Chapter 21 Flashcards
Machining
The process of removing unwanted material in the form of chips
Metal cutting or metal removal
Removing unwanted pieces of metal through machining in the form of chips.
Seven chip formations
Turning, milling, drilling, sawing, broaching, grinding (abrasive machining), and shaping (planing).
Speed
Velocity of cutting tool relative to the workpiece
Feed
Is the amount of material removed per revolution.
Depth of cut
Distances the tool is plunged into the surface.
Metal removal rate
Amount of material removed per pass
Shop equations
Basic equations for lathe operations.
Boring
Produces a larger hold to meet a precision after drilling.
Milling
Milling, slab milling, and face milling are multiple tooth processes.
Orthogonal machining
Carried out for research processes. They simplify tool geometry down from three dimensions to two. This allows them to cut metals and test mechanis and theory and develop values for specific power and energy.
Orthogonal plate machining
Machining a plate, low speed, in a milling machine.
Orthogonal tube turning
End cutting a tube wall in a turning set up
Orthogonal disk machining
End cutting a plate with tool feeding in a face direction. High speed.
Oblique machining
Milling drilling and single point turning. Cutting edge and motion are not perpendicular to one another.
Back take angle
The angle that the tool makes with respect to a vertical from the workpiece.
Shearing
Chip is formed by shearing
Orthogonal tube turning does
Solid cylinders that have had a groove machined in the end to form a tube wall
Plastic deformation
Occurs at the radial compression zone that travels ahead of the tool as it passes the workpiece
Shear angle
Angle as the tool passes the workpiece to make a chip.
Free machining steels
Have small percentages of hard second phase particles
Chatter/Vibration
The mechanism by which a process disssipates energy
Chatter
A self excited vibration that is caused by closed force displacement
Chatter can be caused by?
Changes in velocity, friction, build up, workpiece variation. More energy is inputted than can be dissipated.
Free Vibration
Response to any initial condition or sudden change. The amplitude decreases with time. Interrupted marching is an example.
Forced vibration
Response to a periodic input, repeating with time. The amplitude remains constants as it in periodically inputted. Unbalance, misalignment, tooth impacte are examples
Self excited vibration
Periodic response to a constant input. Vibration may grow in amplitude. Surface waviness is an example
How do you recognize chatter?
Screech, buzz, whine. Results in an unacceptable surface finish. There are visible surface undulations
Important factors that influence stability?
Cutting stiffness, cutting process parameters (speed, feed, DOC, total width), cutter geometry, dynamic characteristic (fixture, workpiece)
Matching operations
Require an overlap of cutting paths
Regenerative chatter
A constant chip thickness results in a steady cutting force and eliminates feedback mechanism.
Factors that influence chatter?
Cutting stiffness: property related to hardness and work hardening, the machinability of materials. Larger cutting forces may be needed and greater displacement happens.
Factors of chatter?
Speed: speed affects the phase shift between overlapping surfaces regeneration of vibration.
Process damping
Interference and friction dissipates energy in the form of heat
Influences of chatter?
Feed; feed controls the severity of the vibration.
Factors of chatter?
DOC: primary cause and control of chatter.
Factors of chatter:
Total width of chip: Influences the stability of the process.
Cutting tool geometry
Influences the magnitude and direction of the cutting force.
Factors of chatter:
A positive back rake angle directs the cutting force to be more tangential, and increases stability
Factors of chatter
Reduced clearance angle: increases friction contact, dissipates heat, and stabilized chatter.
Factors of chatter:
Size, shape, and lead angle of insert: a reduced lead angle and a mess round insert can maintain stability
Dynamics
The product of the static stiffness and damping. Maximizing dynamics leads to stability
