Patent Application
20190070682
This application claims priority to German Patent Application No. 10 2017 120 570.5, entitled “Device for Machining a Work-Piece with a Tool,” filed Sep. 7, 2017, and European Patent Application No. 18192038.0 filed on Aug. 31, 2018, the entire contents of each are hereby incorporated by reference in their entirety for all purposes.
The present disclosure relates to a device for machining a work-piece with a tool including a machine tool for gear-cutting machining.
With such a machine tool, it is possible to machine a work-piece in an effective manner and to generate a gearing on a work-piece. Here, the machining is carried out with the help of a cutting method.
In each metal cutting, as also in the gear-cutting processing, signs of wear arise due to the high thermal and mechanical stresses of the tool, which entail the wear and tear of the tool, or of its cutting edges. Influencing factors on the form and size of the wearing are here the condition of the tool, the material to be cut itself, as well as the corresponding process parameters. Here, the quality of the work-piece machined with the tool may decrease if the tool is not taken out of the process before the tool wear has too great influence on the machining result and excesses of tolerance ensue. As wearing, here sometimes the change of shape of the cutting edge and the cutting surface of the tool are understood. Among other things, the extent of wearing depends on the hardness, the abrasion resistance, the heat resistance, the durability of the work-piece and of the cutting piece, but is also determined by the surface condition of the cutting edge, the friction coefficient, and by the lubricity of a used cutting oil.
In order to therefore prevent the manufacture of work-pieces with a too-strongly worn tool, or to avoid a tool breakage, an exchange is, in the conventional art, undertaken, according to an empirically established tool life, in order to keep downtimes of a machine tool, and the production of rejects to a minimum. Here, wear mark width can be checked, which represents the approximately uniform removal of the cutting material through friction on the tool flank(s). Here, the wear mark width is always measured parallel to the cutting edge. Thus, for example a tool is exchanged in the conventional art, if the wear mark width, according to an empirical appraisal, exceeds a threshold value for a wear mark width with a certain probability. At an optimal juncture in time, at which the size of the wear marks and the regrinding quantities for the tool achieve an optimum result simultaneously taking into account the machining quality to be attained. Alternatively, the exchange of cutting elements, such as for example cutting plates or indexable cutting plates, can also be optimized depending upon machining quality and tool costs.
In addition, it is disadvantageous if processes for monitoring wear slowly approach a reasonable replacement time of the tool first through a preceding learning operation, as is the case in many a learning wear monitoring process. The waste incurred in the meantime can represent a considerable economic disadvantage, and even the smallest changes in the machining lead to often non-foreseeable changes in the wear behavior, so that the “learning curve” must once more approach an acceptable value.
It is therefore the object of the present disclosure to create a device or a method which overcomes the abovementioned disadvantage and provides for an exchange of a tool at exactly the right juncture in time, independent of already-passed tool life. This is of advantage for the efficiency of the device, and creates a consistently high quality of the machined work-piece.
The device according to the present disclosure furthermore offers a possibility for documenting the wear behavior on the tool, in order to so document the wearing process over the tool life. Conclusions and determinations can thus be drawn on suitable regrinding time junctures, or also compare different tool materials, coatings, or tool batches with one another.
The described disadvantages of the conventional art are overcome by means of the method and device described herein. Such a device includes a tool receptacle for releasably clamping a tool including clamping a hob peeling wheel, a machining head, which is provided with the tool receptacle, and is designed to drive a tool clamped therein and move it relative to a work-piece to be machined, as well as an assessment unit with a unit for imaging a tool or a part thereof, in order to detect the state of wear of the tool.
Through the imaging of the tool with the aid of the assessment unit, which can include an optical unit, a optical measuring system, and/or a measuring probe, or through the imaging of a part thereof and the detecting of the state of wear, an exchange or a regrinding can be undertaken, independently of a tool life of the tool, and furthermore the regrinding amount can be established. It is now no longer necessary to assume the wear of a tool on the basis of empirical studies, which are dependent upon the tool life of the tool, but rather, depending on the actual wear, an exchange or a regrinding of the tool can occur. This has the advantage that each tool makes use of its maximum tool life with regard to the wear, without having first to build up empirical values. Here, it is not required to take into consideration certain safety zones or values, so that the desired wear point is thus precisely establishable.
