Machining Titanium Alloys 325

alpha phase

A phase of titanium in its pure state. Alpha phase titanium is relatively easy to machine, but does not possess the desireable properties of the titanium alloys.

alpha stabilizer

An alloying element that favors the alpha crystal structure and raises the alpha-to-beta transformation temperatures. Alpha stabilizers include gallium, germanium, carbon, oxygen, and nitrogen.

alpha titanium alloy

An alloy resulting from mixing alpha phase titanium and alpha stabilizers such as aluminum and tin.

alpha-beta phase

A phase of titanium that has been alloyed with small amounts of aluminum and vanadium. Alpha-beta phase titanium is the most common titanium alloy and is moderately difficult to cut.

alpha-beta titanium alloy

An alloy resulting from mixing alpha and beta phase titanium with alpha and beta stabilizers.

alundum

Aluminum oxide. A ceramic compound that is commonly used as an abrasive and refractory material. Aluminum oxide is very effective for machining steel.

beta phase

A phase of titanium that has been alloyed with beta stabilizers such as molybdenum, silicon, and vanadium. Beta phase titanium alloys are more difficult to machine than alpha-beta phase alloys, but lack toughness.

beta stabilizer

An alloying element that favors the beta crystal structure and lowers the alpha-to-beta transformation temperatures. Beta stabilizers include vanadium, molybdenum, chromium, and copper.

beta titanium alloy

An alloy resulting from mixing beta phase titanium and beta stabilizers such as vanadium, niobium, tantalum, and molybdenum.

body-centered cubic

The crystal structure that contains an atom in the center and one atom in each corner of a cube. Metals with a body-centered cubic crystal structure tend to be hard.

BUE

Built-up edge. Adhesion of workpiece material to the cutting edge of an insert due to high temperatures and pressure welding.

built-up edge

BUE. Adhesion of workpiece material to the cutting edge of an insert due to high temperatures and pressure welding.

commercially pure titanium

Unalloyed titanium characterized by an alpha phase hexagonal close-packed crystal structure. Commercially pure titanium is over 99.6% titanium with traces of carbon, iron, nitrogen, oxygen, and hydrogen.

corrosion cracking

The breaking of a material after it has been subjected to harsh environmental conditions or chemicals.

density

The mass per unit volume. Given two identical volumes of materials, the one with more density has more mass and weight.

dwelling

The process of stalling the tool feed while the the tool is still contacting the workpiece. Dwelling can cause damage to both the workpiece and the tool.

elasticity

The measure of a material's ability to reshape itself after it has been stretched or deformed. Titanium is elastic and thus can flex under pressure without breaking.

exotic metal

Any metal that does not fit within the major materials categories commonly used in manufacturing. Exotic metals are typically nonferrous and many exhibit properties that make them favorable for specific advanced industrial applications.

fatigue strength

The maximum stress a material can withstand prior to its predicted failure.

hexagonal close-packed

The crystal structure that contains a collection of atoms that are closely packed into the shape of a hexagon. Metals with a hexagonal close-packed crystal structure are very difficult to form.

high-speed steel

A category of tool steels used for cutting tool applications. HSS tools offer greater toughness and less hardness than carbide tools and typically contain more than 15% alloy additions of chromium, molybdenum, tungsten, vanadium, and/or cobalt according to grade.

horsepower

A unit of power used to describe machine strength. A machine with increased horsepower has a spindle that can exert a greater amount of force.

hypoallergenic

Not prone to cause negative reactions with human body tissue. Because it is hypoallergenic, titanium is often used as a structural replacement or reinforcement within the human body.

notching

Insert failure characterized by excessive localized wear on both the rake face and flank of the insert at the depth of cut line. Edge notching is particularly common when machining high-temperature alloys.

percent of thread

One-half the difference between the major diameter and the minor diameter of an internal thread, divided by the basic thread height, expressed as a percentage.

physical vapor deposition

PVD. A process that deposits or coats a film of hard refractory materials 2-7 microns thick on a tool's surface. The tools are heated in a vacuum chamber at low temperatures approximately 900°F (500°C). A vaporized or ionized compound is then deposited on the tools by ion plating, magnetron sputtering, or arc evaporation.

properties

Essential characteristics of a material that distinguish it from other materials. Mechanical properties like hardness and modulus of elasticity describe how a material reacts to forces that attempt to stretch, dent, scratch, or break the material, while physical properties like thermal conductivity and melting point describe how a material reacts to other forces like heat or electricity.

