Forging device

Abstract

[Problem] To provide a novel forge welding apparatus that makes it possible to perform solid-phase welding with a plastic flow at a welding interface, at relatively low temperature and in a short time. [Solution] The forge welding apparatus is characterized by comprising a support means that supports a plurality of members to be welded with welded portions thereof laid on one another, from the lower surface side of the welded portions, a pressurizing means that applies pressure from the upper surface side of the welded portions, a stroke control means that controls the interval between the support means and the pressurizing means, and a heating means that contacts the members to be welded directly or indirectly to increase the temperature of the welded portions to a predetermined temperature range, wherein the stroke control means controls the reduction ratio R(T0 / T1), which is the ratio of the thickness T0 of the welded portions before welding and the thickness T1 of the welded portions after welding.

Description

[Technical field]

[0001] The present invention relates to a forge welding apparatus for use in joining similar or dissimilar metallic materials. [Background technology]

[0002] As the electrification of mobility advances rapidly, there is an increasing need for aluminum (Al) and aluminum alloys, which are lightweight, corrosion-resistant, and have excellent functionality such as electrical and thermal conductivity. In the car body, the joining of homogeneous aluminum alloys (Al / Al) and dissimilar materials (Fe / Al) between aluminum alloys and steel (Fe) are particularly important combinations, and in the electrical equipment field such as batteries and motors, joining of Al / Al, Al / copper (Cu), Fe / Al, titanium (Ti) / Al, nickel (Ni) / Al, etc. is required mainly for electrode (terminal) applications. For example, lithium-ion secondary batteries (LIBs), which have high output and are used in electric vehicles, are composed of a large number of cells, but pouch-type cells require that a large number of film-like tab leads made of Al (positive electrode) and Cu (negative electrode) are stacked and joined (same material joining in parallel, dissimilar material joining in series). Various methods have been used to join metal materials. For example, in laser welding, which uses laser light to melt and join metals, and resistance spot welding, which uses the electrical resistance of the overlapping parts of metal materials to heat them by passing electricity through them, the joint is heated to a high temperature at which it melts. In many dissimilar metal welding methods, however, brittle intermetallic compounds (IMCs) easily form at the joint, posing a critical material science problem in that it is difficult to obtain a practical joint strength. Furthermore, with these fusion welding methods, the non-melted areas around the weld are also heated to high temperatures, which increases the thermal effects, reducing the strength of the components and making it difficult to stabilize the strength of the joint. Furthermore, in these fusion welding processes, there is a concern that spatter can reduce the cleanliness of the weld surface, and porosity caused by metal vapor, air, shielding gas, etc. during melting can also reduce the strength of the joint, electrical performance, and other functionalities. For example, when laser welding or resistance spot welding, which are fusion welding methods, are used to connect laminated electrodes (tab leads) made of laminated foils, there is a risk of short circuits due to spatter or connection defects due to blowholes, even when joining the same types of materials. In addition, when joining vehicle structural and panel materials made of different materials, as mentioned above, it is difficult to achieve a joint with sufficient strength using IMC.

[0003] On the other hand, in solid-state joining, ultrasonic joining uses a consumable horn, which is expensive, and burrs and contamination are likely to occur in the joint. In addition, in friction stir welding (FSW), which uses frictional heat, it is difficult to process the beginning and end of the joint.

[0004] For example, Patent Documents 1 and 2 disclose crimping bonding in which a laminated electrode is pressed with a clamping plate or plate member. However, because crimping bonding is not a metallurgical bond, it is difficult to ensure sufficient bonding quality, and it is not suitable for joining panel materials. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2004-71199 [Patent Document 2] Japanese Patent Publication No. 2004-273178 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENT In order to solve the above technical problems, the present invention aims to provide a new forge welding apparatus that enables solid-state welding at a relatively low temperature in a short time while causing plastic flow at the welding interface. [Means for solving the problem]

[0007] The joint device is characterized in that it has a support means for supporting the joint from the underside while overlapping the joints of multiple workpieces, a pressure means for applying pressure from the upper side of the joint, a stroke control means for controlling the distance between the support means and the pressure means, and a heating means for directly or indirectly contacting the workpieces and raising the temperature of the joint to a predetermined temperature range, and the stroke control means controls a reduction ratio R(T0 / T1), which is the ratio between a thickness T0 of the joint before joining and a thickness T1 of the joint after joining. For convenience in this specification, the underside of the joint is referred to as the support means and the upper side as the pressure means, but it is sufficient if the joints of multiple joined materials are stacked and clamped from above and below or from the left and right, and pressure can be applied from one or both sides.

