Milling Processes Milling Processes

Objectives

The students are able to identify: Various Types of Milling Machine & Layout Industrial Applications Milling Tools Operation Factors - Speed, Feed, ... Milling Methods Planning & Setup Procedures Practices

Classification of Machining Processes

Milling Process Milling is a machining

operation in which a workpiece is fed past a rotating cylindrical tool with multiple cutting edge.

Multi-points cutting process

Chips are cut off by the rotating cutter

Workpiece is fed in linear motion

Tool with one cutting edge is called fly-cutter (rarely used)

CuttingDirection

Feed Direction

Workpiece

Milling Cutter

Tooth

Basic Milling Processes Two types of milling processes

Up milling or conventional milling process Down milling or Climb milling process

Up Milling (Conventional Milling) The metal is removed in form of small chips The chip thickness is minimum at the start of the cut and maximum at the end. Cutting force varies from zero to the maximum value

Advantages of Up Milling It does not require backlash eliminator It is safer in operation ( the cutter does not climb on the workpiece) Loads on the teeth are acting gradually Built-up-edge (BUE) fragments are absent from the machined surface The cutter is not affected by the sandy surfaces of the workpiece

Disadvantage of Up Milling The tendency of cutting force to lift the work piece from the fixtures and poor surface finish obtained

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut

FEED

Up Cut Cutter rotates in

a direction opposite to the table feed

FEEDCUTTER

Down Milling (Climb Milling) A cutter rotating in the same directions of the feed of the workpiece. Chip thickness is maximum at the start of the cut and minimum in the end. There is less friction involved and consequently less heat is generated on the

contact surface of the cutter and workpiece

Advantages Fixtures are simpler and less costly, as cutting forces are acting downward Flat workpiece (that cannot be firmly held) can be machined by down-milling Cutter with higher rake angles can be used, which decreases the power requirements Tool blunting is less likely Better surface finish It is characterized by less tendencies of chattering and vibration

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut

FEED

Down Cut Cutter rotates

in the same direction as the table feed

FEEDCUTTER

Up Cut Vs Down Cut

Up Cutting Will not cause

the table to a step motion

Recommended for conventional machine

Down Cutting Better surface

finishing Not suitable for

conventional machine Suitable for CNC

machine or the machine equipped with BACKLASH ELIMINATOR

Types of Milling Cutters

Type of Milling Cutter

Type of Milling Operations

Two basic type of milling operations Peripheral milling (Plain

Milling) Axis of the tool is parallel to

the surface being machined. Face milling

Example of Peripheral Milling (a) Slab milling; (b) Slot Milling; (c) Side Milling

(d) Straddle Milling (e) Form Milling

Peripheral Milling Direction of Cutter Rotation

Two form of milling Up milling and down milling

Up milling (Conventional milling): the direction of motion of the cutter teeth is opposite the feed direction when teeth cut into the workpiece. It is milling “ against the feed”

Down Milling (Climb Milling): the direction of cutter motion is the same as the feed direction when teeth cut into the workpiece. It is milling “ with the feed”

Face Milling The axis of the cutter is perpendicular the surface being milled. Various forms of face milling

(a) Conventional face milling; (b) Partial face milling; (c) End Milling; (d) Profile Milling; (e) Pocket Milling; (f) surface contouring Milling

Milling Method End Milling

Cutter axis perpendicular to the machined surface

Peripheral & end cutting edges

Vertical milling normally

PLAIN MILLING END MILLING

• Plain Milling– Cutter axis parallel to the

machined surface– Peripheral cutting edges– Horizontal milling normally

Milling Machines A Horizontal Milling Machine:

It has a horizontal spindle and well suited for performing the peripheral milling (e.g. slab milling, slotting milling, side milling and straddle milling)

A Vertical Milling Machine: It has a vertical spindle and well suited for

performing the face milling (e.g. end milling, surface contouring milling)

Horizontal Milling Machine

Spindle arbor rotates parallel to the table

Machine table moves along the 3 axes - X, Y, & Z

Cutter being used: Slab milling cutter Side & face cutter Slitting saw

y

x

z

Cutters for Horizontal Milling Machine

SLAB MILLING CUTTER

SIDE & FACE CUTTER

SLITTING SAW

Vertical Milling Machine

Spindle rotates perpendicular to the table normally

Milling Head can be adjusted in different angle

Cutter being used : End mill Face milling cutter

Cutters for Vertical Milling Machine

END MILL FACE MILLING CUTTER

Type of Milling Machines Other than spindle Orientation, Milling machines can

be classified into the following types Knee and Column Milling Machine Bed Type Milling Machine Planer Type Milling Machine CNC Milling machines

Special purposes milling machine Rotary table milling machines Drum type milling machines Tracer Controlled Milling machine Thread Milling Machine Key-way Milling Machine Skin and Spar Milling Machine Planetary Milling machine

Knee and Column Milling Machine

Planer Type Milling Machine

Rotary Table Milling Machine

Surface Finishing Cylindrical marks are left on

surface by end milling Parallel marks are left on

surface by plain milling Roughness of milling is

directly proportional to the feed rate & depth of cut

Finishing measurement (Roughness Value) in millingRa = 6.3 ~ 0.8 mm

END MILLING

PLAIN MILLING

Tool Life Tool life is defined as the length of cutting time that the tool

can be used. Operating the tool until final catastrophic failure is also defined as tool life.

