has been found for a specific shrinkage pairing and a specific heating device, it can be stored in a memory and selectively retrieved. Advantageous further training is the subject of the remaining sub-claims. The invention is explained in more detail below with reference to schematic drawings. These show: Fig. 1 a schematic view of a shrink-fit insert with attached tooling before the shrink-fit process; Fig. 2 a diagram illustrating the heating energy supply for the method according to the invention; Fig. 3 a diagram illustrating a modified embodiment of the method according to the invention, simultaneously showing the surface temperature of the shrink-fit insert during a shrink cycle; and Fig. 4 a diagram similar to Fig. 2 illustrating a modified embodiment of the invention. In Fig. 1, reference numeral 10 denotes a shrink-fit chuck equipped with a cylindrical tool-holding section 12 for the cylindrical shank 14 of a tool 16, such as a drill bit. The chuck, designed as a shrink-fit chuck 10, is positioned with its clamping and retaining ring 20, adjacent to a hollow shank taper (HSK) 18, on a holding plate 22 of a shrink-fit device (not shown). This device thermally clamps and unclamps the tool 16 in the shrink-fit chuck 10 by supplying heat to the shrink-fit chuck in a time-controlled manner and, after the tool 16 has been inserted into the tool-holding section 12, by removing heat. Such shrink-fit devices are well known, so a more detailed description of these devices is unnecessary. Reference can be made, for example, to the prior art described in the introduction. The crucial point is that such shrink-fit devices are regularly equipped with a control unit 30, which supplies thermal energy to a heating device 32 (schematically indicated by a dashed-dotted line). This ensures that the tool holder section 12 reaches the joining dimension after a predetermined time and that the shrink-fit chuck is held open for a certain period of time so that the cutting edge 34 can be positioned relative to the end face 36 of the shrink-fit chuck 10, as described, for example, in document DE 101 38 107 A1. Simultaneously, the control unit 30 can be used to extract heat from the shrink-fit chuck after the joining process of the tool 16. Figure 2 shows a diagram illustrating how the temperature control of the shrink-wrap lining is carried out conventionally or according to the present invention. The dotted line shows the curve according to which the heating device 32 is supplied with energy in the prior art. The abscissa represents the time elapsed at the moment the heating device 32 is activated. The ordinate shows the ratio Q̇ / Q̇M, i.e., the ratio of the heat output Q supplied to the heating device 32 to the maximum heat output Q̇M of the heating device. The dotted line illustrates how the heating element of a known shrink-fit chuck is conventionally controlled. At the moment the heating element is switched on, the heating power is set, for example, to 60% of the maximum heating power Q̇̇Mein. This heating power is maintained even beyond the opening time TO of the shrink-fit chuck and is switched off at an adjustable time after the opening time TO. With this type of control or regulation of the heat output of the heating device 32, the shrink-fit chuck 10 remains open for a predetermined period (TS - TO), roughly indicated by hatching, so that it closes again at time TS. Time TS can be shifted forward by a cooling device. In contrast, the temperature of the shrink-fit lining is controlled according to the invention in such a way that, on the one hand, energy is saved and, on the other hand, the thermal stresses on the shrink-fit lining 10 are noticeably reduced, so that the service life of the shrink-fit lining can be increased. According to the invention, the supply of heat energy is controlled or regulated such that – as shown by the dashed lines in Fig. 2 – the heat output of the heating device is reduced at a time T1, which is before the opening time TO of the shrink-fit chuck 10, compared to a maximum initial heat output WLA. This reduced heat output value is denoted WL* for the dashed line in Fig. 2. At the same time, the total amount of energy QV supplied up to the opening time TO of the shrink-fit chuck 10, which corresponds to the area below the heating power curve, is selected to be large enough that the shrink-fit chuck 10, under the influence of the heat energy absorbed and stored by the material of the shrink-fit chuck – taking into account all other heat transfer losses – still achieves the tool joining dimension. Preferably, the total amount of energy supplied up to the opening time TO of the shrink chuck is chosen to be just large enough that the shrink chuck, under the influence of the heat energy absorbed and stored by the material of the shrink chuck, just barely reaches the tool joining dimension. From the opening time TO, the heat output WL is controlled or regulated in such a way that it is