CNC Machines can be classified based on their underlying technology and their functions as CNC Mills, CNC Routers, CNC Plasma Cutting Machines, CNC Lathes, CNC Laser Cutters, CNC Water-jet Cutters, CNC Electrical Discharge Machines (EDM), and CNC grinders.
Different types of CNC machines
CNC machines differentiate themselves through the function they perform, materials they work upon and the underlying technology of the machine.
1. CNC Milling Machine
CNC Mills are one of the most popular CNC machines, with built in tools used mainly for drilling and cutting.
Mills derive and convert specific programs made up of letters and numbers (G code) in order to route and path the spindle in different ways. After placing the work-piece inside the milling machine, the computer takes control.
The computer code guides and instructs every movement and action of the spindle and tools to cut , and convert the work-piece to a designed custom part with high accuracy.
Tapping, Drilling, Turning, Face milling and Shoulder milling are some of the common functions that a CNC milling machine can perform.
CNC Milling machines have configurations starting from 3 axis, up to to six axis. In the most basic 3 axis CNC, the three axes represent the X axis (horizontal) , Y axis (horizontal) and Z axis (depth) movements.
CNC milling machines are quite large and expensive when compared to other CNC machines like CNC routers. In general CNC Mills are used to machine hard metals and CNC routers are used to machine softer materials like wood, plastics and soft metals.
Okuma, HaaS and DMG Mori are some of the popular CNC milling machine manufacturers.
2. CNC Router
A CNC router is a machine similar to a CNC mill, but is generally used for machining softer materials and is typically less precise compared to CNC Mills.
CNC Routers are significantly cheaper than CNC Mills. A high quality CNC Router can be bought for less then $2,000 whereas even entry level CNC Mills cost upwards of $10,000.
I talk in detail about the cost of various CNC Machines here- How Much Do CNC Machines Cost?
CNC routers are characterized by their ability to use computer numerical control to route spindle and machine tool paths to design and shape materials like wood , steel , composites , aluminium , foam and plastic to the desired design and shape .
CNC routers reduce wastage, increase productivity and accuracy in addition to producing products at a faster rate. Majority of the CNC routers are capable of working on a workpiece on all three dimensions and excel in the creation of small projects and prototypes of simple and complex design.
Like CNC Mills, CNC routers are also available in various axes ranging from three to six.
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3. CNC Plasma Cutting Machine
CNC plasma cutting machines are similar to CNC milling machines in the fact that they share the same function , that is to cut materials . However, CNC plasma cutting machines use a plasma torch to cut through their materials while a milling machine uses an end mill attached to a spindle.
The chief requirement for CNC plasma cutting machines is that whenever plasma cutting is used , the material or workpiece to be cut must be electrically conductive. Typical materials used as workpiece for plasma cutting are brass , copper, aluminum , steel and stainless steel. This could also be considered as a disadvantage of plasma cutting.
A CNC plasma cutting machine is equipped with a high powered torch that is able to cut through even the toughest materials like titanium and steel.
Primarily CNC Plasma cutters are used in heavy industries like shipbuilding, automobile manufacturing, chemical manufacturing and industrial steel construction sites. Consequently the work-piece is generally large and heavy in CNC plasma cutting.
In a CNC plasma cutting machine, the torch is produced by passing high velocity gas through a nozzle. While this process is carried out , an electric arc is produced. The arc forms through the high velocity gas and jumps onto the material being cut, converting an amount of the high velocity gas into plasma (electronically ionised gas).
CNC plasma cutting machine exhibits a close resemblance to the function and property of a handheld gas powered torch. However when the gas powered torch produces temperature up to 10,000 degrees Fahrenheit for welding, plasma torches achieve temperatures ranging from 10,000 degrees Fahrenheit to 50,000 degrees Fahrenheit . The material being cut melts at this temperature due to the amount of heat produced.
4. CNC Lathe Machines
CNC lathes work by spinning the work-piece at a high speed while a blade/knife is applied to the surface to produce the desired product.
Lathes, typically work best for products with cylindrical,conical or flat shapes. This is a distinct difference between CNC Mills and Lathes, because CNC Mills can work on any shape.
Although considered to be less precise and verstaile compared to a CNC Mill, CNC Lathes cost much lesser and are excellent for quick, simple jobs.
CNC lathes gain advantage in the fact that the machine is smaller and more compact , thereby increasing their portability. The machine is also characterized by its ability to rotate the work-piece while in operation.
CNC lathe machines feature a lathe in the centre that is able to rotate and turn the raw materials into position as programmed and commanded by the computer.
Typically, CNC Lathes have two axes. The Z axis, which is the movement along the chuck, controls the length of the work-piece. The X-axis, which is the movement perpendicular to the chuck, controls the diameter of the work-piece. Although it is possible to have additional configurations, this is it's most basic form.
The tools used for cutting the workpiece are fed in a straight or linear path along the spinning or rotating bar stock.
