The difference, characteristics and precautions of cutting and shearing processes

 The difference and types of cutting and shearing

Cutting refers to cutting and separating a workpiece into different objects. Cutting is one of the most widely used processing methods not only in the manufacturing industry but also in our daily lives. Another word similar to cutting is shearing. Here we introduce the difference between cutting and shearing, as well as the types of cutting processing.

• The difference between cutting and shearing

Cutting means to cut or separate something. In other words, cutting is the process of separating workpieces. There are many ways to cut, such as cutting with a tool like a saw, or using an electric arc to melt the material. Shearing is one of these cutting processes.

Shearing refers to the displacement and deformation of the cross section of a component along the direction of the external force under the action of a pair of closely spaced and oppositely directed lateral external forces. When it cannot be deformed, destructive cutting begins, which is the working principle of shearing. One of the most familiar shearing tools is "scissors", which shears paper by applying an up-and-down force relative to the paper.

• Types and characteristics of cutting processes

Cutting processes are classified into the following five types, depending on the tool used for cutting.

Gas cutting: The heat generated by the combustion of gas is used to melt and cut steel materials. When using a gas cutter, similar to welding, the heat of the flame melts the material by burning a gas such as acetylene. The advantage is that it can cut reflective materials or thicker plates. On the other hand, the process requires a high temperature of nearly 900°C, which may cause thermal deformation or material deterioration. Another disadvantage is that it cannot cut materials that are not easily oxidized, such as stainless steel and aluminum.

Mechanical cutting: A method of cutting using the mechanical force of a machine tool. There are many different cutting methods depending on the machine used, but cutting and shearing are the two main methods. Cutting is done by cutting the material little by little using a tool such as a grinder. Shearing is done using a press or shearing machine. Both cutting and shearing have the advantage of fast cutting speed. Cutting can process quite thick materials, while shearing cannot process too thick materials.

Water jetting: refers to a method of cutting materials by spraying water or a mixture of water and abrasive through a fine nozzle. No heat is generated during the process, so it can process materials that are difficult to cut by other methods, such as titanium. Materials that cannot be wetted with water cannot be processed using this method.

Arc cutting (plasma cutting): This method uses the heat of the arc (plasma) generated during discharge to melt and cut the material. Since the arc is generated between the workpiece and the electrode, only conductive materials can be cut. On the other hand, materials such as stainless steel and aluminum that cannot be processed by gas cutting can be processed. It can also cut thicker materials and has the advantage of low operating costs compared to gas cutting or laser cutting.

Laser cutting: A laser beam is focused by a lens and uses the heat it generates to melt and cut the material. Because lasers have the same properties as light, it used to be difficult to process polished materials and materials that easily reflect light, such as stainless steel. However, in recent years, more and more machines are able to process such materials. The advantage is that it can process complex and precise shapes with beautiful cut surfaces; however, the disadvantage is that the machine is expensive and cannot process thicker materials.

• Types and characteristics of shearing

Shearing is a type of cutting, but there are different types of shearing processes, used for different processes and purposes. Here are 5 typical shearing processes.

Shearing (cutting): The process of separating materials from larger materials (such as coils or cut-to-length materials) to a predetermined size that is easy to process. It can be thought of as the process of cutting a wooden board into a size suitable for the processing machine used in production. It mainly uses a machine called a shearing machine. Its characteristics are relatively low processing costs, but it is difficult to process thicker materials.

Die cutting (stamping): As the name implies, die cutting is the process of punching out the desired shape from a metal sheet. It is also called the basis of stamping. It is similar to punching holes for archiving paper. Die cutting uses a die and is suitable for mass production of products of the same shape.

Notching (punching): This is a process that only cuts off part of the edge of the metal plate to form a notch shape. Unlike other processes, it is characterized by partial cutting. This method is suitable for cases where only a notch shape needs to be added after the punching process, or when making a shape with many notches, such as a motor core.

Edge processing (trimming): trimming the excess part of the periphery of the workpiece, similar to "cropping" an image. Usually, trimming is performed on products that have already gone through other processes, and the process where the trimming is performed is a key factor in reducing costs.

Splitting: Splitting is very similar to shearing, but its characteristic is that there will be extra material discarded between the split parts. This is like the packaging film of a rice ball. Pulling the tape at the top will cause the film in the middle to break into thin strips, and the film will separate to the left and right sides.

 4 machines for shearing

Shearing belongs to mechanical cutting in the classification of cutting. Therefore, a variety of machines are used in shearing. This section will introduce the main types of machines used for shearing and their characteristics.

・Shearing machine

A shearing machine is a machine that shears materials between upper and lower blades, similar to scissors. It is a member of the punching machine family. Just like cutting paper with scissors, materials that are too thin and too soft will deform along the gap between the blades and cannot be sheared. If the material is too thick, the shearing resistance will be great and the machine will not be able to cut it. The thickness that can be cut is determined by the material.

・Pressing machine

A punching machine is a machine used for stamping, which uses a die to clamp a sheet of material and apply high pressure to deform it. Depending on the die used, various processes such as cutting, punching or bending can be performed on the material. In addition to stamping, notching, trimming and splitting can also be performed. Since a dedicated die is used, this machine is suitable for mass production of products of the same shape, and high-precision processing can be performed without the need for skilled workers.

・Turret Punch Press

Turret punch presses are a family of presses that can be processed using universal dies. Universal dies are mostly hole-shaped (such as round or square holes), which are punched continuously at close range to form various shapes. These machines are mainly used for blanking or hole-making. Because they use universal dies, they can be used for both small batch and multi-variety production and large batch production.

・Fine blanking press

The fine blanking press is also a member of the stamping machine family and is one of the machines used for precision shearing. The sheet is clamped from top and bottom, and pressure is applied to the parts that need to be stamped and the parts that do not need to be stamped, so that the sheet is stamped out. Since the sheet is pressed strongly, even materials that are difficult to process, such as stainless steel, can be stamped with high precision. As one of the processing methods for automotive precision parts, its use has been increasing.

 Precautions when cutting/shearing

For the cutting and shearing of plates, some special matters need to be paid attention to according to the different processing mechanisms. The following are some matters needing attention when cutting and shearing.

• Precautions for cutting

When cutting, you must pay attention to the thickness of the plate. Basically, the thicker the material, the more difficult it is to process during cutting. For steel, the thickness of the material that is easier to process is as follows:

Steel plate: thickness not exceeding 13mm

Angle steel: thickness not exceeding 13mm

Round steel: rod diameter less than 13mm

• Precautions for shearing

Shearing is also a type of cutting, but the thickness of the plate that can be processed is thinner.

Steel plate: thickness not exceeding 9mm

Angle steel: thickness not exceeding 9mm

Round steel: rod diameter less than 10mm

In addition, for shearing, attention must be paid to the accuracy of the cross section and the clearance between the tools (punch and die) that apply the shearing force. For example, when processing thick materials, the clearance between the punch and die should be larger than when processing thin materials. However, the larger the clearance, the greater the step deformation during shearing. In addition, burrs may appear, and grinding and deburring may be required after shearing.

Summarize

Cutting refers to the process of cutting materials, and shearing is a type of cutting. Shearing is a method of separating materials using shearing force, which is a force that is staggered up and down relative to the material. In addition to gas cutting and mechanical cutting, cutting methods also include arc cutting and laser cutting. Shearing includes shearing, die cutting, notching, trimming and splitting. Commonly used equipment for shearing includes shearing machines, punching machines, turret punching machines and fine blanking presses. When performing cutting, it is necessary to pay attention to the thickness of the sheet. It is generally recommended to consider a maximum of 13mm.