Basic Machining Operations

What is Basic Machining Operations?

Machining operations involve removing material from a workpiece to achieve specific contours or dimensions using one or more cutting tools. Various operations, such as milling, turning, drilling, boring, and grinding, are commonly used to remove metal through shearing processes. There are two types of basic machining operations: Turning and Milling. In a turning operation, the workpiece is clamped with spindles and rotates at a high speed, while a fixed cutting tool removes material from it through a shearing process. On the other hand, milling operations involve a rotating cutting tool that is always clamped with the spindle and spins at a higher speed. The workpiece is mounted on a machine bed, and excess material is removed through the shearing process. In Turning, the cutting tool is fixed and the workpiece rotates, whereas, in Milling, the cutting tool rotates while the workpiece remains stationary. The following pictures illustrate these two basic machining operations: Turning and Milling.

Milling - In milling, a multi-edge cutting tool rotates at high speed while a stationary workpiece removes excess material through shearing. Various milling operations, such as up milling, side milling, and straddle milling, are used for different machining processes. 

Types of milling operation

Milling operations can be categorized into two groups: Peripheral milling and Face milling. In peripheral milling, the milling cutter's surface is parallel to the machining surface of the workpiece, with cutting edges present on the outer surface. Face milling, on the other hand, involves cutting edges on both the rim and outer surface of the cutter, which is positioned perpendicular to the cutting surface of the workpiece.

 

Peripheral Milling - Peripheral milling includes operations such as slab milling, side milling, straddle milling, and slotting, where the cutter is arranged parallel to the workpiece, and the cutting edges are present only on the outer surface. The following pictures depict different peripheral milling operations.

In peripheral milling operations, the relative movement direction of the workpiece with the cutter can occur in two ways: Conventional milling or Up milling, and Climb milling or Down milling. Conventional milling involves the feed direction of the cutting tool being opposite to its rotation, while in climb milling, the cutting tool feeds in the same direction as its rotation. Hence, the key difference between up milling and down milling is the direction of the cutter's rotation relative to the path of travel. The following picture illustrates these two different types of peripheral milling operations. 

Face milling - In face milling, the cutter is arranged perpendicular to the workpiece. This process involves cutting edges present in both the cutter face and outer surface. Various operations, such as conventional face milling, partial face milling, end milling, profile milling, pocket milling, and surface contouring, fall under the category of face milling. The following pictures explain different face milling operations.

 

Turning – This simple machining process, also known as lathe operation, involves rotating the workpiece at a high speed while a stationary cutting tool removes material through shearing. Typically, cylindrical workpieces are created using this machining operation.

 

Types of Turning Operations

Different types of turning operations are performed, including simple turning, facing, boring, drilling, parting, threading, knurling, etc. Turning operations typically produce straight, tapered, and grooved cylindrical workpieces. These operations can be classified into four primary categories: straight turning, taper turning, contour or profile turning, and form tool turning. The following pictures illustrate different turning operations commonly found with CNC lathes or turning machines.

Boring - Boring is similar to turning, except it involves removing material from the internal diameter of the workpiece. A single-point cutting tool is often used to enlarge a drill hole in the boring operation.

Drilling - This operation creates different types of holes in a workpiece. There are various drilling operations, including plain drill, step drill, counter shank, and counterboring.

Grinding - Grinding is a finishing machining operation where a grinding wheel is used to remove a very small amount of material from the surface area of the workpiece. The grinding wheel rotates at high speed while the workpiece moves slowly, resulting in material removal through shearing from the exterior.

Additional Accessories and Equipment

Various types of auxiliary or supplementary accessories and equipment are used with CNC machines to enhance machining operations, making them more flexible and efficient. Some accessories are common to all types of CNC machines, while others are optional. For instance, a 'Tool turret' unit is available only with CNC Turning or Lathe machines, while a 'Tool Magazine' is found in vertical or horizontal CNC machining centers. The following are some commonly used accessories and equipment with CNC machines.