It can thus be provided that an enlarged representation of a cutting edge, or multiple cutting edges, of a tool are displayed to a user of the device, whereupon this user can judge the state of wear in a simple manner, and, if necessary, can correspondingly react. It is advantageous here that the user can also appraise the tool wear at a location distant from the device, and does not have to especially go to the device, in order to undertake a visual inspection of the tool. The accessibility of the tool or of the tool blade, e.g. in a hanging installation, is possible with difficulty, or the lighting situation in the work space makes a qualified observation of the tool in different lighting conditions difficult. In the device according to the present disclosure, the assessment unit or a suitable measuring unit can be configured correspondingly small, and can be supported, as required, through a suitable illumination unit, in order to create a reproducible uniform illumination situation.
According to a further development of the situation, the assessment unit is therefore designed to image at least one of multiple cutting edges, potentially in an enlarged representation, so that a good overview over the actual state of wear of the tool can be obtained. Here, the assessment unit can, along with an optical unit, such as e.g. a camera, also include optical or mechanical measuring units, which are employed for the wear documentation.
Here, it is not absolutely required that all cutting teeth or cutting edges of a tool are imaged or approached through the assessment unit, but it is rather sufficient for the purposes of the present disclosure, if a previously determined number of blades or blade edges are imaged, or only every second or third blade or blade edge.
Here, it can also be provided that the present disclosure is provided with a display unit, in order to display the image generated by the optical unit, to output corresponding characteristic values for the wear mark width, or also to document the wearing.
According to the further development of the present disclosure, the device further comprises a storage unit, in order to store the image produced by the tool, as well as potentially further information in connection therewith. Through the storing of the images, these can be retrieved at any time. Therefore, if the same work-pieces are always machined with the same tool within the tool life cycle, then it is possible that these pictures provide information about the tool life behavior between the respective tool reconditionings (for e.g. a regrinding).
Additionally to the documentation of wear, further machining information can also be stored. Through the recording of the previous tool life of the tool, from motor or control parameters of the machine axes involved in the machining, a correlation can be formed between the machining result, the wear, and from parameters of the machine tool, which makes conclusions and determinations about the machining process possible, and which can be used for the purposes of the process optimization. Possible parameters here are potentially the current consumption, or power input, the input voltage, and/or a target/actual comparison of the NC_axis position, partly referred to as lag distance.
According to a further embodiment, the assessment unit, for the documentation of wear, is a optical unit, such as a camera or a microscope camera, a laser scanner, but also a mechanical measuring device, with which the wear mark can be approached. If one uses a laser scanner as an optical unit, the corresponding offsets of the lines of the laser scanner are determined, and therefrom the state of wear of the edge is determined. When using a camera, the state of wear can be recognized based on the edge quality of the imaged cutting edge of the tool. Via a manual focus function, potentially, however, an autofocus function and measuring in different focal planes, the wear mark depth, for example, can be measured. Thus, through determining the optical distance on which, in certain focal planes parts of the tool are sharply drawn, conclusions and determinations can be drawn about the wear mark width/depth. Further, via focal planes and the machine NC axes, the optical unit can be advanced to the tool, and thus likewise a value for the wear size can be determined.
Furthermore, it can be provided, according to the present disclosure, that the assessment unit is arranged on a separate movement device, which makes a relative movement relative to a resting tool possible. If the tool to be examined, as well as also the assessment unit are arranged on the stand of a machine tool, certain movements of the assessment unit relative to the tool cannot be carried out. In such a situation, the assessment unit is provided with a movement device, so that the assessment can be traversed into the corresponding imaging position relative to the tool.
