Computer numerical control ( CNC ) is machine tool automation by means of a computer executing a pre-programmed sequence of machine control commands. This is different from a machine that is controlled manually by hand wheel or lever, or mechanically automatic by cams only.
In modern CNC systems, the design of mechanical parts and manufacturing programs are highly automated. The mechanical dimensions of this section are defined using computer assistance software (CAD), and then translated into manufacturing directives by computer-assisted software (CAM). The resulting directives are modified (by "post processor software") into specific commands required for a particular machine to generate components, and then loaded into a CNC machine.
Because certain components may require the use of a number of different tools - drills, saws, etc. - Modern machines often incorporate multiple tools into a single "cell". In other installations, a number of different machines are used with external controllers and human operators or robots that move components from machine to machine. In either case, the set of steps required to produce any part is highly automated and produces a part that fits perfectly with the original CAD.
Video Numerical control
Histori
The first NC machines were built in the 1940s and 1950s, based on existing modified tools with motors that drive controls to follow the points entered into the system on the perforated bands. This early mechanism servo is quickly coupled with analog and digital computers, creating a modern CNC machine tool that has revolutionized the machining process.
Maps Numerical control
Description
Motion is controlled along several axes, usually at least two (X and Y), and a spindle tool that moves in Z (depth). The position of this tool is driven by stepper motors or direct drive servo motors to provide highly accurate motion, or in older designs, motors through a series of backward steps. The open-loop control works as long as the power is kept small enough and the speed is not too large. In commercial metalworking machines, closed loop controls are standard and necessary to provide the required accuracy, speed, and repetition.
When controlling hardware evolved, the factory itself also evolved. One change has included the entire mechanism in the big box as a security measure, often with additional security to ensure the operator is far enough away from the workpiece for safe operation. Most newly built CNC systems today are 100% electronically controlled.
CNC-like systems are now used for any process that can be described as a series of movements and operations. These include laser cutting, welding, welding of friction, ultrasonic welding, flame cutting and plasma, bending, spinning, hole punching, clamps, gluing, cutting fabrics, suturing, ribbon and fiber placement, routing, picking and placement, and sawmill.
An example of a CNC machine
Other CNC tools
Many other tools that have CNC variants, including:
- Exercise
- EDM
- Embroidery machines
- Lathes
- Milling machine
- Cycle cycle
- Wood router
- Metal sheet work (Turret punch)
- Cable bending machine
- Hot-wire foam cutter
- Plasma cutter
- Water jet cutter
- Laser Cutting
- Oxy-fuel
- Surface grinders
- Cylinder wheel
- 3D printing
- Induction hardening machine
- Las soaked submerged
- Cutting glass
Tools/engine crashes
In CNCs, "accidents" occur when the machine moves in such a way that is harmful to machinery, equipment, or parts that the machine does, sometimes resulting in bending or damage to cutting tools, accessory clamps, vises and equipment, or causing damage to the machine itself by bending the guiding rails, breaking the screw drive, or causing the structural components to crack or change shape under pressure. Light accidents may not damage machinery or equipment, but may damage parts of the work in progress and should be removed.
Many CNC tools do not have a sense attached to the absolute position of the table or equipment when turned on. They should be manually "homed" or "focused" to have references to work from, and these limits are only to find out the location of the part to work with it, and not really some kind of hard boundary on the mechanism. It is often possible to move the machine beyond the physical limit of its propulsion mechanism, resulting in a collision with itself or damage to the propulsion mechanism. Many machines implement control parameters that restrict the movement of the axis over a certain limit in addition to the physical boundary switch. However, these parameters can often be changed by the operator.
Many CNC tools also do not know anything about their work environment. The machine may have a load sensing system on the shaft and drive shaft, but some do not. They blindly follow the provided machining code and it's up to the operator to detect whether an accident occurred or will occur, and for the operator to manually cancel the active process. Machines equipped with load sensors can stop the movement of the spindle or spindle in response to excessive conditions, but this does not prevent accidents. This may only limit accidental damage. Some crashes may not overload any axes or spindle drives.
If the drive system is weaker than the structural integrity of the engine, then the drive system pushes only against the barrier and the driving force "slips in place". The machine tool may not detect a collision or slip, so for example the tool should now be at 210 mm on the X axis, but actually, at 32mm where it hits the obstruction and keeps slipping. All subsequent tool motions will be turned off by -178mm on the X axis, and all future motions are now invalid, which may result in further collisions with clamps, vises, or the machine itself. This is common in open-ended stepper systems, but is not possible in closed-loop systems unless mechanical slippage between the motor and the driving mechanism has occurred. Instead, in a closed-loop system, the machine will keep trying to move against the load until the driving motor goes into overcurrent or servo condition after an error alarm is generated.
Detection of collisions and avoidance is possible, through the use of absolute position sensors (encoder or optical disks) to verify that motion occurs, or torque sensors or power driving sensors in the drive system to detect abnormal strain when the machine has to move and not cut, but this is not a component common from most CNC hobby tools.
In contrast, most of the hobby CNC tools rely solely on the assumed accuracy of the stepper motors that rotate a certain number of degrees in response to changes in the magnetic field. It is often assumed that the stepper is very accurate and never missteps, so monitoring tool positions involves only counting the number of pulses sent to the stepper over time. Alternative means of monitoring step positions are usually not available, so accidental or slip detection is not possible.
