What is a Cutting Tool?
In the field of machining, a cutter or cutting tool is usually a hardened metal tool used to cut, shape, and remove material from a workpiece using machining tools and abrasive tools through shear deformation.
A cutting tool is a wedge-shaped, sharp-edged tool used to remove excess layers of material from a workpiece by cutting during machining to obtain the desired shape, size, and accuracy. It is firmly attached to the machine tool. The relative speed between the workpiece and the cutting tool is also provided by various mechanical and other arrangements for the cutting motion.
Most of these tools are designed specifically for metal. There are many different types of single-edge cutting tools that are milled from various hardened metal alloys into specific shapes to perform specific parts of the turning process to produce the final machined part.
Single-edge cutting tools are used primarily in turning operations performed on lathes and vary in size and alloy composition depending on the size and type of material being turned.
These cutting tools are held in place by something called a tool post that manipulates the tool to cut the material to the desired shape. Single-edge cutting tools are also a means of cutting material that is performed by metal shaping machines and metal planers that remove material with a single cutting edge.
Milling and drilling tools are often multi-point tools. Drilling is used only to make holes in the workpiece. All drills have two cutting edges that are ground to two equal taper angles that apply a downward rotational force to cut the material.
An end mill or milling bits that cuts material through rotational force. Although these tools are not made for drilling the workpiece. They are cut by a horizontal shear deformation introduced into the tool as the workpiece rotates.
This is known as the tool path determined by the table axis that holds the workpiece in place. This table is designed to accept a variety of clamps and clamping tools to hold the workpiece and move it to the cutter at different angles and directions. There are several different types of end mills for specific types of milling operations.
Classification of Cutting Tools
A cutting tool can have one or more primary cutting edges that simultaneously participate in the cutting process in single pass.
Cutting tools can be classified in different ways. However, the most common method is based on the number of leading cutting edges simultaneously participating in the cutting process. Based on this, cutting tools can be divided into three groups 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 consists of only one main cutting edge that can perform material removal operations at a time. Single point cutting tools are used in turning, shaping, planning and similar operations.
Made of hard materials such as high carbon steel, high speed steel, ceramic and diamond.
With single-point cutting tools, one cutting edge does all the work, and material may not be removed quickly, increasing the chance of edge breakage.
If one of the cutting edges breaks during use, the entire tool must be stopped and replaced before being used again.
A single-point tool, such as a single-blade reamer, has only one cutting edge to remove material. Single blade reamers work with only one edge and are often time-consuming.
The main advantage of single-point cutting tools is that they are very easy and fast to design and manufacture, and such tools are relatively inexpensive.
Single cutting edge also have disadvantages. It is in constant contact with the workpiece during machining.
The result is increased tool wear and reduced tool life. Due to the continuous contact, the temperature rise rate of the tool is high. On the one hand, this accelerates tool wear, and on the other hand, it causes thermal damage to the finished surface.
If the temperature becomes too high, the tool tip may undergo plastic deformation, resulting in poor machining accuracy. The material removal rate (MRR) is much lower because only one cutting edge requires the full depth of cut (chip load) in one pass. So, productivity is low.
2. Double Point Cutting Tool
A double point cutting tool consists of two cutting edges that can cut or shear at the same time in one operation. In contrast, a single-point cutting tool contains only one main cutting edge.
A multi-edged cutting tool contains more than two cutting edges to perform machining operations in a single pass.
Sometimes cutters can only be divided into two groups when double-point cutters are also considered multi-point cutters.
In addition, a cutting edge is obtained through the intersection of a rake face and a flank. Double-point cutting tools, therefore, contain two rake faces and two flanks.
Double Point Cutting Tool Example: Drill is the only example for this category. Note that drills can have more than two cutting edges. However, conventional (without cutting edge modification) metal cutting drills contain two cutting edges.
The simultaneous action of two cutting edges sometimes creates a certain cutting force component in that two cutting edges automatically eliminate (or reduce) one another. This reduces various shocks (such as instability, vibration, etc.) of an unbalanced cutting force.
3. Multi-Point Cutting Tools
A multi-point cutting tool contains more than two main cutting edges that work simultaneously in one pass. Sometimes cutters with two cutting edges are also viewed as multi-cutting tools (rather than double-point cutters).
The number of cutting edges present in a multi-point cutter can vary from three to a few hundred.
In contrast to a single-point tool, a multi-point cutting tool allows more than one cutting edge to be used at the same time. Ultimately, the multi-point tool allows multiple edges of the tool to remove material at once.
This allows multiple-cutting tools or “multi-blade” tools to run faster than single-cutting tools.
Because the amount of heat generated at the cutting edges is distributed across each cutting blade, the tool can often run longer and be more wear-resistant. A Diatool high-performance reamer is a great example of a multi-cutting tool.
Compared to alternative methods, a multi-bladed reamer can shorten cycle times and increase quality.
Multi-point cutting tools have many advantages such as low chip load per tooth, higher speed and feed, high MRR and productivity, also reduced tool wear, low cutting temperature, and longer tool life.
It also has disadvantages such as intermittent cuts, cutting edges, or teeth are exposed to fluctuating loads. This creates noises, vibrations, and permanent failure of the cutter. The cutter is comparatively difficult to design and manufacture. This makes such a cutter more expensive.
Types of Cutting Tools
As the name suggests, cutting tools are used for machining operations in metal cutting technology. The milling cutters can be used in various machining applications. Therefore, the milling cutters were named according to their respective role in the machining.
Here is a list of the cutting tools that are commonly used:
- Single Point Turning Tool. This cutting tool is for performing the turning operation in the lathe machine.
