Optimizing Tool Life and Process 381

abrasive wear

The process of an object losing material over time due to friction caused by rubbing against another object. Abrasive wear always occurs during metal cutting operations, but it can and should be controlled.

adhesion

The build up of workpiece material on a tool during metal cutting. Adhesion causes notch wear.

aluminum

A silver-white metal that is soft, light, and thermally conductive. Aluminum is a ductile metal prone to forming BUE on cutting tools when machined.

aluminum oxide

AL₂O₃. A common coating material used on carbide cutting tools that provides excellent thermal and chemical protection. Aluminum oxide coatings improve tool life.

atoms

The smallest distinguishable unit of an element. Atoms combine to form molecules.

break-in period

The stage of flank wear development during which the cutting point initially wears down to allow the formation of a wear land. The break-in period, also known as the hone-in period, is the initial phase of the flank wear process.

brittle

A material's resistance to being stretched, formed, or drawn. Brittle materials fracture easily and brittleness often increases with hardness.

build up

The formation of an unwanted rough edge on a cutting tool that occurs when pieces of the workpiece pressure weld on the tool during cutting. Build up, more commonly called built-up edge (BUE), is a common cause of tool failure when machining soft, gummy metal.

built-up edge

BUE. Tool wear characterized by the formation of an unwanted rough edge on a cutting tool that occurs when pieces of the workpiece pressure weld onto the tool during cutting. Built-up edge is a common cause of tool failure when machining soft, gummy metal.

carbide

A common cutting tool material created by combining carbon with a hard metal, such as titanium or tungsten. Carbide tools are the most commonly used tools in the metal cutting industry.

carbon

A common, nonmetallic element found in a number of tools. Carbon provides excellent hardness and wear resistance.

catastrophic failure

The sudden and complete breakdown of a tool. Catastrophic failure renders a tool unusable.

centerline

An imaginary line that divides a shape into two equal halves or that runs through the center of a cylindrical object. A centerline can bisect a workpiece along its length or along its width.

ceramic

A material consisting of compounds formed by metallic and nonmetallic elements. Ceramic tools are very hard but also brittle, which can make them prone to fracture.

chatter

Vibrations of the cutting tool or workpiece. Chatter can cause issues such as tool chipping and poor surface finish.

chemical reactions

An interaction between substances that changes the make up of one or more of the substances. Chemical reactions between the tool and workpiece cause softening of the rake face, which in turn leads to cratering.

chip crowding

The bunching of chips around the cutting tool and cutting area. Chip crowding often occurs due to high feed rates, which results in thick chips that do not flow easily.

chip hammering

Tool wear characterized by damage to the rake face of a tool caused by repeated impact of improperly deflected chips. Chip hammering can be prevented by selecting the proper feed and insert geometry.

chip load

The thickness of the chips created during a machining operation. Chip load is related to feed rate and is often measured by feed per tooth (fpt).

chipbreaker

A feature or device designed to prevent chips from forming into long pieces. Chipbreakers are either indentations on the surface of the cutting insert or another wafer clamped above the insert in the toolholder.

chipping

Tool wear resulting in the loss of small fragments from the cutting edge of the tool. Chipping can be caused by a number of factors, including tool or workpiece vibration, excessive depth of cut, and improper tool material selection.

chips

An unwanted piece of metal that is removed from a workpiece. Chips are formed when a tool cuts or grinds metal.

clamping mechanism

A component used to hold a cutting insert or cutting tool in place. Clamping mechanisms include screws and adjustable vises.

clearance

The amount of space or distance between two objects. Clearance between the tool and workpiece in metal cutting is set through tool geometry and, when used properly, can prevent tool wear such as BUE.

clearance angle

The measure of the space between the flank that trails the cutting edge and the workpiece. Increasing the clearance angle can reduce premature flank wear.

clearance angles

The angle that determines how much of the bottom edge of an insert's flank is in contact with the surface of a workpiece. Smaller clearance angles can help reduce the possibility of tool wear, such as plastic deformation.

