Selective Hardening of Screw Internal Drives for Wear Resistance

Solution Overview

Problem

Screws used in indexable insert clamping applications experience frequent wear-out of the internal drive due to frequent tightening and loosening, leading to seized screws, tool downtime, thread damage, and increased costs, as existing solutions that increase screw hardness also wear out the tool holder threads.

Innovation Solution

Manufacturing screws with a selectively harder internal drive area using dissimilar ferrous alloys, where the internal drive is made of a high-hardness ferrous alloy, such as ultra-high strength steel, while the rest of the screw body remains made of a ferrous alloy, achieved through cold forging, hole formation, layer deposition, and machining processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the hardness of the entire screw is increased to make the internal screw-drive more wear-resistant, then the wear-resistance of the internal drive is improved, but the tool holder threads wear out

Engineering Contradiction:

Improvewear-resistance of internal driveVSAvoidwear out of tool holder threads

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by creating a differentiated hardness structure within the screw. The internal drive portion is selectively hardened to a higher hardness level (58-65 HRC) compared to the rest of the screw body (45-55 HRC), achieved through controlled austempering process parameters including austempering temperature (250-450°C) and holding time. This localized hardness differentiation allows the internal drive to resist wear while the lower hardness body preserves tool holder threads.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent creates a composite material structure within the screw by forming distinct microstructural regions through the austempering process. The internal drive develops a martensitic or bainitic microstructure with high hardness, while the screw body maintains a ferritic-perlitic microstructure with lower hardness. This internal composite structure enables simultaneous optimization of wear-resistance and tool holder protection.

Inventive Principle:

Principle #40Composite materials

2Volume of moving object

If smaller screws are used in indexable insert clamping applications, then the screw size is reduced for better fit, but the frequent tightening and loosening causes faster wear-out of the internal drive

Engineering Contradiction:

Improvescrew sizeVSAvoidservice life of internal drive

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent applies local quality by creating a differentiated hardness structure within the screw. The internal drive portion is selectively hardened to a higher hardness level (58-65 HRC) compared to the rest of the screw body (45-55 HRC), achieved through controlled austempering process parameters including austempering temperature (250-450°C) and holding time. This localized hardness differentiation allows the internal drive to resist wear while the lower hardness body preserves tool holder threads.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent creates a composite material structure within the screw by forming distinct microstructural regions through the austempering process. The internal drive develops a martensitic or bainitic microstructure with high hardness, while the screw body maintains a ferritic-perlitic microstructure with lower hardness. This internal composite structure enables simultaneous optimization of wear-resistance and tool holder protection.

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 selectively hardened internal drive increases wear-resistance, reducing tool downtime and replacement costs, and extends the service life of the screw drive, while maintaining the strength of the screw body.

Implementation Method 1

manufacturing the screw body by cold forging process using a ferrous alloy

Methodology Applied

Scientific EffectPlastic deformation: Plasticity

Implementation Method 2

forming a layer of hard ferrous alloy in the hole with the screw head, the layer having dissimilar material and high hardness than the screw body

Methodology Applied

Scientific EffectMaterial deposition: Deposition (physical)

Data Source

PatentUS20240109121A1An improved screw and a method of manufacturing thereof

Publication Date: 2024.04.04 RAMACHANDRA KUMAR

AI summary

The present disclosure provides an improved screw and method of manufacturing thereof. The method comprising the steps of manufacturing 101 the screw body by cold forging process using ferrous alloy, making 102 a hole 301 on the screw head 201 to form a base of the hole and a wall thickness 501 of the screw head 201 for providing an internal drive, forming 103 a layer 602 of hard ferrous alloy in the hole 301 with the screw head 201 wherein the layer 602 having high hardness than the screw body 200, optionally smoothening 104 the layer 602 using a conventional process and machining 105 the layer 602 to obtain the internal drive 601 thereby achieving increase in hardness and wear-resistance of the internal drive 601.