1. Rotary Axis / Table

A rotary axis is used with CNC machines to rotate the workpiece precisely, providing greater flexibility during machining operations. In a horizontal CNC milling machine, the B-axis serves as the rotary axis, also known as the 'Fourth Axis,' allowing for 360-degree movement. Rotary axes are typically available in two types: continuous rotary tables and index tables. A continuous rotary table allows for fractional-degree rotary motion (less than one degree), while an index table moves in one-degree increments without fractional degrees.

In some cases, a rotary axis/table is included as a separate unit with a CNC machine and can be selected as a tilted rotary table. Such rotary tables offer two different rotary movements. One side can rotate a full 360 degrees, while the other has limited rotary motion ranging from 120 to 180 degrees. These tilted rotary tables have lower rigidity and flexibility compared to fixed types, and they are sometimes used as separate units connected to CNC machines. The following picture illustrates a tilted rotary table.

 2. Automatic tool changer unit       

An automatic tool changer (ATC) unit is a crucial component of a CNC machining center. It retrieves tools from the magazine and positions them on the spindle, replacing any tool previously held by the spindle. Typically, the ATC takes between three to seven seconds to complete this task. The ATC arm's rotational movements are powered by an induction motor or sometimes servo motors, which employ a step-by-step action facilitated by a cam mechanism. The design of the ATC arm's rotation movements depends on the specific ATC design and the type of tool magazine used. There are two types of tool magazines commonly found with ATC mechanisms: the drum type and the chain type. The drum-type magazine has a much higher rotation speed compared to the chain type. The chain-type magazines are used when there are more than 30 tool pockets required. The image below depicts a chain-type magazine with an automatic tool changer (ATC).

 

How does the automatic tool changer unit work?

To perform an automatic tool change, the CNC machine's axes must be in a designated position called the tool change position, and the spindle must stop at a specified alignment known as the spindle key-lock position. Upon receiving the tool change command from the CNC controller, the tool magazine first rotates to locate the specific tool in the changing position. If all the conditions for tool changing are met, the ATC arm rotates and securely grips both the spindle and the magazine tool simultaneously. To achieve proper tool gripping, the ATC arm is equipped with specialized grippers at its two ends. These grippers operate against spring tension to securely hold the tools. After gripping the tools, the spindle releases the previously clamped tool. The ATC arm then ejects the tools from the magazine and spindle, simultaneously rotating the arm 180 degrees to interchange the tool-holding position. Once the tool positions have been exchanged, the ATC replaces the tools into the magazine and spindle, effectively switching their positions. The spindle clamps the newly changed tool, and the tool on the magazine side is securely held in place by a special ball and spring mechanism inside the magazine pocket. After clamping and holding both tools, the ATC arm returns to its initial position, marking the completion of the tool-changing sequence. The CNC controller stores the tool numbers, offset values, and magazine location data in the "Tool magazine data" page within its memory. The controller updates the tool magazine data as required after each automatic tool-changing operation. This ATC arrangement is referred to as a random tool change system, where a tool magazine does not have a specific pocket for each tool. In earlier machines, a distinct magazine tool pocket was employed, resulting in a different changing mechanism and relatively longer tool change times compared to a random tool change system.

 3. Tool Turret

The tool turret is a simple tool-changing system commonly found in CNC turning centers. Typically, a turret has eight to twelve tool posts arranged in a circular manner. Unlike the traditional tool-shifting arm mechanism, the turret operates with an automatic tool-changing (ATC) mechanism, resulting in reduced tool-changing time. When receiving a tool-changing command from the CNC controller, the turret's holding part is unlocked from its base and rotates to position the requested tool in line with the machining position (cutting line with the spindle workpiece). A rotary motion is achieved in the tool post segment using an induction or sometimes a hydro motor. To determine the tool position, proximity switches or, in some cases, an absolute encoder are utilized to provide information about the cutting tool's location. Once the desired tool is positioned, the tool post segment is firmly clamped along with the turret base unit. Only one tool is placed on the cutting line with the spindle workpiece at a time, engaging in the machining operation. The image below illustrates a tool turret unit used in CNC turning centers.

