Cutting Tool Geometry

Tool Geometry

• Tool geometry has been around since ancient times as a method for understanding how machines work
• It describes function sizes, shapes and features
• Tool geometry is used in aircraft manufacturing to help design new machinery for production lines to promote quality and effeciency
• The shank and the sharpened cutting portion make up the tool
• Point is defined by the face, side or major flank, end or minor flank, and the base
• Cutting tools have two types: single-point and multiple-point
• Single point cutting tools can be made from Cermics, high carbon steel, and cemented carbide

Diagram Details

• Shank: The main body tool, used to hold the tool
• Flank: Area below and adjacent to the cutting edge
• Face: Surface on which the chips slide
• Heel: Intersection between the flank and the base, a curved section near the bottom
• Nose: Where the side cutting edge and end cutting edge intersect
• Nose radius: With a sharp point can give extended life and a good surface polish
• Cutting edge: Edge on the tool's face that removes material from the workpiece

Defining Angles

• Side cutting edge angles are also known as lead angles, and are made by the tool shank's side cutting edge and the tool shank's side
• End cutting angle is made up of the tool shank's end cutting edge, and a line parallel to it
• Side relief angle is formed by a line perpendicular to the tool's base, and measured at a right angle to the end flank
• The side flank portion is immediately below the side cutting edge
• The line is perpendicular to the tool's base and measured at a right angle to the end flank
• End relief angle is the line perpendicular to the tool's base and measured at a right angle to the end flank and the section of the end flank immediately below the end cutting edge
• Back rack angle is formed between the tool face and a line running parallel to the tool's base and perpendicular to the side cutting edge
• A positive back rack angle occurs if the side cutting edge slopes downward from the point towards the shank
• A negative back rack angle occurs if the slope is reversed
• Side rack angle is formed between the tool face and a line parallel to the tool's base
• It is measured in a plane perpendicular to the tool's base and side cutting edge
• This angle determines the slope of the tool's face from the cutting edge
• Negative side rack angles occur if the slope is toward the cutting edge
• Positive side rack angles occur if the slope is away from the cutting edge

Single Point Cutting Tool Advantages & Properties

• Designing and constructing the tool is simple
• Single point cutting tools are less expensive
• Tool wear rate is a tad high here and tool life is reduced

Cutting Tool Materials

• Materials can be divided as follows:
• High Carbon Steel is hardened and tempered
• High-Speed Steel contains vanadium, cobalt, molybdenum, tungsten, and chromium
• Cemented Carbides are produced with powder metallurgy
• Stellite is a cast non-ferrous alloy containing cobalt, tungsten, chromium, and carbon
• Ceramics
• Diamond

Properties of High Carbon Steel Tools

• High carbon steel has small amounts of silicon, chromium, manganese, and vanadium to refine 0.6–1.5% carbon and grain size
• The max hardness is approximately 62 HRC Rockwell
• Wear resistance and hot hardness are very low
• High-speed steel, cobalt steel, carbide steel have gradually replaced this material

Important Facts about High-Speed Steel Tools

• High-speed steel was first produced in the 1900s
• They contain high concentrations of vanadium, cobalt, molybdenum, tungsten, and chromium
• This increases the ability to maintain hot hardness when working in hot conditions and wear resistance
• These can be hardened to various depths with proper heat treatment
• High-speed steel is now a commonly used material for taps, drills, reamers, gear tools, end cutters, slitting, brochures etc.

Info on Cemented Carbides

• Cemented carbides began use in the 1930s
• These are important toll materials due to high hot hardness and wear resistance
• Cemented carbides have low toughness
• These materials are produced from powder metallurgy by sintering tungsten carbide grains in a cobalt matrix
• Titanium carbide (TiC) or tantalum carbide (TaC) can be found in the mixture
• Cemented carbide is available as inserts, which are mechanically coupled to the tool holder by clamps or brazed with tool holders

Tungsten Carbide Advantages

• Tungsten carbide can work at higher speeds than high-speed steel
• These are more economical for machining large quantities of parts
• This tool can quickly remove metal while providing a surface finish

Tungsten Carbide Disadvantages

• Tungsten carbide is typically more expensive
• Only diamond grinding wheels can grind these tools
• The machine and fittings must be very firm to use these tools

Stellite Properties

• Stellite is a cast non-ferrous alloy containing 43 to 48% cobalt, 17 to 19% tungsten, 30 to 35% chromium, and 2% carbon
• Very hard and can be used for heavy cuts
• It does not lose its temper, even at around 1,000° C
• It is also a very expensive tool material

