EXPIRECTION PROCESS AND ROTARY EXPIRECTION MACHINE

Description

[0001] The invention relates to an extrusion method having the features of the patent claim and to a rotary extrusion machine according to patent claim 6.

[0002] WO 2018 / 134018 A1 discloses a continuous extrusion process for a metal-containing bulk material for producing an extruded body. The metal-containing bulk material is introduced into a press channel of a metal powder extrusion press. The press channel is defined by a rotating extrusion wheel and press tool components. The press tool components comprise an inlet area with sealing plates and a deflection area with a counterholder and a feed plate. The metal-containing bulk material is fed to the counterholder via a circumferential groove of the rotating extrusion wheel and by deflecting the compacted metal-containing bulk material in the deflection area through an opening in a feed plate of a die. At least one of the sealing plates arranged in the inlet area is cooled by a cooling device.In this process, the individual cold powder particles are welded into a fully compacted strand due to shear forces without melting the powder particles. The frictional and deformation forces caused by the rotation of the extrusion wheel generate the required temperatures and pressures for continuous extrusion through the die. It has been found that cooling the inlet area of ​​the extrusion channel can prevent powder adhesion to the sealing plates, thus ensuring a continuous powder feed and a uniform pressure build-up.

[0003] Continuous rotary extrusion, also known as radial extrusion, is a special form of conventional extrusion for the continuous extrusion of simple or geometrically complex finished or semi-finished products, particularly from cast copper wire. The finished or semi-finished products extruded using continuous rotary extrusion can, in particular, be busbars made of pure copper material (Cu-OFE) with a copper content of 99.99 wt.%. These busbars are increasingly being used as solid flat conductors for high-voltage applications in electric vehicles. Cu-OFE is characterized by the combination of very high electrical conductivity (≥ 58.6 MS / m) and good weldability.

[0004] During rotary extrusion, friction and the high degree of deformation generate high temperatures, leading to recrystallization processes in the microstructure. For example, extruded flat conductors using conventional rotary extrusion tools exhibit an inhomogeneous microstructure with coarse grains throughout the extruded cross-section. This microstructure composition can negatively impact the properties of the final products, particularly in sharp-edged bending applications. Sharp-edged bending applications are those with bending angles greater than 90°. In these cases, the inhomogeneous microstructure of the extruded flat conductors leads to undesirable surface defects (orange peel effect) and even surface cracks and complete failure.

[0005] The invention is therefore based on the object of demonstrating an extrusion process which improves the surface topography of the extruded products, in particular with regard to the undesirable orange peel effects during sharp-edged bending of the extruded products.

[0006] The invention is further based on the object of demonstrating a suitable rotary extrusion machine by means of which the desired products with improved surface topography can be produced with high economic efficiency.

[0007] The invention is achieved by an extrusion process having the features of patent claim 1. A rotary extrusion machine, in particular for carrying out the process, is the subject of patent claim 6. The extrusion process according to the invention is based on the feeding of a copper material in the form of a wire, a powder, or granules to a friction wheel of a rotary extrusion press. Rotary extrusion presses or rotary extrusion systems operate continuously and more cost-effectively than conventional extrusion systems. In this process, the supplied copper material is heated by the energy introduced by friction and shear until it becomes plastic. The plastic copper material is directed away from the friction wheel and into a retention channel in a retention plate. The shaping die is arranged downstream of the retention plate.

[0008] The exit cross-section of the retention channel immediately before entering the die is larger than a shaping extrusion channel in the die. This creates a dead zone for the plastic copper material before entering the die. The dead zone serves to build up the pressure necessary for the extrusion process, so that the extrusion channel is evenly filled with the copper material.

[0009] The term "exit cross-sectional area" refers to the end cross-sectional area of ​​the retention channel. It is assumed that the die covers this end cross-sectional area, leaving only the extrusion channel free for the passage of the plastic copper material. Therefore, copper material does not exit from the entire exit cross-sectional area, but only where the die allows it.