Typically, during a turning operation, the workpiece rotates (clamped with the spindle), while the cutting tools on the tool post remain fixed or non-movable. The cutting material is removed by the selected tools as they move over the rotating workpiece. In the case of CNC "Turn-Mill" machines, some tools holding the tool posts are considered live tools. These live tools can rotate at high speeds independently, driven by a servo motor and integrated with the turret assembly using a typical mechanism. As a result, CNC turn-mill centers employ both fixed tools for turning operations and live or rotating tools for milling processes.

4. Power Chuck

Power chucks are used in conjunction with the spindles of CNC turning machines to securely grip cylindrical workpieces during the machining process. Typically, power chucks operate using hydraulic pressure. They feature three to four adjustable jaws, which can be moved toward or away from the spindle center by hydraulic pressure. Since the power chuck jaws have a limited influence, the chuck's holding diameter needs to be adjusted to match the workpiece's outside diameter. The application of hydraulic pressure to hold the workpiece involves moving a small hydraulic cylinder inside the power chuck. This cylinder positions the jaws, bringing them together towards the center of the spindle, and tightly clamps the workpiece inside the spindle. To release or unclamp the workpiece from the spindle, the cylinder moves in the opposite direction. The image below illustrates a typical power chuck assembly commonly used with CNC turning machines.

5. Automatic pallet changer unit

An automatic pallet changer (APC) unit is employed with CNC machines to enhance productivity. A pallet unit refers to a device used for holding workpieces during machining operations. CNC machining centers often incorporate multiple pallet units to increase productivity. While one pallet is engaged in the machining operation inside the machine, another pallet can be prepared for machining. This involves clamping or holding the workpieces on the outside pallet, typically located outside the machining area. As machining progresses with the internal pallet, the machine operator can load workpieces onto the outside pallets, saving loading time. Once the machining operations are completed on the internal pallet, the outer pallet automatically moves into the machining zone, while the inner pallet is released from the machining zone. The machine operator manually removes the finished workpieces from the pallet and loads new ones for the next machining operation. This arrangement, provided with CNC machines, saves cycle time and increases machine efficiency. The image below depicts a two-station automatic pallet-changing system commonly found in CNC machining centers.     

An automatic pallet changer unit consists of two separate mechanisms: pallet clamp/unclamp and automatic changing mechanism. The clamp mechanism securely fastens the pallet to the machine bed, while the unclamp mechanism quickly releases it. Pallet clamp/unclamp operations with CNC machines are carried out using hydraulic pressure. The pallet changing mechanism facilitates the movement of the pallet from the loading station to the machining area and transfers the machined pallet back to the loading station. The changing process is executed by a linear hydraulic or pneumatic cylinder and, in some cases, an induction motor, supported by a rack and pinion mechanism.

 

6. Automatic bar loader unit

The automatic bar loader unit is an independent assembly commonly used with CNC turning machines. This accessory facilitates the automatic and continuous feeding of workpiece blanks to the machining area. A long, rounded bar is used as the workpiece blank for preparing cylindrical jobs through turning operations. The bar feeds from the rear of the spindle, and as the machining (turning) operation progresses, the required workpiece length is reduced from the remaining bar. Once the machining operation on a bar is complete, another bar is positioned through the spindle using a separate mechanism. Consequently, manual loading of workpieces by the operator is not required repeatedly, resulting in increased overall machine efficiency. The bar loader/feeder unit may be hydraulically or pneumatically controlled, depending on the specific application. The image below illustrates a bar feeder unit applied to CNC turning machines.

 

7. Lubrication system

In a CNC machine, the lubrication system plays a crucial role. The meeting points of linear guideways and ball screws are the most significant and critical frictional parts of the machine. The precision and efficiency of the machine depend solely on these components. Excessive friction inside the guideways and ball screws can cause irregular and jerky movement of the axes, resulting in chattering marks on the workpiece during machining operations. To eliminate this issue, it is mandatory to use a lubrication system with a CNC machine. The lubrication system provides a small amount of lubricating oil to the contact points of the linear guideways and ball screws at regular intervals. While the machine is running, the lubricating oil is injected into different contact points within specific time intervals. This process reduces friction forces between the contact points and protects them from rust and corrosion. The following picture shows a typical lubrication unit used with CNC machines.     

