Machining is one type of manufacturing operation where excess material is gradually removed by shearing in the form of a chip from a preformed blank. A rigid, hard, wedge-shaped device, called a cutting tool, is employed for compressing the work material and thereby shearing the excess layer of material.
So the purpose of a cutting tool (also called a cutter) is to compress a particular layer of work material in order to shear it off. Therefore, the cutter must have a wedge shape with a sharp edge for smoothly and efficiently removing material requiring minimum power.
At the same time cutter material should be sufficiently hard so as to withstand the intense rubbing occurred during machining. Along with the definition and example, the purposes, various features, designations, materials, and classification of cutting tools are discussed in the following sections.
What is a Cutting Tool?
Cutting tools are wedge-shaped, sharp-edged tools used during machining to cut extra layers of material from a workpiece to achieve the desired shape, size, and accuracy. It has a secure connection to the machine tool.
The tool must be able to endure the heat and force produced during the machining process, and the cutting tool material must be harder than the material being cut (workpiece).
Additionally, the tools need to have a specific geometry with clearance angles so that only the cutting edge of the tool touches the workpiece’s surface.
The width, number, and shape of the flutes or teeth, as well as the angles of the cutting face, are all significant factors of the cutting tools.
All of these variables, as well as the speed and feed at which the machine operates, must be optimized for a longer lifespan. Single-point cutting tools and multi-point cutting tools can both be used for cutting.
Let’s move on to the following sections to learn more about types of cutting tools.
Types of Cutting Tools
A cutting tool might have one or more cutting edges that take part in simultaneous cutting in a single pass. The most popular method of classifying a cutting tool is based on how many major cutting edges are actively engaged in the cutting process at any given time.
Based on Common Names of Cutting Tools
Based on this, the cutting tool can be divided into the three categories listed below.
#1. Single Point Cutting Tool.
A single-point cutting tool refers to a tool with a single cutting edge used in the machining process to remove material from a workpiece.
A single-point cutting tool is so named because it only has one edge, unlike a multi-point cutting tool, which has multiple edges.
On lathes and milling machines, single-point cutting tools are frequently used for turning, facing, and boring operations. Typically, the tool’s body is made of a more durable, more flexible material, such as steel. In contrast, the cutting edge is made of a hard, wear-resistant material, such as tungsten carbide or ceramic.
Tool cutting edges are shaped and ground to produce the desired geometry, such as sharp points for drilling and rounded noses for turning.
There are many factors that influence the cutting properties of tools, including their surface finish, accuracy of machined surfaces, and their angle and shape.
Advantages of a Single-Point Cutting Tool
- Simple and easy to manufacture.
- Easy to regrind and reuse.
- Cost-effective for small batch production.
- Suitable for both roughing and finishing.
- Compatible with various machine tools.
Disadvantages of a Single-Point Cutting Tool
- Compared to milling cutters, single-point cutting tools have a limited cutting speed, resulting in slower machining times.
- Due to their limited geometry options, single-point cutting tools may not be suitable for all machining operations.
- If single-point cutting tools are not used properly, workpiece damage may result.
- As opposed to other cutting tools, these tools require a higher level of skill to use.
- The use of single-point cutting tools may be limited in some applications because they may not be suitable for all materials, such as hard or brittle materials.
#2. Double Point Cutting Tool.
A double-pointed cutting tool has two cutting edges that can cut and shear simultaneously in one motion.
Single-point cutting tools contain one main cutting edge, while multi-point cutting tools contain more than two cutting edges for performing machining action in one pass.
In some cases, the only two categories into which cutters can be divided are double-point and multi-point.
Additionally, a cutting edge is created by intersecting a rake surface and a flank surface. Consequently, double-point cutting tools have two flank surfaces and two rake surfaces.
The only example of a double-point cutting tool is a drill. Drills may have more than two flutes, but the typical metal-cutting drill only has two flutes. Drills’ modified cutting edges might also have more cutting edges, which would classify them as multi-point cutters.
Advantages of Double Point Cutting Tool
- During machining operations, it absorbs shocks like vibrations.
- It is capable of producing a fixed cutting element.
- Unlike single-point cutting tools, this one has two cutting edges working simultaneously.
Disadvantages of Double Point Cutting Tool
- The edges of this tool could be altered.
- The issue with tool precision might arise.
#3. Multi-Point Cutting Tool.
A cutting tool with multiple points has more than two cutting edges that cut simultaneously during a pass. Cutting tools with more than one cutting edge is sometimes considered multi-point cutting tools (instead of double-point cutters).
In a multi-point cutter, the number of cutting edges can range from three to several hundred. As cutting edges appear at the intersection of rake and flank surfaces, rake and flank surfaces are also necessary for each cutting edge.
A popular example of this category is milling cutters. Other cutters are typically multi-point, except the fly milling cutter (a single-point cutter). For example, a small end mill might have three cutting edges, while a large heavy-duty cutter might have up to forty.
