What Is Cutting Tool?- Name, Types, And Materials

What is a Cutting Tool?

In machining processes, the cutting tool often referred to as a cutter is a specialized, hardened metal instrument employed to cut, shape, or remove material from a workpiece.

This is typically achieved through the action of machining and abrasive tools, utilizing shear deformation as the primary mechanism for material removal.

A cutting tool is fundamentally a wedge-shaped device with a sharpened edge, specifically engineered to shear away surplus layers from the workpiece. This shearing process is essential for achieving precise shapes, dimensions, and surface finishes according to the intended specifications.

For effective operation, the cutting tool is rigidly secured to the machine tool. The cutting action itself is made possible by inducing a relative motion between the workpiece and the tool, which can be accomplished through various mechanical arrangements.

Most cutting tools are optimized for machining metals and are produced from robust metal alloys. In the realm of turning operations, single-edge cutting tools are prevalent. These tools are ground to specific geometries that correspond to their particular function within the turning process, ultimately leading to the finished component.

Single-edge cutting tools are primarily used with lathes, and their size and alloy composition are chosen based on both the scale of the operation and the material properties of the workpiece.

These tools are held firmly in place by a tool post, a fixture designed to accurately manipulate the tool during the cutting process to achieve the desired workpiece geometry.

Beyond lathes, single-edge tools are also integral to metal shaping and planning machines, both of which rely on a single cutting edge to systematically remove material.

Contrastingly, tools used in milling and drilling often feature multiple cutting edges. Drilling, for instance, is dedicated to producing holes in a workpiece.

Each drill bit incorporates two cutting edges, meticulously ground to identical angles, which enable the bit to penetrate material under the application of downward rotational force.

Milling tools, such as endmills, also employ rotational motion to cut. Unlike drill bits, their primary purpose is not to produce holes but to remove material horizontally through shear deformation.

In milling, the workpiece is advanced along a path relative to the rotating tool this path is determined by the movement of the machine’s table, which can be adjusted in multiple directions and angles thanks to a variety of vises and clamping devices.

There is a wide range of endmill designs, each suited to specific milling operations. The selection of the appropriate endmill depends on the desired milling action and the characteristics of the workpiece material.

Classification of Cutting Tools

When it comes to cutting tools, it’s not uncommon for a single tool to feature multiple major cutting edges, all of which can be engaged in the cutting process at once during a single pass.

There are several ways to classify cutting tools, but the approach most widely used involves counting how many major cutting edges are active during operation. Based on this criterion, cutting tools generally fall into three categories, which are outlined below.

• Single Point Cutting Tool
• Double Point Cutting Tool
• Multi Point Cutting Tool

1. Single Point Cutting Tools

A single point cutting tool features just one main cutting edge responsible for removing material during each pass. These tools find their primary application in operations such as turning, shaping, and planing essentially, whenever precision shaping of material is required.

Manufacturers typically use durable materials for these tools, including high-carbon steel, high-speed steel, ceramics, and even diamond, depending on the demands of the job.

One of the things you’ll notice when working with a single point cutting tool is that all the cutting is done by that one edge. This means material isn’t removed as quickly as with multi-edge tools, and it also puts more stress on the edge itself. If the edge fails—say, it chips or wears out—you’re left with no choice but to pause your work and replace the whole tool.

Single-blade reamers fall into this category as well. Since there’s only one edge actively removing material, the process tends to be slower than with tools that have multiple edges sharing the workload.

On the bright side, the design and manufacturing process for single point cutting tools is straightforward, which makes them more affordable and less time-intensive to produce.

However, there are clear drawbacks. With only one cutting edge in constant contact with the workpiece, tool wear is inevitable and tends to happen fairly quickly. This constant friction also leads to a rapid rise in temperature, which not only accelerates wear but can also cause thermal damage to the surface you’re working on. In extreme cases, the tip might even deform due to the heat, which affects machining accuracy.

