CNC, Turning, Milling, Cutting, Drilling, Grinding, Boring and Precision machining
Machining is a term used to describe a variety of material removal processes in which a cutting tool removes unwanted material from a workpiece to produce the desired shape. The workpiece is typically cut from a larger piece of stock, which is available in a variety of standard shapes, such as flat sheets, solid bars, hollow tubes, and shaped beams. Machining can also be performed on an existing part, such as a casting or forging.
Parts that are machined from a pre-shaped workpiece are typically cubic or cylindrical in their overall shape, but their individual features may be quite complex. Machining can be used to create a variety of features including holes, slots, pockets, flat surfaces, and even complex surface contours. Also, while machined parts are typically metal, almost all materials can be machined, including metals, plastics, composites, and wood. For these reasons, machining is often considered the most common and versatile of all manufacturing processes
As a material removal process, machining is inherently not the most economical choice for a primary manufacturing process. Material, which has been paid for, is cut away and discarded to achieve the final part. Also, despite the low setup and tooling costs, long machining times may be required and therefore be cost prohibitive for large quantities. As a result, machining is most often used for limited quantities as in the fabrication of prototypes or custom tooling for other manufacturing processes. Machining is also very commonly used as a secondary process, where minimal material is removed and the cycle time is short. Due to the high tolerance and surface finishes that machining offers, it is often used to add or refine precision features to an existing part or smooth a surface to a fine finish.
As mentioned above, machining includes a variety of processes that each removes material from an initial workpiece or part. The most common material removal processes, sometimes referred to as conventional or traditional machining, are those that mechanically cut away small chips of material using a sharp tool. Non-conventional machining processes may use chemical or thermal means of removing material. Conventional machining processes are often placed in three categories – single point cutting, multi-point cutting, and abrasive machining. Each process in these categories is uniquely defined by the type of cutting tool used and the general motion of that tool and the workpiece. However, within a given process a variety of operations can be performed, each utilizing a specific type of tool and cutting motion. The machining of a part will typically require a variety of operations that are performed in a carefully planned sequence to create the desired features.
Material removal processes
- Single-point cutting
- Planing and shaping
- Multi-point cutting
- Abrasive machining
- Ultrasonic machining
- Abrasive jet machining
- Chemical machining
- Electrochemical machining (ECM)
- Torch cutting
- Electrical discharge machining (EDM)
- High energy beam machining
Single point cutting refers to using a cutting tool with a single sharp edge that is used to remove material from the workpiece. The most common single point cutting process is turning, in which the workpiece rotates and the cutting tool feeds into the workpiece, cutting away material. Turning is performed on a lathe or turning machine and produces cylindrical parts that may have external or internal features. Turning operations such as turning, boring, facing, grooving, cut-off (parting), and thread cutting allow for a wide variety of features to be machined, including slots, tapers, threads, flat surfaces, and complex contours. Other single point cutting processes exist that do not require the workpiece to rotate, such as planing and shaping.
Multi-point cutting refers to using a cutting tool with many sharp teeth that moves against the workpiece to remove material. The two most common multi-point cutting processes are milling and drilling. In both processes, the cutting tool is cylindrical with sharp teeth around its perimeter and rotates at high speeds. In milling, the workpiece is fed into the rotating tool along different paths and depths to create a variety of features. Performed on a milling machine, milling operations such as end milling, chamfer milling, and face milling are used to create slots, chamfers, pockets, flat surfaces, and complex contours. Milling machines can also perform drilling and other hole-making operations as well.
In drilling, the rotating tool is fed vertically into the stationary workpiece to create a hole. A drill press is specifically designed for drilling, but milling machines and turning machines can also perform this process. Drilling operations such as counterboring, countersinking, reaming, and tapping can be used to create recessed holes, high precision holes, and threaded holes. Other multi-point cutting processes exist that do not require the tool to rotate, such as broaching and sawing.
Abrasive machining refers to using a tool formed of tiny abrasive particles to remove material from a workpiece. Abrasive machining is considered a mechanical process like milling or turning because each particle cuts into the workpiece removing a small chip of material. While typically used to improve the surface finish of a part, abrasive machining can still be used to shape a workpiece and form features. The most common abrasive machining process is grinding, in which the cutting tool is abrasive grains bonded into a wheel that rotates against the workpiece. Grinding may be performed on a surface grinding machine which feeds the workpiece into the cutting tool, or a cylindrical grinding machine which rotates the workpiece as the cutting tool feeds into it. Other abrasive machining processes use particles in other ways, such as attached to a soft material or suspended in a liquid. Such processes include honing, lapping, ultrasonic machining, and abrasive jet machining.