Commercial CNC metal machining machines use closed feedback controls for axis movement. In a closed loop system, the control realizes the true position of the axis at any time. With proper programming control, this will reduce the chance of a collision, but it still depends on the operator and the programmer to ensure that the machine is operated in a safe manner. However, during the 2000s and 2010s, software for machining simulations was rapidly maturing, and it was no longer unusual for all machine tool envelopes (including all axes, spindles, chucks, turrets, tool holders, tailstocks, equipment, clamps and stocks) to be modeled accurately with 3D solid models, allowing simulation software to predict quite accurately whether the cycle will involve an accident. Although the simulations are not new, their accuracy and market penetration change significantly due to computing advances.
Numerical precision and backlash equipment
In the numerical system of CNC programming it is possible for the coder to assume that the controlled mechanism is always very accurate, or that the precision tolerance is identical for all direction of cutting or movement. This is not necessarily the actual state of the CNC tool. CNC devices with a large number of mechanical reactions can still be very precise if the drive or cutting mechanism is only moved so as to apply cutting power from one direction, and all driving systems are pressed together in one direction of the cut. However a CNC device with high reactions and boring cutting tools can cause a cutter chitch and possibly gouge workpiece. Backlash also affects the accuracy of some operations that involve the movement of the reversal shaft during cutting, such as circular milling, where the motion of the axis is sinusoidal. However, this can be compensated if the number of counter-attacks is appropriately known by the linear encoder or manual measurement.
The high counter-feedback mechanism itself does not always depend on the exact timing for the cutting process, but some reference objects or other precision surfaces can be used to zero in on mechanisms, by applying strict pressure to the reference and setting it as zero reference for all following CNC movements -encoded. This is similar to a manual machine tool method of clamping a micrometer to a reference ray and adjusting the Vernier dial to zero using that object as a reference.
Positioning control system
In a numerical control system, the position of the tool is determined by a set of instructions called part program.
Position control is handled either by open loop or closed-loop system. In open loop systems, communication takes place in one direction only: from the controller to the motor. In a closed-loop system, feedback is given to the controller so that it can correct errors in position, velocity, and acceleration, which can arise due to variations in load or temperature. Open loop systems are generally cheaper but less accurate. Stepper motors can be used in both types of systems, while servo motors can only be used in closed systems.
Koordinat Cartesian
G & amp; The position of the M code is all based on a three-dimensional Cartesian coordinate system. This system is a typical field that we often see in math when you are making a graph. This system is needed to map out machine tool paths and other types of actions that need to occur in certain coordinates. Absolute coordinates are what are generally used more commonly for machines and represent (0,0,0) dots on planes. This point is set on the stock material to provide a starting point or "Home position" before starting the actual machining.
M-codes
[Miscellaneous Code Function (M-Code)] M-codes are other miscellaneous machine commands that do not move the motion axis. The format for M-code is the letter M followed by two to three digits; as an example:
- [M02 End of Program]
- [M03 Start Spindle - Clockwise]
- [M04 Start Spindle- Counter Clockwise]
- [M05 Stop Spindle]
- [M06 Tool Change]
- [M07 Coolant On]
- [M53 Retract Spindle] (raise the tool spindle above the current position to allow the operator to do whatever it takes)
Code M is very important in the ALL CNC program to make sure the code line is working. All the complete CNC programs have the M code in the first and last line of code.
G-codes
G-code is used to command certain movements of the machine, such as machine movement or drilling functions. The format for G-code is the letter G followed by two to three digits; eg G01. G-code is slightly different between mill app and lathe. as an example:
- [G00 Rapid Motion Positioning]
- [G01 Linear Interpolation Motion]
- [G02 Motion-Clockwise Interpolation]
- [G03 Interpolation Circular Motion Clockwise]
- [G04 Dwell (Group 00) Mill]
- [G10 Set Offset (Group 00) Mill]
- [G12 Circular Pocketing-Clockwise]
- [G13 Circular Pocketing-Counter Clockwise]
Coding
Example:
- %
- o0001
- G20 G40 G90 G90 G94 G54 (Inch, Clear Component Cutter, Disable all cycles of cans, move axes to machine coordinates, feed per minute, original coordinate system)
- M06 T01 (Tool changed to tool 1)
- G43 H01 (tool length tool in positive direction, long compensation for tool)
- M03 S1200 (Spindle converts CW at 1200 RPM)
- G00 X0. Y0. (Rapid Traverse to X = 0. Y = 0.)
- G00 Z.5 (Rapid Traverse to z =.5)
- G00 X1. Y-.75 (Quickly searches X1 Y-.75)
- G01 Z-.1 F10 (Plunged into section at Z-.25 at 10in per minute.)
- G03 X.875 Y-.5 I.1875 J-.75 (CCW cuts an arc into X.875 Y-.5 with a radius of origin at I.625 J-.75)
- G03 X.5 Y-.75 I0.0 J0.0 (CCW cuts an arc into X.5 Y-.75 with a radius of origin at I0.0 J0.0)
- G03 X.75 Y-.9375 I0.0 J0.0 (CCW cuts an arc into X.75 Y-.9375 with a radius of origin at I0.0 J0.0)
- G02 X1. Y-1.25 I.75 J-1.25 (CW cuts an arc into X1 Y-1.25 with a radius of origin at I.75 J-1.25)
- G02 X.75 Y-1.5625 I0.0 J0.0 (CW cuts an arc into X.75 Y-1.5625 with the origin of the same radius as the previous arc)
- G02 X.5 Y-1.25 I0.0 J0.0 (CW cuts an arc into X.5 Y-1.25 with the same radius as the previous arc)
- G00 Z.5 (Quick search to z.5)
- M05 (stop spindle)
- M30 (End of Program)
- % G00 X0.0 Y0.0 (Mill back to original)
Source of the article : Wikipedia
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