CNC machining is a standard in many manufacturing processes – such technology provinces precision, agility, and possibility to optimize cost.
In most applications, CNC is based on well-known machining techniques such as milling, turning, or grinding.
Thanks to the utilization of numerical control these processes can be executed faster and more precisely.
Although many advantages of such technology – in some applications – seem to be replaced by more and more efficient 3D printing technology.
It is an additive technology that allows to manufacture of objects of complicated shape and form out of many materials and at its core differs from machining.
What are the key differences between CNC machining and 3D printing and how these technologies can coexist to deliver even more efficient processes?
What is CNC machining and its applications?
Under the umbrella of 'CNC machining,' there are a lot of numerically controlled methods of shaping material like CNC milling, turning, grinding, laser cutting, water jet, or EDM.
To simplify – in the following article I'll be naming 'computer numerical control (CNC) machining' a 'CNC machining'.
Each of these technologies provides typical features of CNC processes: high precision and repetitiveness of work, with minimal maintenance from the operator.
In other words, the controller executes sequences of movements and cuts that in traditional machining should be performed by an operator, often manually or with the help of templates.
The machining is a form of removal processing – the final shape of the part is created by removing material in the form of chips.
That means the machined part is lighter than the block of material it is made of.
Contemporary CNC machining as a process allows for to precise formation of even very complicated objects repeatedly, especially with more advanced devices (eg. 5-axis mills).
Often as a part of supplementary machining, electrical discharge machining (EDM) forms inside of the parts or hard-to-access surfaces.
Currently, CNC machining is used in manufacturing processes for almost any industry.
As the most important customers it is worth mentioning:
- automotive industry,
- aeronautic industry (it is worth mentioning: CNC machining was created on order from the US Air Force and has thrived since then in other industries),
- medical industry,
- space industry,
- home goods industry (electronics and appliances),
- computer industry,
- electrical industry,
- and many, many more
What is 3D printing and what are the most popular applications of such technology?
3D printing – in other words: three-dimensional printing – is a new technology of parts and object manufacturing (introduced in 1984, patented in 1986).
It is an additive technology (often called 'additive manufacturing') – the final object is 'built' (printed) layer by layer from the selected material.
The term 'three-dimensional printing' includes many technologies and manufacturing methods that differs by:
- medium (material used to create elements – most often polymers and recently even alloys),
- and the methodology of printing.
Among the most popular techniques of 3D printing, it is worth highlighting the following:
- FDM (fused deposition modeling) – is one of the most popular 3D printing technologies. Focuses on 'squeezing out' thermoplastic material through special nozzles in precisely defined sequence. Cooled-out material became the base for the next layer,
- DLP (digital light processing) – uses light of precisely defined parameters to harden the following layers of applied polymer,
- SLA (stereolithography) – that used specialized light sensible resins. The following layers are hardened in contact with light,
- SLS (selective laser sintering) – next layers of polymer dust are 'added' in the process of melting it by laser or other high-power light source,
- DMLS (direct metal laser sintering) – in a nutshell: metal alloys 3D printing. The rule of manufacturing is almost identical to the SLS process which differs mainly by medium. The source of high-power light melts metal alloy dust into the desired shape.
It is worth mentioning that the procedure of 3D printing is based on technological developments of the CNC.
That is why 3D printers can execute repetitively complex sequences of moves and 'build-up' part of the desired shape.
Currently, that technology has many applications and its continuous development allows to use of new materials.
Although the most popular remains polymers (PVA, nylon, etc.), 3D printing uses even materials such as metal alloys, concrete, resins, and – to some extent – human tissue.
Currently, that technology is used in situations that require manufacturing parts of complicated geometries, especially internal.
In other words: 3D printing can shape internal and external surfaces just as efficiently when CNC machining is focused mainly on external.
Even usage of EDM or very precise casting forms rarely can achieve a precision of internal structure that can be provided by a well-calibrated 3D printer.
Contemporary applications of 3D printing are:
- fast prototyping, especially single objects or parts,
- manufacturing of small parts for hobby applications,
- manufacturing specialized objects, like prosthetics elements,
- gadget manufacturing,
- production of small batches of complicated parts, especially with complex parts with meticulous internal structure, unavailable to achieve with other, more popular methods,
- in the future (closer than further) – printing whole human organs (bioprint 3D allows currently 'only' tissue printing).
Key differences between 3D printing and CNC machining
To better understand these two technologies it is worth to highlight the differences between additive manufacturing and removal processes.
In other words – the key differences between CNC machining and 3D printing are:
- manufacturing method – 3D printing is an additive technology. To create a part material is 'added' during the whole process. CNC machining is a removal process – parts are shaped by removing excess material from the surface,
- applications – 3D printing remains a standard for manufacturing small batches of parts and rapid prototyping. CNC machining is a perfect solution for mass production.
- maturity of the technology and its ability for mass production – even industry-grade 3D printers, that can deliver precise DMLS print still have no capacity for rapid production of big batches of parts. It is still a very young technology. To highlight the efficiency problem – printing one element can take from a few minutes (very simple elements and very efficient printer) to dozens of hours (more complex/bigger).
On the other hand, CNC machining – in its perfect applications – can shape parts in almost no time: from a few seconds to almost a few hours,
- achieved effects and precision of parts manufacturing – to this day 3D printing can cause a lot of problems and frustration. That is why memes with very expensive '3D printed spaghetti' made by poorly prepared devices are still a thing on the internet. Of course – the technology made a huge leap forward and these problems are more often related to operator error than the machine. It is worth mentioning that the printed parts often require additional sanding and/or grinding to achieve the expected smooth surface. CNC machining delivers a very smooth surface of manufactured parts that often requires only short sanding to provide perfect results. On top of that: both of these technologies require perfectly calibrated devices and drivers to perform to their abilities,
- level of manufactured parts complication – 3D printers provide the possibility to manufacture elements with almost unlimitedly complex internal structures, impossible to achieve with other manufacturing techniques. On the other hand are less than optimal for building flat and long surfaces, especially in comparison with CNC machining,
- work safety – many materials used in 3D printing are possibly dangerous to human health (toxic, cancerogenic). That is why most additive processes are executed inside special (vented) chambers. It is worth mentioning that many CNC machining processes can be also dangerous for the operators, just like additional galvanic surface bettering – like anodization.
Taking that in mind: both of these technologies – although completely different – are interchangeable and inextricably connected.
