Metal may be a boring topic for those not from the industry. The associated keywords for metal are factory, industrial use or even building. But if we try to understand it better, metal is versatile and used for countless purposes.
Bruce Lee said to ‘be like water.’ Water can be in solid, liquid or steam forms. Through different forms, each has its distinct strengths.
As for metal, it can be used for a roof, a facade or a metal plant box. If done correctly, it’s also an excellent material for decorative items.
But metal must undergo a process. Depending on what we’re expecting out of it, the list is non-exhaustive. To know what metal fabrication is, read here. Among the steps involved are cutting, forming, joining and finishing.
In this article, we will discuss ‘cutting’ which falls under ‘metal shearing’.
What Is Metal Shearing?
In simple words, two blades cut a piece of metal sheet. Another name for the two blades is a punch and a die. It refers to the upper and lower blades, known as flat blades and dished blades.
Shearing commonly involves dividing the sheet metal into rectangular shapes. It also cut the big pieces of sheet metal into smaller pieces.
The only force used in the process is from the machine. Although metal can be melted, metal shearing is the only method that does not require burning or melting to change the shape of the metal.
Blade
Shearing machines are generally used to separate metal into sheets or strips. The shear blade is sensitive. It’s capable of cutting metal with a specific thickness only. Thick metal isn’t suitable for shearing. Materials like concrete or wood will damage it.
How it works is similar to a pair of scissors. When we use scissors meant to cut paper for meat, it will ruin the blade. The cost of replacing shear blades is costly.
Type Of Shearing Machines
There are various shearing machines for different purposes. See below:
Air/Pneumatic Shear
This is the most frequently used machine in the factory.
The machine comes in various sizes, a standing one or a portable one that can be put on a table. It relies on compressed air from a cylinder. Capable of cutting sheet metal with a thickness of 1.5mm and a length below 1.5 metres.
Hydraulic Shears
Similar to the previous machine, powered by compressed air. But, a hydraulic cylinder with oil inside pumps the motor that moves the upper blade move.
This machine produces a higher force for cutting thicker items. In brief, this machine’s operation takes a longer stroke, slowly descending from top to bottom with only the upper blade to perform the shearing action.
The force is so high that it requires clamps to secure the workpiece.
Mechanical Shears
The blades for other machines are generally stationary. But this one consists of a moving blade. The blade’s movement is powered by a rotary motor connected to a toggle, screw, lever and others.
Compared with hydraulic shear, this one’s capable of more strokes, up to 100 strokes per minute.
Straight Knife Shearing Machine
The shearing operation for this machine is economical, especially for cutting blanks from the strip, plate, and sheet of thickness less than 50mm,
The mechanism of this machine involves two blades. One movable upper blade and another stationary lower blade. When the upper blade starts running downward and lands on the lower fixed blade, it cuts a blank, which is the useful part.
Alligator Shearing Machine
As the name states ‘alligator’, there must be some part of the machine that resonates with it. It refers to the ‘holder’ ‘clamp’ to clamp a thick metal bar from moving around when cutting. The zig-zag design of the clamp is to secure the position of the metal bar.
So it comes with an alligator clamp first. Then behind the alligator clamp is a blade cutting upwards like a paper cutter.
*Malaysia’s way of explaining: The alligator clamp will first ‘kiap’ the metal bar, then ‘potong’ the metal bar.
Rotary Shearing Machine
Imagine a pizza cutter wheel. A cook uses it to cut pizza into many slices.
This machine cuts sheet metal just like that. The mechanic has to hold the workpiece to go through the machine. But the entire rotary shearing machine is standing still.
While the rolling blade is secured on the machine, the mechanic moves the sheet metal to let the rolling blade cut.
For context, imagine the pizza is being moved to be cut instead of rolling the cutter.
The Operation Of Shearing Machine
After explaining all the machines, each of them operates differently. See below:
Blanking
Let’s say we want a heart-shaped metal plate. We have a big piece of square sheet metal that is cut into 16 pieces of smaller metal plates. Each piece is cut by tracing the desired shape. In this case, the heart shape.
It’s easier if we dissect the big square sheet of metal into four strips. For each strip, we cut out four smaller metal plates. Then by using a heart-shaped upper blade, stamp on the stationary blade below to form the end product.
Think of the paper punching machine. The scrap is the valuable part.
*Please see the image below (From Praveen Singh: Solidwork fun YouTube)
Piercing
It shares the exact same process with blanking or punching involved. Except that it’s the opposite. This scrap is no longer a useful part. It’s the cut-out with the designated shape.
Punching
Punching is a combination of both piercing and blanking.
*Please see the image below (From Praveen Singh: Solidwork fun YouTube)
Notching
Some interpret notching as cutting corners. To be distinct from the above-mentioned operation, notching is usually cutting at the edge of the sheet metal or blanks. It cuts only a small amount of metal. The notches can be in different shapes.
Nibbling
Nibbling is another cut-out technique. The mechanism is similar to a sewing machine. The mechanic will outline the desired shape and then cut it out.
Let’s say the desired shape is an oval. An oval shape will be drawn on the sheet metal. Instead of punching out the entire shape, the machines do it in small outer areas of the oval.
Perforating
Perforating is a repetitive punching technique. So the end product of using the method is metal mesh or net. The shapes are customizable.
It doesn’t have to be just round. Diagonal is possible as well. It depends on the metal fabrication company and what shape template they have.
Pros Of Metal Shearing
Metal shearing requires a specific temperature to perform the process. Room temperature is sufficient to conduct the metal fabrication.
Metal shearing applies to many types of metal, such as iron, copper, aluminium, bronze, and stainless steel. It’s the most compatible technique with softer metal.
Last but not least, it’s cost-effective for productions that produce a thousand pieces per hour.
Cons Of Metal Shearing
Metal shearing risks deforming the stainless steel sheets if it’s not done well. When it comes to a clean and cut finishing effect, it’s not the best technique for it involving any thickness of metal below 3.175mm.
For example, it’s not recommended to cut hard metal such as tungsten. Tungsten being exceptionally hard yet brittle may fracture during the cutting process.
This naturally means it’ll wear out the blade quicker. Where cost will increase with wear and tear at a higher rate.
*This article is merely for general knowledge purposes. To select or decide which metal shearing method is the most suitable one, it needs more expert experience to finalise it.
Need more information?
There are many more methods and processes involved in Sheet Metal Fabrication. With over 30 years of experience, NS Metal Fabrication Specialist offers a highly personalised approach to the customisation and supply of high-quality metal and steel.
Contact us today to discuss your sheet metal fabrication needs or simply to get further information on how we can work together.
