An ultrasonic welding method for battery pack casing

Abstract

This invention discloses an ultrasonic welding method for battery pack casings, relating to the field of battery casing manufacturing technology. The battery pack casing includes a box and a cover that interlock. The method includes: before the box and cover are interlocked, pre-positioning a separator in a predetermined area of ​​their mating surface, the thickness of which is less than or equal to the inherent assembly gap between the box and cover at that location; ultrasonically welding the interlocked box and cover to fuse the remaining areas on the mating surface except for the predetermined area occupied by the separator, forming an annular sealing strip; after welding, removing the separator, creating a permeable micro-slit connecting the inside and outside of the casing on the annular sealing strip. This invention utilizes the separator to physically prevent plastic fusion during ultrasonic welding, and the removal of the separator after welding precisely forms a permeable micro-slit. The process is simple, consistent, and requires no additional openings or parts, thus producing a battery pack casing that combines pressure balance and splash protection.

Description

Technical Field

[0001] This invention relates to the field of battery casing manufacturing technology, and more specifically to a welding method for housing a lithium-ion battery pack and sealing it using ultrasonic welding. Background Technology

[0002] For lithium-ion battery packs in handheld power tools such as sprayers, the casing must have good sealing properties to prevent external moisture and dust from entering and causing short circuits or cell damage. In existing technology, the casing body and cover are usually designed as interlocking structures, and ultrasonic welding is performed along their joint surface to form a continuous annular sealing band.

[0003] However, in high-temperature environments, such fully sealed structures can cause significant pressure differences between the inside and outside of the casing due to the expansion of air inside the casing, ultimately leading to bulging and deformation. To address this issue, the applicant's utility model patent application filed on the same day proposes a battery pack casing structure that proactively incorporates an unwelded area on the annular sealing strip. This area utilizes the assembly gap between the housing and the cover to create a permeable microslit connecting the inside and outside of the casing, allowing air molecules to pass freely while blocking water droplets at normal pressure due to surface tension, thus balancing pressure balance and splash protection.

[0004] However, to put the above structural design into mass production, a key technological challenge is faced: how to accurately, reliably, and cost-effectively form such a breathable micro-slit during continuous and efficient ultrasonic welding. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide an ultrasonic welding method for battery pack casings, addressing the process requirements of mass production for the aforementioned structural solutions. This method can precisely form a breathable micro-slit connecting the inside and outside of the casing during ultrasonic welding, and the process is simple, consistent, and does not increase the risk of casing damage.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] An ultrasonic welding method for a battery pack casing, the battery pack casing comprising a box body and a cover body that interlock with each other, the method comprising the following steps:

[0008] Before the box body and the lid are fastened together, a spacer is pre-placed in a predetermined area of ​​the joint surface between the two; the thickness of the spacer is not greater than the assembly gap between the box body and the lid (usually between 0.05mm and 0.13mm).

[0009] The snap-fitted box and cover are placed in an ultrasonic welding device and ultrasonically welded to fuse the remaining areas on the joint surface except for the predetermined area occupied by the isolation plate, forming an annular sealing strip.

[0010] After welding is completed, the isolation plate is pulled out, and a breathable micro-slit connecting the inside and outside of the shell is formed in situ on the annular sealing strip.

[0011] The ingenuity of the above technical solution lies in using a separator as a physical barrier. Under the high-frequency vibration and pressure of ultrasonic welding, the area occupied by the separator is blocked, preventing direct contact between the upper and lower plastic surfaces and thus preventing fusion. After welding, the separator is smoothly pulled out in a direction parallel to the joint surface, immediately leaving a precise gap in place with a width equal to the thickness of the separator and a length equal to the width of the separator, which is the required breathable micro-slit.

[0012] When the microslit width is 0.05 mm, the capillary effect is most significant, allowing air molecules to pass freely in a viscous flow manner without affecting air permeability. When the microslit width is between 0.05 mm and 0.13 mm, airflow is smoother, while still effectively preventing water droplets from entering under normal pressure.

