Forming method and application of aluminum shell

Abstract

The invention discloses a forming method and application of an aluminum shell. The forming method comprises the steps that an aluminum blank is subjected to cold extrusion forming to obtain the aluminum shell, and then stretching and notching are conducted; cold extrusion forming refers to stretching forming of the aluminum blank in the reverse direction; the stretching step is carried out in a die A, and the die A comprises a punch and a female die; the stretching step comprises the steps that a punch is sleeved with the aluminum shell subjected to extrusion forming, an aluminum blank penetrates through a female die under the action of the punch, and the aluminum blank subjected to cold extrusion is subjected to plastic deformation again. According to the invention, the production of the aluminum shell with higher precision, higher material utilization rate and higher strength is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and particularly relates to a forming method and application of an aluminum shell. Background Art

[0002] The aluminum shell of a power battery needs to have good sealing performance. Therefore, the manufacturing process of the aluminum shell of the power battery is very important. To produce an aluminum shell, in the current common forming process of the aluminum shell, the stretching forming process mainly punches and blanks an aluminum strip with a certain thickness, and then forms the aluminum shell through multi-stage ironing. To improve the feeding efficiency for rapid production, an aluminum coil is generally used as the raw material. The required material shapes for stretching square and circular aluminum shells are oval and circular. That is, during production, only a part of the aluminum coil is punched and cut according to the required material shape for stretching, and the material utilization rate after punching is relatively low: between 65% and 70% for square aluminum shells, and between 60% and 67% for circular aluminum shells. In addition, due to the limitations of the die structure and process characteristics of the stretching process, the die punch has a relatively long structural design (generally within 2 times the height of the aluminum shell, and the part fixed by clamping only accounts for less than 1 / 3 of the total length of the punch; in terms of process characteristics, since the stretching process is an ironing process, when the punch feeds the aluminum shell material into the die cavity, the aluminum material will generate a relatively large extrusion force on the punch and the die. Therefore, during stretching forming, the deformation amount of the aluminum material opposite to the punch is generally set to be the same to prevent excessive differences in deformation amounts from forming an extrusion pressure difference. Due to the limitations of the process characteristics of the extrusion process, the die and the aluminum rod need to be heated before extrusion (the die needs to be heated to above 300°C, and the aluminum rod needs to be heated to about 500°C), and then extrusion shaping is carried out. Due to the influence of temperature rise and fall, the square tube will have a shrinkage phenomenon during the process from forming to complete cooling, so the wall thickness, outer dimension, etc. of the square tube also fluctuate greatly. Moreover, this process can only form an aluminum shell with both ends open and cannot manufacture an aluminum shell with a bottom. At the same time, due to the process characteristics of heating required, the strength of the square tube after extrusion forming is insufficient, currently usually in the range of 90 - 120 MPa. When performing drawing processing, the phenomenon of breaking often occurs. Another characteristic of the drawing process is coordinated forming. That is, during the drawing process, the core head is in a floating state. Affected by the wall thickness and extrusion pressure of the extruded square tube, the core head will move left and right and up and down. Therefore, the wall thickness of the aluminum shell will also fluctuate greatly, currently only controllable within the range of ±0.1 mm; secondly, during the drawing process, to reduce the drawing resistance, the working zones of the core head and the die are generally only designed to be 3 - 5 mm in length. Affected by the core head positioning method and accuracy, the phenomenon of misalignment between the core head and the working zone of the die often occurs during the drawing process, resulting in poor dimensions such as the inner and outer cavities, wall thickness, and R angle of the aluminum shell. Currently, the maximum fluctuation of the R angle can reach ±0.3 mm.

[0003] Therefore, a forming method for an aluminum shell with high precision and higher strength is needed. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. For this purpose, the present invention realizes the production of aluminum shells with higher-precision external dimensions and R-angle control that can reach ±0.1 mm respectively, higher material utilization rate and higher strength, and the strength of the aluminum shell can reach up to 180 MPa - 220 MPa.

