GB2094999A - Free hammer-forging process - Google Patents

Abstract

A free hammer-forging process in which ingots are moved by a manipulator in a computer controlled forging press includes using the computer to determine, during the process, a maximum permitted workpiece deformation value. This value is determined from data obtained prior to forging (e.g. ingot composition, size and tool dimensions) and data obtained during forging (e.g. spaced workpiece deformation characteristics).

Description

SPECIFICATION Free hammer-forging process The invention relates to a free hammer forging process for ingots which are adapted to be moved into theirforging positions by means of a manipulator in a process-computer-controlled forging press in which the forging plan is 'computed and fed into the press-control system through the process computer.

It is known in this kind of process to use a computer which from data relating to temperature, ingot measurements, final measurements and the workpiece, works out forging schedules or plans which can be selectively called up by the operator who controls the forging press. An extensive forging programme requires a very large number of such forging plans as well as a separate computer which is not part of the programme-control system, and a corresponding data store in the control system of the forging press. By using such forging plans it is possible to arrive at a fully programmed forging process whereby a substantial reduction in forging time can be achieved. However, this is true only if the degrees or ratios of deformation provided for in each selected forging plan correspond at least approximately to the potential maximum values.

However, due to the differential heating up of the ingots and to material variations from charge to charge, even ingots of the same measurements and same material show a considerable deviation range in permitted deformation ratio and forging forces. In order to enable the press operatorto take these perceptible differences into account when he selects the forging programme he must have a choice of several forging plans with different deformation ratios in each case even for forging of like starting and finished measurements and like material, which means that a forging press with a varying production programme already needs, and must correspondingly store, several hundred forging plans. This involves a considerable outlay so that in practice only forging plant with restricted production programme could be converted to programmed forging.

In this situation the present invention aims to achieve a high time-unit capacity factor also in forging presses with a highly differential production programme, taking into account the fact that the performance capacity of a forging plant depends not solely on forging-technology data but also on the dynamics of press and manipulator and that here again the manoeuverability and speed of the manipulators set primary limits to the degree of utilisation of the forging press.

In accordance with the invention, a maximally permitted workpiece deformation value is set up in the process computer in the course of the forging operation on the basis of continuously scanned distinctive deformation characteristics displayed by the workpiece, the data relating to material composition, tool- and workpiece measurements are fed into the process computer prior to the start of the forging operation and in each case for at least one pass of the workpiece through the press, the control data required for controlling the press are computed in the process computer.

Accordingly the relevant data can be ascertained for each pass of the workpiece and in each case the pre-selection of the maximally permitted material deformation ensures that the actual deformability of the workpiece is fully exploited. For determining maximally possible material deformation, which also includes the selection of the maximally permitted deformation ratio and of optimum pass rate or "bite" the measured values of press forces generated during deformation, of press force increase and of deformation temperature are the chief data to be taken into account. Beyond this use is also made of the perceptions of opto-electronic detector means, such as for example diodeline scanning camera arrays according to German OS 25 1 6 756 or surface-scanning apparatus (Proc.

Int. Conf. on Steel Rolling, Tokyo 1980, page 87), in association with learning circuits, for example according to GE-OS 2826313. For orientation as well as for correction the personal observations of the skilled operator who controls the forging press may also be taken into account. The observations are made in respect of such characteristics which qualify as essential criteria for the evaluation of material deformation, that is to say, as a general rule of deformation ratio. For example, the forging cross can be observed externally on the ingot as the lower limit of an effective deformation.Furthermore there are clearly observable signs for the approach to the upper limit of deformation ratio, for example the appearance of edge cracking which can still be compensated or the distortion of the cross section of the forging to lozenge or diamond configuration.

The deformation is also associated with characteristic noises issuing from the workpiece which can be identified audioelectronically as well as by the machine operator. Earlier heating-up time as well as the position of the material in the furnace may also be taken into account for calculating maximum possible deformation. In as much as with the aid of the above mentioned critical data particularly the maximally permitted deformation ratio and maximally applicable pass rate may be continuously matched to the deformation behaviour of the workpiece the activity of the process computer is continually readjusted thereby enabling the latter to work out the optimum parameters for each next pass and make them available to control the forging pass in progress. There is no time loss because sufficient computing time is available during each pass.

The data which have to be fed only once into the computer are essentially those concerning material composition, initial and final workpiece measurements and tool measurements deformation resistance, that is to say, the deformation force related to effective saddle surface area, and deformation strength of the workpiece can be calculated from tool- and workpiece measurements and measured forging force values.

In the case of steel blooms or ingots -for which the process according to this invention is particularly intended, it may be assumed that even for very variable material compositions deformation strength of the material decreases with rising temperature. Deformability, on the other hand, improves with rising temperature. The maximally permitted degree of ratio of deformation can therefore be calculated from deformation strength which is determined by the measured forging force. Further influential parameters taken into account in the determination of permitted deformation ratio are the relative variation of deformation strength during deformation and deformation temperature.

In hammer forging the spread of the workpiece depends essentially on the workpiece geometry, on the ratio of the width or breadth of the "bite" to the breadth of the workpiece and on deformation strength. Spread is one of the most important factors in the context of data calculation for hammer forge control because it can only be calculated in advance and because in the final analysis for a given maximally permitted deformation ratio it fixes the effective forging range, that is to say how closely the forging tools may be approached to each other In fixing the width or breadth of the bite, or the manipulator travel which is to be "set" up, it is important to take into account the known rule that in the interests of adequate penetration of the forging action the ratio of bite width and workpiece height should be higher than 0.3 to 0.4 but in the interests of avoiding undue spread it should not exceed the value of 0.1 The skilled man will be familiar with these relations from "Stahl und Eisen", 1971, pages 864 to 876.

