EP0172300B1 - Method and device for obtaining close work piece tolerances in forging processes, in particular in isothermic forging processes - Google Patents

Description

The invention is based on a method for achieving narrow workpiece tolerances in drop forging according to the preamble of claim 1 and on a device according to the preamble of claim 5.

When forging relatively complex, asymmetrical workpieces, the two die halves undergo a relative movement in the plane (xy) perpendicular to the pressing direction (z) in the course of the mutual approach during the pressing process. This relative movement, which generally consists of displacements and rotations and largely determines the achievable workpiece tolerance, can have its causes in imperfect guidance, in thermally and / or mechanically induced deformations, in asymmetrical flow and frictional forces of the material to be forged, etc. In conventional forging, attempts have already been made to counteract these movements by appropriate additional guidance of the tools (K. Lange, Textbook of Forming Technology, Vol. 2, Massive Forming, pp. 149-155, Springer, Berlin, Heidelberg, New York 1974; Metals Handbook 1970, 8th Edition, Ohio 44073, Vol. 5, Forging and Casting, Locks and Counterlocks, p.21-23).

If you want to achieve tight workpiece tolerances, a subsequent shifting of a tool half after a first attempt proves to be unavoidable. This can require a lengthy series of tests, since the ideal condition can only be gradually approached by interrupting the pressing process and waiting for the workpiece and possibly the tool to cool down. Repeated re-measuring of the workpiece is complex and requires a lot of time, since the workpiece must also be mechanically processed (deburred) before measuring in order to be able to assess its shape and dimension. The forging press stops during this dead time.

DE-B-1232439 specifies a test device for the pneumatic monitoring of a die press, the back pressure of a compressed air column serving as a criterion for the spatial position of the upper die relative to the lower die. Channels are worked into the two halves of the die, the openings of which, in the case of an exact match of their relative position, come to coincide exactly. The resulting dynamic pressure of a compressed air flow introduced into one of the die halves is measured. If the position of the die halves deviates from the target value due to a lateral shift, additional flow resistances arise which increase the dynamic pressure. The size of the side shift can be concluded from the pressure comparison. Although this device allows indirect lateral deviations of the die halves to be monitored, the correction must, however, be made after the pressing process has been interrupted by readjustment (lateral shifting possibly by hand). The above shortcomings remain.

For the present reasons, there is a notable need, particularly in isothermal drop forging, to refine the work process and make it more efficient.

The invention is based on the object of specifying a method and a device according to which narrow workpiece tolerances can be achieved in a simple manner, in particular in isothermal die forging with heated tools, while at the same time being economical to produce. The method and equipment should be such that they can also be used by less experienced and trained personnel.

This object is achieved by the features of claims 1 and 5.

• Fig. 1 den schematischen Aufriss einer Schmiedepresse mit den zugehörigen Werkzeughälften;
• Fig. 2 die schematische Darstellung eines Messprinzips für das Werkzeug mittels Laser-Interferometer;
• Fig. 3 die Anordnung einer Messvorrichtung für die Gesenkhälften mittels Taster im Aufriss/ Schnitt und Grundriss;
• Fig. 4 die grundsätzliche Anordnung einer Verschiebevorrichtung für eine Gesenkhälfte mittels Stellschrauben im Grundriss;
• Fig: 5 die grundsätzliche Anordnung einer Verschiebevorrichtung für eine Gesenkhälfte mittels Hebeln im Grundriss;
• Fig. 6 eine schematische Darstellung der Verschiebung einer Gesenkhälfte in derxy-Ebene mittels Hebelmechanismus;
• Fig. 7 eine schematische Darstellung der Drehung einer Gesenkhälfte in der xy-Ebene mittels Hebelmechanismus;
• Fig. 8 ein Blockdiagramm des grundsätzlichen Verfahrensablaufs.

The invention is described with reference to the following exemplary embodiment, which is explained in more detail by means of figures. It shows:

• 1 shows the schematic elevation of a forging press with the associated tool halves.
• 2 shows the schematic representation of a measuring principle for the tool by means of a laser interferometer;
• 3 shows the arrangement of a measuring device for the die halves by means of a button in elevation / section and plan;
• Figure 4 shows the basic arrangement of a displacement device for a die half by means of set screws in the plan.
• 5 shows the basic arrangement of a displacement device for a die half by means of levers in the plan;
• 6 shows a schematic illustration of the displacement of a die half in the xy plane by means of a lever mechanism;
• 7 shows a schematic representation of the rotation of a die half in the xy plane by means of a lever mechanism;
• Fig. 8 is a block diagram of the basic process flow.