Ceramic Properties

• Ceramic products consist of fine grain, high purity aluminum oxide (Al2O3) that does not undergo pressurization or sintering
• Available in two forms: white/ cold-pressed, or black/ hot-pressed
• Alunimun oxide (Al2O3) only sintering at high temperatures, cold-pressed have pressurized inserts
• Black/hot-pressed contain 70% AI, O, and 30% Tic
• Both ceramic types are suitable for continuous operation such as finish turning of cast iron and steel at very high speeds

Diamond Properties

• Most hardened material
• Used to finish and cut very hard materials like mirrors, ceramics, etc

Properties of Cutting Tool Materials

• Properties will vary for cutting toll materials

Properties of Carbon Tool Steel

• Unstable and cheap
• Heat sensitive
• Mostly obsolete but still used for tap and die, hacksaw blades, and reamers
• Hardness is roughly 65 HRC
• Possible fast-cutting edges

High-Speed Steel Material

• Unstable
• Retain hardness at moderate temperatures
• Now the most commonly used cutting material is used extensively for drill bits and taps
• Hardness up to 67 HRC
• Fast cutting edges possible

HSS Cobalt Material

• Unstable & medium cheap
• Resistant to heat and therefore excellent for machining of abrasive materials such as titanium and stainless steel
• Extensive use for milling cutters and drill bits
• Hardness up to approximately 70 HRC
• Fast cutting edge possible

Cast Cobalt Alloy Material

• Stable & costly
• High machining speed due to low hardness
• Not much use
• Hardness up to around 65 HRC
• Fast cutting edges possible

Cemented Carbide Material

• Stable & only moderately expensive
• Highly used in industry with high abrasion resistance
• High resistance to abrasion
• Used for turning tool bits, milling cutters, and saw blades
• Hardness up to 90 HRC
• Fast edges are not recommended

Ceramics Material

• Stable, medium cheap
• Resistance to extreme heat
• Desirable in high-speed applications
• Most common ceramics are based on alumina (aluminum oxide), silicon nitride, & silicon carbide
• Almost completely in use for turning tool bits
• Hardness approx 93 HRC
• Away from sharp cutting edges and positive rake angles

Cermets Material

• Stable and moderately expensive
• Based on titanium carbide and nickel binders
• Higher abrasion resistance than tungsten carbide
• Mainly used in turning tool bits
• Hardness up to 93 HRC
• Fast edges are not recommended

Diamond Tool Materials

• Stable and very valuable
• Most rigid material
• Has very high resistance to abrasion
• Used as a coating on turning tool bits and on many types of tools but sharp edges are not recommended

Desirable Properties of Tool Materials

• Good tool materials must have the following properties

Hot Hardness

• Hardness is measured at room temperature Hot hardness indicates hardness at high temperature
• Hardness decreases with temperature
• In metal cutting, heat is generated, so the tool material must be able to maintain its hardness, wear resistance, and strength at temps from 600 to 1800 degrees Celsius

Required material properties

• Toughness is necessary to withstand intermittent use
• Resistance in its composition is also necessary
• Wear resistance must help the toll continue cutting
• Chemical stability or inertness should be kept with the work material to avoid undesirable reactions
• Shock resistance protects against thermal and mechanical shocks, especially in intermittent cutting
• Low friction, so generated heat lowered, increasing tool life
• Favorable cost since tool material cost must be favorable for profits
• Thermal conductivity and specific heat in cutting tool material are ideal if high
• Must have a sufficient machinability for its intended use

Important considerations/requirements

• Select tool based on its property requirements during machining or cutting process
• Material properties like red hardness, abrasion resistance, and hardness
• Tool material impacting surface quality, machining efficiency, and life of tool
• Productivity, life of tool, consumption of tool, tooling costs, machining accuracy, and surface qualities depend on tool materials

Manufacturing process

• Extract material from a work through shear deformation
• Use single or multipoint methods
• Single-point devices spinning, forming, and readying materials, with one cutting edge extracting material
• Multi-point devices for milling and drilling
• Abrasive grains act as single-point microscopic cutting edge and sheers a small coin
• metal material must be tougher than the steel its is slicing
• Must therefore have a precise configuration, with clearance angles built to allow the cutting edge to touch the work piece without dragging the remainder of the device onto the work piece surface
• Its important to automate speed and feed rates

Tungsten Processing

• Tungsten carbide, or carbide, is common in market due to its success in metal cutting
• The combination of tungsten and carbon made has revolutionized metal cutting
• Guarantees faster speed and feeds, ensuring equipment has longer lives