The machine then applies a subtractive method, that is it removes material around the circumference of the material until the desired diameter for the custom design is achieved. Since the machine has the feature to rotate the raw materials , it requires and has a lesser number of axes for the movement of their tools , leading to their smaller form factor.
CNC lathe machines are mainly used for their ability to create external and internal features on the workpiece such as drill holes , bores and threads .
CNC Lathe machines are similar in how they are controlled to CNC mills and can read both G code and proprietary programming languages. Shafts, bolts and screws are some of the components made on CNC lathes and turning machines. Some of the manufacturers of CNC Lathes are HaaS , Okuma , DMG Mori.
5. CNC Laser Cutting Machine
CNC laser cutting machines resemble CNC plasma cutters in their ability to cut through tough materials . However, CNC laser cutting machine uses a strong and highly focused laser to perform the task unlike a plasma cutter which uses plasma (ionized gas).
Since lasers have a smaller point of contact and spread when compared to torches, CNC laser cutting machine typically provide a higher level of accuracy and a better surface finish when compared to CNC plasma cutters.
Also, CNC laser cutters are much costlier compared to CNC Plasma cutters of similar specs (accuracy and cutting depth). but costs higher. However, CNC plasma cutters offer a higher strength of cutting as plasma is quite strong when compared to lasers.
Theyare predominantly used for cutting plastic, metals and hard wood. Depending on the density and strength of materials, the laser intensity can be tweaked to cut through the material more easily .
In CNC laser cutters, material shape is often in a sheet form. The laser beam then moves to and fro on the material to produce an accurate cut . The heating effect of the laser vaporizes or melts the workpiece to create the exact cut.
CNC laser cutters are often able to produce a variety of designs when compared to other cutting machines. Often, the cuts and edges produced are so precise and clean that they do not require additional finishing. Hence CNC laser engravers are often used for part making and engraving of machine components .
Laser engraving is highly used in decorative works such as sign making, woodworking art and glass engraving. CNC Laser cutting is opted for when the tolerances are tight and a precise output is required.
Lasers such as CO2 and neodymium (Nd)-doped yytrium-aluminum-garnet (Nd:YAG) are commonly used in CNC laser cutting machines .
6. CNC Waterjet Cutting Machine
CNC Waterjet cutters, as the name suggests, use high pressure jets of water to cut through materials.
Typically CNC Water-jet Cutting is opted for when the material to be worked upon is sensitive to temperature and could melt at high temperatures, such as plastic and aluminum.
Although, these machines can cut with just water, usually additional abrasive materials like garnet (a mineral) or aluminum oxide are added to the water for more efficient cutting.
A CNC Water-jet cutting machine costs more than a plasma cutter with similar specifications. But it costs less compared a CNC Laser cutter with similar specifications.
One disadvantage of a CNC water-jet cutter is that it is typically slower than CNC plasma cutters and CNC laser cutters.
7. CNC Electrical Discharge Machine
CNC Electrical discharge machines (EDM) also termed as spark CNC machines. It can also be called wire burning, die sinking, spark machining or spark eroding. CNC electric discharge machines use electrical sparks which produce high temperatures to manipulate and shape materials into the desired form.
The erosive effect of electrical discharge, i.e, its ability to deform materials is taken advantage of in CNC electrical discharge machines.
Electrical discharge CNC machines produces a series of controlled sparks or recurring electrical discharges producing temperatures up to 21,000 degrees Fahrenheit to reshape materials.
The materials or work-piece are placed in between two electrodes, the top and bottom electrode. Based on the G code, the computer instructs the amount of electrical discharge that must be produced by the electrodes.
This process creates sparks that consumes the material on the work-piece as per the design. The materials consumed by the sparks are flushed/washed by a dielectric fluid which completes the process.
Electrical Discharge Machine is distinguished by its ability to create precise slots , micro holes, angled or tapered features, which are usually difficult to machine using traditional CNC methods.
Since, EDM's use sparks for cutting rather than bits or end-mills, the machining in an EDM is non-contact. This helps avoid deflections in the work-piece, a distinct advantage when working with small-thin workpieces. An example of this would be a sprocket gear.
8. CNC Grinder
A CNC Grinder, uses abrasive tools to smooth and finish a machined product. Grinders are typically used in applications requiring extremely high precision such as machining of engine parts.
Generally, the product is first created with a rough surface using a CNC Mill or Lathe and then moved to the CNC Grinder for the final finishing.
CNC Grinders comes in various types such as surface grinders, roll grinders, and cylindrical grinders among others. There is a lot of variety in the type of abrasive used for grinding as well, such as plated or vitrified CBN, Diamond grinding wheels, and Aluminum Oxide and Ceramic Blend Grinding Wheels among many others.
These are the most common types of CNC machines that are in use today. The choice of machine depends on the type of job, the accuracy required, job budget and the time available to complete the job.