12 Types of Metal Machining Processes
In the enormous realm of manufacturing, machining is a fundamental process that transforms raw materials into finished products. This manufacturing technique uses various cutting tools to create the desired shapes, features, and finishes from a workpiece. Machining processes are diverse, ranging from conventional machining operations such as milling and turning to non-conventional machining processes such as ultrasonic machining and chemical machining. Each of these operations has unique features and properties and is, therefore, best suited to certain applications.
Understanding machining processes is crucial to the successful execution of your manufacturing project. In this article, we’ll discuss conventional and unconventional machining operations in detail. You can choose the ideal manufacturing method for your project based on the information we’ve provided below.
What Is Metal Machining?
Metal machining is the process of creating products by removing material from a workpiece until the final metal part is complete. Machining is also known as a subtractive manufacturing process. It’s the opposite of additive manufacturing techniques which create objects by building them one layer at a time. Machining offers high precision and is used in various industries to manufacture a wide range of products.
Metal machining can be done manually through handheld tools. That being said, most machining operations today have been automated thanks to CNC machining. This technology uses computer software to guide the movements of the cutting tool. By integrating a CNC machine into your manufacturing process, you can improve the accuracy, efficiency, and quality of finished parts.
Now, that we’re familiar with the basic concepts of metal machining, let’s discuss the common types of machining processes.
The Different Types of Machining Operations
There are many types of machining operations to match different project requirements. Machining processes can be classified into two categories; conventional and unconventional machining techniques.
Conventional machining processes are also known as traditional machining processes. These techniques use physical cutting tools such as cutting blades and drilling bits to complete machining actions. Common examples of conventional machining processes include milling, turning, planing, drilling, boring, and sawing.
Non-conventional machining processes do not require traditional cutting tools or mechanical forces to remove material from a workpiece. Instead, they rely on other forms of energy such as chemical, thermal, and electrical to erode material from a workpiece’s surfaces. Examples of non-conventional machining processes include laser beam machining (LBM), electrical discharge machining (EDM), chemical machining process, electrochemical machining (ECM), ultrasonic machining, and abrasive jet machining.
Let’s discuss the common machining techniques in greater detail.
1. Turning
Turning is one of the basic machining operations. It involves using a stationary cutting tool to remove unwanted material from the outer diameter of a rotating workpiece. The turning process creates rotational parts and typically utilizes a single-point cutting tool.
Metal turning is either conducted on a turning machine or a lathe. This precision machining technique is ideal for a wide variety of metal materials including iron, aluminum, steel, titanium, brass, and nickel alloys.
2. Drilling
Drilling is a machining operation that uses a drill bit to produce cylindrical holes. During the drilling process, the bit is pressed against the solid material and rotated at high speeds. This removes unwanted material and creates blind holes (holes that reach a specified depth and have only one open side) or through holes (holes that go all the way through the workpiece). The drilled hole characteristics will vary depending on the chosen drill bit.
Drilling operations can be conducted on almost any type of metal material — from aluminum to steel and titanium. CNC drilling allows machinists to achieve precise hole diameters and depths efficiently. Common types of drilling machines include:
Sensitive drilling machines
Gang drilling machines
CNC drilling machines
Radial drilling machines
Micro drill press
Deep-hole drilling machines
3. Milling
Milling is a subtractive manufacturing process that utilizes a rotating cutting tool to remove material from a stationary workpiece. Milling operations require four key components: a milling machine, workpiece, jig, and milling cutter.
This conventional machining process utilizes multi-point cutting tools to achieve the desired shape and surface finish. in a CNC milling machine, the motion of the milling tools is guided by computer software resulting in accurate parts with precise tolerances.
Common types of milling operations are:
End milling
Chamfer milling
Face milling
Thread milling
Slot milling
4. Grinding
Grinding removes a relatively small amount of material from the workpiece’s surface using a rotating abrasive wheel. The grinding wheel consists of embedded abrasive particles or grains, each serving as a miniature cutting tool. Commonly used grinding wheel abrasives include aluminum oxide, silicon carbide, and cubic boron nitride (CBN). Due to the hardness of these grains, grinding can be used to process a wide range of metals. As the abrasive particles get dull due to repeated use, they fall off the tool making new, sharp grains prominent. Therefore, the abrasive wheel is regarded as a self-sharpening cutting tool.
Grinding can be used for both roughing and finishing operations depending on the size of the abrasive particles. Coarse grits, with larger grains, allow for a higher material removal rate and are suitable for rough grinding. Conversely, fine grits are ideal for precision grinding and fine finishes.
