Milling by milling are both ferrous and

Milling machine – training Program

 

Introduction

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?     
Milling produces
3-dimensional shapes with a rotating multi-edge cutting tool by removing
material.

?     
Milling Machines are
versatile machine tools with wide range of metal cutting capacity, can
performing multiple operations like milling, drilling, indexing, gang milling,
straddle milling etc.

?     
Milling is the process of machining flat, curved, or
irregular surfaces by feeding the work piece against a rotating cutter
containing a number of cutting edges..

?      Various materials commonly
processed by milling are both ferrous and nonferrous components obtained by the
following processes: castings, forgings, Hot and cold rolled or drawn shapes,
Extrusions, Powder metal and cold formed

 

Parts produced

 

Milling process in used to
produce Several components like engine casings, couplers, flanges, turbine
blades, automobile engine blocks and automobile cylinder heads, open end
wrenches and other hand tools, gearboxes, brackets, ribs, fittings, flanges,
spars, beams, pumps, printing presses, machine tool components, aircraft parts,
etc.

 

Types Of Milling Machines

?      Milling Machines are
classified into two main types namely Horizontal Milling Machine and Vertical
Milling Machine. The name Horizontal or Vertical is given to the machine by
virtue of its spindle axis.

?      For conventional machines,
the axes are controlled by manual rotation of knobs, if these axis are
controlled by Computer numerical control (CNC) they are called CNC Horizontal
Machining center and CNC Vertical Machining center respectively

 

Common Parts
for both Vertical & Horizontal Milling Machine

?      Base: The base of the milling
machine, along with the column, are the major structural components. They hold,
align, and support the rest of the machine.

?      Column: The column houses the
spindle, the bearings, the gearbox, the clutches, the shafts, the pumps, and
the shifting mechanisms.

?      Knee: The knee mounted in
front of the column is for supporting the table and to provide an up or down
motion along the Z axis.

?      Saddle: the saddle is mounted
on top of knee. It provides motion along y axis. The saddle consists of two
slide ways, one on the top and one at the bottom located at 90º to each other,
for providing motions in the X or Y axes by means of lead screws.

?      Table: The table is mounted
on top of the saddle and can be moved along the X axis. On top of the table are
some T-slots for the mounting of work piece or clamping fixtures.

?      Spindle: The spindle holds
the tool and provides the actual tool rotation.

?      Spindle Reverse Lever: This
knob controls the direction of spindle rotation, the lever position of this
knob determines the spindle direction. The middle position is the neutral
position. Moving this lever up, rotates the spindle clockwise, moving
this lever down, rotates the spindle anti-clockwise.Never move the
spindle reverse lever when the spindle is turning.

?      Feed Rate Selection Lever:
The feed rate selection lever is used to change the feed rate setting. The feed
rate settings are expressed in inches per minute.

?      Spindle Start and Stop
Buttons: The Spindle start and stop Buttons control the power to the main motor
for the machine. Switching the start button will start the spindle rotation,
switching the stop button will stop the spindle rotation.

 

Exclusive Parts of Horizontal Milling Machine

?      Arbor: The arbor is an
extension of the spindle for mounting cutters.

?      Overarm: The overarm provides
for correct alignment and support of the arbor and various attachments. It can
be adjusted and locked in various positions, depending on the length of the
arbor and the position of the cutter

 

Exclusive Parts of Vertical Milling Machine

?      Spindle Speed Wheel: The
spindle speed wheel is used to change the spindle R.P.M. the spindle speed can
only be changed only when the spindle is stopped condition. The machine usually
has a geared head so the spindle speed can only be changed when the spindle is
stopped.

?      HI-NEUTRAL-LO LEVER: The Hi-Neutral-Lo Lever is used to put the
attachment into either back gear or direct drive. Neutral is provided to permit
free spindle rotation for indicating and setup work. In the high speed position
(direct drive) the spindle is driven by tapered clutch teeth.

?      Drawbar: A drawbar or spindle
drawbar is a clamping mechanism for tool holders on machine tools. The tool
holder or machine taper itself is held by the drawbar and applies force to the
spindle

?      Spindle Brake : it is used
apply brake on the spindle, without stopping the machine

?      Quill Lock: it is used to lock
the movement of quill. Rotate handle clockwise to lock quill in position;
counter-clockwise to release

?      Gibb lock; they are used to
lock the table & saddle movements.

