Fasteners for New Energy Vehicles: Three Main Lines across Battery Pack, Electric Control, and Body
Executive Summary
Fastener problems in new energy vehicles are never a single-part problem. The three main lines—battery pack, electric control, and body—each bear completely different loads and media, yet share one selection logic across the same vehicle. This article breaks down operating-condition parameters, failure risks, and selection directions by the three lines, gives responses to galvanic corrosion and thermal mismatch brought by light-alloy use, and explains why fastener decisions must be made extremely early in the project.
Table of Contents
Three main lines, three failure logics
Engineers working on NEV projects often share the same feeling: the same M6 bolt, whether installed at a battery pack lifting point, on a motor controller housing, or on an exposed body bracket, meets completely different problems.
A battery pack lifting point bears shock and fatigue; whole-vehicle vibration, rapid acceleration and deceleration, and road input all reach the lifting point, and the lifting point is a safety component with severe failure consequences. The core conflict of an electric control housing is an electrical problem: a trade-off must be made between conduction and insulation, while eddy-current and leakage risks are suppressed. Exposed body parts, by contrast, are a typical environmental durability problem; long-term attack from de-icing salt, car wash agents, and heat and humidity gradually eats away the connection margin.
Because the failure logics of the three lines differ, their selection logic naturally cannot be shared. Treating them as one thing is the most common fastener mistake in NEV projects.
Line one: the battery pack
The battery pack is the region of the NEV with the highest fastener density and the highest safety class. By function it can be roughly divided into four connection types, each with very different operating conditions and challenges.
| Connection Location | Main Operating Condition | Key Challenge |
|---|---|---|
| Pack lifting point (body connection) | Shock + alternating load; repeated removal and installation during maintenance | Load-bearing safety component, also serving as the lifting load path |
| Upper cover and lower housing | Vibration + sealing (airtight and watertight) | Uniform sealing-surface pressure; leakage prevention and anti-loosening equally important |
| Module-to-end-plate connection | Thermal cycling + vibration; high quantity | Tact-time pressure; high torque-consistency requirement |
| High-voltage interface and busbar | Long-term energization + temperature rise | Leakage prevention; eddy-current heating prevention |
Line two: electric control and the three-electric system
The electric control system covers the motor controller, on-board charger, DC-DC, and electric-drive assembly housing. Fasteners here not only bear mechanical loads but also participate in building the electrical safety boundary, and three special requirements must be met simultaneously.
- Insulation and leakage prevention: near high-voltage areas, creepage distance and clearance must be ensured to avoid forming a conductive path; insulating washers or sleeves are used for isolation when necessary.
- Eddy-current and local heating prevention: near high-current conductors, magnetic steel fasteners generate eddy-current heating in alternating magnetic fields, increasing losses and possibly causing temperature rise to exceed limits.
- Temperature resistance and thermal cycling: the electric-drive housing works at elevated temperatures for long periods, so residual preload must be calculated for creep and relaxation.
| Location | Temperature Order of Magnitude | Fastener Concern |
|---|---|---|
| Electric control housing (low-temperature zone) | Below 105 ℃ | Sealing, anti-loosening, torque consistency |
| Motor and reducer housing | 120–160 ℃ | High-temperature relaxation, thermal expansion matching |
Line three: body and structural parts
Compared with the three-electric system, the failure consequences of body fasteners are usually less fatal, but their usage volume is large and the exposed proportion is high, making them the main source of corrosion and appearance complaints.
- Galvanic and crevice corrosion: the contact interface between steel fasteners and aluminum bodies, and between aluminum fasteners and magnesium parts, is a high-corrosion area, and corrosion often progresses inward from crevices.
- Preload decay caused by thermal expansion mismatch: exposed parts directly bear day-night temperature differences and seasonal cycles, which is especially obvious for aluminum parts.
- Appearance consistency: coating color difference, scratches, and rust on exposed fasteners directly enter the user evaluation system.
| Application | Recommended Direction | Reason |
|---|---|---|
| Steel body structural parts | 10.9 grade carbon steel + zinc-aluminum coating | Balance strength and corrosion protection; controllable cost |
| Aluminum body and subframe | High-strength aluminum alloy bolts, or steel bolts + insulating washer | Suppress galvanic corrosion; match thermal expansion |
Why fastener decisions must be moved earlier
The project-lifecycle cost-influence model reveals an often underestimated fact: the core challenge enterprises face during R&D is that the early decision window is extremely short yet locks in most of the cost; although later investment is huge, the cost of correction is extremely high, with a serious mismatch between risk and return.
Fasteners are precisely the most typical footnote to this model. Once a bolt's specification is set at the drawing stage, the subsequent dies, production-line process parameters, tightening-equipment programs, and inspection specifications are all locked. If improper selection is not discovered until the whole-vehicle test phase, what is changed is the drawing, and what is paid for is the dies and the production line.
The visible purchase cost of one fastener accounts for only 15% of its full-lifecycle cost; the other 85% is hidden in design and selection, assembly efficiency, quality rework, and even after-sales. Choosing the wrong one screw can cost the tact time of an entire production line.
Selection checklist for the three main lines
Laying the differences of the three lines onto one table can serve as an item-by-item basis during project review.
| Check Dimension | Battery Pack | Electric Control / Three-Electric | Body Structure |
|---|---|---|---|
| Dominant failure mode | Fatigue, shock, and sealing | Thermal relaxation and electrical safety | Corrosion and preload decay |
| Material preference | Lightweight + potential matching | Temperature resistance + non-magnetic low interference | Corrosion protection + cost balance |
| Thread insert needed | Usually needed for light-alloy substrate | Depends on housing material | Depends on die-cast alloy grade |
| Tightening strategy | Torque-angle method or multi-stage tightening | Torque control + process monitoring | Torque control method |
| Traceability requirement | High (involves safety parts) | High | Medium |
Conclusion: give the three lines to one solution
The three main lines—battery pack, electric control, and body—look like three different technical problems, but in fact share the same underlying capability: judgment of material and potential matching, calculation of load and relaxation, design of the tightening process, and reverse tracing through failure analysis.
YF Zhichengjia has focused on precision fasteners since 2003, with production bases covering Pingshan (Shenzhen), Gucheng (Hubei), Qingxi (Dongguan), as well as India and Indonesia. Around the three main lines of NEVs, we support customers with professional design consulting, rapid engineering samples, professional testing, and professional failure analysis, getting the selection decisions for all three lines right at once, extremely early in the project.
