Process monitor for open die forging

This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application PCT/EP2023/063564, filed on May 22, 2023, which claims the benefit of German Patent Application DE 10 2022 207 121.2, filed on Jul. 12, 2022.

The disclosure relates to a method for monitoring and controlling open die forging presses and to an open die forging press that is connected to a control and regulation unit and is designed and set up to perform this method.

Open die forging is a forming technique associated with forging that aims to improve the mechanical properties of a workpiece and produce blanks. During open die forging, a workpiece is formed under pressure using tools that move against one another, wherein the tools can be smooth or partially contain the shape of the workpiece itself. The workpiece shape is created by guiding the workpiece in a targeted manner and by controlling the forming force applied to the workpiece by the tools. This typically requires many working strokes of the tools until the workpiece has assumed its desired shape.

The workpieces are typically gripped by a forging manipulator and formed step-by-step over the entire length to be formed between a start line at the start of the region to be formed and an end line at the end of the region to be formed. Thus, the workpiece length can be ascertained from the distance between the end line and the start line.

Open die forging is carried out as a hot forming process within a predefined temperature window for the workpiece. This workpiece temperature depends on the material and also typically takes into account the desired forming of the workpiece up to the final geometry along with the forming energy specified by the pass schedule and applied to the workpiece.

US 2005/0247092 A1 describes a method and a device for optimizing the forging process. WO 23005/113172 A1 also discloses a method and a device for optimizing the forging process. However, these devices and methods known from the prior require extremely cost-intensive measurement technology for optimizing the forging process and do not allow online temperature calculations or control of the open die forging process. Moreover, the solutions known from the prior art do not take into account round billets, stepped shafts, partially forged-over regions and conical cast billets when calculating the change in shape of distribution of the change in shape within the workpiece. The solutions known from the prior art are thus cost-intensive and do not provide the desired results for controlling different types of open die forging processes.

The disclosure provides a method and an open die forging press that are capable of providing a comprehensive solution for process monitoring in open die forging pressing without the need to rely on cost-intensive measurement systems. This object is achieved by a method and by an open die forging press as disclosed and claimed.

A method for monitoring and controlling open die forging presses is provided, which comprises the steps of (a) calculating the geometry evolution of a workpiece during open die forging by using empirical models, (b) in parallel with step (a), that is to say at the same time or at least partially overlapping in time with step (a), calculating the workpiece temperature across the cross-section of the forged workpiece, (c) calculating the distribution of the change in shape over the length of the workpiece, preferably by using the geometry evolution calculated in step (a), and (d) of automatically or manually controlling the distribution of the change in shape in a predefined region on the basis of the distribution of the change in shape calculated in step (c).

As a result, a comprehensive solution for process monitoring during open die forging is provided. Cost-intensive measurement systems can be avoided as far as possible, preferably completely. During open die forging, an elongation of the workpiece along the longitudinal axis of the workpiece is intended, such that the length increases by the value AL with each stroke, while the width increases by AB based on the free lateral surfaces of the workpiece. The ratio of change in length to change in width, the so-called elongation, is strongly dependent on the material, temperature and tool. Thus, predicting/pre-calculating the geometry is only possible to a limited extent. Existing measurement solutions for capturing geometry evolution have the disadvantage that they are extremely complex and cost-intensive based on the harsh environmental conditions and can therefore only be used in a few forges.

The solution in accordance with the disclosure for overcoming these problems provides for the workpiece to be moved to a defined starting position, where preferably a start line for the forging process is set. Subsequently, the workpiece is forged and passed step-by-step through the press until it reaches a predefined end position, which is preferably defined as the end line. On the manipulator side, the end line is defined as the start of the workpiece, which extends to the start line described above. Thus, the difference between the end line and the start line results in the workpiece length.

During forging, the geometry evolution is then calculated using the pass schedule and the relationships regarding spreading known to a person skilled in the art.

At predefined points in time, e.g. after every second pass, the measurement of the distance between the start line and the end line can now be repeated, as a result of which it is possible to record the real geometry evolution and correct any errors in the geometry calculation. In relation to the geometry calculation model, this makes it possible to record the material-dependent stretching and spreading behavior.

Furthermore, it is preferred if the press stroke, the press force and/or the manipulator position are recorded by means of suitable sensors and used by the press and, if applicable, by the manipulator to determine the spreading and the change in length of the workpiece. The implementation is typically carried out in operation with one or two manipulators, wherein the transfer of the workpiece from the first to the second manipulator is preferably also taken into account when using two forging manipulators.

It is preferred if all the parameters mentioned are stored in a database in parallel with the process, as a result of which it is possible to obtain a self-learning and continuously improving model for geometry measurement and calculation in open die forging.

The temperature is a decisive target variable during open die forging, because it has a significant influence on the material properties, in particular the microstructure of the workpiece. During forging, the temperature can only be measured on the surface, while the temperature inside cannot be measured. The method thus provides for the calculation of the workpiece temperature over the cross-section of the forged workpiece, wherein this calculation of the workpiece temperature is carried out simultaneously or at least partially overlapping in time, thus parallel to the step of calculating the geometry evolution of the workpiece during open die forging using empirical models.

Preferably, the calculation of the temperature distribution is carried out using of one or more measuring systems, e.g. pyrometers or thermographic systems, which measure the surface temperature at one or more points on the workpiece surface. The calculation of the temperature distribution inside the workpiece is then carried out with the aid of temperature models known to a person skilled in the art. Preferably, the calculated temperature distribution is displayed to the press operator, as a result of which the monitoring and controlling of the open die forging process is advantageously supported. In particular, this gives the operator the option of interrupting the process at any time or modifying it as required.