[0010] The temperature of the plastic copper material in the dead zone and in the die is adjusted to a target value of no more than 550°C by reducing the volume of the dead zone. Since the copper material does not reach higher temperatures in any other area, the entire forming process takes place at temperatures up to a maximum of 550°C.

[0011] Rotary extrusion makes it very difficult to record the temperatures of the copper material in the dead zone and in the die area. Due to the complex conditions, the local temperature conditions in the radial extrusion process cannot be calculated precisely. Temperatures can only be recorded using in-situ measurements. In the invention, this was achieved using thermal drag elements. With knowledge of the measured values, mathematical models were adapted so that the temperature curve can be determined with a very good approximation. It has been found that the time-temperature curve during radial extrusion initially shows a steady increase in the temperature of the copper material from room temperature until it very quickly passes through two characteristic temperature maxima. These two temperature peaks represent the material shear and the deformation in the die.Measurements have shown that by reducing the volume of the dead zone, the forming temperature can be reduced by approximately 50°C to a maximum of 550°C. Surprisingly, reducing the dead zone has an impact on the microstructure of the fully recrystallized microstructure in the extruded profile. Investigations have shown that, at comparable extrusion speeds, increasing the forming temperature by 50°C to a maximum of 550°C can be used specifically for grain refinement on the order of approximately 20 µm. This means that the mean weighted average of the grains in the crystal structure has been reduced by approximately 20 µm, resulting in a mean weighted grain diameter in the range of 45 µm to 65 µm.

[0012] Due to the lower forming temperatures, especially in the dead zones at the transition to the die, grain growth is inhibited. This significantly reduces the coarse-grained microstructure. The microstructure becomes more homogeneous. Radial extrusion using a rotary extrusion press can achieve an increase in strength and a significant improvement in yield strength of up to 20 MPa, particularly for materials in the Cu-OFE group. In addition, an average HV0.5 microhardness increase of approximately 10% can be observed.

[0013] The increased ductility combined with a more homogeneous microstructure distribution improves the surface topology of solid flat conductors under deformation-intensive bending stresses. The extrusion process according to the invention significantly reduces or even eliminates undesirable orange peel effects.

[0014] Due to the relatively lower forming temperatures and the associated lower thermal load on the forming tools, the newly developed extrusion process or the tool concept used to improve the process is suitable for reducing wear and thus also for increasing the economic efficiency of the operation of the continuous rotary extrusion plant.

[0015] The extrusion process is carried out with a retention channel that expands exclusively in a funnel shape in the dead zone area. The term "exclusively funnel-shaped" means that there should be no area towards the end of the retention channel where the cross-section of the dead zone or retention channel no longer expands. It has proven particularly advantageous if the dead zone expands continuously in a funnel shape. The expansion of the funnel-shaped area thus occurs in the flow direction of the copper material from each cross-sectional plane to the next cross-sectional plane of the retention channel.

[0016] Grain growth is inhibited by using a stagnation channel with an exit cross-sectional area that is not too large compared to the entry cross-sectional area of ​​the extrusion channel and is 40% to a maximum of 60% larger than the entry cross-sectional area of ​​the extrusion channel. If the difference is greater than 40-60%, for example, 100%, a large dead zone forms in which the flow velocity of the copper material can drop to zero. At the same time, the large diameter difference between the exit cross-sectional area and the entry cross-sectional area leads to a characteristic temperature maximum, which the invention aims to avoid. If the exit cross-sectional area is only 40-60% larger than the entry cross-sectional area, a target value of no more than 550°C can be achieved in this dead zone and thus also in the transition to the extrusion channel.