[0008] In conventional resistance spot welding, heating is performed by passing an electric current through the electrical resistance of the materials to be joined, and the joining temperature is unstable. Therefore, the present invention is characterized in that it uses an indirect heating means for the materials to be joined by thermal conduction, and in that it makes it possible to control the pressure (pressure condition) of the joint by the reduction ratio R. In this bonding apparatus, the bonding principle of the bonding interface is diffusion. In diffusion, the state of the diffusion path strongly influences the progress of the reaction. This device applies pressure to the joint, and by doing so, stretches and breaks up or makes very thin contaminated layers, such as oxide films on the surfaces of the joined materials, which are factors that impede diffusion, through plastic flow in the inward direction of the joint surface (in other words, creates a newly formed surface or a joint surface with a high level of cleanliness similar to that of a newly formed surface), thereby improving the condition of the diffusion path (joint interface) and achieving efficient diffusion. In addition, by simultaneously and stably controlling the joining temperature, which has a dominant effect on the diffusion reaction, as described above, the joining conditions necessary to obtain a sound joint are guaranteed (the reduction ratio and joining temperature are the basic parameters that control the joint strength).

[0009] In the present invention, the heating means may be a heating body in contact with the outer periphery of the joint, and further the support means and / or pressure means may be a rod whose stroke is controlled toward the joint, and the stroke-controlled rod is arranged in an insertion hole provided in the heating body, resulting in a forge welding device with a simple structure and high productivity. In the present invention, the optimum joining conditions vary depending on the metal material, but there is no problem as long as the strength of the joint is such that the base material breaks in a tensile shear test. The rolling reduction ratio may be determined by evaluating the state of the oxide film at the bonding interface through line analysis or area analysis using an electron probe microanalyzer (EPMA) or the like. Generally, the joining temperature is preferably about 330 to 450° C., and the reduction ratio R is preferably 2.0 or more. In the present invention, the temperature riser may have a hole (recess) for allowing the materials to escape during joining, and the rod may be provided with a step for allowing the materials to escape during joining. Effect of the Invention

[0010] The forge welding apparatus of the present invention can perform solid-state welding at a lower temperature than conventional fusion welding, and can manage the joining strength by controlling the reduction ratio, resulting in stable joining quality and high productivity. [Brief description of the drawings]

[0011] [Figure 1] Schematic diagrams showing the configuration of a forge welding device according to the present invention, where (a) is a cross-sectional view, (b) is a cross-sectional view showing the operation during welding, and (c) is a cross-sectional view of an example configuration in which a relief portion is provided in the rod. [Diagram 2] An example of forge welding of aluminum alloy panel material is shown. (a) shows the appearance of the joint (digital microscope image), and (b) shows the image quality (IQ) + inverse pole figure (IPF) map of the cross section of the joint by electron backscatter diffraction (EBSD). [Diagram 3] The effects of the reduction ratio and joining temperature on the tensile shear load of the joint and its fracture mode are shown. [Figure 4] The effect of the reduction ratio and bonding temperature on the EPMA oxygen intensity of the bonded interface is shown. [Diagram 5] The results of EPMA analysis of the bonded interface are shown as backscattered electron images (CP) and area analyses of the elements Al, Fe, Si, Mn, and O. (a) shows a sample with a bonding temperature of 390°C and a reduction ratio of R1.9, and (b) shows a sample with a bonding temperature of 390°C and a reduction ratio of R3.4. [Figure 6] An example of bonding of laminated aluminum foils is shown. (a) is the appearance of the bond (digital microscope image), (b) is an optical microscope image of the cross section of the bond (after etching), and (c) is an even larger image. [Figure 7] The IQ+IPF map taken by EBSD of the joint cross section of laminated aluminum foil is shown. [Figure 8] The effect of the reduction ratio and joining temperature of the laminated aluminum foil joint on the tensile shear load of the joint and its fracture morphology is shown. [Figure 9] This shows an example of joining between cold-rolled steel sheet (SPCC) and aluminum alloy sheet (A5052). (a) is a photograph of the joint appearance, (b) is an optical microscope image of the joint cross section (macro cross section), (c) is an EBSD image near the axis of the joint cross section (top: IQ map, bottom: IPF map), and (d) is a transmission electron microscope (TEM) bright-field image of the joint interface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An example of the configuration of a forge welding apparatus according to the present invention and an example of material evaluation of a joint obtained by this apparatus will be described below with reference to the drawings.

