EP1199150B1 - Method for determining parameters for pressing articles of complexe construction - Google Patents

Abstract

The pressing appliance comprises pressure rams which move to and fro in one pressing direction. The movement of the rams is measured. The density and or height of a pressed part is/are measured to determine the parameters of the pressed parts. A calculator assesses the die-fill for a next pressing-test. The initial material for pressing is in granular or powder form.

Description

The invention relates to a method for determining pressing parameters for pressing complex-structured compacts with the preamble features of claim 1.

In general, the state of a single- or multi-segment constructed, pressed from powdery raw materials by specifying the dimensions and densities of individual segment sections of this is given. An in Fig. 1 represented pressed part, hereinafter also referred to as compact, for example, consists of three segments, each having a decisive in the context of a powder pressing operation segment height hsi with i = 1, 2 and 3 and per segment have a segment density ρi. At the in Fig. 1 not all three segment sections start at the same basic level, so that, in the case of corresponding calculations, the distances x1 or x3 from a support surface or a base level also have to be taken into account. However, to simplify the principles explained below, a compact is considered below in which all three segment sections S1, S2 and S3 extend upward from a base level, as is also the case Fig. 2A is apparent.

How out Fig. 2B It can be seen, there is an exemplary pressing device for pressing powdery raw materials to such compacts 9 in particular from a punch guide 1, in particular a main punch 2, hereinafter also referred to as a top bar, is guided up and down. On the underside, two pistons 3, 4 and 5 are fastened to the upper bear, which for actuating individual punches, also referred to below as segment punches 6, 7 and 8, respectively, serve. The segment punches 6, 7 and 8 can be moved up and down relative to the main punch 2 by means of the pistons 3, 4 and 5, respectively. The segment punches 6, 7 and 8 are guided in a mold which is assumed here identical to the punch guide 1 for the purpose of simplified drawing. The mold is used to hold a granulated or powdered base material to be pressed and closes down with a bottom 10 from. In conventional presses, however, there is usually instead of such a base 10, a comparable ram arrangement, via which a pressing force in the direction of the press mold can be exerted from below by means of a main ram and / or a plurality of individual segment punches. At the in Fig. 2B position shown, the arrangement is in the pressing position with lowered main punch 2 and lowered segment punches 6, 7 and 8. In this case, the compact 9 takes the form of in Fig. 2A represented compacts.

In order to achieve the required segment densities ρ1, ρ2 and ρ3 of the individual segment sections S1, S2 and S3 in the compact 9, a significantly larger volume of powder must be filled into the respective subsegments S1, S2 and S3 before the pressing process , Usually, the ratio of filling volume and pressed volume of pulverulent raw materials is between 1.8 and 2.3. After filling of the powdery base material, a pressing force for compacting the powdery base material is applied to the upper bears 2 by a correspondingly formed pressing device. The shaping of the compact 9 is effected by the relative to the upper ram 2 independently movable segment punches 6, 7 and 8, which move relative to the main pressing movement of the upper ram or main ram 2.

In order to achieve exact densities and heights of the individual segment sections S1, S2 and S3 of the compact 9, the main punch 2 and the segment punches 6, 7 and 8 with Position measuring systems 11 - 14 equipped, which detect the position of the Oberbären 2 or the stamp 6 - 8. A problem with such pressing devices is that such Wegemesssysteme 11-14 can not be attached directly to the plate ends or stamp ends, but more or less far away at the top of the plate or the top of the stamp 2, 6-8 are arranged.

Although the arrangement of Wegeesssysteme does not affect subsequent pressing operations, but this arrangement is problematic for determining the required pressing parameters. Due to the high compression pressures that are used for pressing the powdery raw materials, the individual main and segment punches 2, 6 - 8 are compressed during pressing. Usual deflections of these components of a press are in the mm range, while the accuracy requirements for the compacts are in the 0.01 mm range.

