antifriction guideways, feed drives, spindles

ANTIFRICTION GUIDEWAYS, FEED-DRIVES, SPINDLES.

V.Vedamsh Reddy B.Sai Kumar S.Trishool R.Sujith Reddy

Antifriction Or Linear Motion Guideways.Introduction• The main function of the guideway is to make sure that the cutting tool

or machine tool operative element moves along predetermined path.

• The Linear Motion Guideways provide a smooth and linear motion in machine tools, due to which higher accuracy and precision can be obtained.

Types of linear motion guideways

• Sliding contact linear motion guideways

• Rolling contact linear motion guideways

Rolling Contact Guideways• This type of linear guideways allows a type of linear motion that utilizes rolling elements such as balls or rollers.• By using placing rolling elements between the rails and the block, a linear guideway can achieve high precision linear motion and reduce friction.• These have less friction coefficient than slideways.

Lubrication When using an LM system, it is necessary to provide effective lubrication.

A lubricant has effects such as the following:

1. Minimizes friction in moving elements to prevent seizure and reduce wear.

2. Forms an oil film on the raceway to decrease stress acting on the surface and extend rolling fatigue life.

3. Covers the metal surface to prevent rust formation.

Advantages• High positional accuracy.• Long life with highly accurate motion.• High speed motion is possible with a low driving force.• Equal loading capacity in all directions.• Easy lubrication.

Feed drivesIntroduction

• The driving system is an important component of a CNC machine as the accuracy and

repeatability depend very much on the characteristics and performance of the driving system.

• The driving system is classified as spindle drives and feed drives.

• The spindle drives are used to provide angular motion to the work piece or a cutting tool.

• The feed drives are used to drive the slide or a table.

• The feed drive consists of an electricmotor and mechanical transmission elements.

Working principle of feed drive

Requirements of cnc feed drives.

• High torque-to-weight ratio.

• Low armature or rotor inertia.

• Low electrical and mechanical time constants.

• Permanent magnet construction.

• Maximum speed up to 3000rpm.

• High peak torque for quick response.

• The required constant torque for overcoming frictional and working force must be provided.

Electric motor• An electric motor is an electric machine that converts electrical energy into

mechanical energy

• Two types of electrical motors are commonly used.

I. Servomotors.

1. DC Servomotors.

2. AC Servomotors.

II. Stepper motors.

Servo motorWorking of a servo motor :

13

3.2 Components of servo controlled cnc

Motor speed control

Motor lead screw rotation table moves

position sensed by encoderfeedback

DC Servo Motor • This is the most common type of feed motors used in CNC machines• The principle of operation is based on the rotation of an armature

winding in a permanently energized magnetic field.

AC servomotor

• In an AC servomotor, the rotor is a permanent magnet while the stator is equipped

with 3-phase windings

• The speed of the rotor is equal to the rotational frequency of the magnetic field of the

stator, which is regulated by the frequency converter.

• AC motors are gradually replacing DC servomotors

• The main reason is that there is no commutator or brushes in AC servomotor so that

maintenance is virtually not required

• AC servos have a smaller power-to-weight ratio and faster response.

Stepping Motor

• A stepping motor is a device that converts the electrical pulses

into discrete mechanical rotational motions of the motor shaft

• This is the simplest device that can be applied to CNC machines

since it can convert digital data into actual mechanical

displacement

SPINDLES• It clamps the workpiece or cutting tool in such a way that the

workpiece or cutting tool is reliably held in position during the machining operation. • It imparts rotary motion or rotary /translatory motion to the cutting

tool or workpiece. • It is used for centering the cutting tool in drilling machine, milling

machine, etc. while it centers the workpiece in lathes, turrets, boring machine, etc.

Requirements of spindle • The spindle should rotate with high degree of accuracy. The accuracy

of rotation is calculated by the axial and radial run out of the spindle nose. • The spindle unit must have high dynamic stiffness and damping. • The wear resistance of mating surface should be as high as possible. • Deformation of the spindle due to heat transmitted to it by workpiece,

cutting tool, bearings etc. should be as low as possible. Otherwise it will affect the accuracy of the machining accuracy.

Thank you