Manufacturing Process II

Unit: 3 Milling

According to WBSCTE revised syllabus of 2022

3.1 Basic concept on milling (up milling, down milling).
3.2 Classification of milling machines.
3.3 Basic parts and their functions of plain milling machine and universal milling machine.
3.4 Specification of milling machines.
3.5 Types of milling cutters.
3.6 Nomenclature of plain milling cutter.
3.7 Milling machine operations: Plain milling, face milling, side milling, straddle
milling, angular milling, gang milling, form milling, end milling, milling keyways, grooves and slots.
3.8 Cutting parameters and machining time calculation for plain milling operation (simple numerical)

Basic Concept

• A milling machine is a machine tool that removes metal as work piece fed against a rotating multipoint cutter.
• A milling cutter is a cutting tool of milling ( machine ), which are available in many shapes and standards.
• Milling can be used for enlarging or making a hole, producing slots, removing layer of material from a surface, making internal & external threads, gear cutting etc.
• In Conventional Milling generally the tool rotates at one fixed place and the feed is provided to the work piece.
• But in case of CNC Milling the tool also moves relative to the work piece that means feed motion is provided by relative movement of work piece table and the cutting tool.

Basic parts and their functions of Plain Milling

1. Base
2. Column
3. Knee
4. Saddle
5. Table
6. Overhanging arm
7. Front brace
8. Spindle
9. Arbor

Fig: Schematic diagram of a plain milling machine

Basic parts and their functions of Plain Milling

Base:

• It is the foundation member for all other parts of a milling machine.
• It carries the column at one end.

Column:

• It is the main supporting member mounted vertically on the base.
• It is a boxed shaped column.
• It houses all the driving mechanism for the spindle and the table feed.
• The front vertical face of the column is machined very accurately & it has a dovetail guide way to support the knee.

Knee:

• Knee is a large & rigid machine part, generally made up of Grey cast iron.
• Knee can move up & down along the vertical guide way provided on the column.
• It is supported by an elevating screw, which is mounted on the base & is also used to adjust the height of the knee.
• The knee houses different controls of the feed mechanism of the table.

Saddle:

• It is placed on the top of the knee.
• It can slide on the guide ways set exactly at 90˚ to the column face.
• The top of the saddle provide guide way for the table.

Over Hanging Arm:

• It is mounted on the top of the column, which extend beyond the column face.
• It acts as a bearing support for the other end of the arbor.

Spindle:

• It is located in the upper part of the column.
• It receives power from the main motor through belt drive or gear drive via a clutch.
• Clutch engages and disengages the main motor with the arbor at the will of the operator.

Arbor:

• It is the mechanism where the milling cutter is mounted & is allowed to rotate for metal removal.
• The arbor assembly consists of the following parts like arbor, spindle, spacing collars, bearing, cutter, draw bolt, lock nut, keyblock, set screw.

Types of Milling Machine

Horizontal Column and Knee type Milling Machine

•It is the simplest form of milling ( machine ).
•In this milling, the work piece can be fed in all three axes and this process is suitable for short production.
•In this milling heavy work piece cannot machined and the operation is slow because of large number of controls.

Vertical Column and Knee type Milling Machine

•In this machine, cutter spindle have vertical position and the table movements are horizontal, vertical and transverse.
•In vertical milling, over arm is small and provides a strong support for the spindle and spindle can be moves up and down to perform the operations like grooving, facing etc.

Universal Column and knee type Milling Machine

•It is similar to the horizontal milling but the table is placed on the swivel and swivel is placed on the saddle.
•The machine can be produce spur, spiral, bevel gears, twist drills, reamers, milling cutters, etc. besides doing all conventional milling operations.

Planner Milling Machine

• It’s mostly use for facing operation in mass production.
• These cutters can perform the facing operations simultaneously.

Note: Notice that it looks similar to a planner, but can perform milling, and the worktable can not reciprocate.

Milling Machining Centre/ CNC Milling

Its a completely automatic milling machine, which is capable of performing various types of machining operations. We will dicuss more about this machine tool, in 5th Semester.

Special Purpose Milling Machine

• These machines are the modern milling machines which are developed to easy the milling operations according to the requirement of the job (special job requires special machine tool).

a. Rotary table milling machine
b. Drum milling machine
c. Planetary milling machine
d. Pantograph, Profiling & Tracer controlled milling etc.

Note: You do not need to know much about these machines, just remember the names.

Specification of a Milling Machine

• The dimensions of the working surface of the table,
• Maximum length of longitudinal, cross & vertical travel of the table,
• No of spindle speeds & feeds,
• Power available,
• Floor space required,
• Net weight of the machine.

Types of Milling Cutters

• A milling cutter is a cutting tool of milling ( machine ), which are available in many shapes and standards.
• The teeth may be straight or at a helix angle and helix angle helps milling cutter for a slow engagement of the tool to distribute the forces.

1. Plain cutters
2. End milling cutter
3. Face milling cutter
4. Slab milling cutter
5. Hollow milling cutter
6. Metal slitting saws
7. Side and face milling cutter
8. Single, double and equal angle cutters
10. T -slot, dovetail, single and double corner rounding cutters etc.

Note: You can remeber and understand the types of milling cutter with their uses, i.e., types pf milling operation that they can perform.

Nomenclature of Plain Milling Cutter

Types of Milling Machine Operations

1. Plain milling or Slab milling
2. Face milling
3. Side milling
4. Angular milling
5. Gang milling
6. Form milling
7. End milling

8. Profile milling
9. Saw milling
10. Key way milling
11. Gear cutting milling
12. Helical milling
13. Flute milling
14. Straddle milling
15. Thread milling

Plain milling or Slab milling

• It is a method of producing a plain, flat, horizontal surface parallel to the axis of
rotation of the cutter.
• Depending upon the direction of cutter and work piece movement plain milling can be sub-divided into two types i.e.,

Up-Milling & Down-Milling

Up-Milling

Down-Milling

Face Milling

• It is a method of producing a flat surface at right angle or perpendicular to the axis of the
cutter.
• The type of milling cutter used in this process is known as face milling cutter.

Side Milling

• It is a method of producing of a flat vertical surface on the side of a work piece, using a side milling cutter.

Angular Milling

• It is a method of producing of a flat surface with an angle to the axis of
the cutter.
• The type of milling cutter used in this process is known as angular milling cutter.

Gang milling

• It is a method of milling with the help of two or more milling cutters at a time having
same or different diameters mounted on the Arbor of the milling machine.
• The type of milling cutter used in this process is known as gang milling cutter.

Form Milling

• It is a method of producing a surface having an irregular
geometry.
• The type of milling cutter used in this process is known as form milling cutter.

End Milling

• It is method of producing slots, flat surfaces & various types of profiles.
• The type of milling cutter used in this process is known as end milling cutter.

An end milling process consists of a cylindrical cutter that has multiple cutting edges on both its periphery and its tip, permitting end cutting and peripheral cutting. These cutting edges or flutes are usually made helical to reduce the impact that occurs when each flute engages the workpiece.