In line with the previous picture, a lubrication system consists of different units, such as a motor with a pump, pressure and level sensors, and an oil tank. Usually, a small gear pump, driven by an induction motor at regular intervals, is used in conjunction with the lubrication system. The pump extracts lubricating oil from a container and sends it to various parts of the machine, such as guideways and ball screws, through thin copper or PVC tubes. The lubrication pump does not run continuously; its running and stopping times depend on the PLC program, usually written by the machine builder. A 'dozer' is included at the end of the lubrication pipeline opening, which determines the amount of lubricating oil injected into the guideways or ball-screw junction points. A complete lubrication system is equipped with two separate sensors: a float switch that senses the oil level inside the oil tank and a pressure switch that sends feedback on the oil pressure to the CNC controller. A pressure gauge is also attached to the lubrication system, which indicates the lubricating pump oil pressure and is visible from the outside. CNC machines commonly use higher VG (viscosity grading) lubricating oil, such as SERVO-68.

8. Coolant system

The coolant system is an essential component associated with the machining operation in CNC machines. A complete coolant system consists of additional components or devices like a cooling agent, a coolant pump with a tank, and a coolant delivery system.

Cooling agent or coolant - Different types of cutting fluids, such as oil, oil-water emulsion, and aerosol, are used as cooling agents or coolants with various metal cutting CNC machines. Most metal cutting machines use a 'semi-synthetic coolant' or 'soluble oil and water mixed' coolant as a cooling agent. SERVOCUT, a water-mixed emulsifier coolant, is one of the most popular coolants employed with CNC machines. The pH value of the coolant used in metal cutting operations typically ranges from 8 to 9.5. A device called a 'refractometer' is used to measure the concentration of the coolant. An ideal coolant for metal cutting operations should possess three properties: cooling, lubricating, and chip cleaning.

            

         Cooling – The heat generated during metal cutting operations has a significant impact on the cutting tool's life. While a small amount of heat during metal cutting is beneficial as it softens the workpiece material, excessive heat softens the edges of the cutting tool tips and causes them to become blunt quickly. A cooling agent or coolant is employed during metal cutting to overcome this heating problem and increase the tool life.

           Lubrication - The lubricating property of the coolant helps to cut the workpiece material effortlessly. During machining operations, the movements of the cutting tool across the workpiece generate metal chips and considerable heat due to friction. The lubrication property of the coolant reduces the heat generated during metal cutting.

       Chips cleaning - A pile of metal chips generated during metal cutting can be re-cut, leading to an inferior cutting surface finish on the workpiece. A sufficient cooling spray pushes the chips away from the cutting tool edge and protects it from damage.

Coolant pump and tank - CNC machines may have two or more coolant pumps for different purposes, with varying pressure and coolant delivery systems. Typically, centrifugal or gear pumps are used for delivering lower coolant pressure, while screw pumps are used for higher pressure. The coolant pumps are usually mounted on top of the coolant tanks. The coolant pump draws the coolant flow from the tank and delivers it to the machining area through different control valves and pipelines. A return pump is used to send back the coolant accumulated in the machine to the tank. The schematic diagram below shows a complete coolant delivery system with a CNC machine, including a coolant pump, tank, and other essential components.

Coolant delivery system - CNC metal cutting machines employ three types of coolant delivery systems: spray coolant, through-tool coolant, and flash coolant delivery. Each type may or may not be used in all types of metal-cutting machines.

              Spray coolant delivery - This coolant delivery system is used in almost all types of CNC machines. The coolant is supplied from a low-pressure pump through a pipeline with flexible and adjustable nozzles to discharge coolant at the cutting edges of the tool. It reduces the heat generated during metal cutting and removes the chips away from the cutting area.

