Application Technology

As the industrial landscape increasingly shifts towards electrification, the demand for components that meet both conductive and insulating requirements has surged. Here, Arne Schlichting, technical specialist in new mobility at KAMAX Automotive GmbH, delves into the technical challenges and solutions associated with bolted joints in electrified environments.

Bolted joints, essential in assembled machines and vehicles, now face heightened expectations to manage these electrical demands while maintaining their core mechanical functions. In any mechanical assembly, bolted joints serve as the critical link between multiple components, providing the necessary clamp load to ensure a stable and durable connection. However, in electrified systems these joints also have the potential to create unintended electrical pathways. 

Thus, the challenge is twofold, firstly ensuring that the bolted joint does not inadvertently conduct electricity where it’s not wanted and secondly protecting the joint itself and the surrounding components from electrical hazards, such as creepage currents and voltage surges. 

The primary technical requirements for bolted joints in electrified systems include high clamping force transmission – the joint must provide sufficient force to secure the components reliably; durability under dynamic loads – the joint must withstand vibrations and dynamic stresses, especially in environments subject to movement or impact; space efficiency – the design must be compact to fit within the often limited space available in machinery; and corrosion resistance – the joint must resist environmental degradation, especially in harsh conditions like those found in automotive applications. Other technical requirements include ease of assembly and disassembly – the joint should be designed for straightforward installation and removal without compromising its insulating properties; mechanical injury protection – the design must minimise the risk of injury during handling and maintenance; and finally defined clamping force – precision in clamping force is crucial for maintaining the integrity of the assembly.

With the integration of electric drives, additional electrical insulation requirements must be met by bolted joints, including the prevention of unintended electrical conductivity. The joint must prevent any electrical current from passing between the assembled components unless specifically designed to do so. There must also be protection against voltage surges – the bolted joint should prevent voltage surges from causing damage or creating hazardous conditions. As well as this is creepage current mitigation – the joint must minimise the risk of current leakage along the surface of insulating materials and human protection from electric shock – with the design ensuring the joint is safe to handle, even in a live system.

To effectively address these challenges, it’s essential to consider the different areas of a bolted joint, such as the head with wrench grip. This area must protect against human contact with the joint during assembly and disassembly, ensuring the insulating layer remains intact. The underhead must also be considered as this area experiences significant wear during tightening and must be designed to withstand high pressure while providing effective insulation. As well as this, the shank must have minimal coating thickness to fit within the component’s bore while maintaining adequate insulation. The thread area must also be considered as it transmits significant force and has limited space for coatings, which must provide insulation without compromising the joint’s strength.

KAMAX solutions for electrified systems

For the head area, KAMAX offers bolt heads coated with specially modified polymers, which are designed to protect against accidental human contact with live components, as well as have a high clamp load with minimal risk of damage to the insulating layer. The bolt heads also have adequate insulation to prevent voltage surges and creepage currents up to 5kV.

For the shank, KAMAX provides advanced powder coating technologies that offer a minimal coating thicknesses of less than 200µm, suitable for tight tolerances with a high insulation strength of 50kV/mm. The technologies also provide high corrosion resistance, withstanding over 720 hours of salt spray testing (NSS per ISO 9227), as well as enhanced chemical resistance – capable of withstanding exposure to acids, alkalis and organic solvents.

The underhead of the bolt is particularly critical as it transmits approximately 50% of the clamp load. KAMAX’s solutions therefore focus on low friction during assembly, ensuring easy and accurate torque application and long-term durability under mechanical and thermal stresses. They also exhibit high insulation properties to prevent electrical failures due to voltage surges or creepage currents.

For bolt threads, KAMAX does not currently offer standard insulating solutions but is equipped to collaborate with customers to develop customised solutions based on existing technologies.

Hydrogen fuel cell industry

Besides the regular electrified systems, joints in fuel cells play a significant role as those joints have additional requirements. In addition to the clamp load transmission and the insulation, to avoid any electrical short in the fuel cell stack, those joints have to compensate for the high swelling of the fuel cell without increasing the pressure in the cells and their components, such as bipolar plate, membranes and sealings. KAMAX has developed such an element, called STACKFLIX, which fulfils all the three requirements and includes the media flow.

The shift towards electric drives imposes new technical challenges on bolted joints, requiring innovations that address both mechanical and electrical requirements. KAMAX is at the forefront of developing solutions that meet these dual demands, offering robust, reliable, and cost-effective options for a wide range of industrial applications, particularly in the demanding automotive sector. By focusing on insulation, corrosion resistance, and mechanical integrity, KAMAX ensures that its bolted joints deliver superior performance in electrified environments. 

For further technical discussions or bespoke solutions, KAMAX’s engineering team is ready to assist, leveraging their extensive experience in both the mechanical and electrical aspects of bolted joint design.