continuous chips

A chip that does not break apart and continues to fold in on itself. Continuous chips are usually created when machining ductile materials and can cause chip hammering.

crater wear

Tool wear characterized by the formation of concave depressions in the rake face of the cutting tool, adjacent to the cutting edge. Crater wear, also called cratering, can be prevented through proper selection of cutting speed and tool material.

crater wear

Tool wear characterized by the formation of concave depressions in the rake face of the cutting tool, adjacent to the cutting edge. Crater wear, also called cratering, can be prevented through the proper selection of cutting speed and tool material.

cratering

Tool wear characterized by the formation of concave depressions in the rake face of the cutting tool, adjacent to the cutting edge. Cratering, also called crater wear, can be prevented through proper selection of cutting speed and tool material.

cratering

Tool wear characterized by the formation of concave depressions in the rake face of the cutting tool, adjacent to the cutting edge. Cratering, also called crater wear, can be prevented through the proper selection of cutting speed and tool material.

cutting edge

The leading edge of a cutting tool that is in direct contact with the workpiece and performs material removal. The cutting edge is subject to a number of forms of tool wear that can be minimized through proper control of cutting variables.

cutting fluids

Any fluid used to cool or lubricate a metal cutting process. Cutting fluids can be used to optimize tool life and the quality of a finished part.

cutting forces

The various stresses involved in a machining process. Cutting forces are determined by a combination of speed and feed rate, tool angle, workpiece material, and other factors.

cutting point

The corner of the insert where the flanks and tool face meet that performs the actual cut. The cutting point wears down quickly during the break-in phase of the flank wear process.

cutting variables

An adjustable component of a metal cutting operation. Cutting variables include tool geometry, tool material, and feed and speed.

defect

An irregularity or imperfection on an object. A tool defect, such as a wear land, can eventually lead to catastrophic tool failure.

deforms

The distortion of the original shape of an object. A tool often deforms when subjected to excessive heat or pressure during a cutting operation.

degrades

The deterioration of a material. When machining, friction degrades the cutting point of a tool, which leads to flank wear.

depth of cut

The measurement of how far a cutting tool penetrates the workpiece. Depth of cut is the distance from the uncut surface to the machined surface.

depth-of-cut line

DOC line. The line formed as a tool makes a pass along a workpiece. The depth-of-cut line is where the cutting point of a tool engages a workpiece, which leads to increased cutting forces that can cause a number of types of tool wear, such as notch wear.

depth-of-cut notching

DOC notching. Tool wear characterized by the formation of valleys on either the rake face or flank of the cutting tool at the depth-of-cut line. Depth-of-cut notching, also called notch wear or notching, often occurs when cutting hard materials such as nickel.

diagnostic tool

A device used to help operators assess wear or defects in a tool or part. Diagnostic tools include microscopes and optical comparators.

diffuse

The process of spreading from an area of high concentration to an area of low concentration. Hard carbon atoms in the tool sometimes diffuse into workpiece chips and weaken the tool.

DOC line

Depth-of-cut line. The line formed as a tool makes a pass along a workpiece. The DOC line is where the cutting point of a tool engages a workpiece, which leads to increased cutting forces that can cause a number of types of tool wear, such as notch wear.

DOC notching

Dept-of-cut notching. Tool wear characterized by the formation of valleys on either the rake face or flank of the cutting tool at the depth-of-cut line. DOC notching, also called notch wear or notching, often occurs when cutting hard materials such as nickel.

ductile

A material that can be easily be stretched drawn, or formed without fracturing. Ductile metals are easier to cut but can cause the formation of BUE on the tool.

edge hone

A rounded and blunted cutting edge used to add edge strength. An edge hone decreases wear resistance.

failure region

The stage of flank wear development where the wear land has grown to the point that it could fail at any time. The failure region often indicates the end of usable tool life.