The calculation of the geometry evolution of the workpiece during open die forging is preferably the basis for a further substantial step of the method, namely the calculation of the distribution of the change in shape over the workpiece length. The geometry variables obtained when calculating the geometry evolution are then used as input variables for a change of shape model, in order to calculate the distribution of the change in shape in parallel with the process and thus the core compaction during open die forging. A common change of shape model for this has been described by Dominik Recker, for example, in the publication “Entwicklung von schnellen Prozessmodellen und Optimierungsmöglichkeiten für das Freiformschmieden” from 2014, Shacker-Verlag, Aachen. The calculation of the distribution of the change in shape over the length of the workpiece is of great importance for open die forging, since the process characteristics of open die forging result in an inhomogeneous distribution of the change of shape in the workpiece.

It is preferred if the change of shape model, in particular the change of shape model according to Recker described above, is extended by further geometries of the workpiece to be forged, in particular with regard to partially forged-over blocks, conical blocks, polygonal blocks and round blocks. For this purpose, the distribution of the change in shape depending on the special geometries of the workpieces to be produced must be taken into account when using the change of shape model in a manner known to a person skilled in the art.

Finally, the distribution of the change in shape is controlled in a predefined range on the basis of the pre-calculated distribution of the change in shape. The disclosure thus provides a holistic system for process control in open die forging, in which the process and quality variables of geometry, change of shape and temperature are used with the aid of process data along with control algorithms.

In this context, it is particularly preferred if the predefined temperature window for the open die forging process is monitored and, preferably, a warning is issued to the press operator if the temperature window defined as permissible for the workpiece is exited. It is particularly preferred if the method proposes, preferably automatically, suggestions for continuing the open die forging process with the aim of achieving an ideal distribution of the change in shape and, if applicable, implements them independently or at least after approval by the press operator.

It is particularly preferred if the method does not use any further measurement data in addition to the measurement of the workpiece temperature and any existing measurement signals from the open die forging press and/or the at least one workpiece manipulator, preferably the press stroke, the press force and the manipulator position(s). As a result, the use of measuring sensors and the associated complexity is limited to the necessary minimum, while still making possible the complete process monitoring of open die forging.

It is particularly preferred if steps (a)-(c), i.e. the calculation of the geometry evolution, the parallel calculation of the workpiece temperature over the cross-section and the calculation of the distribution of the change in shape over the workpiece length, are calculated online during the open die forging process, in order to make possible the fastest possible readjustment of the open die forging process.

In particular, it is preferred if the calculation of the geometry evolution comprises the calculation of the stretching and spreading behavior of the workpiece, preferably depending on the material. As a result, both the monitoring and the control of the open die forging process itself are advantageously supported.

In a further preferred embodiment of the method, the parameters ascertained during the calculation of the geometry evolution of the workpiece using empirical models are used as input variables for a change of shape model, which ascertains the distribution of the change of shape and, preferably, in the case of an inhomogeneous distribution over the cross-section and/or length of the workpiece, also ascertains the core compaction. As a result, a method is provided that allows the best possible information about the open die forging process and the properties of the machined workpiece, in particular for workpiece geometries that deviate from round geometries, in particular for stepped shafts.

In this context, it is preferred if a control and regulation unit is provided which is connected to a database in which all recorded measurement data and calculated parameters are stored. This creates a method that is preferably capable of self-learning to adjust the control algorithms in such a way that the best possible forging result is achieved, even when producing complex workpiece geometries and special workpiece grades.

It is particularly preferred if the control and regulation unit displays the calculated variables of geometry distribution and/or distribution of the change in shape and/or temperature change distribution to the operator, preferably also issues warnings in the event of deviations from predefined ranges and/or issues suggestions for regulating the open die forging process with the aim of maintaining the predefined ranges and/or achieving an ideal distribution of the change in shape. As a result, a method is provided which is capable of producing optimum open die forging results, optimized pass schedules and optimum workpiece grades.

In accordance with a further aspect, an open die forging press is provided which is connected to a control and regulation unit and which is designed and set up to perform the method in accordance with the first aspect described above.

Thus, all the advantages and technical effects associated with the method in can also be achieved using such an open die forging press.

shows an open die forging presswith two forging tools,arranged so that they can move relative to one another. The upper forging toolis arranged movably against the lower forging toolwithin the open die forging press, wherein the workpiece, held by a forging manipulator, is brought to the forging tools,at the start of the open die forging process. At this point in time, a start lineis defined, which defines the start of the workpieceor at least its length to be forged.

shows the same open die forging pressas in, wherein the workpiecehas been completely formed between the forging tools,at the end of the open die forging process. At this point in time, an end lineis defined, which defines the end of the workpieceto be formed. The elongation ΔL of the workpieceduring the open die forging process can then be determined from the difference between the start linefromand the end line. From this, a person skilled in the art can also determine the material-dependent spreading ΔB based on the mass and volume constancy. During the forging process, the geometry evolution can be calculated using the pass schedule carried out during the forming of the workpieceand known relationships regarding spreading. Such material-dependent relationships are sufficiently known to a person skilled in the art, for example, from Tomlinson, A; Stringer, J. D.: “Spread and elongation in flat tool forging” from the Journal of the Iron and Steel Institute 193, 1959, pp. 157-162. As a result, it can be avoided that errors caused by unknown workpiece behavior arise, which would otherwise accumulate continuously.