Computer numerical control (CNC) machines form the backbone of many production lines around the world. Their ability to produce accurate parts quickly and efficiently makes them the machines of choice for working with a range of materials from wood to titanium. Find out what does a CNC machine do, and what are their advantages over other production methods.
What is a CNC machine and what does it do?
The specific output of a CNC machine can vary widely depending on the needs of the manufacturer using it, but its ultimate purpose is always the same. CNC machines are powerful, high-accuracy tools that marry the accuracy and automation of computers with the power and functionality of various tools.
A CNC machine can use drills, saws, lathes, laser cutters, and many other parts to achieve its goals. A computer informs the machine and carries out every action in terms of direction, orientation, and time needed to cut and form the workpiece as desired. CNC machining is known as a subtractive process, as it removes layers of material from the original piece – say, a block of plastic – to create the necessary part.
CNC machines are as large and heavy as they are powerful. They’re stationary workstations rather than tools you would move around a warehouse, making them more suited as keystones of a production line. Due to the high power of their parts, CNC machines must be operated with the utmost safety and awareness, and CNC operators are deadly serious about the intelligent use of their machines (and for good reason).
What are the main types of CNC machine?
CNC machines at their core do the same thing – reading programming languages like G-code to move their tools and/or the workpiece to subtract material for the finished product, such as milling a piece of plastic into the shape of a pipe.
However, CNC machines are built with a specific type of tool in mind which can set one machine apart from another. These include:
Milling machines are among the most popular machine tools used, partly thanks to the versatility and multifunction of milling tools themselves. Milling tools often resemble drill bits at a glance, but they’re designed for much more and milling machines can handle both drilling and cutting tasks.
Milling machines can perform many specific actions to shape a workpiece and cut features into their surfaces, such as helical milling for circles and blind holes and shoulder milling to shape the edges and corners of a workpiece.
Milling machines are a great example of what CNC manufacturing can achieve with speed and accuracy.
Lathes and turning
In a sense, CNC lathes work in the reverse of other machine tools. Instead of holding the workpiece still and applying a spinning tool to cut, the workpiece is spun at high speeds and the stationary tool is applied to cut away material. This is known as turning, and CNC-aided lathes are also known as turning machines or turning centres.
Turning centres are often distinguished from lathes by their capability to handle three, four, and five-axis movement as opposed to simply two. This makes the machines much more versatile and enables cutting around corners.
CNC lathes work best for cylindrical and conical shapes and are excellent at trimming pieces down to smaller diameters. They’re ideal for making threaded pieces and cutting screws.
CNC routers are less expensive than something like a milling machine, but they do similar work for softer materials like wood, plastic, and foam. Some routers can handle softer metals like aluminium but they’re generally unsuited for materials like steel.
CNC mills work more precisely than routers. This is due to the fact that mills move the workpiece in tandem with the tool itself, allowing for more accurate angles and edge work. Routers only move the tool along their axes.
For less complex parts being made from materials like wood, a CNC router may be a better option than a mill particularly for cost-effectiveness.
CNC laser cutters have the advantage of superb accuracy thanks to the micron-level precision of the cutting beam. Laser cutters can handle a range of materials and their method of cutting eliminates the need for finishing.
Due to the precision of a laser beam, these machines are also ideal for engraving parts with wording or logos. However, lasers are hindered by the relatively shallow amount of material they’re able to cut, and aren’t suited to cutting down chunkier workpieces as easily as other options.
CNC grinders are often more for finishing than shaping. They employ an abrasive wheel that spins at high speeds. This generates a lot of friction and CNC grinders typically need to be equipped with a coolant system to prevent the machine from overheating.
Grinders are useful for precision machine parts and other pieces that have tight tolerances, meaning they must adhere to a strict specification and cannot vary more than a matter of millimetres in size and shape.
Plasma cutters use torches powered by ionised gas to cut through material similar to a laser cutter. These torches reach incredible temperatures of many thousands of degrees, melting through the workpiece to make its cuts.
Typically, plasma cutters are used for metals as their usage requires the workpiece to be electrically conductive. This makes them great for steel and copper, but not so much for wood and plastic. Having said that, the plasma flow is so strong as it makes the cut that it leaves the edge polished, so for manufacturers working with electrically conductive metals, they’re a great option.
Some CNC manufacturing uses electrical discharge machines (EDMs), which utilise electrical sparks to shape materials. This is also known as spark eroding, wire burning, spark machining, and several similar names.
