Easy CNC Documentation

Modular CNC software for Arduino controller

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CNC machine

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CNC machine

CNC machine

Computer Numerical Control (CNC) is the automation of machine tools that are operated by precisely programmed commands encoded and played by a computer, as opposed to controlled manually via hand wheels or levers, or mechanically automated via cams alone.

In modern CNC systems, end-to-end component design is highly automated using Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) programs. The programs produce a computer file that is interpreted to extract the commands needed to operate a particular machine via a post processor, and then loaded into the CNC machines for production. Since any particular component might require the use of a number of different tools – drills, saws, etc., modern machines often combine multiple tools into a single "cell". In other installations, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either case, the series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design.

The CNC technology can be applied to wide variety of operations like drafting, assembly, inspection, sheet metal working, etc. But it is more prominently used for various metal machining processes like turning, drilling, milling, shaping etc. Due to CNC all the machining operations can be performed at the fast rate resulting in bulk manufacturing becoming quite cheaper.

CNC example.

How it works?

The CNC machine comprises of the computer in which the program is fed for cutting of the metal of the job as per the requirements. All the cutting processes that are to be carried out and all the final dimensions are fed into the computer via the program. The computer thus knows what exactly is to be done and carries out all the cutting processes. CNC machine works like the Robot, which has to be fed with the program and it follows all your instructions.

Some of the common machine tools that can run on the CNC are: Lathe, Milling machines, Drilling Machine etc. The main purpose of these machines is to remove some of the metal so as to give it proper shape such as round, rectangular, etc. In the traditional methods these machines are operated by the operators who are experts in the operation of these machines. Most of the jobs need to be machined accurately, and the operator should be expert enough to make the precision jobs. In the CNC machines the role of the operators is minimized. The operator has to merely feed the program of instructions in the computer, load the required tools in the machine, and rest of the work is done by the computer automatically. The computer directs the machine tool to perform various machining operations as per the program of instructions fed by the operator.

You don’t have to worry about the accuracy of the job; all the CNC machines are designed to meet very close accuracies. In fact, these days for most of the precision jobs CNC machine is compulsory. When your job is finished, you don’t even have to remove it, the machine does that for you and it picks up the next job on its own. This way your machine can keep on doing the fabrication works all the 24 hours of the day without the need of much monitoring, of course you will have to feed it with the program initially and supply the required raw material.

Most of the manufacturing companies are now equipped with the CNC machines as the markets have got very competitive; however, getting the expert labors for operating these machines is becoming quite difficult. Even the machine operators of these days prefer to operate the machine by programming instead of operating it manually. In most of the machine tools training institutes the new operators are taught manual machining as well as CNC machining and programming.

Advantages of the CNC Machines

There are various valid reasons for the popularity of the CNC machines:

Editing the program: Since the program of instructions is saved in the computer memory, they can be edited and changed as per the requirements. Thus the CNC system is highly flexible. One can also make necessary changes in the program for providing variable speeds and feeds for the manufacture of the jobs resulting in economic manufacturing.

Highly flexible: The CNC machines are highly flexible. One can easily make the changes in the program and store them as the new program. One can also introduce new control options like the new interpolation scheme quite easily. It is easier to make updates in the CNC machines with lesser cost; hence risk of the obsolescence of the CNC machine is reduced.

Easier programming: The programs are written in the CNC machine using language which has statements similar to the ordinary English language statements. The programmer can easily master the CNC programming language and use it for the wide range of the machining operations of the job. The programmer can set the various dimension of the job, the machining operations to be carried out and their sequence, the amount of metal to be removed in each cutting operation, the speed of cutting, etc. The program of instructions is written as per the available size of the raw materials and also the surface finish required for the final finished job. Some of the programs take the form of the macro subroutines stored in the memory of the CNC machine and the programmer can use them frequently whenever required. Some of the programs are stored in the library and they can be used wherever required completely or as a small part of the big program.

CNC capability

Most of the work centers are equipped with computer controlled vertical movement of the spindle able to produce engravings, sculptures and machining of high precision. Working realized with these machines can be indistinguishable to a not so expert eye with respect to a precision handmade one. Using spherical or conical cutters, CNCs can create completely smooth surface, high precision, so quickly and automatically at a very low cost. Best CNC machines can reach an accuracy of one ten-thousandth of a millimeter (100 nanometers).

