CNC machining

CNC stands for "Computer Digital Control" and refers to a set of commands issued by the machine to control by the controller. The command code issued by the controller is usually in the form of a list of coordinates, called a G-code. Any machine controlled by such codes can be called a CNC machine, including milling machines, lathes, and even plasma cutters. Below we will focus on the different types of CNC milling machines and lathes and their combinations. The movement of CNC machines can be defined by their axes, including X, Y, and Z, and more advanced machines include A, B, and C. The X, Y, and Z axes represent the main Cartesian vectors, and the A, B, and C axes represent the rotation of the axes. CNC machines usually use up to 5 axes.

Typical CNC machines are listed below:

• CNC Lathes – This type of lathe works by rotating the material in the chuck of the lathe. The tool then moves in 2 axes to cut out the cylindrical part. CNC lathes are capable of forming curved surfaces, while manual lathes are difficult or even impossible to form. Tools are usually non-rotating, but can be moved if they are powered tools.
  CNC Milling Machines – CNC milling machines are often used to manufacture flat parts, but more complex machines have more degrees of freedom and are capable of producing complex shapes. The material is stationary, the spindle rotates with the tool, and the tool moves in 3 axes to cut the material. In some cases, the spindle is stationary and the material moves.
• CNC Drilling – This machine is similar to a CNC milling machine, but it is specifically designed to cut in only one axis, that is, only down the Z axis into the material, and never in the X and Y axes.
• CNC Grinding Machine – This type of machine brings the grinding wheel into contact with the material, producing a high-quality surface. It is designed to remove small amounts of material from hard metals; It is therefore used as a surface treatment operation.

Subtractive manufacturing

CNC machining produces parts through subtractive manufacturing. This type of processing basically removes the material from the solid billet and finally forms the desired shape. It can be done by any of the methods we have mentioned above, such as milling, turning, grinding, or drilling. Additive manufacturing is the opposite process, adding material from scratch to form a part, such as 3D printing.

Frock

The tooling performs all cutting work. Tools are usually mounted on tool racks or loaded onto spindles as needed. Many different tools are used in the process of manufacturing complete parts, and there is no one-size-fits-all manufacturing method. The tools commonly used in typical machining are listed below.

Milling tools

End Mill – End mill is a common fixture that is usually capable of cutting in 3 directions. It is divided into different styles, such as flat head, rounded radius, ball head, and taper shank, etc.; Available in different edge counts, helix angles, substrates and coating materials.

Face milling cutter – Face milling cutters cut on a large surface area, i.e. positive plane milling. Its cutting edge is usually on the edge of the tool, and the milling teeth are usually carbide inserts.

Thread milling cutter – Thread milling cutter produces threads that work by rotating them in a threaded manner around the wheel axle, thus cutting out the thread shape.

Cut milling cutters – Use these milling cutters to form T-grooves along the length of the assembly. Due to the geometry of this tool, it must enter and exit from the open end of the material.

Lathe tools

OD turning – As the name suggests, this fixture is designed to cut on the outside diameter of a part. It may be a solid fixture that machines the part into the desired shape, or it may be a carbide insert.

Inside diameter grooves and threads – These tools are typically thin and can be drilled into the inside of the part, grooving on the inside diameter, or forming threads inside.

Cut – The Cut off tool is used to cut off a part after all other operations have been completed as a final operation.

Drilling – Used to drill holes in the longitudinal direction of a part, the holes drilled must be reamed or drilled to achieve final tolerances.

Tooling materials

Tool types can be further subdivided by the material of the tool itself. Commonly used tooling materials are listed below:

• High Carbon Steel – It is the lowest cost machining tool and does not last long. It loses hardness at temperatures of about 200°C.
• High Speed Steel (HSS) – It is more commonly used than carbon steel tools because it lasts longer and only loses its hardness at 600°C, allowing it to be cut faster.
• Carbide – Carbide tools are harder than HSS, but less rigid and can break if not handled properly. It can withstand temperatures up to 900°C.
• Ceramics – These cutting tools are extremely hard and are usually only used to cut hard materials at very high temperatures. It has two common materials, namely aluminum nitride and silicon nitride.
• Cubic Boron Nitride – This tool is ideal for quenched steels and superalloys with excellent friction and thermal resistance.

Advantages and disadvantages of CNC machining

CNC machining has gradually become mainstream in the manufacturing industry because it is more efficient than machines that use manual operation. Some of the advantages and disadvantages of CNC machines are listed below.

Types of CNC milling and turning machines

CCNC milling machines

• Vertical Machining Center (VMC) – The spindle of a vertical machining center remains in the same position and the lathe moves under it. In some cases, the lathe moves upwards, making contact with the spindle, or the spindle can move up and down in the Z axis. The high rigidity of these machines enables the production of high-precision components. Its disadvantage is the relatively small working area. A VMC may have 3 axes (X, Y, Z), 4 axes (X, Y, Z, A), or even 5 axes (X, Y, Z, A, B).
• Horizontal Machining Center (HMC) – The spindle of an HMC machine is horizontal, not vertical. This type of machine is ideal for long-term production, as it can process up to three times as many parts as VMC, given enough workload. HMCs are far more expensive than VMCs. While another part is being manufactured, a piece of material can be fixed to the lathe of the machine. This enables continuous production and the spindle can be easily moved to the next piece of material ready for quick replacement.