feed

The rate at which the cutting tool and/or workpiece move in relationship to one another. Feed is often measured in inches per minute (ipm) or millimeters per minute (mm/min).

fissures

A narrow opening caused by the splitting of a material. Fissures on a tool are caused by thermal cracking and can lead to tool failure.

flank

The flat surface of an insert perpendicular to the rake face. The flank passes over the the newly cut surface immediately after the cutting edge, which causes it to wear over time.

flank wear

Tool wear characterized by the gradual wearing away of the cutting edge and flank, which is mostly caused by abrasion. Flank wear is the only acceptable form of tool wear because it is inevitable, controllable, and predictable.

fracture

The catastrophic failure of a tool due to the separation of a large section of tool material. Fracture can happen without warning or as the result of other forms of tool wear.

friction

A force that resists the movement of two objects sliding against each other. Friction is one of the primary causes of tool degradation.

grinding

The process of using an abrasive to remove material from a tool or part. Grinding can be used to resharpen tools that have dulled during use.

hard

The ability of a material to resist penetration, indentation, or scratching. Hard materials tend to be very wear resistant.

heat

The accumulation of elevated temperatures. Heat is often the result of friction.

high-speed steel

HSS. A specialized metal used to create cutting tools. High-speed steel is tougher than carbide but offers less hardness and wear resistance.

hone-in period

The stage of flank wear development during which the cutting point initially wears down to allow the formation of a wear land. The hone-in period, also known as the break-in period, is the initial phase of the flank wear process.

impact shock

The sudden force generated when a cutting tool initially engages or reengages with a workpiece. Impact shock is most common in milling because milling involves intermittent cutting.

indexed

Rotated to expose a fresh cutting surface. Tool inserts can be indexed if flank wear progresses to the failure region on one side of the tool.

insert

An indexable and replaceable cutting tool with a geometric shape and multiple cutting surfaces. Insert wear can be controlled through setting the correct cutting variables.

intermittent cutting

A metal removal process in which one or more edges of the cutting tool repeatedly enter and exit the workpiece surface. Intermittent cutting, sometimes called interrupted cutting, causes temperature fluctuations in the tool that can lead to thermal cracking.

interrupted cutting

A metal removal process in which one or more edges of the cutting tool repeatedly enter and exit the workpiece surface. Interrupted cutting, also called intermittent cutting, causes temperature fluctuations in the tool that can lead to thermal cracking.

lead angle

The measurement of how a tool's cutting edge is tilted in relationship to a line perpendicular to the workpiece's surface in both turning and milling. The lead angle controls the severity of some cutting forces and can be adjusted, usually in the positive direction, to reduce several forms of wear.

life

The length of time a cutting tool is expected to be operational before it must be replaced. Tool life can be extended through optimized implementation, including using the the proper tool geometry or cutting with cutting fluids.

load

The amount of force or pressure placed on an object. Load on a cutting tool is a combination of several cutting variables including feed rate and DOC.

low-carbon steel

A plain carbon steel that contains less than 0.30% carbon. Low-carbon steel is prone to adhering to tools, which can cause built-up edges (BUE) or notch wear.

mechanical force

A stress that attempts to bend, stretch, break, indent, or otherwise deform a material. Mechanical forces are responsible for most forms of tool wear.

metal cutting

A machining process that uses a tool to remove metal from a workpiece. Metal cutting processes include turning, drilling, and milling.

metal removal rate

MRR. The volume of metal removed in a given amount of time. Metal removal rate is measured in cubic inches per minute (in.³/min) or cubic centimeters per minute (cm³/min).

microscope

A magnifying device used to view small objects or examine a small portion of a larger object. A microscope can be used to assess tool wear on a cutting tool.

mill

A machine that uses a rotating multi-point tool to remove metal from the surface of a workpiece. Common types of mills include face mills and end mills.

milling

A cutting operation in which a rotating multi-point cutting tool is fed along the surface of a part to remove material. Milling operations generally produce flat surfaces.

