Hardened Edge-Layer Joining Element for High-Strength Steel

Solution Overview

Problem

Existing joining elements fail to reliably connect components made of high- or ultra-high-strength steel with tensile strengths above 800 MPa without separation of a slug or failure of the joining element during high-speed bolt setting.

Innovation Solution

A joining element with a hardened edge layer, formed by processes like nitriding or quenching and tempering, is used to create a hard outer edge and a softer interior, allowing for secure connection of components with tensile strengths up to 2000 MPa without slug separation or deformation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a joining element with uniform hardness is used to connect high-strength steel components, then the joining element can penetrate the component, but the joining element fails or separates a slug due to insufficient ductility

Engineering Contradiction:

Improvehardness of joining elementVSAvoidjoining element failure

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The joining element features a differentiated hardness structure with a hardened outer layer (edge layer) and a softer interior core. The edge layer has higher hardness to enable penetration of high-strength steel components, while the softer interior maintains ductility and prevents joining element failure or slug separation during the joining process.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The joining element is constructed as a composite structure combining two material zones with different properties: a hardened outer layer providing high strength and penetration capability, and a softer interior providing ductility and toughness. This composite structure allows the joining element to simultaneously achieve both penetration and reliability.

Inventive Principle:

Principle #40Composite materials

2Strength

If the joining element is made entirely of hard material to prevent deformation, then penetration is achieved, but the notched bar impact work and ductility decrease

Engineering Contradiction:

Improveresistance to deformationVSAvoidnotched bar impact work

Core Design Contradiction:

StrengthVSUse of energy by moving object

Solution Approach 1:

The joining element features a differentiated hardness structure with a hardened outer layer (edge layer) and a softer interior core. The edge layer has higher hardness to enable penetration of high-strength steel components, while the softer interior maintains ductility and prevents joining element failure or slug separation during the joining process.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent applies different heat treatment parameters to different regions of the joining element. The outer layer undergoes hardening treatment (e.g., nitriding, induction hardening) to increase surface hardness, while the interior retains a softer state. This parameter differentiation optimizes both strength and energy absorption characteristics.

Inventive Principle:

Principle #35Parameter changes

3Strength

If a hardened joining element is used for high-strength components, then connection strength is improved, but the joining element becomes brittle and fails under mechanical or temperature loads

Engineering Contradiction:

Improveconnection strengthVSAvoidbrittleness under load

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The joining element features a differentiated hardness structure with a hardened outer layer (edge layer) and a softer interior core. The edge layer has higher hardness to enable penetration of high-strength steel components, while the softer interior maintains ductility and prevents joining element failure or slug separation during the joining process.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The joining element is constructed as a composite structure combining two material zones with different properties: a hardened outer layer providing high strength and penetration capability, and a softer interior providing ductility and toughness. This composite structure allows the joining element to simultaneously achieve both penetration and reliability.

Inventive Principle:

Principle #40Composite materials

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 hardened edge layer enables reliable connection of high-strength steel components without slug separation, increased notched bar impact work, and improved ductility, tolerating mechanical and temperature loads without adverse effects on the connection.

Implementation Method 1

A joining element with a hardened edge layer, formed by processes like nitriding or quenching and tempering

Methodology Applied

Scientific EffectNitriding: Nitriding

Implementation Method 2

A joining element with a hardened edge layer, formed by processes like nitriding or quenching and tempering

Methodology Applied

Scientific EffectQuenching and tempering: Heat Treatment

Data Source

PatentUS20210239146A1Joining element, connection structure with the joining element, manufacturing method of the joining element and corresponding connection method

Publication Date: 2021.08.05 BOLLHOFF VERBINDUNGSTECHNIK GMBH

AI summary

A joining element for manufacturing a connection between at least two components, which includes: a head at a first axial end, an end portion at a second axial end opposite the first axial end, and a shaft arranged between the end portion and the head, wherein the shaft defines a longitudinal axis of the joining element between the first and the second axial end. At least the shaft and the end portion of the joining element comprise a hardened edge layer so that a material of the shaft and the end portion has in the interior a lower hardness compared to an adjacent surface of the edge layer.