CNC lathes

CNC lathes are capable of machining with only one chuck and two shafts. CNC lathes are divided into the following types:

• Normal lathe – It is basically a standard lathe and is relatively versatile. It contains the word "Engine" in its English name, as such lathes used to be driven by pulleys of engines mounted outside the machine. An ordinary lathe is a lathe with a motor on a lathe.
• Turret lathes – Turret lathes can significantly speed up production because all the tools needed are loaded onto the turret before manufacturing. When you need a new tool, simply rotate it to the appropriate position.
• Tool Room Lathes – Tool room lathes are used for high-precision, low-volume operations. As the name suggests, such lathes are used to make tools and molds. The functions of tool room lathes are also very versatile.
• High-speed lathes – This type of lathe is mainly used for light work, and its structure is very simple, including the headstock box, tailstock and tool holder.
• CNC Turning Centers – These lathes are very advanced and offer a range of features including milling and turret tool holders, and even a second spindle. Turning centers are also divided into vertical and horizontal types. Horizontal lathes let chips falling from parts enter the chip conveyor, while vertical lathes let gravity help remove chips when parts snap into the chuck. Vertical lathes are easier to automate. Which type of lathe is more suitable depends on the specific application.

material

CNC machines are capable of handling a wide range of materials, from aluminum to superalloys such as Inconel. Each material has its own set of challenges that require specific tooling, speed, and feeding.

aluminium

Since aluminum is a very soft metal, there is a risk of sticking to the cutting tool. In view of the low melting point of aluminum, proper tempering of aluminum to increase hardness can improve its machinability.

carbon steel

Since steel is divided into many grades, many factors can affect the overall processability of the material, such as cold work, chemical composition, microstructure, etc. In general, elements such as lead and tin are able to increase cutting speed due to lubrication, and sulfur reduces strain hardening of chips.

titanium

There are many alloy types of titanium, each with its own challenges. Ideally, the tool must be in constant contact with the material, as staying in an area can lead to friction, heat build-up, work hardening, and tool wear. Pure titanium has properties similar to aluminum and also sticks to cutting tools, but its alloy is usually harder, which can lead to heat build-up and tool wear. Low rotational speeds and high chip loads extend tool life as temperatures can be reduced.

Superalloys

Superalloys have high strength at high temperatures, making them difficult to machine. To process such materials, more powerful machines are necessary. Superalloys work harden quickly, making subsequent machining more difficult. It is generally recommended to keep the cutting speed low.

copper

Copper is notoriously a very difficult material to machine because it is malleable and often rolls around the tool without being able to cut. It is mainly used in power components and heat exchanger assemblies where high electrical conductivity and high heat transfer coefficient are required. For pure copper, high-speed feeds are usually available. Compared to pure copper, copper alloys are much easier to machine.

plastics

Plastics are divided into thousands of types, from thermosets to ordinary thermoplastics, etc. The hardness and mechanical properties of plastics also vary widely. Only rigid plastics work well and stay within tolerances, while soft plastics often deform as they pass through cutting tools, resulting in components that do not meet specifications. Since plastic is an insulator, heat often accumulates at the cutting edge, and if you are not careful, the plastic will melt.

What can go wrong?

Although there are many uses and functions implemented by CNC machines, there are also some risks. Some of the errors that often occur in CNC machining are listed below.

CNC system collapse – CNC machines don't think on their own; It will only act according to human instructions. If programmed incorrectly, the machine may allow the cutting tool to cut itself within a millisecond. The machine usually detects a system crash and stops functioning, but damage may have been done by this time. There are a variety of software tools to help mitigate such risks. Tool operation paths can be simulated before the code is uploaded to the machine. Using standard computer-aided manufacturing (CAM) software, it is difficult to simulate complex 5-axis machines, and additional software is required between writing the CAM code and uploading the code to the machine.

Improper speed and feed – Speed and feed are critical to producing high-quality machined components. Using the wrong settings will increase tool wear, resulting in substandard finishes and tolerances. The correct setting of speed and feed is a complex subject, as each material and its alloy requires different settings to achieve the desired cutting result. Reaching a reasonable setup usually requires several attempts.

Lack of maintenance – As with any complex machine, lack of maintenance can cause CNC machines to break down quickly. Machines must be kept clean and strictly adhere to OEM maintenance schedules.

Major industries that use CNC technology

Any industry involved in component production is directly or indirectly affected by CNC machining. Some of the major industries that use CNC machining are listed below.

Aerospace – Aerospace requires components with high precision and repeatability, including turbine blades in engines, tooling for other components, and even combustion chambers used in rocket engines.

Automotive and machine building – The automotive industry requires the manufacture of high-precision molds for casting parts such as engine mounts or machining parts with high tolerances such as pistons. Gantry machines can cast clay modules for use in the design phase of automobiles.

Military – The military industry uses high-precision components with tight tolerances, including missile components, gun barrels, and more. All machined parts in the military industry benefit from the precision and speed of CNC machines.

Medical – Medical implantable devices are often designed to fit the shape of human organs and must be manufactured with high-grade alloys. Since no manual machine is capable of generating such shapes, CNC machines become a necessity.

Energy – The energy industry covers all areas of engineering, from steam turbines to cutting-edge technologies such as nuclear fusion. Steam turbines require high-precision turbine blades to maintain balance in the turbine, and the shape of the R&D plasma suppression cavity in nuclear fusion is very complex, manufactured using advanced materials, and requires the support of CNC machines.

Current trends in CNC technology

With the acceleration of technological development in recent years, we feel that additive manufacturing will become the mainstream of CNC machining, but it is more likely that more and more emerging manufacturing centers will combine multiple technologies into one machine, so as to take full advantage of the advantages of subtractive and additive manufacturing machines to develop machines that are more powerful than the sum of the two. Early applications of such machines have already emerged.

In addition, through the Fourth Industrial Revolution, automation has made great progress, and more automated systems will be developed, capable of self-diagnosis and self-optimization with little human intervention. In the future, products are expected to be manufactured to the individual requirements of consumers, and CNC machines are able to make this vision a reality thanks to their outstanding flexibility.