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5 Reasons to Use an Adhesive for Battery Box Bonding

( 03/18/2020 ) Written by: Delphine Andrivot

Assembling electric vehicle (EV) battery boxes using structural adhesives instead of mechanical fasteners not only results in process efficiencies but can help installed boxes perform better. Here are five ways how:

1. Containment

EV battery boxes have an important job to do, structurally speaking. If chemicals leak from the battery, the battery box needs to contain those chemicals. The continuous seal created by structural adhesives establishes a barrier, keeping chemicals from leaking out, whereas mechanical fasteners and welding allow gaps and leakage. Tests on certain structural adhesives have shown that they are resistant to a wide range of exposure, including hot solutions of ethylene/propylene glycol and water. In addition to chemicals, pressure can rise inside a battery box, and this, too, should be contained within the box. Pressure tests on LORD® 850 and 852 acrylic adhesives (used in combination with LORD Accelerator 25GB), performed one hour after assembly and dispensing, demonstrated that the adhesives can withstand pressures of 3-5 bar (0.3-0.5MPa).

2. Material Strength and Integrity

The integrity of a box’s materials (metals as well as coatings) is maintained when structural adhesives are used in place of welding or mechanical fasteners. Spot welding weakens metals, which means the part can’t be reused if a mistake is made during assembly. Structural adhesives, on the other hand, can be cleaned off of the part (before curing) and, since the integrity of the materials has been maintained, the part can be reused.

3. Manufacturing Efficiency and Cost

Maintaining a metal’s structural integrity results in cost savings. To compensate for strength loss associated with welding, manufacturers typically buy a 6000-aluminum alloy—even though the final strength of a 3000 alloy is all that’s required. When using adhesive, the more cost-effective 3000 alloys can be purchased, since there will be no strength loss associated with an assembly. Savings associated with brazing ovens is another benefit. In most electric vehicles, battery boxes are as large as a queen-size mattress. The large size of these battery boxes means that brazing ovens must also be large to accommodate them. This represents a significant investment—not to mention the space these ovens take up within a facility, and the time manufacturers spend procuring such capacious ovens. Using structural adhesives eliminates the need for large ovens, resulting in time and cost savings.

4. Vehicle Performance

The benefits of using structural adhesives aren’t confined to the manufacturing phase. Lighter-weight cars can travel farther per charge than heavy vehicles. Welding requires metals that are thicker—and therefore heavier—than those required for adhesive bonding. The ability to use thinner materials with an adhesive enhances design freedom. LORD 850/25GB even allows bonding of dissimilar substrates, which can lead to further money savings and weight reduction. Adhesive use also reduces the risk of material distortion, which is a concern among EV manufacturers; battery boxes must be dimensionally stable. Because adhesives are more elastic than mechanical fasteners, they are flexible enough to move with the aluminum during expansion and contraction. This is especially important in hybrid bonding. For example, steel is often bonded to aluminum, and the two materials expand and contract at different rates when exposed to temperature change. Considering the high temperatures created by EV batteries, structural adhesives offer a significant advantage.

5. Health and Safety

Occupational noise is a growing health, safety, and welfare concern—and mechanical fastening operations can be noisy. Some research puts welding torch noise at 84 dBa or greater. Using structural adhesives eliminates noise associated with assembling a battery box, an improvement not only for the operator but a for overall environmental noise levels within the plant.

The advantages of structural adhesives, and the synergies between them, can result in great cost savings associated with automotive assembly and performance. Learn more at LORD.com/cooltherm

Delphine Andrivot

Delphine Andrivot is EMEA Business Development & Technical manager for Structural Adhesives and Thermal Management who's focus is on the electric vehicle market. Her formal education was in Sales, Marketing and Organic Chemistry and she has over 15 years of experience in the Industrial and Automotive markets.

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