Ch.5 Material Removal

Methods of holding workpiece in a lathe

(a) Holding the work between centers (b) chuck (c) collet (d) face plate

Boring

*Different than turning (lathe-ing) -Boring is performed on the INSIDE diameter on an existing hole -Turning is performed on the OUTSIDE of an existing cylinder Boring machines can be horizontal or vertical - refers to the orientation of the axis of rotation of machine spindle

Climb Peripheral milling

*Down milling -Shorter chip -Increased too life -Pushes part down -Better surface finish

Conventional Peripheral milling

*Up milling -Longer chip -Lifts the part up

Kerf

*Width of material that is removed by a cutting process

Broaching

-A multiple tooth cutting tool is moved linearly relative to work in direction of tool axis -Internal or external -Cutting tool = "Broach" Advantages: ▪ Good surface finish ▪ Close tolerances ▪ Variety of work shapes possible

Devices to hold stock or tools

-Collet -Chuck (3 jaw, 4 jaw) -Center (dead, live) -Vice

Cutting Conditions

-Cutting temperature -Cutter speed -Depth of cut -Feed rate -Stock (work piece) Cutting fluid

Computer Automation

-G-code -CNC -CAD -CAM

Types of Machines

-Lathe -Mill -Drill press -Band saw (vertical & horizontal) -Machining Center

Drilling Opperations

-Reaming -Tapping -Counterbore -Countersink -Through hole Blind hole

Types of Cuts

-Rough cut -Finish cut -Conventional milling -Climb milling -Kerf cut

Machining Operations

-Turning -Drilling -Milling -Boring -Broaching -Sawing -Form milling -Hobbing -High Speed Machining

Swaging (diagrams)

-Vertical, band saw -Horizontal, band saw (power hacksaw) -Circular saw

Horizontal boring

1) Boring bar is fed into a rotating work part 2) Work is fed past a rotating boring bar

Two forms of milling

1) Peripheral milling 2) Face milling

3 Dimensions of machining

1- Cutting speed (primary) 2- Feed (secondary) 3- Cut Depth

Gear shaping

2 forms ▪ Single-point tool to gradually shape each gear tooth spacing ▪ Cutter has general shape of the gear but with cutting teeth on one side

Mill-Turn center

Automated machine tool that performs turning, milling, and drilling operations in one setup. ▪ Can position a cylindrical work part at a specified angle so a rotating cutting tool can machine features into outside surface of part ▪ Conventional turning center cannot stop work part at a defined angular position and does not include rotating tool spindles

Machining center

Automated tool that performs multiple machining operations with CNC control in one setup. Typically performs milling and drilling. Operated on 3,4, or 5 axes. Automatic tool changes.

Drilling

Creates a round hole in a work part ▪ Compare to boring which can only enlarge an existing hole ▪ Cutting tool called a drill or drill bit ▪ Machine tool: drill press

High speed machining (HMS)

Cutting speeds significantly higher than conventional machining operations. Faster production, shorter lead time, and reduced cost. Good for complex geometries. Common in aircraft, and Die & mold industry. **Multiple machining operations on aluminum to produce automotive, computer, and medical parts ▪ Quick tool changes and tool path control important

Blind hole

Drill does not exit the opposite side of the part

Through hole

Drill exits opposite side of workpiece

Finishing cuts

Finishing - completes part geometry ▪ Final dimensions, tolerances, and finish ▪ Low feeds and depths, high cutting speeds

Vertical Boring

Good for large, heavy work parts that have low L/D ratio

Gear hobbing

Hob has a slight helix and its rotation is coordinated with much slower rotation of the gear blank ▪ Special milling machines (called hobbing machines) accomplish the relative speed and feed motions between cutter and gear blank

Milling

Machining operation in which work is fed past a rotating tool with multiple cutting edges ▪ Axis of tool rotation is perpendicular to feed direction ▪ Cutting tool called a milling cutter ▪ Cutting edges called teeth ▪ Basic milling operation creates a planar surface

Material removal rate

R = v*f*d

Operations related to drilling

Reaming (tight diameter tolerance) Tapping Counterboring Countersinking (memorize picture) Center drilling Spot facing

