Exploring Advanced Manufacturing Technologies. Steve Krar
and Heavy (H): machining operations for maximum stock removal and severe conditions that include high depth of cut and feedrate combinations.
CoroKey insert recommendations cover the most common types of turning and rotating types of machining, with recommended first choice for versatility and two complementary choices for increased productivity or added security. See various Sandvik guides and catalogs for more details on specific insert selections, material applications, and machining operations.
VALENITE’S SPECTRA TURN SYSTEM
Valenite Inc. developed a complete version of its Spectra System™ Turn Application Guide whose purpose is to allow the user to hold tighter dimensional tolerances. When the correct insert is used on the proper application, Table 3-2-5, the Spectra Turn inserts should extend tool life by almost 400%.
Valenite has developed a Spectra Turn Application Guide, a color-coded guide that covers 95% of turn applications and the nine grades and thirteen chipbreakers that make up its Spectra Turn line of turning inserts. The guide differs from traditional ISO groupings and bases its recommendations on the similarity of machinability intended for workpiece materials that share common failure modes. The Color-coding groupings are:
Fig. 3-2-11 Insert grades for finishing, medium machining, and roughing operations. (Kennametal, Inc.)
▪Blue for carbon, alloy, and tool steels.
▪Yellow for stainless steels, titanium, and high temperature alloys.
▪Red for gray and ductile irons, aluminum, and non-ferrous materials.
The insert grade application range, Fig. 3-2-12, shows the applications, failure modes, and suggested speed ranges that can be used as a guide when selecting an insert to suit a particular application. The typical failure modes are identified for applications that include heavy roughing, roughing, semifinishing, and finishing.
Insert failure analysis is a method of determining how close an insert and application match the optimum insert life span, as prescribed by the manufacturer. The idea is to look at the primary failure mode for various workpiece materials and select an insert that minimizes this primary failure mode. For example, some alloys of stainless steel may produce a build-up edge on the insert that may result in premature, catastrophic failure of the insert.
Selecting an insert having the features designed to reduce build-up edge will extend insert life. Failure mode analysis is a method to help a shop specify an insert with substrate, coating, chipbreaker, edge preparation, and coolant designed to reduce build-up edge enough for the insert to wear out at a consistent and predictable rate.
Applying failure mode analysis to insert selection enables the user to reduce or eliminate the primary causes of insert failure.
▪When insert selection is approached from a failure mode, workpiece material groupings are changed: steel is blue; stainless are yellow and gray; and ductile irons and aluminum are red.
▪Materials are classified based on their machinability characteristics rather than chip formation type.
Failure mode analysis looks at two types of insert failure: primary and secondary. Primary, the initial or underlying problem will eventually result in secondary failure. For example, the build-up edge can result in chipping or breaking away edge of the tool, a secondary failure mode that would constitute a catastrophic failure of the insert edge.
Fig. 3-2-12 Application speed, grade ranges, and applications. (Valenite, Inc.)
Table 3-2-5 Spectra System application guide for insert grades. (Valenite, Inc.)
PART 3 COATINGS COATED CARBIDE INSERTS
Research shows that cemented-carbide tools coated with a film of titanium carbide, titanium nitride, or aluminum oxide can increase tool life, improve material-removal rates as much as 30%, and produce freer-flowing chips. The coating acts as a permanent lubricant, greatly reducing cutting forces, heat generation, and tool wear, Fig. 3-2-13. This permits higher speeds to be used during the machining process, particularly when a good surface finish is required. The lubricity and antiweld characteristics of the coating greatly reduce the amount of heat and stress generated when making a cut.
Fig. 3-2-13 Coatings act as a lubricant, reduce tool wear and cutting forces, and heat generation. (Balzers Tool Coating, Inc.)
The use of hard, wear-resistant coatings of carbides, nitrides, and oxides to carbide inserts have greatly improved the performance of carbide-cutting tools. Inserts are available with a combination of two or three materials in the coating to give the tool special qualities. Strong wear-resistant titanium carbide forms the innermost layer. This layer is followed by a thick layer of aluminum oxide, which provides toughness, shock resistance, and chemical stability at high temperatures. A third, very thin layer composed of titanium nitride is applied over the aluminum oxide. This provides a lower coefficient of friction and reduces the tendency to form a built-up edge.
Coatings increase tool life and manufacturing productivity, while reducing machining costs, Fig. 3-2-14. Some of the coatings used for cemented carbide tools that have been successful are titanium carbide (TiC), titanium nitride (TiN), aluminum oxide (Al2O3), and titanium carbonitride (TiCN):
▪Titanium Nitride (TiN), a gold-colored coating, is an excellent general purpose coating for protecting a wide variety of tools from wear. TiN coated tools are used for machining high alloy steels and low alloy steels at medium and high cutting speeds. Tool life is three to five times longer than uncoated HSS and carbide end mills.
▪Titanium Carbonitride (TiCN), a blue-gray colored coating, is a high performance coating for milling cutters used for machining stainless steel at low cutting speeds, machining alloy steels, and when increased speed and feed rates are desired.
▪Chromium Nitride (CrN) is a silver-gray colored coating that resists adhesive wear, corrosion, and oxidization. It is used for machining copper alloys, bronze, aluminum bronze, nickel silver titanium, and titanium alloys.
▪Chromium Carbide (CrC), a silver-gray colored coating, has high temperature oxidization-resistant properties used for aluminum and magnesium die-castings.
▪Titanium Aluminum Nitride (TiAIN) is a violet-gray colored multi-layer coating used for machining cast iron, stainless steel, nickel-base high temperature alloys and titanium alloys. This coating is used for high-speed dry and semi-dry machining operations.
▪Tungsten Carbide/Carbon (WC/C) is a black-gray colored coating of hard tungsten carbide particles in a soft amorphous carbon matrix. It is used for precision components with abrasive and adhesive wear, seizure problems (poor lubrication) and for dry machining applications.
Fig. 3-2-14 Coatings on inserts help to increase productivity. (Niagara Cutter, Inc.)
▪Polycrystalline Diamond (PCD), a layer of diamond fused to the cutting tool, is used for machining abrasive non-metallic, non-ferrous materials, graphite, plastics, green compacts, and composites.
For a list of properties and applications for thin wear-resistant coatings refer to Table