1 shows the schematic elevation of a forging press with the associated tool halves for the purpose of illustrating the problem. Certain symmetry relationships were assumed and a suitable coordinate system with the axes x, y, and z laid through the virtual center of the press was chosen, the latter coinciding with the pressing direction (direction of movement of the punch or press table). 1 is the upper, 2 the lower die half, which is attached to the upper press table 3 or the lower fixed press table 4 via respective intermediate members. The corresponding upper 5 and lower 6 base plates are screwed directly onto the press tables 3 and 4. The base plates 5 and 6 in turn carry the insulating bodies 7 and 8, respectively. The upper insulating body 7 is firmly embedded in the upper base plate 5, while the lower insulating body 8 is arranged laterally movable in relation to the lower base plate 6 in the xy plane. The jaws 9 are used to guide and fix the latter during the pressing process. The entire structure of the forging press, including the tool, can generally be assumed to be centrally symmetrical to the z-axis, with circular cross sections of the individual components, but of course the shape and dimensions of the workpiece are appropriate other cross-sectional shapes (for example square or rectangular) are also conceivable.

2 shows the schematic representation of a measuring principle for the tool with the aid of a laser interferometer. 1, 2 represent the two overlapping die halves in the floor plan. 10 is a thin rod serving as a mirror support, 11 each a mirror. 12 is a laser generator and interferometer, on which the displacements of the die halves 1 and 2 transmitted via 10 and 11 can be read on two mutually perpendicular coordinate axes. 13 is the laser beam. This principle of the optical measurement of distances requires no further explanation.

3 shows the arrangement of a measuring device for the die halves by means of a button in elevation or section and in plan view. The reference numerals 1, 2, 5, 6 correspond exactly to those in FIG. 1. 14 represents a rod-shaped measuring probe, 15 the associated cooling jacket serving for its cooling. With 16, the corresponding measuring probe / cooling jacket is in the intended position bringing delivery mechanism referred. 17 is the lower half of the die 2 carrying, in the xy plane movable adjustment plate. The arrows 18 represent the measurement directions to be recorded. The axes x, y, z correspond to those of FIG. 1.

Fig. 4 shows the basic arrangement of a displacement device based on set screws for a die half in the plan. The reference numerals 2 and 6 correspond to those of Fig.1.19 is a radially arranged rotating arm embedded in the adjusting plate 17, which enables the rotation of the lower die half 2. The lateral connection in the x or y direction (in the xy plane) is accomplished by adjusting screws 20. 21 is the servomotor belonging to a set screw 20 or the rotary arm 19. The directions of movement are indicated by the arrows 22.

Fig. 5 relates to the basic arrangement of a lever-based displacement device for a die half in the plan. The meaning of the reference numerals 2, 6, 17 and 21 can be seen in FIG. 4. The lower die half 2 can be displaced or rotated in the xy plane by a total of four on the axes x and y, with their joint heads 24 engaging in corresponding joint sockets 25 of the adjusting plate 17 and each rotating by a bolt 26. The possible directions of movement 22 are marked by arrows.

FIG. 6 shows a schematic illustration of the displacement of a die half in the xy plane by means of a lever mechanism according to FIG. 5. All reference numerals correspond to those in this last figure. The example shows an opposite pivotal movement of the adjusting lever 23 arranged on the x-axis, which is indicated by arrows and dashed lines, which means a displacement of the lower die half 2 in the y direction, indicated by arrows 22.

FIG. 7 shows a schematic illustration of the rotation of a die half in the xy plane by means of a lever mechanism according to FIG. 5. All reference numerals correspond to those of this latter figure. The example shows a pivoting movement of all adjusting levers 23 shown in the same direction with arrows and dashed lines, which means a rotation of the lower die half 2 in the xy plane about the z axis (not shown, perpendicular to the plane of the drawing), indicated by arrows 22.

8 shows a block diagram of the basic sequence of the present working method. The individual means required to carry out the method are indicated schematically by rectangles. 27 is the entirety of the measuring device (e.g. according to FIG. 3). 28 is an electronic data processor 1 (translator), which converts the measurement data into a suitable form and forwards them to the computer 29. Here, the additional data necessary for the correction (displacement, rotation of the lower die half 2) of the tool position are entered and the resulting control command is sent to the servomotors 21 via the electronic data processor II (translator 30). The control loop is closed mechanically by the tool, which is connected to the measuring device 27 (not shown).

Design example:

A workpiece blank in the form of a stepped double cone was forged isothermally. The blank had the following dimensions:

The workpiece blank consisted of a material with the trade name «Nimonic 901» and had the following composition:

In a first process step, a first workpiece blank was first heated in a furnace to a temperature of 1100 ° C. and then placed in a press equipped with heated tools and set up for isothermal forging. The upper (1) and lower (2) die halves were cylindrical in shape and had an outside diameter of 250 mm. They consisted of a molybdenum-based alloy, but could just as well consist of a specially heat-resistant nickel-based alloy. The die halves 1 and 2 had been preheated to a temperature of 1050 ° C.

