cnc 2 unit palanivendhan cnc elements
DESCRIPTION
PALANIVENDHAN CAM CNC ELEMENTS FEATURES OF CNCTRANSCRIPT
Computer Aided Manufacturing
M.PALANIVENDHAN
Department of Automobile Engineering
SRM University, kattankulathur campus
HISTORY
US Air Force commissioned MIT to develop the first "numerically controlled" machine in 1949. It was demonstrated in 1952.
At 1970-1972 first Computer Numeric Control machines were developed.
Today, computer numerical control (CNC) machines are found almost everywhere, from small job shops in rural communities to companies in large urban areas.
Basics of CNC
A numerical control, or “NC”, system controls many machine functions and movements which were traditionally performed by skilled machinists.
Numerical control developed out of the need to meet the requirements of high production rates, uniformity and consistent part quality.
Programmed instructions are converted into output signals which in turn control machine operations such as spindle speeds, tool selection, tool movement, and cutting fluid flow.
Coordinates of CNC
All computer controlled machines are able to accurately and repeatedly control motion in various directions. Each of these directions of motion is called an axis. Depending on the machine type there are commonly two to five axes.
Additionally, a CNC axis may be either a linear axis in which movement is in a straight line, or a rotary axis with motion following a circular path.
Basic principle of CNC
Each axis consists of a mechanical component, such as a slide that moves, a servo drive motor that powers the mechanical movement, and a ball screw to transfer the power from the servo drive motor to the mechanical component. These components, along with the computer controls that govern them, are referred to as an axis drive system.
CNC SYSTEM ELEMENTS
A typical CNC system consists of the following six elements
1. Part program
2. Program input device
3. Machine control unit
4. Drive system
5. Machine tool
6. Feedback system
CNC CLASSIFICATION 1.Motion control: point to point (PTP) continuous (contouring) path 2. Control loops: open loop closed loop 3. Power drives: hydraulic, electric or pneumatic 4. Positioning systems: incremental absolute positioning 5. Hardwired NC and soft wired Computer
Numerical Control (CNC)
Classification of CNC system
Point-to-Point . each axis driven separately and at different velocities
Moves at max velocity initially then slows as gets to desired position
After operation complete tool is retracted and moved rapidly to next position and repeats operation
Eg:Mainly used in drilling, punching, and straight milling operations
POINT TO POINT CONTROL
Classification of CNC system
Continuous Path . positioning and cutting operations both controlled along paths but at different velocities
Tool is cutting as it travels
Requires synchronization of velocities and movements
Continuous path control
Open and closed loop control
OPEN LOOP SYSTEM
In open-loop control system step motors are used
Step motors are driven by electric pulses
Every pulse rotates the motor spindle through a certain amount
By counting the pulses, the amount of motion can be controlled
No feedback signal for error correction
Lower positioning accuracy
CLOSED LOOP SYSTEM
In closed-loop control systems DC or AC motors are used
Position transducers are used to generate position feedback signals for error correction
Better accuracy can be achieved
More expensive
Suitable for large size machine tools
INTERPOLATION
Types of Interpolation
Linear . tool moves in straight line from start to end in 2 or 3 axes
Circular . needs start and end points, coordinates of center of circle, radius, and direction of tool along the arc
Parabolic and Cubic . paths approximated by curves using higher order mathematical equations
TYPES OF INTERPOLATION
CNC MILLING
CNC LASER CUTTING
CNC Plasma cutting
AUTOMOTIVE INDUSTRY Engine Block
Different products
AEROSPACE INDUSTRY Aircraft Turbine Machined by 5-Axis CNC Milling Machine
Advantages of CNC Productivity
Machine utilisation is increased because more time is spent cutting and less time is taken by positioning.
Reduced setup time increases utilisation too.
Quality
Parts are more accurate.
Parts are more repeatable.
Less waste due to scrap.
Advantages of CNC Reduced inventory
Reduced setup time permits smaller economic batch quantities.
Lower lead time allows lower stock levels.
Lower stock levels reduce interest charges and working capital requirements.
Machining Complex shapes
Slide movements under computer control.
Computer controller can calculate steps.
First NC machine built 1951 at MIT for aircraft skin milling.
