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CNCMachine
MachineComponents
Section (1)
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CNC Machine Components:
1. Machine structure (Base, Column, Bed).2. Guideways.
3. Spindle & Spindle Bearings.
4. Ballscrews.
5. Torque Transmission units.
6. Tool Changing Mechanism.
7. Coupling & Connection.
Machine Structure:
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Bed:
It is the means of holding and moving the work and tool. It comes under the linking structure and
generally made up of cast iron. it supports the table mounted on base guideways.
Table:
It is placed upon the saddle for the purpose of holding the work piece and moving it in desired
position in X axis on commanding. It is made up of cast iron.
Column:
This is vertical orientation made of cast iron, with column it is possible to move head up on
down and perform the process of cutting or milling.
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Saddle:
The mechanical components of the machine must be rigid and strong to support the quickly
moving parts.
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Cast iron used to be the material of choice for metal-working machines. Today, most
machines make liberal use of weldments of hot-rolled steel and wrought products such
as stainless steel to reduce cost and allow fabrication of more intricate frame designs.
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Ballscrews:
The mechanisms that move the bed or spindle are called ballscrews. These change rotary
motion of the drive motors into linear motion and consist of a screw shaft and support
bearings. As the shaft turns, a bearing mount follows the spiral grooves in the shaft and
produces a very accurate linear movement that moves either the worktable under the
spindle, or the spindle carrier itself. These ballscrews are bolted to the base with the
bearing mount bolted to the worktable or spindle carrier.
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S pindle
The spindle is machined and ground, mounted to its drive motor, and then bolted to the
movable spindle carrier. Each axis of motion has a separate ballscrew and set of ways in
most machining center.
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CNC Machine Guideways:
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High speed high accuracy linear guide way
1. Linear guide ways with zero backlash ensures consistent cutting surface on curve or slope
cutting.
2. Suitable for high speed travel and the power requirement is minimized.
3. By using rolling contact instead of sliding contact, linear guide reduces friction loss but
increases positioning accuracy.
4. The loading capacity is high on multiple directions. Cutting rigidity can be ensured.
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5. Long service life is guaranteed by its high durability.
Hydrostatic Guideways:
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Advantages of Hydrostatic Linear Guideways :
Superior vibration damping
Improved hard turning capabilities
Significantly longer tool life
Longer machine life
Increased axis speeds
Improved part roundness
Improved part surface finish
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Linear bearings with balls, rollers or needles:
Because of the problem of metal to metal contact the relative high amount of friction is
generated, which exits between the faces in contact, typically 0.15 for lubricated steel sliding on
steel. A number of machines have flat roller bearings fitted to the carriages to provide a rolling
motion rather than sliding motion. The rollers are in contact with the guideways machined on the
bed of the machine.
To reduce the problem of machining an accurate form on the bed of the machine, hardened steel
rails with special guide forms (figure....) may be bolted on the casting of the machine tool.
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Tool Changing Mechanism:
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The CU system is a mechanical cam-driven tool changer that combines an intermittent
series of linear and rotary movements necessary to change the tool:
-cone gripping
-extraction (from the tool pocket and from the spindle)
-changeover
-insertion (in the tool pocket and in the spindle)-release
A mechanical tool safety lock on the gripper holder arm makes sure the tools are
transferred safely during the changeover phase.
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Tool extraction station operated by a pneumatic cylinder
Rigid Coupling
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This type of coupling has no flexibility or resilience, hence it is necessary for the shafts
that are to be connected to be in good alignment, both laterally and angularity, in order
excessive loads on the coupling, on the shafts, or on the shaft bearings.
Rigid couplings do not accommodate misalignment and consequently should not be
used indiscriminately.
Types of Rigid Couplings:-
1.1 Sleeve or muff coupling
1.2 Clamp coupling
1.3 Flange coupling
Easiest, lowest cost, for CNC
routers and cnc lathes, they are easily available, are self-aligning, do not damage the
motor shaft, and make a 100% connection from motor to screw, one trick when using a
solid coupling is to use a simple thrust washer, placed on the motor shaft between the
motor face and coupling, using a thrust washer will take any linear load of the screw,
allowing the motor, coupling and screw a total direct connection with almost zero end
play.
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Driving System :
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Types Of Drives:
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