The following article on the geometry of cutting inserts was prepared by Iscar Ltd. and edited by Bruce Vernyi, Editor-in-Chief
The evolution of cutting tool shapes and cutting edge geometry is an interesting experience of traveling in time.
The development of new alloy materials and the introduction of new materials to the production floor, together with the constant drive for high productivity and machining efficiency, called for speeding up the evolution of smart and sophisticated tools.
In scientific terms, indexable inserts for metal cutting have gone through a full evolutionary scale, incorporating geometry modification and redesigned shapes.
In the middle of the 20th century, the International Standard Organization published and issued an ISO standard, detailing the specific dimensions and features that have to be complied with when manufacturing indexable inserts. This ISO standard aimed to guarantee the compatibility between indexable inserts and toolholders; even if produced by different manufacturers.
The ISO standard was a common practice for machine operators, setup facilitators and foremen on the production floor, but the new revolution brought tools designed like never seen before, with impressive geometries that met the industry’s rigorous demands for tools that work faster while maintaining long edge life.
The drive for more productivity and Fast Metal Removal (FMR) has instigated the ongoing pursuit for sophisticated unusual cutting-edge geometry design that did not always conform to the ISO standard. One way to achieve these goals was to find a way for increasing cutting speeds and feeds in order to remove large amounts of material in as minimum a time possible.
However, the attempt to improve edge geometry to provide better machining efficiency was occasionally obstructed by low spec CNC machining centers, that is, machines with insufficient spindle power, low torque, poor fixture clamping and other limiting factors.
Given these constraints, cutting tool manufacturers focus their efforts on designing insert edges that exert less cutting forces. The reduction in cutting forces enables running machining operations comparatively smoother, even when higher feedrates or cutting speeds were applied. Moreover, the reduction in cutting forces also moderates vibration to a certain extent.
The development of carbide submicron grain size, coupled with a variety of coatings to combat excessive heat and friction, in addition to the advances in pressing technology for powder metal, have all contributed to the success of producing revolutionized cutting tool edge geometry with unusual shapes.
R&D engineers and tool designers also have benefited from the progress in the field of computation, CAD/ CAM systems and other design software.
Computer software, Finite Element Analysis systems and simulation software were the prime instruments for supporting and assisting the R&D engineers to meet their goals. This software offered the right data for decision making that helped optimize the geometrical shape of the cutting edge for improved machining efficiency and to raise productivity.
This innovative trend brought about the helical cutting edges that reduce power consumption, enabling intensive work on a lower power machine. The same innovative trend is also responsible for the design of positive cutting edges, tangential clamping mechanisms and other economical considerations, such as more cutting edges per insert.
Milling
Milling illustrates the best example for which a line of tools took great advantage of an innovative design of indexable insert shapes and advance geometries for the benefit of improving machining performance.
In mathematical terms, the importance of increasing cutting speeds and feeds plays a crucial role in milling, due to the direct influence on material removal rate volumes, indicated as Q on the graph.
This graph displays ISCAR’s drive towards promoting geometric alterations and newly developed shapes and designs for the cutting edge, in order to provide the enduser with higher Q, meaning higher Material Removal Rate.
The evolution proceeds with more developments within the anatomy of milling inserts. The drive for improving productivity has brought about the development of a new milling concept, designed for very high feed rates, aiming to generate high-volume metal removal.
An example is the Iscar Feedmill trigon shaped insert that features a large radius and cutting edge configuration to allow the tool to run at high feeds while carrying a large amount of removed metal per tooth.
In addition, the insert is designed with a cylinder on the bottom that is seated in a matching hole in the pocket. That enables the inserts to bear higher cutting forces, and allow it to run at higher-than-normal feedrates. With this design, the insert is much more rigidly clamped, which works to relieve most of the stresses that normally are exerted on the clamping screw. Due to the unique geometry design, the cutting forces are directed axially toward the spindle, helping to provide stability even when machining long overhang applications.
Tangential milling systems with butterfly-shaped inserts feature optimal chip control. The tangential clamping mechanism reduces the strain exerted on the screw and in turn eliminates screw failure potential. Tangmill inserts enable machining accurate 90-degree shoulders to 14 mm in one pass. Tangential milling inserts are equipped with positive geometry cutting edges to generate less cutting forces while machining.
