U-Shaped Cutting Insert Edge to Prevent Back-Turning Surface Roughening

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Solution Overview

Problem

In back turning operations, lengthened chips often contact the machined surface of a workpiece, leading to surface roughening, particularly during groove and outer diameter machining, where high chip management is required.

Innovation Solution

A cutting insert with a rake surface, peripheral side surface, and cutting edges configured such that the main cutting edge is curved in a U shape over its effective edge range, with the deepest point positioned closer to the corner, promoting chip bending instead of torsion upon collision with a breaker wall, thereby preventing surface roughening.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If back turning is performed with conventional cutting edges, then machining capability is maintained, but chips become lengthened and contact the machined surface causing roughening

Engineering Contradiction:

Improvemachined surface qualityVSAvoidchip lengthening and contact with machined surface

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The main cutting edge is curved into a U shape over its entire effective edge range, with the deepest point positioned in a specific range closer to the corner. This curvature creates a decentered inflection portion in the chip cross-section that generates stiffness to prevent torsion, causing chips to bend instead of twist when colliding with the breaker wall surface, thereby preventing surface roughening

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The cutting insert applies different geometric characteristics to different portions of the cutting edge. The U-shaped curvature is specifically applied to the main cutting edge while the front cutting edge maintains a different configuration. This localized geometric modification targets the specific problem of chip control during back turning without affecting other machining functions

Inventive Principle:

Principle #3Local quality

2Productivity

If chips are allowed to form naturally during back turning, then cutting action is maintained, but chip torsion occurs facilitating contact with the machined surface

Engineering Contradiction:

Improvecutting action continuityVSAvoidchip torsion and surface contact

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The U-shaped curvature of the main cutting edge creates a decentered inflection portion in the chip cross-section. This inflection portion acts as an internal stiffening element that resists torsional deformation, forcing chips to bend rather than twist when subjected to collision forces with the breaker wall surface, thus preventing surface contact

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentUS11911827B2Cutting insert

Publication Date: 2024.02.27 TUNGALOY CORP

AI summary

There is provided a cutting insert having a low possibility that chips roughen a machined surface of a workpiece in back turning. The cutting insert includes a rake surface, a peripheral side surface, a front cutting edge which is provided on a ridge of the rake surface and the peripheral side surface, and a main cutting edge which is provided on the ridge so as to be continuous with the front cutting edge and has an extension direction which forms an obtuse angle with an extension direction of the front cutting edge, the main cutting edge is curved into a U shape over an entire length of an effective edge range which functions as a cutting blade, and the deepest point of the U shape is positioned in a range closer to a side of a corner than a position which divides a straight line connecting both ends of the main cutting edge at a ratio of 2:1 from the side of the corner positioned adjacent to the front cutting edge.