Sheet Metal

Table of Contents

What is Sheet Metal?

Sheet metal is a shape/form which metal ca be bought in. Typically, it will be metal that has a thickness between 0.5 – 6mm. Sheet metal encompasses foils, sheets, and plates, with the differences between the three being their thicknesses [1].

Sizing

Thickness/Gauge

Thickness can be measured in millimeters, mils , and gauges. A mil is 1/1000 of an inch, not to be confused with the short form of “millimeters”.

Another unit for measuring sheet metal thickness is gauge. This represents the thickness of a metal in relation to its weight per square foot. This means that the higher the gauge number, the smaller the thickness of a piece of sheet metal. Since the gauge is relating to the weight of a metal, the piece of metal’s thickness would be different for various metals. For example, the gauge for a 12mm piece of steel will be different from that of a 12mm piece of aluminum [1].

Standard Sizes

Standard measurements consider sheet sizes as well as thicknesses.

Types

Metal foil is commonly used with aluminum. In this form, it’s typically referred to as tinfoil. Foils have a thickness of up to 0.2mm.

Sheet metals have thicknesses starting from 0.5mm and go up to 6mm. Thin sheet metal is easy to form and still provides good strength. Since its relatively cheap, it’s a good fit for most engineering purposes, which is why it is so commonly used.

Any metal with a thickness above 6mm is considered a plate [1].

Production

Hot Rolling

Hot rolling is used for cost-efficiency purposes. However, there may be a minimum thickness at which the sheet metal can be hot-rolled depending on the base metal. Additionally, hot-rolled metals aren’t usually used for precision applications. After the metal is cooled, it shrinks slightly and so the shape of the sheet metal may change [1]. With hot rolling, the heat causes recrystallization of the grains, and so the material becomes more ductile. However, this means that the mechanical properties are decreased (the material is softer/weaker) [5].

Cold Rolling

Cold rolling covers all measurements of sheets . This method is preferred for precision applications because there is more control over the final dimensions (the steel won’t change once the process has finished). Despite being call cold rolling, this process takes place at room temperature. The material being cold rolled is washed with acid and heat treated so it achieves a good finish [1]. With cold rolling, there is no recrystallization of the grains, and so the material becomes stronger. However, this means that the grain structure is different in different areas of the material, and the material is more brittle [6].

Fabrication

The typical stages of sheet metal fabrication are cutting/forming, joining, and finishing [4].

Forming Processes

Bending

The metal is bent into the desired shape by applying stress. The sheet metal is bent so the shape change is permanent (plastic deformation) [1]. This can be achieved by using press brakes and rolling machines [7]. The most common form of bending is V-bending. This process is where a V-shaped die and punch press are used in conjunction to bend the metal to its desired shape. Parts such as flanges are created using this method [1]. Another standard shape is a U-bend, which is done in a similar process to that of V-bending. When bending a metal, it is crucial to make sure the operator bends the metal more sharply than the intended final angle. This is because “spring back”, which is when the metal eventually tries to regain its original flat shape after being bent. To prevent this occurrence, the part must be bent so that the spring back angle is the desired final angle [7].

Press Brake Forming

In this process, a long sheet of metal is bent around a straight axis that passes through the material. The material can be formed into an ‘A’, ‘V’, or ‘U’ shape depending on the punch and die [1].

Curling

In this process, a circular ring is formed at the edge of the metal to make it safer to handle [1].

A curl can be formed on a panel bender or a brake press. With a panel bender, curling is generally limited to off center curls due to their limited tooling profiles. With forming curls on brake presses, the curls are formed in three stages. The first two stages form the curves needed to form the curl, and the third stage closes the curl.

Decambering

This is the process where the camber of a metal sheet is removed. A camber is a horizontal bend that is produced when metal is flattened into sheets. To remove this bend, the edges are flattened by applying force and pushing them into straight form. This process is usually carried out on sections of the metal [1].

Deep Drawing

A sheet’s shape can also be changed via deep drawing. This is done in multiple stages using a series of dies. If the depth of the shape formed is more than the original diameter of the sheet, it is considered deep drawing. During the process, different punches and dies are used so the sheet is converted into many shapes before reaching its final form. Items such as fuel tanks, sinks, and automobile parts are fabricated using this method [1].

Hydroforming

With hydroforming, the metal is placed on a die and high-pressure fluid is used to form the sheet, as opposed to a punch. More complex parts can be manufactured in less time with this process. Additionally, it is cheaper and requires less work than other methods. This process is compatible with nearly all metals and since matching dies are not required, hydroforming can be used to form unconventional shapes [1].

Laser Cutting

Laser cutting is precise (+/- 0.1mm tolerance) [7] and the finish is very smooth. To do this, CNC machines are used. After inputting the program, the cut is carried out by the laser. Specific shapes can be created using this process and are based on the program that is fed to the machine. Metal sheets can be cut into extremely complex pieces and if a change in shape is needed, it can be done easily, giving laser cutting the advantage of flexibility [1]. This is a shear-less process and is better suited for industrial applications and is time efficient [7].

Laser Cutting vs Plasma Cutting

With laser cutting, the laser is essentially a focused beam of light. However, with plasma cutting, a mixture of gases is used to create a cut and is cheaper than laser cutting. For simple shapes that don’t require an extremely tight tolerance or doesn’t have many cutouts/intricate notching, plasma cutting is typically used [12].

Punching

Punching is a common technique for making holes in sheet metal. This process consists of a punch and a punching die [1], which are often made from a hard metal [7]. When the punch and the die meet, the material is compressed and punctured due to the shearing force. This process is simple and relatively cheap in large quantities. Various sizes of holes can be created, but it is recommended for the diameter of the hole to be larger than the thickness of the material being punched for the result to still have structural integrity [1]. Punching can also be used to create indentation in the sheet metal [7].

Rolling

Rolling may be done on sheet metals to decrease the overall thickness of the sheets or make the sheet thickness more uniform. To do this, the sheet metal is passed through a series of rolls [fractory].

Joining

After the sheet metal is formed to the desired shape, its ends may need to be joined together. It is common for projects to consist of multiple metal sheets, and so these sheets must be fused together by welding, brazing, riveting, and/or adhesives [4].

Welding

With welding, the metal is joined together by melting the edges of the part and adding filler. By doing this, a metallurgical bond between the pieces is created that strongly fuses them together [7]. For information on welding, please visit the weldments page.

Finishing

As the final step in the sheet metal fabrication process, a surface finish must be added to the final product. Finishes include powder and paint coatings, silk screening, and adding sealants or other layers of protections. Different finishing treatments can improve or increase some of the properties of the sheet metal, such as conductivity or resistance [4].

Applications

The fabrication and forming of sheet metal is a flexible process, thus it is used in most industries to create an assortment of objects. These industries include automotive, aerospace, construction, HVAC, consumer goods, robotics, electronics, energy sectors. Additionally, a product made from sheet metal is easier and faster to produce and therefore less expensive [16].

References