[0005] The present invention also proposes an application of the aluminum shell prepared by the forming method in a battery housing.

[0006] According to one aspect of the present invention, a forming method of an aluminum shell is proposed, which includes cold-extruding an aluminum blank to form an aluminum shell and then performing stretching and cutting.

[0007] The cold extrusion forming is to stretch and form the aluminum blank in the reverse direction.

[0008] The stretching step is carried out in die A, and the die A includes a punch and a die.

[0009] The stretching step includes: sleeving the extruded aluminum shell onto the punch, and under the action of the punch, making the aluminum blank pass through the die, so that the cold-extruded aluminum blank undergoes plastic deformation again.

[0010] According to the first aspect of the present invention, it has at least the following beneficial effects:

[0011] The aluminum shell forming process of the present invention uses cold extrusion process as the first forming process. First of all, the aluminum material does not need to be heated before cold extrusion forming. After forming, its surface temperature is also below 120°C, far lower than the softening temperature of the aluminum material. When its temperature drops to room temperature, its shrinkage is <1%, so its wall thickness can also be controlled within the range of ±0.03mm. In addition, cold extrusion forming is a forced forming process, and the forming process is relatively more stable, and currently it can be controlled within the range of ±0.05mm. Finally, the cold extrusion forming process is reverse extrusion forming. The aluminum block is plastically deformed by the pressure of the punch and flows out reversely through the gap between the punch and the die to form an aluminum shell. After forming, the bottom structure of the aluminum shell can be retained, so the production of aluminum shells with bottoms can be compatible. The second process is the drawing process. After cold extrusion forming, through the structural design of the punch and the die, during drawing, first, the aluminum shell after cold extrusion forming is sleeved on the punch. Through the action of the movement of the drawing machine, the punch and the cold-extruded aluminum shell are driven to pass through the die, and through the clearance fit between the die and the punch, the cold-extruded aluminum shell is plastically deformed again. The problems such as surface roughness and pits remaining during cold extrusion can be eliminated, and the surface roughness of the aluminum shell after drawing can reach Ra1.0. In addition, the strength problem can also be solved. After being thinned by drawing, the surface of the aluminum shell is equivalent to being cold-worked, and its strength will be greatly improved. At the same time, because the drawing process is a forced forming process, that is, both the die punch and the die are in a fixed state and will not be affected by the fluctuation of the material thickness and affect their positions, and the drawing process does not require heating, so the drawing process is carried out under relatively stable conditions, and the dimensional accuracy of the aluminum shell after drawing is relatively stable. The wall thickness can be controlled within the range of ±0.05mm, the outer dimension can be controlled within the range of ±0.1mm, and the R angle can be controlled within the range of ±0.1mm. The third cutting process: This process is mainly to precisely cut one end or both ends of the aluminum shell according to the length of the finished aluminum shell. Cutting one end is mainly for aluminum shells with bottoms, and cutting both ends is mainly for double-pass aluminum shells. After precise cutting, the final forming of double-pass or bottomed aluminum shells can be achieved.

[0012] The process method of the present invention combines the cold extrusion process and the drawing process. Firstly, through the backward extrusion method of the cold extrusion process, higher material utilization rate, higher product dimensional accuracy, and more aluminum shell structures (with bottom and without bottom structures) can be obtained. The current material utilization rate after the aluminum shell is formed: for the double-pass aluminum shell, it is 82.5% - 88.3% (the material utilization rate changes with the height of the aluminum shell), and for the aluminum shell with bottom, it is 86.7% - 93.5%; the wall thickness can be controlled within the range of ±0.03 mm; the R angle is also relatively more stable, and currently can be controlled within the range of ±0.05 mm; the process characteristics of its reverse forming can also meet the forming conditions of the aluminum shell with bottom. Secondly, it is the drawing process. Through the processing technology, the aluminum shell can obtain higher dimensional accuracy, a smoother surface, and higher strength after drawing. The wall thickness of the aluminum shell after drawing can be controlled within the range of ±0.05 mm, the external dimensions can be controlled within the range of ±0.1 mm, and the R angle can be controlled within the range of ±0.1 mm; at the same time, problems such as surface roughness and pits remaining during cold extrusion can be eliminated, and the surface roughness of the aluminum shell after drawing can reach Ra1.0; its strength will also be greatly improved, reaching within the range of 180 MPa - 220 MPa.