just sufficient to maintain the open state. This type of control or regulation of the heat output results in energy savings, which are characterized by the densely hatched area between the dotted curve and the heating output curve according to the invention, represented by a dashed line. Tests have shown that it is readily possible in this way to save a considerable amount of heating energy, for example 10 to 25%, without having to shorten the period in which the shrink sleeve 10 remains open or without noticeably delaying the opening time TO. As illustrated by the dash-double-dot curve in Fig. 2, the heating power curve can also be varied to result in an earlier opening of the shrink-fit chuck, indicated by arrow F, which shifts the opening time TO forward. This can be achieved, for example, by slightly increasing the initial heating power WLA over a certain period T1* and then reducing it below the value WL* at time T1*. The opening time can be influenced by the energy supply during the opening phase of the shrink-fit chuck. For example, by slightly delaying the time T3, at which the heating device is switched off, to T3*, the time TS in Fig. 2 can be shifted to the right, indicated by arrow S. In a test with the same shrink-fit chuck, it was demonstrated that, compared to a heating control with a constant initial heating power of 60% of the maximum heating power, where the shrink-fit chuck opened after 5 seconds and remained open for 4 seconds, the inventive method, with an initially slightly increased heating power of 70% of the maximum heating power (Q̇̇Mund) followed by a gradual reduction of the heating power, achieved opening of the shrink-fit chuck after only 4 seconds, while still saving approximately 10% heating energy. This reduction in heating power simultaneously reduces the thermal stress on the chuck and is equivalent to increasing the service life of the shrink-fit chuck. With reference to Fig. 3, which shows another heating power curve according to the invention, it is explained how the method according to the invention affects the stress on the shrink-fit chuck. In addition to the heating power Q̇ / Q̇̇M, which is related to the maximum heating power Q̇̇M, the surface temperature of the shrink-fit chuck 10 and the absolute heating power Q̇ are given in tabular form in Fig. 3 over time T. It can be seen that, despite a reduction in heating power after 3 s, the temperature of the shrink-fit chuck 10 reaches the opening temperature a short time later and maintains this temperature despite a further reduction of the heating power to about 30% of the maximum heating power Q̇̇M, with only a slight overshoot of the surface temperature to about 260°C occurring. After 7 s, the heating device can be switched off. Naturally, the power control or regulation of the heating device described above can be varied without departing from the basic concept of the invention. For example, as shown in Fig. 4, the heating power can be changed according to a continuous curve instead of in steps. Starting from an initial heat output WLA of, for example, 50%, it can be increased to a maximum initial heat output WLAM at a time T1** and then continuously reduced following a control curve. The heating output curve from Fig. 2, marked with a dash-two-dot-dash curve, is shown with a dashed line in Fig. 4. The vertically hatched areas indicate the energy savings, and the horizontally hatched areas indicate the additional energy expenditure until the shrink-fit chuck opens. It is understood that the heating output is determined with a view to optimizing the opening time TO for a given holding time ZH. This optimization is preferably carried out iteratively, i.e., the parameters (dQ / dt(t)) of the heating control are repeatedly adjusted.- Regulations are determined iteratively depending on the material and / or the design and / or the dimensions of the shrink chuck and / or the type of heating device (32) and / or, if applicable, the dimensions and / or the material of the tool. The invention therefore provides a method and a device for controlling or regulating the temperature of a shrink-fit chuck for tools, in which heat energy is supplied to the shrink-fit chuck by means of a heating device with a predetermined time profile in such a way that a receiving section of the shrink-fit chuck reaches a tool joining dimension after a warm-up opening time and remains open for a predetermined holding time.The special feature is that the supply of heat energy is controlled or regulated in such a way that the heat output of the heating device is reduced compared to a maximum initial heat output at a time that lies before the opening time of the shrink chuck, and the total amount of energy supplied up to the opening time of the shrink chuck is chosen to be so large that the shrink chuck still achieves the tool joining dimension under the influence of the heat energy absorbed and stored by the material of the shrink chuck.