Finally, since that single edge takes on the full chip load with every pass, the material removal rate stays relatively low—meaning productivity is not as high as it could be with multi-point tools.

2. Double Point Cutting Tool

A double-point cutting tool is designed with two cutting edges, allowing it to cut or shear material simultaneously in a single operation. By comparison, a single point cutting tool features just one main cutting edge and handles the work alone.

There’s also another category: multi-edged cutting tools. These are equipped with more than two cutting edges, so they can perform machining tasks in one pass, making them highly efficient for certain jobs.

It’s worth mentioning that the way we classify cutters isn’t always strict. Sometimes, double-point cutters are grouped together with multi-point cutters, since they both have more than one cutting edge.

From a structural perspective, a cutting edge is formed where the rake face and flank of the tool meet. So, in the case of a double-point cutting tool, you’ll find two rake faces and two flanks.

The classic example of a double-point cutting tool is the drill. While some drills can have more than two cutting edges, standard metal-cutting drills those without any special modifications typically come with two.

One interesting aspect of double-point tools is how the two cutting edges work together. When both edges are engaged at the same time, they can actually help balance out the forces involved.

In some cases, the force from one edge offsets the other, reducing problems like vibration, instability, or other shocks that can occur with an unbalanced cutting force.

3. Multi-Point Cutting Tools

A multi-point cutting tool is characterized by having more than two main cutting edges that operate at the same time during a single machining pass.

While there is some debate, even cutters equipped with just two edges are occasionally categorized as multi-point tools rather than simply double-point cutters.

The actual number of cutting edges on these tools can range from as few as three to well into the hundreds, depending on the application and design.

Unlike single-point cutting tools, which rely on one edge for material removal, multi-point tools take advantage of several cutting edges working together. This setup allows them to remove material more efficiently by engaging multiple points simultaneously.

One immediate benefit is speed. Multi-blade or multi-edge tools generally operate at higher speeds than their single-edge counterparts. Because the heat produced during cutting is distributed across several blades, these tools often last longer and are more resistant to wear.

For example, the Diatool high-performance reamer is frequently cited as an effective multi-point cutting tool, valued for its efficiency.

When compared to alternative approaches, a multi-bladed reamer can notably decrease machining cycle times while also improving the overall quality of the finished piece.

The design of multi-point cutting tools brings several advantages to the table: each tooth experiences a lower chip load, which contributes to higher possible speeds and feeds, greater material removal rates (MRR), and, ultimately, improved productivity. There’s also less tool wear and lower cutting temperatures, resulting in longer tool life.

However, these tools aren’t without their challenges. Since each tooth or cutting edge is exposed to varying loads thanks to the intermittent nature of their cutting this can result in noise, vibration, and, over time, the risk of tool failure.

Moreover, designing and manufacturing such cutters is more complex compared to single-point tools, which naturally makes them more expensive to produce.

Types of Cutting Tools

As the term implies, cutting tools play a vital role in machining processes within the field of metal cutting technology.

Among these, milling cutters stand out for their versatility, as they can be applied in a wide range of machining tasks. Interestingly, the names of different milling cutters often reflect the specific functions they serve during machining.

Below are some of the most commonly used cutting tools:

• Single Point Turning Tool: This is your go-to tool when it comes to turning operations on a lathe. It’s simple but effective, with a single cutting edge that shapes the workpiece as it spins. You’ll see it used constantly in basic lathe work.
• Drill: If you’ve ever needed to make a hole in something, you’ve probably used a drill. Drills are everywhere from your household toolbox to high-precision manufacturing. What sets them apart is the sharp cutting edge at the tip and the helical groove along the body, which helps chips escape as you drill. There’s a huge range of shapes and sizes out there, depending on whether you’re tackling a quick DIY job or working with specialized industrial materials.
• Milling Cutter (Mill): Think of milling cutters as the multitaskers of the machining world. Unlike single-point tools, mills have several cutting edges either around the outside or at the end, and they get to work by spinning at high speeds. Milling is mostly done on milling machines and machining centers, with tool materials ranging from high-speed steel to carbide and even diamond or CBN. End mills are a popular type of milling cutter you’ll run into often.
• Reamer: Once you’ve drilled a hole, sometimes you need it to be even smoother or more precise. That’s where the reamer comes in. It’s designed to finish up drilled holes to a specific size or tolerance. You’ll find reamers made from materials similar to other cutting tools, and they can have just one edge or several, depending on the hole’s size. Some reamers, like step reamers, are built with multiple “steps” so you can perform different finishing operations in one go.
• Broach: Broaching is a bit more specialized. The broach itself is a long, rod-like tool with many cutting edges arranged in sequence along its length. As the broach is pushed or pulled through (or over) a workpiece, it gradually shapes the surface either inside a hole or along the exterior. It’s a clever way to create complex profiles in one smooth motion.
• Fly Cutter: Fly cutters are used for what’s called “fly milling.” It’s a simple but effective way to machine large, flat surfaces using a single-point cutting tool mounted in a rotating holder on the milling machine.
• Shaper: Need to create a specific shape with accuracy? The shaper is the tool for that job. It’s used on a shaping machine, where the cutter moves back and forth across the workpiece, gradually sculpting it into the desired form.
• Planer: Planers are similar in principle to shapers, but they’re built for bigger jobs. Here, it’s the workpiece itself that moves back and forth, while the cutting tool stays in place. This makes planers perfect for handling large, heavy pieces that wouldn’t fit on a standard shaping machine.
• Boring Bar: When you want to enlarge an existing hole, you reach for the boring bar. It’s used on a boring or drilling machine to perform boring operations, essentially refining the hole’s size and finish.
• Hob: Hobs are specialized cutters used in hobbing machines, mainly to create gears and splines. The tool’s unique shape allows it to cut these complex forms efficiently.
• Grinding Wheel: Last but not least, the grinding wheel is an abrasive tool used for grinding operations. Mounted on a grinding machine, it removes tiny amounts of material from a workpiece, perfect for achieving high precision and a smooth finish.

Classification of the Cutter Depending on the Shape

The classification of milling cutters can be further refined based on the geometry of the tool itself. If we consider the shape as our main criterion, it becomes possible to group cutting tools into specific categories according to their physical form. Let’s take a closer look at how these cutting tools are organized based on their shape:

• Solid
• Tipped Tool
• Tool Bit
• Grain Size
• Pointed Tool

1. Solid

Typically, this type of cutter serves as a turning tool on a lathe, where it is primarily used to carry out various turning operations.

2. Tipped Tool

This particular cutter is constructed using a combination of materials. Specifically, the main body is manufactured from one set of materials, whereas the cutting edge itself is crafted from another, often more suitable, material.

To assemble these two distinct parts, various joining methods can be employed—common approaches include clamping or welding, among others. A familiar example of this type of tool is one that features a tungsten carbide tip.

In such cases, the cutting edge (the tip) is made from tungsten carbide and attached to a body made from a different material, which helps optimize both performance and durability.

3. Tool Bit

This type of tool is classified as a non-rotating cutter. It’s typically used on shaping or planing machines to accurately shape or smooth the workpiece as needed. The applications aren’t limited to just those processes—there’s a fair amount of flexibility depending on the machining requirements.

Belonging to the broader category of cutting tools, this particular cutter is notable for having just a single main cutting edge.

Some familiar examples include tools made from cast non-ferrous satellite cobalt and lathe tools mounted in machine holders. These are commonly found in machine shops and are valued for their precision and reliability in various metalworking tasks.

4. Grain Size

The effectiveness of cutting tools is closely linked to both the grain size and the number of grains present. When the grains are finer, they tend to remove material from the workpiece more efficiently and with greater precision.

On the other hand, larger grains typically shear off a greater volume of material with each pass, which can affect the finish and overall accuracy.

Take grinding wheels, for instance these rely on abrasive grains as the cutting elements. The performance and outcome during grinding are significantly influenced by whether those abrasive grains are fine or coarse.

