Cutting tools include a wide range of instruments for shaping, carving, or removing material, such as drills, saws, knives, and milling cutters. All metal parts that are used mechanically and in day-to-day life are machined through a variety of machines.
There exists a tool that helps in cutting the surface of any part to provide it with the desired shape; this tool is known as the cutting tool. A cutting tool is always harder than the material being cut.
Cutting tools are used in machining and consist of hardened metal implements employed to contour and shape a workpiece by removing parts of it through shear deformation. Alligator shears, abrasive saws, bandsaws, diamond saws, and milling machines are examples of cutting tools.
Moreover, they can be categorized into single-point and multiple-point tools, where single-point tools can also perform boring and enlarging of holes.
In this article, we will explore these tools, including their classification, and delve deeper into the materials used and their relevance in the cutting action.
What is a Cutting Tool?
In the world of machining, a cutting tool or cutter commonly refers to a hardened metal tool that performs cutting, shaping, and material removal through machining processes using various machining tools as well as abrasive tools through shear deformation.
A cutting tool is a device with edges that are sharp and wedge-shaped. It is designed to cut through and remove material layers from the workpiece during machining to achieve a certain shape, size, and accuracy.
A cutting tool is rigidly fastened to the machine tool, and the workpiece is fixed on a spindle. Various other mechanical and non-mechanical systems provide the necessary relative motion to the workpiece and the cutting tool to enable cutting action.
The greater part of these tools are specifically designed for metals. Many single-edge cutting tools are made out of different alloys of hardened metals, all of which are ground into particular shapes and are designed to accomplish certain tasks during the turning process to yield a finished machined part.
Single-edge cutting tools find their primary application in lathe turning operations, and their quantity, size, and alloy composition change with the material being turned and its dimensions.
The tool post is what holds the cutting tools in place and is used to control the movements and manipulations of the intended cuts made on the material to achieve the desired shape.
As with other tools, single-edge tools are employed with machines such as the metal shaping and metal planning machines that cut materials using a single cutting edge.
A typical feature of drilling and milling tools is that they are often multipoint tools. A drilled workpiece always has holes in it. The two edges of every drill bit are sharpened and ground so that the sides are cut into tapered angles, and they will turn about a vertical axis and apply downward pressure to the material below.
Rotational force is also used by end mills or milling bits to cut workpieces, not boring holes in them. The internal structure of these tools allows for a special type of cutting where it’s accomplished through horizontal shear deformation while the tool rotates, as the workpiece moves into the tool.
This is referred to as the tool path, which is set by the axis on the table that grips the workpiece.
This table can accept different kinds of vises and locking devices, making it possible to position the table towards the cutter in multiple directions while keeping the workpiece fixed. Endmills are a diverse class of cutters that execute specific milling functions.
Materials of Cutting Tools
- High-Speed Steel (HSS): It is a form of steel used for tools, which contains elements like tungsten, molybdenum, chromium, and vanadium.
- Carbide: also known as Tungsten Carbide. A cutting tool that consists of particles of tungsten carbide with a binder, usually cobalt.
- When machining hardened steels, super alloys, and other heat-resistant materials, alumina and silicon nitride-based ceramics are used.
- Polycrystalline Diamond (PCD): A synthetic material used for cutting tools. This material is produced by sintering diamond powders together with a binder.
Classification of Cutting Tools
A cutting tool is composed of one or several large main cutting edges whose functions are carried out concurrently in a single pass of the tool.
Cutting tools can be divided in multiple ways, nevertheless, the most popular way is by the number of main cutting edges working simultaneously during the cutting process. Based on this criterion, there are three classes of tools as shown below:
- Single Point Cutting Tool
- Double Point Cutting Tool
- Multi-Point Cutting Tool
#1. Single Point Cutting Tools.
A Single Point Cutting Tool, as the name suggests, has one principal cutting edge that completes a material removing operation using rotary action in a single pass. Such tools are single-point tools and are used in turning, shaping, planning, and other similar operations.
Single-point cutting tools can be made from hard materials, which include:
- High carbon steels,
- High-speed steel,
- Ceramics,
- Diamonds.
Crafting these tools can be inefficient due to the breakdown of edges. Since only one edge performs the cutting, infrequently faster cutting chances arise, and thinner edges tend to give out more frequently.
The tool that needs to be substituted with single-edged versions will come with a requirement that every edge is replaced once an edge that breaks down is reached.
A surgically designed tool, such as a single-bladed reamer, has only one edge that cuts at a time. The single-blade reamer is less efficient than its counterparts, as only one edge does the work.
Single-point cutting tools make the job simpler as the design and manufacture are straightforward and quicker, and materials are also comparatively less expensive.
The benefits of having a single-edge cutting tool bear its disadvantages as well. The main flaw is enduring contact with the workpiece for all the motion.
Because there is constant contact, high wear to the tool increases and decreases its durability. The wear is accelerated due to rapid contact, and along with fragile surfaces, they increase thermal damage too.
If there is a discrepancy in the temperature of the tooltip, it may be deformed, making the machining alignment less accurate.
