How to choose and purchase a car threshold beam

　　The threshold beam of a car is a crucial structural component on the side of the body. It is not only the foot pedal for passengers to get on and off the car, but also the core safety component that constitutes the vehicle's side structure and resists side collisions. Choosing or evaluating threshold beams requires consideration from multiple dimensions such as materials, structure, craftsmanship, and compatibility with the entire vehicle.

　　Core selection dimension

　　1. Material: Balance between strength and lightweight

　　This is the basis for determining the performance of the threshold beam. The current mainstream solutions are high-strength/ultra high strength steel and aluminum alloys.

　　High strength/ultra high strength steel: With relatively low cost and extremely high strength, it is the main material for dealing with side collisions and preventing intrusion into the passenger compartment. Usually used for inner or reinforcing plates.

　　Aluminum alloys (such as 6 series and 7 series): significant lightweighting effect (about 30% -50% lighter than steel), good corrosion resistance. Mostly used for luxury cars and electric vehicles that are sensitive to weight (to enhance range). But its material cost and molding process cost are higher.

　　Mixed material structure: currently advanced and mainstream designs. For example:

　　Outer layer (decorative panel or energy absorbing area): Made of medium strength steel or aluminum alloy, responsible for initial energy absorption and styling.

　　Inner layer (core bearing area): Made of hot formed steel (usually with a tensile strength of over 1500MPa), it forms an indestructible "safety cage" body and serves as a defense line against side impacts.

　　2. Structural design: Multi cavity and partition reinforcement

　　The modern threshold beam is not a simple "beam", but a multi cavity composite structure.

　　Closed multi cavity design: Multiple closed cavities are formed by welding or riveting the inner plate, outer plate, and reinforcing plate. This structure is like the "I-beam" in architecture, which can greatly enhance the bending and torsional stiffness of the section, and disperse the impact force to the entire body of the vehicle during collision.

　　Reinforcement of inner and outer panel partitioning: The inner panel (near the passenger compartment) is usually made of high-strength materials; The outer panel may use slightly lower strength materials to balance energy absorption and styling. Structural foam will be filled in the middle, which will expand and solidify rapidly at the moment of collision to further strengthen the structure, restrain deformation and reduce noise.

　　3. Manufacturing process: determines performance

　　Materials need to go through advanced processes to become high-performance threshold beams.

　　Hot forming/stamping hardening: This is a key process for manufacturing ultra-high strength steel components. Heat the steel to the austenitic state, then rapidly press and cool it to obtain extremely high strength. This is the standard process for the core component of the "safety cage".

　　High pressure cast aluminum: used for manufacturing complex shaped aluminum alloy components, which can achieve highly integrated design and good weight reduction effect.

　　Laser welding: Welding steel plates of different thicknesses and strengths together and stamping them to achieve precise performance distribution of "hard parts are hard, soft parts are soft".

　　Connection technology: In addition to spot welding, self piercing riveting, flow drilling screws, etc. are more suitable for connecting steel aluminum dissimilar materials to ensure connection strength.

　　4. Integration with vehicle design: systematic safety

　　The threshold beam does not exist in isolation, its selection is coordinated with the overall vehicle architecture.

　　Battery pack integration (crucial for electric vehicles): In electric vehicles using CTB/CTC battery body integration technology, the role of the threshold beam has undergone a qualitative change. It is not only a structural component of the vehicle body, but also the lateral support beam and side collision beam of the battery pack. Its strength, stiffness, and sealing directly affect battery safety. At this point, the design of the threshold beam needs to be deeply integrated with the battery pack cover, seat crossbeam, etc., forming a "well" - shaped or "field" - shaped superstructure to provide comprehensive protection for the battery.

　　Connection with B-pillar, floor crossbeam, and longitudinal beam: The threshold beam needs to be firmly connected to the lower part of the B-pillar, front and rear floor crossbeams, and longitudinal beams to form a complete force transmission ring. In the event of a side collision, the impact force is effectively dispersed throughout the entire vehicle body to avoid stress concentration and local collapse.

　　Selection strategy and evaluation recommendations

　　Suggestions for different roles are as follows:

　　As a consumer purchasing a vehicle:

　　Refer to authoritative safety test reports: Pay attention to the side collision and 25% offset collision results of companies such as China Insurance Research Institute C-IASI and China Automotive Research Institute C-NCAP. Behind excellent performance, there must be strong side structures such as threshold beams to support it.

　　Understand platform technology: What platform is the vehicle built on (such as Toyota TNGA, Volkswagen MQB/MEB, Geely CMA, etc.). Advanced platforms typically apply more unified and leading standards in vehicle structure and materials.

　　Pay attention to the special design of new energy vehicles: For electric vehicles, you can check if they adopt integrated technologies such as CTB/CTC, which usually means that the threshold beam has been redesigned to provide higher levels of battery protection.

　　As an engineer or industry practitioner, choose the following options:

　　Clarify performance goals and cost constraints: Firstly, define the vehicle's safety level (collision star rating), weight target (fuel/electricity consumption), and cost budget.

　　Conduct multi scheme CAE simulation: In the early design stage, conduct extensive computer collision simulation analysis on different material combinations (steel, aluminum, mixed) and structures (number of cavities, plate thickness) to find optimal solutions.

　　Consider process feasibility and supply chain: The selected material structure must match the factory's production capacity and process. For example, whether the hot forming production line and aluminum alloy connection process are available.

　　Conduct sample testing verification: Verify the effectiveness of the design through static crushing, three-point bending, and vehicle side impact testing of physical samples.

　　summary

　　Choosing a car threshold beam is essentially seeking an engineering balance between safety, lightweight, cost, and manufacturing feasibility. The threshold beam of modern cars is developing towards the direction of "material ultra-high strength, structure multi cavity, process integration, and functional integration". For ordinary consumers, choosing a car model with excellent side protection in authoritative collision tests usually means that it has a well-designed and solid material threshold beam structure, which is the invisible "life line" that safeguards side safety.