Fundamentals of Cutting Cutting-Tool Materials and Cutting Fluids

Fundamentals of Cutting Cutting-Tool Materials and Cutting Fluids
Group #2 Zach Ratzlaff Moises Narvaez Weston Dooley Todd Miner Fundamentals of Cutting Cutting-Tool Materials and Cutting Fluids

Fundamentals of Machining
Mechanics of Cutting Cutting Forces and Power Temperatures in Cutting

Common Machining Operations
November 7, 2005 Group #2

The cutting process, and how chips are produced

Factors that influence the cutting process.
Cutting speed, Depth of cut, feed rate, and cutting fluids. Tool Angle Continuous chip Built-up edge chip Discontinuous Chip Temperature rise Tool wear Machinability November 7, 2005 Group #2

(f) (b) (a) (c) (d) (e) November 7, 2005 Group #2

Chip breakers Schematic illustration of the action of a chip breaker. The chip breaker decreases the radius of curvature of the chip. (b) Chip breaker clamped on the rake face of a cutting tool. (c) Grooves in cutting tools acting as chip breakers. November 7, 2005 Group #2

Cutting With an Oblique Tool
The majority of machining operations are done with an 3D shaped cutting tool this is called oblique cutting. November 7, 2005 Group #2

Cutting Forces and Power
Data on cutting forces is essential so that: Machine tools can be properly designed. To ensure that the work piece is capable of withstanding the forces without excessive distortion. Power requirements must be taken into account when selecting machinery. November 7, 2005 Group #2

Cutting Force, Thrust Force and Power.

Temperatures in cutting
As in all metal working where plastic deformation is involved, the energy dissipated in cutting is converted into heat which, in turn raises the temperature in the cutting zone. November 7, 2005 Group #2

Effects of temperature rise
Excessive temperature lowers the strength, hardness, stiffness, and wear resistance of cutting tools. Increased heat causes uneven dimensional changes in the part. Excessive temperature rise can cause thermal damage to the surface of the part. November 7, 2005 Group #2

Temperature Distribution
Typical temperature distribution over the cutting zone. November 7, 2005 Group #2

Heat distribution during machining.
Percentage of the heat generated in cutting going into the work piece, tool, and chip, as a function of cutting speed. November 7, 2005 Group #2

TOOL LIFE: Wear and Failure
Cutting tools are subjected to many factors that determine the wear of the tool. Some of the most important are: High localized stresses at the tip of the tool. November 7, 2005 Group #2

High temperatures. Sliding of chips along the rake face. Sliding of tool along cut work piece. November 7, 2005 Group #2

Wear is a gradual process, and it also depends on: Tool and workpiece materials. Tool geometry. Process parameters. Cutting Fluids. November 7, 2005 Group #2

Tool wear and changes in tool geometry manifest as: Flank wear. Crater wear. Nose wear. Notching. Chipping or gross fracture. Plastic deformation of the tool tip. November 7, 2005 Group #2

FLANK WEAR: Occurs on the relief face of the tool (flank) due to rubbing of the tool on the machined surface, causing adhesive and /or abrasive wear, and high temperatures. November 7, 2005 Group #2

CRATER WEAR: It is attributed to the diffusion of atoms across the tool-chip interface. Diffusion rates increase with temperature; thus, crater wear increases with increasing temperature. November 7, 2005 Group #2

The location of the maximum depth of crater wear coincides with the location of the maximum temperature at the tool-chip interface. November 7, 2005 Group #2

TOOL LIFE: Wear and failure
NOSE WEAR: Rounding of a sharp tool due to mechanical and thermal effects. Affects chip formation and causes rubbing of the tool over the workpiece increasing the temperature. November 7, 2005 Group #2

NOTCHING: A groove or notch develops in a region that undergoes work-hardening. This region develops a thin work-hardened layer that can originate a groove. Oxide layers on a workpiece also contribute to notch wear because these are hard and abrasive. To prevent this, the depth of the cut must be grater than oxide layer thickness. November 7, 2005 Group #2

CHIPPING: Sudden loss of material due to mall fragments of the cutting edge of the tool breaking away. It occurs typically on brittle tool materials such as ceramics. Chipping also occurs in a region where a small crack or defect already exists. The two main causes of chipping are mechanical shock and thermal fatigue. November 7, 2005 Group #2