[0017] In addition, a retention channel is used in which the funnel-shaped, widening area, which can also be referred to as the retention funnel, is not too long, i.e., it begins at a reasonable distance from the die. The retention funnel has an inlet cross-sectional area at a distance from the die, whereby the distance is max. 30% larger than the smallest diameter of the extrusion channel in the inlet cross-sectional area of ​​the extrusion channel. In the production of extruded flat conductors, the extrusion channel has an essentially rectangular shape. The distance of the inlet cross-sectional plane of the retention funnel is based on the smallest diameter of the extrusion channel, i.e., for example, on the thickness of the flat conductor and not on its width.Accordingly, the funnel-shaped, widening hopper is not entirely truncated cone-shaped, but rather widens from a square or round inlet cross-sectional area, for example, to the outlet cross-sectional area, which is 40-60% larger than the inlet cross-sectional area and located a maximum of 30% from the beginning of the hopper. The hopper should be proportionally slightly larger than the extrusion channel at its end in all circumferential areas of the extrusion channel to ensure a uniform material flow into the extrusion channel and also to achieve a uniform temperature distribution within the hopper and the extrusion channel. Proportionally larger means that the outlet cross-sectional area is, for example, rectangular with the proportions of the flat conductor or the extrusion channel.

[0018] The extrusion process is particularly suitable for the radial extrusion of pure copper. This refers to high-purity, oxygen-free copper with a copper content of at least 99.99 wt. percent, particularly Cu-OFE copper. This is non-deoxidized, oxygen-free copper that contains no elements that vaporize in a vacuum and exhibits very high electrical and thermal conductivity. The permissible alloying constituents are 0.0025% Ag, 0.0015% S, 0.0010% Ni, 0.0010% Fe, 0.0003% P, up to 0.0005% As, 0.0002% Bi, 0.0001% Cd, 0.0005% Mn, 0.0005% Pb, 0.0004% Sb, 0.0002% Se, 0.0002% Sn, 0.0002% Te, and 0.0001% Zn (all values ​​in mass percent). The oxygen content is adjusted so that the material meets the hydrogen resistance requirements according to DIN EN 1976. The material designations are EN Cu-OFE, CW009A in Europe, ASTM(UNS) C10100 in the USA, and JIS C1011 in Japan.

[0019] Preferably, the extruded profile is cooled immediately after exiting the die to prevent grain growth outside the die. This maintains the grain refinement effect and increases the ductility of the final product.

[0020] The method according to the invention is carried out in particular on a rotary extrusion machine according to the features of patent claim 6. Such a rotary extrusion machine comprises a friction wheel for heating a copper material supplied in the form of a wire, a powder, or granules. Furthermore, the rotary extrusion machine for continuous radial extrusion comprises a baffle plate into which the plastic copper material is radially diverted. Even before entering the baffle plate, the temperature of the copper material is increased to values ​​of up to approximately 500°C. After the copper material is diverted into the baffle channel, the temperature drops, only to rise again to a maximum value as it continues along the baffle channel until immediately before entering the forming die. The highest values ​​are reached in the dead zone area, which is located immediately upstream of the inlet cross-sectional area of ​​the die.To create the dead zone, the retention channel has an exit cross-sectional area that is 40-60% larger than the inlet cross-sectional area of ​​the extrusion channel. The size of the dead zone is deliberately limited to prevent the compressed, plasticized material from reaching excessively high temperatures in this area. The pressure required to fill the extrusion channel is built up, but without passing through the temperature ranges in the edge area that are unfavorable for grain refinement.

[0021] The retention channel is exclusively funnel-shaped in the dead zone area. In particular, it is continuously funnel-shaped and has no diameter jumps, stagnant diameter areas, or other gradations. The expansion of the retention channel is preferably continuous and uniform from the beginning of the retention funnel to the end of the retention funnel. Furthermore, in the rotary extrusion machine according to the invention, the retention channel, which has a funnel-shaped retention funnel that widens toward the die, should not be too long. The distance between its inlet cross-sectional area and the die should be a maximum of 30% greater than the smallest diameter of the extrusion channel in the inlet cross-sectional area of ​​the extrusion channel.

[0022] Flat conductors can be produced according to the method according to the invention, the structure having an average grain diameter in a range of 45-65 µm.