According to the present disclosure, it can be further provided that the present disclosure includes a semi- or fully automatic tool changer, which is designed to receive a tool located in the tool receptacle, and to clamp a different tool in the tool receptacle, wherein the assessment unit is designed to image the tool received by the tool changer, or to image a part thereof, and wherein the assessment unit is potentially arranged on the tool changer.
In machine tools, it is customary to change the tool with the help of a tool changer. In cutting gear machines, potentially in large-scale use, a tool changer can likewise find use. The manual changing operation is thereby omitted, whereby the efficient of such a machine can be increased. Thus, the present disclosure if the assessment unit is potentially arranged in such a changing device, so that the operation for imaging the tool, with which a machining of a work-piece has been undertaken, does not lead to an unnecessary interrupting of a work operation of the machine tool.
It can thus be provided that the tool changer receives the tool after a machining of a work-piece, and is examined through the assessment unit before or after a laying down in a tool magazine. Here, the movement devices already present on the tool changer can be used in order to displace the tool in a region or to hold it in a region, in which the assessment unit can undertake an imaging of the of the tool. If needed, it can also be provided here that the assessment unit is provided with a movement device, which makes a relative movement of the assessment unit relative to the tool received by the tool changer possible.
It can further be provided here, that the tool is clamped in a rotatable mounting during the measuring and documenting of the wear marks through the assessment unit. Thus, in a consistent receiving area of the assessment unit, a neighboring cutting edge can, through rotating of the tool, be rotated in the receiving area of the assessment unit, without a moving of the assessment unit or a re-setting of the imaging settings of the assessment unit required. This ensures a rapid generation of an imaging sequence, which involves multiple portions of the tool.
Potentially, the device according to the present disclosure is a gear cutting machine, such as a hob peeling machine. The gear cutting machine is designed to generate or to define a gearing in a work-piece with a tool such as a hob peeling wheel.
In gear cutting machines, the quality of production of a gearing depends, inter alia, on the faultless state of the quality of the cutting edges of the tool. It is therefore, in such gear cutting machines, of advantage, if the tool is not exchanged before an optimal wear point, and also not after an optimal wear point. In this way, an effective and economical operation of a gear cutting machine be provided.
According to an embodiment of the present disclosure, the assessment unit includes a measuring probe, and/or includes a measuring probe as well as a camera or a laser scanner.
According to a further modification of the present disclosure, the device further includes a computing unit for processing the image and measurement results generated by the assessment unit, as well as for representing and/or highlighting the state of wear of the imaged tool, wherein the calculating unit is, along with the representing of the state of wear, potentially also designed to represent a wear limit of a cutting edge in the image, in order to be able to recognize, in a viewing of the image, the current degree of wear of the tool, in a simple manner.
A simple optical examination of the tool is possible, in which an observer of the image can make the decision, in a simple manner, about the further use of the tool, based on the represented or the highlighted state of wear in the image. Thus, for example, in the image of a cutting edge of the tool, a line can be employed in the image, which line represents an just tolerable level of an abrasion of the cutting edge. If the cutting edge is, by contrast, behind such a line as the state of wear is correspondingly bad, the observer of the image modified thusly recognizes that an exchange or a regrinding of the tool is useful.
The present disclosure further includes a method for recognizing a tool wearing in a device according to one of the abovementioned variants, wherein, in the method, after a machining of a work-piece with a tool, the assessment unit creates an image of the tool wear, such as a cutting edge of the tool, and the image is displayed on via a display unit. It is thereby made possible for an observer, without actual physical presence at the device, to judge the state of wear of the tool. The exchange of a tool is therefore no longer undertaken due to empirical criteria.
It is further possible in the method, that an imaging, generated through the optical unit, is stored in a storage unit, in order to be able to retrieve it at a later juncture in time. If the same work-pieces are always machined with the same tool within the tool life cycle, then these pictures can also provide information about the tool life behavior between the respective tool reconditionings (for e.g. regrinding the tool), coating variants, tool and work-piece batches.
