Stainless Self-Drilling Screw Preforming for Thick Steel Penetration
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Solution Overview
Problem
Existing methods for producing self-drilling screws face challenges in achieving high strength and corrosion resistance while avoiding the complexity and cost of bimetallic screws, particularly in penetrating steel sheets thicker than 1.5 mm without pre-drilling.
Innovation Solution
A method for producing a high-strength self-drilling screw entirely from stainless steel, involving multi-stage cold forming processes that include upsetting, diameter reduction, preforming, and final forming of the drill bit, without the need for heat treatment, along with optional coatings for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If carbon steel is used to achieve high hardness, then the hardness of the screw is improved, but the corrosion resistance deteriorates
Solution Approach 1:
The patent uses a bimetallic construction combining carbon steel and stainless steel in a single fastener. The carbon steel portion provides the required hardness and strength for self-drilling, while the stainless steel portion ensures corrosion resistance. This composite material approach resolves the contradiction by integrating two materials with complementary properties into one functional unit.
2Strength
If bimetallic screws are used to combine hardness and corrosion resistance, then both properties are improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the carbon steel wire and stainless steel wire into a single bimetallic blank through welding, followed by integrated cold forming operations. The head, shaft, and drill point are formed in one continuous process without separate manufacturing steps for each component. This merging approach reduces manufacturing complexity compared to traditional multi-step bimetallic construction methods.
Solution Approach 2:
The patent performs preliminary welding of the carbon steel and stainless steel wires to create a unified blank before any forming operations. This preliminary action establishes the bimetallic structure in advance, allowing subsequent cold forming, threading, and drill point creation to proceed as integrated operations, thereby simplifying the overall manufacturing process.
3Reliability
If stainless steel is used to ensure corrosion resistance, then the corrosion resistance is improved, but the penetration capacity deteriorates
Solution Approach 1:
The patent applies local quality by using different materials in different regions of the fastener. The carbon steel portion is positioned at the drill point and shank where high hardness and penetration capacity are required, while the stainless steel portion is positioned at the head and threaded shaft where corrosion resistance is prioritized. This spatial differentiation of material properties resolves the contradiction between penetration capacity and corrosion resistance.
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 method enables the production of high-strength self-drilling screws with enhanced surface hardness and corrosion resistance, capable of penetrating steel sheets thicker than 1.5 mm without pre-drilling, while simplifying the manufacturing process and reducing costs.
Implementation Method 1
involving multi-stage cold forming processes that include upsetting, diameter reduction, preforming, and final forming of the drill bit
Implementation Method 2
which is known to lead to work hardening of the formed material
Data Source
Figure 1A~1F
AI summary
A method for producing a high-strength self-drilling screw (100) made entirely of stainless steel is described, wherein the self-drilling screw (100) does not need to undergo a heat treatment process downstream of the manufacturing process to improve the material hardness. A shaft-shaped blank (110) is provided as a wire section (105) made of stainless steel. A screw head (140) is formed by cold forming at a first longitudinal end (120) of the blank (110). The diameter of an end portion of the blank is subsequently reduced by cold forming. A drill bit (150) is then produced at the second longitudinal end (130) of the blank (110) by a pinching movement transverse to the longitudinal axis. In a subsequent process step, the drill bit (160) is finished. Any projecting material lugs (170) remaining on the cutting edges (180) of the drill bit (160) are sheared off during the subsequent thread rolling process.During preforming, so-called contour edges (190) are formed in the area of the future cutting edges (180), where the remaining material thickness is between 0.3 mm and 1.0 mm. The final forming of the drill bit is achieved by reshaping the contour edges (190) into cutting edges (180), with the remaining material thickness between the cutting edge (180) and the material flange (170) being between 0.05 mm and 0.2 mm. Local perforations are permitted.