Group Two (The Calipers) We’re “DEAD ON!”  Anthony Menicucci  Keith Jansen  Bill Fan  Chris King  Nathan Burns

“Fundamental Of Machining” and “Cutting-Tool Materials and Cutting Fluids” Above: Lathe cutting tool Side: Nano Drill-Bit = 1 um 2

Types of Machining

Straight Turning and Cutting Off

Slab Milling

End Milling

Types Of Chips produced Continuous Discontinuous Serrated or Segmented Built Up Edge

Continuous and Discontinuous Chips

Chip Breakers Chip Breakers can be used to prevent discontinuous chips from forming.

Serrated or Segmented (f) (b)(a)(c) (d)(e) Serrated chips, looked at under a microscope, resemble a saw tooth pattern because of the semi-continuity of the chip as in Figure (a).

(a) Built Up Edge Built Up edges affect the performance of a cutting tool because of their hardness and the perceived dulling of the tool. Chip BUE

Hardness of a BUE 230 Chip

Oblique cutting Most machining operations involve oblique cutting. Why, on the most basic level, is this this so?

Other forms of oblique cutting

Quick Review  Types of Machining  Turning and Cutting off  Slab Milling  End Milling  Chip Formation  Continuous  Discontinuous  Built Up Edge  Oblique Cutting

21.4 Temperatures in Cutting  As in all metalworking processes where plastic deformation is involved, the energy dissipated in cutting is converted into heat which in turn, raises the temperature in the cutting zone.

Major Effects  Excessive temperature lowers the strength, hardness, stiffness, and wear resistance of the cutting tool; tools also may soften and undergo plastic deformation; thus tool shape is altered.

Major Effects  Increased heat causes uneven dimensional changes in the part being machined, making it difficult to control its dimensional accuracy and tolerances.

Major Effects  Excessive temperature rise can induce thermal damage and metallurgical changes in the machined surface, adversely affecting its properties.

Temperature Distribution  The maximum temperature is about halfway up the tool-chip interface.

Techniques for Measuring Temperature  Thermocouples embedded in the tool.  Thermal emf (electormotive force) at the tool- chip interface, which acts as a hot junction between two different materials.  Infrared radiation from the cutting zone may be monitored with a radiation pyrometer. Traditional Infrared Thermometer

21.5 Tool Life: Wear and Failure  Tool wear is a major consideration in all machining operations. Tool wear adversely affects tool life, quality of the machined surface and its dimensional accuracy, and cutting operations

Tool Wear  Crater Wear  Tool-chip interface  Predominant at high speed  Mitigated by efficient use of carbides Flank wear Flank wear  Tool-work piece inter  Predominant at low speeds

Tool Wear  (a) Crater Wear  (b) Flank wear on a carbide tool

Flank Wear

Tool Life Curves  Effect of work piece microstructure on tool life in turning. Tool life is given in terms of the time(min) required to reach a flank wear land of a specified dimension. (a) ductile cast iron. (b) Steels, with identical hardness. Note the rapid decrease in tool life as the cutting speed increases.

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. (b) Relationship between measured temperature during cutting and tool life (flank wear). Note that high cutting temperatures severely reduce tool life.

Extended Taylor’s Equation

Crater Wear Relationship between crater wear rate and average tool chip interface temperature. (a) High speed steel, (b) Carbide, ( c ) C5 carbide

Other Types of Wear, Chipping and Facture  (a) Schematic illustration of types of wear observed on various cutting tools.  (b) Catastrophic tool failures.

Chapter 21 Sections 6 & Surface Finish and Integrity 21.7 Machinability

21.6 Surface Finish and Integrity  Surface Finish describes the geometric features of a surface.  Surface integrity pertains to the material properties.

Building exterior suffers from unsightly damage of mold infestation due to high humidity. The strong oxidation effect of photocatalyst effectively removes mold and protects the surface integrity

Effects of tool-tip profile  Built-up edge has the greatest influence on surface finish. (a)(b) Figure Surfaces produced on steel by cutting, as observed with a scanning electron microscope: (a) turned surface and (b) surface produced by shaping. Source: J. T. Black and S. Ramalingam.