[0013] Depending on the material of the isolation sheet, the embodiments of the present invention can be divided into two categories:

[0014] The first type is a metal foil separator. As a preferred embodiment, the separator is a metal foil, more preferably a stainless steel foil or aluminum foil. The metal foil has a smooth surface and stable chemical properties; it neither melts nor adheres to the plastic at the high temperature during welding, ensuring a clean and residue-free extraction process and guaranteeing the unobstructed flow and dimensional consistency of the ventilation micro-slits. The thickness of the metal foil can include commercially available ultra-thin stainless steel foil (down to 0.003mm) and aluminum foil (down to 0.005mm), or can be selected within the 0.05mm range, comparable to the thickness of ordinary A4 printing paper, resulting in low extraction resistance.

[0015] The second type is high-temperature resistant polymer film. This type of separator utilizes the heat resistance or non-stick properties of the polymer film to prevent the plastic from fusing during ultrasonic welding. After welding, it can be removed, and a breathable micro-slit can be formed in situ.

[0016] The beneficial effects of this invention are:

[0017] Balancing air pressure balance and water splash protection: The battery pack casing produced by this method has hidden breathable micro-slits that can automatically release pressure at high temperatures to eliminate the risk of bulging, while utilizing capillary effect and shielding structure to achieve daily water splash protection.

[0018] Residue-free cleaning and molding: The separator does not participate in the fusion process, leaving no residue after extraction, and the micro-seam is immediately cleared without the need for subsequent cleaning procedures.

[0019] Zero damage: The isolation plate is smaller than or equal to the inherent assembly gap between the box and the cover at that location, and welding does not damage the shell.

[0020] The process is simple and highly compatible: it only requires adding two actions to the existing ultrasonic welding production line, namely placing and removing the isolation plate, which can be easily integrated through automated devices, resulting in extremely low modification costs. Attached Figure Description

[0021] Figure 1 This is a longitudinal sectional view of the housing and cover of the battery pack involved in this invention.

[0022] Figure 2 This is an overall cross-sectional view of the battery pack casing.

[0023] Figure 3 This is a ring-shaped sealing strip structure with full circumferential sealing welding in the existing technology;

[0024] Figure 4 The ultrasonically welded annular sealing strip structure of the present invention is shown, illustrating the unwelded section in this design;

[0025] Figure 5 for Figure 4 Longitudinal and transverse sectional views of the unwelded section;

[0026] Figure 6 This is a flowchart of the ultrasonic welding method of the present invention.

[0027] In the diagram: 1. Cover; 11. Upper shoulder; 12. Outer edge shielding part; 2. Box body; 21. Lower shoulder; 22. Inner edge opening; 3. Annular sealing strip; 31. Unwelded section; 32. Breathable micro-slit. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0029] Example 1 (Metal Foil - Stainless Steel Foil)

[0030] This embodiment provides an ultrasonic welding method for battery pack casings, used to manufacture battery pack casings with air pressure balancing function. For example... Figure 1 and Figure 2As shown, the battery pack casing includes an upper cover 1 and a lower housing 2. The cover 1 has an upper shoulder 11 and a downwardly extending outer edge blocking portion 12 on its edge. The upper edge of the housing 2 has a lower shoulder 21 and an upwardly extending inner edge opening 22. The mating surfaces of the cover 1 and the housing 2 are stepped structures that fit together. The assembly gap between the housing 2 and the cover 1 is 0.05 mm.

[0031] The operation steps of this method are as follows: Figure 6 As shown, the details are as follows:

[0032] S1. Prepare an isolation sheet. The isolation sheet is made of stainless steel foil with a thickness of 0.003mm, cut into small strips 3mm wide and 20mm long.

[0033] S2. Before the box body 2 and the cover body 1 are fastened together, a release liner is attached to the predetermined position where the "unwelded section" needs to be formed on the box body 2.

