What is machining?

Machining is a term related to production that includes a wide range of technologies and techniques. It can be roughly defined as the process of removing material from a workpiece using machine tools to shape it into the intended design.

Machining is a process of manufacturing and prototyping that creates the desired shape by removing unwanted material from a larger piece of material. Since the part is built by removing the material, this process is also known as subtractive production.

What materials are used in machining?

Machining supports a variety of materials. It is most commonly performed on metal workpieces, including iron, steel, aluminum, bronze, and copper. In addition, workpieces made of non-metallic materials, including wood, ceramics, plastics and composites, can be processed.

Generally speaking, workpieces made of harder materials required more machine work. For example, a steel workpiece may require a sharper cutting tool as well as greater force than a wood workpiece.

History and terminology

The precise meaning of the term machining has evolved over the past century as technology has advanced.

In the 18th century, the word machinist simply meant a person who built or repaired machines. The work of this person was done mostly by hand, using procedures such as wood carving and manual forging and manual metal filing. At the time, mills and builders of new types of engines, such as James Watt or John Wilkinson, would fit the definition. The noun machine tool and the verb to process did not yet exist.

Around the middle of the 20th century, the latter words originated when the concepts they described evolved into widespread existence. Therefore, during the machine age, machining referred to (traditional) machining processes, such as turning, drilling, milling, drawing, sawing, shaping, planing, reaming and other. In these "traditional" or "conventional" machining processes, machine tools, such as lathes, milling machines, drills or others, are used with a sharp cutting tool to remove the material to achieve the desired geometry.

Since the advent of new technologies in the post-World War II era, such as electric discharge processing, electrochemical processing, electron beam processing, photochemical processing and ultrasonic processing, the retronim "conventional processing" can be used to distinguish these classical technologies from the newer ones. In current usage, the term “unprofessional machining” usually implies traditional machining processes.

In the decades of the 2000s and 2010s, as additive manufacturing (AM) evolved beyond its earlier laboratory and rapid prototyping contexts and began to become commonplace at all stages of production, the term subtractive manufacturing, in logical contrast with AM, covering in basically any removal process previously covered by the term machining. These two terms are in fact synonymous, although the long-standing use of the term „machining“ reversal continues.

Types of machining

Various processing techniques have existed for decades, but most fall into three basic procedures, each requiring a specific tool. Those are:

  • Turning - turning or laminating involves rotating the workpiece on the machine, while the single-edge cutting tool remains stationary. The cutting tool moves slowly parallel to the rotational axis of the workpiece, removing material in motion.
  • Drilling - drilling results in the creation of a round hole by rotating a cylindrical tool parallel to the axis of rotation of the workpiece. A hole equal in diameter to the tool used was created.
  • Milling - milling is the process of removing material, using rotary cutters, from a workpiece in motion perpendicular to the rotary axis of the cutting tool. This is one of the most common forms of processing used today.

There are also various processing operations that do not fall into one of the three categories of processing operations mentioned above. For example, grinding is a machining process that relies on a sliding contact to deform the workpiece surface. Polishing is usually used on plastic workpieces to obtain a smooth surface. Various machining processes such as griding are unique because they generally do not produce chips. Turning, milling and drilling produce chips as a by-product. Various processing processes, however, do not produce chips or sawdust.

Machine tools

A machine tool is a machine for handling or processing metal or other solid materials, usually by cutting, drilling, grinding or other forms of deformation. Machine tools use some type of tool that performs cutting or shaping. All machine tools have some means of restricting the workpiece and allow guided movement of machine parts.

Thus, the relative movement between the workpiece and the cutting tool (called the tool path) controls or restricts the machine at least to some extent, instead of being completely "independent" or "free".

Shaping is done in four general ways: (1) by cutting excess chipboard material from the part; (2) shearing the material; (3) squeezing the metal parts to the desired shape; and (4) applying electricity, ultrasound, or corrosive chemicals to the material. The fourth category includes modern machine tools and processes for processing ultra-hard metals that cannot be processed by older methods.

Machine tools that shape parts by removing metal chips from the workpiece include lathes, planers, drills, milling machines, grinders, and electric saws. Cold forming of metal parts, such as cooking utensils, bodies and similar objects, is performed on presses, while hot forming of glowing empty forms into dies of the appropriate shape is performed on forging presses.

Modern machine tools cut or shape parts to tolerances of plus or minus one ten-thousandth of an inch (0.0025 millimeters). In special applications, precision cutting machines can produce parts located at plus or minus two millionths of an inch (0.00005 millimeters). Due to the precise dimensional requirements of the parts and the large cutting forces on the cutting tool, machine tools combine weight and stiffness with sensitive accuracy.

Types of machine tools:

There are many types of machine tools, and they can be used alone or together with other tools at different stages of the production process to achieve the intended geometry of the part. The main categories of machine tools are:

  • Drilling tools: Typically used as finishing equipment to enlarge holes previously cut in the material.
  • Cutting tools: Devices such as saws and scissors are typical examples of cutting tools. They are often used to cut materials of predetermined dimensions, such as sheet metal, into the desired shape.
  • Drilling tools: This category consists of two-blade rotary 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 make light cuts on the workpiece.
  • Milling tools: The milling tool uses a rotating cutting surface with several blades to create circular holes or cut unique designs from the material.
  • Turning tools: These tools rotate the workpiece around its axis while the cutting tool shapes it into shape. Lathes are the most common type of turning equipment.

