Flow Drill Screw Tip Geometry for Consistent Casting Bushings
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The use of flow drill screws (FDS) with structural castings in automotive applications results in inconsistent bushing quality, leading to reduced thread engagement and joint strength, as well as corrosion concerns, due to the material properties of castings differing from traditional body structure materials.
Innovation Solution
A screw design featuring a flow-hole-forming tip with a convex radiused lower zone, concave radiused middle zone, and radiused distal end zone, without a cutting edge, optimized for penetrating castings, including those made of aluminum or magnesium, with a multi-helix threaded shank and optional friction coating, to create a higher quality bushing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional flow drill screw with a cutting edge is used, then penetration into traditional body structure materials is effective, but bushing quality becomes inconsistent when used with structural castings
Solution Approach 1:
The patent changes the geometric parameters of the tip by eliminating the cutting edge and replacing it with a flow-hole-forming geometry characterized by specific radius values (R1, R2, R3) and angle relationships. This parameter change adapts the tip geometry to work with the material properties of structural castings, producing consistent bushing quality and reliable thread engagement.
Solution Approach 2:
The patent applies curvature by designing the tip with multiple radiused surfaces instead of sharp edges. The convex surface with radius R1, the concave surface with radius R2, and the rounded distal end with radius R3 create a flow-hole-forming geometry that smoothly displaces material during installation, resulting in consistent bushing formation in structural castings.
2Ease of operation
If a flow drill screw is used with structural castings, then one-sided joining is achieved, but joint strength is reduced due to improper installation
Solution Approach 1:
The patent modifies the tip geometry parameters to optimize penetration and bushing formation in structural castings. By changing the radius values and angle relationships in the flow-hole-forming tip, the screw achieves proper installation in one-sided applications, thereby maintaining joint strength despite the joining constraint.
Solution Approach 2:
The patent applies local quality by designing the tip with different radius values at different locations: a larger radius R1 at the leading convex surface for initial penetration, a smaller radius R2 at the concave surface for material displacement, and a rounded radius R3 at the distal end for clean hole formation. This localized variation in geometry optimizes each stage of the installation process.
3Ease of manufacture
If a flow drill screw is used with structural castings, then assembly is simplified, but corrosion concerns arise due to lower quality bushing
Solution Approach 1:
The patent changes the tip geometry parameters to ensure proper bushing formation in structural castings. By optimizing the radius values and angle relationships in the flow-hole-forming tip, the screw creates high-quality bushings that prevent corrosion while maintaining the simplified assembly process enabled by one-sided joining.
Data Source
AI summary
A screw includes a head portion, an externally threaded shank extending from the head portion, the externally threaded shank having an external surface, and a flow-hole-forming tip disposed at a distal end portion of the externally threaded shank. The flow-hole-forming tip includes a convex radiused lower zone having an external surface, a concave radiused middle zone having an external surface tangent to the external surface of the convex radiused lower zone, and a radiused distal end zone having an external surface tangent to the external surface of the concave radiused middle zone.