Sheet metals are one of the important and well-known metals in the engineering world, as they serve a lot of purpose in our daily lives. Sheet metals are very common as they can be seen on cars, machinery, house facades, and furniture. It is mostly seen on parts serving as housing.
As an engineer, you are expected to know the standard measurements, materials, differences in manufacturing, properties, and forming methods before thinking of applying sheet metals to any project. Sheet metals are formed by an industrial process into thin, flat pieces, mostly used by metalworkers.
It can be cut and bent into different sizes and shapes, making it applicable to different fabrication projects. Sheet metals are used historically for plate armor worn by cavalry and are widely used for decorative purposes. Well, in this reading, we’ll explore what sheet metal is, its uses, types, materials, forming process, and sizes of sheet metals.
Let’s get started!
What is Sheet Metal?
Sheet metal is an industrial process that forms thin, flat pieces of metal, such as steel and tin, into coils. In the U.S., the thickness of sheet metal is typically specified by its gauge, which ranges from 30 gauge to about 7 gauge. Other metals like aluminum, brass, copper, steel, tin, nickel, and titanium can also be used in sheet metal.
For decorative purposes, silver, gold, and platinum are important sheet metals. Sheet metal is processed through technologies like cold rolling and hot rolling, with hot-dip galvanizing sometimes used to prevent rusting.
Color-coated metal sheets are also available for decorative purposes. Sheet metal is used in various applications, including automobile and truck bodies, major appliances, airplane fuselages, and roofing.
What are the Uses of Sheet Metals?
Sheet metals are used historically for plate armor worn by cavalry and are widely used for decorative purposes. The applications of sheet metals include automobile and truck (lorry) bodies, medical tables, airplane fuselages, and wings, roofs for buildings (architecture), and many other applications.
Sheet metal is a versatile material used in various applications, including automotive parts, greenhouse equipment, buckets, irrigation pipes, and marine vessels. Carbon steel sheet is a popular choice due to its affordability and superior tensile strength compared to copper and aluminium. Galvanized steel sheet, a form of carbon steel sheet, undergoes a galvanizing process to protect it from rusting. This makes it suitable for automotive parts and objects exposed to water.
Stainless steel sheet, with its enhanced corrosion resistance, is more expensive than galvanized or carbon steel but is widely used in critical applications like aerospace engine components, high-performance marine structures, pharmaceutical processing equipment, and food handling equipment. Its aesthetic appeal makes it popular for signage and appliances.
Aluminum sheet, with its lightweight and corrosion resistance, is a popular choice for boat components, marine structures, cookware, automotive parts, and aerospace parts. Copper sheet, known for its electrical conductivity, aesthetic appeal, and malleability, is used in equipment where electricity must be easily transferred to a workpiece. It is also commonly used in home decor and other forms of artwork due to its malleability and superior aesthetic qualities.
Related: What is Iron (FE)? its Properties, Types & Raw Materials
Types of sheet metals
The various types of sheet metals include stainless steel, aluminum, brass, galvanised steel, cold-rolled steel, pre-plated steel, tool steel, carbon steel, and alloy steel.
1. Stainless Steel
the stainless is of three grades, grade 304 is the most common. It offers good corrosion resistance as it maintains formability and weldability. #2B, #3, and #4 are its available finishes.
The 316 grade possesses more corrosion resistance and strength at a higher temperature compared to 304. It is used for chemical equipment, and marine applications and is common on parts like pumps, valves, etc. The stainless steel of grade 410 is a heat treatable one, but it has a lower corrosion resistance than the previously listed one. it is widely used for producing cutlery.
Popular among all, grade 430 has a low-cost alternative compared to 300’s grades. It is considered when high corrosion resistance is not an issue. It is used for appliance products.
2. Aluminium
Aluminium is another popular metal used in making sheet metals due to its flexibility, cost-effectiveness, wide range of options, and other properties. It is pronounced as aluminum in British English and is of four grades which include; 1100-H14, 3003-H14, 5052-H32, and 6061-T6
The grade 1100-H14 is pure aluminum, highly chemical and weather resistant. It is weldable and ductile enough for deep drawing but has low strength. Its applications are mostly in chemical processing equipment, jewelry, and light reflectors. When low cost and formability are to be considered, grades 3003-H14 must come in place. It is stronger than the 1100 version, corrosion-resistant, and also weldable. It is often used in mailboxes, spun and drawn parts, cabinets, fan blades, stamping, etc.
