Machining Processes
Chapter ITheory of Metal Machining
◦Overview of machining Technology◦Theory of chip formation in metal machining
The orthogonal cutting model Actual chip formation
◦Force relationships and the Merchant Equation Forces in metal cutting The Merchant Equation
◦Power and Energy relationships in machining◦Cutting Temperature
Analytical methods to compute cutting temperatures Measurement of cutting temperature
Before beginning
Material Removal
Processes
Conventional Machining
Abrasive Processes
Nontraditional machining and thermal
cutting processes
Turning and related operations
Drilling and related operations
Milling
Other machining processes
Grinding
Other abrasive processes
Electro- discharge machining
Electrochemical machining
Thermal energy processes
Chemical machining
Some basic definitions… Material removal processes
A family of shaping operations in which excess material is removed from a starting workpart so that what remains is the desired final geometry.
Conventional machining processesProcesses in which a sharp cutting tool is used to mechanically cut the material to achieve the desired geometry.
Abrasive processesProcesses in which material is mechanically removed by the action of hard, abrasive particles
Nontraditional processesProcesses that used various energy forms other than sharp cutting tool or abrasive particles to remove material
MachiningA manufacturing process in which a sharp cutting
tool is used to cut away material to leave the desire part shape.
The predominant cutting action in machining involves shear deformation of the work material to form a chip; as the chip is removed, a new surface is exposed.
Advantages and DisadvangesWhy is it so important?
•Variety of work materials•Variety of part shapes and geometric features•Dimensional accuracy•Good surface finishes
•Wasteful of material•Time consuming
Overview of Machining Technology
To perform a machining operation, relative motion is required between the tool and work.
This relative motion is achieved in most
machining operations by means of a primary motion, called the CUTTING SPEED, and a secondary motion, called the FEED.
The shape of the tool and its penetration into the work surface, combined with these motions, produces the desired geometry of the resulting work surface
Tipos de procesos de mecanizado
The Cutting ToolA cutting tool has one or more sharp cutting edges and is made of a material that is harder than the work material. Single-point cutting tool (turning)
Multiple-cutting-edge tools (milling and drilling)
There are two angles of interest in a single-point cutting tool◦Rake angle α◦Relief angle
Cutting ConditionsCutting speed (m/s) – v – meters of chip per
secondFeed (mm/rev) – fDepth of cut (mm) - d
Cutting ConditionsMaterial removal rate (mm3/s)
Machining operations ◦Rough cutting: removal of big quantities of
material with the highest speed Feed = 0.4 to 1.25 mm/rev Depth = 2.5 to 20 mm
◦Finishing cutting: lower cutting speed and depth of cut in order to finish the work piece. Tolerances and surface finishing. Feed = 0.125 to 0.4 mm/rev Depth = 0.75 to 2 mm
Cutting ConditionsCutting fluids: usually applied to cool or
lubricate the cutting tool
Cutting ConditionsThe term is applied to those machines
that perform machining operations. However the term is also applied to those machines that perform bulk deformation processes: rolling, die forging, etc.
Theory ofChip Formation in Metal MachiningTHE ORTHOGONAL CUTTING MODEL
Theory ofChip Formation in Metal MachiningTHE ORTHOGONAL CUTTING MODEL
Lo = Length of shear planeto = chip thickness before cuttingtc = chip thickness after cuttingΦ = shear angle1. Define chip thickness ratio
r = to/tc2. Define interest triangles 3. Obtain formula for Φ
Theory ofChip Formation in Metal MachiningTHE ORTHOGONAL CUTTING MODEL
Theory of Chip Formation in Metal MachiningTHE ORTHOGONAL CUTTING MODEL – Chip straining in parallel shear plates theory
1. Define shear strain = /b = AC/BD =(AD+DC)/BD
2. After practicing some algebra
Homework 1!!Finish the derivation of the formulas presented in classes for the “shearing angle Φ” and for the “shear strain ”
DUE DATE: October 22nd. (Via Sidweb)