Mining Carbide

• Tungsten processed extracted to tungsten or carbide
• Carburized tiny tungsten oxide give tungsten carbide
• Combine oxide of tungsten mix mixed with graphite, & heated to more than 1200 C
• The chemical reaction will eliminate oxygen from the oxide, mixing carbon with tungsten

Tungsten Carbide Mixing

• Particulate tungsten carbide in proportion to rice grain
• Scale can be from half to 10 microns
• Carbide mixed at grade powder
• Carbide with category materials/vessel
• Cobalt metal adhesion, binding intact for substance
• Additional tools strengthen attributes: titanium niobium and tantalum
• Drain solvent from spray dryer, packed into molds

Tungsten Carbide Heating

• Structures larger squeezes
• Pulled from graphite/molybdenum on plate, heated to 1100-1300 C in hydrogen/air in sintering heater
• Thick/hard when expelled, cooled after heated, the parts cleaned to get extent

Style coatings

• Chemical Vapor Deposition (CVD) or Physical Vapor Deposition (PVD) prolong tool life

Deposition facts

• High edge toughness helps the CVD surface be 5-20 microns thick
• High edge toughness makes Milling, drilling 5-8 microns
• General PVD coatings are two to four microns wide

Coating applications

• Designed for products that cut based on cobalt titanium, nickel, steel
• Companies create carbide designs for machines to allow better rates

Important Problems In Design

• General Problem occurs when tool design gets difficult
• General problem failures are because tool can't achieve components
• Unknown uncertainties create strength varieties, effecting size, manufacturing, etc.

Chip formation

• When usage tools, heat formed between tools, reducing strength
• Defects cut accuracy tool angle
• Improper material tools ineffective
• Cyclic fatigue strength

Tool failure facts

• Corrosion is seldom a design problem
• Heat lubricant failures electro chemicals
• Geometry failure excessive tool wears

Issues arising

• Electrochemical, oxidization issue
• Manufactures cast issues
• Cutting/temperature high brittle fractures
• Gradual cutting failing

Gradual wear

• Gradual wear is a good failure
• Fails on top and side
• Rake v Flank

Measure of tool wear

• Flank, with Crater growth graph

tool life equation

VTool = C

• Cutting/feed materiel

Criteria when to end production

• Sound changes, Edge Wear and Operator view

variable effect

• Speed/Material

Cutting Material

• Metal, in chip form

Process steps, tool formation

• Cutting a V
• Cutting is angle
• Angles affect deformation and process

Cut to create size

• Plastic Deformed, Sheared at angle
• Chips have high compression ratio

cutting zone

• Cut between chips on a tool side

Types or cuts

• Cutting edge is set to move strain
• Blade cutting at an angle

Cutting edge count:

• One is Sharp part, the other is several cutting parts

cutting conditions/operation

• Set by three elements:
• tool relative Velocity
• edge length of the tool
• Tool for process

three common chip forms

• Brittle work with negative angles at speeds
• Surface shine, materials, angles, and high-speeds
• Build up edge with metal and face for tool edge.

Chip Control

• Reduce user risk, does not reduce cutting and process errors
• Select cutting condition to eliminate

Cutting Tool Property

• Avoid Temperatures and quality to control:

High Carbon Steel

• Oldest of tool with lower end

High-Speed Steel

• Vanadium alloy used

Cemented carbides.

Main in today's market

Ceramic Tools

High resistance with smooth runs

boron nitride (CBN)

Diamond substance for cutting

Machinability

Material cutting process

The Machinability rating or index

• The machinability rating (KM or the Machinability index) is standardized, and is taken from a relative index with relative formula: KM= V60/V60R

Cutting Forces

• Stresses and deformations where tool face F touches

CUTTING FORCE COMPONENTS

• Resolve component from cutting using tool to find:

Cutting force FC:

• Total Force and Power =VFc

THRUST FORCE F♭:

• Feed motion/power
• Three-dimensional side of third force.

Tool Wear

• Process with force, temperature and slide with machine wear

Tool Wear Failure

• Flank and Crate failure, by edge

Tool life Equation

• Production criteria to cut
• Tool has limited life, with failure

Single Point Cutting Tool

• Assist tool with turning production to define the point with side

Types of Single Point Cutting Tool

• Single and multiple

Angle Definitions with shape

• Speed/High temperatures

• Avoid Temperatures and quality to control:

Side cutting edge angle: Angle between the side edge/ tool

End cutting edge angle: Between End cutting edge and tool

Blade Face: Face on where angles touch parts

Face angle: With side to face normal angle

Back Rack: Slope to tool where cut

Factors and selections

Increased angles, for optimum use

Select cutting condition to fit

• Part Geometry
• General or cutting tool?

To optimize and balance materials and cutting type