5. Planing
Planing, also known as planar machining, is a subtractive manufacturing technique that produces large flat surfaces. With this machining process, the workpiece is secured to a horizontal table that moves back and forth under a stationary single-point cutting tool. In addition to machining flat surfaces, planing is also used for cutting slots. Depending on your machining needs, you can choose from different types of planer machines including;
Double housing planer machine
Open-side planer machine
Pit planer machine
Edge planer machine
Divided table planer machine
6. Sawing
Sawing is regarded as a traditional machining process. While it may be less fascinating than modern manufacturing techniques, it remains one of the most vital operations in a machine shop.
Sawing machining uses a cutting tool known as a saw to remove unwanted material along a predefined path. There are four main types of saws — hacksaws, bandsaws, circular saws, and abrasive saws. Each type has specific capabilities and applications in the manufacturing sector.
7. Broaching
Broaching is a common machining process that uses a broach to remove material from a workpiece. Broaching tools typically have multiple teeth and are made from durable materials such as high-speed steel and carbide.
During the broaching process, the cutting tool is pushed or pulled into the workpiece removing material in a single pass. This creates accurate parts with excellent surface finish. Broaching is broadly classified into two categories:
Internal broaching is applied when machining internal surfaces such as holes and keyways.
External broaching is suitable for external shapes such as gear teeth.
8. Reaming
Reaming is a precision machining process used to modify the accuracy and finish of a pre-existing hole. A rotary cutting tool, known as a reamer, is used to scrape away thin layers of material enhancing the dimensional accuracy and smoothness of the hole surface. This machining process does not create new holes from scratch. Instead, it improves existing holes that have already been made through machining operations such as drilling, boring, or coring.
Different reaming tasks call for different types of reamers. Some of the common reaming tools are hand reamers, shell reamers, stub screw-machine reamers, and taper pin reamers. Reaming is an essential machining operation in industries that require precise features. For example, it is used in the aerospace, medical devices, and automotive sectors to produce accurate and smooth holes.
9. Tapping
Tapping is a simple, popular, and efficient manufacturing process. It creates internal threads inside the hole of a workpiece using a cutting tool known as a tap. During this machining process, the cutting faces of the tap remove material from the workpiece’s surface creating the thread profile. These threaded holes accommodate bolts, screws, and other fasteners facilitating secure fastening.
There are two primary types of tapping tools.
Hand taps: As the name implies, hand taps are used when manually cutting threads.
Machine taps: These cutting tools are used with machines such as a drill press and CNC machines.
Other types of tapping tools include forming taps, cutting taps, straight-flute taps, and spiral-flute taps.
10. Knurling
Knurling is a machining technique that creates a textured pattern on the surface of a finished part. This process serves three main functions; it improves the aesthetics of a part, enhances the grip of handhold areas of components, and prepares parts of a press fit.
Hand knurling is a manual process that is typically used for machining softer materials. Machine knurling is carried out on a lathe machine and yields finer details in harder metals. Common applications of this conventional machining process are:
Tool handles
Mechanical pencils
Pistol grips
Barbel bars
11. Boring
Boring is one of the common traditional machining processes. It utilizes boring tools to enlarge an existing hole and improve its surface finish. Boring is similar to reaming in that it processes an existing hole. However, unlike reaming, this manufacturing technique uses a single-point cutting tool. Another difference between the two is that boring is capable of achieving superior positional accuracy.
Boring is often conducted on a lathe. This machining process can also be completed on CNC milling machines.
12. Electrical Discharge Machining (EDM)
Electrical discharge machining (EDM) is a non-conventional machining process that uses thermal rather than mechanical forces for material removal. Specifically, an electric discharge is converted into thermal energy that melts unwanted material from the surface of the workpiece. Electric discharge machining is only applicable to conductive materials, and it can create complex shapes and high-precision parts. Machinists usually turn to EDM when conventional machining operations have reached their limits. Features such as deep cavities and internal edges are exclusively processed through EDM.
Electrical discharge machining processes are grouped into three primary categories:
Die sinking EDM
Wire EDM
Hole drilling EDM
Metal machining can be done manually using hand-held cutting tools. That being said, most machining operations today have been automated thanks to CNC machining. This technology uses a CNC machine to guide the movement of the cutting tool during material removal. CNC machining has drastically improved the accuracy and efficiency of machining processes. Further, it enables manufacturers to produce high-quality parts with exceptional surface finishes.
There are different types of machining operations to suit various project requirements. All machining processes are broadly classified into two categories; conventional and unconventional machining processes.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.