[0013] Figure 1 shows a schematic example of a double-action press type forge welding device (showing the example used in this test evaluation). A temperature riser 10 that moves up and down is disposed above the workpiece (metal material M1), and has an upper rod 11 that moves up and down through an insertion hole provided in this temperature riser 10. A lower heating body 20 that moves up and down is disposed below the material to be joined (metal material M2), and has an underrod 21 passing through an insertion hole in the center thereof.

[0014] The upper rod 11 may be directly controlled to move in the vertical direction, but in this embodiment, the upper rod 11 is pressed from above by a pressure punch 31, and the pressing stroke can be managed by a stopper 30. In this way, by adjusting the gap dimension d with the stopper 30, the amount of pressure stroke can be easily controlled, and the reduction ratio R of the joint can be easily controlled. In addition, the reduction ratio R can be controlled by detecting the load applied to the upper rod. Alternatively, when driving a rod with an AC servo motor or the like, the stroke can be controlled by a displacement meter (encoder, etc.).

[0015] The under rod 21 side has a similar structure to the upper rod 11 side, and this is an example in which pressure can be applied from the upper rod 11 side or from the under rod 21 side, allowing pressure application from only one side or simultaneous pressure application from both sides. In this way, it is possible to select the optimum pressing operation according to the upper and lower combinations of the workpieces having different plate thicknesses or different materials.

[0016] FIG. 1(b) shows a schematic diagram of two metal materials M1 and M2 stacked and joined together. FIG. 1(b) shows a state of joining operation in which only the upper rod 11 applies pressure without operating the lower under rod 21 side. The upper rod 11 descends, and pressure is applied to the joint, at the same time causing plastic flow at the joint interface. In this embodiment, in order to promote this plastic flow, an upper escape portion 12 of a predetermined size is formed between the upper rod 11 and the lower end side of the temperature rising body 10 shown in Figure 1 (a), and a lower escape portion 22 of a predetermined size is formed between the under rod 21 and the upper end side of the lower temperature rising body 20. As shown in FIG. 1(c), the recess (12a, 22a) may be provided on the rod side.

[0017] FIG. 1 is a schematic diagram illustrating the basic functions of the forge welding apparatus according to the present invention, and the drive mechanisms for the temperature raising body 10, the lower temperature raising body 20, the upper rod 11, and the under rod 21 can be designed to match a known double-action press. In the joining method according to the present invention, it is not always necessary to apply pressure from both sides, and the apparatus can be simplified by fixing one of the heating elements and the rod. When one of the heating elements and the rod is fixed, the heating element and the rod can be integrally molded. Moreover, the heating method and temperature control of the temperature riser 10 and the lower temperature riser 20 can be performed by using known methods used in hot pressing. In order to efficiently heat the materials to be joined, the rod may be provided with a heating function. As shown in the structure above, by independently arranging the heating body and rods on the top and bottom, it becomes possible to more actively heat the high-strength component (materials that are difficult to plastically deform) while keeping the joining temperature at the desired low temperature, especially in the case of joining dissimilar materials. In other words, it becomes possible to reduce the difference in plastic deformability of both components during joining and introduce an appropriate reduction ratio (plastic flow at the interface) for each component (the effect of independent temperature control on the top and bottom). This mechanism and control is more effective for components that have strength differences at the desired joining temperature and have large plate thicknesses.

[0018] Next, a joining experiment and evaluation of the panel materials were carried out, which will be explained below. Panel materials made of aluminum alloy JIS A5052 were forge welded together. The sample pieces were two pieces with a thickness of 0.8 mm, a width of 25 mm, and a length of 100 mm joined together. A preliminary investigation was carried out regarding the bonding temperature. Temperature sensors were attached to the heating body and the panel material and a temperature rise experiment was conducted. It was found that although there was a certain time lag and temperature difference between the temperature rise of the heating body and the temperature rise of the joint of the panel material, it was possible to control the temperature of the joint of the metal materials by interpolating this difference. Hereinafter, the bonding temperature means the temperature of the bonding interface.

