Sheel metal shearing is one of the most widely used metal-cutting processes commonly used in fabrication and HVAC applications.
But what exactly is metal shearing and how is it performed?
Sheet metal shearing is the process of cutting metal sheets by applying a shearing force on the workpiece. It generally consists of a sharp blade that slices through the workpiece producing the desired cut. It is ideal for making straight cuts, but can also be used to cut different shapes.
This article provides a detailed guide on sheet metal shearing such as the process, its types, tools used, and advantages.
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What is Sheet Metal Shearing?
Sheet Metal Shearing is a metal-forming process in which unwanted parts of metal sheets are removed using die punches consisting of a sharp edge to shear the metal.
The metal sheets are placed between the shearing tool's upper and lower blades (or dies), which are then pressed together to yield exact cuts.
Since metal shearing is based only on the application of blade pressure, it eliminates heating defects and chip formation, making the method cost-effective and precise.
Due to these properties, sheet metal shearing is an ideal choice in manufacturing industries requiring straight cuts and high-volume production.
Generally, sheet metal shearing involves three stages: deformation, penetration, and fracture.
The cutting blade applies the shearing force producing a plastic deformation in the workpiece, followed by penetrating through the grains of the workpiece.
Finally, the workpiece undergoes fracture, resulting in the desired cut.
Important Parameters in Sheet Metal Shearing
Clearance refers to the gap between the shearing blades and is an important factor in determining the efficiency and quality of the process.
This space is needed to facilitate the fracture of the metal sheet.
However, improper clearance values may result in inconsistent cuts and unexpected product dimensions.
An appropriate clearance value depends upon the material's strength, type of shearing, and sheet thickness.
A clearance value that is too small requires more pressure and will cause the blades to rub against each other, causing uneven cuts and quick tool wear.
Whereas a large clearance will result in large plastic deformation of the drawn metal, leading to low quality and rough cuts.
According to the general rule of thumb, the clearance gap is maintained around 10-15% of the sheet thickness.
Additionally, it is preferable to keep the dimensions of the workpiece slightly larger than required to account for tolerances and allow surface finishes after the shearing process.
Shearing uses strong slicing forces, so it is essential to ensure that the workpiece is held firmly in place during the shearing process.
Poor clamping can cause the workpiece to bend and develop excessive stress on the shearing tools.
Consequently, resulting in inaccurate cuts and a reduction of shearing tool life.
In worst cases, this can result in injury if the scrap from the loosely held sheet flies off.
Type of Metal being Sheared
As shearing is a cold metalworking process, it is best suited for softer metals with good ductility, such as brass, mild steel, aluminum, and bronze.
Ductile materials can easily deform and stretch under the shearing forces, resulting in an easy passage of shearing blades.
As a result, the cuts on ductile metals are smooth, the cutting speed is faster, and the pressure requirements are lower.
On the other hand, brittle or hard materials are resistant to deformation and can break or crack during the shearing process.
Brittle materials also cause excessive stress on the blades, reducing the cutting speeds, and increasing the required blade pressure to shear the metal.
Out of these processes, annealing results in the highest ductility and reduced hardness of materials, making it a preferable heat treatment process for improving shearing performance.
Force Applied for Shearing
For precise and consistent shearing, it is essential to use shearing forces of appropriate magnitude.
Therefore, different amounts of force are required for shearing different materials efficiently.
Metals that are ductile and have low shearing strength require less force for deformation than brittle and hard metals.
Blade or die sharpness is another important factor determining the precision and quality of the shearing procedure.
Generally, a blunt blade causes excessive bending of the workpiece, increases clearance, and produces jagged or rough cuts.
In contrast, a sharper blade makes cleaner cuts with minimal clearance requirements.
Moreover, the sharpness of the blades also influences the force requirements. A sharp blade can slice the metal with less effort, thereby reducing the need for strong shearing forces.
Therefore, it is advised to maintain the sharpness of the blades to ensure clean and efficient metal shearing.
Rake Angle of the Blade
Rake angle (also called shearing angle) refers to the angle of the moving blade relative to the workpiece.