Types of Machining Tools
There are many types of machining tools, and they may be used alone or in conjunction with other tools at various steps of the manufacturing process to achieve the intended part geometry. The major categories of machining tools are:
- Boring tools: These are typically used as finishing equipment to enlarge holes previously cut into the material.
- Cutting tools: Devices such as saws and shears are typical examples of cutting implements. They are often used to cut material with predetermined dimensions, such as sheet metal, into a desired shape.
- Drilling tools: This category consists of two-edged rotating devices that create round holes parallel to the axis of rotation.
- Grinding tools: These instruments apply a rotating wheel to achieve a fine finish or to make light cuts on a workpiece.
- Milling tools: A milling tool employs a rotating cutting surface with several blades to create non-circular holes or cut unique designs out of the material.
- Turning tools: These tools rotate a workpiece on its axis while a cutting tool shapes it to form. Lathes are the most common type of turning equipment.
Types of Burning Machining Technologies
Welding and burning machine tools use heat to shape a workpiece. The most common types of welding and burning machining technologies include:
- Laser cutting: A laser machine emits a narrow, high-energy beam of light that effectively melts, vaporizes, or burns material. CO2 and Nd:YAG lasers are the most common types used in machining. The laser cutting process is well-suited for shaping steel or etching patterns into a piece of material. Its benefits include high-quality surface finishes and extreme cutting precision.
- Oxy-fuel cutting: Also known as gas cutting, this machining method employs a mixture of fuel gases and oxygen to melt and cut away material. Acetylene, gasoline, hydrogen, and propane frequently serve as gas media due to their high flammability. This method’s benefits include high portability, a low dependence on primary power sources, and the ability to cut thick or hard materials, such as sturdy steel grades.
- Plasma cutting: Plasma torches fire an electrical arc to transform inert gas into plasma. This plasma reaches extremely elevated temperatures and is applied to the workpiece at high speed to melt away unwanted material. The process is often used on electrically conductive metals that require a precise cut width and minimal prep time.
Types of Erosion Machining Technologies
While burning tools apply heat to melt excess stock, erosion machining devices use water or electricity to erode material off the workpiece. The two main types of erosion machining technologies are:
- Water jet cutting: This process uses a high-pressurized stream of water to cut through material. Abrasive powder may be added to the water stream to facilitate erosion. Water jet cutting is typically used on materials that can suffer damage or deformation from a heat affected zone.
- Electric discharge machining (EDM): Also known as spark machining, this process uses electric arcing discharges to create micro-craters that rapidly result in complete cuts. EDM is used in applications requiring complex geometrical shapes in hard materials and at close tolerances. EDM requires the base material to be electrically conductive, which limits its use to ferrous alloys.
Any machining process that requires unusually small cutting tolerances (between 0.013 mm and 0.0005 mm, as a rule of thumb) or surface finishes finer than 32T may be considered a form of precision machining. Like CNC machining, precision machining can be applied to a wide number of fabrication methods and tools. Factors such as stiffness, damping, and geometric accuracy can influence the exactness of a precision tool’s cut. Motion control and the machine’s ability to respond at rapid feed rates are also important in precision machining applications.
CNC machining is a manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machinery. The process can be used to control a range of complex machinery, from grinders and lathes to mills and routers. With CNC machining, three-dimensional cutting tasks can be accomplished in a single set of prompts.
Short for “computer numerical control,” the CNC process runs in contrast to — and thereby supersedes — the limitations of manual control, where live operators are needed to prompt and guide the commands of machining tools via levers, buttons and wheels. To the onlooker, a CNC system might resemble a regular set of computer components, but the software programs and consoles employed in CNC machining distinguish it from all other forms of computation, It requires software and programming, usually in the G-code language, to guide a machining tool in shaping the workpiece according to preset parameters.
Some of its benefits include:
- High production cycles: Once the CNC machine has been properly coded, it usually needs minimal maintenance or downtime, allowing for a faster production rate.