Claims

Method for controlling the temperature of a shrink-fit chuck (10) for tools (16), in which heat energy is supplied to the shrink-fit chuck (10) by means of a heating device (32) with a predetermined time profile in such a way that a tool holding section (12) of the shrink-fit chuck (10) reaches a tool joining dimension after a warm-up opening time elapsed up to an opening time (TO) and remains open for a predetermined holding time (ZH), characterized in that the supply of heat energy is controlled or regulated such that the heat output (Q̇, WL) of the heating device (32) is lower than a maximum initial heat output (WLAM) at a time (T1; T1*;T1**), which is before the opening time (TO) of the shrink chuck (10), is reduced, and the total amount of energy (QV) supplied up to the opening time (TO) of the shrink chuck (10) is chosen to be large enough that the shrink chuck (10) still achieves the tool joining dimension under the influence of the heat energy absorbed and stored by the material of the shrink chuck (10). Method according to claim 1, characterized in that the total amount of energy (QV) supplied up to the opening time (TO) of the shrink chuck (10) is selected to be just large enough that the shrink chuck (10) just barely reaches the tool joining dimension under the influence of the heat energy absorbed and stored by the material of the shrink chuck (10). Method according to claim 1 or 2, characterized in that the heat output (Q̇, WL) is controlled such that it is just sufficient to maintain the open state from the opening time (TO). Method according to one of claims 1 to 3, characterized in that the heat output (Q̇, WL) is continuously reduced starting from the maximum initial heat output (WLAM). Method according to one of claims 1 to 3, characterized in that the heat output (Q̇, WL) is changed in stages. Method according to one of claims 1 to 5, characterized in that the parameters (dQ / dt(t)) of the control unit or regulating unit (30) are iteratively determined depending on the material, design and dimension of the shrink-fit chuck (10) and the type of heating device (32) and / or optionally on the dimension and material of the tool (16). Device for carrying out the method according to one of claims 1 to 6, comprising a shrink-fit device in which a shrink-fit chuck (10) for tools (16) can be received, a heating device (32) with which heat energy can be supplied to the shrink-fit chuck (10), and a control unit or regulating unit (30) with which the heat output (Q̇, WL) of the heating device (32) can be supplied over time in such a way that a tool receiving section (12) of the shrink-fit chuck (10) reaches a tool joining dimension after a warm-up opening time elapsed up to an opening time (TO) and remains open for a predetermined holding time (ZH), characterized in that the control unit or regulating unit (30) adjusts the heat output (Q̇, WL) of the heating device (32) relative to a maximum initial heat output (WLAM) at a time (T1; T1*;T1**), which lies before the opening time (TO) of the shrink chuck (10), is reduced in such a way that the total amount of energy (QV) supplied up to the opening time (TO) of the shrink chuck (10) becomes just large enough that the shrink chuck (10) still achieves the tool joining dimension under the influence of the heat energy absorbed and stored by the material of the shrink chuck (10). Device according to claim 7, characterized in that the control unit or regulating unit (30) controls or regulates the heat output (Q̇, WL) of the heating device (32) in such a way that it is just sufficient to maintain the open state from the opening time (TO). Device according to claim 7 or 8, characterized by a programming module with which the parameters (dQ / dt(t)) of the control unit or regulating unit (30) can be iteratively determined depending on the design and / or dimension of the shrink-fit chuck (10) and / or the type of heating device (32) and / or the dimension and / or material of the tool (16).

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