 

        Through tool coolant delivery – During deep-hole drilling operations inside the workpiece, a spray coolant from the outside is not sufficient to separate the chips from the cutting edge. In such cases, CNC metal cutting machines implement a 'through-tool coolant' delivery system. Here, the coolant flows through the rear side of the cutting tool and is transferred inside the tool, reaching and discharging at the cutting edge. The coolant is dispatched from a high-pressure coolant pump, and the delivery line passes through a rotary union located at the rear side of the spindle. From the rotary union, the coolant passes through a draw tube (situated inside the spindle) to the end of the tool pull-stud (used to clamp the tool within the spindle) and finally reaches the cutting edge through the pull stud. The configuration of a through-tool holder differs from a standard tool holder. High-pressure coolant pumps are used with the through-tool coolant delivery system to remove chips evenly during deep-hole drilling operations.

            Flash coolant delivery - A flash coolant or flood coolant delivery system is applied in CNC machines to remove the chips accumulated during machining operations. Metal chips formed during machining operations are usually scattered over the machining area and accumulate inside the machine. The flash coolant flow carries the metal chips to a conveyor to prevent chip buildup within the machining area. A conveyor unit collects all the chips and discharges them into a bin located outside the machine.

Coolant filtration system - Chips generated during the machining process are typically removed from the machine using a chip conveyor system. However, very fine or tiny chips cannot be removed by the conveyor system, and they mix with the cutting coolant, leading to quick degradation of the coolant's properties. To overcome this problem, advanced CNC machines employ a separate coolant filtration unit. This unit has an independent pump that extracts the contaminated coolant from the machine coolant tank and passes it through a filter. The filtered, contamination-free coolant is stored in a separate tank located under the filter, and the refreshed coolant is sent back to the machine tank using a different pump unit. The whole system functions automatically with sensors such as float and pressure switches, which are integrated into the CNC machine's control mechanism to prevent coolant overflow or drying. By maintaining the coolant's properties, this system improves machine productivity and increases the life of cutting tools. The picture below shows a typical coolant filtration unit found in metal-cutting CNC machines.

9. Chip conveyor system

A chip conveyor system is used with CNC machines to remove metal chips that accumulate during machining operations and discharge them into a container or bin. It is equipped with an overload protection mechanism to prevent damage due to jamming during chip transport. Chip conveyor systems used with CNC machines are built with heavy-duty and high-efficiency motors, conveyor belts or chains, and guides to handle heavy loads. In addition to removing chips from the machining area, these systems also separate the metal chips from the cutting coolant used during machining operations. There are three commonly used chip conveyor systems in CNC machines: hinge belt type, scraper type, and magnetic type.

Hinge belt Chip conveyor - The hinge belt chip conveyor is the most commonly used system with CNC machines. It efficiently transfers heavy and solid chips, and the metal chips generated during machining are directly released onto the conveyor belt. A 3-phase induction motor with a reduction gear mechanism drives the conveyor belt, carrying the chips outside the machine. The picture below shows a typical hinge belt-type chip conveyor.

Scraper-type chip conveyor - When small chips are generated during machining operations, a scraper-type chip conveyor is commonly used with CNC machines. In this system, metal chips are dropped directly onto the conveyor belt and guided by scrapers to the end of the conveyor. A 3-phase induction motor with a reduction gear mechanism rotates the scrapers. The picture below shows a typical scraper-type chip conveyor.

Magnetic Type Chip Conveyor - A magnetic type chip conveyor is employed in CNC machines when machining ferrous materials that produce small chips. With this conveyor, the machined chips directly drop onto a stationary stainless steel surface and are dragged by a powerful magnet that rotates beneath the steel surface, ultimately settling them into a bin. Similar to other chip conveyors, a 3-phase induction motor with a reduction gear mechanism is used to rotate the magnet. The picture below shows a typical magnetic-type chip conveyor.