milling cutter

A multi-point cutting tool that has inserts, or teeth, around its cutting surface. Milling cutters include face and end mills.

negative rake angles

A tool position that moves the rake face toward the workpiece in both turning and milling. Negative rake angles can lead to the formation of BUE.

nickel alloys

A metal made of a combination of nickel and at least one other metal. Nickel alloys are hard and corrosion resistant.

nose radius

The degree of roundness between two cutting edges of a tool. The nose radius is described by the insert number and influences factors such as surface finish and insert strength.

notch wear

Tool wear characterized by the formation of valleys on either the rake face or flank of the cutting tool at the depth-of-cut line. Notch wear, also called depth-of-cut notching (DOC notching) or notching, often occurs when cutting hard materials such as nickel.

notching

Tool wear characterized by the formation of valleys on either the rake face or flank of the cutting tool at the depth-of-cut line. Notching, also called notch wear or depth-of-cut notching (DOC notching), often occurs when cutting hard materials such as nickel.

notching

Tool wear characterized by the formation of valleys on either the rake face or flank of the cutting tool at the depth-of-cut line. Notching, also called, depth-of-cut notching (DOC notching) or notch wear, often occurs when cutting hard materials such as nickel.

operators

A person trained to run a specific machine. Operators are responsible for helping ensure that a machine runs properly, efficiently, and safely.

optical comparator

A measuring instrument that projects an image of a part onto a screen to examine its shape, size, or other features. An optical comparator can be used to examine a cutting tool for wear or potential failure.

oxidation

A chemical reaction involving the addition of oxygen, the removal of hydrogen, or the removal of electrons from a material. Oxidation weakens and degrades a material.

oxides

A chemical compound containing oxygen and one other element. Oxides are formed during oxidation and often cause material degradation.

perpendicular

An intersection of two lines or objects at a right angle. The fissures and cracks caused by thermal cracking form perpendicular to the cutting edge of the tool.

physical vapor deposition

PVD. A process that deposits a thin, even layer of coating on the surface of a tool. Physical vapor deposition creates tools that are tougher but less hard than other coating processes such as chemical vapor deposition (CVD).

plastic deformation

Tool wear characterized by the warping of the tool shape that occurs due to extreme pressure and temperature and intense mechanical contact. Plastic deformation can be prevented by using a harder tool material or reducing speed or feed.

plastic deformation

Tool wear characterized by the warping of the tool shape that occurs due to extreme pressure and temperature and intense mechanical contact. Plastic deformation, also called thermal deformation, can be prevented by using a harder tool material or reducing speed or feed.

positive rake angle

A tool position that moves the rake face away from the workpiece. A positive rake angle can help prevent the formation of BUE.

positive rake angle

Tool geometry that moves the rake face of the tool away from the workpiece centerline. A positive rake angle can help prevent tool wear, such as cratering.

pressure

The exertion of a mechanical force upon an object. In metal cutting operations, the amount of pressure is usually related to the feed rate.

rake angle

The measurement of the tilt of the rake face either toward or away from the workpiece centerline when turning or the position of the cutting edge in relation to the mill when milling. Positive rake angles reduce cutting forces, encourage chip removal, and prolong tool life.

rake face

The top surface of the cutting tool. The rake face is subject to crater wear and chip hammering because chips make contact with it as they are separated from the workpiece.

rigid

A workpiece, machine, or machine setup characterized by being stiff and inflexible. Rigid machine setups can improve tool life and the quality of the finished part.

round insert

A circular indexable cutting tool. Round inserts have the greatest edge strength.

setup

All the necessary preparation of tooling and fixturing that occurs on a machine before operation begins. Proper machine setup is an important factor in optimizing tool life.

speed

The rate at which the surface of the workpiece rotates past the cutting edge of a tool at the point of contact. Speed is often measured in revolutions per minute (rpm).