[0023] Such a flat conductor preferably has a tensile strength of 210-220 MPa with a yield strength of over 70 MPa, particularly in the range of 70-80 MPa. The extrusion speeds in the extrusion process according to the invention or in the rotary extrusion machine preferably range from 6-10 revolutions / min. The design of the retention chute or retention channel and the resulting dead zone have a significant influence on the microstructure. The surface topography for crack-free and deformation-intensive bending stress can be significantly improved with a properly designed retention chute.By improving the bending capacity of extruded copper flat conductors, new products for future mobility concepts can be developed, especially since bending over the narrow edge of the flat conductor enables other cable routings of the flat conductors, especially in connection with electromobility.

[0024] The invention is explained in more detail below with reference to exemplary embodiments illustrated in schematic drawings. They show: Figure 1a schematic representation of a continuous rotary extrusion machine; Figure 2the rotary extrusion machine of the Figure 1 partly in section; Figure 3 a longitudinal section to illustrate the material flow through the rotary extrusion machine of Figure 2 ; Figure 4a horizontal cross section through a baffle plate and a die (state of the art); Figure 5a vertical cross section through a baffle plate and the die of the Figure 4 (Prior art); Figure 6 shows a horizontal cross section through a baffle plate and a die according to an embodiment of the invention; Figure 7 shows a vertical cross section through the baffle plate and the die of the Figure 6 ; Figure 8 shows the flow rates of the copper material in the extrusion die set according to the design of the Figures 4 and 5 (State of the art); Figure 9 shows a representation of the flow rates of the copper material in the extrusion tool set according to the inventive design of the Figures 6 and 7 ; Figure 10 a representation of the temperature distribution in the tool set of the Figures 4 and 5 (state of the art); Figure 11 shows a representation of the temperature distribution in the tool set according to the invention of Figures 6 and 7; Figure 12 shows a diagram illustrating the tensile strength and yield strength as a function of the rotational speed and as a function of the design of the tool set; Figure 13 shows a micrograph through a quadrant of a flat conductor in comparison of the prior art in comparison with the embodiment according to the invention; Figure 14 shows a plan view of the radially outer bending zone of a flat conductor that has been bent by 180°, in an enlarged representation according to the prior art; Figure 15 shows a plan view of the radially outer bending zone of a flat conductor that has been bent by 180°, in an enlarged representation according to the solution according to the invention.

[0025] The Figures 1 and 2 show a schematic representation of a rotary extrusion press 1, to which a copper wire 2 is fed in order to produce a flat conductor 3 with a rectangular cross-section by radial extrusion. The copper wire 2 is guided through a gripping zone 5 ( Figure 3). The copper wire 2 is formed from a round cross-section into a partially flattened cross-section. The temperature of the copper material increases slowly until the copper material reaches a compression zone 6 following the gripping zone, where it softens and becomes plastic. The compression zone 6 opens into a radially branching retention channel 7 in a retention plate 8. The plasticized copper material is fed directly from the retention channel 7, which widens in the flow direction, to a die 9. The area relevant for the invention is in Figure 2 and concerns the design of the tool set arranged there, consisting of baffle plate 8 and die 9.

[0026] First, the state of the art is examined based on the Figures 4 and 5 explained. The Figures 4 and 5show a horizontal and a vertical sectional plane through one and the same baffle plate 8 and the die 9 following it. In the die 9 there is an extrusion channel 10 which is slightly funnel-shaped up to a central constriction at its start and end area. The die 9 has an inlet cross-section 11 which directly borders the outlet cross-section 12 of the baffle channel 7. The two cross-sections coincide in one plane. The bafflement of the copper material is necessary to ensure uniform filling of the extrusion channel 10 in the die 9. For this purpose, the baffle channel 7 has an initial cross-section which can be square with rounded corners, for example. This is followed by a funnel-shaped widening area which is referred to as the baffle funnel 13. This funnel-shaped widening area opens into an end area with an essentially constant cross-section shortly before the exit cross-sectional area 12.This area, with a substantially constant cross-section, forms a dead zone 14, which is filled with the plastic copper material. The copper material accumulates there and is then transferred into the extrusion channel 10 of the die 9. The depth R1 denotes the depth of the accumulation funnel 13, measured from the edge area of ​​the extrusion channel 10. The depth R2 according to . Figure 5 is to be understood in the same way. Due to the different dimensions in the longitudinal and transverse direction of the extrusion channel 10, the depth R2 is proportionally smaller than the depth R1 in the first section plane according to Figure 4 .