The usual procedure for setting the height and density values of the individual segment sections S1, S2, S3 of a compact 9 comprises a multiplicity, as a rule significantly more than 15 iteratively approximate compression tests. In one or more first pressing trials, a compact 9 is first produced with a density which allows the compact 9 to be touched and measured. Then one tries to set the required part height hs1, hs2 and hs3 with iterative press tests. After reaching the required part heights required for this press position or pressing height, for. Defined and set by fixed stops.

After setting or retracting the required part heights hs1-hs3, the part density is usually optimized with a further large number of iterative press tests. By feeding or removing powdered base material from the respective segment, the density can be increased or reduced there.

If, for example, the density is increased in the segment hs1 by the increased filling of powder, then the associated plate or the associated segment punch 6 springs more during pressing due to the increased pressing force. As a result, the local part height hs1 of the segment portion S1 changes. In addition, the entire pressing device also springs differently due to the pressing force difference, which is also transmitted to the segment heights hs2, hs3 of the segment sections S2 and S3 and to their densities ρ2 and ρ3. Consequently, the values of the segment segments S2 and S3 which are not actually affected must also be readjusted accordingly if changes in the parameters are required in the region of the segment segment S1. In other words, with each change in position and / or density in a segment section Si, this leads to corresponding changes in the parameters of the remaining segment sections Si via corresponding interactions.

By way of illustration, in Fig. 2B a height h _OB from a ground level to the path measuring system 11 of the main punch 2, which can trace the movement of the main punch 2 in up or down direction. The problem is, as stated, the portion of the main punch 2, which lies in the up and down direction between the path measuring system 11 and the lower edge of the main punch 2, since this portion of the main punch 2 is compressed differently when applying a first pressing pressure, as when creating a to different second pressing pressure. The same applies to the measuring sections of the individual plates or arrangements of pistons 3, 4, 5 with segment punches 6, 7 or 8, where the measuring sections h1, h2 and h3 each only the distance between a piston top edge and the corresponding position measuring systems 12-14 detect, but not depending on the pressing pressure different strong deformations of the sections between the Wegemesssystemen 12 - 14 and the corresponding lower edges of the segment punches 6 - 8. These with regard to the compression not clearly measurable sections are in Fig. 2B outlined by spring symbols c _OB , c1 - c3.

Out JP 2000 042793 A a method for automated press operation is known. In this, the weight and height or thickness of compacts are analyzed in order to possibly update the reference pressing force. Thus, a fill level correction is described by returning the force during the current production and not a parameter determination before a production is started. The reference pressing force is based on the measured pressing force value at the time when the measured weight and the measured thickness of the compact are within a permissible range based on each individual reference value.

Out EP 0 490 148 A For example, a method and apparatus for operating a briquetting press are known. In this method, filling material is filled into a filling container, whereby the weight of the filling material and the filling height are determined. Depending on this, in an actual pressing chamber, which is independent of the filling container, a pressing ram is retracted only as far as necessary, before the filling material is filled into the pressing chamber. To be achieved with this method that briquettes always with the same weight and - with the same specific weight of the starting material - can be produced with the same height. It is expressly stated to achieve briquettes with the same height and weight that an identical specific weight, ie an equal bulk density of the filler material is assumed.

Out DE 42 09 767 C1 For example, a method and an apparatus for producing multi-stage compacts are known. The starting point is a state of the art in which, in the case of a too low or too high nominal density, the filling volume of the material to be pressed is changed. To avoid cracks due to density differences Pressings with different high segments, it is proposed that, together with the correction of the filling volume to a setpoint respectively different strong changes in fill levels on the individual lower punches are made such that the ratio values of the corrected filling heights in a first approximation the ratio values of the desired heights of the respective stages in the Correspond to press body.