[0034] S3. Attach the cover 1 to the box 2. At this point, the insulating sheet is clamped between the cover 1 and the box 2. Place the assembled unit into the welding fixture of the ultrasonic welding equipment.

[0035] S4. Start the ultrasonic welding equipment, press down the welding head to cause high-frequency vibration friction and fusion between the mating surfaces of the cover 1 and the box 2. In the area occupied by the isolation sheet, the plastic does not fuse because the stainless steel foil prevents direct contact between the plastics. Welding parameters: frequency 20kHz, pressure 0.25MPa, welding time 0.5 seconds.

[0036] S5. After welding, use tweezers to hold the tail of the separator plate remaining outside the shell and smoothly pull it out in a direction parallel to the joint surface. After pulling it out, a through gap with a length L of 3mm and a width W of 0.05mm is left in the original position, which is the ventilated micro-slit 32.

[0037] like Figure 4 and Figure 5 As shown, there is an unwelded section 31 on the annular sealing strip 3, and the gap reserved at this unwelded section 31 is the ventilated micro-slit 32. The opening of the ventilated micro-slit 32 is completely covered by the upper shoulder 11 of the cover body 1, the outer edge blocking part 12, and the lower shoulder 21 of the box body 2, so the opening is not visible from the outside, and water flow cannot directly impact it. Upon inspection, the inner wall of the ventilated micro-slit 32 is smooth, without plastic burrs or residue, and the gap is unobstructed.

[0038] Example 2 (Metal Foil - Aluminum Foil)

[0039] This embodiment is basically the same as Embodiment 1, except that the isolation sheet is made of aluminum foil with a thickness of 0.05mm.

[0040] Example 3 (High-Temperature Resistant Polymer Film)

[0041] This embodiment is basically the same as Embodiment 1, except that the assembly gap between the box body 2 and the cover body 1 is 0.13mm, and the separator is made of a 0.13mm thick polyimide (PI) film, cut into small strips 1mm wide and 20mm long. This film can withstand the instantaneous high temperature during ultrasonic welding without melting. After welding, the PI film is smoothly pulled out with tweezers in a direction parallel to the joint surface. After extraction, a breathable micro-slit with a length L of 1mm and a width W of 0.13mm is formed. Testing shows that the inner wall of the micro-slit is smooth, without plastic burrs or residue, and has good permeability.

[0042] To verify the beneficial effects of the present invention, the battery pack casings prepared using Examples 1, 2, and 3 were compared with existing fully sealed casings in the following comparative tests:

[0043] Pressure balance test: Placed in a constant temperature environment of 60℃ for 2 hours. Existing technology shells show obvious bulging and deformation visible to the naked eye; the shell produced by the method of this invention remains intact and without any deformation.

[0044] Water splash resistance test: Sprayed for 10 minutes according to IEC 60529 standard IPX4 rating. After the test, the casing was opened for inspection, and no water ingress was found inside.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ultrasonic welding method for a battery pack casing, the battery pack casing comprising a box body and a cover body that interlock, characterized in that, The method includes the following steps: Before the box body and the lid are fastened together, a partition plate is pre-placed on the joint surface of the two; the thickness of the partition plate is not greater than the assembly gap between the box body and the lid. The snap-fitted box and cover are placed in an ultrasonic welding device and ultrasonically welded to fuse the remaining areas on the joint surface except for the predetermined area occupied by the isolation plate, forming an annular sealing strip. After welding is completed, the isolation plate is pulled out, and a breathable micro-slit connecting the inside and outside of the shell is formed in situ on the annular sealing strip.

2. The method according to claim 1, characterized in that, The separator is a metal foil.

3. The method according to claim 2, characterized in that, The metal foil is a stainless steel foil or an aluminum foil.

4. The method according to claim 1, characterized in that, The separator is a high-temperature resistant polymer film.

5. The method according to claim 1, characterized in that, The assembly gap is 0.05 mm to 0.13 mm.

6. The method according to claim 1, characterized in that, The isolation plate is pulled out in a direction parallel to the mating surface.

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