Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools References http://www.Haniblecarbide.com http://www.crucibleservice.com/ http://www.azom.com/details.asp? ArticleID=268&head=Sialons#_Cutting_Tools http://www.manufacturingcenter.com/tooling/archives/0304/0304w estec_pages.asp Introduction Characteristics of cutting tool : Hardness (Elevated temperatures) Toughness (Impact forces on tool in interrupted operations) Wear resistance (tool life to be considered) Chemical stability or inertness (to avoid adverse reactions) Cutting Tool Materials The selection of cutting tool material and grade is an important factor to consider when planning a successful metal cutting operation. A basic knowledge of each cutting tool material and its performance is therefore important so that the correct selection for each application can be made. Considerations include the workpiece material to be machined, the component type and shape, machining conditions and the level of surface quality required for each operation. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Cutting Tool Materials Tool bits (inserts) generally made of seven materials: High-speed steel, Cast alloy (such as stellite), Cemented carbide, Ceramic, Cermet, Cubic Boron Nitride, Polycrystalline Diamond. Cutting Tool Properties Hot Hardness Hardness of various cuttingtool materials as a function of temperature Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Wear Resistance Able to maintain sharpened edge throughout the cutting operation, Same as abrasive resistance. Shock Resistance Able to take the cutting loads and forces. Shape and Configuration Should be available for use in different sizes and shapes. Letter Symbols Specifying The Designation of Hard Cutting Materials Hard metals: HW Uncoated hard metal containing primarily tungsten carbide (WC). HT Uncoated hard metal, also called cermet , containing primarily titanium carbides (TIC) or titanium nitrides (TIN) or both. HC Hard metals as above, but coated. Carbon and Medium Alloy Steels Oldest of tool materials; Used for: drills, taps, broaches, reamers; Inexpensive, easily shaped, sharpened; No sufficient hardness and wear resistance; Limited to low cutting speed operation. High speed steels (HSS) Hardened to various depths, Good wear resistance, Suitable for high positive rake angle tools. High Speed Steel May contain combinations of tungsten, chromium, vanadium, molybdenum, cobalt, Can take heavy cuts, withstand shock and maintain sharp cutting edge under red heat. Generally two types (general purpose): Molybdenum-base (Group M), Tungsten-base (Group T). Cobalt added if more red hardness desired. M-series - Contains 10% molybdenum, chromium, vanadium, tungsten, cobalt Higher, abrasion resistance, H.S.S. are majorly made of M-series. T-series - 12 % - 18 % tungsten, chromium, vanadium & cobalt undergoes less distortion during heat treating. H.S.S. available in wrought ,cast & sintered (Powder metallurgy) Coated for better performance, Subjected to surface treatments such as case-hardening for improved hardness and wear resistance or steam treatment at elevated temperatures, High speed steels account for largest tonnage High Speed Steels (HSS) Good wear resistance Relatively inexpensive Suitable for: High positive rake tools (small angles) Interrupted cuts Tools subjected to vibration and chatter (indent) Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Typical Wear Patterns on Highspeed-steel Uncoated and Titaniumnitride Coated Tools Schematic illustration of typical wear patterns of high-speedsteel uncoated and titanium-nitride coated tools. Note that flank wear is significantly lower for the coated tool. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Cast-cobalt Alloys Commonly known as stellite tools: Composition ranges – 38% - 53 % cobalt, 30%33% chromium, 10%-20% tungsten Good wear resistance (higher hardness) Less tough than high-speed steels and sensitive to impact forces Less suitable than high-speed steels for interrupted cutting operations Continuous roughing cuts – relatively high g=feeds & speeds Finishing cuts are at lower feed and depth of cut Cast Alloy Usually contain 25% to 35% chromium, 4% to 25% tungsten and 1% to 3% carbon Remainder cobalt Qualities High hardness High resistance to wear Excellent red-hardness Operate 2 ½ times speed of high-speed steel Weaker and more brittle than high-speed steel Cutting tool materials have different combinations of hardness, toughness and wear resistance, and are divided into numerous grades with specific properties. Generally , a cutting tool material that is successful in its application should be: Hard, to resist flank wear and deformation Tough, to resist bulk breakage Non-reactive with the workpiece material Chemically stable, to resist oxidation and diffusion Resistant to sudden thermal changes. Cemented Carbide Definition and properties Cemented carbide is a powdery metallurgical material; a composite of tungsten carbide (WC) particles and a binder rich in metallic cobalt (Co). Cemented carbides for metal cutting applications consist of more than 80% of hard phase WC. Additional cubic carbonitrides are other important components, especially in gradient sintered grades. The cemented