  

10. Heat exchanger & Cooling unit

A heat exchanger, also known as an oil refrigerator or chiller unit, is primarily used with CNC machines to cool hydraulic oil and cutting coolant. The hydraulic pump operates as long as the CNC machine is running, causing the hydraulic oil to gradually heat up. Additionally, the cutting coolant may also heat up due to excessive cutting load during machining operations. It is necessary to decrease the temperature of the oil or coolant to prevent its cooling properties from deteriorating. Typically, two different cooling methods are employed: heat exchange and freezing cycle.

There are two types of heat exchange cooling processes available: radiator-type and water cooling. In a radiator-type heat exchanger system, the warm hydraulic oil circulates through a zigzag pipeline, and a cooling fan is used to cool the pipeline. On the other hand, in a water cooling system, cold water circulates through a metallic channel submerged in a hydraulic oil tank, chilling the heated oil. The freezing cycle type cooling process involves conveying the hydraulic oil to a condenser unit through a pump and returning it to the oil tank after chilling.

For cooling the cutting coolant, a dipping-type cooling process can be employed, where a cooling coil is submerged inside the coolant tank. The following picture shows a freezing cycle-type cooling unit commonly used in hydraulic oil cooling systems.

11. Servo Controlled Voltage Stabilizer

A three-phase servo-controlled voltage stabilizer ensures a constant three-phase AC output with minimal variation in the incoming voltage supplied to a CNC machine. This type of stabilizer consists of five main elements: a buck/boost transformer, autotransformer, motor, motor driver, and control circuit power supply.

The buck/boost transformer connects one side winding between the main input line and the load output terminal, while the autotransformer is connected to the incoming power source. An arm and brush mechanism in the other winding of the buck/boost transformer allows one terminal to rotate over the autotransformer winding. This mechanism is usually driven by a low-capacity DC motor, controlled by the motor driver, which is an electronic circuit. The control circuit power supply provides a constant DC voltage to the various electronic circuits.

There are three sets of separate buck/boost transformers, control circuits, autotransformers, and motors for controlling the three-phase AC voltage. The following picture shows a servo-controlled voltage stabilizer and the block diagram of a single-phase circuit. 

Using this configuration, an automatic voltage regulator circuit continually senses the incoming voltage of the primary supply line and adjusts the motor driver circuit accordingly. The motor driver circuit rotates the motor shaft and the Arm and Brush over the autotransformer winding based on the instability or fluctuation of the incoming voltage. This, in turn, changes the voltage induced within the primary winding of the buck/boost transformer, resulting in a changing voltage between the stabilizer's output terminals. By positioning the arm and brush over the autotransformer, the motor driver circuit ensures a stable output voltage with the secondary winding of the buck/boost transformer, thus providing a constant output voltage. This arrangement is used separately for each phase, controlling the three-phase input supply.

12. Switched-mode power supply or SMPS

A switched-mode power supply (SMPS) is commonly used in CNC machines to provide a constant 24 Volt DC supply for various electronic circuits, sensors, and actuators. Compared to a general-purpose transformer-based power supply unit, an SMPS offers the same current output in a smaller size and higher efficiency. The input supply to the SMPS can be single-phase or three-phase AC, and it always delivers a constant DC output, even with slight deviations in the incoming voltage. Additionally, SMPS is integrated with short circuit protection. The picture shows a standard SIEMENS-made 24VDC SITOP power supply, which is commonly found in CNC and other machinery.

SMPS has four main elements: input rectifier, inverter, voltage converter, and output regulator. The AC input is supplied to the rectifier unit, where it is converted into DC voltage. The DC voltage is then further converted into high-frequency AC using a power oscillator circuit in the inverter section. The high-frequency AC is fed to the voltage converter section, where it is transformed by a transformer input, resulting in a low-voltage AC depending on the desired output DC voltage. The low-voltage and high-frequency AC output from the transformer is then rectified back to DC voltage in a rectifier unit. An output regulator circuit continuously monitors the output DC voltage and adjusts it accordingly, ensuring a stable DC voltage output is always available.