An angle tilted forward and in the cut's direction is referred to as a positive rake angle that aids in lowering the amount of cutting force needed to shear the metal.
However, it puts the blade under additional stress, which can speed up the rate at which it becomes dull.
On the other hand, a negative rake angle is tilted away from the cut direction and backward.
A negative angle can lower the number of malformations and burrs but requires greater power to shear the metal.
Types of Metal Shearing
Alligator shearing or crocodile shearing, is a cost-effective method, typically used for cutting large metal sheets or for preparing metal scraps.
The process involves using durable and powerful alligator shears that can quickly process a large volume of material.
However, this method comes with the downside of its inability to produce smooth or precise cuts.
Alligator shearing is thus employed in projects such as cutting I-beams, reinforcing bars, pipes, and angle iron, where quick material removal is preferable over accuracy.
The bench shear or lever shear consists of a fixed flat bench on which the shear is mounted.
A handle or lever is used to operate the shear blades and can be adjusted to yield quick and accurate cuts of desired angles.
Bench shear is a versatile tool to cut 90-degree angles, T-sections, and round and square bars.
Due to its compound mechanism, bench shearing applies to large and medium-sized workpieces with reduced physical effort, but the drawback is its inability to work with delicate projects.
Guillotine shears (also called squaring shears) consist of a shear-table, ram, holding clamps, gauges, a moving blade, and a fixed blade.
The metal sheet is clamped with a ram, which follows the descent of the moving blade across the fixed blade for shearing.
Guillotine shearing applies to many projects, including metal sheets, plates, bolts, and coils.
The main advantages of guillotine shearing include cost-effectiveness and speed, while the downside is that it produces rough cuts.
Unlike bench shear, guillotine shear is suitable for shearing delicate metals, making it ideal for intricate projects.
Power shears are shearing tools that cut straight lines or curves of large radii into sheet metal.
These hand tools can be pneumatically or electrically powered and are typically used to cut bulk material that is difficult to transport.
Power shears are efficient, accurate, yield quality finishes, and can cut curves, making them one of the most versatile shearing devices.
This shearing tool is extremely flexible as it does not require the sheets to be clamped, hence the name.
The ability of throatless shear to work with loose sheets makes it possible to cut any complex shape into the material as it can move freely under the blade.
However, the blades of throatless shear are best suited for cutting thinner metals like aluminum and mild steel.
Tools Used for Sheet Metal Shearing
Hand Shearing Tools
Hand shearing tools are manual tools that are powered by human effort and are generally suitable for small-scale shearing applications.
Snips are hand tools that resemble scissors and are used for cutting sheet metals and other thin materials.
Like scissors, snips are equipped with dual blades that press against each other to slice metal sheets.
Snips come in various types and can be used for almost all types of cut shapes.
However, the cuts yielded by snips are inaccurate and rough, so they are mostly used to trim excess material and to size metal sheets.
They are of two types: tinner snips and compound action snips.
Low-carbon tin or mild steel can be cut using tinner snips as they have long handles and short blades.
Depending upon the type of cuts they yield, tinner snips can be further categorized into straight patterns and duckbill snips.
Duckbill pattern tinner snips cut more acute curves, while straight pattern tinner snips are best used for cutting straight lines.
On the other hand, the compound action snip can shear stainless steel, mild steel, or aluminum.
Based on the way they cut, compound action snips are also of various types, including straight-cut, left-cut, right-cut, upright-snip, long-cut snip, and hard-snip.
The main advantage of snips is their precision and ability to work with a range of delicate materials; however, the hand-held operation makes them labor extensive and time-consuming.
Hand snips, such as Crescent Wiss, can cut through cold-rolled 18 gauge low-carbon steel.
Hand Lever Shear
These machines work similarly to motorized machines, but the power is transmitted mechanically.
Lever shears can shear various materials with good precision, including plates, bars, and thick metal sheets.
They come in a variety of sizes and with different features making them suitable for DIY projects and industrial applications.
The only limitation of hand-lever shear is the manual application of mechanical force which is not suitable for shearing thick workpieces.
