What is CNC Machining?
Computer Numerical Control (CNC) Machining is a manufacturing process that uses pre-programmed computer software to manipulate a base material into useful parts and products.
CNC machines rely on computer code to control a wide variety of machining tools, including grinders, lathes, drills, boring tools and more.
You start the process by creating a 2D or 3D CAD drawing before translating this into computer code to be inputted into the CNC system. Known as G-code, these instructions tell the machine how to move, where to cut and how fast to go.
Unlike additive manufacturing techniques like 3D printing, CNC machining is a subtractive process. This involves trimming or cutting away at a base material to an exact specification.
CNC machining is particularly important in metal and plastic manufacturing processes, but it can also be used on other base materials like wood and ceramic.
Advantages of CNC Machining
CNC machining holds several advantages over alternative manufacturing processes.
Lower labour costs
One of the key advantages of CNC machining is that it can reduce a company’s labour costs.
CNC technicians need to be able to set up, monitor and maintain machines. But it doesn’t take a skilled craftsman to run a CNC machine, unlike with some more traditional manufacturing processes.
Inexperienced CNC operators can be trusted to create products with little training. And because CNC machines eliminate much of the potential for human error, CNC machines can also help improve the quality of your products.
Practically, one CNC technician can often work across multiple machines without specialising in one craft, leading to a further saving on labour cost.
CNC machines don’t (often) make mistakes. Barring faults with the machine or errors made by an operator, CNC machines will create your products to precise specifications laid out in your CAD drawing.
Precision can vary slightly from machine to machine, but the CNC machining can be used to create sensitive products where tolerances are very small.
CNC machines come with a high initial price tag. But they also speed up processes, leading to increased productivity and lower running costs.
And because machines don’t need sleep or toilet breaks, CNC machines can be run around the clock without resorting to caffeine to boost performance. The only time a CNC machine needs to stop working is when it is being repaired or maintained.
Repetition, repetition, repetition
When you are creating a single, custom-built product or part then conventional machining might make sense.
But if you have high production quotas and need to produce and reproduce a part or product multiple times, CNC machining makes life much easier.
Once you have the CAD drawing and the G-code to tell your CNC machine what sequence of actions to follow, you can create the same part or product, again and again, ad infinitum.
This master design can be stored safely and retrieved in a month, a year or a decade when you decide to create the product again to exactly the same specification.
Speed up prototyping
Prototyping can slow down product development. CNC software speeds up the process, letting you simulate production on software before putting it into a quick and painless production process.
CNC machining can provide more design complexity than other manufacturing processes like 3D processing.
If your product has a lot of fine detailing on the exterior of the product then CNC machining is preferable. But there are some design features that you can’t achieve with CNC machining.
Disadvantages of CNC Machining
Like every manufacturing process, CNC machining is not without its drawbacks.
CNC machines are advanced bits of kit and they don’t come cheap. But it is important to see the high price tag as an investment in long-term financial savings, efficiency, quality and reliability.
Losing the old ways
CNC machine operators don’t need as much training. And there is some understandable worry that the art and craft of manual machining will disappear with the current generation.
Some people think that these skills have an inherent value in and of themselves. The loss of traditional machining jobs could also result in some manual machinists struggling to find the same work.
Small changes are tricky
When you are machining something manually, making a small product change is relatively straightforward. Shaving a few millimetres here and drilling a new hole there is no problem for a skilled operator.
But these small changes are harder with CNC machining. It involves going back to the drawing board and rewriting the program to account for a relatively minor change.
The case of waste
Compared with some alternative manufacturing processes like additive manufacturing, CNC machining produces a lot more waste. This is because it’s a subtractive process, so necessarily involves the stripping away of useless bits of material.
Although these bits of material can often be repurposed or recycled, there is still an environmental cost of this waste. It also means that you need to use more raw material.
Is CNC Machining Right for My Project?
CNC is used to produce parts and products in a broad range of industries where accuracy, consistency and efficiency is important. Some industries that regularly make use of CNC machined parts include:
CNC manufacturing and 3D printing are two of the most popular automated manufacturing processes that can make parts and products from a digital design file.
When deciding which manufacturing process is right for your business you need to look at several key factors and answer a number of questions about the product you are trying to create.
You need to know how complex the product is to make and whether it has any design features that would make it impossible to create using CNC machining processes.
It may also depend on the material that you want to make the product out of and the quality of the product.
Finally, you need to know what volume of products you intend to create and what kind of timeline you are working to. 3D printing is still relatively slow and cannot be used for high volume manufacturing. It may, however, be better for creating a prototype of your product.
In short, if producing quickly, accurately and with precision is important to your business and you are producing metal fabricated parts, then CNC machining is likely going to be right for your business.
CNC Machining Tools
There are many different machining tools that can be used in a CNC machine.
Because some products or parts will need to be machined using several different tools, many modern CNC machines combine multiple tools like drills, lathes and boring tools into a single cell.
Other CNC machines only have one tool and parts may need to be transported between different computer-controlled machines by humans or robots.
A CNC milling machine can cut and drill materials like metal, wood and plastic using a cylindrical drill called a milling cutter. Most milling machines are 3-axis machines, which can operate vertically up and down and horizontally forwards, backwards, left and right.
4-axis and 5-axis machines are more complicated because they add the ability to rotate the x-axis (4-axis) and x and y-axis (5-axis).
A traditional lathe cuts and shapes a workpiece as it rotates on a spindle, a bit like a rotisserie chicken. It uses cutting tools and drill bits to make products that are symmetrical about their axis. On a CNC lathe machine, an operator can program the machine to make more difficult cuts with a precision that would be practically impossible on a regular lathe.
Most CNC lathes operate in one of two axes – vertical or horizontal, although some more advanced lathes work in different axes.
Like a handheld router, which is usually used to cut or shape flat pieces of wood, a CNC router is commonly used on wood, composites, plastic, foam and some metals. Many woodworkers use CNC routers to cut wood quickly and precisely into what can be quite complicated shapes.
A CNC router will typically take instructions from a CAD file that is converted into a vector format.
CNC Plasma Cutter
One of the more advanced CNC operations, CNC Plasma Cutters cut materials using a high-powered plasma torch. Plasma cutters work by sending an electrical arc through a pressurised gas to create a fourth state of matter – plasma.
This plasma is at a sufficient temperature to cut through materials like steel, aluminium, brass and many other materials while some of the gas will be used to blow the molten metal away from the cut.
CNC Electric Discharge Machining
Electric Discharge Machining is a solution for high accuracy machining applications for metals that are difficult or impossible to remove.
The process passes an electric current between an electrode and a workpiece separated by a dielectric liquid, which acts as an insulator unless the voltage is high enough to make it into a conductor. This creates a spark that gradually erodes the workpiece until it is in the desired shape. There are several different types of Electric Discharge Machining but they all work from the same principal of erosion by electrical discharge.