 13. Manual Pulse Generator

A manual pulse generator, also known as a handwheel unit, allows for manual control of CNC machine axes by rotating a wheel without pressing the movement command button on the controller. The handwheel generates square wave electrical pulses with each rotation, which are considered as axis movement commands. Different manual pulse generators are available with various machine specifications, including mechanical, optical, and magnetic types. It is typically connected to the CNC controller using a long cable, enabling axis movement away from the operator panel. The manual pulse generator includes an axis selector switch to specify the axis to be moved and an incremental setting switch to determine the increment movement of the axis for each generated pulse, corresponding to one step of wheel rotation. The following picture shows a typical manual pulse generator unit used with CNC machines.    

14. Data communication system

Effective communication with CNC machines is essential, and CNC controllers employ various media and communication protocols to download or upload programs, parameters, and offsets. Different communication processes and devices, such as USB communication through a pen drive, compact flash card (CF card), Ethernet communication, and RS 232 communication system, can be used to interface with CNC controllers. USB and CF card communication allow for the direct uploading and downloading of programs and parameters to the controller. Ethernet communication enables the CNC controller to interface with other controllers, computers, and PLCs. The RS 232 data communication system is still used with some older CNC controllers and involves a serial and two-way communication process using a data loader or computer. The data loader unit is typically preloaded with communication software, facilitating communication with the controller via a serial port (RS 232 port) and an extended cable. Software such as Winpcin, installed on a PC, communicates with the CNC controller during RS 232 communication. Although communicating with a CNC controller via RS 232 may be inconvenient, it provides a secure method that prevents the installation of any virus programs on the CNC controller from external devices like computers. Many critical CNC machines still utilize the RS 232 communication system. The following picture shows the basic architecture of an RS-232 serial data communication system.

15. Probing system

A probing system is an integral component of advanced metal-cutting CNC machines, enhancing productivity by accurately measuring multiple dimensions and ensuring precise shaping of machined workpieces. A complete probing system consists of a probe unit, receiver unit, machine interface, and controller. Different probing systems are available for CNC machines, depending on the signal transmittance from the probe unit, such as optical, radio, inductive, and direct signal transmitting systems. The following picture shows a commonly used optical signal-transmitting probing system on a CNC machine.

In a complete probing system, the probe unit contains a movable stylus (visible in the picture), which facilitates precise measurements. When the stylus is displaced by one micron (.001 mm) in either direction, the probe unit generates an electronic signal using an internal electronic circuit and transmits it. In an optical probing system, an optical interface module collects the signal from the probe unit and transmits it directly to the machine interface module through a cable. The probe unit does not have direct contact with the optical interface module, but the machine interface module interfaces directly with the CNC controller. The dimensions of the workpiece are measured from the machine's zero position during axis movement, guided by the controller. This ensures accuracy within one micron by touching the probe stylus to the workpiece. In most cases, the probe unit is coupled with the machine spindle, and the optical interface module is secured or clamped inside the machine body, away from the machining area. Popular probing systems like RENISHAW and MARPOSS are commonly used in modern CNC machines for precise measurement.

16. Laser Cutter Head

A CNC laser cutter is a machine that uses a high-powered laser beam to mark, cut, or engrave materials, forming customized profiles. It operates through a non-contact, thermal-based process. The laser cutter consists of a laser head, which contains a lens assembly and a nozzle. The laser beam, a column of intense light, is focused on the workpiece, melting it to create the desired form. Compressed gas is used to cool the lens and remove vaporized metal from the workpiece. The three most commonly used types of laser cutters are CO2 laser cutters, Crystal laser cutters, and Fiber laser cutters.

CO2 laser cutters utilize carbon dioxide as the active laser medium. Due to their high power output and efficiency, they are the most commonly used type. They are ideal for cutting precise angles, especially in sheet metals, and can also produce good cut quality on thicker metal surfaces. Fiber laser cutters use a diode bank and a fiber-optic cable to create and focus the laser beam. They provide faster and cleaner cutting compared to CO2 laser cutters. Crystal laser cutters employ beams generated by crystals like neodymium-doped yttrium aluminum garnet (Nd: YAG) and neodymium-doped yttrium ortho-vanadate (Nd: YVO). They offer higher-intensity laser power than CO2 laser cutters. The image below shows a typical laser cutter head used with a CNC machine.