carbide body is formed, either through powder pressing or injection moulding techniques, into a body, which is then sintered to full density. WC grain size is one of the most important parameters for adjusting the hardness/toughness relationship of a grade; the finer grain size means higher hardness at a given binder phase content. The amount and composition of the Co-rich binder controls the grade’s toughness and resistance to plastic deformation. At equal WC grain size, an increased amount of binder will result in a tougher grade, which is more prone to plastic deformation wear. A binder content that is too low may result in a brittle material. Cubic carbonitrides, also referred to as γ-phase, are generally added to increase hot hardness and to form gradients. Gradients are used to combine improved plastic deformation resistance with edge toughness. Cubic carbonitrides concentrated in the cutting edge improve the hot hardness where it is needed. Beyond the cutting edge, a binder rich in tungsten carbide structure inhibits cracks and chip hammering fractures. Applications Medium to coarse WC grain size Medium to coarse WC grain sizes provide the cemented carbides with a superior combination of high hot hardness and toughness. These are used in combination with CVD or PVD coatings in grades for all areas. Fine or submicron WC grain size Fine or submicron WC grain sizes are used for sharp cutting edges with a PVD coating to further improve the strength of the sharp edge. They also benefit from a superior resistance to thermal and mechanical cyclic loads. Typical applications are solid carbide drills, solid carbide end mills, parting off and grooving inserts, milling and grades for finishing. Cemented carbide with gradient The beneficial dual property of gradients is successfully applied in combination with CVD coatings in many first choice grades for turning, and parting and grooving in steels and stainless steels. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Uncoated Cemented Carbide (HW) Definition and properties Uncoated cemented represent a very small total assortment. These straight WC/Co or have cubic carbonitrides. carbide grades proportion of the grades are either a high volume of Applications Typical applications are machining of HRSA (heat resistant super alloys) or titanium alloys and turning hardened materials at low speed. The wear rate of uncoated cemented carbide grades is rapid yet controlled, with a self-sharpening action. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Cermet (CT) Definition and properties A cermet is a cemented carbide with titanium based hard particles. The name cermet combines the words ceramic and metal. Originally, cermets were composites of TiC and nickel. Modern cermets are nickel-free and have a designed structure of titanium carbonitride Ti(C,N) core particles, a second hard phase of (Ti,Nb,W)(C,N) and a W-rich cobalt binder. Ti(C,N) adds wear resistance to the grade, the second hard phase increases the plastic deformation resistance, and the amount of cobalt controls the toughness. In comparison to cemented carbide, cermet has improved wear resistance and reduced smearing tendencies. On the other hand, it also has lower compressive strength and inferior thermal shock resistance. Cermet can also be PVD coats for improve wear resistance. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Applications Cermet grades are used in smearing applications where built-up edge is a problem. Its self-sharpening wear pattern keeps cutting forces low even after long periods in cut. In finishing operations, this enables a long tool life and close tolerances, and results in shiny surfaces. Typical applications are finishing in stainless steels, nodular cast irons, low carbon steels and ferritic steels. Cermets can also be applied for trouble shooting in all ferrous materials. Hints: Use low feed and depth of cut. Change the insert edge when flank wear reaches 0.3 mm. Avoid thermal cracks and fractures by machining without coolant. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Coated Cemented Carbide (HC) Coated cemented carbide currently represents 80-90% of all cutting tool inserts. Its success as a tool material is due to its unique combination of wear resistance and toughness, and its ability to be formed in complex shapes. Coated cemented carbide combines cemented carbide with a coating. Together they form a grade which is customized for its application. Coated cemented carbide grades are the first choice for a wide variety of tools and applications. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Coating Materials Titanium nitride (TiN) Titanium carbide (TiC) Titanium Carbonitride (TiCN) Aluminum oxide (Al2O3), thickness range – 2-15 µm Techniques used: Chemical –vapor deposition (CVD) Plasma assisted CVD Physical-vapor deposition(PVD) Medium –temperature chemical- vapor deposition(MTCVD) Coating – CVD Definition and properties: CVD stands for Chemical Vapor Deposition. The CVD coating is generated by chemical reactions at temperatures of 700-1050°C. CVD coatings have high wear resistance and excellent adhesion to cemented carbide. The first CVD coated cemented carbide was the single layer titanium carbide coating (TiC). Alumina coatings (Al2O3) and titanium nitride (TiN) coatings were introduced later. More recently, the modern titanium carbonitride coatings (MT-Ti(C,N) or MT-TiCN, also called MT-CVD) were developed to improve grade properties through their ability to keep the cemented carbide interface intact. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Modern CVD coatings combine MT-Ti(C,N), Al2O3 and TiN. The coating properties have been continuously improved for adhesion, toughness and wear properties through microstructural optimizations and posttreatments. MT-Ti(C,N) - Its hardness provides abrasive wear resistance,resulting in reduced flank wear. CVD-Al2O3 – Chemically inert with low thermal conductivity , making it resistant to crater wear. It also acts as a thermal barrier to improve plastic deformation resistance. CVD-TiN - Improves wear resistance and is used for wear detection. Post-treatments - Improve edge toughness in interrupted cuts and reduce smearing tendencies. Applications CVD coated grades are the first choice in a wide range of applications where wear resistance is important. Such applications are found in general turning and boring of steel, with crater wear resistance offered by the thick CVD coatings; general turning of stainless steels and for milling grades in: ISO P (steel), ISO M (stainless steel), ISO K(cast iron) . For drilling, CVD grades are usually used in the peripheral insert. ISO Classification of Carbide Cutting Tools Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Carbides Most cost effective, versatile tool used in manufacturing Two major types of carbides (Tungsten and Titanium) Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Coating – PVD Definition and properties Physical Vapor Deposition (PVD) coatings are formed at relatively low temperatures (400-600°C). The process involves the evaporation of a metal which reacts with, for example, nitrogen to form a hard nitride coating on the cutting tool surface. PVD coatings add wear resistance to a grade due to their hardness. Their compressive stresses also add edge toughness and comb crack resistance. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools The main PVD-coating constituents are described below. Modern coatings are combinations of these constituents in sequenced layers and/or lamellar coatings. Lamellar coatings have numerous thin layers, in the nanometer range, which make the coating even harder. PVD-TiN - Titanium nitride was the first PVD coating. It has all-round properties and a golden color. PVD-Ti(C,N) - Titanium carbonitride is harder than TiN and adds flank wear resistance. PVD-(Ti,Al)N - Titanium aluminium nitride has high hardness in combination with oxidation resistance, which improves overall wear resistance. PVD-oxide - Is used for its chemical inertness and enhanced crater wear resistance. Multi Phase Coatings Reduces abrasion and chemical reactivity Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Diamond Coated Tools Use of Polycrystalline diamond as a coating, Difficult to adhere diamond film to substrate, Thin-film diamond coated inserts now commercially available, Thin films deposited on substrate with PVD & CVD techniques, Thick films obtained by growing large sheet of pure diamond, Diamond coated tools particularly effective in machining non-ferrous and abrasive materials. New Coating Materials Titanium carbo nitride (TiCN) Titanium Aluminum Nitride(TiAlN) Chromium Based coatings Chromium carbide Zirconium Nitride (ZrN) Hafnium nitride (HfN) Recent developments gives nano-coating & composite coating Ion Implementation : Ions placed into the surface of cutting tool No change in the dimensions of tool Nitrogen-ion Implanted carbide tools used for alloy steels & stainless steels Xeon – ion implantation of tools as under development Applications PVD coated grades are recommended for tough, yet sharp, cutting edges, as well as in smearing materials. Such applications are widespread and include all solid end mills and drills, and a majority of grades for grooving, threading and milling. PVD-coated grades are also extensively used for finishing applications and as the central insert grade in drilling. Letter Symbols Specifying The Designation of Hard Cutting Materials Ceramics: CA Oxide ceramics containing primarily aluminium oxide (Al2O3). CM Mixed ceramics containing primarily aluminium oxide (Al2O3) but containing components other than oxides. CN Nitride ceramics containing primarily silicon nitride (Si3N4). CC Ceramics as above, but coated. Ceramic (CA, CM, CN, CC) Definition and properties All ceramic cutting tools have excellent wear resistance at high cutting speeds. There are a range of ceramic grades available for a variety of applications. Oxide ceramics are aluminium oxide based (Al2O3), with added zirconia (ZrO2) for crack inhibition. This generates a material that is chemically very stable, but which lacks thermal shock resistance. (1) Mixed ceramics are particle reinforced through the addition of cubic carbides or carbonitrides (TiC, Ti(C,N)). This improves toughness and thermal conductivity. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools (2) Whisker-reinforced ceramics use silicon carbide whiskers (SiCw) to dramatically increase toughness and enable the use of coolant. Whisker-reinforced ceramics are ideal for machining Ni-based alloys. (3) Silicon nitride ceramics (Si3N4) represent another group of ceramic materials. Their elongated crystals form a self-reinforced material with high toughness. Silicon nitride grades are successful in grey cast iron, but a lack of chemical stability limits their use in other workpiece materials. Have good hardness Good thermal shock resistance Good for machining cast irons and nickel based super alloys Sialon (SiAlON) grades combine the strength of a self-reinforced silicon nitride network with enhanced chemical stability. Sialon grades are ideal for machining heat resistant super alloys (HRSA). Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Sialon Applications Seals and bearings Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools CC620 Oxide ceramic for high speed finishing of grey cast iron in stable and dry conditions. CC6050 Mixed ceramic for light, continuous finishing in hardened materials. CC650 Mixed ceramic for high speed finishing of grey cast irons and hardened materials, and for semi-finishing operations in HRSA with low toughness demands. CC670 Whisker ceramic with excellent toughness for turning, grooving and milling of Ni-based alloys . Can also be used for hard part turning in unfavorable conditions. CC6190 Silicon nitride grade for rough to finish turning and high speed dry milling of cast iron, perlitic nodular CC6090 cast irons and hardened cast irons. CC6090 Coated silicon nitride grade for light roughing to finish turning of cast iron. GC1690 Sialon grade for optimized performance when turning pre-machined HRSA in stable conditions. CC6060 Predictable wear due to good notch wear resistance. CC6065 Particle reinforced Sialon for turning operations in HRSA that demand tough inserts. Letter Symbols Specifying The Designation of Hard Cutting Materials Diamond: DP Polycrystalline diamond* Boron nitride: BN Cubic boron nitride* *(Polycrystalline diamond and cubic boron nitride are also called superhard cutting materials ). Polycrystalline Cubic Boron Nitride, CBN (BN) Definition and properties Polycrystalline cubic boron nitride, CBN, is a material with excellent hot hardness that can be used at very high cutting speeds. It also exhibits good toughness and thermal shock resistance. Modern CBN grades are ceramic composites with a CBN content of 40-65%. The ceramic binder adds wear resistance to the CBN, which is otherwise prone to chemical wear. Another group of grades are the high content CBN grades, with 85% to almost 100% CBN. These grades may have a metallic binder to improve their toughness. CBN is brazed onto a cemented carbide carrier to form an insert. The Safe-Lok™ technology further enhances the bondage of CBN cutting tips on negative inserts Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Applications CBN grades are largely used for finish turning of hardened steels, with a hardness over 45 HRC. Above 55 HRC, CBN is the only cutting tool which can replace traditionally used grinding methods. Softer steels, below 45 HRC, contain a higher amount of ferrite, which has a negative effect on the wear resistance of CBN. CBN can also be used for high speed roughing of grey cast irons in both turning and milling operations. CB7015 PVD coated CBN grade with ceramic binder for continuous turning, and light interrupted cuts in hardened steels. CB7025 CBN grade with ceramic binder for interrupted cuts and high toughness demands when turning hardened steels. CB7050 High content CBN grade with metallic binder for heavy interrupted cuts in hardened steels and for finishing grey cast iron. PVD coated .hardness demands when turning hardened steels. Diamond Hardest known substance Low friction, high wear resistance Ability to maintain sharp cutting edge Single crystal diamond of various carats used for special applications Machining copper—front precision optical mirrors for ( SDI) Diamond is brittle , tool shape & sharpened is important Low rake angle used for string cutting edge Polycrystalline Diamond, PCD (DP) Definition and properties PCD is a composite of diamond particles sintered together with a metallic binder. Diamond is the hardest, and therefore the most abrasion resistant, of all materials. As a cutting tool, it has good wear resistance but it lacks chemical stability at high temperatures and dissolves easily in iron. CD10 PCD grade for finishing and semi-finishing of non-ferrous and non-metallic materials in turning and milling. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Polycrystalline-diamond (PCD) Tools Used for wire drawing of fine wires, Small synthesis crystal fused by high pressure and temperaturę, Bonded to a carbide substrate, Diamond tools can be used for any speed, Suitable for light un-interrupted finishing cuts, To avoid tool fracture single crystal diamond is to be re-sharpened as it becomes dull, Also used as an abrasive in grinding and polishing operations. Diamond Edge Saw Blade Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Diamond Tip Drill Bits Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Properties for Groups of Tool Materials Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Relative Time Required To Machine With Various Cutting-tool Materials Relative time required to machine with various cutting-tool materials, indicating the year the tool materials were first introduced. Note that machining time has been reduced by two orders of magnitude with a hundred years. Source: Courtesy of Sandvik. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Inserts And Toolholders Individual cutting tools with several cutting points A square insert has 8 cutting points The holes in the inserts are standardized for interchangeability Typical carbide inserts with various shapes and chip-breaker features: Round inserts are also available, as can be seen in The holes in the inserts are standardized for interchangeability in toolholders. Source: Courtesy of Kyocera Engineered Ceramics, Inc. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. CARBIDES - Insert Attachment Methods of attaching inserts to toolholders: Clamping Wing lockpins Examples of inserts attached to toolholders with threadless lockpins, which are secured with side screws Insert brazed on a tool shank Methods of mounting inserts on toolholders: (a) clamping and (b) wing lockpins. (c) Examples of inserts mounted with threadless lockpins, which are secured with side screws. Source: Courtesy of Valenite. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Insert Edge Properties Relative edge strength and tendency for chipping of inserts with various shapes. Strength refers to the cutting edge indicated by the included angles. Source: Courtesy of Kennametal, Inc. Insert shape affects strength of cutting edge To further improve edge strength and prevent chipping, all insert edges are usually honed, chamfered, or produced with a negative land. Edge preparation for inserts to improve edge strength. Source: Courtesy of Kennametal, Inc. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Insert Edge Properties Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Wear on Cutting Edges To understand the advantages and limitations of each material, it is important to have some knowledge of the different wear mechanisms to which cutting tools are subjected. Abrasive Flank wear The most common type of wear and the preferred wear type, as it offers predictable and stable tool life. Flank wear occurs due to abrasion, caused by hard constituents in the workpiece material. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Chemical Adhesive Built-up edge (BUE) This wear type is caused by pressure welding of the chip to the insert. It is most common when machining sticky materials, such as low carbon steel, stainless steel and aluminium. Low cutting speed increases the formation of built-up edge. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Adhesive Notch wear Insert wear characterized by excessive localized damage on both the rake face and flank of the insert at the depth of cut line. Caused by adhesion (pressure welding of chips) and a deformation hardened surface. A common wear type when machining stainless steels. Thermal Plastic deformation Plastic deformation takes place when the tool material is softened. This occurs when the cutting temperature is too high for a certain grade. In general, harder grades and thicker coatings improve resistance to plastic deformation wear. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Thermal Thermal cracks When the temperature at the cutting edge changes rapidly from hot to cold, multiple cracks may appear perpendicular to the cutting edge. Thermal cracks are related to interrupted cuts, common in milling operations, and are aggravated by the use of coolant. Mechanic, impact force Edge chipping/breakage Chipping or breakage is the result of an overload of mechanical tensile stresses. These stresses can be due to a number of reasons, such as chip hammering, a depth of cut or feed that is too high, sand inclusions in the workpiece material, built-up edge, vibrations or excessive wear on the insert. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Tool-life Curves Tool-life curves for a variety of cutting-tool materials. The negative inverse of the slope of these curves is the exponent n in the Taylor tool-life equation and C is the cutting speed at T = 1 min, ranging from about 200 to 10,000 ft./min in this figure. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Allowable Average Wear Land for Cutting Tools Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Types of Wear Seen in Cutting Tools (a) Schematic illustration of types of wear observed on various cutting tools. (b) Schematic illustrations of catastrophic tool failures. A wide range of parameters influence these wear and failure patterns. Source: Courtesy of V. C. Venkatesh. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Surface Finish Factors Affecting Surface Finish: Nose radius of tool Cutting speed Rigidity of machining operation Temperature generated during machining process Direct relationship between temperature of workpiece and quality of surface finish High temperature yields rough surface finish Metal particles tend to adhere to cutting tool and form built-up edge Cooling work material reduces temperature of cutting-tool edge Result in better surface finish Machined Surfaces Produced on Steel (a) (b) Machined surfaces produced on steel (highly magnified), as observed with a scanning electron microscope: (a) turned surface and (b) surface produced by shaping. Source: Courtesy of J. T. Black and S. Ramalingam. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Dull Tool in Orthogonal Machining Schematic illustration of a dull tool with respect to the depth of cut in orthogonal machining (exaggerated). Note that the tool has a positive rake angle, but as the depth of cut decreases, the rake angle effectively can become negative. The tool then simply rides over the workpiece (without cutting) and burnishes its surface; this action raises the workpiece temperature and causes surface residual stresses. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Feed Marks on a Turned Surface Surface roughness: f2 Ra 8R w here f fe e d R to o l - n o s e ra d iu s Schematic illustration of feed marks on a surface being turned (exaggerated). Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Effects of Cutting Fluids Perform three important functions Reduce temperature of cutting action Reduce friction of chips sliding along tool face Decrease tool wear and increase tool life Three types of cutting fluids Cutting oils Emulsifiable (soluble) oils Chemical (synthetic) cutting fluids Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Cutting Fluids Generally used for machining: steel, alloy steel, brass and bronze with high-speed steel cutting tools Not used with cemented-carbide tools If used, great quantities of cutting fluid are applied to ensure uniform temperatures to prevent carbide inserts from cracking Not generally used with cast iron, aluminum, and magnesium alloys. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Cutting Fluids Purpose of cutting fluids: Reduce friction and wear Cool cutting zone Flush chips away from the cutting zone Protect the machined surface from environmental corrosion These factors improve tool life and help make a better more efficient cut. Image of cutting fluid and its container Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Cutting Fluids Lubricants reduce friction Coolants effectively reduce high temperatures of tools/ work pieces At times, using a cutting fluid may cause the material to become “curly”, which concentrates the heat closer to the tip. This is detrimental because it decreases the tool’s life. It is these defects that have turned machinists to “near-dry machining” Cutting Fluids Types of cutting fluids: Oils : mineral, animal, vegetable, compounded, and synthetic oils. Only used in operations where temp rise is ins ignificant. Em uls ions : mixture of oil and water and additives. Good for operations where temperature rise is s ignificant. S e m is ynthe tics : chemical emulsions containing little mineral oil diluted in water with additives that reduce size of particles. S ynthe tics : chemicals with additives, diluted in water, without oil. Image of a “synthetic” cutting fluid. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Cutting Fluids Methods of Application Flooding: most common; rates of up to 225 L/min for multi-tooth cutters; poor visibility; 1002000 Psi. Mist: most effective w/ water based fluids; requires venting but is popular because of good visibility; similar to using an aerolsol can; 10- 80 Psi. High-pressure systems: use a powerful jet/nozzle to target the hot area; 800- 5000 Psi; can be used as a chip-breaker to clear debris away. Through the cutting tool system: passages are made in the tool/ tool handle that allow for a direct route for the coolant to the hot area. Cutting Fluids Special Considerations for use of cutting fluids Machines need to be washed after fluids have been used. Used cutting fluids may undergo chemical changes. Settling, skimming, centrifuging and filtering help to avoid any bad effects they may cause. Cutting fluids containing: Sulfur should not be used on Nickel based alloys. Chlorine should not be used with Titanium Cutting Fluids Through the cutting tool system flooding method Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Cutting Fluids Multi-Jet Delivery System Flooding Method Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Proper Methods of Applying Cutting Fluids Schematic illustration of the proper methods of applying cutting fluids (flooding) in various machining operations: (a) turning, (b) milling, (c) thread grinding, and (d) drilling. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Near-dry and Dry Machining Introduced in 1990’s to minimize use of metalworking fluids. In these processes, chips are removed from the cutting zone by application of pressurized air. Dry machining: Used for turning, milling, and gear cutting on steels, steel alloys, and cast irons. Near-dry cutting: The application of a mist of a mixture of water and cutting fluid (vegetable oil) inserted through the spindle of the machine tool. Near-dry and Dry Machining Cryogenic Machining Cryogenic gases such as nitrogen and carbon dioxide are used as a coolant. They are shot through a small nozzle at temperatures around -200 C; good for tool life, good for the environment. Image of a liquid nitrogen cooling system. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools Machinability Machinability is defined in terms of: 1. Surface finish and surface integrity of machined part 2. Tool life 3. Force and power required 4. The level of difficulty in chip control Good machinability indicates good surface finish and surface integrity a long tool life and low force and power requirements Note, continuous chips should be avoided for good machinability 80 Results of (Free-machining) Modifications Three main machining characteristics become evident Tool life is increased Better surface finish produced Lower power consumption required for machining Machinability Machinability ratings (indexes) These have been used also to determine machinability available for each type of material and its condition not used much anymore due to misleading nature e.g.: AISI 1112 steel with a rating of 100: for a tool life of 60 min, choose 30 m/min cutting speed (for machining this material) These are mostly qualitative aspects - not sufficient to guide operator to machining parts economically Other guides for various materials should include: cutting speed, feed, depth of cut, cutting tools and 82 shape, cutting fluids Grain Structure Machinability of metal affected by its microstructure Ductility and shear strength modified greatly by operations such as annealing, normalizing and stress relieving Certain chemical and physical modifications of steel improve machinability Addition of phosphorus, sulphur, lead, or sodium sulphite Cold working, which modifies ductility Machinability Machinability here discussed for the following: Ferrous Metals (e.g. steels, stainless steels, cast iron, etc.), Nonferrous Metals (e.g. aluminum, copper, magnesium), Miscellaneous Materials (e.g. thermoplastics, ceramics), Thermally assisted machining. Machinability of Ferrous Metals: Steels Carbon steels have a wide range of machinability If a carbon steel is too ductile, chip formation can produce built-up edge, leading to poor surface finish If too hard, it can cause abrasive wear of the tool because of the presence of carbides in the steel Cold-worked carbon steels: preferred machinability 84 Machinability of Ferrous Metals Steels (cont) Free-machining steels: contain sulfur + phosphorus Sulfur forms: manganese sulfide inclusions Important to choose size, shape, distribution of inclusions These act as stress raisers in primary shear zone, chips are small, break easily (i.e. machinability ↑) Phosphorus has two major-desirable-effects 1. Strengthens ferrite - better chip formation, surface finish ↑ 2. Increases hardness - short (non-continuous chips) Note, soft steels have low machinability since have tendency to form BUE - poor surface finish Machinability of Ferrous Metals Steels (cont) Leaded steels (e.g. 10L45 steel) High percentage of lead solidifies at the tips of manganese sulfide inclusions, Lead acts as a solid lubricant (due to low shear strength) at tool-chip interface during cutting, It also acts: liquid lubricant when temp. is high in front of tool, It also ↓ shear stress at primary shear zone - ↓ forces and ↓ power consumption, Lead is, however, dangerous environmental toxin, there’s trend to eliminate use of lead in steel: “lead-free steels”, Good substitutes: bismuth, tin (but performance is lower). 86 Low-carbon (Machine) Steel Large areas of ferrite interspersed with small areas of pearlite Ferrite: soft, high ductility and low strength Pearlite: low ductility and high strength Combination of ferrite and iron carbide More desirable microstructure in steel is when pearlite well distributed instead of in layers High-carbon (Tool) Steel Greater amount of pearlite because of higher carbon content More difficult to machine steel efficiently Desirable to anneal these steels to alter microstructures Improves machining qualities Machinability of Ferrous Metals Steels (cont) Calcium-deoxidized steels They contain oxide flakes of calcium silicates (CaSO) these reduce the strength of the secondary shear zone they also decrease tool–chip interface friction and wear - temp. increases are lower- less crater wear Alloy steels They have a large variety of compositions and hardnesses machinability can’t be generalized but they have higher hardness and other properties Can be used to produce good surface finish, integrity, dimensional accuracy 89 Alloy Steel Combinations of two or more metals. Generally slightly more difficult to machine than low-or high-carbon steels. To improve machining qualities Combinations of sulfur and lead or sulfur and manganese in proper proportions added, Combination of normalizing and annealing. Machining of stainless steel greatly eased by addition of selenium Machinability of Ferrous Metals Effects of Various Elements in Steels Presence of aluminum and silicon is harmful in steels Reason: combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive -tool wear increases and machinability is reduced Note that as machinability↑, other properties may ↓ e.g. lead causes embrittlement of steel at high temp. (although has no effect at room temp.) e.g. sulfur can reduce hot workability of steel Machinability of Ferrous Metals Stainless Steels Austenitic (300 series) steels are difficult to machine (needs machine