For further illustration of the invention reference will be made to the accompanying schematic drawings in which: Figure 1 is a time-motion-diagram for the mode of operation of the press and for the mode of operation of the manipulator, Figure 2a illustrates the relationship between the deformation strength and deformability of the workpiece and temperature, Figure 2b shows the variation of deformation strength during deformation, Figure 3a a comparison of calculated and measured spread and 3b coefficients, Figure 4 shows the computing pattern which is applied to the process computer and Figure 5 is a schematic representation of the process according to this invention.

The interlinked relation of the forging press movements (3) which are to be controlled on the one hand and the manipulator (13) on the other with respect to time (12) will be observed from Figure 1. This shows first and foremost that time losses can be avoided if the travel time (1) of the manipulator falls as neatly as possible into the period (2) of the return stroke of the forging press.

In the first place the diagram shows switching points (4, 5, 6, 7, 8) along the press motion which, due to the position of the press give rise to switching operations which control the press drive. However, there is also a switching point (9) in the path of the return stroke which triggers (at 10) the drive of the manipulator. The manipulator thereupon executes a travel pass (11) whereby the breadth of the bite is determined.

Part of a workpiece (1 5) together with the forging saddle (16) thereabove is schematically indicated on the right hand side of the drawing.

This part illustrates the aforementioned concepts of the effective forging range (17) and of the depth of penetration (18). It also shows that the breadth of bite (19) is less than to the breadth (20) of the forging saddle (16).

Figure 2a shows the decrease in deformation strength (22) and increase in deformability (23) with temperature (24) for a steel material in the conventional forging temperature range.

Figure 2b illustrates the very differential growth of deformation strength (22) under different conditions of deformation (I, II) during the penetration of the forging saddle into the bloom, or ingot.

Figure 3 demonstrates the high degree of reliability of computed coefficients of spread, parts a and b of this Figure providing a comparison between computed (24) and measured (25) values. The coefficient of spread (26) is expressed as a ratio of logarithmic breadth deformation to logarithmic height deformation in relation with various values for the ratio of bite breadth to workpiece breadth (27) (S/B). In Figure 3a allowance has also been made for the bread/height ratio of the workpiece.

The computing pattern or scheme is shown in the block-circuit diagram of Figure 4. Both, the data which are measured uniquely at the start of the forging process and relating to initial and final workpiece measurements and tool measurements.

as well as the measured values of forging force and deformation temperature taken in the course of the forging process are all fed into the block marked "INPUT".

Figure 5 illustrates the arrangement of the process-computer within the context of the process according to this invention. Accordingly the following inputs or settings must first of all be made by the operator who controls the forging press: he must key-in the final effective forging range (via 45), - he must feed in the ingot measurements by placing the saddle on top of the latter and transferring the ingot height measurement provided by the digital measuring system of the press by means of caliper feelers (43). After each pass, or bite, he must operate a switch (44) to move on to the next pass or bite.

The measurement values of forging force and deformation temperature (42) as well as lightbarrier signals (from 41') which determine the direction of travel or movement are fed continuously into the computer (39). Deformation ratio (40) as well as pass rate (11) and direction of travel (41 ) for the manipulator may be set on automatic or for orientation as well as correction.

The necessary data namely effective forging range (1 7), manipulator travel (11), return stroke (2) and manipulator release (10), required to control the forging press and manipulator movements according to Figure 1 are then provided by the process computer (39), after computation stages indicated by reference (48) and outputting of signals indicated by reference (49).

The use of the computing pattern or scheme shown in Figure 4 affords the advantage of combining small data storage space requirement with short computing times. In this fashion the required process-controlling data can be computed for each successive pass without loss of time.

Claims (7)

1. A free hammer-forging process for ingots which are adapted to be moved into their forging positions by means of a manipulator in a processcomputer-controlled forging press in which the forging plan is computed and fed into the presscontrol system through the process computer, characterised in that a maximally permitted workpiece deformation value is set up in the process computer in the course of the forging operation on the basis of continuously scanned distinctive deformation characteristics displayed by the workpiece, the data relating to material composition, tool- and workpiece measurements are fed into the process computer prior to the start of the forging operation and in each case for at least one pass of the workpiece through the press, the control data required for controlling the press are computed in the process computer.

2. A process according to Claim 1, in which the maximally permitted deformation ratio is adjusted during the forging operation.

3. A process according to Claim 1, in which optionally an additional pre-setting value is provided for optimum pass rate of the manipulator.

4. A process according to Claim 1, in which the effective forging range, the pass rate, the return stroke and the manipulator release are pre-set for the forging operation by the process computer.

5. A process according to Claim 4, in which a signal which characterises the direction of travel of the manipulator is set up at the process computer.

6. A process according to Claim 1 , in which the stepping mechanism for the working pass is triggered after each completed pass.

7. A process according to Claim 1, in which the measured distinctive deformation characteristics are the forging force, the deformation temperature, the shape of the workpiece and the condition of the workpiece surface, which are fed as input signals into the process computer during the forging operation.