If there is only one edge available for the chip load, there is a need to lower the material removal rate MRR per pass to allow for better accomplishment of the depth of cut. This leads to lowered productivity.
#2. Double Point Cutting Tool.
A double-point cutting tool features two edges that can simultaneously cut or shear during one motion. A single-point cutting tool has only one primary cutting edge, while a double-point tool has two.
A multi-edged cutting tool is characterized by having more than two cutting edges, which allows performing machining operations in a single pass.
Sometimes, cutters can only be subdivided into two classes when double-point cutters are considered multi-point cutters.
Besides, a cutting edge is defined as the intersection of a rake face and a flank, and thus, a double-point wielding tool has two rake faces and two flanks.
Example of a Double Point Cutting Tool: Drill. This is the only tool belonging to this class. Drills can have more than two cutting edges, but ordinary metal cutting drills, without some alterations to the cutting edges, have only two cutting edges.
The action of a pair of cutting edges simultaneously working may, in some cases, give rise to a certain component of a cutting force, in that the two cutting edges tend to cancel (or reduce) each other. This damping effect reduces some shocks, instability, vibration, and other unbalanced forces, making them more chaotic.
#3. Multi-Point Cutting Tools.
Multi-point cutting tools utilize two or more main cutting edges to provide simultaneous cutting action in a single operation. Unlike in most cases, where tools with two cutting edges are considered cutters of two cutting edges are regarded as multi-cutting tools instead of double-point cutters.
Three to hundreds of cutting edges can compose a multi-point cutter.
Unlike a single-point tool, a multi-point cutting tool permits the use of more than one cutting edge simultaneously. In this case, a multi-point tool utilizes several edges to cut through the material simultaneously.
This permits multiple cutting tools or “multi-blade” tools to operate at higher speeds than single cutting tools.
Due to heat being generated at the cutting edges, the multi-blade tool is often able to withstand greater periods of use and become less susceptible to wear due to being able to distribute heat across the blades. A clear example of a multi-cutting tool is a Diatool high-performance reamer.
A multi-blade reamer can compare cycle times for other methods and increase its quality efficiency.
Advantages of multi-point cutting tools include increased productivity and efficiency by having low chip load per tooth, higher speed and feed, low cutting temperature, reduced tool wear, high MRR, longer tool life, and tool longevity.
The tool has disadvantages, including periodic cuts, exposure of cutting edges or teeth to variable loads, and failure, which causes noise and vibrations to the cutter.
Machining the cutter makes it difficult to perform due to the higher cost of such a design.
Types of Cutting Tools
There are seven ways to divide cutting tools into categories, as all of them are equally important. The most commonly used one is based on the number of cutting edges that those tools use concurrently to cut material. Let us begin with the different types in each category.
Based on the Motion of the Tool
These tools have a very special function since they correspond to particular machines.
- Translatory Motion: When a body moves in such a way that every one of its particles moves parallel, it is said to be translatory motion. The lathe machine tools, which do operations like facing, turning, parting, or grooving are follow the translational motion.
- Reciprocating Motion: The repetition of an upward or downward, or forward and backward linear motion is known as reciprocating motion or reciprocation. It can be observed in shaping machines where the shaping tool moves in a linear fashion (reciprocates) and erases the material on each linear stroke.
- Rotary Motion: If a body rotates around a fixed axis, that motion is referred to as rotatory motion. Rotation of a moving wheel is an example of rotatory motion. The milling machine follows a rotary motion, that is, the tool rotates in a vertical axis parallel to the workpiece, while the drilling machine follows the rotational movement perpendicularly to the axis of the workpiece.
Based on the Material Used for the Cutting Tool
Stronger materials are used for cutting tools because they are usually more robust than the workpiece. This makes tool classification based on the material a central concern for any machine shop. The tools in this category will be discussed next.
High Carbon Steel
The cutting tool can operate in extremely hard conditions due to the high percentage of carbon included in the composition. It is important to note that with greater temperature, its hardness reduces.
Tools such as these have a high range of wear resistance and hardness, so they are referred to as tool steel. These types of cutting tools can withstand temperatures up to 400 degrees Celsius without any effect on the internal structure or composition of the tool.
High Speed Steel
These tools are much quicker, resulting in high-speed steel tools having faster cutting speeds. This specific tool is classified under cobalt, tungsten, and chromium alloyed steel.
These materials require 550 degrees Celsius to 650 degrees Celsius for operations, causing tools made out of this strong, hard, and temperature-resistant material to function effectively.
Owing to the presence of strong, harder materials, they are primarily employed in the production of a variety of cutting tools such as drills, taps, milling cutters, drill and tool bits, gear cutters, power saw blades, and even planer tools.
Ceramic Tools
One of the most heat-resistant tools for cutting and machining is made of ceramic. It is noted that this equipment operates between temperatures of 1160 degrees Celsius to 1210 degrees Celsius. Therefore, it is employed during the finishing operations on a lathe or milling machine.
Cemented Carbide
This tool is an alloy consisting of tungsten, titanium, and other metals. These significantly increase the strength and hardness of the tool. Moreover, it can sustain high temperatures due to the presence of carbon. The operating temperature of this tool is between 900 degrees Celsius to 1000 degrees Celsius.