 

17. Water jet Nozzle

CNC water jets utilize high-pressure water to cut various materials. Water alone is used for cutting soft materials like wood and rubber, while water mixed with an abrasive substance like garnet or aluminum oxide is used for cutting hardened materials. A water jet nozzle directs a thin stream of high-speed water, sometimes containing sharp rock pieces, to bombard the material being cut. The nozzle connects to a high-pressure water pump that supplies it with sufficient pressure. To reduce noise and splash, the water pressure is typically maintained between 20,000 and 55,000 PSI. The cutting process usually takes place underwater. The nozzle is integrated with multi-axis motion equipment, where the head is mounted on a robotic arm. Water is supplied to the water jet unit using a high-pressure pump and filter. The filtering process is critical as only clean water can achieve the ultra-high pressure required for a consistent cutting stream. The image below shows a typical water jet nozzle used with a CNC water jet cutter.

18. Electrical Discharge Machining 

Electrical Discharge Machining (EDM) is a process where electrical energy is used to erode workpiece material. It involves generating high-frequency sparks between an electrode (made of Brass, Copper, Tungsten, etc.) and an electrically conductive workpiece. As the sparks leap from the electrode to the workpiece, they carry away tiny particles, which are flushed away by a dielectric fluid. Dielectric fluid, usually a specialized non-conductive oil or deionized water, is used in this process. There are three common types of EDM: Wire EDM, Hole Drills EDM, and Sinker EDM, all of which work on the same principle. Flushing is a crucial part of the EDM process. Inefficient flushing can lead to short circuits, resulting in poor part quality and potential damage to the electrode.

Wire-cut EDM employs a continuous feed of copper or brass alloy wire that passes through the workpiece. The wire diameter typically ranges from .004 inches to .012 inches and is widely used in the tool and die industry for cutting small slots. Hole Drilling EDM involves a tubular electrode through which dielectric fluid flows. Graphite or copper is commonly used as the electrode in Sinker EDM, and it is often machined to mirror or reverse the workpiece shape. The image below shows a typical EDM system. 

19. Plasma Torch Head

Plasma cutting is a thermal cutting process that utilizes ionized gas to cut metal. Plasma is created by subjecting a gas, such as compressed air or nitrogen, to intense heating. The gas is transformed into plasma, which is an electrically conductive ionized substance. A plasma cutter uses ionized gas, typically combined with compressed air, to generate a plasma stream. When the plasma arc contacts the metal, its high temperature melts the metal, and high-speed gases blow away the molten material.

CNC plasma cutters commonly employ the Pilot arc method. In this method, a spark is formed inside the torch by a high voltage, creating a small amount of plasma. The actual cutting arc is formed when the pilot arc makes contact with the workpiece. A plasma torch head, equipped with a spring-loaded mechanism, presses against the workpiece to establish a short circuit and initiate the current flow. The image below shows a plasma torch head used in a CNC plasma cutter machine. 

20. Robotic Arm

Robotic arms are programmed to perform specific tasks quickly and accurately. They consist of joints, articulations, and manipulators that work together similar to a human arm. Various types of robotic arms are available, each designed with specific capabilities and functions for particular industrial requirements. The most common types of robotic arms used in machining industries are Cartesian, Delta, Fast Pick, and Collaborative Robotic Arms.

A Cartesian robotic arm has three principal linear axes at right angles to each other, along with three sliding joints to move the wrist up-down, in-out, and back-forth. Delta robotic arms, with their three to four lightweight arms extending downward from the main robot body, are commonly used in pick-and-place and packaging applications. Fast-pick robotic arms operate at high speed for lifting objects from one location and placing them in another. Collaborative robotic arms are capable of learning multiple tasks and working safely alongside human workers in shared workspaces. The image below shows a typical robotic arm used with a CNC machine.