Lecture 2 Notes PDF

Machining Processes Cutting Tool Materials Dr.-Ing. Amr Nounou Introduction Success in metal cutting depends on the selection of the proper cutting tool (material and geometry) for a given work material. Improvements in cutting tool materials have led to significant...

Machining Processes Cutting Tool Materials Dr.-Ing. Amr Nounou Introduction Success in metal cutting depends on the selection of the proper cutting tool (material and geometry) for a given work material. Improvements in cutting tool materials have led to significant increases in cutting speeds and productivity. As the speed increases, so does the metal removal rate. Clearly, the cutting tool material, cutting parameters, and tool geometry selected directly influence the productivity of the machining operation. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 2 Introduction The selection of the cutting tool material and geometry followed by the selection of cutting conditions for a given application depends on many variables Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 3 Introduction The typical relationship of temperature at the tool/chip interface to cutting speed shows a rapid increase. Correspondingly, the tool wears at the interface rapidly with increased temperature, often created by increased speed Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 4 Introduction There are three main sources of heat in metal cutting: (1) primary shear zone; (2) secondary shear zone at the tool/chip interface; (3) tool flank. The peak temperature occurs at the center of the interface, in the shaded region, in the right schematic Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 5 Introduction Distribution of heat generated in machining to the chip, tool, and workpiece. Heat going to the environment is not shown. Figure based on the work of A. O. Schmidt Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 6 Introduction Hardness is the most critical characteristic. The tool material must be hard (to resist wear) and tough (to resist cracking and chipping). Tools used in interrupted cutting, such as milling, must be able to resist impact loading as well. Tool materials must sustain their hardness at elevated temperatures. Cutting tool materials that do not lose hardness at the high temperatures associated with high speeds are said to have “hot hardness.” Obtaining this property usually requires a trade-off in toughness, as hardness and toughness are generally opposing properties. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 7 Introduction The hardness of various tool materials is compared, ranging from iron to diamond Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 8 Introduction Comparing the properties for various cutting tool materials, overlapping characteristics exist in many cases. Important properties of cutting tool materials a Cutting Tool Materials Adapted from the source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 9 Introduction Decreasing hardness with increasing temperature is called hot hardness. Some materials display a more rapid drop in hardness above some temperatures. (From Metal Cutting Principles, 2nd ed. Courtesy of Ingersoll Cutting Tool Company) Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 10 Cutting Tool Materials In nearly all machining operations, cutting speed and feed are limited by the capability of the tool material. Speeds and feeds must be kept low enough to provide for an acceptable tool life. If not, the time lost changing tools may outweigh the productivity gains from increased cutting speed. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 11 Cutting Tool Materials Coated high-speed steel (HSS) and uncoated and coated carbides are currently the most extensively used tool materials. Coated tools cost only about 15% to 20% more than uncoated tools, so a modest improvement in performance can justify the added cost. Diamond and CBN (cubic boron nitride) are used for applications in which, despite higher cost, their use is justified. New ceramic materials called cermets (ceramic material in a metal binder) are having a significant impact on future manufacturing productivity. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 12 Cutting Tool Materials Tool Steels Carbon steels and low-/medium-alloy steels, called tool steels, were once the most common cutting tool materials. Plain-carbon steels of 0.90% to 1.30% carbon when hardened and tempered have good hardness and strength and adequate toughness and can be given a keen cutting edge. Low-/medium-alloy steels have alloying elements such as molybdenum and chromium, which improve hardenability, and tungsten and molybdenum, which improve wear resistance. These tool materials also lose their hardness rapidly when heated and they have limited abrasion resistance. Consequently, low-/medium-alloy steels are used in relatively inexpensive cutting tools (e.g., drills and broaches) for certain low-speed cutting applications. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 13 Cutting Tool Materials High-Speed Steels High-alloy steel is superior to tool steel in that it retains its cutting ability at temperatures up to 1100°F (≈590°C) , exhibiting good “red hardness.” Compared with tool steel, it can operate at about double or triple cutting speeds to about 100 sfpm with equal life, resulting in its name: high-speed steel, often abbreviated HSS. Today’s high-speed steels contain significant amounts of tungsten, molybdenum, cobalt, vanadium, and chromium besides iron and carbon. High-speed steel is still widely used for drills and many types of general-purpose milling cutters and in single-point tools used in general machining. For high-production machining, HSS has often been replaced by carbides, coated carbides, and coated HSS. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 14 Cutting Tool Materials Titanium Nitride Coated High-Speed Steels Coated high-speed steel provides significant improvements in cutting speeds, with increases of 10% to 20% being typical. TiN-coated HSS tools have demonstrated their ability to more than pay for the extra cost of the coating process. In addition to gear-shaper cutters and drills, HSS tooling coated by TiN now includes broaches, bandsaw and circular saw blades, insert tooling, form tools, end mills, and an assortment of other milling cutters. The main advantage of TiN-coated HSS tooling is reduced tool wear. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 15 Cutting Tool Materials Carbide or Sintered Carbides Carbide cutting tool inserts are traditionally divided into two primary groups: 1. Straight tungsten grades, which are used for machining cast irons, and nonferrous and nonmetallic materials. 2. Grades containing major amounts of titanium, tantalum, and/or columbium carbides, which are used for machining ferritic workpieces. There are also the titanium carbide grades, which are used for finishing/semifinishing ferrous alloys. Carbides, which are nonferrous alloys, are also called sintered (or cemented) carbides because they are manufactured by powder metallurgy techniques. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 16  Tool Geometry The figure shows the cutting-tool geometry for a single-point HSS tool used in turning in oblique, threeforce machining. Standard terminology to describe the geometry of single- point tools: (a) three dimensional views of tool, (b) oblique view of tool from cutting edge, (c) top view of turning with single-point tool, (d) oblique view from shank end of single-point turning tool. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 17 Tool Geometry The back rake angle affects the ability of the tool to shear the work material and form the chip. Back Rake Angle: The angle formed between the tool face and line parallel to the base. Side Rake Angle: the angle formed between the tool face and a line perpendicular to the shank. Source: DeGarmo's Materials and Processes in Source: https://www.mechanicalbooster.com/2016/12/single-point-cutting-tool.html Manufacturing, SI Version, 12th Edition, Global Retrieved 10/11/2021 Edition, Wiley, 2017. Cutting Tool Materials Dr.-Ing. Amr Nounou - Winter 2024-2025 18 Tool Geometry End Relief Angle: The angle formed between the minor flank and a line normal to the base of the tool. It avoids the rubbing of the workpiece against tool. Side Relief Angle: the angle formed between the major flank surface and plane normal to the base of the tool. It avoids the rubbing between workpiece and flank when the tool is fed longitudinally. Source: https://www.mechanicalbooster.com/2016/12/single-point- Source: DeGarmo's Materials and Processes in cutting-tool.html Manufacturing, SI Version, 12th Edition, Global Retrieved 10/11/2021 Edition, Wiley, 2017. Cutting Tool Materials Dr.-Ing. Amr Nounou - Winter 2024-2025 19 Tool Geometry The side and end cutting-edge angles define the nose angle and characterize the tool design. Increasing the nose radius usually End Cutting Edge Angle: The angle decreases tool wear and improves formed in between the end cutting surface finish. edge and a line perpendicular to the shank. Side Cutting Edge Angle: The angle formed in between the side cutting edge and a line parallel to the shank. Source: https://www.mechanicalbooster.com/2016/12/single-point- Source: DeGarmo's Materials and Processes in cutting-tool.html Manufacturing, SI Version, 12th Edition, Global Retrieved 10/11/2021 Edition, Wiley, 2017. Cutting Tool Materials Dr.-Ing. Amr Nounou - Winter 2024-2025 20 Tool Failure and Tool Life In metal cutting, the failure of the cutting tool can be classified into two broad categories, according to the failure mechanisms that caused the tool to die (or fail): 1.Physical failures mainly include gradual tool wear on the flank(s) of the tool below the cutting edge (called flank wear) or wear on the rake face of the tool (called crater wear) or both. 2.Chemical failures, which include wear on the rake face of the tool (crater wear) are rapid, usually unpredictable, and often catastrophic failures resulting from abrupt, premature death of a tool. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 21 Tool Failure and Tool Life Other modes of failure are outlined in the Table. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 22 Cutting Fluids The cutting fluid acts primarily as a coolant and secondly as a lubricant, reducing the friction effects at the tool/chip interface and the work flank regions. The cutting fluids also carry away the chips and provide reductions in friction and forces in regions where the bodies of the tools rub against the workpiece. Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 23 Economics of Machining The cutting speed has such a great influence on the tool life compared to the feed or the depth of cut that it greatly influences the overall economics of the machining process. Adding up each of the individual costs results in a total unit cost curve that is observed to go through a minimum point. For a turning operation, the total cost per piece C = Machining cost + Tooling cost + Tool-changing cost + Handling cost per piece Cost per unit for a machining process vs cutting speed Cutting Tool Materials Source: DeGarmo's Materials and Processes in Manufacturing, SI Version, 12th Edition, Global Edition, Wiley, 2017. Dr.-Ing. Amr Nounou - Winter 2024-2025 24 Cutting Tool Materials Dr.-Ing. Amr Nounou - Winter 2024-2025 25 Enhance your German terminology … English term German term Steel Stahl Lubricant Schmiermittel Increase Zunahme Decrease Abnahme Angle Winkel Cutting Tool Materials Dr.-Ing. Amr Nounou - Winter 2024-2025 26  Thank you for your attention... Cutting Tool Materials Dr.-Ing. Amr Nounou - Winter 2024-2025 27