Effect of tool-tip profile  Ceramic and diamond tools generally produce better surface finish than other tools because of their much lower tendency to form a BUE.

Dull Tools  Large radius along its edge.  If tip radius of the tool is large in relation to the depth of cut, the cool simply will rub over the machined surface.  May cause surface damage, such as tearing and cracking

Vibration and chatter  Vibration and chatter will affect the dimension of the workpiece surface finish adversely.  Vibrating tool periodically changes the dimensions of the cut.  Excessive chatter also can cause chipping and premature failure of the more brittle cutting tools.

Factors influencing surface integrity  Temperatures generated during processing and possible metallurgical transformations.  Surface residual stresses.  Severe plastic deformation and strain hardening of the machined surfaces, tearing, and cracking.

Finish Machining and Rough Machining  In finish machining, it is important to consider the surface finish to be produced  In rough machining, the main purpose is to remove a large amount of material at a high rate. Surface finish is not a primary consideration.

Finish and Rough Machining

21.7 Machinability  Machinability can be defined in terms of four factors:  1. Surface finish and surface integrity of the machined part.  2. Tool life.  3. Force and power required.  4. The level of difficulty in chip control.

Machinability  Good Machinability indicates good surface finish and integrity, long tool life, and low force, and low power requirement.  Tool life and surface roughness are considered to be the most important factors.

Machinability Ratings (index)  Standard material: AISI 1112 steel, with a rating of 100.  This means; for a tool life of 60min, this steel should be machined at a cutting speed of 100ft/min (30m/min).  Some examples; 3140 steel at 55; free- cutting brass at 300; 2011 wrought aluminum at 200.

Machinability of ferrous metals  Machinability of steels, alloy steels, stainless steels, and cast iron.  Pg: 638.  Effects of various elements in steels.  Presence of aluminum and silicon in steel is harmful.  Carbon and manganese have various effects depending on their composition.

Machinability of nonferrous metals  Examples of nonferrous metals are:  Aluminum, Copper, Magnesium, Titanium, and Zirconium.  Pg: 640

Machinability of miscellaneous materials  Thermoplastics  Thermosetting plastics  Polymer-matrix composites  Metal-matrix and ceramic matrix composites  Graphite and Ceramics  Wood  Pg: 641

Thermally assisted machining (hot machining)  Metals and alloys that are difficult to machine at room temperature can be machined more easily at elevated temperatures.  A source of heat (such as a torch, induced coil, electric current, laser-beam, electron- beam, and plasma arc) is focused onto an area just ahead of the cutting tool.

Hot machining  General advantages;  Reduced cutting force  Increased tool life  Higher material-removal rates  Reduced tendency for vibration and chatter.

Chapter 22 Cutting-Tool Materials and Cutting Fluids

Cutting Tool Properties  Hot hardness  High hot hardness means higher speeds and feed rates (higher production rates and lower costs).  Toughness and Impact strength  Tool does not chip or fracture  Thermal shock resistance  Wear resistance  Tool does not have to be replaced as often  Chemical stability and inertness  To minimize adverse reactions

Hot hardness

Cutting Tool Materials  High-speed steels  Cast-cobalt alloys  Carbides  Coated tools  Ceramics  Diamond

High-speed steels  Molybdenum (M-series)  Contains up to 10% Molybdenum  High abrasion resistance  Low distortion during heat treating  Low cost  95% of all high-speed steels are M-series  Tungsten (T-series)  Improved strength and hot hardness  More expensive than M-series

Cast-cobalt alloys  38 to 53% cobalt  High hardness  Not as tough as high-speed steels  Used for deep continuous roughing cuts  High feed rates

Carbides  Tungsten carbides (WC)  Bonded together in a cobalt matrix  Sintered  6 to 16% cobalt  Have largely replaced HSS tools  Used for cutting steels and cast irons

Carbides  Titanium carbides (TiC)  Bonded in a Nickel- molybdenum matrix  Higher wear resistance than WC  Not as tough as WC  Used for cutting steels and cast irons  Suitable for higher speeds than WC

Inserts  Cuts down on tool changing time  Increases number of cutting points  Have advanced chip breaker features  Come in various shapes and sizes

Inserts  Insert shape determines strength  Various ways if holding insert in place

Coated tools  Coating properties  Lower friction  Higher adhesion  Higher resistance to wear and cracking  Acting a a diffusion barrier  Higher hot hardness and impact resistance

Coating materials  Titanium-nitride  Low friction and high hardness  Titanium carbide  Improves wear resistance on WC  Ceramics  Diamond  Increases tool life ten fold compared to other coatings

22.6: Alumina Based Ceramics  Ceramic Tools  Primarily made of aluminum oxide  Introduced in the early 1950s  After being cold pressed into insert shapes under high pressure and sintered at high temperature, they are known as “white ceramics”.