[0019] Figure 2 shows an example of joining panels (plates) made of aluminum alloy JIS A5052. The joining conditions are as follows: rod diameter (forge diameter) 6 mm, relief diameter 9 mm, joining temperature 390°C, and reduction ratio R2.4. FIG. 2(a) shows an external photograph of the upper rod 11 side as viewed from the pressure punch side, and FIG. 2(b) is an EBSD IQ+IPF map of the joint cross section. It can be seen that there are no defects such as cracks or voids at the bonding interface, and that the crystallinity is high and good solid-state bonding has been achieved.

[0020] Figures 3 and 4 show graphs summarizing the results of joining experiments on aluminum alloy JIS A5052. FIG. 3 shows the tensile shear load of the joint when the reduction ratio R is changed at each joining temperature. The tensile shear load was measured by chucking both ends of the two joined plate materials and applying a tensile load. In the graph, BM indicates base material fracture, and BI indicates bond interface fracture. In this experiment, it was found that the reduction ratio R has a greater effect on the joining strength than the joining temperature. It can be seen that when the joining temperature is in the range of 360 to 450°C, if the reduction ratio is controlled to R2.4 or more, a sound joining strength that does not cause base metal fracture can be obtained. FIG. 4 shows the results of measurement of the oxygen intensity (peak intensity) at the bonded interface by EPMA line analysis. As mentioned above, in order to stabilize the joining quality of the joint (good diffusion in a short time at low temperature), it is important that there is as little contaminated layer at the interface as possible, which is an obstacle to diffusion. Therefore, the reduction ratio R was changed for each bonding temperature, and the oxygen peak intensity at the bonding interface was measured as a monitor of the contaminated layer (diffusion barrier layer). As a result, it was found that, as the joining temperature increases, the oxygen peak intensity tends to increase due to oxidation during preheating, but at any joining temperature, as the reduction ratio R is increased, the oxygen peak intensity decreases due to plastic flow that occurs at the joining interface (division and thinning of the contaminated layer due to surface expansion) (effect of reduction ratio on joining interface cleanliness). In forge welding, the larger the reduction ratio, the cleaner the joint interface becomes, and there is a tendency for joining to be possible at lower temperatures. However, in Figure 3, the reduction ratio R at which the fracture mode transitions from BI to BM was approximately the same at R2.4 between these joining temperatures, and the effect of the joining temperature was not significant. Considering this together with the oxygen peak intensity results in Figure 4 (the higher the temperature, the stronger the oxygen peak), it can be understood that in this experiment (this material), the influence of the contaminant layer, which acts as an obstacle to diffusion, and the bonding temperature, which acts as the driving force for diffusion, were roughly balanced. Figure 5 shows the EPMA surface analysis results of the bonded interface at a bonding temperature of 390°C, (a) with a reduction ratio of R1.9, and (b) with a reduction ratio of R3.4. CP is a backscattered electron image, and the other maps show the results of area analysis of each element. The results of the tensile shear test showed that (a) R1.9 showed an interface fracture, but (b) R3.4 showed a base material fracture. The results of the EPMA analysis show that by increasing the reduction ratio R, the contaminated layer at the bond interface is broken up and appears extremely thin, reducing its effect as a diffusion barrier (making the contaminated layer harmless), and resulting in a high-quality bond interface that allows efficient diffusion even at low temperatures. By adjusting the joining conditions (reduction ratio, joining temperature) based on these basic principles and behaviors, it is possible to establish appropriate joining conditions in this joining device.