[0013] 2. By combining the cold extrusion, drawing, and cutting processes, the forming of aluminum shells with different structures such as equal-wall, unequal-wall, with bottom, and double-pass can be realized. Firstly, it is the cold extrusion process. By adjusting the clearance between the female die and the punch, the initial forming of aluminum shells with equal wall thickness and unequal wall thickness can be carried out, and the flow ratio of the material is planned. Currently, the forming of aluminum shells with one thick side and three thin sides, equal thickness on the opposite sides, and equal thickness on all four sides can be realized. For the aluminum shell with one thick side and three thin sides: the wall thickness of the thick side can be made 1.2 - 3.0 mm, and the other three sides can be made 0.5 - 1.0 mm. For the aluminum shell with equal thickness on the opposite sides: the thickness of the thick side can be made 0.7 - 1.4 mm, and the thickness of the thin side can be made 0.4 - 1.0 mm. For the aluminum shell with equal thickness on all four sides: the wall thickness can be made 0.4 - 0.8 mm. Secondly, it is the drawing process. Through the drawing process, the surface of the aluminum shell is smoother and the strength is higher. After drawing, problems such as surface roughness and pits remaining during cold extrusion can be eliminated. The surface roughness of the aluminum shell after drawing can reach Ra1.0, and at the same time, its strength will also be greatly improved, reaching within the range of 180 MPa - 220 MPa. Finally, it is the cutting process. By precisely cutting one end or both ends of the aluminum shell, the aluminum shell structures with bottom and double-pass can be obtained. If only one end is cut off, the bottom surface of the aluminum shell is retained, thus obtaining the finished aluminum shell with bottom; if both ends are cut off at the same time, the mouth and bottom of the aluminum shell are cut off, thus obtaining the finished double-pass aluminum shell.

[0014] In some embodiments of the present invention, in the step of drawing, the downward pressing speed of the punch is: 180 - 200 mm / s.

[0015] In some embodiments of the present invention, the stroke accuracy in the stretching step is 0.05 - 0.07 mm.

[0016] In some embodiments of the present invention, the wall thickness reduction of the aluminum shell obtained after stretching is 25 - 70%.

[0017] In some embodiments of the present invention, the wall thickness reduction of the aluminum shell obtained after stretching is 40 - 70%.

[0018] In some embodiments of the present invention, the cold extrusion forming step is carried out in die B, and the roughness of the contact surface between die B and the aluminum blank is 1 - 0.2.

[0019] Because during cold extrusion forming, the aluminum blank is designed with a maximum unilateral shrinkage of 0.1 mm according to the formed size, and the aluminum blank is a planar structure. During cold extrusion forming, the aluminum material will flow out simultaneously along the die gap position and is only affected by the size of the die matching gap during the flow process. After forming, the maximum height difference at the mouth can be controlled within 15 mm, and for a circular aluminum shell, it can be controlled within 7 mm. Therefore, only the different parts at the mouth need to be cut off after forming. The current material utilization rate of the aluminum shell after forming: for a double - pass aluminum shell, it is 82.5% - 88.3% (the material utilization rate changes with the height of the aluminum shell), and for a bottom - equipped aluminum shell, it is 86.7% - 93.5%. The cold extrusion process is through the size matching of the female die and the punch. According to the requirements of the aluminum shell wall thickness size, a corresponding gap is reserved. During cold extrusion, when the aluminum material is under the pressure of the punch, the material flows out reversely from the gap between the female die and the punch to form the aluminum shell; both the punch and the female die are precision - processed and formed, and the processing accuracy can reach 0.005 mm. Moreover, the aluminum material does not need to be heat - treated before cold extrusion forming, and its surface temperature after forming is also below 120°C, far lower than the softening temperature of the aluminum material. When its temperature drops to room temperature, its shrinkage is <1%, so its wall thickness can also be controlled within ±0.03 mm; in addition, cold extrusion forming is a forced forming process, and the material will flow along the gap between the female die and the punch, so its R - angle is relatively more stable and can currently be controlled within ±0.05 mm.