Taylor Tool Life Equation is expressed as

Milling cutter is a Multi-point cutting tool Ground by special grinding machine Precision cutting angles

Cutter re-shape is very time consumable Tool life can be increased by

Correct spindle speed & feed rate Apply cutting fluid Correct cutting method

used.criterion life tooland toolingmaterials, work cut, ofdepth

feed,on depend values whoseparameters are and

(min); life tool (m/min); speed cutting Where,

Cn

TV

CVT n

Tool Material High Speed Steel

An alloy of iron, chromium, nickel, cobalt & some molybdenum etc..

High resistance to wear, loss hardness at 600°C Two basic types:

Tungsten –type (T-grades by AISI) Molybdenum –type (M-grades by AISI)

Carbide Widely apply in modern industry Suitable for very higher cutting speed, hard material, &

high accuracy Smooth surface

Ceramic & Diamond cutting tool

Cutting Speed Cutting Speed of milling is defined by the

movement of each cutting edge per minute (m/min)

TOOLMATERIAL

HIGH SPEEDSTEEL

CARBIDE

MATERIAL

ALUMINUM

MILD STEEL

HARDEN STEEL

Cutting Speed

m / min.

Cutting Speed

m / min.

Feedmm/Tooth

Feedmm/Tooth

25

100

0.08

0.15

100

500

50

0.15

0.3

0.1

Machining Variables and RelationshipsFormula

Cutting Speed

Feed rate

Cutting Time

Material Removal Rate

Power, hp (cutter)HP (actual)=HP (tare) + HP (actual)/Em

1000

DNV

NnfF tr

F/LT dFWMRR c

MRRHPCutterHP u

efficiencyMotor

air) (cutting machinerun to(kW) horsepower HP(tare)

milling,slab/slot for

(mm) milling, Face/endfor Lead, ofLength

; cut ofDepth ;Overtravel and Pretravel Length Lead Length Piece

/minmmMRR th,cutter tee ofnumber mm/rev; mm/min, rpm,

mm, diameter, or toolDiameter Workpiecem/min; ,Speed Cutting

22

3

m

tr

E

dDddRRl

Dl

dL

nfFN

DV

Example An end mill is used to put a 25-mm slot with a depth of 5 mm in a cast

iron block with a high-speed cutter. The block is 50 mm wide, 20 mm tall, and 100 mm long. The cutter, a high-speed cutter with a diameter of 25 mm, has four teeth. The pretravel and overtravel combine to a total length of 5 mm. The cut will be made at a feed rate of 0.130 mm/tooth and a cutting speed of 40 m/min. The unit kilowatt power is 0.005 kW/mm3/min, the tare horsepower is 75 kW and the motor efficiency is 80 %. Figure indicates the final shape to be produced.

(1) What is the RPM used?

(2) What is the length of the lead?

(3) What is the cutting time?

(4) What is the metal removal rate?

(5) What is the power (kW) required at the cutter?

(6) What is the motor horsepower requirements?

Sample Calculation

Data Given Width of cut, Wc = 25 mm Depth of cut, d = 5 mm Diameter of cutter, D = 25 mm Number of teeth , nt = 4 Pretravel and Overtravel = 5 mm Feed , fr = 0.130 mm/tooth Unit horsepower, HPu = 0.005 kW/mm3/min Tare horsepower, Hptare = 75 kW Motor efficiency, Em= 80% = 0.8

(1) Cutting speed:

(2) Length of Lead for end milling, l = D = 25 mm(3) Cutting time, T= L/F Length of Lead, L = Piece length+ Lead length +

pretravel and Overtravel L = 100+25+5 = 130 mm

(4) Material removal rate:

(5) Power(6) Motor power requirement

rpm 510(25)

(40)10001000

1000

D

VN

DNV

min 49.0265

130

F

LT time,cutting The

mm/min 2655104130.0 rate, Feed

NnfF tr

/minmm 33125265525MRR 3 dFWc

kW 155/minmm 331250050 3 .MRRHPcutterHP u

kW 75268kW/0.8 155kW 75/minmm 331250050 3 ..

E/cutterHP)Tare(HP)Actual(HP m

Cutting Fluid Cooling the workpiece & the cutting tool

Maintain hardness of cutting tool Provide lubrication

Reduce fraction between workpiece & cutting tool

Wash away the chips Prolong tool life

Soluble oil is widely use in our workshop 5 ~ 20 % soluble oil mixed with water

SAFETY

Consult Staff Where are the Dangerous Points

Familiar with the Controls

Stop the Machine in Emergency

Only One Man Operates One Machine

Suitable & Safety Protection of Yourself

Don't Leave the Machine when it is Running

Don't Touch the Work while it is Running

Don't Operate the Machine Without Staff Supervised

End End