Turning insert, a tool part, a method as well as a machine tool for chip-cutting metal machining

A tool part formed for chip-cutting metal machining of a workpiece that rotates in a direction of rotation at a first speed of rotation around a workpiece axis, the tool part comprising:

• at least one turning insert that is formed as an integrated part of the tool part, the turning insert comprising a front surface;
• an envelope surface;
• and
• a circular cutting edge located where the front surface meets the envelope surface, the cutting edge extending around the front surface and lying in a plane that forms an acute angle α with the envelope surface, a tool axis extending through the turning insert in a normal direction in respect of the plane, and the turning insert, during the chip-cutting metal machining, being formed to rotate around the tool axis at a second speed of rotation,
• wherein the envelope surface forms a chip surface and is arranged to meet chips formed in the chip-cutting metal machining, and the chip surface comprises chip breaking means,
• wherein the chip surface comprises a circumferential first portion that borders on the cutting edge and a circumferential second portion that borders on the circumferential first portion,
• wherein the circumferential first portion has one of a concave shape and a conical shape as seen in a cross-sectional plane including the tool axis, and
• wherein at least a portion of the envelope surface of the circumferential second portion projects radially outward past at least a portion of the envelope surface of the circumferential first portion.

A machine tool for chip-cutting metal machining, comprising:

• a workpiece spindle having a holder member formed to hold a workpiece;
• a first driving member that is arranged to rotate the workpiece spindle and the workpiece in a direction of rotation around a workpiece axis at a first speed of rotation;
• a tool having a turning insert, the turning insert including a front surface, an envelope surface, and
• a circular cutting edge located where the front surface meets the envelope surface, the cutting edge extending around the front surface and lying in a plane that forms an acute angle α with the envelope surface, a tool axis extending through the turning insert in a normal direction in respect of the plane;
• a second driving member that is arranged to rotate the tool and the turning insert around the tool axis at a second speed of rotation;
• and
• a feeding device that is arranged to bring the rotating turning insert into engagement with the rotating workpiece and feed the turning insert in relation to the workpiece,
• wherein the envelope surface forms a chip surface and is arranged to meet chips formed in the chip-cutting metal machining, and the chip surface comprises chip breaking means,
• wherein the chip surface comprises a circumferential first portion that borders on the cutting edge and a circumferential second portion that borders on the circumferential first portion,
• wherein the first portion has one of a concave shape and a conical shape as seen in a cross-sectional plane including the tool axis, and
• wherein at least a portion of the envelope surface of the circumferential second portion projects radially outward past at least a portion of the envelope surface of the circumferential first portion.