stainless steels

A type of steel that contains more than 11% chromium and exhibits excellent corrosion resistance. Some types of stainless steels, such as ferritic or austenitic, are gummy and can cause BUE to form on a cutting tool.

steady-state region

The stage of flank wear development during which the wear land slowly progresses while the tool is in use. The steady state region should be the longest period of flank wear development.

steel

An alloy of iron and carbon containing less than 2.0% carbon. Steel can cause cratering when cut with a pure tungsten carbide cutting tool.

strength

The ability of a material to resist forces that attempt to break or deform it. Inserts with good strength can operate at higher feed rates and withstand tool wear such as chipping.

surface finish

The measured surface profile characteristics of a completed workpiece. Surface finish begins to degrade as a tool enters the failure region of the flank wear process.

tantalum carbide

TaC. A compound of tantalum and carbon. Tantalum carbide is used as an alloy with tungsten carbide to increase a cutting tool's resistance to cratering and thermal deformation.

thermal cracking

Tool wear characterized by small cracks and fissures caused by temperature fluctuations. Thermal cracking, also called thermal fatigue, can be prevented by using tougher tool materials or properly applying cutting fluid.

thermal deformation

Tool wear characterized by the warping of the tool shape that occurs due to extreme pressure and temperature and intense mechanical contact. Thermal deformation, also called plastic deformation, can be prevented by using a harder tool material or reducing speed or feed.

thermal fatigue

Tool wear characterized by small cracks and fissures caused by temperature fluctuations. Thermal fatigue, also called thermal cracking, can be prevented by using tougher tool materials or properly applying cutting fluid.

titanium carbide

TiC. A compound of titanium and carbon that can be used as the basis for a cutting tool material, added to tungsten carbide for steel cutting grades, or used as a coating. Titanium carbide offers improved chemical stability and crater resistance.

tolerance

An unwanted but acceptable deviation from a given dimension defined by a blueprint. Tolerance is a key measure of tool performance and a decrease in tolerance helps indicate when a tool should be replaced.

tool

A device made of hard, tough materials that is used to remove metal by creating chips. A tool can be protected from premature wear by utilizing them at the correct feed and speed, among other methods.

tool geometry

The collective angles formed by the dimensions of the cutting tool and the positioning of the tool. Tool geometry is a key factor in tool life, production efficiency, and part quality.

toolholder

A device used to hold a cutting tool in place during machining. A toolholder's positioning and setup are key to preventing tool wear such as chipping.

tough

A material that can absorb energy without breaking or fracturing. Tough cutting tools are able to withstand sudden stresses but are less hard and wear resistant.

toughness

The ability of a material to absorb energy without breaking or fracturing. Cutting tools with good toughness are able to withstand sudden stresses but are less wear resistant.

tungsten carbide

WC. A compound of tungsten and carbide that was used as the original carbide tool. Pure tungsten carbide tools are hard but prone to cratering when used to machine steels.

turning

A machining operation where a cylindrical workpiece is rotated while a single-point tool is guided along the length of the part. Turning is a common machining operation performed on the lathe.

visual inspection

An assessment where an operator examines a tool, machine, or part for defects or wear without the use of an assistive device. Visual inspection is usually supplemented with mechanically-assisted inspection.

wear

The erosion of material as a result of friction. Types of tool wear include crater wear, flank wear, and notch wear.

wear land

The worn, flattened section that forms on the flank of the tool due to abrasive wear from contact with the workpiece. The wear land can be measured to determine the rate of flank wear and the remaining service life of the tool.

weld

The process of permanently joining two or more materials through the use of heat or pressure. Some workpiece materials can weld onto a tool and cause issues such as BUE or notch wear.

work harden

To increase the hardness of a material through the use of pressure and shaping processes. Metals that work harden may cause notch wear in tools because they resist being cut.

workpiece

A part that is subjected to one or more manufacturing procedures such as welding, machining, or casting. Workpiece material is a key consideration in extending tool life.