PLASTIC DEFORMATION: May occur when the tool undergoes stresses higher than the yield strength of the tool material. November 7, 2005 Group #2

(b) (c) (a) Flank and crater wear in a cutting tool. Tool moves to the left. (b) View of the rake face of a turning tool, showing nose radius R and crater wear pattern on the rake face of the tool. (c) View of the flank face of a turning tool, showing the average flank wear land VB and the depth-of-cut line (wear notch). See also Fig (d) Crater and (e) flank wear on a carbide tool. November 7, 2005 Group #2

TOOL-LIFE CURVES: Plots of experimental data obtained from cutting tests under different cutting conditions such as cutting speed, feed, depth of cut, and tool material and geometry. November 7, 2005 Group #2

The tool-life curves are derived from the approximation: Where V is the cutting speed, T is the time needed to develop a certain flank wear land, C and n are tool material constant November 7, 2005 Group #2

Notice the rapid decrease in tool life as the cutting speed increases. Several tool materials have been developed that resist high temperatures such as carbides, ceramics, and cubic boron nitride November 7, 2005 Group #2

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 equations and C is the cutting speed at T = 1 min. November 7, 2005 Group #2

ALLOWABLE WEAR LAND: In order to have good dimensional accuracy, surface finish, and to keep within the allowed tolerances, cutting tools need to be replaced or resharpened when: The surface finish of workpiece begins to deteriorate. Cutting forces increase. Temperature rises significantly. November 7, 2005 Group #2

The following table shows the average allowable wear for various machining operations. Notice that allowable wear for ceramic tools is about 50% higher. November 7, 2005 Group #2

TOOL-CONDITION MONITORING: Computer controlled machine tools require precise and reliable cutting tools that are able to perform repeatedly. Direct methods: Involve optical measurement of wear and changes on the tool profile. Requires to stop operations. Example: Use of a tool’s maker microscope. November 7, 2005 Group #2

Indirect methods: Determine the tool condition by measuring process parameters such as cutting forces, power, temperature rise, vibration, workpiece surface finish. Example: Acoustic Emission technique which analyzes acoustic emissions that result vibrations and stresses. Example 2: Tool-cycle time. November 7, 2005 Group #2

SURFACE FINISH AND INTEGRITY: Surface Finish: refers to the geometric characteristics of the surface. Factors affecting surface finish are: -A dull tool with a large tip radius will rub over the machined surface causing residual surface stresses, tearing and cracking. November 7, 2005 Group #2

-Vibration and Chatter may cause variations of the dimensions of the cut, and chipping and premature failure of brittle cutting tools. November 7, 2005 Group #2

M ACHINABILITY: Good machinability indicates good surface finish and surface integrity. The machinability of a material is defined by: Surface finish and integrity Tool life Force and power required Level of difficulty on chip control November 7, 2005 Group #2

Machinability of Ferrous Metals: Low Carbon steels: Have a wide range of machinability depending on ductility and hardness. Free-machining steels: Contain sulfur and phosphorous allowing a decrease on size of chips and an increase in machinability. Leaded Steels: Pb is insoluble in Fe, Cu and Al. Works as a solid lubricant. Consider that Lead is toxic pollutant. November 7, 2005 Group #2

Alloy Steels: Machinability can not be generalized because of the wide variety of composition and hardness. Machinability of Nonferrous Metals: Aluminum: Easy to machine, although the softer grades tend to form build up edge resulting on poor surface finish. Possible dimensional tolerance problems due to thermal expansion. November 7, 2005 Group #2

Copper: Difficult to machine when Cu is in wrought condition. Cast Cu alloys are easy to machine as well as Brasses, especially if these contain lead. Beryllium: Easy to machine, but be aware that fine particles produced while machining are toxic - requires machining in controlled environment. November 7, 2005 Group #2

Machinability of Thermo Plastics: These materials have low thermal conductivity and elastic modulus, and are thermally softening. Therefore, require sharp tools with positive rake angles and small depths of cuts and feeds. Machinability of Ceramics: These materials have improve machinability due to the development of machinable ceramics and nanoceramics. November 7, 2005 Group #2