Advantages of Multi-Point Cutting Tool
- It has a small chip load per tooth.
- These types of cutting tools facilitate higher speed, feed, and depth of cut.
- Multi-point tools have a high material removal rate and productivity.
Disadvantages of Multi-point Cutting Tool
- These tools are made with complex design and fabrication processes.
- Multi-point cutting tools are more expensive than other types.
- Inherently intermittent cutting.
Based on the Motion of the Tool
The tools under this category are always dedicated to specific machines.
- Translatory Motion: When a body moves in such a way that every one of its particles moves parallel, it is said to be in a translatory motion. The lathe machine cutting tools that perform operations like facing, turning, parting, or grooving follow the translational motion.
- Reciprocating Motion: Repetition of an upward and downward -or forward and backward linear motion is referred to as reciprocating motion or reciprocation. It is found in shaping machines where the shaping tool follows a reciprocating motion and removes the material along a single stroke.
- Rotary Motion: If a body rotates around a fixed axis, that motion is referred to as rotatory motion. Rotatory motion is exemplified by a wheel in motion. The milling machine follows a rotary motion where the tool rotates in the axis parallel to that of the workpiece, whereas the drilling machine follows the rotary motion perpendicular to the axis of the workpiece.
Based on Common Names of Cutting Tools
Based on this, the cutting tool can be divided into the following categories, listed below.
#1. Drill.
A drill is a type of cutting tool that is employed to create circular holes or to drive fasteners. It is equipped with a bit, either a driver chuck or a drill bit.
Due to their greater efficiency and usability, cordless battery-powered types are rapidly replacing hand-operated ones in terms of popularity.
These cutting tools are attached to drilling, milling, or lathe machines because they perform drilling operations. Various types of drills are used in woodworking, metalworking, construction, machine tool fabrication, and utility projects.
#2. Milling Cutter.
In milling machines or machining centers, milling cutters are cutting tools used to perform milling operations (and occasionally in other machines).
By moving inside the machine (such as in a ball nose mill) or by removing material directly from the cutter’s shape (such as in a hobbing cutter), these tools remove material.
#3. Fly Cutter.
Fly cutters are rotary tools used for plane surfacing that have one or more single-point tools. The fly cutter is a single-point cutting tool mounted in a special holder that resembles a lathe tool.
To machine large and flat surface areas, fly cutters are typically used on a milling machine. There is no need for additional arbors when using fly cutters in manual mills and machining centers.
#4. Shaper.
Cutting tools in shapers are single-point tools with clearances, rakes, and other angles similar to those on lathes. Shaper tools are significantly more rigid and heavy to withstand the shock that the cutting tool experiences at the start of each cutting stroke.
For cast iron and steel, the side clearance angle in a shaper tool is only 2 and 40, respectively.
The most typical material for a shaper tool is high-speed steel, but harder materials can also be machined using shock-resistant, cemented carbide-tipped tools. This tool is used on a shaping machine to give the workpiece a precise shape and accuracy.
#5. Planer.
On a planer machine, only single-point cutting tools are employed. These tools are similar in shape and tool angles to those commonly found on lathes or shaper machines. However, these tools are heavier and have larger cross-sections.
To make heavy cuts over extended cutting strokes, planer tools must operate on coarse feeds. There are three different types of planner tools: solid, forge, and bit. The bits are constructed from cementite carbide, stellite, or high-speed steel.
#6. Boring Bar.
Boring bars are commonly used in metalworking and woodworking. A common technique in construction is boring. For centuries, woodworkers have used boring as a type of drilling. Boring tools are used to make circular plunge cuts in woodworking.
Boring differs slightly in metalworking because the hole it creates doesn’t have to be circular. To create a perfectly circular hole, the tool is pushed and pulled up and down (on the Z axis) while plunging and dragging on the X and Y axes.
#7. Reamer.
A reamer is a device used to enlarge or finish pre-drilled holes, holes that have been bored, or holes that have been cored to produce a good finish and precise dimensions. A reamer is a multi-toothed cutter used to remove relatively little material.
Reamer tools have cutting surfaces that are either straight, slightly twisted, or spirally fluted and are ground to a very precise diameter.
Reamers can be divided into some categories based on their use, design, and shape. These types of cutting tools are used on the drilling machine to carry out reaming operations.
#8. Broach.
A broaching tool has a series of distinct cutting edges along its length that is referred to as cutting teeth. By increasing the step between any two succeeding teeth on the broach, feed is accomplished. Broaches are typically made of high-speed steel (HSS).
The linear movement of the tool to the workpiece determines the broach’s cutting speed. The broach’s cutting edges’ contours determine the shape of the cut surface (machined surface). On the broaching machine, this cutting tool performs the broaching operation.
#9. Hob.