[0020] In some embodiments of the present invention, the die - matching gap in the cold extrusion forming step is ≤0.06 mm.

[0021] According to the second aspect of the present invention, an application of the aluminum shell prepared by the forming method in a battery shell is proposed.

[0022] In some embodiments of the present invention, the aluminum shell includes an unequal - wall aluminum shell or an equal - wall aluminum shell. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a forming process diagram of the aluminum shell;

[0024] Figure 2 The aluminum shell product diagram prepared in Example 1;

[0025] Figure 3 The aluminum shell product diagram prepared in Example 2. Detailed implementation manners

[0026] The concept of the present invention and the technical effects produced will be clearly and completely described below in conjunction with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

[0027] In the raw materials of the present invention:

[0028] Raw materials for the aluminum shell: AL3003;

[0029] Among them, the backward extrusion machine includes a horizontal multi-link toggle type cold extrusion machine, a punch installed on the cold extrusion machine, and a backward extrusion die arranged directly below the punch. The upper die of the backward extrusion die is made of tungsten steel, and the die cavity is made of tungsten steel inlay, such as YG8, YG15, YG20, etc. The manufacturing process of the extrusion die generally needs to go through processes such as grinder processing, slow wire cutting processing, quenching, inlay processing, cryogenic treatment, surface polishing treatment, etc. The specific process varies according to the uses of each component. The extrusion machine selects the cold extrusion press or cold extrusion punch with the most suitable tonnage according to the extrusion force required for the cold extrusion forming of the aluminum shell.

[0030] The drawing die includes: an upper die base, a punch, a lower die base, a die cavity insert, etc. The upper and lower die bases are made of materials such as 45# or Cr12, the punch is made of DC53 material, and the die cavity insert is made of tungsten steel material. The manufacturing process of the drawing die generally needs to go through processes such as grinder processing, slow wire cutting processing, quenching, inlay processing, cryogenic treatment, surface polishing treatment, etc. The specific process varies according to the uses of each component. The drawing machine selects the drawing machine tool with the most suitable tonnage according to the pressure required for the drawing forming of the aluminum shell.

[0031] Example 1

[0032] This embodiment provides a forming method for an aluminum shell, which is the following steps:

[0033] S1: Stir the aluminum block and the lubricant evenly so that the lubricant adheres to the surface of the aluminum block. The ratio of the lubricant to the aluminum block is 25:1 (weight ratio), the stirring time is 8 - 15 minutes, and the rotation speed is 25 - 30 revolutions per minute;

[0034] S2: Feed the aluminum blocks after frying into the cold extrusion die through the feeding mechanism. Only one block can be fed each time. Then, under the action of the cold extruder, make the punch of the cold extrusion die move towards the die cavity and act on the surface of the aluminum block. Through continuous pressure, the aluminum block deforms, and the aluminum material flows out from the gap between the punch and the die cavity to form an aluminum shell structure. The gap between the outer wall of the aluminum blank and the inner wall of the die cavity is less than 0.06 mm. The punch moves at a speed of 230 mm / s. Through the gap design between the die punch and the die, the gap design is thick on one side and thin on three sides. The wall thickness of the thick side is set at 1.5 mm, the wall thickness of the thin side is set at 0.5 mm, and the gap of the thick side is 1.0 mm larger than that of the thin side.

[0035] S3: Before ironing, use a polishing grinding head to polish the working belt of the ironing die to make its surface roughness less than Ra0.1. Then, perform ironing forming processing on the cold-extruded aluminum shell blank on this die. After forming, test that the surface roughness of the aluminum shell is between Ra0.3 and Ra0.6, with an average of about Ra0.45. The ironing punch moves at a speed of 190 - 200 mm / s. After the ironing process, the surface roughness is between Ra0.3 and Ra0.6, the dimensional tolerance of the outer shape can be controlled within ±0.1 mm, and the inner and outer R corners can be controlled within ±0.1 mm.

