Glossary of Selected Terms
(defined in the context of micromechanical machining)
Ablation - the removal of a material by adding heat and turning it to vapor, such as laser
ablation
Amplitude Ratio - in the study of a dynamic system influenced by a force, it is the ratio
of [the steady-state amplitude of vibration of the system due to a time-varying exciting
force] divided by [the static displacement of the system had it been influenced by a
constant force of the same maximum amplitude as the dynamic force]. For example, if a
spring-mass system is excited by a dynamic force, F = 20 sin(wt), it will come to some
steady-state amplitude (maximum displacement) of vibration. The static displacement
for the system is its equilibrium position from rest had it been subjected to the constant
force F = 20. Amplitude ratio is used to study the vibration of a spindle, for example,
which has an imbalance causing a dynamic and periodic force on the rest of the machine
tool.
Analog - varying continuously without instantaneous changes
Angstrom - a unit of length equal to one ten-billionth of a meter, the spacing of atoms in solids is
typically a few Angstroms
Atomic Force Microscope - one of the class of scanning probe microscopes which uses a small
cantilever with a pyramidal point to interact with the surface of a sample. The deflection
of the cantilever at the tip as it is scanned across the sample surface is measured and used
to indicate surface topography, the AFM utilizes the attractive or repulsive forces
between the tip and the sample to deflect the cantilever. The deflection of the cantilever
is measured by the change in location on a split-type optical detector of a laser beam
reflected off the back side of the cantilever.
Cantilever Beam - a structural member which is constrained from rotation and translation
at one end, and is free at the other.
Chisel Edge - the apparent point of a drill, it is actually a cutting edge with a length some
fraction the diameter of the drill. The chisel edge cuts with a very large negative rake
angle.
CNC - computer numerical control, usually refers to machines which operate under
closed-loop control by means of a programmed computer
Coupled Motions - motions which are not independent of each other, motions whereby one
motion will cause some movement of another portion of the structure (machine), present
in many mechanisms
Cutting Force - one component of the machining force, acting along the line of action of the
cutting speed
Cutting Speed - the relative speed between the cutting edge of a tool and the uncut work
material just ahead of the cutting edge
Cutting Tool - the portion of a machine tool which has edges designed to shear the work
material. The cutting tool is normally replaceable and can be made of different materials
such as steel, diamond, carbides, etc depending on the application.
Damped Natural Frequency - in the study of a dynamic system, it is the steady-state
frequency of vibration of a system with damping. If the damping is large (over-damped)
the system will not freely oscillate after an excitation ceases. If the damping is critical,
the system will return to its rest position in the shortest possible time. If the system is
under-damped, it will freely oscillate for some period of time at the undamped natural
frequency. Therefore, this frequency depends not only on the mass and elastic
characteristics of the system but also on the damping present.
Deadband - in a feedback device, it is a zone where a small motion will not be
represented by a change in the output, it is an increment of motion smaller than the
resolution of the encoder, for example. It is more formally referred to as hysteresis.
Degree of Freedom - an independent motion (rotation or translation) of a mechanism
Determinism - the philosophy whereby all actions which obey physical laws should be
quantified and predictable, a philosophy whereby apparent randomness should be
explainable and predictable
Diamond Machining - machining with diamond (natural, polycrystalline, or synthetic) as
the cutting tool material, generally refers to a single cutting edge, not grinding
Digital - signals or states which have discrete values and do not vary continuously,
opposite of analog
Displacement Transmissibility - see Transmissibility Ratio
Edge Sharpness - the radius of the cutting edge of a cutting tool at the intersection of the
rake face and the flank surface
Electron Beam Lithography - exposing a photoresist with electrons, it generally scans the
electron beam across the photoresist in a programmed pattern, capable of very high
resolution by varying the electron dose along pattern edges (referred to as proximity
correction)
Encoder - a feedback device, analog or digital, which provides an indication of motion,
rotary or linear, potentiometers can be used as an analog encoder providing a
continuously varying voltage output with position, an opaque glass scale with
transparent slits can act as a digital encoder providing discrete pulses as position changes
Energy Model - a method of estimating the cutting force and thrust force in machining
based on the energy required to remove a given volume of work material
Euler Column - a slender column and one which is regarded as the weakest type of column
Feed - the distance a cutting edge moves per revolution of the tool or work piece in
machining, used to calculate the volume of material removed, sometime referred to as the
tooth loading
Feedrate - the distance a cutting edge moves in a given time, to calculate the feed the
rotational speed of the tool or work piece must also be known
Fixture - a structure used to securely hold a work piece during machining, the fixture is
normally clamped to the machine tool and should not induce deformation into the
material to be machined
Fluence - the area energy density in laser micromachining, usually expressed in Joules
per square centimeter, or per micrometer
Focused Ion Beam - a method for atomic-scale machining where ions (typically gallium)
are accelerated and focused and steered onto the work piece, all in a high vacuum, work
piece atoms are ejected by the kinetic energy and subsequent scattering by the incident
ions
Frequency Ratio - in the study of a dynamic system, it is the ratio of [the frequency of
the forcing function, force or displacement] divided by [the undamped natural frequency
of the system]. A frequency ratio near unity can lead to large amplitudes of vibration.