Introduction Carbon and Medium-Alloy Steels High-Speed Steels
Cast-Cobalt Alloys Carbides Coated Tools Alumina-based ceramics Cubic boron nitride Silicon-nitride-based ceramics Diamond Whisker-reinforced materials & nanomaterials Various types of cutting materials First two are not used very often in manufacturing because they do not have significant wear resistance and hot hardness at high speeds. (non-profitable) November 7, 2005 Group #2

Introduction Cutting tools are subjected to: High Temperatures
High Contact Stresses Rubbing along tool-chip interface Various problems to consider when selecting a cutting material November 7, 2005 Group #2

Choosing a Cutting Tool
Hot Hardness Toughness and impact strength Thermal shock resistance Wear resistance Chemical stability and inertness Hot Hardness = does not undergo plastic deformation, and thus retains its shape and sharpness. Toughness and impact strength = Impact forces do not chip or fracture the tool (mechanical shock), important for milling Thermal shock = Resistance withstand the rapid temperature cycling encountered in interrupted cutting Wear resistance = acceptable tool life is obtained before the tool has to be replaced Chemical Stability and inertness = minimize any adverse reactions, adhesion, and tool-chip diffusion that would contribute to tool wear. November 7, 2005 Group #2

Hot Hardness Hardness of various cutting-tool materials as a function of temperature The hardness of various cutting-tool materials as a function of temperature (hot hardness). The wide range in each group of materials is due to the variety of tool compositions and treatments available for that group. High-Speed steels are tough, but have limited hot hardness Ceramics have high resistance to temperature and wear, but they are brittle and can chip. Many different tables to assist choosing a cutting material November 7, 2005 Group #2

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 High toughness (resistance to fracture) Can be coated to improve performance November 7, 2005 Group #2

Cast-Cobalt Alloys Higher hot hardness than HSS
Cuts almost twice as quick as HSS Main use: Remove large amounts of materials as quick as possible (roughing cuts) Less suitable than HSS for interrupted forces because of toughness November 7, 2005 Group #2

Carbides Most cost effective, versatile tool used in manufacturing
Two major types of carbides (Tungsten and Titanium) High hardness over a wide range of temperatures Toughness, high thermal conductivity, thermal shock resistance, high cutting speeds, low thermal expansion November 7, 2005 Group #2

Types of Carbides Tungsten Carbides
Manufactured using powder-metallurgy Used to cut steels, cast iron, and abrasive non ferrous metals Titanium Carbides Higher wear resistance than Tungsten Carbides but is not as tough Cuts at higher speeds than Tungsten Tungsten-carbide particles bonded together in a cobalt matrix Tungsten carbides are slowly replacing HSS Titanium Carbides cut mainly the same types of materials. November 7, 2005 Group #2

Carbide Inserts November 7, 2005 Group #2

Edge Strength Relative edge strength and tendency for chipping and breaking of insets with various shapes. Strength refers to the cutting edge shown by the included angles. Edge preparation of inserts to improve edge strength. November 7, 2005 Group #2

Multi Phase Coatings Reduces abrasion and chemical reactivity
Multiphase coatings on a tungsten-carbide substrate. Three alternating layers of aluminum oxide are separated by very thin layers to titanium nitride. Inserts with as many as thirteen layers of coatings have been made. Coating thicknesses are typically in the range of 2 to 10 m. Different types of coating processes for various types of cutting-tools November 7, 2005 Group #2

Machining Time In less than 100 years the time to machine parts has reduced by 2 orders of magnitude Relative time required to machine with various cutting-tool materials, indicating the year the tool materials were introduced. November 7, 2005 Group #2

Ceramic Tool Materials
Ceramic tool materials were introduced in the early 1950’s A very effective cutting tool Types: Alumina based Ceramics Cubic Boron Nitride Silicon Nitride Carbide A compound of carbon with one or more metallic elements. November 7, 2005 Group #2

Alumina-Based Ceramics
These ceramic tools have some good properties which make it good for cutting Very High Abrasion Resistance Hot Hardness Chemically more stable than high speed steels and carbides Abrasion Resistance The ability of a material to withstand mechanical action such as rubbing, scraping, or erosion, that tends progressively to remove material from its surface. Such an ability helps to maintain the material's original appearance and structure. Hot Hardness The ability of a material to retain its hardness properties at high temperatures. Also known as "red hard" Chemically more stable means that there is lees chance for the tool to adhere to the metal during cutting and a lower tendency to form a built up edge. November 7, 2005 Group #2