[0036] S4: According to the length of the aluminum shell finished product, precisely cut one end of the aluminum shell to obtain an aluminum shell with a bottom. The cutting steps are as follows: rough cutting (cut by sawing to remove the bottom and the mouth of the aluminum shell after ironing, leaving about 0.5 mm of length at both ends) → precise cutting (cut by a die - rotary cutting to remove the remaining 0.5 mm of length to make the length of the aluminum shell meet the customer requirements, and the precision can be controlled within ±0.1 mm). The main parameters of the cutting machine: the repeat positioning accuracy of the rotary cutting die is below 0.03 mm. The picture of the obtained aluminum shell is as Figure 2 shown.

[0037] Example 2

[0038] This example provides a forming method for an aluminum shell with equal thickness on both sides, specifically as follows:

[0039] S1: Stir the aluminum blocks and the lubricant evenly so that the lubricant adheres to the surface of the aluminum blocks. The ratio of the lubricant to the aluminum blocks is 25:1 (by weight). The stirring time is 8 - 15 minutes, and the rotation speed is 25 - 30 revolutions per minute.

[0040] S2: Through the feeding mechanism, the aluminum blocks after frying are sent into the cold extrusion die, with only one block being sent each time. Then, under the action of the cold extruder, the punch of the cold extrusion die moves towards the die cavity and acts on the surface of the aluminum block. Through continuous pressure, the aluminum block deforms, and the aluminum material flows out from the gap between the punch and the die cavity, forming an aluminum shell structure. The gap between the outer wall of the aluminum blank and the inner wall of the die cavity is less than 0.06 mm. The punch moves at a speed of 230 mm / s. Through the gap design between the punch and the die of the die, the gaps of the two large surfaces are the same, and the gaps of the two small surfaces are the same. Moreover, the gap of the small surface is 0.2 - 0.3 mm larger than that of the large surface, thereby obtaining an aluminum shell structure with equal wall thickness on opposite sides.

[0041] S3: Before ironing, use a polishing grinding head to polish the working belt of the ironing die to make its surface roughness between Ra0.1 - 0.4. Then, perform ironing forming processing on the aluminum shell blank after cold extrusion on this die. After forming, test that the surface roughness of the aluminum shell is between Ra0.5 - 0.8, with an average of about Ra0.65. The ironing punch moves at a speed of 190 mm / s. After the ironing process, an aluminum shell with a surface roughness between Ra0.5 - 0.8 is obtained, and the dimensional tolerance of the outer shape can also be controlled within ±0.1 mm, and the inner and outer R corners can be controlled within ±0.1 mm.

[0042] S4: According to the length of the finished aluminum shell, one end of the aluminum shell is precisely cut to obtain an aluminum shell with a bottom. The cutting steps are as follows: rough cutting (removing the bottom surface and the mouth part of the aluminum shell after ironing, leaving about 0.5 - 1 mm of length at both ends), and precise cutting (cutting off the reserved 0.5 - 1 mm of length to make the length of the aluminum shell meet the customer's requirements, with the precision controllable within ±0.1 mm); the main parameters of the cutting machine: the repeated positioning precision of the cutting is below 0.03 mm; the picture of the obtained aluminum shell is as Figure 3 shown; the product dimensions of the obtained aluminum shell are shown in Table 1.

[0043] Table 1. Dimensions and test data

[0044]

[0045] Example 3

[0046] This example provides a forming method for an aluminum shell with equal thickness on four sides. The difference between this example and Example 2 is that in step S2, the gaps on the four sides are controlled to be the same at 0.4 - 0.8 mm to ensure that the thickness of each side of the formed aluminum shell is consistent, and the other conditions are the same as those in Example 2.

