CNC Turning and Milling centres

Presentation on

Presented by

ACHYUTH P & TEAM

BOARD OF TECHNICAL EDUCATION, KARNATAKA

DEPARTMENT OF MECHANICAL ENGINEERING

Information source: Internet

Reference websites:

www.wikipedia.com/metal lathe

www.elearning.vtu.ac.in

Contents

Classification of CNC Machining centres

Special features of CNC Turning and Milling centres

Configuration of CNC Machine control unit

Advantages of CNC Turning and Milling centres

Introduction to CNC, Turning and Milling operations

CNC:-It indicates “Computer and Numerically controlled”, It is defined as

“Automation of machine tools operated by precisely programmed commands with

computer playing important role of control ”

Milling:-Milling is a machining operation of producing flat, helical surfaces by

means of multiple cutting edged rotating tools called “Milling Cutters”. After the

advent of computer numerical control (CNC), milling machines evolved into

milling machining centers

CNC MILLING CENTER

Turning:-Turning is a machining process carried out in lathe machine, Where tool

moves parallel to axis of lathe and removes diameter of material.

CNC Lathes or Turning centres are rapidly replacing older producing lathes

CNC LATHE or CNC TURNING CENTER

CNC Machining centres are classified THREE types

1.A vertical machining centre (VMC) :-It has its spindle on a vertical axis relative to

the work table vertical machining centre is typically used for flat work that requires

tool access from top.

Milling Centre is a type of vertical machining centre

2.A horizontal machining centre (HMC):-It is used for cube shaped parts where tool

access can be best achieved on the sides of the cube.

Turning centre or Lathe is a type of Horizontal machining centre

3. A universal machining centre (UMC) :-It has a work head that swivels its spindle

axis to any angle between horizontal and vertical making this a very flexible machine

tool.

CNC machining centers are usually designed with features to reduce non productive

time. The features are:

• Automatic tool changer :-

The tools are contained in a storage unit that is integrated with the machine tool.

When a cutter needs to be changed, the tool drum rotates to the proper position and an

automatic tool changer (ATC) operating under program control, exchanges the tool in

the spindle for the tool in the tool storage unit. Capacities of tool storage unit

commonly range from 16 to 80 cutting tools.

• Automatic work part positioner:-

Many horizontal and vertical machining centers have the capability to orient the work

part relative to the spindle. This is accomplished by means of a rotary table on which

work part is fixtured. The table can be oriented at any angle about a vertical axis to

permit the cutting tool to access almost the entire surface of the part in a single setup.

• Automatic pallet changer:-Machining centers are often equipped with two (or more) separate pallets that can be

presented to the cutting tool using an automatic pallet changer. While machining is

performed with one pallet in position at the machine, the other pallet is in a safe

location away from the spindle. In this location, the operator can unload the finished

part and then fixture the raw work part for next cycle.

Memory

• ROM – Operating System

• RAM – Part Program

Central Processing Unit (CPU)

• Operator panel

• Tape reader

Machine tool controls

• Position control

• Spindle speed control

Sequence controls

• Coolant

• Fixture clamping

• Tool changer

System bus

Configuration of CNC machine control unit

CNC PROGRAMMING

CNC is the part program is a set of encoding information, giving

co-ordinates and other details to indicate how a tool should move

in a relation to a work piece in a machine should perform

desirable operation on the job.

CNC controls will be the program and execute the operations. The

program is prepared by co-ordinate values (XYZ) of the entire tool

path as suited to machine to complete the component and it also

contains the following basic information.

•Preparatory function (G code)

•Miscellaneous function (M code)

•Spindle speed (S)

•Feed rate (F)

•Tool number (T)

A part program contains a set of instruction which is written in

different block in the order of execution of different operations to

be performed on the job.

The part program contains a string of blocks which defined as the

sequence of operations. Each block contains a set of letters and

numerical values and followed by and charecters. The length of

the block is sufficient to accommodate 120 charecters and at the

each time.It can display 80 charecters. The block numbers will be

entred with adress N. The block numbers are freely selectable.

Structure of CNC part program

Structure of CNC part program

Preperatory functions (Or) G codes

These codes are assosiated with the axis movement of the machine. The G code starts

from zero and end upto 96.Normally the G codes will define path of the tool.

M- codes (Miscellaneous functions)These codes are concerned with the operation of the machine tool.

Following are some of the important M-codes used in the part

programming.

CNC milling is a specific form of computer numerical controlled (CNC) machining. Milling itself is a machining process similar to both drilling and cutting, and able to achieve many of the operations performed by cutting and drilling machines. Like drilling, milling uses a rotating cylindrical cutting tool. However, the cutter in a milling machine is able to move along multiple axes, and can create a variety of shapes, slots and holes. In addition, the work-piece is often moved across the milling tool in different directions, unlike the single axis motion of a drill.

CNC milling devices are the most widely used type of CNC machine. Typically, they are grouped by the number of axes on which they operate, which are labeled with various letters. X and Y designate horizontal movement of the work-piece (forward-and-back and side-to-side on a flat plane). Z represents vertical, or up-and-down, movement, while W represents diagonal movement across a vertical plane. Most machines offer from 3 to 5 axes, providing performance along at least the X, Y and Z axes. Advanced machines, such as 5-axis milling centers, require CAM programming for optimal performance due to the incredibly complex geometries involved in the machining process. These devices are extremely useful because they are able to produce shapes that would be nearly impossible using manual tooling methods. Most CNC milling machines also integrate a device for pumping cutting fluid to the cutting tool during machining.

Example of CNC Milling program

HOW IT WORKS ?

During CNC milling the computer translates the design into instructions on how the drill needs to move to create the shape.

Typically, the drill can move up down, or tilt at an angle, and the table moves the part laterally.

For complex parts, the part may need to be rotated at some point in the milling process.

Because the process is run by a computer, high resolutions, and greater throughput are possible.

Materials used for CNC Milling Tools Aluminum Carbon Steel

Stainless Steel

Titanium

Brass

Copper

Fiberglass

Magnesium

Plastic

Plasticized Woods

Foam

CNC TURNING

CNC Turning is manufacturing process in which a

round(cylindrical) material is held in a chuck and rotated

while a tool is fed to the piece to remove material to create

the desired shape. CNC lathes or turning centers have

tooling mounted on a turret which is computer-controlled.

CNC’s with “live” tooling

Example for CNC Turning programProgram

O 1005

[BILLET X32 Z60

G21 G98

G28 U0 W0

M06 T03

M03 S1200

G00 X32 Z1

G01 X5 F45

Z0

X10 Z-10

Z-15

G02 Z-25 R10 F25

G01 Z-30 F45

G03 X25 Z-37 R10 F25

G01 X25 Z-37 R10 F25

G01 Z-42 F45

X30 Z-45

Z-52 G28 U0 W0

M05

M02

How it works ?

Designed mainly for machining shaft-type workpieces

supported by chuck and heavy-duty tailstock center

On four-axis machines, two opposed turrets, mounted on

separate cross-slides

One above and one below center line of work

Balance cutting forces so extremely heavy cuts can be

taken on workpiece

Turning Center Equipments

Steady rest◦Allow facing and threading on end of shafts

Follower rest◦Used to support long, thin shafts

Bar-feeding mechanism◦ Permits machining of shafts and parts from bar stock

smaller than spindle through-hole Production part loader◦ Can complete part changeover when individual precut

shafts machined

Reduced lead time

Elimination of operator errors

Less Operator activity

Less Labor Cost

Longer Tool Life

Elimination of special Jigs and Fixtures

Flexibility in changes of product design

Reduced inspection

Reduced Scrap

Accurate costing and scheduling