Thin Sheet Metal Yielding Post With Partial Laser Weld
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Solution Overview
Problem
Existing street lighting posts with roll-formed, conical cross-sections and welded longitudinal joints face challenges in bending effectively upon collision due to resistance from large diameters at the base, and their production is not efficient or cost-effective.
Innovation Solution
The use of posts with longitudinal welded butt joints where the weld is thinner than the sheet metal thickness, positioned to face traffic, allowing for easier deformation upon impact while maintaining strength against wind forces, and production is simplified through laser welding that covers less than ¾ of the sheet metal thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the post has a large diameter at the bottom to be sturdy against wind forces, then the resistance before bending becomes undesirably great, but the post needs to bend effectively upon collision
Solution Approach 1:
The post has different properties at different locations: the base maintains full sheet metal thickness for wind resistance, while the welded joint area has reduced thickness (weld thinner than sheet metal) to facilitate bending upon collision. This local variation in material properties resolves the contradiction between overall strength and localized deformability.
Solution Approach 2:
The welded joint is pre-formed with a thickness smaller than the sheet metal thickness during manufacturing. This preliminary creation of a weakness zone ensures that when collision occurs, the post will bend at the predetermined joint location rather than requiring the entire structure to deform, thus enabling effective bending while maintaining overall structural integrity against wind forces.
2Strength
If the weld covers the whole sheet metal thickness to be strong, then the post cannot bend easily upon direct impact, but the post needs to deform upon collision
Solution Approach 1:
The weld is designed with non-uniform penetration: it provides sufficient strength for wind loads while intentionally leaving the sheet metal thickness not fully covered, creating a localized weakness zone that enables controlled deformation during collision. The weld strength is optimized to be adequate for static loads but insufficient to prevent bending under dynamic impact forces.
Solution Approach 2:
The weld thickness parameter is specifically controlled to be smaller than the sheet metal thickness. This parameter change creates a deliberate discontinuity in the structural integrity, allowing the post to maintain strength under normal conditions while enabling easy deformation when impacted, thus resolving the contradiction between weld strength and deformability.
3Strength
If the weld thickness equals the sheet metal thickness to ensure strength, then the production is slower and more costly, but the invention aims for faster and more reliable production
Solution Approach 1:
Instead of welding through the entire sheet metal thickness (excessive action), the process applies partial welding action where the weld thickness is intentionally kept smaller than the sheet metal thickness. This partial action is sufficient to achieve the required strength for wind resistance while dramatically reducing production time and cost, thus resolving the contradiction between strength and productivity.
Solution Approach 2:
The weld depth parameter is optimized to be less than the full sheet metal thickness. This parameter optimization allows the welding process to complete faster with less energy input and material displacement, significantly improving production speed and reliability while maintaining adequate weld strength for the application requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables posts to bend upon collision while providing sufficient strength against wind forces, reducing production costs and time, and ensuring reliable performance.
Implementation Method 1
The edges of the opposing sheets 11, 12 have bevels 21, 22, so that the contact surfaces of the edges are smaller than the sheet metal thickness and are welded together, preferably by laser welding
Data Source
Figure 1~2
Figure 3
AI summary
Street lighting is positioned with lamp posts of sheet metal that have a round or polygonal cross-section and one or more longitudinal welded joints (17-20; 24). Posts are used that have one longitudinal welded butt joint with a weld that covers only a part of the sheet metal thickness and the posts are positioned so that this joint is directed towards the traffic.