- Drill. A drill is a cutting tool that drills a hole in a workpiece that has a cutting edge at the tip and a groove in the body for evacuating chips. It is the most common tool among cutting tools, with various shapes and types for use from DIY to specialty 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 the milling machine and machining center; The blade material includes diamond/CBN, high-speed steel, and carbide. An end mill is also a type of milling tool.
- Reamer. A reamer is a tool used to finish the hole opened by a drill according to the required accuracy. Similar to the cutting tool, the blade material includes diamond/CBN, high-speed steel, and carbide. The number of cutting edges ranges from one to several, depending on the hole diameter and application. With the step reamer, the blade is divided into several steps, which means that several operations are possible with a single reamer.
- Broach. A broaching machine is a tool for machining the surface of a workpiece or the inner surface of a hole in the broaching machine, in which numerous cutting edges are arranged in the order of dimension along the axis of the rod-shaped main body outer periphery.
- Fly cutter. This tool does the task of fly milling on the milling machine.
- Shaper. This cutter is for giving specific shape and accuracy to the workpiece and is performed on the shaping machine.
- Planer. This wedge device is similar to a shaper. However, in this process, the larger workpieces are employed which move during the process, whereas in shape, the cutter moves.
- Boring bar. This cutting device is performed on the boring or drilling machine to execute the boring operation.
- Hob. This cutter is to perform the hobbing operation on the hobbing machine.
- Grinding wheel. This grinding tool is an abrasive device used on the grinding machine for the grinding operation.
Classification of the Cutter Depending on the Shape
Depending on the shape of the milling cutter, the cutting tool is now further differentiated. Let’s look at the category that the cutting tool can be divided into in terms of shape:
- Tipped Tool
- Tool Bit
- Grain Size
- Pointed Tool
In general, such a kind of cutter is employed as a lathe turning tool to perform the turning operations.
2. Tipped Tool
This cutter was developed from different materials. That is, the body of the cutter is made of several different materials while its cutting part is developed from a different material.
These two parts of the cutting tool can be joined by following any process including clamping, welding, etc. Examples of tools with tipping are tools with tungsten carbide tipping,
3. Tool Bit
This is a non-rotating cutter. You can use this tool on the shaping or planing machine to shape and plan the workpiece accordingly and much more.
It falls under the cutting tools category, which means that this cutting tool only has one main cutting groove. Some common examples of this type of cutting tool are the cast non-ferrous satellite cobalt, the lathe tool in the machine holder, etc.
4. Grain Size
Cutting tools depend on the grain size and the number of grains. Assuming the grain is smaller, it will shear off more of the material from the workpiece.
Conversely, if the grain size is larger, more material will be sheared off. For example, the abrasive type of cutting tool is used in grinding wheels.
5. Pointed Tool
As the tool name suggests, the Tio of this cutter is pointed and fine. All edges coincide in one line. A few examples of such cutting devices include hard carbide cutters and pointed diamonds mounted on the holder.
Cutting Tool Material
Cutting tool materials are used to make cutting tools used in machining (drill bits, tool bits, milling cutters, etc.) but not other cutting tools like knives or punches.
Cutting tool materials must be harder than the material of the workpiece, even at high temperatures during the process.
The following properties are required for the cutting tool:
- hardness, hot hardness and pressure resistance
- bending strength and toughness
- inner bonding strength
- wear resistance
- oxidation resistance
- small prosperity to diffusion and adhesion
- abrasion resistance
- edge strength
No material shows all of these properties at the same time. Very hard materials, have lower toughness and break more easily. The following cutting tool materials are used:
- Tool steels. They are relatively cheap and tough. Their hardness is sufficient to machine other steels.
- Carbon tool steels. Carbon steels have been used since the 1880s for cutting tools. However, carbon steels start to soften at a temperature of about 180oC. This limitation means that such tools are rarely used for metal cutting operations. Plain carbon steel tools, containing about 0.9% carbon and about 1% manganese, hardened to about 62 Rc, are widely used for woodworking and they can be used in a router to machine aluminum sheet up to about 3mm thick.
- High-speed steels. They lose their hardness at 600 °C and are widely used in machining. HSS tools are tough and suitable for interrupted cutting and are used to manufacture tools of complex shape such as drills, reamers, taps, dies, and gear cutters. Tools may also be coated to improve wear resistance. HSS accounts for the largest tonnage of tool materials currently used. Typical cutting speeds: 10 – 60 m/min.
- Cutting ceramic. They are even harder than cemented carbides but have lower toughness. Aluminum oxide and silicon nitride are used. The latter has higher toughness, but can’t be used for machining Steel, due to very high wear.
- Cemented carbide. Cemented carbide cutting tool consists of tantalum, tungsten, and titanium carbide with cobalt as a binder. These carbide tools are very hard and can withstand temperatures well above a 900-degree Celsius.
- Ceramics tools. Aluminum oxide and silicon nitride are considered the most common ceramic materials. They have high compressive strength and can withstand temperatures up to 1800-degree Celsius. Due to their low friction between tool face and chip and low heat conductivity, they usually require no coolant and provide an excellent surface finish.
- Cubic boron nitride tool (CBN). CBNs are the second hardest material after diamond. They offer high resistance to abrasion and use an abrasive in grinding wheels.
- Diamond tool. Diamonds are the hardest material and not to mention also quite expensive. It has a very high thermal conductivity and melting point. They offer a low friction coefficient, low thermal expansion, and high abrasion-resistant. Diamonds are excellent for dimensional accuracy and surface finish.
- Other Materials. To improve the toughness of tools, developments are being carried out with whisker reinforcement, such as silicon nitride reinforced with silicon carbide whiskers.