Axes

The main feature of the CNC machines is the number of freedom degrees, said axes of the machine. For the milling machines, they are from 3 to 5, for lathes from 2 to 4, punching and cutting machines have generally 2 or 3, while the paneling machine can have up to 24 axes.
The commonest types are:
- 2 axes: movements only on the X and Y axes, creation of easy component without variation of the depth.
- 2.5 axes: movements on three axes: X, Y and Z. But usually the movements on Z-axis are discretized. They are the cheapest.
- 4 and 5 axes: in addition to X, Y and Z axes, they can rotate the axes.

Anatomy of a CNC

Usually, a CNC machine is composed by the following components:
- Encoder: it is a component that informs the computer about the actual movement and the position for each axis. They can be of two types: linear encoder or rotary encoder. Moreover, some of them provides an absolute position, that is the exact position of the axis. Other of them are relative, it means that the encoder counts the number of steps of the motion along an axis and it recognizes also the direction.
- Electric motors: the machine needs a special types of electric motors to move along an axis, that allows a precise control of the rotation.
- Drivers: they are special units that power and control the electric motors. Their technology and complexity depends on the type of electric motors.
- Control: it gets the data from encoders and the operator's instructions or the program, it establishes the position of the tool and it manages the tool movements to perform the working program. The modern machines divide the contro into two parts: one into the machine and the second into the operator's console, separated from the machine. This part shows information and control menu on the screen, takes commands from a keyboard and loads G-code programs.

What is G-code?

G-code (also RS-274) is the common name for the most widely used numerical control (NC) programming language. It is used mainly in computer-aided manufacturing (CAM) for controlling CNC machines. G-code is sometimes called G programming language.

In fundamental terms, G-code is a language in which people tell computerized machine tools how to make something. The how is defined by instructions on where to move, how fast to move, and through what path to move. The most common situation is that a CNC machine with a cutting tool is moved according to these instructions through a toolpath, cutting away excess material to leave only the finished workpiece. The same concept also extends to noncutting tools such as forming or burnishing tools, plotting, additive methods (for instance 3D printers), and measuring instruments.

Examples of CNC machines

Mills: CNC mills use computer controls to cut different materials. They are able to translate programs consisting of specific number and letters to move the spindle to various locations and depths. Many use G-code, which is a standardized programming language that many CNC machines understand, while others use proprietary languages created by their manufacturers. These proprietary languages while often simpler than G-code are not transferable to other machines.

Lathes: Lathes are machines that cut spinning pieces of metal. CNC lathes are able to make fast, precision cuts using indexable tools and drills with complicated programs for parts that normally cannot be cut on manual lathes. These machines often include 12 tool holders and coolant pumps to cut down on tool wear. CNC lathes have similar control specifications to CNC mills and can often read G-code as well as the manufacturer's proprietary programming language.

Plasma cutters: Plasma cutting involves cutting a material using a plasma torch. It is commonly used to cut steel and other metals, but can be used on a variety of materials. In this process, gas (such as compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut, turning some of that gas to plasma. The plasma is sufficiently hot to melt the material being cut and moves sufficiently fast to blow molten metal away from the cut.

Electric discharge machining: Electric discharge machining (EDM), sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking, or wire erosion, is a manufacturing process in which a desired shape is obtained using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric fluid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the "tool" or "electrode," while the other is called the workpiece-electrode, or "workpiece."
When the distance between the two electrodes is reduced, the intensity of the electric field in the space between the electrodes becomes greater than the strength of the dielectric (at least in some point(s)), which breaks, allowing current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor. As a result, material is removed from both the electrodes. Once the current flow stops (or it is stopped – depending on the type of generator), new liquid dielectric is usually conveyed into the inter-electrode volume enabling the solid particles (debris) to be carried away and the insulating proprieties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. Also, after a current flow, a difference of potential between the two electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur.

Water jet cutters: A water jet cutter, also known as a waterjet, is a tool capable of slicing into metal or other materials (such as granite) by using a jet of water at high velocity and pressure, or a mixture of water and an abrasive substance, such as sand. It is often used during fabrication or manufacture of parts for machinery and other devices. Waterjet is the preferred method when the materials being cut are sensitive to the high temperatures generated by other methods. It has found applications in a diverse number of industries from mining to aerospace where it is used for operations such as cutting, shaping, carving, and reaming.

Other CNC tools:
- Laser cutting
- Hot-wire foam cutters
- 3D printing

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Easy CNC by Francesco Giurlanda is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
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