Out DE 29 51 716 A1 For example, a method and an apparatus for pressing moldings are known, in which the increase of a force exerted on a metal powder by punches and / or punches during the compacting process are measured and compared with desired values for a desired density of the shaped body. In the case of a deviation of the measured data from the nominal value of the filling volume of the die, the filling volume is changed in the case of a force increase which deviates from the nominal value. For the fill level correction, the densification process, especially the force increase during compaction, is used to indirectly determine a density of the molding. However, this does not allow a correct density determination of a compact.

In addition, the general state of the art on pressing methods form the further printed publications US 5,476,631 A . US 5,288,440 A and US 5,043,111 as well as in the parallel process to the interim US patent US 4,849,142 and US 4,770,826 ,

The object of the invention is to propose a method for determining pressing parameters for pressing complex-structured compacts, in which the number of pressing trials is reduced.

This object is achieved by a method for determining pressing parameters for pressing complex-structured compacts, in particular powder metallurgical or ceramic compacts, having the features of claim 1.

Advantageous embodiments are the subject of dependent claims.

Fig. 1

einen komplex aufgebauten Pressling mit mehreren Segmentabschnitten unterschiedlicher Höhe;

Fig. 2A

ein Beispiel für einen vereinfacht aufgebauten Pressling mit mehreren unterschiedlich hohen Segmentabschnitten;

Fig. 2B

eine Pressenanordnung zum Pressen eines pulverförmigen Grundstoffes zu einem Pressling und

Fig. 3

ein Ablaufdiagramm für ein Pressverfahren gemäß dem bevorzugten Ausführungsbeispiel.

An embodiment will be explained in more detail with reference to the drawing. Show it:

Fig. 1

a complex structured compact with several segment sections of different heights;

Fig. 2A

an example of a simplified structured compact with several different high segment sections;

Fig. 2B

a press arrangement for pressing a powdery raw material into a compact and

Fig. 3

a flow diagram for a pressing method according to the preferred embodiment.

As can be seen from the flowchart of Fig. 3 it can be seen, there is a preferred method for determining pressing parameters for pressing complex-structured compacts, in particular ceramic compacts of preferably granular or powdery raw materials from two process sections. In a first process section, essentially only the density of the individual segment sections is optimized by powder extraction or powder feed, but the adjustment of the height is neglected. Only in a second step, after setting in the desired or target densities, is the setting of the desired heights of the individual segment sections undertaken.

If the parameters for a new compact 9 or the production of a compact 9 is to be carried out in a new press, into the mold 1 before the application of the ram 2, 6 - 8 powder with a powder height H _powder with about twice the height of the desired target height H _Let the compact sections S1-S3 be filled. Thereafter, the ram 2, 6-8 are set and the filled powder is pressed. For an automated algorithm, for each segment i, a variable describing the height of the last filled powder level H _PulverAlt with the value of the previous powder height H _powder before pressing is occupied.

After pressing, the density ρi is determined for the individual compact segments Si with i = 1 - 3 here.

In a next step, the measured density value ρ _measurement is compared with the target value for the density ρ _target. If the measured value for the density ρ _meas and the nominal value for the density ρ _deviate from one another for one or all of the segment sections Si, the press mold is filled again with powder. The product from the old powder height H _PulverAlt and the quotient of the target density value ρ _setpoint and the measured density value ρ _measured for the individual segments i for determining the new powder height H _PulverNeu is determined. After filling the powder, this is pressed again, wherein the individual ram 2, 6 - 8 each to the previous height h _OB , h1 - h3, so that the individual height values h _OB , h1 - h3 are kept constant at the press. The height values on the compact are usually still changing. For an automated algorithm, the variable for the old powder level H _{PulverAlt is filled} with the now used powder level H _PowderNew . Thereafter, the process returns to the determination of the density values ρi for the compact segments Si.