[0021] Next, we will explain the results of an experiment in which 50 sheets of aluminum JIS A1N30H foil with a thickness of 0.012 mm were stacked and joined in a sandwich structure with an aluminum plate material JIS A1050 with a thickness of 0.5 mm on the upper side and an aluminum plate material JIS A1050 with a thickness of 0.8 mm on the lower side. The test piece had a width W of 30 mm and a length L of 100 mm. Figure 6(a) shows a digital microscope photograph of the appearance of the joint when the joining was performed under the conditions of a joining temperature of 420°C, a reduction ratio of R2.4, a rod diameter of 6 mm, and a clearance diameter of 9 mm. (b) shows an optical microscope macro-photograph of the cross section of the joint (after etching), and (c) shows an enlarged view of the same. Figure 7 shows the IQ+IPF map of EBSD in Figure 6(c) (analyzed before etching). From this, it can be seen that none of the 50 sheets of aluminum foil broke, each material had an appropriate reduction ratio, and was satisfactorily solid-state welded (the black dots in the enlarged image are not voids but inclusions in the material).

[0022] Figure 8 shows the tensile shear load of the joint versus reduction ratio R at each joining temperature. In the graph, BM_U indicates base material fracture in the upper aluminum plate, BM_L indicates base material fracture in the lower aluminum plate, and BI_U and BI_L indicate interfacial fracture in the upper aluminum plate and interfacial fracture in the lower aluminum plate, respectively. In this experiment, no peeling occurred between the foils under any of the conditions. This shows that as the joining temperature increases, the reduction ratio at which the base metal fracture occurs decreases and the joining strength also improves. In other words, the higher the reduction ratio, the more likely it is that a sound joining can be achieved even at a lower temperature. It can be seen that, regardless of the joining temperature, base metal fracture occurs at a reduction ratio of generally 2.0 or more. Considering the processing conditions under which the joining strength is generally stable, it can be seen that in the case of joining this laminated aluminum foil, the preferable ranges are a joining temperature of 330° C. or higher and a reduction ratio R of 2.0 or higher.

[0023] Next, the results of stacking and forging a cold-rolled steel plate JIS SPCC, thickness t 0.4 mm, and an aluminum alloy JIS A 5052, thickness t 0.8 mm (both width W 30 mm, length 100 mm) are shown. This is an example where the joining temperature is 420°C, the reduction ratio is R3.3, the rod diameter is 3 mm, and the relief diameter is 10 mm. Figure 9(a) shows the appearance of the joint, (b) shows a macroscopic view of the joint cross section taken by an optical microscope, (c) shows the EBSD analysis results near the axis of the joint cross section (top: IQ map, bottom: IPF map), and (d) shows a TEM bright field image of the joint interface. The tensile shear load of this joint was 1,454 N, and the fracture morphology was sound, with base material fracture (plug fracture). As can be seen from (d), the thickness of the reaction layer (RL) that formed at the joint interface was about 20 to 50 nm, and since the standard thickness for IMC such as Fe / Al that is generally considered to be brittle is about 1 μm, it can be said that the joint is essentially IMC-free. This joining device uses RL, including IMC, as the metallurgical joining mechanism at the interface, while neutralizing its brittleness, and can achieve high-strength dissimilar material joining, as shown in this example. [Industrial Applicability]

[0024] The forge welding apparatus according to the present invention is capable of solid-state welding at low temperatures and allows quality control by adjusting the welding temperature and reduction ratio, and therefore can be used to weld various metal materials. [Explanation of symbols]

[0025] 10. Rising Temperature 11 Upper Rod 12 Upper relief 20 Lower heating element 21 Underrod 22 Lower relief 30 Stopper 31 Pressure punch

Claims

1. With multiple joined parts overlapping, A support means for supporting the joint from a lower surface side; A pressure applying means for applying pressure from an upper surface side of the joint; a stroke control means for controlling a distance between the support means and the pressure means; A heating means is provided which directly or indirectly contacts the workpieces and heats the joint to a predetermined temperature range; The stroke control means controls the thickness T ０ and the thickness of the joint after joining T １ The reduction ratio R (T ０ / T １ ) A forge welding apparatus characterized in that the supporting means and / or pressure means are rods whose stroke amount toward the joint is controlled by a displacement gauge or a stopper.

2. the heating means is a temperature riser that contacts the outer periphery of the joint, 2. The forge welding apparatus according to claim 1, wherein the rod with a controlled stroke amount is disposed in an insertion hole provided in the heater.

3. 3. The forge welding apparatus according to claim 2, wherein the heating body has a hole for allowing the materials to escape during the joining.

4. 3. The forge welding apparatus according to claim 2, wherein said rod has a step for allowing the workpieces to escape during said welding.

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