How to choose the right turning insert

Issuing time:2024-04-07 10:02

There are many parameters to consider when selecting a turning insert. Carefully select the insert geometry, insert grade, insert shape (tip angle), insert size, tip radius and lead angle (lead angle) to achieve good chip control and machining performance.


Choose insert geometry based on the selected operation (e.g. finishing)


Choose the largest possible tip angle on the insert for strength and economy


Choose insert size based on depth of cut


Choose the largest possible tip radius for insert strength


If there is a tendency to vibrate, choose a smaller tip radius



l = cutting edge length (insert size)


RE = Tool nose radius



Nose angle



Turning insert geometry

Turning geometries can be divided into three basic types, optimized for finishing, semi-finishing and roughing. This diagram shows the working area of each geometry, based on acceptable chip breaking, in relation to feed and depth of cut.

roughing

High cutting depth and feed rate combinations. Operations requiring maximum edge security.

Moderate

Medium to light roughing. Wide range of depth of cut and feed rate combinations.

finishing

Operations with small cutting depths and low feed rates. Operations requiring low cutting forces.



Turning wiper geometry


Use wiper inserts to improve surface finish with standard cutting data or to maintain surface finish at significantly increased feed rates.


-WMX wiper geometry is preferred and a good starting point for most applications. When conditions change, there is always an effective alternative.


Choose a positive wiper geometry to reduce forces and maintain productivity when vibration is a problem.


Choose wiper geometry as follows:


-WL: Improves chip control when moving to lower f n / a p.


-WF: Improves chip control at lower f n / a p. Also reduces cutting forces when vibration occurs.


-WMX: Always preferred in a wide range of chip applications. Provides maximum productivity, versatility and best results.


-WR: When a stronger edge line is required, for example, for interrupted cuts.



Turning insert material


The choice of insert grade is mainly based on:


Component material (ISO P, M, K, N, S, H)


Type of method (finishing, semi-finishing, roughing)


Processing conditions (good, normal, difficult)


Insert geometry and insert grade complement each other. For example, the toughness of the grade can compensate for the lack of strength in the insert geometry.


Turning insert shape

The blade shape should be selected based on the accessibility of the cutting edge angle required by the tool. The largest possible nose angle should be selected to provide blade strength and reliability. However, this must be balanced with the variation in the cuts that need to be performed.


Large nose angles are strong but require more machine power and have a higher tendency to vibrate.


Small nose angles are weaker and have less cutting edge engagement, both of which make them more sensitive to the effects of heat.



Cutting edge strength (larger nose angle)


Stronger cutting edge


Higher feed rates


Increased cutting forces


Increased vibrations


Less tendency to vibrate (smaller nose angle)


Increased accessibility


Less vibrations


Lower cutting forces


Weaker cutting edge


Turning insert size


Select the insert size based on the application requirements and the space available for the cutting tool in the application.


The larger the insert size, the better the stability. For heavy-duty machining, insert sizes above IC 25 mm (1 inch) are usually used.


Once completed, the size can be reduced in many cases.


How to choose blade size

  1. Determine the maximum cutting depth p


    Determine the necessary cutting length LE, taking into account the toolholder’s entering angle, cutting depth a p and machine specifications


    Based on the necessary LE and a p, the correct cutting edge length, L and IC of the insert can be selected

Turning insert nose radius

Nose radius RE is a critical factor in turning operations. Inserts are available in a variety of nose radius sizes. The selection depends on depth of cut and feed, and affects surface finish, chip breaking and insert strength.

Cutting depth and cutting force

The relationship between nose radius and depth of cut affects vibration tendency. As depth of cut increases, the radial forces pushing the insert away from the cutting surface become more axial.


It is preferred that axial forces be greater than radial forces. High radial forces negatively affect the cutting action, resulting in vibration and poor surface finish.


As a general rule of thumb, select a nose radius that is equal to or less than the depth of cut.


Direct or reverse turning insert styles

Negative blades have an angle of 90° (0° clearance angle), while positive blades have an angle less than 90° (e.g. 7° clearance angle). The illustration of a negative blade shows how the blade is assembled and angled in the holder. Listed below are some characteristics of the two blade types:

Forward turning inserts

  • One-sided


    Low cutting forces


    Side clearance


    First choice for internal and external turning of slender parts

Clearance Angle

Negative turning inserts

  • Double and/or single sided


    High edge strength


    Zero clearance


    First choice for external turning


    Heavy cutting conditions

Clearance Angle

Turn entry angle

The lead angle KAPR (or lead angle, PISR) is the angle between the cutting edge and the feed direction. Selecting the correct lead angle/lead angle is very important for a successful turning operation. The lead angle/lead angle affects:


Chip formation


Direction of cutting forces


Length of cutting edge during cutting


Large entering angle (small entering angle)

  • Force is directed towards the chuck. Less tendency to vibrate


    Ability to turn the shoulder


    Higher cutting forces, especially at cut entry and exit


    Notch wear tendency for HRSA and case-hardened workpieces

Small entering angle (large lead angle)

  • Increased radial force into the workpiece will result in a tendency to vibrate


    Reduces load on cutting edge


    Produces thinner chips = higher feed rates


    Reduces notch wear


    Cannot turn 90° shoulder