[0027] The design of the Figure 6 shows the variant according to the invention. The previously introduced reference numerals continue to be used for components with essentially the same function.

[0028] The design of the Figures 6 and 7shows an extrusion channel 7, which has a significantly smaller dead zone 14 in the hopper 13 in terms of volume. The hopper 13 is also shorter overall. Figure 7 shows the distance A1 between an inlet cross-sectional area 15 of the hopper 13 and the die 9. The said distance A1 is max. 30% larger than the smallest diameter D1 in the inlet cross-sectional area 11 of the extrusion channel 10, as can be seen from the Figure 7 can be seen.

[0029] Furthermore, it can be seen that the depths R3, R4 of the dead zone 14 are significantly smaller than in the embodiment according to the Figures 4 and 5 The exit cross-sectional area 12 of the retention channel 7 is only 40-60% larger than the entry cross-sectional area 11 of the extrusion channel 10 in the die 9. The following figures illustrate the effects of this tool modification.

[0030] The Figures 8 and 9illustrate the differences in the flow rates of the copper material, once in the prior art and once in the embodiment according to the invention, each related to a quadrant of the extruded profile. It can be seen that in the larger dead zone 14 according to Figure 8 the flow velocity is very low due to the dark color and drops to zero. The smaller dead zone 14 according to the embodiment of the invention ( Figure 9 ) also exhibits a reduction in flow velocity, however, only a smaller portion of the material must be redirected from the low velocities and accelerated to reach the extrusion channel 10, where the flow velocity is approximately 70 mm / s. The energy input into the dead zone is lower.

[0031] The Figures 10 and 11 show in the same comparison as the Figures 8 and 9the temperature distribution in an embodiment of the prior art ( Figures 4 and 5 ) and in the inventive solution ( Figures 6 and 7 ), each based on a quarter strand of the extrusion profile. Particularly striking is that the Figure 10 shows a temperature range T1 extending from the dead zone 14 into the extrusion channel 10. The copper material flowing from left to right is heated to temperatures above 600°C in the edge area. This causes structural changes and unwanted grain growth. Bending a flat conductor over its high edge leads to the undesirable orange peel effect on the surface or even to microcracks.

[0032] The inventive solution ( Figure 11) shows a completely different temperature profile in the area of ​​the dead zone 14. It can be seen that the temperature range T2, which corresponds to a temperature window of 484-542°C, is not only present in the core of the extruded profile, but also in the entire dead zone 14 and also in the entire edge area of ​​the material in the extrusion channel 10. The result is a more uniform grain growth. The material properties are thereby significantly improved. Figure 12 shows a comparison of the achievable tensile strength and yield strength for the conventional design ( Figures 4, 5 ) and for the design modified according to the invention ( Figures 6, 7 Each individual column pair refers to different speeds of the friction wheel 4. The speed levels are 6, 8, or 10 revolutions per minute. The tensile strength Rm is in the range of 210-220 MPa and tends to be somewhat higher than with the conventional design of the tool set.

[0033] More significant is the difference in terms of the yield strength RP02, which is above 70 MPa in the variant according to the invention (6-mod, 8-mod, 10-mod) and is approximately 20 MPa higher than the design in the state of the art (6-, 8-, 10-conv).

[0034] The Figure 13shows a micrograph through a quadrant of a flat conductor produced using the method according to the invention. The micrograph for the conventional production method is in the image plane on the left. The micrograph for the variant according to the invention is in the image plane on the bottom right. The values ​​indicated in the circles are local measured values ​​in the respective zone of the flat conductor. The upper values ​​refer to the image plane on the left. The lower values ​​refer to the image plane on the right. It is clear that the structure is significantly finer and more homogeneous and that the average weighted grain diameter is in a range of 45-65 µm in contrast to 70-77 µm in the prior art.

