Group 2 Zach Ratzlaff Moises Narvaez Weston Dooley

• Group #2 Zach Ratzlaff Moises Narvaez Weston Dooley Todd Miner Fundamentals of Cutting-Tool Materials and Cutting Fluids November 7, 2005 Group #2

Fundamentals of Machining Mechanics of Cutting Forces and Power Temperatures in Cutting November 7, 2005 Group #2

Common Machining Operations November 7, 2005 Group #2 3

The cutting process, and how chips are produced November 7, 2005 Group #2 4

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 5

(a) (d) November 7, 2005 (b) (c) (e) (f) Group #2 6

Chip breakers (a) 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 7

Cutting With an Oblique Tool The majority of machining operations are done with an 3 D shaped cutting tool this is called oblique cutting. November 7, 2005 Group #2 8

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 9

Cutting Force, Thrust Force and Power. November 7, 2005 Group #2 10

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 11

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 12

Temperature Distribution Typical temperature distribution over the cutting zone. November 7, 2005 Group #2 13

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 14

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 15

TOOL LIFE: Wear and Failure • High temperatures. • Sliding of chips along the rake face. • Sliding of tool along cut work piece. November 7, 2005 Group #2 16

TOOL LIFE: Wear and Failure 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 17

TOOL LIFE: Wear and Failure • • • 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 18

TOOL LIFE: Wear and Failure • 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 19

TOOL LIFE: Wear and Failure • 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 20

TOOL LIFE: Wear and Failure 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 21

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 22

TOOL LIFE: Wear and Failure • NOTCHING: A groove or notch develops in a region that undergoes workhardening. 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 23

TOOL LIFE: Wear and Failure • 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 24

TOOL LIFE: Wear and Failure • PLASTIC DEFORMATION: May occur when the tool undergoes stresses higher than the yield strength of the tool material. November 7, 2005 Group #2 25

TOOL LIFE: Wear and failure (b) (a) (d) (c) (e) (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. 20. 18. (d) Crater and (e) flank wear on a carbide tool. November 7, 2005 Group #2 26

TOOL LIFE: Wear and failure 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 27

TOOL LIFE: Wear and failure 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 28

TOOL LIFE: Wear and failure 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 29

TOOL LIFE: Wear and failure Tool-life curves for a variety of cuttingtool 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 30

TOOL LIFE: Wear and failure 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 31

TOOL LIFE: Wear and failure 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 32

TOOL LIFE: Wear and failure 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 33

TOOL LIFE: Wear and failure • 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 34

TOOL LIFE: Wear and failure 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 35

TOOL LIFE: Wear and failure -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 36

TOOL LIFE: Wear and failure 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 37

TOOL LIFE: Wear and failure 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 38

TOOL LIFE: Wear and failure • 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 39

TOOL LIFE: Wear and failure • 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 40

TOOL LIFE: Wear and failure 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 41

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 November 7, 2005 Group #2 42

Introduction Cutting tools are subjected to: • High Temperatures • High Contact Stresses • Rubbing along tool-chip interface November 7, 2005 Group #2 43

Choosing a Cutting Tool • • • Hot Hardness Toughness and impact strength Thermal shock resistance Wear resistance Chemical stability and inertness November 7, 2005 Group #2 44

Hot Hardness • Hardness of various cutting-tool materials as a function of temperature November 7, 2005 Group #2 45

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 November 7, 2005 Group #2 46

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) November 7, 2005 Group #2 47

Carbides • Most cost effective, versatile tool used in manufacturing • Two major types of carbides (Tungsten and Titanium) November 7, 2005 Group #2 48

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 November 7, 2005 Group #2 49

Carbide Inserts November 7, 2005 Group #2 50

Edge Strength November 7, 2005 Group #2 51

Multi Phase Coatings • Reduces abrasion and chemical reactivity November 7, 2005 Group #2 52

Machining Time • In less than 100 years the time to machine parts has reduced by 2 orders of magnitude November 7, 2005 Group #2 53

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 November 7, 2005 Group #2 54

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 November 7, 2005 Group #2 55

Cermets • Good chemical stability and resistance to edge build up • Brittle • High cost • Mostly aluminum oxide • Performance between a ceramic and a carbide November 7, 2005 Group #2 56

Properties for Groups of Tool Materials November 7, 2005 Group #2 57

Cubic Boron Nitride (CBN) • Hardest material presently available other than Diamond • Very high wear resistance and has a good cutting edge strength November 7, 2005 Group #2 58

Cubic Boron Nitride (CBN) November 7, 2005 Group #2 59

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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 November 7, 2005 Group #2 62

Sialon Applications • seals and bearings. November 7, 2005 Group #2 63

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 November 7, 2005 Group #2 64

Diamond Edge Saw Blade November 7, 2005 Group #2 65

Diamond Tip Drill bits November 7, 2005 Group #2 66

Diamond Polishing November 7, 2005 Group #2 67

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. November 7, 2005 Group #2 68

WG-600 Whisker Reinforced Ceramic Cutting Tool November 7, 2005 Group #2 69

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 November 7, 2005 Group #2 70

Cutting Fluids November 7, 2005 Group #2 71

Cutting Fluids November 7, 2005 Group #2 72

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: November 7, 2005 Group #2 73

Machining Processes 1. 2. 3. 4. 5. 6. 7. 8. Sawing Turning Milling Drilling Gear cutting Thread cutting Tapping Internal broaching November 7, 2005 Increasing Severity Group #2 74

Types of Cutting Fluids 1. 2. 3. 4. 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. November 7, 2005 Group #2 75

Methods of Cutting fluids 1. 2. 3. 4. 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 November 7, 2005 Group #2 76

Application of Cutting Fluids November 7, 2005 Group #2 77

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Effects of Cutting Fluids • The effect on the work piece and machining tools • Biological Considerations • The Environment November 7, 2005 Group #2 79

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 November 7, 2005 Group #2 80

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 81

References • http: //www. Haniblecarbide. com • http: //www. crucibleservice. com/ • http: //www. azom. com/details. asp? Arti cle. ID=268&head=Sialons#_Cutting_T ools • http: //www. manufacturingcenter. com/ tooling/archives/0304 westec_pa ges. asp November 7, 2005 Group #2 82