Controlled electric discharges are released from two electrodes separated by a dielectric (insulating) liquid, with the microcomputer aiding the CNC machine calculating the discharge necessary to cut through the material. The sparks reach temperatures high enough to cut through metal, though the nature of using electricity to shape material makes it unsuitable for wood and, currently, plastic.
There are other methods that CNC manufacturing utilises to cut and shape materials beyond these ones. Some use high-pressure water jets, and others can swap between tools to widen the possible actions of a single machine.
How does a CNC machine work?
CNC machines rely on computer languages to read the paths their tools have to take. The most common of these languages is called G-code or ISO code, and its earliest standardised form has existed since the 1960s.
Reading the actions outlined in the code, the machines move their tools in the described paths at the necessary speed and timings as well as feeding coolant and pausing when needed. Some machines only possess two-axis X and Y movement, whereas others can use the Z axis for increased movement range or the A, B, and C rotational axes.
CNC machinery works automatically, needing little operator input once the workpiece has been safely loaded into the machine and the program has started. Cutting away material from the workpiece means that CNC manufacturing is a form of subtractive manufacturing.
This contrasts with additive manufacturing – like 3D printing – which builds an object up in layers.
What can you make with a CNC machine?
CNC machines can effectively make anything that can be created using hand tools. Wood, plastic, and metal can all be formed in different ways using CNC machinery, creating small objects like handles and pipes to large, heavy machine components.
There is a limit to the maximum size of the objects that CNC machines can create due to the physical limitations of their range. Though industrial-scale, warehouse-sized machines exist, the vast majority of machine tools have rather small travel ranges and are best suited for many smaller pieces rather than large individual pieces.
CNC machines possess excellent precision that can’t be beaten by humans working by hand. For this reason, they’re ideal at boring threaded holes, cutting material at exact angles, and working at exact integers without the need to stop and measure the workpiece as a person would need to do.
Thanks to their ability to cut precise holes, CNC machines are also great for creating close-fitting parts like plastic fascia covers for machines, electronics, and appliances. They can create pieces like these repeatably.
What are the advantages of CNC machines?
CNC machines have the main advantage of being computer controlled. As long as the instructions in their prepared coding are accurate, the machine won’t make any of the errors that a human doing a same job is prone to.
CNC machinery also produces less waste due to the accuracy of its work, completes jobs quickly, and uses energy efficiently. All of these factors are important for businesses carrying out manufacturing work as they allow for more jobs to be taken and completed, and a good reputation for ‘right first time’ work that doesn’t impact on customer supply chains.
This benefits the producer just as much – more accurate work and less waste means less cost being burnt on scrap and failed parts, and less time being spent on redoing jobs. Machines are costing money with every second that the spindles are turning, so that cost needs to be funnelled into successful work.
Another strength of CNC machines is their ability to create a part without any prior experience needed. And for operators and part designers, by understanding the intricacies of CNC coding languages, bespoke parts can be designed and cut to suit specific needs and suit exact tolerances.
What do I need to know before buying a CNC machine?
CNC machines are ultimately an investment. They’re not an ideal purchase unless you’re a manufacturer or need a large amount of parts constantly being made (and have the necessary cash to afford upkeep).
If you need a batch of parts made, it will almost always be far cheaper and overall more cost effective to consult a manufacturer with access to their own machines to create the parts for you.
Whilst accurate and powered by computer-aided accuracy, CNC machines won’t simply automatically iron out errors in their coding. If a path has been coded into the machine that won’t work – for example, being told to lower the tool by 100mm when the solid plate of the machine is only 80mm away – this causes what machinists call a ‘crash’.
Crashes can break tools and ruin the part in progress, causing significant cost to a business. G-code programs can commonly run for multiple pages in their entirety, and when a single digit can cause the job to go awry, it’s vital that you have operators with a firm grasp of CNC code.
How much does it cost to use a CNC machine?
The cost of using CNC machinery varies depending on the machine being used and how long its individual job is going to take.
The cost of running a CNC router won’t be as high as something heavier and more power-consuming such as a laser cutter. Upfront cost also won’t be as high for the former, which can be purchased for under £10,000, as opposed to a heavy-duty machining centre which cost tens of thousands.
There is extra cost to consider for buying and restocking tool heads that break from crashes or inevitably wear down over time, as well as material costs and essential maintenance costs.
Are CNC machines worth it?
CNC machines are definitely worth it for those who need accurately produced parts created, though the worth may derive more from paying for the use of them rather than buying your own.
Machinists who have their own range of CNC machinery can give you a fairly priced quote for producing parts for you according to your designs and needs.
CNC manufacturing with plastic
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To find out more about expert plastic fabrication, get in touch with us today.