Machining Fundamentals Flashcards
What is machining?
The process of removing material from a base piece to form a part
What deformation does the cutting action form?
Shear deformation
Which materials are usually machined
Metals
What are the main upsides to machining?
Variety of shapes and dimensional accuracy
What are the main downsides to machining?
Wastes material, time consuming
When is machining performed?
Usually after the forming processes
What are the 3 most common machining types?
Turning, drilling, and milling
What is turning?
A cutting tool moves parallel to the work axis while the work piece rotates on said axis
What is the speed of a turning operation?
Surface speed of work piece
What is drilling?
The tool (drill bit) rotates while moving towards a stationary work piece
What is the speed of a drilling operation?
Speed of the tool rotation
Which operations have feed motions that are done by the tool?
Drilling and turning
When the workpiece is fed towards a stationary rolling cutter, what is the process called?
Milling
What is a single point cutting tool?
There is one dominant cutting edge, and the point is rounded to form a nose radius
What is a multiple cutting edge tool?
There are more than one cutting edge, and the motion is achieved by the tool rotating
What is the rake face?
The part of the cutting tool that directs the chip flow
What is the flank?
The part of the cutting tool lifted an angle from the new surface of the work part to provide relief
How is material removal rate computed?
Cutting speed * feed * cut depth [length/time * length * length]
What is roughing?
The process of removing large amounts of material from the starting work part, getting close to the desired shape
What is finishing?
Completes part geometry by cutting to required tolerances and finish
What is the rake angle?
The angle that the tool makes with the perpendicular axis of the workpiece
What is the shear angle?
When the chip is formed, the angle of the remaining workpiece relative to the projected new surface
What is the shear strain
The measure of angular deformation of a material when subjected to a shear force
What is the primary shear zone
Where deformation of the material takes place
What is the secondary shear zone?
The area along the rake face, where friction is happening
What determines the chip type of a cutting process?
Material properties, cutting condition,
What causes continuous chip?
Ductile material when the tool has a sharp cutting edge, high cutting speeds or rake angle , small feed and depth of cut
What properties does the resultant machined surface have?
Good surface finish
What is the issue with continuous chip?
The chip tangles and can get caught by the tool
What is a chip breaker?
An addition to then rake face of the tool that forces the chip to break
What is a built up edge chip?
Continuous chip where parts of the metal begin to adhere to the edge of the cutting tool
What causes BUE?
Low/medium cutting speeds; local high temperatures and extreme pressure in the cut zone
How to reduce BUE?
Reduce depth of cut, use a positive rake angle, apply coolant, or increase cutting speed
What is a serrated chip?
The chip is jagged away from the rake face
What causes serrated chips?
Difficult materials, high cutting speeds
What is a discontinuous chip?
Chip cannot stay continuous, and breaks on formation
What causes discontinuous chips?
Brittle materials, low cutting speed, large feed and depth of cut, low rake angle, lack of coolant.
What is the transition of chips as the velocity is increased?
Discontinuous, to sliding, to sticking
Where does the friction force occur?
Parallel to the rake face, going towards the work piece.
Where does the normal force occur?
Perpendicular to the friction, pointing towards the chip
Where does the shear force occur?
Along the raised part of the shear angle
Where does the normal shear force occur?
Perpendicular to the shear force, pointing at the chip
Which forces involved in cutting are able to be measured?
Cutting and thrust force
Where does cutting force occur?
Along the projected new surface, pointing towards the tool
Where does the thrust force occur?
Perpendicular the the new surface
What is the Merchant Circle Diagram?
Visual representation of all forces acting upon a workpiece
What does the Merchant’s Equation describe?
The relationship between the shear, rake, and friction angle
What does the merchant’s equation imply?
- Increase in rake angle causes a larger shear angle
- decrease in friction angle causes larger shear angle
- Turning can be reduced to orthogonal cutting if the feed is small relative to cut depth
How is the cutting power of a machining operation found?
The product of the cutting force and cutting speed
What is the factor of conversion from ft*lbf/min to HP
Dividing by 33000
How is the gross power found?
Dividing the cutting force by the mechanical efficiency of a tool