 

Milling
Tools

The teeth of
milling cutters may be made for right-hand or left-hand rotation, and with
either right-hand or left-hand helix. The vertical milling machines uses the
cutters with shank and the horizontal milling machine cutters are hollow. Milling cutters are broadly
classified as,

(a) Profile sharpened cutters – where the geometry of the machined surfaces
are not related with the tool shape, viz;
i. Slab or plain milling cutter : ? straight or helical fluted
ii. Side milling cutters – single side or both sided type
iii. Slitting or parting tools
iv. end milling cutters – with straight or taper shank
v. Face milling cutters

 

(b) Form relieved cutters – where the job profile
becomes the replica of the tool-form,

i. Form cutters
ii. Gear (teeth) milling cutters
iii. Spline shaft cutters
iv. Tool form cutters
v. T-slot cutters
vi. Thread milling cutter

 

Horizontal Milling Machine Cutters

?      Slab Mills: For heavy cutting
of large and flat surfaces.

?      Side and Face Cutters: This type
of cutters has cutting edges on the periphery and sides of the teeth for
cutting shoulders and slots.

?      Slitting Saws: For cutting
deep slots or for parting off.

?      Angle Milling Cutters: Common
operations performed with angle cutters are cutting V-notches and serrations.
Angle cutters may be single-angle milling cutters or double-angle milling
cutters. The single-angle cutter contains side-cutting teeth on the flat side
of the cutter. The angle of the cutter edge is usually 30°, 45°, or 60°, both
right and left. Double-angle cutters have included angles of 45, 60, and 90
degrees.

?      Gear Hob: Hobs are generally
used for such work as finishing spur gears, spiral gears, and worm gears. They
may also be used to cut ratchets and spline shafts.

?      Concave and Convex Milling
Cutters: Concave and convex milling cutters are formed tooth cutters shaped to
produce concave and convex contours.

?      Corner Rounding Milling
Cutter: The corner-rounding milling cutter is a formed tooth cutter used for
milling rounded corners on workplaces up to and including one-quarter of a
circle. Generally used for such work as finishing spur gears, spiral gears, and
worm wheels. They may also be used to cut ratchets and spline shafts.

 

Vertical Milling Machine Cutters

?      End Mills: Commonly used for
facing, slotting and profile milling.

?      Rough Cut End Mills: For
rapid metal removal.

?      Slot Drills: For producing
pockets without drilling a hole beforehand.

?      Face Milling Cutters: For
heavy cutting.

?      T-slot milling cutter: The
T-slot milling cutter is used to machine T-slot grooves in worktables, fixtures,
and other holding devices.

?      Special Shaped-Formed Milling
Cutter: Formed milling cutters have the advantage of being adaptable to any
specific shape for special operations. The cutter is made especially for each
specific job.

 

Single purpose end mills such as Woodruff key seat
cutters, corner rounding cutters, and dovetail cutters are used on both
vertical and horizontal milling machines. Several other types of milling
cutters are employed for many other machining work like cam milling, keyway
cutting, and making hob cutter and so on. For enhancing capability range of
milling work a number of attachments are fitted in the milling machines. Such milling
attachments include
• universal milling and spiral milling attachment
• indexing head – simple, compound and differential type
• universal milling and spiral milling attachment
• copying attachment (mechanical and hydraulic)
• slotting attachment

 

Selection of
milling cutters

 

·        
High-speed steel
(HSS), stellite, and cemented carbide cutters are widely used. The advantage of
HSS is that it can be re-sharpened if the cutting edge is worn out.

·        
The harder the
material, the greater will be the heat that is generated in cutting. Cutters
should be selected for their heat-resisting properties.

·        
Use a coarse-tooth
milling cutter for roughing cuts and a finer-toothed milling cutter for light
cuts and finishing operations.

·        
The milling cutter
should be small enough in diameter so that the pressure of the cut will not
cause the work piece to be sprung or displaced while being mille.