Roughing cuts

Removes large amounts of material from starting work part ▪ Some material remains for finish cutting ▪ High feeds and depths, low speeds *Usually multiple roughing cuts & 1-2 finishing cutss

Turning

Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape

Machine tool operations (NC)

Used for machining operations like turning, drilling, and milling. Motivated development of machine centers. Other machine tools: ▪ Grinding machines ▪ Sheet metal press-working machines ▪ Thermal cutting processes

Drilling

Used to create a round hole, usually by means of a rotating tool (drill bit) with two cutting edges

Gear hobbing

also milling but using a special cutter called a "hob"

Cutting fluid

coolant designed for metalworking. Include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases. Properties: help to maintain stable temp., maximize life of cutting tip, prevents rust.

Gear broaching

for internal and external gears

Form milling

use of a form milling cutter. Used to make gear teeth. Teeth on form miller have shape of spaces between gar teeth. *Gear blank is indexed between each pass to establish correct size of gear tooth.

Computer Numerical Control (CNC)

▪ A form of programmable automation in which the mechanical actions of a piece of equipment are controlled by a program containing coded alphanumeric data - The data represent relative positions between a work head (cutting tool) and a work part ▪ NC operating principle is to control the motion of the work head relative to the work part and to control the sequence of motions

Machining fun facts

▪ Approximately 98% of the energy in machining is converted into heat ▪ This can cause temperatures to be very high at the tool-chip ▪ The remaining energy (about 2%) is retained as elastic energy in the chip (hence safety glasses!)

Swaging

▪ Cuts narrow slit in work by a tool consisting of a series of narrowly spaced teeth ▪ Tool called a "saw blade" ▪ Typical functions: -Separate a work part into two pieces -Cut off unwanted portions of part -Cut outline of flat part

Peripheral Milling

▪ Cutter axis parallel to surface being machined ▪ Cutting edges on outside periphery of cutter *looks like a log

Face Milling

▪ Cutter axis perpendicular to surface being milled ▪ Cutting edges on both the end and outside periphery of the cutter

Machining in maufacturing sequence

▪ Generally performed after other basic ("Second Op") manufacturing processes, such as casting, forging, and bar drawing -Other processes create the general shape of the starting work part -Machining provides the final shape, dimensions, finish, and special geometric details that other processes cannot create

Cutting temps important

▪ High cutting temperatures result in the following: -Reduce tool life -Produce hot chips that pose safety hazards to the machine operator -Can cause inaccuracies in part dimensions due to thermal expansion of work material

Machining

▪ Material removal process in which a sharp cutting tool is used to mechanically cut away material so that the desired part geometry remains ▪ Most common application: metal parts ▪ Most versatile of all manufacturing processes for producing a variety of part shapes and geometric features with high precision and accuracy ▪ Casting can also produce a variety of shapes, but in general is not as accurate as machining

CNC benefits

▪ Reduced non-productive time ▪ Results in shorter cycle times ▪ Lower manufacturing lead times ▪ Simpler fixtures ▪ Greater manufacturing flexibility ▪ Improved accuracy ▪ Reduced human error

Milling

▪ Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface ▪ Two forms: peripheral milling and face milling

Requirements for HMS

▪ Special bearings designed for high rpm ▪ High feed rate capability (e.g., 50 m/min) ▪ CNC motion controls with "look-ahead" features to avoid "undershooting" or "overshooting" tool path ▪ Balanced cutting tools, toolholders, and spindles ▪ Coolant delivery that provides higher pressures ▪ Chip control and removal systems to cope with much larger metal removal rates

Machining operations

▪ Turning ▪ Drilling ▪ Milling ▪ Broaching ▪ Sawing ▪ Boring ▪ Form milling ▪ Hobbing

Disadvantages of Machining

▪ Wasteful of material -Chips generated in machining are wasted material ▪ Time consuming -A machining operation generally takes longer to shape a given part than alternative shaping processes ▪ COST

Why is Machining important?

▪Variety of work materials can be machined -Most frequently used to cut metals ▪ Variety of part shapes and special geometric features possible: -Screw threads -Accurate round holes -Very straight edges and surfaces ▪ Good dimensional accuracy and surface finish