tool with high stiffness to avoid chatter) Ferritic stainless steels (also 300 series) have good machinability Martensitic (400 series) steels are abrasive, tend to form BUE Precipitation-hardening stainless steels: strong and abrasive, require hard, abrasion-resistant tool Cast Irons Gray irons: machinable, but abrasive (esp. pearlite) Nodular, malleable irons: machinable with hard materials 92 Cast Iron Consists generally of ferrite, iron carbide, and free carbon Microstructure controlled by addition of alloys, method of casting, rate of cooling, and heat treating White cast iron cooled rapidly after casting hard and brittle (formation of hard iron carbide) Gray cast iron cooled gradually composed by compound pearlite, fine ferrite, iron carbide and flakes of graphite (softer) Cast Iron Machining slightly difficult due to iron carbide and presence of sand on outer surface of casting. Microstructure altered through annealing Iron carbide broken down into graphitic carbon and ferrite Easier to machine Addition of silicon, sulfur and manganese gives cast iron different qualities. Machinability of Nonferrous Metals Aluminum very easy to machine but softer grades: form BUE, poor surface finish recommend high cutting speeds, high rake and relief angles Beryllium requires machining in a controlled environment this is due to toxicity of fine particles produced in machining Cobalt-based alloys abrasive and work hardening require sharp, abrasion-resistant tool materials, and low feeds and speeds Copper can be difficult to machine because of BUE formation 95 Aluminum Pure aluminum generally more difficult to machine than aluminum alloys Produces long stringy chips and harder on cutting tool Aluminum alloys Cut at high speeds, yield good surface finish Hardened and tempered alloys easier to machine Silicon in alloy makes it difficult to machine Chips tear from work (poor surface) Copper Heavy, soft, reddish-colored metal refined from copper ore (copper sulfide) High electrical and thermal conductivity Good corrosion resistance and strength Easily welded, brazed or soldered Very ductile Anneal: heat at 650º C and quench in water Does not machine well: long chips clog flutes of cutting tool Coolant should be used to minimize heat Copper-based Alloys: Brass Alloy of copper and zinc with good corrosion resistance, easily formed, machines, and cast Several forms of brass Alpha brasses: up to 36% zinc, suitable for cold working Alpha 1 beta brasses: Contain 54%-62% copper and used in hot working Small amounts of tin or antimony added to minimize pitting effect of salt water Used for water and gas line fittings, tubings, tanks, radiator cores, and rivets Copper-based Alloys: Bronze Alloys of copper and tin which contain up to 12% of principal alloying element Exception: copper-zinc alloys Phosphor-bronze 90% copper, 10% tin, and very small amount of phosphorus High strength, toughness, corrosion resistance Used for lock washers, cotter pins, springs and clutch discs Copper-based Alloys: Bronze Silicon-bronze (copper-silicon alloy) Contains less than 5% silicon Strongest of work-hardenable copper alloys Mechanical properties of machine steel and corrosion resistance of copper Used for tanks, pressure vessels, and hydraulic pressure lines Copper-based Alloys: Bronze Aluminum-bronze (copper-aluminum alloy) Contains between 4% and 11% aluminum Other elements added Iron and nickel (both up to 5%) increases strength Silicon (up to 2%) improves machinability Manganese promotes soundness in casting Good corrosion resistance and strength Used for condenser tubes, pressure vessels, nuts and bolts Copper-based Alloys: Bronze Beryllium-bronze (copper and beryllium) Contains up to 2% beryllium Easily formed in annealed condition High tensile strength and fatigue strength in hardened condition Used for surgical instruments, bolts, nuts, and screws Machinability of Nonferrous Metals Magnesium very easy to machine, good surface finish, prolonged tool life Caution: high rate of oxidation and fire danger Titanium and its alloys have very poor thermal conductivity, high temp. rise and BUE, difficult to machine Tungsten brittle, strong, and very abrasive, machinability is low Zirconium Good machinability Requires cooling cutting fluid (danger of explosion, fire) 103 Machinability of Miscellaneous Materials Thermoplastics Machining requires sharp tools with positive rake angles, large relief angles, small depths of cut and feed and high speeds Cooling also required to keep chips from sticking to tools Polymer-matrix composites: Very abrasive , difficult to machine Also, requires careful handling; avoid touching, inhaling fibers Metal-matrix and ceramic-matrix composites Can be difficult to machine depending on the properties of the matrix material and the reinforcing fibers Graphite Abrasive Requires sharp, hard, abrasion-resistant tools 104 Machinability Of Miscellaneous Materials Ceramics Have steadily improving machinability (e.g. nanoceramics) Require appropriate processing paramters Wood Properties vary with grain direction, type of chips and surfaces vary significantly depending on the type of wood and its condition Basic requirements: sharp tools, high cutting speeds Thank You For Your Attention