Diamond
Cutting tools manufactured from diamonds are currently the hardest material. They can naturally be harvested from the earth. This enables the tool to have the added advantages of extreme temperature resistance, durability, and resilience to shocks. These implements are used for the cutting of tough, solid, and durable materials.
Abrasives
In general, all abrasive-type cutting tools cut by repeatedly rubbing a hard object on the desired object. As the name implies, an abrasive material is hard, rough, and coarse, and wears away whatever it touches.
This type of equipment is embedded with abrasive material. Possibly the most basic example is the grinding wheel, which is a common type of grinding machine.
Based on the Angle of Cutting
The angle of cutting is important for any machining operation. Thus, the three major types of tools are:
- Orthogonal Cutting: The cutting edge is parallel to the direction that the tool is moving when slicing orthogonally. The cutting edge angle is zero, and chip formation occurs in the orthogonal plane. With orthogonal slicing, radial force is absent, yielding two remaining force components.
- Oblique Cutting: In this case, the angle between the cutting edge and the tool’s direction is less than 900circ. This type of cutting is often associated with turning operations. It invariably involves three components of force applied at right angles to one another.
Based on Common Names of Cutting Tools
The technical terms are known, but industrial terms for cutting tools differ for each machine and operation. Let us understand the cutting tools under this category.
Solid Tool
A solid-shaped cutting tool is most commonly used in turning operations, as in a lathe machine.
Tool Bit
The tool bit is disc-shaped, and it can be classified as a single-point non-rotary-type cutting tool. Its application includes shaping and planning operations. These tool bits are composed of cobalt-bearing non-ferrous alloys.
These types of tools are often dubbed as single-point cutting tools. The cutting edge is able to be ground or modified for a certain machining operation.
Tipped Tool
Tipped tools are defined as any cutting tool that has a separate piece for the cutting edge, which is brazed, welded, or clamped to a body made of a different material.
Tipped tools can be found in power saw blades, end or face mills, fly cutters, and other tool bits and milling cutters. The copper-tipped or clamped-clipper cutters (CBN) are known to have tipped-grade materials cemented carbides, polycrystalline diamond, and cubic boron nitride.
Pointed Tool
A pointed tool having a sharpened tip is only useful as a cutting tool at one end: the tip of the tool. These tools are mostly used for marking or scribing on metals before cutting or drilling activities, or for making punch holes into wood.
Grain Size
The tools in this category cut depending on the size and number of grains. For example, if the grain is finer, more work will be done on the concrete. It is the opposite when the grain size is bigger.
Based on the Direction of Handling
The movement of the workpiece that the tool cuts is referred to as the direction of handling; the cutting tool is relative to the workpiece. These are two tools.
- Right-Handed Tool: The movement of a right-hand cutter is from the left side to the right. Such motion is, as earlier observed, adopted in a right-handed machining where an operator is used to shift the tool sideways in a cutting action.
- Left-Handed Tool: The motion for a left-hand cutter is from right to left. This is also the way manual machines worked.
Types of Cutting Tools
In metal cutting technology, cutting tools are utilized in machining operations because they serve the purpose indicated in their name.
Since the milling cutters can be employed for more than one process in the machining operation, they were given names based on their various functions in the machining process.
In machine shops, these are the tools that are considered for use without further specification of whether them being basic or advanced:
- Grinding wheel. This grinding tool is a type of abrasive used on the grinding machine during the grinding operation.
- Single Point Turning Tool. This is a turning tool used in a lathe machine for the turning operation.
- Drill. A cutting tool used to make circular holes in a workpiece and has an edge on the tip and a helical groove on the body for clearing the shavings is a drill. He is the best-known of all cutting tools. It comes in many shapes and types, from simple household devices to specialized machining tools.
- Mill (or Milling cutter). A milling tool is a generic term for tools with several cutting edges on the outer surface or the end surface of a disk or a cylindrical body; it cuts the workpiece as it rotates. It is mainly used in milling machines and CNC machines, and the blade material includes diamond/CBN, high-speed steel, and carbide. End mills are also a type of milling tool.
- Reamer. Reamers are tools used to finish enlarging a hole already drilled to the specific level of accuracy required. It is similar to cutting tool in that it has blades made of diamond/CBN, high-speed steel, and carbide. The cutting edges number anywhere from one to many based on the application and diameter of the hole. With the step reamer, the blade is multifaceted, meaning multiple processes can be performed with a single reamer.
- Broach. A broaching machine is a tool in the category of machine tools that carries out surface machining of the outer cylindrical surface or of a hole surface in a broaching machine employing a series of cutting tools arranged in axial and radial increasing order, mounted on the rod-type body outer surface.
- Fly cutter. This tool performs fly milling on a milling machine.
- Shaper. The workpiece requires specific shapes and certain accuracies, this work will be done with this cutter on a shaping machine.
- Planer. This wedge tool is like a shaper. However, here the bulkier workpieces are used that move in the process while the cutter moves in shaping.
- Boring bar. This instrument is used for cutting on the boring or drilling machine where the boring operation is executed.
- Hob. This cutter is to complete the hobbing operation on the hobbing machine.