Originally published at: https://www.3dtek.xyz/2021/01/29/the-novice-guide-to-the-cnc-machinery-processes/
As a beginner to the CNC process, you’d be forgiven for undoubtedly having a few questions.
When studying anything new, the very best place to start is by gaining a basic understanding of that in which you’re hoping to learn.
In this case, we’ll first need to understand what a CNC router is and how the entire CNC process works as a whole.
What is CNC?
CNC stands for Computer Numerical Control, which means that the physical movement of CNC machinery is dictated by a computer system, using a complicated mathematical coordination system.
The process can be used to regulate a range of intricate machinery, from grinders and lathes to mills and routers. With CNC machining, three-dimensional cutting assignments can be achieved with a single set of data prompts.
The computer controls the router or spindle on the machine in one of the directions, or axes, the most basic functions of which are:
- X-Axis – moves the spindle from side-to-side.
- Y-Axis – moves the spindle from front to rear.
- Z-Axis – moves the spindle up and down.
Whether the CNC router is a basic system used at home by hobbyists or used in a manufacturing capacity with machines costing millions of pounds, the process remains more or less the same.
Although, manufacturing systems use far more complex software to cope with high-demand operations, the basic processes and principles scarcely change.
CNC Machinery & Programming
Once a CNC system is turned on, the desired cuts can be programmed into the software, depending on the desired outcome and machinery used, to carry out the dimensional tasks as required.
In CNC programming, the code generated within the numerical system directs the placements of a tool known simply as the ‘part programme‘.
The language these inputs is written in is often referred to as ‘G-Code’, which is used to control the machine’s behaviours, such as speed, axes coordination and feed rate.
On a basic level, CNC machines can be controlled by pre-programmed parameters to dictate the machinery functions’ speed and position in repetitive and controllable cycles, with little interaction from human beings.
These characteristics make CNC machinery ideal in manufacturing environments such as metal and plastic production.
Once a 2 or 3D CAD drawing is created, it can then be translated to G-Code for the CNC to process and execute. Once the programme has been inputted, the operator can run test processes to ensure no coding flaws.
Different Kinds of CNC Machines
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The earliest version of the numerical control machines dates back to the 1940s when specialised motors were first developed to control the movement of pre-existing tools, to aid in the production of helicopter blades.
As technologies advanced throughout the 1960s and 70s, the mechanisms were improved and the scope of what they were used for increased. This coincided the rise of analogue computers and digital computers, which inevitably gave way to the CNC machining processes we recognise today.
The vast majority of the CNC’s these days are 100% electronic and are used, most commonly, for ultrasonic welding, hole-punching and laser cutting. The most frequently used machines include:
CNC mills can run on programmes made up of letter and number-based prompts, which will guide pieces across the machine as required. The programming language could utilise the aforementioned G-Code or a custom language developed by the operators.
As we covered at the beginning of this blog, the most basic mills will consist of an X, Y and Z axis-system, although more advanced systems can accommodate three additional axes.
When using a lathe machine, pieces can be cut in circular motions with indexable tools. Utilising CNC technology means that these cuts can be undertaken very quickly and with razor-sharp precision.
Lathes are most often used to produce more complex pieces that simply wouldn’t be attainable on more basic machinery. The control functions of CNC mills and lathes are quite similar. As with the former, lathes can be programmed with either G-Code or another custom language, but only consist of two axes: X and Z.
As the name suggests, plasma cutters cut material with a torch. This is generally a process consigned to metalwork, but it can also be used on other surfaces.
In order to generate the requisite speed and heat necessary to cut through metal, plasma is generated through a mixture of compressed-air gas and electrical arcs.
Electric Discharge Machines
The electric discharge machining process, often referred to as die sinking and spark machining, uses electrical sparks to mould pieces into specific shapes. With EDM, the discharge of the current occurs between two electrodes, which in turn removes parts of the piece in question.
When the distance between each electrode decreases, electricity becomes more intense and more vigorous, which removes pieces from the material as the field passes between the electrodes.
There are also several subversions of this method too:
- Wire EDM – this is where spark erosion is used to erode portions of material from a conductive material.
- Sinker EDM – this method is when an electrode and the material are soaked in a dielectric fluid with the intent of piece formation. In a process known as flushing, the debris produced by each finished product is carried away by the liquid, which is visible once the current between the two electrodes has stopped, thereby eliminating further electric charges.
This subtractive manufacturing equipment uses a potent light beam to melt down, burn away, or incinerate material.
A desktop laser cutter will normally follow directions from computer numerical control (CNC) or the G-Code, that we talked about earlier.
The method begins with an exceptionally small laser beam that is emitted from a tube as the current passes through. The current then causes the laser to reflect off a reflective surface and points through a focal lens in the head of the machine.
Following the vector file that holds a 2D design, the laser beam will chip away at a piece of material until the image resembles the original drawing.
These machines are capable of creating finely detailed patterns with a high-quality surface finish. There is a broad range of laser cutting methods that you can use.
- CO2 Lasers – CO2 powered laser cutters are the most frequently used of the three laser machinery methods.
They generally only use limited power, come at a relatively low price point, yet they are incredibly efficient and compatible with the broadest range of materials. The laser source is produced from a gas mixture that largely consists of carbon dioxide.
- Neodymium (Neodymium-Doped Yttrium Aluminium Garnet) – This laser, created with neodymium-doped crystals, has a reduced wavelength and a higher concentration when compared to CO2 lasers.
This enables the laser to cut through far thicker and stronger material, including most metals and even some ceramics. The drawback to this kind of laser, though, is that machine parts require a higher degree of maintenance.
- Fibre – Created from a “seed laser” and amplified through special glass fibres. This laser has a high intensity that rivals Neodymium but is easier to maintain due to the machine’s construction.
Fibre-based laser cutters are most commonly used for laser marking, which involves labelling pieces with information, such as tools for example.