- Low manufacturing costs: Due to its turnover speed and low manual labor requirements, CNC machining can be a cost-efficient process, particularly for high-volume production runs.
- Uniform production: CNC machining is typically precise and yields a high level of design consistency among its products.
TYPES OF CNC MACHINES
The earliest numerical control machines date to the 1940s when motors were first employed to control the movement of pre-existing tools. As technologies advanced, the mechanisms were enhanced with analog computers, and ultimately with digital computers, which led to the rise of CNC machining.
The vast majority of today’s CNC arsenals are completely electronic. Some of the more common CNC-operated processes include ultrasonic welding, hole-punching and laser cutting. The most frequently used machines in CNC systems include the following:
CNC mills are capable of running on programs comprised of number- and letter-based prompts, which guide pieces across various distances. The programming employed for a mill machine could be based on either G-code or some unique language developed by a manufacturing team. Basic mills consist of a three-axis system (X, Y and Z), though most newer mills can accommodate three additional axes.
In lathe machines, pieces are cut in a circular direction with indexable tools. With CNC technology, the cuts employed by lathes are carried out with precision and high velocity. CNC lathes are used to produce complex designs that wouldn’t be possible on manually run versions of the machine. Overall, the control functions of CNC-run mills and lathes are similar. As with the former, lathes can be directed by G-code or unique proprietary code. However, most CNC lathes consist of two axes — X and Z.
Deep Hole Drilling and Trepanning
Drilling provides a given hole size with a single machining pass. It may be through the part, or partially through (blind).
In a plasma cutter, material is cut with a plasma torch. The process is foremost applied to metal materials but can also be employed on other surfaces. In order to produce the speed and heat necessary to cut metal, plasma is generated through a combination of compressed-air gas and electrical arcs.
Electric Discharge Machines:
Electric-discharge machining (EDM) — alternately referred to as die sinking and spark machining — is a process that molds work pieces into particular shapes with electrical sparks. With EDM, current discharges occur between two electrodes, and this removes sections of a given work piece.
When the space between the electrodes becomes smaller, the electric field becomes more intense and thus stronger than the dielectric. This makes it possible for a current to pass between the two electrodes. Consequently, portions of a work piece are removed by each electrode.
Subtypes of EDM include:
- Wire EDM, whereby spark erosion is used to remove portions from an electronically conductive material.
- Sinker EDM, where an electrode and work piece are soaked in dielectric fluid for the purpose of piece formation.
In a process known as flushing, debris from each finished work piece is carried away by a liquid dielectric, which appears once the current between the two electrodes has stopped and is meant to eliminate any further electric charges.
FURTHER USES OF CNC MACHINES
In addition to the aforementioned machines, further tools and components used within CNC systems include:
- Embroidery machines
- Wood routers
- Turret punchers
- Wire-bending machines
- Foam cutters
- Laser cutters
- Cylindrical grinders
- 3D printers
- Glass cutters
CNC Machining Materials
|Metal||Aluminum – 1050||AL 1050|
|Metal||Aluminum – 1060||AL 1060|
|Metal||Aluminum – 2024||AL 2024|
|Metal||Aluminum – 5052-H11||AL 5052-H11|
|Metal||Aluminum – 5083||AL 5083|
|Metal||Aluminum – 6061||AL 6061|
|Metal||Aluminum – 6082||AL 6082|
|Metal||Aluminum – 7075||AL 7075|
|Metal||Aluminum – bronze||AL + Br|
|Metal||Aluminum – MIC-6||AL – MIC-6|
|Metal||Aluminum – QC-10||AL QC-10|
|Metal||Brass||Cu + Zn|
|Metal||Copper – beryllium||Cu + Be|
|Metal||Copper – chrome||Cu +Cr|
|Metal||Copper – tungsten||Cu + W|
|Metal||Phosphor bronze||Cu + Sn + P|
|Metal||Steel – Stainless 303||SS 303|
|Metal||Steel – Stainless 304||SS 304|
|Metal||Steel – Stainless 316||SS 316|
|Metal||Steel – Stainless 410||SS 410|
|Metal||Steel – Stainless 431||SS 431|
|Metal||Steel – Stainless 440||SS 440|
|Metal||Steel – Stainless 630||SS 630|
|Metal||Steel 1040||SS 1040|
|Metal||Steel 45||SS 45|
|Metal||Steel D2||SS D2|