5. Pointed Tool

As the name implies, this cutter features a tip that is both sharp and precise. All of its edges come together to form a single, fine line.

Common examples of this kind of cutting tool include hard carbide cutters and pointed diamonds that are carefully mounted on holders. These tools are designed specifically for tasks that require high accuracy and delicate handling.

Cutting Tool Material

When it comes to machining processes like drilling, turning, or milling the choice of cutting tool material plays a critical role. These materials are specifically engineered for making tools such as drill bits, tool bits, and milling cutters.

It’s important to note that we’re not talking about everyday cutting tools like kitchen knives or punches; machining tools face very different demands.

One key requirement for cutting tool materials is that they must be significantly harder than the workpiece they’re cutting. This hardness isn’t just important at room temperature; the material needs to maintain its edge and durability even under the intense heat generated during machining operations.

If the tool material softens at high temperatures, it quickly loses its effectiveness, which can compromise the entire 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: Tool steels are widely recognized for being both affordable and durable. Their level of hardness makes them perfectly capable of machining other steel materials, which explains their broad use in workshop and manufacturing environments.
• Carbon Tool Steels: If we take a step back in history, carbon steels have been part of the toolkit for cutting applications since the late 19th century. That said, their popularity for metal-cutting isn’t what it used to be. The main drawback? They start to lose their edge (literally) at temperatures above 180°C. As a result, carbon steel tools typically containing about 0.9% carbon and 1% manganese and hardened to roughly 62 on the Rockwell C scale are now more commonly seen in woodworking. Interestingly, they can also handle light duty tasks like routing aluminum sheets up to 3 mm thick, but that’s about as far as their metalworking goes.
• High-Speed Steels (HSS): Now, if you’re looking for a workhorse in the world of cutting tools, high-speed steel fits the bill. HSS manages to retain its hardness up to around 600°C, which is one reason why it’s so popular in machining. These tools are tough, resilient during interrupted cutting, and versatile enough for making everything from drills and reamers to taps, dies, and even gear cutters. Manufacturers sometimes add coatings to bump up their wear resistance. Not surprisingly, HSS dominates the market in terms of sheer volume used. When it comes to typical cutting speeds, you’ll find them ranging between 10 and 60 meters per minute.
• Cutting Ceramics: Ceramics take things up a notch in hardness, surpassing even cemented carbides, though this comes at the cost of reduced toughness. You’ll often see aluminum oxide and silicon nitride in this category. Of the two, silicon nitride stands out for its better toughness, but it’s not suitable for machining steel because of rapid wear issues.
• Cemented Carbide Tools: A cemented carbide tool is basically a blend of tantalum, tungsten, and titanium carbides, with cobalt acting as the binder. These tools are extremely hard and maintain their integrity at temperatures soaring well beyond 900°C, which makes them a staple for heavy-duty machining tasks.
• Ceramic Tools: When it comes to ceramics for cutting, aluminum oxide and silicon nitride are the main players. What makes them special is their remarkable compressive strength and their ability to handle temperatures up to 1800°C. Because of their low friction and poor heat conductivity, these tools usually don’t need coolants and can deliver a top-notch surface finish.
• Cubic Boron Nitride (CBN) Tools: CBN tools come in just behind diamond in terms of hardness. They’re especially valued for their incredible abrasion resistance, which is why you’ll often find them used as abrasives in grinding wheels.
• Diamond Tools: Diamonds are in a league of their own they’re not only the hardest material out there but also come with a steep price tag. They excel in thermal conductivity and have a high melting point, plus they offer low friction and minimal thermal expansion. For jobs that demand pinpoint accuracy and an exceptional surface finish, diamond tools are the gold standard.
• Other Materials: To push the boundaries of tool toughness, researchers have been experimenting with “whisker” reinforcement. One example is silicon nitride that’s reinforced with silicon carbide whiskers a field that continues to see new developments as technology advances.

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