PVD

Physical vapor deposition. A process that deposits or coats a film of hard refractory materials 2-7 microns thick on a tool's surface. The tools are heated in a vacuum chamber at low temperatures approximately 900°F (500°C). A vaporized or ionized compound is then deposited on the tools by ion plating, magnetron sputtering, or arc evaporation.

rigidity

The quality of a workpiece, machine, or machine setup characterized by being stiff and inflexible. A setup for machining titanium requires excellent rigidity to reduce vibration, deflection, and chatter.

semi-synthetic coolant

A class of metalworking fluid that is composed of lubricant-based oil and water. Semi-synthetic oil is mixed with a range from 10 to 40 parts water.

silicon carbide

A hard, brittle material used as an abrasive and as a refractory material. Also referred to as crystolon, silicon carbide has excellent hardness that approaches diamond and is indicated by the letter "C."

smearing

A condition that causes a tool to leave burrs on a workpiece when it is not properly lubricated during machining. Smearing causes a poor surface finish.

soluble oils

A class of metalworking fluid that is composed of lubricant-based oil, emulsifiers, and other additives. Soluble oil is obtained as a concentrate and is then mixed with water.

strength

The ability of a metal to resist forces that would otherwise break or deform the metal. A material exhibits tensile, compression, or shear strength, depending on the direction of the force.

strength-to-weight ratio

The relationship between a material's strength and its weight. Because titanium is both extremely light and strong, it has a high strength-to-weight ratio.

stress cracking

The breaking of a material after it has been subjected to a force that would otherwise cause deformity.

superalloy

A metal alloy consisting of three or more elements that is very expensive and designed to exhibit high strength at elevated temperatures.

synthetic fluid

A coolant that contains no petroleum and is manufactured from chemicals or additives not found in nature.

tetragonal crystal structure

A crystal structure characterized by a rectangular lattice and square base and height. A body-centered tetragonal crystal structure has an atom on each corner and an atom in the center.

thermal conductivity

A physical property that indicates how well heat flows through a material. Titanium is a poor thermal conductor, which means heat does not flow through it well.

through-spindle coolant

A machine feature that delivers coolant fluid directly to the cutting edge of a tool through the spindle. Through-spindle coolant greatly extends tool life when machining titanium.

Ti

Titanium. A silvery white "space age" metal with a high strength-to-weight ratio, excellent flexibility, and exceptional corrosion resistance. Titanium is commonly used in medical components and in aerospace applications.

Ti-6Al-4V

An alpha-beta titanium alloy consisting of 6% aluminum and 4% vanadium. Ti-6Al-4V is commonly found to jet engine components.

TiAlN

Titanium aluminide nitride. An insert coating designed to improve the wear resistance of carbide inserts at elevated temperatures.

titanium

Ti. A silvery white "space age" metal with a high strength-to-weight ratio, excellent flexibility, and exceptional corrosion resistance. Titanium is commonly used in medical components and in aerospace applications.

titanium aluminide

A phase of titanium that is extremely difficult to machine. Though it was first developed over four decades ago, TiAl only recently began appearing in advanced aerospace applications.

titanium aluminum nitride

TiAlN. An insert coating designed to improve the wear resistance of carbide inserts at elevated temperatures.

torque

The force that produces rotary motion such as that required to turn a spindle. Cutting titanium requires machines with excellent torque capability.

water-based coolant

A coolant with a high percentage of water content. Water-based coolants are not flammable and have additives to increase its boiling point.

work harden

The increase in hardness of a material due to the heat and pressure of a machining process.

workholding device

A device used to support, locate, and hold a workpiece. The workholding device establishes a relationship between the cutting tool and the workpiece.