Exploring Advanced Manufacturing Technologies. Steve Krar
CARBIDE TOOL IDENTIFICATION
There are four basic groups of cutting tool materials used in metal-removal operations: tungsten carbide, cermet, ceramic, and polycrystalline. There are two basic tool types used in carbide cutting - indexable insert tool and standard brazed on insert tool. Indexable insert tools, Fig. 3-2-2, are the most economical and those commonly used all types of metal-cutting operations. The inserts provide a number of low cost, indexable cutting edges. After all cutting edges are worn, it is generally more economical to replace the insert than to have someone regrind the insert. Various methods are used to lock the insert in position. A cam-type lock pin, or a clamp, or combination of lock pin and clamp are among the techniques used.
Standard brazed-on tools, low in initial cost, can be used for special and some general-purpose machining operations. They are rarely used in manufacturing today because of the time it takes to recondition and reset a tool once it has become dull.
Fig. 3-2-1 The powder metallurgy process of manufacturing cemented-carbide tools. (Carboloy, Inc.)
Table 3-2-1 Suggested uncoated carbide grades for metalcutting. (Valenite, Inc.)
Fig. 3-2-2 A variety of indexable carbide inserts. (Hertel Carbide, Ltd.)
Indexable Carbide Tool Identification
Numerous manufacturers throughout the world make cemented carbide indexable inserts in a wide variety of shapes and sizes. The more inserts available, the more difficult it is for those in industry to select the correct tool insert consistently. The ANSI and ISO coding systems, Table 3-2-2, that identify codes for inserts are recognized as standards throughout the world.
Turning Inserts
Most turning inserts today are .187 in. (5mm) thick, .50 in. (13mm) IC (inscribed circle) radius with 35°, 55°, 60°, and 80° geometries. The 60° triangular insert, with six cutting edges, is a good choice for general-purpose machining, Fig. 3-2-3.
▪For turning steel, the Sandvik PR inserts have been developed to achieve good chip control especially during roughing cuts. These inserts have a positive insert geometry with the top rake increased to 22° to enable high productivity where toughness is required, Fig. 3-2-4.
▪For heavy interrupted cuts or similar roughing operations, sturdier inserts such as the square or round inserts are recommended.
Fig. 3-2-3 The triangular 60° insert with six cutting edges is used for general-purpose machining. (Sandvik, Inc.)
Milling Inserts
Carbide milling inserts are available in a wide variety of geometric shapes and sizes. The Sandvik CoroKey geometry insert codes are illustrated in Fig. 3-2-5.
Code: L or light operations: Extra positive geometry for low cutting forces, suitable for small machines and sticky materials
M or medium operations: Positive geometry for general use, has high edge toughness and is the basic insert for most materials
H for heavy operations: Reinforced cutting edge that allows the highest possible feed rate, reliable in operations where the recutting of chips may occur
Table 3-2-2 ANSI and ISO codes for inserts. (Hertel Carbide Ltd.)
In the midst of all these insert styles, the simple round insert is emerging as the first choice milling insert for a growing number of machinists, programmers, and engineering. Round carbide inserts are strong, versatile and economical. Despite the simple shape, there are complex and sophisticated cutting tools. Subtle changes in geometry, depth of cut, lead angle and rake can make a big difference.
Carbide Tool Advantages
▪Excellent wear resistance
▪Greater hardness than high-speed steel tools
▪Ability to maintain a cutting edge under high-temperature conditions
▪Inserts can be replaced quickly when they are dull and therefore minimize the amount of machine downtime
▪Higher cutting speeds and feed rates can be used, increasing productivity
Fig. 3-2-4 The positive 22° rake on the insert provides high productivity where toughness is required. (Sandvik, Inc.)
Fig. 3-2-5 The CoroKey insert codes cover various machining conditions. (Sandvik, Inc.)
PART 2 INSERT SELECTION SYSTEMS
INSERT SELECTION
Dramatic advances in coating technology, chipbreaker design, and carbide metallurgy in the last few years have reduced the number of choices users face when selecting an insert for a particular application. Major suppliers offer a variety of coated carbides and chipbreaker geometries to machine almost all ferrous alloys effectively. Molded inserts and even molded chipbreakers, as precise as traditional ground carbides, provide a new generation of carbide tool family. Use Table 3-2-3 as a general guide for selecting the proper tooling to suit various machining applications.
The selection of inserts to suit a machining operation must consider five factors: the part material, insert geometry, selection of the chipbreaker type, grade of the carbide tool, and optimum cutting speed and feed.
Table 3-2-3 The tooling and selection guides for inserts and machining conditions. (Carboloy, Inc.)
1. Part Material
Most carbide manufacturers produce tool inserts to suit each of the following material groups:
▪Steel and cast steel, unalloyed to high alloy, case hardening and heat treatable steels, carbon steel, and structural steels.
▪Stainless and acid-proof steel, high heat-resistant alloys based on nickel and cobalt content.
▪Cast iron, grey cast iron, malleable cast iron, and chilled iron.
2.Insert Geometry
The shape of the insert selected must suit the type of machining operation to be performed (roughing or finishing), the contour of the form to be machined, the shape and hardness of the part, and the surface finish required. The following are some general guidelines to follow when selecting the shape of the insert.
▪Square inserts have the strongest structural shape (90° point angle). They are used where a lead angle is desirable and for chamfering tools.
▪Triangular inserts have a 60° point angle that allows producing square shoulders, cutting contour forms, chamfering, and plunge cutting.