·        
In selecting a
milling cutter for a particular job, choose one large enough to span the entire
work surface so the job can be done with a single pass. If this cannot be done,
remember that a small diameter cutter will
pass over a surface in a shorter time than a large diameter cutter which is fed
at the same speed.

 

 

Types of
Milling

 

Up Cut Milling or
conventional milling: In up cut milling, the cutter rotates in a direction
opposite to the table feed. Down cut milling or climb milling: the cutter
rotates in the same direction as the table feed, will require less power in
feeding the table and give a better surface finish on the work piece

 

?      Plain Milling: Plain milling
is the milling of a flat surface with the axis of the cutter parallel to the
machining surface. It can be carried out either on a horizontal machine or a
vertical machine.

?      End Milling: End Milling is
the milling of a flat surface with the axis of the cutter perpendicular to the
machining surface.

?      Gang Milling: Gang milling is
a horizontal milling operation that utilizes three or more milling cutters
grouped together for the milling of a complex surface in one pass.

?      In straddle milling, a group
of spacers is mounted in between two side and face milling cutters on the
spindle arbor for the milling of two surfaces parallel to each other at a given
distance.

?      Face milling. Machining flat
surfaces which are at right angles to the axis of the cutter

?      Angular milling. Machining
flat surfaces which are at an inclination to the axis of the cutter.

?      Form milling. Machining
surfaces having an irregular outline

?      Special Operations:
Explanatory names, such as sawing, slotting, gear cutting, and so forth have
been given to special operations. Routing is a term applied to milling an
irregular outline while controlling the work piece movement by hand feed.

 

IV. Slab (Horizontal) Milling

Terms Used:

N: RPM of
Cutter

n: Number
of Teeth on Cutter

W: Width of
cut (may be full cutter or partial cutter)

t: depth of
cut

V: cutting
speed — a Handbook value

L: Length
of pass or cut

fm:
Table (machine) Feed

ft:  feed/tooth of cutter — a Handbook value

D: Cutter
Diameter

 

Cutting Speed:

 

 

 

 

 

 

 

If Cutting Speed for a given
RPM rate is desired, solve above equation for V: V = pND/k

 

B. Table Feed Rate:

 

 

C. Cutting Time:

 

 

 

 

D. Material Removal Rate:

 

 

 

 

Remember that the length of
approach calculated here puts the cutter against the work at the start, we will
add a small additional air gap to spin the tool to speed and allow the table to
achieve target feed rate before chip making begins.  When determining cutting time and MRR, care
must be exercised.  Ask yourself if total
cutting time or time to make one pass across the part is being requested, ie.
is a single or multiple pass operation to be studied.  Also, note that in the MRR equation the
“cutting time” term does not include the time of partial engagement (LA).  Again, if a multi-pass operation is being
employed, the appropriate width term should be used in the MRR equation.

V. Face (Vertical)
Milling

 

 

Terms Used:

N: RPM of
Cutter

n: Number
of Teeth on Cutter

W: Width of
cut (may be full cutter or partial cutter)

t: depth of
cutter engagement

V: cutting
speed — a Handbook value

L: Length
of pass or cut

fm:
Table (machine) Feed

ft:  feed/tooth of cutter — a Handbook value

D: Cutter
Diameter

LA:
Approach Length

LO:
Length of “OverTravel”

 

 

 

A.   Cutting Speed:

 

 

If Cutting Speed for a given
RPM rate is desired, solve above equation for V: V = pND/k

 

B. Table Feed:

 

 

 

 

 

 

C. Cutting Time. Here
several situation must be considered, these include:

1. Tool Not
Fully Engaged with W D/2

3. Tool
Fully Engaged, Roughing
Pass — Doesn’t require
“Full Wipe”

4. Tool
Fully Engaged, Finishing
Pass — requires “Full
Wiping Action”

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D: Metal Removal Rate:

 

 

 

 

 

 

Again, the cautions on
single vs. multiple pass CT and MRR apply as with Slab Milling. Remember too,
that the length of approach here puts the cutter against the work at the start,
we will add a small additional air gap to spin the tool to speed and allow the
table to achieve target feed rate before chip making begins.  Also, care should be exercised with regards
to units.