Friction Angle - the inverse tangent of the coefficient of friction between materials, in
machining it is normally the inverse tangent of the kinetic coefficient of friction between
the cutting tool rake face and the chip of work material leaving the cutting zone, the value
can be altered by the presence of cutting fluids, etc
Heat Affected Zone - the immediate region around a thermal machining process (laser
ablation, electrical discharge machining, etc) where the mechanical properties of the
work material are changed by rapid cooling (quenching), usually makes work material
locally more brittle
Interferometer - a device for measuring the displacement of an object using the
interference of light, the beam from an optical source (usually laser) is split into a
reference leg and a measurement leg, then recombined to form an interference (phase
difference) pattern, as the optical path length of the measurement leg changes, the
interferogram changes and can be measured, heterodyne-type interferometers use the
Doppler shift in an optical beat- frequency for velocity measurement which is integrated
to get displacement
Lithography - the process, similar to printing a photograph, where energyby is selectively
passed or blocked by a mask transferring the mask pattern into an energy sensitive
material, the type of lithography is named based on the type of energy used (optical
wavelengths, ultraviolet, x-ray, etc).
Machine Tool - the entire structure, actuators, feedback devices, and controllers used to
hold a work material, the cutting tool, and provide all motions and rigidity to fulfill a
machining operation
Machining Forces - in general, all the forces and torques on the cutting tool, machine tool, and
work piece as a result of material removal
Mandrel - a circular structure, in microdrilling the polished portion of the drill which
rides against the vee-block bearings and is integral with the microdrill
Mechanistic Model - a machining force model based on solid mechanics and the equilibrium of
forces and torques, rather than energy for material removal
Microdrilling - no formal size defines microdrilling but is generally in the sub-millimeter
range and requires the use of a vee-block to reduce eccentricity of the drill
Micrometer - one-millionth of a meter, visible light has a wavelength of approximately
0.5 micrometers
Micromilling - no formal size defines micromilling but is generally in the sub-millimeter
range and may or may not use a vee-block, larger micromilling must be done with the
tool held in a collet due to bending load on the tool end, the load would cause a vee-block
mounted milling tool to loose contact with the bearing surfaces
Millimeter - one-thousandth of a meter, approximately 0.039 inches
Nanometer - one-billionth of a meter, or 10 Angstroms
Nose Radius - for a cutting tool, the radius of the cutting edge which forms the shape of
the tool, not the edge sharpness, a larger nose radius generally results in smoother
surfaces for similar machining conditions
Orthogonal - mutually perpendicular for axes, in machining a condition where the
direction of the chip motion is not perpendicular to the cutting edge
Photoresist - the energy-sensitive material into which the mask pattern is transferred by
incident energy (also called resist)
PMMA - polymethyl methacrylate (also called plexiglas), a material used as an x-ray
photoresist and commonly in injection molding replication of microstructures, it is an
excellent material for micromechanical machining
Point Angle - the angle at the end of a drill which forms the chisel edge, standard point
angle of 118 dgerees or 135 degrees for harder materials are most common
Polymerization - the process whereby energy is used to solidify a photopolymer, such as
laser polymerization
Rake Angle - the angle between the normal to the cutting speed direction and the rake
face of a cutting tool, if the rake face tilts toward the incoming work material the sign of
the rake angle is negative, rake angle strongly affects the magnitude of the machining
forces
Resist - the energy-sensitive material into which the mask pattern is transferred by
incident energy (also called photoresist)
Resonance - in the study of a dynamic system, resonance occurs when the forcing
function, force or displacement, has a frequency equal to the undamped natural frequency
of the system. If there is no damping present in the system to remove energy, the
displacement of the system will increase. This build-up of displacement requires time so
excessive displacements can be avoided if the input frequency is not allowed to remain
equal to the undamped natural frequency.
