Numerical control
[3] CNC offers greatly increased productivity over non-computerized machining for repetitive production, where the machine must be manually controlled (e.g. using devices such as hand wheels or levers) or mechanically controlled by pre-fabricated pattern guides (see pantograph mill).
For some prototyping and small batch jobs, a good machine operator can have parts finished to a high standard whilst a CNC workflow is still in setup.
In modern CNC systems, the design of a mechanical part and its manufacturing program are highly automated.
On commercial metalworking machines, closed-loop controls are standard and required to provide the accuracy, speed, and repeatability demanded.
[7] Another trend is the combination of AI, using a large number of sensors, with the goal of achieving flexible manufacturing.
[8] EDM can be broadly divided into "sinker" type processes, where the electrode is the positive shape of the resulting feature in the part, and the electric discharge erodes this feature into the part, resulting in the negative shape, and "wire" type processes.
Machines equipped with load sensors can stop axis or spindle movement in response to an overload condition, but this does not prevent a crash from occurring.
Instead, most hobby CNC tools simply rely on the assumed accuracy of stepper motors that rotate a specific number of degrees in response to magnetic field changes.
In a closed-loop system, the controller monitors the actual position of each axis with an absolute or incremental encoder.
However, during the 2000s and 2010s, the software for machining simulation has been maturing rapidly, and it is no longer uncommon for the entire machine tool envelope (including all axes, spindles, chucks, turrets, tool holders, tailstocks, fixtures, clamps, and stock) to be modeled accurately with 3D solid models, which allows the simulation software to predict fairly accurately whether a cycle will involve a crash.
[11] Within the numerical systems of CNC programming, the code generator can assume that the controlled mechanism is always perfectly accurate, or that precision tolerances are identical for all cutting or movement directions.
While the common use of ball screws on most modern NC machines eliminates the vast majority of backlash, it still must be taken into account.
However, a CNC device with high backlash and a dull cutting tool can lead to cutter chatter and possible workpiece gouging.
[citation needed] In numerical control systems, the position of the tool is defined by a set of instructions called the part program.
In a closed-loop system, feedback is provided to the controller so that it can correct for errors in position, velocity, and acceleration, which can arise due to variations in load or temperature.
This system is required to map out the machine tool paths and any other kind of actions that need to happen in a specific coordinate.
G-codes differ slightly between a mill and lathe application, for example: [Code Miscellaneous Functions (M-Code)][citation needed].
The format for an M-code is the letter M followed by two to three digits; for example: Having the correct speeds and feeds in the program provides for a more efficient and smoother product run.