22.6: Alumina Based Ceramics  Characteristics  Chemically stable  Not very tough  High abrasion resistance  Hot hardness  Poor tensile strength

22.6 Alumina Based Ceramics  Cermets (Black Ceramics)  Consist of ceramic materials in a metallic matrix  Typically: 70% Aluminum Oxide, 30% Titanium Carbide  Not widely used due to high cost Cermets tip cutting blade.

22.7: Cubic Born Nitride  Cubic Boron Nitride  cBN: 2 nd hardest material available  Formerly known as Borazon  Polycrystalline cubic boron nitride is bonded to a carbide substrate by sintering under high pressure and temp.  High thermal conductivity  Excellent wear resistance CBn coated cutting inserts

22.8: Silicon-Nitride-Based Ceramics  Consist of silicon nitride, aluminum oxide, yttrium oxide, and titanium carbide.  Characteristics:  Tough  Hot hardness  Good thermal shock resistance Sialon sink roll bearing

22.9: Diamond  Characteristics:  Hardest material known today  High wear resistance  Low friction  Maintains a sharp cutting edge  Produces a very accurate cut and good surface finish.  Most effective in light uninterrupted finishing cuts.

22.9: Diamond  Synthetic diamonds are preferred because natural diamonds have flaws which at times make them unpredictable. Image of a synthetic Russian diamond

22.9: Diamond  Polycrystalline Diamond Tools  Known as compacts  May be used as dies for fine wire drawing  Between.5 and 1 mm of diamond are bonded to a carbide substrate. (similar to cBN tools) Image of a compact

22.10: Whisker-Reinforced Tool Materials  Due to the high reactivity of silicon carbide with ferrrous metals, SiC tools are unsuitable for machining irons and steels.  Whisker-reinforced cutting tools include:  silicon-nitride based tools with silicon-carbide whiskers  Aluminum-oxide based tools reinforced with % silicon- carbide whiskers Image of whisker- reinforced ceramics

22.11: Tool Costs and Reconditioning of Tools  Factors that affect tool cost:  Material  Size  Shape  Chip-breaker features  Quality

22.11: Tool Costs and... Typical costs of a typical.5 inch insert: Cubic Boron Nitride: – –$60-90 Diamond-coated carb.: – –$50-60 Ceramics – –$8-12 Coated carbides: – –$6-10 Uncoated carbides: – –$2-10 Diamond-tipped insert: – –$ Tooling costs account for approximately 2 to 4 % of manufacturing costs.

22.11: Tool Costs and...  Reconditioning tools allows for longer use.  Resharpening  Recoating of coated tools  Tools will only be reconditioned if it is economical  Often times tools will be recycled Equipment used in the reconditioning of cutting tools

22.12: 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

22.12: 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” (22.12).

22.12: Cutting Fluids  Types of cutting fluids:  Oils: mineral, animal, vegetable, compounded, and synthetic oils. Only used in operations where temp rise is insignificant.  Emulsions: mixture of oil and water and additives. Good for operations where temperature rise is significant.  Semisynthetics: chemical emulsions containing little mineral oil diluted in water with additives that reduce size of particles.  Synthetics: chemicals with additives, diluted in water, without oil. Image of a “synthetic” cutting fluid.

22.12 Cutting Fluids  Methods of Application  Flooding: most common; rates of up to 225 L/min for multi- tooth cutters; poor visibility; Psi.  Mist: most effective w/ water based fluids; requires venting but is popular because of good visibility; similar to using an aerolsol can; Psi.  High-pressure systems: use a powerful jet/nozzle to target the hot area; 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.

22.12 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

22.12: 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, 85 psi.

22.12: 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.