Cermets Good chemical stability and resistance to edge build up
Brittle High cost Mostly aluminum oxide Performance between a ceramic and a carbide Cermets comes from the word ceramic and metals. Ceramic particlea in a metallic matrix 70 percent aluminum oxide 30 percent titanium carbide November 7, 2005 Group #2

Properties for Groups of Tool Materials
Figure Ranges of properties for various groups of tool materials. See also Tables 21.1 through 21.5. November 7, 2005 Group #2

Cubic Boron Nitride (CBN)
Hardest material presently available other than Diamond Very high wear resistance and has a good cutting edge strength Cubic Boron Nitride tools also are made in small sizes without a substrate Figure Construction of a polycrystalline cubic boron nitride or a diamond layer on a tungsten-carbide insert. November 7, 2005 Group #2

Cubic Boron Nitride (CBN)
Figure Inserts with polycrystalline cubic boron nitride tips (top row) and solid polycrystalline cBN inserts (bottom row). Source: Courtesy of Valenite. November 7, 2005 Group #2

Silicon Nitride Based Ceramics
Consists of Silicon Nitride with additions of Aluminum oxide and titanium carbide. Have good hardness Good thermal shock resistance Example: Sialon (silicon,aluminum,oxygen and nitrogen) Good for machining cast irons and nickel based super alloys Thermal shock Resistance November 7, 2005 Group #2

Sialon Applications seals and bearings.
Used for some Aerospace applications seals and bearings. November 7, 2005 Group #2

Diamond Hardest of all known materials
Desirable cutting tool properties Low Friction High Wear resistance Sharp Edge (able to maintain) Good Surface Finish Good Dimensional Accuracy Synthetic diamonds are now being used because natural diamonds have flaws and performance can be unpredictable Tool shape and sharpness are important because of hoe brittle a diamond can be. Low rake angles are used to provide a good cutting edge Diamond tools can be used at almost any speed and provide good results November 7, 2005 Group #2

Diamond Edge Saw Blade November 7, 2005 Group #2

Diamond Tip Drill bits Good for milling and drilling accurate holes

Diamond Polishing Pipes that have been polished (left picture)
Polishing wheel diamond coated (right picture) The finish on the pipes are done using diamond polishing techniques, as you can see they produce a very shiny and smooth finish. November 7, 2005 Group #2

Whisker Reinforced Tool Materials
High fracture toughness Resistance to thermal shock Cutting edge strength Creep resistance Whiskers are used as reinforcing fibers in composite cutting tool materials. Whiskers are a reinforcing fiber matrix much like the fiber used in composites usually have a unique mesh size depending on the application. Example: Silicon Carbide Whiskers typically 5 to 100uM long with a .1 to 1 uM in diameter. November 7, 2005 Group #2

WG-600 Whisker Reinforced Ceramic Cutting Tool
WG-600 is a second-generation whisker-reinforced ceramic composite cutting tool. It provides excellent wear and thermal shock resistance in machining high-strength alloys, hardened steels, hard irons, and plasma spray materials. WG-600 is especially well suited for finishing high-strength alloys, achieving length-of-cut times as much as six times better than present whisker-reinforced ceramic insert grades. WG-600 is available in all standard ceramic styles as well as special designs. November 7, 2005 Group #2

Cutting Fluids Cutting fluids have been extensively used in machining operations Reduce Friction and wear Reduce force and energy consumption Cool the cutting zone Flush away chips Protect the Machined surface from environmental corrosion The primary function of cutting fluid is cooling and lubrication. Cooling and lubrication are also important in achieving the desired size, finish and shape of the work piece A secondary function of cutting fluid is to flush away chips and metal fines from the tool/work piece interface to prevent a finished surface from becoming marred and also to reduce the occurrence of built-up edge November 7, 2005 Group #2