The workpiece blank was now isothermally formed into a forging in a conventional manner. It was asymmetrical in shape and had convex and concave boundary surfaces in its thin part. At its thicker end it had a maximum width (approximately in the y direction, Fig. 3) of approximately 40 mm and a maximum height (approximately in the z direction) of approximately 30 mm, while it was approximately in the middle of the thinner Partly had a width (approximately in the y direction) of approximately 40 mm and an average thickness (approximately in the z direction) of approximately 5 mm with a maximum thickness along an edge of the thinner part of approximately 15 mm. Its total length (approximately in the x direction) was approximately 125 mm. This first process step of isothermal pressing took about 10 minutes. The strong asymmetry of the forging triggered forces in the xy plane, which caused a relative displacement of the lower die half 2 compared to the upper die half in both the x and y directions and also a rotation about the z axis, because the press is not infinitely rigid. These changes in the position of the die halves 1 and 2 were now measured in the closed, pressed state by means of a measuring device according to FIG. 3 and evaluated according to the diagram according to FIG. 8, the corresponding target values being predefined. The two die halves 1 and 2 were then separated from one another and the forging removed from the press. 5, the lower die half 2 was then displaced or rotated in the xy plane relative to the upper die half 1 until the presumably optimal correction was achieved. Neither the press nor the tool need be cooled down. The correction can be carried out when the die halves 1 and 2 are warm.

In a second process step, a second workpiece blank was then heated to a temperature of 1100 ° C. and introduced into the press. The entire process of isothermal pressing, measuring and, if necessary, correcting was then repeated in the manner described above. Generally, the desired accuracy of the forging is achieved after inserting the second or third workpiece blank into the press. A larger series of workpieces can then be forged one after the other, the relative position of the two die halves 1 and 2 relative to one another being measured at random from time to time and any necessary correction being carried out immediately.

The advantages of the new method and the proposed devices and apparatus are the time saved, especially the considerable shortening of the dead times in the entire forging process, in particular when setting up. In addition, the cumbersome cooling and measuring of the cooled workpiece and the complicated conversion for the conventional correction of the entire geometric pressing parameters are avoided.

Claims (6)

1. Method of achieving close workpiece tolerances in drop forging, in particular in isothermal forging of heat-resistant materials, wherein the two die halves (1, 2) which are at workpiece temperature or almost at workpiece temperature and represent the tool are moved relative to one another under the effect of the press forces in such a way that their mutual position deviates from the geometric nominal value during the course of the press operation, and the die halves (1, 2) are then corrected in their position, characterized in that a first workpiece is put into a forging press between the die halves, in that the mutual position of the die halves (1, 2) in an xy-plane perpendicular to the direction z of the applied press force, after a first step of the press operation when the die halves (1, 2) are closed, is measured with mechanical (14, 15, 16) or physical (10, 11, 12, 14) means and evaluated via a computer and control unit (27, 28, 29, 30) arranged outside the forging press, and in that, in a second step, the forging press is temporarily relieved of load and the two die halves (1, 2) are separated from one another and the first workpiece is removed from the forging press, and in that the mutual position of the two die halves (1, 2) is automatically corrected by mechanical means (6, 17, 19, 20, 21; 6, 7, 21, 23, 24, 25, 26) in accordance with the result of the measurement, a second workpiece is put into the forging press and the press operation is completed in a single stroke in a third step of the method with the die halves (1, 2), corrected in their position, while avoiding any cooling of workpiece and tool.

2. Method according to claim 1, characterized in that the measurement and the correction of the relative position of the die halves (1, 2) to one another includes both a displacement in the x-direction and/or y-direction and a rotation in the xy-plane through an angle about the z-axis.

3. Method according to claim 1, characterized in that the measurement of the mutual position of the two die halves (1, 2) is made by means of heat-resistant mechanical measuring probes (14).

4. Method according to claim 1, characterized in that the measurement of the mutual position of the two die halves (1, 2) is made by means of laser interferometers (12) while using bars (10), designed as reflector supports, reflectors (11) and laser beams (13).

5. Device for achieving close workpiece tolerances in drop forging, in particular in isothermal forging, by means of a press which consists of an upper press table (3), moveable in press direction z, a lower fixed press table (4), an upper baseplate (5), having an insulating body (7), and a lower baseplate (6), having an insulating body (8) which is laterally displaceable in a plane xy perpendicular to the press direction z and has clamping jaws (9), and is fitted with an upper die half (1) and a lower die half (2) and has a test device for determining deviations from the nominal position of one die half relative to the other, characterized in that a mechanical measuring device consisting of measuring probes (14), arranged in the xy-plane and provided with cooling jackets (15), and feed mechanisms (16), or an optical measuring device consisting of bars (10) arranged in the xy-plane, fitted with reflectors (11) and having a laser generator and interferometer with associated laser beams (13) is provided for detecting the relative position of the two die halves, and in that, furthermore, a computer and control unit, having a measuring device (27), electronic data processors (28, 20) and a restorer (9), and a mechanical adjusting device consisting of a baseplate (6), an adjusting plate (17), a rotary arm (19) and regulating screws (20) arranged in the xy-plane and having associated servomotors (21), or of a baseplate (6), an adjusting plate (17), having joint sockets (25), adjusting levers (23), having joint heads (24), and pins (26) are provided for correcting the position of one die half (1) relative to the other (2).

6. Device according to claim 5, characterized in that the adjusting device has two pairs each of adjusting levers (23) which act as eccentrics, are arranged on the x-axis or y-axis, are located in an xy-plane perpendicular to the axis z of the press direction and, with their joint heads (24), engage into corresponding joint sockets (25) in an adjusting plate (17) carrying the die half (2) to be adjusted.

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