A sturdy hand shear, such as KAKA Industrial HS-6 can shear through a 1/8" steel plate or 1/2" steel rod.
Power Shearing Tools
A nibbler is a shearing tool that mimics the action of a punch to cut away small pieces of sheet metal, allowing it to indent complex patterns into the sheet rapidly.
Metal nibblers are usually employed to obtain complex cuts into thick sheet metals, which are difficult to cut using other simpler tools.
These are inexpensive and simple to use, making them a good fit for DIY projects.
A powerful electric nibbler, such as ZFE 380W can be used to shear stainless steel, aluminum, and even plastics.
Swivel Head Electric Shear
These hand-held devices with adjustable speed outputs can cut different metals, including meshes, plastic, carpets, and metal sheets.
The cutting head can rotate in all directions, making it ideal for shearing material fixed in a difficult-to-reach location.
Certain Swivel shears also come with variable torque outputs, making them suitable for cutting different metals with variable thicknesses.
The main advantages of swivel head shears include adaptability, accuracy, quality finish, and reduced operator fatigue.
A capable swivel head electric shear, such as WEN 3650 can cut through 20 gauge stainless steel.
Benchtop Metal Shear
A benchtop metal shear is a compact and portable metal shearing machine.
Compared to bigger industrial shearing machines, these devices are usually meant to be utilized on a workbench or table and have a limited cutting capacity.
Electric motors usually power benchtop metal shearing machines which are often used to cut sheet metal for projects such as HVAC ducting, automobile components, etc., that require precise cuts.
These machines are available in both, manual and electric variants, and selection of the right variant depends upon your application requirements.
Benchtop machines such as KAKA Industrial 3-IN-1 provide the ability to perform shearing, breaking, and rolling on a single machine.
These are computer-driven shearing machines that require minimal manual labor.
CNC shears are generally large in size and are operated using a CNC controller.
The CNC controller can automatically calculate the mechanical parameters required for precise shearing.
The advantages include robustness, high productivity, accuracy, and simpler adjustments.
Due to their size and cost, CNC shears are best suited for industrial applications.
Common Sheet Metal Shearing Defects
Worn blades, incorrect clearance, and improper shearing pressures usually cause deformed edges.
These defects result in rough or improper edges that reduce the aesthetics of the workpieces.
Twisting refers to the curling or spinning of the workpiece along its axis.
It is usually a result of a large rake angle and results in workpieces with faulty dimensions and shapes.
Bowing refers to an undesirable bent or curve in the metal sheet and is usually seen in the shearing of thin, long, and narrow metal strips.
Many factors, including improper clamping, uneven feeding, internal stresses, and a large rake angle, can cause it.
A workpiece with bowing defects cannot meet the required specifications and cannot be used for the intended application.
Back support and the minimum possible rake angle can be used to avoid bowing in the metal sheet.
Cambering usually occurs when the material being sheared travels away from the sheet horizontally, resulting in a variance in thickness and the breadth of the metal sheet.
The degree of deflection on a material is known as camber.
Increasing the speed of the ram or changing the rake angle on your metal shearing machine can help avoid cambering.
Tips to Improve Sheet Metal Shearing Output
Use High-quality Shears
A high-quality shear will have sharper blades, which allow for cleaner and more precise cuts.
Therefore, it is vital to invest in a shearing tool specifically designed for the type and thickness of metal you will be cutting.
Maintain Appropriate Clearance
Setting the correct blade gap will ensure that the metal is cut cleanly and without deformities.
You should properly adjust the blade clearance according to the thickness and type of metal being cut.
Use Proper Lubrication
Lubrication can help reduce friction and heat during the shearing process, which can help improve the quality of the cut.
Generally, oil-based cutting fluids are recommended to reduce friction and produce clean cuts.
Use Optimal Cutting Speed
The cutting speed of the shear should be adjusted based on the thickness and type of metal being cut.
Using a slower cutting speed can help to improve the quality of the cut, but it's important to find a balance between cutting speed and productivity.
Apply Proper Hold-down Pressure
Hold-down pressure is the pressure applied to the metal being cut to keep it in place while it is being sheared.