Cutting Fluids November 7, 2005 Group #2

Cutting Fluids Multi-Jet Delivery System Flooding Method

Considerations for Selecting cutting fluids
Need for a lubricant or Coolant, or both. Levels of temperatures expected Forces encountered Cutting speed The need for a cutting depends on severity of the operation: Fluid Types The main types of cutting fluids fall into two categories based on their oil content: Oil-Based Fluids - including straight oils and soluble oils Chemical Fluids - including synthetics and semi synthetics Straight oils or neat oils are the oldest class of engineered metal removal fluids. They are composed of a base mineral or petroleum oil and often contain polar lubricants such as fats, vegetable oils, and esters, as well as extreme pressure additives of chlorine, sulfur and phosphorus Synthetic fluids (chemical fluids) Semi synthetics fluids also called semi chemical) contains a lower amount of refined base oil (5-30%) in the concentrate November 7, 2005 Group #2

Machining Processes Sawing Turning Milling Drilling Gear cutting
Thread cutting Tapping Internal broaching Increasing Severity Cutting fluids have to me more carefully selected as you go down the list. More considerations have to be made fro the processed further down the list November 7, 2005 Group #2

Types of Cutting Fluids
Oils - often called straight oils, includes mineral, animal, vegetable, compounded, and synthetic oils. Emulsions- often called soluble oils, mixtures of oil and water and additives. Semi-synthetics- chemical emulsions containing little mineral oil, reduced size of oil particles Synthetics- chemicals with additives diluted in water and contain no oil. 1.) typically used for low speed applications where temperature rise is not significant 2.) Generally used for high speed operations because temperature rise is significant. Very effective Coolant. November 7, 2005 Group #2

Methods of Cutting fluids
Flooding- Most common method. Flow rates depend on application. Mist- Supplies fluid to inaccessible areas. Similar to using an aerosol can (spray paint or hairspray) High Pressure Systems- use specialized nozzles that aim powerful jet of fluid towards the cutting zone. Through the cutting tool system- an effective method. A narrow passage can be produced in the cutting tool, where it can be applied under high pressure 1.) flood the part with the fluid washing any residue and material and cooling. 2.) This method allows for better visibility of what is being machined compared to the flood method which does not allow much visibility 3.) this method was developed because of increase of speed in machining processes and computer controlled machines.good from removing heat from the cutting zone 4.) Examples: Gun drilling and boring bars Gun drilling is especially suitable on jobs where close tolerances are required on diameter, roundness, hole location, taper and concentricity. Precision holes using other methods usually require secondary operations, such as reaming, boring, honing and grinding. Gundrilling can frequently produce a finished hole in one operation. Many parts can be redesigned for the gun drilling process to take advantage of its benefits and in most cases will produce a more accurate part at a much lower cost. The aircraft industry has shown a growing preference for one piece construction over previous methods, such as joining tow or more pieces by flash welding, pressure welding, etc. Applications: Aluminum and Steel Hydraulic Cylinders drilled from solid catins, bar stock or forgings Landing Gear Components Jack Screw Tubes and Motor Shafts for Electrical Aircraft Actuators Lightening Holes in Aircraft Hydraulic Pistons Aluminum and Steel Hydraulic Valve Bodies Hydraulic Manifolds Oil Tools Steam and Coolant Holes for Rubber and Plastic Die Platens Fluid Passage Holes in Machine Tool Spindles November 7, 2005 Group #2

Application of Cutting Fluids
Figure Schematic illustration of proper methods of applying cutting fluids in various machining operations: (a) turning, (b) milling, (c) thread grinding, and (d) drilling. Using flooding method in each scenario November 7, 2005 Group #2

Effects of Cutting Fluids
The effect on the work piece and machining tools Biological Considerations The Environment November 7, 2005 Group #2

Near Dry Machining Economic and environmental concerns have caused a trend to eliminate metalworking fluids. Near dry machining Benefits Relieve Environmental impact of using cutting fluids Reduce Cost Improved Surface Quality The principle behind near dry cutting is the application of a fine mist of air fluid mixture containing a very small amount of cutting fluid including vegetable oil November 7, 2005 Group #2

Cryogenic Machining Most recent development
Uses nitrogen and carbon dioxide as coolant in machining (-200 C) Liquid nitrogen injected into the cutting zone. Allows higher cutting speeds, tool life enhancement and machinibilty increase. Nitrogen simply evaporates, no environmental impact November 7, 2005 Group #2

References http://www.Haniblecarbide.com

Fundamentals of Cutting Cutting-Tool Materials and Cutting Fluids

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Fundamentals of Cutting Cutting-Tool Materials and Cutting Fluids

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