However, a new development in machining processes is the introduction of CNC machining. Computer numerical control, CNC, is the addition of a computer to machining processes, so instead of relying on human capabilities, CNC machining provides various tools for cutting, grinding, drilling, etc. which are controlled by a computer with a precise design. Advanced machining techniques also include electric discharge treatment (EDM), electrochemical treatment (ECM), laser cutting or water jet cutting to form metal workpieces.

CNC machining

CNC machining is a manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machines. The process can be used to control a range of complex machines, from grinders and lathes to mills and routers. With CNC machining, three-dimensional cutting tasks can be accomplished in a single set of queries.

Briefly from "computer numerical control", the CNC process works contrary to - and thus replaces - the limitations of manual control, where operators are required to send and direct machining tool commands via handles, knobs and wheels. For observers, a CNC system may resemble a regular set of computer components, but software programs and consoles in CNC machining distinguish it from all other forms of computation.

CNC programming

In CNC machining, machines are controlled by numerical control, whereby the software program is intended for object control. The language behind CNC machining is alternately called G-code, and it is written to control the different behaviors of the corresponding machine, such as its speed, input speed, and coordination.

Basically, CNC machining allows you to pre-program the speed and positions of machine tool functions and run them via software in repetitive, predictable cycles, all with little involvement of human operators. Thanks to these possibilities, the procedure has been adopted in all parts of the manufacturing sector, and is especially important in the areas of metal and plastic production.

To begin with, a 2D or 3D CAD drawing is conceived, which is then translated into computer code to execute the CNC system. After entering the program, the operator runs it on a trial basis to ensure that there are no errors in the coding.

Types of processing tools

A cutting tool or cutter a wedge-shaped tool that compresses the workpiece material during machining to gradually remove excess material by shearing and to obtain the desired shape, size and accuracy.

Geometry, orientation, and material are three important factors that affect the performance of a cutting tool in material removal. Every common machining process uses a physical cutting tool. Although the basic shape and feature of such a cutting tool varies greatly depending on the type of operation to be performed, each cutting tool must have a wedge-shaped section with a sharp cutting edge, which can help shear and thus cut material smoothly and efficiently.

A particular cutting tool may contain one or more main cutting edges and can therefore be classified into three categories - single-point, double-point and multi-point cutting tools. As the name suggests, a single-point cutting tool contains only one main cutting edge, a two-point cutting tool contains two cutting edges, while a multi-point cutting tool contains more than two main cutting edges. The number of cutting edges present in a particular cutter plays a vital role in several aspects, including chipboard load, material removal rate, cutting force, cost, and so on.

Similarities between single-point and multi-point cutting tools

Both single-blade and multiple cutters follow the same material removal principle (i.e., compressing a thin layer of workpiece material to gradually cut it off in the form of chipboard).

Both are easily used in conventional machining processes; however, a particular machining process uses a particular type of cutter.

Both types of cutters necessarily contain a sharp cutting edge; however, the number of cutting edges is different. In fact, this is the primary goal of classifying cutters as single and multiple.

Geometry and material affect the factors of both types of cutters.

Differences between single-point and multi-point cutting tools

Multi-point cutting tools contain more than one (even up to a hundred) cutting edges in the cutter body.

With single-point tools, one blade remains in constant contact with the workpiece, so the rate of heat generation and consequent increase in tool temperature is high, while with multi-point tools it is low.

A low feed rate and depth of cut are usually applied when machining with single-blade cutting tools. Accordingly, material removal rate (MRR) and productivity are low. A higher feed rate can be applied when machining is performed using a multiple blade cutting tool. That increases MRR and productivity. Accordingly, the machining process becomes more economical.

Examples of single point cutters:

  • Turning tool
  • Shaping tool
  • Planing tool
  • Slotting tool
  • Boring tool

Examples of multi-point cutters:

  • Milling cutters
  • Hobs
  • Broach
  • Grinding wheels
  • Reamer
  • Knurling tool

Conclusion

Machining is one of the secondary production processes by which excess material is removed by shearing from the previously formed raw material in the form of sawdust using a wedge cutting tool to obtain the desired shape, processing and tolerance.

Machining is also known as metal cutting operation; however, non-metallic materials can also be cut, such as plastic, wood, ceramics, etc. Basically, metal is one type of solid material, the other two are polymer and ceramic.
The goal of machining is to remove only excess material. Obviously, one should not cut the material when the desired shape is achieved. Therefore, processing is also called subtractive production process. In contrast, rapid prototyping is a type of additive manufacturing process.

There are several types of machining, and the three most basic processes are: milling, turning and grinding.

In modern production, the processing is most often done using a CNC machine, which is an abbreviation of Computer Numeric Control. Basically, the machine uses computer software to create CAD design models and map tool paths, converting the design into 3D machined parts.

In conclusion, machining is the most versatile and accurate of all manufacturing processes in its ability to produce a variety of part geometries and geometric features.

Klara Markotić
Content Creator at MachineDesk with a particular interest in marketing and social media.
marketing@machine-desk.com