As soon as it is determined during the interrogation that the target density values ρ _desired and the measured density values ρ _{Mess are} identical or deviate from one another only within permissible tolerances, the method proceeds to the next method section. First, the individual heights hsi for the individual compact segments Si are determined. If these measured height values hsi, _Mess for the compact segments Si do not coincide with the desired height values hsi, _Soll , the mold is filled again with powder in order to carry out a further pressing test. The new powder height H _PulverNeu determined time by the product of the old powder height H recently used _PulverAlt and the quotient of the nominal height hsi, _Soll and the measured height hsi, _measured for the individual segments Si. Then the filled powder is compressed with a constant pressing force or constant pressing force compared to the last pressing step. In an automated process, the variable for the last used powder height H _{PulverAlt is} again _filled with the last used height value H _PowderNew . Thereafter, the process flow for determining the individual heights hsi for the compact segments Si returns.

If, in the comparison of the desired heights hsi, _Soll and the measuring heights hsi, _mess for all compact segments Si identity or a deviation within allowable tolerance limits, the required pressing parameters are determined and the process can be completed.

In the first test trials, the previous total number of usually significantly more than 15 press trials could be reduced to 3 to 4 press trials. The proposed method makes use of the fact that the entire press, including the segment punches 6-8 and the main punch 2, is in a compressed state after the first pressing attempts to set the individual segment section densities ρ1-ρ3. After reaching the target densities for the individual segment heights, the heights for the individual subsegments can be calculated and set independently with no effect on each other using the second formula. As a rule, only one single step is required to calculate all partial heights if the densities for the individual segment sections have previously been determined and retracted. Ideally, with appropriate knowledge of parameters for certain powders and parameters to be pressed on the behavior of the individual press elements, a further optimized determination of the press parameters should be possible, as in the previously performed experiments.

While in Fig. 2B To simplify the explanation, only one press with press dies above the press mold is shown, conventional presses for the production of complex pressings also have punch arrangements below the press mold. The proposed method is of course also applicable to such press arrangements.

The method is in a correspondingly equipped device having a pressing device with a plurality of press dies (2, 6-8) which are movable back and forth in a pressing direction, displacement measuring means (11-14) for measuring the movements of the stamps (2, 6 - 8). 8), a pressing parameter determining means for determining density and / or height parameters (ρ1 - ρ3, hs1-hs3) of a compact (9) and a calculating device for calculating a Pressgutfüllhöhe for a respective next pressing test partially or completely automatable.

Claims (5)

1. Method for determining pressing parameters for the pressing of compacts (9) from a basic material to be pressed, with the steps:

   - Pressing of a tentatively pressed compact (9) and

   - as long as a measured density (p_Mess) is outside a tolerance quantity of a nominal density (p_Soll), producing another tentatively pressed compact (9) with always a new pressing material height (H_PulverNeu),

   - after achieving a nominal density (p_Soll) of the tentatively pressed compact (9)

   - determining the height (hsi) of the compact and comparing it with a nominal height (hsi_,Soll), and

   - as long as nominal height (hsi_;Soll) and measured height (hsi_,Mess) do not differ within a tolerance, pressing again with a new height of pressing material (H_PulverNeu) at constant pressing force.
2. Method according to claim 1, in which the determination of the new height of pressing material (H_PulverNeu) when determining the compact density is carried out as product of the preceding height of pressing material (H_PulverAlt) times the quotient of nominal density (p_Soll) and measured density (p_Mess) and by pressing again at constant pressing height (h_OB, h1 - h3).
3. Method according to a preceding claim, in which the determination of the new height of pressing material (H_PulverNeu) is carried out after having achieved the nominal density (p_Soll) as product of the height of pressing material (H_PulverAlt) used last times the quotient of nominal height (hsi_,Soll) and measured height (hsi_,Mess).
4. Method according to a preceding claim, in which the comparative measurements, comparisons and new determinations for different segments (S1 - S3) of compacts (9) of complex shape are carried out for each segment (S1 - S3).
5. Method according to a preceding claim, in which the basic material to be pressed, respectively the pressing material, is a granular or powdery material.

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