[0047] Example 4

[0048] This embodiment provides a forming method for an aluminum shell. The difference between this embodiment and Embodiment 1 is that during cold extrusion forming, the wall thickness of each surface of the aluminum shell is designed to be 0.90 - 1.0 mm. After the drawing process, the wall thickness of each surface of the aluminum shell thins to about 0.5 mm, the average wall thickness of each surface thins by about 0.45 mm, the thinning amount is about 45% - 50%, the average wall thickness of each surface thins by about 0.4 mm, the thinning amount is about 45%, and the other conditions are the same.

[0049] Comparative Example 1

[0050] This comparative example provides a forming method for an aluminum shell. The difference between this comparative example and the embodiment is that the thinning amount of the aluminum shell in step S2 is about 8%, and the other conditions are the same.

[0051] Comparative Example 2

[0052] This comparative example provides a forming method for an aluminum shell. The difference between this comparative example and the embodiment is that the thinning amount of the aluminum shell in step S2 is about 15%, and the other conditions are the same.

[0053] Comparative Example 3

[0054] This comparative example provides a forming method for an aluminum shell. The difference between this comparative example and Embodiment 1 is that before drawing, a polishing head is used to polish the working belt of the drawing die so that its surface roughness is between Ra0.8, and other conditions are the same as those in Embodiment 1.

[0055] Under the above conditions, the surface roughness of the aluminum shell is Ra1.2 - Ra1.5, and an out-of-tolerance phenomenon occurs.

[0056] Comparative Example 4

[0057] This comparative example provides a forming method for an aluminum shell. The difference between this comparative example and Embodiment 1 is that before drawing, a polishing head is used to polish the working belt of the drawing die so that its surface roughness is Ra 1.1, and other conditions are the same as those in Embodiment 1.

[0058] Under the above conditions, the surface roughness of the shell is Ra1.6 - Ra2.4, and an out-of-tolerance phenomenon occurs.

[0059] Test Example:

[0060] Test standard: Cut each surface of the aluminum shell in step S2 into standard splines and use a tensile testing machine for tensile testing. The results are shown in Table 2. The mechanical property test refers to "GB / T 228.1 2021 Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0061] Table 2. Performance Test

[0062]

[0063] Under the above conditions, the grain thinning amount of the comparative example is low and the grains are not optimized, which may also result in insufficient improvement of the strength of the aluminum alloy. In some cases, too little deformation may cause the internal stress of the material not to be effectively dispersed, affecting the mechanical properties of the aluminum shell.

[0064] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for forming an aluminum shell, characterized in that: It includes cold extruding the aluminum billet to obtain the aluminum shell, and then stretching and cutting; The cold extrusion forming is to stretch the aluminum billet in the reverse direction; The step of drawing is carried out in a die A, which comprises a punch and a die; The step of drawing comprises: putting the extruded aluminum shell onto a punch, and allowing the aluminum billet to pass through a die under the action of the punch, so that the cold-extruded aluminum billet undergoes plastic deformation again.

2. The forming method according to claim 1, characterized in that: In the step of drawing, the pressing speed of the punch is 180-200 mm / s.

3. The forming method according to claim 1, characterized in that: The stroke accuracy in the stretching step is 0.05 to 0.07 mm.

4. The forming method according to claim 1, characterized in that: The wall thickness of the aluminum shell obtained after the stretching is reduced by 25-70%.

5. The forming method according to claim 1, characterized in that: The wall thickness of the aluminum shell obtained after the stretching is reduced by 40-70%.

6. The forming method according to claim 1, characterized in that: The cold extrusion step is performed in a die B, and the roughness of the contact surface between the die B and the aluminum billet is 1-0.

2.

7. The forming method according to claim 6, characterized in that: The die gap in the cold extrusion step is ≤0.06 mm.

8. Use of the aluminum shell prepared by the forming method according to any one of claims 1 to 7 in a battery shell.

9. The use according to claim 8, characterized in that: The aluminum shell includes an unequal-wall aluminum shell or an equal-wall aluminum shell.

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