A hob is a cutting tool used for cutting teeth into a workpiece. It has helical cutting teeth and a cylindrical shape. To facilitate cutting and chip removal, these helical cutting teeth have grooves that run the entire length of the hob.
Additionally, there are special hobs made for unique gears like sprockets and spline gears. These types of cutting tools are used to perform hobbling operations on the hobbing machine.
#10. Grinding Wheel.
The grinding wheel contains abrasive compounds for grinding and machining. The abrasive grains give the wheel its cutting ability, helping finish the material to the required dimensional accuracy and surface finish.
These wheels are employed in grinding machines. Grinding wheels are consumables, though their lifespan can range from a few hours to many years, depending on their use.
As the wheel cuts, individual abrasive grains are periodically released, usually because they become dull and are pulled away by the increased drag.
Based on the Shape of the Cutting Tool
The cutting tools are now further divided based on the shapes of the cutters. Let’s take a closer look at the size-based category into which cutting tools can be categorized:
#1. Solid.
Typically, this type of cutter is used as a turning tool on a lathe to carry out the turning operation.
#2. Tipped Tool.
These cutters were created using a variety of materials. In other words, the cutters’ bodies are constructed from various materials, while the materials used in their cutting mechanism vary.
There are numerous ways to join these two components of the cutting tools, such as clamping, welding, etc. Examples of the tipped tools include tungsten carbide-tipped tools.
#3. Pointed Tool.
The cutter’s teo is fine and sharp, and the edges all meet in a single line. Examples of such cutting tools include sharp diamonds mounted on holders and hard carbide cutters.
#4. Grain Size.
Depending on the size and quantity of the grains, they are classified as cutting tools. If the grain is fine, this will remove more material from the workpiece.
However, more material will be removed if the grain size is large. For instance, grinding wheels use cutting tools of the abrasive type.
#5. Tool Bit.
This cutter doesn’t rotate. This tool can be used on shaping or planning machines to shape and plan the workpiece according to requirements, among other things.
Since it falls under the category of cutting tools, there is only one primary cutting groove on this particular cutting tool. Cast non-ferrous satellite cobalt, lathe tools in machine holders, etc., are a few typical examples of these types of cutting tools.
Based on Materials Used for Cutting Tools
There are different cutting processes done on varying conditions. Depending on the cutting conditions and the requirements of the respective cutting tool, it is important that they are of the right properties.
The type of material selected for a specific application depends on what is being machined. Here is a classification of these materials.
Carbon Tool Steel
This is one of the inexpensive metal cutting tools common in low-speed machining operations. These carbon steel cutting tools are constructed with a composition of 0.6%-1.5% carbon and small amounts, less than 0.5%, of Si and Mn. To enhance the hardness, other materials such as V and Cr could also be added.
Carbon tool steels are preferred because they are abrasion-resistant and can maintain the cutting edge for a long period. However, they lose their hardness when temperatures reach 250 °C. This means that they are not good for high-temperature operations.
Common applications that use carbon steel tools include milling tools, twist drills, and forming tools.
High-Speed Steel (HSS)
This is another high-carbon steel featuring a significant quantity of alloys like chromium and tungsten to increase its hardness and wear resistance. HSS loses its hardness when temperatures hit 650 °C.
It is, therefore, advisable to use coolants to increase tool life. The following surface treatment is also used on HSS to improve the properties.
- Super-finishing to lower friction.
- Chromium electroplating to lower friction.
- Nitriding to increase wear resistance.
- Oxidation to reduce friction.
High-speed steel tools are common in broaches, single-point lathe tools, and milling cutters.
Cemented Carbide and Cement
The cemented carbide cutting tool is created using metallurgy method. It is made from tungsten, titanium carbide, and tantalum with cobalt as a binder.
The most notable thing about the cemented carbide tools is that they are very hard and can be used for cutting at high speeds and temperatures. For example, you can use them for cutting at temperatures of 1000 °C without losing their properties.
For rough cuts, it is better to use a high cobalt tool, while low-combustion tools are ideal for finishing applications.
Ceramics
The common ceramic materials used in cutting tools are silicon nitride and aluminum oxide. When the ceramic material powder is compacted and inserted at very high temperatures, the resulting tools are inert and resistant to corrosion. Therefore, they have high compressive strength.
The ceramics are stable when operating even in temperatures of up to 1800°C and are about 10 times faster than HSS. Because the friction between the chip and surface is low and the heat conductivity is also low, you do not need an additional coolant.
Cubic Boron Nitride (CBN)
CBN is the second hardest material and is commonly used in hand machines. They provide high abrasion resistance and utilize abrasives in grinding wheels. They are ideal at speeds of 600-800m/min.
Diamond
This is the hardest material used in tools. It features a high melting point and thermal conductivity. Therefore, it provides excellent abrasion resistance, low thermal expansion, and a low friction coefficient.
It is considered ideal for machining hard materials like glass, nitrides, and carbides. Note that diamond is not ideal for machining steel.