Another example is Iscar’s Shredmill family of milling cutters that feature round inserts with serrated cutting edges. The inserts have a protruding cylinder on the bottom, and they have four indexing orientation options. When very deep cavities are machined, chip evacuation, even with air blow, is problematic because of the shape of the chips, their weight and their size.
In deep cavities, there is a tendency for long chips to become trapped. Then they are prone to be re-cut.
When using inserts such as the Shredmill that have unique serrated cutting edge shape, small chips are produced, and they are less likely to be re-cut.
The serrations on the insert’s cutting edge were designed to overlap, and to provide a “fully effective” cutter configuration. Large cavity depths with long tool overhang may cause vibration and instability.
Rectangular inserts such as those in Iscar’s Helido series have 4 helical right-hand cutting edges and feature thick and strong characteristics.
These inserts, which can have a wiper to improve surface finish, are clamped into a dovetail inclined pocket that provides rigid clamping. The standard corner radius is 0.8 mm.
Due to their strong construction and a unique chip deflector with positive cutting angles and excellent grade combinations, these new 90 degree and 45 degree milling tools feature high durability, low cutting forces and excellent tool life.
These inserts can be used for machining steel, stainless steel and cast iron at very high machining parameters.
Three proven ideas have merged into the Helido inserts for high feed rough milling and cavity work in die & mold shops. They feature helical cutting edges for smoother entry, 17 degree lead angles to reduce lateral forces and Iscar’s Sumo Tec surface treatment for longer edge life.
Each trigon shaped insert provides six peripherally ground cutting edges and is seated securely into an inclined dovetail pocket to prevent movement.
Iscar also has developed a 16Mill insert that features 16 cutting edges and 16 cutting corners specially designed for high table speed.
These unique inserts offer high clamping security and reliable radial and axial edge location, to ensure repeatability when machining. Tool changes also are made easier with easy mounting and indexing of the inserts within the cutter.
Grooving & Parting
For grooving and parting, the advancement in insert geometry and shapes proceeds from single-edged, conventionally designed inserts to pentagonal shaped inserts that have five cutting edges with chipbreakers imbedded in each.
From a geometric point of view, it has a back stopper that provides high radial accuracy.
Multifunction lathe tools, capable of operating in a sequence of grooving and side and face turning modes can turn at large depths of cut and high feeds, to allow machining between walls with a high degree of accuracy. Tangentially gripped inserts, such as Iscar’s Tang- Grip, are single-ended, and attached by a revolutionary clamping method.
The design allows for rigid clamping in a tangentially oriented pocket to increase pocket life and, in addition, enable machining at high feedrates while providing straightness and good surface finish.
With these tools, machining forces are supported by a long and rigid rear wall.
This new design is recommended for parting large diameter parts and for interrupted cuts, in a form of free, unobstructed chip flow, due to the absence of upper jaw (compared to the previous clamping systems). All of these advantages provide a solution to the problem of inserts being pulled out from the cutting zone during tool retraction.
The pentagonal shaped inserts with five cutting edges and chipbreakers imbedded in each deliver economical performance for grooving, parting and side turning.
The pentagonal shape is designed to create a stronger insert for higher machining parameters, delivering straightness and surface quality, especially on groove bottoms and sidewalls.
Summary
The manufacturing world is now heading towards higher productivity. An increasing number of manufacturers are trying to optimize the production performance in order to drive the production cost to the bare minimum.
This pursuit of productivity brought a need for changes and modifications to the shape, geometry and chipbreaker design.
New alloy and new materials recently introduced to the production floor, together with the constant drive for high productivity and machining efficiency, dictated the demand for speeding up the evolution of innovative and sophisticated tools.
This trend brought the helical cutting edges that reduce power consumption, enabling intensive work on lower power machines. Similarly, this innovative trend is also responsible for the implementation of positive cutting edges, a tangential clamping mechanism and other factors that deliver increased productivity.
http://www.americanmachinist.com/304/Issue/Article/False/83663/Issue