Advantages of CNC Management Control
CNC leads to CAD
Process planning
Production planning
Draw backs of CNC
High capital cost Machine tools cost $30,000 - $1,500,000 Retraining and recruitment of staff New support facilities High maintenance requirements Not cost-effective for low-level production on
simple parts As geometric complexity or volume increases
CNC becomes more economical Maintenance personnel must have both
mechanical and electronics expertise
Features of CNC Machining Centers
CNC Machine Components
Cutting Tool / Collet Caddy
Very common to have 100 or more diverse cutting tools loaded into a collet caddy
They are numbered for ease of identification
The operator must know the common tools by simple visual observation
Boxford Vertical Mill Cutting Tools
Collet Caddy # Tool in Collet (different lengths)
5 2mm end mill, ball end
6 2mm end mill, slot drill
3 4mm end mill, slot drill
4 6mm end mill, slot drill
1 8mm end mill, slot drill
2 25 mm end mill, facing cutter
CNC Bench Vise
Notice the smooth machined surfaces; be careful not to damage surfaces
CAM & X-axis Table Alignment
To machine a part with CNC, the end of the tool must be known relative to the bench vise, x-axis table, or some other fixed distance
Z-axis Arbor
Keep the lands clean and oiled
A slight tilt will cause noticeable cut deformations
Align the protrusions with slots in the cutting tool quick change adapter body
Air Nozzle
Used for:
Keeping cutting area free of excessive cutting debris
Quick cleaning
When supplied with misting, provides cutting tool cooling
End Mill / Facing Cutter
Hogs off large amounts of material
Radius of cut very large
Provides a known surface from which to measure from
Requires workpiece to be robustly supported due to high torque created
Quick Change End Mill Adapter
Helps provide quick changing of cutting tools without having to use complex setup procedures
Power Panel
Lockable On-Off Switch
Circuit Breakers
Power Cord
Control Panel
1. FEED HOLD
Acts as an interrupt control to the program when pressed, preventing
any further tool movement until canceled. During an Automatic cycle,
after canceling CYCLE START must be pressed to resume the cycle.
2. SINGLE BLOCK
With machine running in automatic mode controlled from the PC, this
allows the operation of only a single block (line) of the program at a
time to be toggled on/off. Press CYCLE START to proceed.
3. CYCLE START This sets the machine in automatic mode and starts the machining
from the PC program. Also used to resume an Automatic cycle after
a FEED HOLD is canceled and to action the next line if Single Block
is active.
Control Panel
4. FEED SPEED CONTROL
Provides stepless control of tool feed speed in the X, Y and Z axes from 0 to 100% in 10% increments.
5. JOG TABLE AXIS CONTROLS
These four buttons control manual movement of the table in the X and Y axes.
Move the table in the X axis while held pressed.
Move the table in the Y-axis while held pressed.
6. JOG HEAD AXIS CONTROLS
Move the head in the Z axis while held pressed.
Pressing this button together with any of the other six axis control buttons provides rapid movement of the axes in the indicated direction.
Control Panel
7. MANUAL When lit, machine is operated from control panel (Manual mode). Pressing MAN puts light out and machine is controlled by computer (Automatic mode). Press MAN again to revert to manual mode operation.
8. AIR MIST CONTROL Switches on or off the optional air mist coolant when fitted.
9. DATUM M/C - PROGRAM ABORT After initially powering up the machine and pressing the Power Reset button (23), with the machine in Manual mode (Manual mode button lit) press to datum the machine axes.
• With the machine in Manual mode, the machine can be re-datumed at any point. This should always be done if a physical stall of the axes has occurred.
•During an Automatic Cycle with a Feed Hold (1) active, pressing will Abort the current job.
Control Panel
10. TOOL CHANGE With auto tool changer fitted, press to change to next tool automatically.
11. TOOL RELEASE Releases the tool holder from the spindle if fitted with the auto tool changer. Guard door must be open and tool holder held.
12. WORK HOLDING UN-CLAMP Controls un-clamping of workpiece in pneumatic work holder vice, when fitted.
13. WORK HOLDING CLAMP Controls clamping of workpiece in pneumatic work holder vice, when fitted.
14. DOOR OPEN Controls opening of the automatic doors when fitted.
Control Panel
15. DOOR CLOSE Controls closing of the automatic doors when fitted.
16. SPINDLE CONTROLS These control the speed and direction of rotation of the spindle.
Spindle Forward - Pressing this button starts the spindle rotating forward. Holding it down increases forward speed. Pressing and holding the 'Spindle Reverse' button reduces speed in the forward direction.
Spindle Reverse - Pressing this button starts the spindle rotating in reverse direction. Holding it down increases spindle speed in reverse direction. Pressing and holding the 'Spindle Forward' button reduces speed in the reverse direction.
Spindle Stop - Pressing this button stops spindle rotation.
Control Panel
17. EMERGENCY STOP Pressing this pushbutton stops all machine movement and switches off the electronics, and the button locks in the depressed position.
If the machine is in production, an appropriate message is displayed on the PC screen.
The button must be turned to release it and the Hard Reset button (23) pressed to enable the machine to be started. The machine must be datumed using the Datum M/C key (9).
If the machine was performing a production cycle, the cycle must be repeated from the beginning.
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
CNC Machine Tool Assembly
Courtesy: UTS(EMCO)
CNC Machine Tool Assembly