Scanning Tunneling Microscope - one of the class of scanning probe microscopes which uses a
relatively small wire in very close proximity to a sample surface with a small electrical
potential difference causing electrons to jump across the gap (tunneling current), the wire
is moved vertically as it scans across the surface to maintain a constant tunneling current,
the vertical motion is mapped to provide an indication of the electrochemistry of the
surface
Scanning Electron Microscope - a microscope which operates similar to a cathode ray tube,
electrons are focused and scanned across a sample causing electrons to be released from
the surface, the electrons are gathered and converted to an electrical signal proportional to
the number and energy of the liberated electrons, this signal is sent to a synchronized
CRT display where an image of the surface is built by rastering of the incident and
display beams
Scanning Probe Microscope - a class of microscopes based on a thin cantilever used to measure
deflection due to surface roughness, surface mechanical, electrical, magnetic, etc
properties, using a bi-morph cantilever very small temperature changes can be detected, if
caused to vibrate very small masses can be measured, for example
Shear Plane Angle - the approximate plane along which the chip is separated from the
work material in a cutting operation, the angle is measured from the line of action of the
cutting speed
Spade Drill - a type of drill which does not have spiral flutes to help remove chips from a hole
being drilled, due to the complex geometry of a twist drill they are not available smaller
than 50 micrometers in diameter, a spade drill is made of intersections of planes which
can be ground and polished at very small sizes
Specific Cutting Energy - the experimentally measured amount of energy needed to
remove a unit volume of work material, it also has the same units as the power required
for a volumetric removal rate of work material, it also has the units of stress or pressure
so it is sometimes called cutting pressure
Structural Loop - the structure of a machine tool which has a common point at the interface of
the cutting edge of the cutting tool and the newly generated surface of the work material,
the loop starts at the cutting edge goes through the tool, tool holder, kinematic slides and
spindles, the structure of the machine, and back into the work piece
Synchrotron - a device used to generate a high energy collimated beam of x-rays used in
deep x-ray lithography, see for example: www.nsls.bnl.gov/ ; www.src.wisc.edu/ ;
www.tn.cornell.edu/
Thrust Force - the component of the machining forces which is perpendicular to the
cutting force and the line of action of the cutting speed, the thrust force normally tries to
separate the cutting edge of the tool from the newly generated material surface
Transmissibility Ratio - in the study of a dynamic system influenced by a displacement
of the boundary to which the system is attached through spring(s) and damper(s), it is the
ratio of [the steady-state maximum amplitude of vibration of the system] divided by [the
maximum amplitude of displacement of the boundary]. For example, if the floor under a
precision machine tool is vibrating with a function described by Y = 5 cos(wt) due to a
another nearby piece of machinery, then the maximum amplitude of steady-state
vibration of the spindle of the precision machine tool (X) will be the maximum amplitude
of the boundary displacement Y = 5, times the transmissibility ratio.
Twist Drill - a drill having helical flutes to help remove chips from the drilled hole, the type of
drill commonly found in machine shops
Undamped Natural Frequency - in the study of a dynamic system, it is the frequency at
which the system will prefer to freely vibrate (with no external periodic excitation) due to
its mass and elastic characteristics. For a simple spring-mass system with no damping
(all materials have some internal damping), the undamped natural frequency is given by
the square root of {K / M} where K is the spring constant and M is the suspended mass.
The undamped natural frequency is usually referred to as the natural frequency (opposed
to the damped natural frequency).
Vee-Block - a type of bearing whereby the drill or milling tool is supported by four
contact pads, it is a centerless-type chucking arrangement which, so long as the drill was
ground in a vee-block, eliminates virtually all eccentricity in rotation
Warpage - in spindles an eccentric motion causes by the fact that the spindle is bent, in
an air spindle differential temperature in and on the spindle surface can cause differential
expansion or contraction which will cause the spindle to bend
Windage - in air spindles the aerodynamic effect of turbulence around a face plate or
chuck attached to the spindle, air spindles have lower stiffness than mechanical bearings
and aerodynamic forces on the rotating faceplate can cause the spindle to rotate
eccentrically