group #2group #2 fundamentals of cutting cutting-tool materials and cutting fluids zach ratzlaff...

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Fundamentals of Cutting

Cutting-Tool Materials and Cutting Fluids

Zach Ratzlaff Moises Narvaez Weston Dooley Todd Miner

Fundamentals of MachiningFundamentals of Machining

Mechanics of CuttingCutting Forces and PowerTemperatures in Cutting

November 7, 2005 Group #2 3

Common Machining OperationsCommon Machining Operations


The cutting process, and how The cutting process, and how chips are producedchips are produced


Factors that influence the cutting Factors that influence the cutting process.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


(f)

(b)(a) (c)

(d) (e)


Chip breakersChip 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.


Cutting With an Oblique ToolCutting With an Oblique ToolThe majority of machining operations are done with an 3D shaped cutting tool this is called oblique cutting.


Cutting Forces and PowerCutting Forces and PowerData 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.


Cutting Force, Thrust Force and Cutting Force, Thrust Force and Power.Power.


Temperatures in cuttingTemperatures 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.


Effects of temperature riseEffects 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.


Temperature DistributionTemperature Distribution

Typical temperature distribution over the cutting zone.


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


TOOL LIFE: Wear and FailureTOOL 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.



• High temperatures.• Sliding of chips along the rake face.• Sliding of tool along cut work piece.



Wear is a gradual process, and it also depends on:

• Tool and workpiece materials.• Tool geometry.• Process parameters.• Cutting Fluids.



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.



• 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.



• 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.



The location of the maximum depth of crater wear coincides with the location of the maximum temperature at the tool-chip interface.


TOOL LIFE: Wear and failureTOOL 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.



• 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.



• 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.



• PLASTIC DEFORMATION: May occur when the tool undergoes stresses higher than the yield strength of the tool material.



(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.

(e)(d)

(a) (b) (c)



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.



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

CVT n



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



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.



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.


TOOL LIFE: Wear and failureTOOL 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.

TABLE 20.4 Allowable Average Wear Land (VB)for Cutting Tools in Various Operations

Allowable wear land (mm)Operation High-speed Steels Carbides

TurningFace millingEnd millingDrillingReaming

1.51.50.30.4

0.15

0.40.40.30.4

0.15Note: 1 mm = 0.040 in.



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.



• 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.



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.



-Vibration and Chatter may cause variations of the dimensions of the cut, and chipping and premature failure of brittle cutting tools.



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



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.



• 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.



• 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.



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.


IntroductionIntroduction

• 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


IntroductionIntroduction

Cutting tools are subjected to:• High Temperatures• High Contact Stresses• Rubbing along tool-chip interface


Choosing a Cutting ToolChoosing a Cutting Tool

• Hot Hardness• Toughness and impact strength• Thermal shock resistance• Wear resistance• Chemical stability and inertness


Hot HardnessHot Hardness

• Hardness of various cutting-tool materials as a function of temperature


High Speed Steels (HSS)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


Cast-Cobalt AlloysCast-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)


CarbidesCarbides

• Most cost effective, versatile tool used in manufacturing

• Two major types of carbides (Tungsten and Titanium)


Types of CarbidesTypes 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


Carbide InsertsCarbide Inserts


Edge StrengthEdge Strength


Multi Phase CoatingsMulti Phase Coatings• Reduces abrasion and chemical reactivity


Machining TimeMachining Time

• In less than 100 years the time to machine parts has reduced by 2 orders of magnitude


Ceramic Tool MaterialsCeramic Tool Materials

• Ceramic tool materials were introduced in the early 1950’s

• A very effective cutting toolTypes:Alumina based CeramicsCubic Boron NitrideSilicon Nitride


Alumina-Based CeramicsAlumina-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


CermetsCermets

• Good chemical stability and resistance to edge build up

• Brittle• High cost• Mostly aluminum oxide • Performance between a ceramic and

a carbide


Properties for Groups of Tool Properties for Groups of Tool MaterialsMaterials


Cubic Boron Nitride (CBN)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 (CBN)Cubic Boron Nitride (CBN)


Silicon Nitride Based CeramicsSilicon 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


Sialon ApplicationsSialon Applications

• seals and bearings.


DiamondDiamond

• Hardest of all known materials• Desirable cutting tool properties

Low FrictionHigh Wear resistanceSharp Edge (able to maintain)Good Surface Finish Good Dimensional Accuracy


Diamond Edge Saw BladeDiamond Edge Saw Blade


Diamond Tip Drill bitsDiamond Tip Drill bits


Diamond PolishingDiamond Polishing


Whisker Reinforced Tool MaterialsWhisker 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.


WG-600 Whisker Reinforced WG-600 Whisker Reinforced Ceramic Cutting ToolCeramic Cutting Tool


Cutting FluidsCutting Fluids

• Cutting fluids have been extensively used in machining operations Reduce Friction and wearReduce force and energy consumptionCool the cutting zoneFlush away chipsProtect the Machined surface from environmental corrosion


Considerations for Selecting Considerations for Selecting cutting fluidscutting fluids• Need for a lubricant or Coolant, or

both.• Levels of temperatures expected• Forces encountered • Cutting speed The need for a cutting depends on

severityof the operation:


Machining ProcessesMachining Processes

1. Sawing2. Turning3. Milling4. Drilling5. Gear cutting6. Thread cutting7. Tapping8. Internal broaching

Increasing Severity


Types of Cutting FluidsTypes of Cutting Fluids

1. Oils - often called straight oils, includes mineral, animal, vegetable, compounded, and synthetic oils.

2. Emulsions- often called soluble oils, mixtures of oil and water and additives.

3. Semi-synthetics- chemical emulsions containing little mineral oil, reduced size of oil particles

4. Synthetics- chemicals with additives diluted in water and contain no oil.


Methods of Cutting fluidsMethods of Cutting fluids

1. Flooding- Most common method. Flow rates depend on application.

2. Mist- Supplies fluid to inaccessible areas. Similar to using an aerosol can (spray paint or hairspray)

3. High Pressure Systems- use specialized nozzles that aim powerful jet of fluid towards the cutting zone.

4. 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


Application of Cutting FluidsApplication of Cutting Fluids


Effects of Cutting FluidsEffects of Cutting Fluids

• The effect on the work piece and machining tools

• Biological Considerations• The Environment


Near Dry Machining 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 CostImproved Surface Quality


Cryogenic Machining 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


ReferencesReferences

• 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/0304/0304westec_pages.asp

http://www.crucibleservice.com/

group #2group #2 fundamentals of cutting cutting-tool materials and cutting fluids zach ratzlaff...

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