Using the correct hold-down pressure can help improve the cut's quality and reduce the risk of deformities or defects.
Regular Maintenance of Shearing Tool
Regular maintenance of the tool, such as sharpening the blades, can help improve the overall shearing performance and the cut quality.
Following the manufacturer's recommended maintenance schedule is essential to ensure that your shearing tool is always in optimal condition.
Advantages of Sheet Metal Shearing over Other Methods
Metal shearing has various advantages over other metal cutting methods, making it a preferable metal forming method.
Suitable for Hard and Soft Metals
Most softer metals respond well to shearing since the procedure doesn't create chips, burn, or melt the substance.
However, metal shearing is also applicable to harder metals, but more powerful equipment is needed.
Compared to other sheet metal cutting techniques, shearing is quick and effective, making it an excellent choice for high-volume production where productivity is of utmost importance.
Shearing involves precision cuts with no or minimal chip formation.
As a result, you require fewer cleanups and less metal to invest in, making shearing a DIY-friendly process.
High Precision Cuts
Shearing equipment is made to create precise cuts with little distortions or burrs.
In applications where the product needs accurate measurements or a flawless finish, this is particularly beneficial.
Shearing is typically an affordable way to cut sheet metal, especially for large production runs.
This is because of fewer labor requirements and fewer tool expenses.
Shearing machines offer great versatility since they come in numerous forms and sizes.
Moreover, you can use them to cut a wide variety of sheet metals with varying thicknesses.
Guards and interlocks are included in the design of shearing machines to help safeguard operators from potential risks.
Sheet Metal Shearing vs Die Cutting
|Parameters||Metal Shearing||Die Cutting|
|Type of Blades||Straight edged||Curved|
|Shape of cuts||Mostly straight||Mostly complex|
|Accuracy||Comparatively lower||Comparatively higher|
|Cost||Relatively lesser||Relatively more|
Differences Based on their Type of Blades
The type of shearing blades is the basic difference between die cutting and shearing.
Die cutting involves the use of custom blades with required shapes, whereas shearing is carried out using straight blades.
Differences Based on the Shape of Cuts
Even though shearing can make complex cuts in the metal sheet, it is tricky and requires complex maneuvers.
On the other hand, die cutting uses customized templates that can virtually create any complex shape with relative ease.
Differences Based on their Accuracy
When compared to shearing, die cutting is typically more accurate and has a higher tolerance for precise measurements.
This is because the custom-built die is created to fit the intended shape precisely.
Differences Based on their Speed
Shearing requires fewer adjustments and lesser setup time as compared to die-cutting.
This makes shearing one of the fastest metal-cutting methods for high-volume productions.
Differences Based on their Cost
The cost of metal shearing and die cutting depends on several factors, including the type and thickness of the metal being cut and the quantity of material produced.
However, die cutting is usually a more expensive method as it requires a die that must be specifically created.
On the other hand, a single shearing machine can be used for different types of cuts.
Moreover, shearing uses a set of blades, which are typically less expensive to produce.
Sheet metal shearing is a popular manufacturing process that uses blades and shearing force to cut sheet metal into specific shapes or sizes.
This process is typically faster and more cost-effective than other methods of cutting sheet metal, such as die cutting.
As a result, it is often used in the automotive, aerospace, and construction industries, as well as in the production of appliances, electronic devices, and other products.
Due to their simplicity, tools such as snips, lever shears, and swivel-head electric shears are best-suited for DIY projects.
Frequently Asked Questions (FAQ)
What safety precautions should be taken when performing sheet metal shearing?
The safety precautions that should be taken during sheet metal shearing include wearing protective equipment, such as goggles, gloves, and earplugs, and following the manufacturer's instructions for the tools being used.
What are the disadvantages of sheet metal shearing?
The disadvantages of sheet metal shearing include the need for deburring, material thickness limitations, difficulty in cutting complex shapes, and inability to be used on very hard materials like tungsten.
What are the four phases of sheet metal shearing?
The four phases in sheet metal shearing are initial plastic deformation, penetration stage, fracturing stage, and full material separation.