Material science: sheet metal

Yet the challenge is to process these metal sheets as reliably and efficiently as possible. Especially for newcomers to the sheet metal fabrication industry, it is essential to obtain an understanding of sheet metal as a material. In this article, you will learn about the available metal sheet forms, how they are fabricated and the key processing techniques.

There is a diverse range of sheet metal fabrication and processing techniques. Accordingly, it is difficult to provide a clear definition and categorization. In addition to the multitude of designations and classifications, these are also often used differently in colloquial language. Furthermore, other terms or brands exist which have been coined by various manufacturers. One example is laser sheets, for which there is no official definition. This is generally understood to be metal sheets that exhibit particularly good laser cutting properties. However, these are usually not specially produced sheets but rather particularly carefully selected sheets which are offered at a corresponding surcharge specifically for laser cutting customers.

Metal sheets are available in many different formats as a rolled metal product. It is important to distinguish between coils and blanks. Whereas a coil is a wound metal strip weighing several tons and often several hundred meters long, a blank – also known as a panel – is a rectangular sheet that has already been cut from the coil to a specific length.

Service centers process the coils from the steel mill into smaller coils or blanks (or sheets). Then they are delivered to the sheet metal processing companies with the correct dimensions and quantities. In addition to steel and stainless steel, almost every type of metal ranging from precious metals such as gold and silver to diverse steel alloys and aluminum can be fabricated into metal sheets. Metal sheets are always wider and longer than they are thick.

Metal sheets are generally categorized as thin sheet and heavy plate. Thin sheet is any sheet that is thinner than 3 mm. They are usually cut from strips. In contrast, heavy plates are all metal sheets more than 3 mm thick. Metal sheets are available in small, medium, large and maxi formats. These often have the following standard dimensions:

• Small format: 1,000 mm x 2,000 mm (39 inches x 79 inches)
• Medium format: 1,250 mm x 2,500 mm (49 inches x 98 inches)
• Large format: 1,500 mm x 3,000 mm (59 inches x 118 inches)
• Maxi format: 2,000 mm x 4,000 mm (79 inches x 157 inches)

In addition, diverse standards also summarize the initial materials of the sheets according to their properties. This helps to maintain an overview of the many types of sheet metal.

Metal sheets are available in many different formats as a rolled metal product. It is important to distinguish between coils and blanks. Whereas a coil is a wound metal strip weighing several tons and often several hundred meters long, a blank – also known as a panel – is a rectangular sheet that has already been cut from the coil to a specific length.

Service centers process the coils from the steel mill into smaller coils or blanks (or sheets). Then they are delivered to the sheet metal processing companies with the correct dimensions and quantities. In addition to steel and stainless steel, almost every type of metal ranging from precious metals such as gold and silver to diverse steel alloys and aluminum can be fabricated into metal sheets. Metal sheets are always wider and longer than they are thick.

Metal sheets are generally categorized as thin sheet and heavy plate. Thin sheet is any sheet that is thinner than 3 mm. They are usually cut from strips. In contrast, heavy plates are all metal sheets more than 3 mm thick. Metal sheets are available in small, medium, large and maxi formats. These often have the following standard dimensions:

• Small format: 1,000 mm x 2,000 mm
• Medium format: 1,250 mm x 2,500 mm 
• Large format: 1,500 mm x 3,000 mm 
• Maxi format: 2,000 mm x 4,000 mm 

In addition, diverse standards also summarize the initial materials of the sheets according to their properties. This helps to maintain an overview of the many types of sheet metal.

Diverse methods exist for cutting metal sheets. The following are the most commonly used techniques:

With punching, the sheet metal is punched out of a blank and separated by a manually or automatically operated press, punching machine or punching tool. Punching is mainly used to produce small components from flat metal strips.

Nibbling is characterized by its parting line, the tool-independent cutting process and free shaping. The metal sheet is separated via the up and down movement of a punching tool which is open on one side. This tool can be powered manually or electrically but can only be used by hand. In addition, nibbling is a very imprecise process that is used less and less.

Laser cutting:

With this cutting method, the heat of a laser beam cuts the metal sheet. The laser is a highly flexible tool and especially suitable for processing thin sheet metal. Laser cutting is the most common method of flexible sheet metal processing where the finest kerfs and highest quality are required.

This process is one of the thermal cutting methods. The heat of a plasma flow is used to liquify the material. The plasma flow’s high kinetic energy blows the liquified material out of the cut. Plasma cutting is primarily used for metal sheet/plate thicknesses between 10 mm and 50 mm (0.4 inches and 2 inches).

In this cutting process, the sheet is heated to ignition temperature by using oxygen and fuel gas (such as acetylene, MAPP, propylene, propane or natural gas). Adding oxygen creates a kerf at which the sheet metal is then separated. Flame cutting is the most common method of cutting very thick materials.

After cutting, the metal plates can be shaped using further processing techniques. The most common procedures include:

Bending:

Bending or creasing describe processes for shaping sheet metal. The metal sheet is placed on the die of a press brake. A tool then moves downward from above onto the material and bends the desired angles into the component.

Round rolling is another frequently used shaping process. The metal plate is plastically deformed generally via three rollers to bend it into a round shape.

This process is another method of forming. The metal sheet is unwound from a coil and passes through several pairs of rollers, one after the other, until it is bent into the desired shape. This process is usually used for long profiles in large quantities.

During forming, a tool presses the metal sheet into the desired shape. As a rule, the tools are powered using automatic punching machines or forming presses. As the tooling costs often involve considerable one-off costs for the production, the processes are generally used for large quantities.

Folding, riveting, soldering and welding are the usual methods of joining two or more metal sheets together.

Important for working with metal sheets: Processing always generates a mechanical load or heat. Since sheet metal is usually easily formable, stresses and unevenness quickly arise in the material. However, very flat metal sheets largely free of internal stresses are highly important for all downstream manufacturing processes in the sheet metal fabrication industry. In addition, the vast range of different sheets combined with the diverse manufacturing and processing methods make it exceptionally difficult to predict the behavior of metal sheets and panels during processing. This is why leveling and deburring metal sheets after processing is essential. DIN EN 10029 defines the flatness tolerances for the individual metal sheets.