Fasteners in Automotive Sheet Metal Joining: Requirements and Applications

Fasteners in Automotive Sheet Metal Joining: Requirements and Applications

Fasteners are crucial components for assembling automotive parts, playing a pivotal role in understanding automotive engineering design and connection methods. This study analyzes automotive sheet metal joining requirements and explores the application of various fasteners with practical examples. The findings underscore the critical importance of selecting fasteners to achieve design objectives.

Given the imperative of automotive lightweighting, high-strength steel plates are increasingly used, with some designs incorporating aluminum alloy plates to reduce overall vehicle weight further. Consequently, sheet metal joining is essential in automotive production and assembly, encompassing body welding, component attachment, and interior installation. Fasteners are critical in these applications, serving as the primary means of connection apart from welding. Due to the multitude and variety of fasteners used in automotive applications, research into their optimal use in sheet metal joining is essential.

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Joining Requirements

1. Sheet Metal Materials

The proliferation of high-strength steel in automotive applications addresses the weight-strength trade-off posed by conventional materials. Typically formed through stamping, high-strength steel serves as a principal structural element in vehicle bodies before the white body stage. While welding is predominant, the weldability of steel is influenced by carbon and alloy content, necessitating adjustments in welding parameters and processes. Galvanized steel, more commonly used, offers lower tensile strength but facilitates processes like punching, bending, and forming. Zinc's high electrical resistance affects the welding characteristics of steel plates. When fasteners are selected for joining, welding bolts or nuts are generally avoided for high-strength and galvanized steel applications.

The use of aluminum alloy plates primarily hinges on their lightweight properties. Due to their poor weldability, they replace steel in non-critical load-bearing areas of vehicles, making fasteners the preferred choice.

2 Joining Strength and Performance

The strength and performance of automotive sheet metal joints must meet specific requirements for safety, collision protection, and pedestrian safety. For instance, door hinges are typically secured to the vehicle body sheet metal using dual screws combined with welding nuts, ensuring passenger safety during vehicle collisions or rollovers by preventing deformation and facilitating smooth passenger escape.

The design and selection of joint strength are fundamental to ensuring reliability. Accurate calculations and analysis control preload forces in threaded connections and prevent loosening. Excessive preload can lead to fastener failure or damage to connected parts, while insufficient preload reduces clamping force, diminishing friction between jointed components and causing looseness.

3 Joining Techniques

Automotive production involves highly streamlined assembly line operations where joining techniques must balance production cadence and resource allocation. During body assembly, attaching components typically involves welding nuts or bolts onto the vehicle body during welding phases, followed by final assembly in the general assembly stage to enhance efficiency and ensure precision installation. Selecting joining techniques must account for mitigating potential galvanic corrosion from dissimilar metal stack-ups and factor into production costs, with prudent fastener selection reducing unnecessary processes and operations.