According to a further modification of the method, the optical unit, in the imaging process of the tool, makes recordings from multiple perspectives, such as recordings from multiple viewing directions on an blade of the tool, in order to make a better appraisal of the degrees of wear possible. Therefore, the optical unit can be moved with a movement device, or consist of multiple camera units with different orientations.
In a step cut, this is of advantage, as one here would like to obtain a three-dimensional impression, in order to detect the state of the step cut.
Potentially, the stored images of a tool and the further information standing in connection therewith, such as a juncture in time of recording, the tool life of the tool, and/or motor and control parameters of the machine axes are, with help from statistical methods, evaluated, in order to obtain conclusions and determinations about the machine behavior and the material behavior of the tool employed. The correlations occurring here in the stored information, or in the systematic changes of the motor parameters, in addition allow conclusions and determinations about the material behavior employed.
Further, according to an embodiment of the present disclosure, the state of wear of the said tool can be determined on the basis of the imaging of a tool, potentially with the help of a computing unit, wherein, depending thereon, a regrinding or an exchange of the tool by a tool changer is permitted automatically by the computing unit.
The exchange or the regrinding of the tool is therefore undertaken on the basis of an assessment of the imaging generated through the optical unit. The assessment here occurs by means of a computing unit.
According to a further modification of the present disclosure, the assessment unit is designed to carry out an automatic image processing, such as image recognition, potentially in the framework of a pattern recognition, it is thusly possible to automatically determine the state of wear from a picture. It is therefore no longer necessary, as hitherto set out, that an observer must look at the picture in order to judge the state of wear. For a typical course of a wearing can be searched for an recognized as a sample, as well as the course of the cutting edge. Current camera systems or optical measuring system with suitable software can, based on picture data, e.g. a point cloud, detect the course of the cutting edge. If one carries out this measuring in comparison to the tool edge on the new tool, virtual regions can be defined (one or more parallel regions to the cutting edge (similar to the course of contour lines in maps)), in the exceeding of which, the tool is judged to be worn. Potentially, it is provided that the machine operator can still intervene, in order to enable the tool for a further usage, until a further wear range is exceeded. Alternatively thereto, the tool can also be removed and sent for re-machining.
The removing of the tool can here be carried out fully-automatically, without involvement of a machine operator. The machine can therefore also fully automatically replace the tool if it is worn, and/or document the development of the wear. The course of the wear can also then thus be detected via the profile. The thusly configured assessment unit thus comprises functionalities, which go beyond an image processing to supporting the machine operator, as it can now automatically be decided, through image processing and a corresponding logic, by the assessment unit, if a state of wear is present and tool exchange is to be undertaken. The assessment unit can be supported by a computing unit for the carrying out of image processing, which computing unit carries out the corresponding steps of the image processing.
Further advantages, features and properties of the present disclosure are discernible based on the following figure description.
As a person skilled in the art knows the mode of action and the capability of a gear cutting machine 1, a detailed description is avoided.
Next to the gear cutting machine 1, a tool changer 8 is arranged, which is in a position to automatically or semi-automatically change the tool 3 from the tool receptacle 4. To that end, the tool 3 is removed from the tool changer, and with the help of the movement device, is supplied to a tool magazine 9. According to the present disclosure, it is now provided that, on the way to the tool magazine 9, the state of wear of the tool 3 is detected by means of the optical unit 6. Upon completion of this procedure, the used tool 3 is then supplied to the tool magazine 9, in that is inserted in a tool holder 10 provided therefor.
Thus, it is possible to estimate and to judge the state of wear of the tools 3 located in the tool magazine 9, if a regrinding or an exchanging of the tool 3 is necessary. It is not necessary to rely upon an empirical tool life, which does not often hit the right juncture in time for changing or for regrinding the tool. Rather, for the evaluation of the state of wear, the actual wearing of the tool 3 is judged, based on the recording of the wear of assessment unit. The evaluation can here also be undertaken by means of a computing unit.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 120 570.5 | Sep 2017 | DE | national |
| 18192038.0 | Aug 2018 | EP | regional |
