Threaded Friction Joining Element for High-Strength Steel Sheets
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Solution Overview
Problem
Existing friction welding techniques struggle to effectively join high strength steel sheets due to insufficient plastic deformation of the upper sheet, leading to inadequate joint strength when using a steel sheet as the upper sheet.
Innovation Solution
A friction joining element with a specially designed side surface featuring a screw thread on the mandrel, which engages and fastens the high strength steel sheet, ensuring sufficient plastic deformation and mechanical joining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional friction welding technique is used to join high strength steel sheets, then the lower sheet can be connected by friction welding, but the upper sheet cannot be sufficiently fastened due to insufficient plastic deformation
Solution Approach 1:
The joining element is divided into functionally distinct segments: a mandrel portion for friction welding with the lower sheet and a head portion with a collar for mechanical engagement with the upper sheet. This segmentation allows each portion to perform its specific function optimally - the mandrel creates friction welds while the collar provides mechanical fastening through screw thread engagement with the plastically deformed upper sheet.
Solution Approach 2:
The joining element combines two different joining mechanisms into a single composite structure: friction welding (thermal-mechanical process) for the lower sheet and mechanical screw thread engagement for the upper sheet. This composite approach allows the element to effectively join both sheets despite their different material properties and deformation characteristics.
2Ease of manufacture
If fusion bonding such as resistance spot welding is applied to high strength steel sheets, then bonding can be achieved, but joint strength reduces due to embrittlement of solidification microstructures
Solution Approach 1:
The invention replaces fusion bonding processes (resistance spot welding) with a mechanical joining system. Instead of using heat and pressure to melt and fuse the steel sheets, which causes embrittlement, the joining element uses mechanical friction welding and screw thread engagement to achieve strong joints without melting the base materials, thereby avoiding microstructure embrittlement.
Solution Approach 2:
The invention converts the high strength and low ductility characteristics of high strength steel sheets, which make them difficult to weld by fusion, into an advantage for mechanical joining. The screw thread structure effectively engages with the relatively undeformed upper sheet, transforming the material's resistance to plastic deformation into a beneficial feature for mechanical fastening.
3Strength
If a steel sheet is used as the upper sheet in friction welding, then the material strength is maintained, but plastic deformation is insufficient and the collar cannot contact the upper sheet
Solution Approach 1:
Instead of trying to plastically deform the upper sheet to enable collar contact (which is difficult with high strength steel), the invention inverts the approach: the screw thread on the mandrel plastically deforms the upper sheet during insertion, creating engagement features that allow the collar to effectively contact and fasten the sheet. This reverses the conventional sequence of deformation and engagement.
Solution Approach 2:
The screw thread structure performs preliminary plastic deformation of the upper sheet during the insertion phase, before the collar needs to engage the sheet. This preliminary action prepares the upper sheet surface and creates engagement features that facilitate subsequent collar contact and fastening, solving the problem of insufficient deformation.
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 element provides a mechanically joined joint with good joint performance by securely fastening the high strength steel sheets, even when used as the upper sheet, through the engagement of the screw thread with the sheet.
Implementation Method 1
a screw thread is formed on the side surface of the mandrel of the friction joining element, and this allows the friction joining element to engage the upper sheet
Implementation Method 2
the plastic deformation of the upper sheet is insufficient
Implementation Method 3
an element rotated at high speed is pressed into a sheet set to join the sheet set by friction joining
Implementation Method 4
The forward end of a mandrel portion of a joining element (element) is connected to a lower sheet by friction welding
Data Source
AI summary
A friction joining element for mechanically joining a sheet set prepared by stacking two or more metal sheets including a high strength steel sheet as an upper sheet. The friction joining element includes a mandrel having an overall length adjusted to be equal to or less than the total thickness of the sheet set, and a collar disposed at an upper portion of the mandrel. The friction joining element has a screw thread on a side surface of a head-side portion of the mandrel.