[0035] The Figures 14 and 15 show the final result on the radial outer surface of a flat conductor bent by 180°. Figure 14shows the state of the art and the clearly visible orange peel effect in the surface. Figure 15 shows the noticeably more uniform surface topology of the flat conductor sought according to the invention. Reference symbol:

[0036] 1 -Rotary extrusion machine 2 -Wire 3 -Flat conductor 4 -Friction wheel 5 -Gripping zone 6 -Upsetting zone 7 -Stowage channel 8 -Stowage plate 9 -Die 10 -Extrusion channel 11 -Inlet cross-sectional area of ​​10 12 -Exit cross-sectional area of ​​7 13 -Stowage funnel of 7 14 -Dead zone 15 -Inlet cross-sectional area of ​​13 A1 - Distance between 15 and 12 D1 - Diameter of 10 R1 - Depth of 14 R2 - Depth of 14 R3 - Depth of 14 R4 - Depth of 14 T1 - Temperature range over 600°C T2 - Temperature range between 484°C and 542°C

Claims

1. An extrusion method with the following steps: a) A continuously supplied copper material in the form of a wire (2), a powder or a granulate is heated by a friction wheel (4) of a rotary extruder (1); b) The copper material plasticised by heating is fed through an accumulation channel (7) widening in cross-section in a baffle plate (8) to a downstream shaping die (9), wherein the exit cross-section (12) of the accumulation channel (7) immediately before entry into the die (9) is larger than a shaping extrusion channel (10) in the die (9) to form a dead zone (14) for the pressure build-up of the plastic copper material before entry into the die (9); characterised by the following step: c) The temperature of the plastic copper material in the dead zone (14) and in the die (9) is set to a target value of at most 550 °C by reduction of the volume of the dead zone (14), wherein an accumulation channel (7) is used which widens exclusively in a funnel shape in the region of the dead zone (14) and has an exit cross-sectional area (12) which is 40 to 60% larger than an entry cross-sectional area (11) of the extrusion channel (10) in the die (9), wherein the accumulation channel (7) has an accumulation funnel (13) widening towards the die (9) in a funnel shape, having an entry cross-sectional area (15) at a distance (A1) from the die (9), wherein the distance (A1) is at most 30% larger than the smallest diameter (D1) of the extrusion channel (10) in the entry cross-sectional area (11) of the extrusion channel (10).

2. The extrusion method according to claim 1, characterised in that a high-purity and oxygen-free copper with a copper content of at least 99.99 wt.-% is used as the copper material.

3. The extrusion method according to claim 1 or 2, characterised in that the extruded profile is cooled immediately after exit from the die (9).

4. The extrusion method according to any one of claims 1 to 3 for manufacturing extruded flat conductors.

5. The extrusion method according to any one of claims 1 to 4, using a rotary extruder (1) according to the features of claim 6.

6. A rotary extruder (1) having a) a friction wheel (4) for heating a copper material supplied in the form of a wire (2), a powder or a granulate, and b) an accumulation plate (8) with an accumulation channel (7) in order to accumulate the plasticised copper material heated by friction upstream of a downstream shaping die (9) before the plastic copper material enters an extrusion channel (10) of the die (9), characterised in that c) the accumulation channel (7) has an exit cross-sectional area (12) which is 40 to 60% larger than an entry cross-sectional area (11) of the extrusion channel (1) to form a dead zone (14), d) wherein the accumulation channel (7) in the region of the dead zone (14) is exclusively widened in a funnel shape, e) wherein the accumulation channel (7) has an accumulation funnel (13) widening towards the die (9) in a funnel shape, having an entry cross-sectional area (15) at a distance (A1) from the die (9), wherein the distance (A1) is at most 30% larger than the smallest diameter (D1) of the extrusion channel (10) in the entry cross-sectional area (11) of the extrusion channel (10).