This grade 5052-H32 is much stronger than the 3003 as it still maintains good formability. The weldability and high corrosion resistance are also in a good situation in this version. Its applications are found in electronic chassis, pressure vessels, and tanks.
The grade 6061-T6 is superior among all grades, as it’s a common heat-treated structural aluminum alloy. It is weldable, corrosion-resistant, and stronger than the 5052 version. However, some strength will be lost when welded and it’s not formable. This aluminum grade is mostly used in modern aircraft structures.
3. Brass
Brass is a copper alloy, which is also used as sheet metal. It also has good properties such as conductivity, formability, corrosion resistance, and strength.
The issue with sheet metals made of brass is the variation in incoming sheet coil properties. The material has experienced a high rejection rate due to the observed inconsistent behavior in production. Though there are discriminating methods for testing incoming sheet material formability.
4. Galvanized Steel
Steel is composed of two varieties: electro-galvanized sheets and hot-dipped metallic-coated sheets. Electro-galvanized sheets are composed of cold-rolled annealed steel with a pure zinc coating, while hot-dipped metallic-coated sheets are composed of cold-rolled hard steel plates coated with a mixture of pure zinc and an iron-zinc alloy.
5. Cold Rolled Steel
Cold rolled steel (CRS) offers superior material strength and a superior surface finish. It can be laser cut, punched, and formed with excellent results, similar to HRPO sheet. However, parts made from CRS must be painted or protected immediately to prevent surface rust.
6. Pre-Plated Steel
Pre-plated steel is a sheet metal material that is either hot-dipped galvanized or galvanealed, which is then annealed to prevent rust and corrosion. Galvanization is a protective zinc coating applied to steel, while annealing alters the material’s microstructure, reducing hardness and increasing ductility for easier fabrication.
7. Tool Steel
Tool steel, a versatile alloy with about one percent carbon, varies in type and ratio depending on the desired application. Its properties, including resistance to abrasion and extreme temperatures, make it ideal for construction of tools like punches, dies, blades, and hammers.
8. Carbon Steel
Steel, a material alloyed with carbon, offers high strength due to its high carbon result. Manufacturers can select from low, medium, or high levels of carbon content, depending on the desired application. Low carbon steel is versatile, used in everyday objects like fences and gates, while medium carbon steel is popular for automotive vehicles and appliances. High carbon results in a slightly more fragile product, ideal for delicate items.
9. Alloy Steel
Alloy steel offers a customizable set of properties, combining carbon steel with tungsten for rigidity and vanadium and nickel for strength. This versatile material, with its affordability, offers a wide range of properties to suit various needs.
Sheet Metal Materials
Different sheet metal materials can be made into sheet metal, metals like aluminum, copper, brass, tin, nickel, and titanium. Some expensive metals are used to create sheets for decorative purposes, such as silver, gold, and platinum. Choosing the right sheet metal for a particular project is determined by the application and requirement of the product.
Some materials have the same mechanical properties as other metal materials in the project. Just as steel sheets have high tensile strength and durability, making them suitable for machinery and construction work.
Metal Foil, Sheet, and Plate
These metals come in different thicknesses, the extremely thin sheets are considered foil or leaf. Sheet metals thicker than 6mm (0.25 in) are considered plate or structural steel. They are available in flat pieces or coiled strips. The coils are formed by running a continuous sheet of metal through a roll slitter. Metal foils are often produced with aluminum.
Metal foil, often used with aluminium, is a common material with a thickness of up to 0.2 mm. Sheet metal, on the other hand, has a thickness ranging from 0.5 mm to 6 mm, making it suitable for engineering purposes.
Foil is easy to form and provides great strength, while sheet metal is thin and easy to form, making it a popular choice for various applications. The thickness of a metal plate is typically above 6 mm, making it a suitable material for various applications.
Metal thickness is measured in three ways: millimetres, mils, and gauges. Millimetres are a straightforward unit, while mils and gauges are common in engineering and manufacturing. One mil equals a thousandth of an inch, while gauges represent the thickness of a metal in relation to its weight per square foot. Although official standards discourage the use of gauges, they are not uncommon and a higher gauge number indicates a smaller thickness.
Standard Sizes and Thickness of Sheet Metals
Standard sheet sizes are crucial for optimizing part layouts in metal production. These measurements apply to both small and large sheet sizes, with some workarounds for large sheet sizes through welding. Understanding these measurements helps in optimizing part layouts and reducing scrap and overall costs.
It is important to consider the availability of different sheet sizes, as not all fabricators have the machinery to cut large sheets. Knowing manufacturers’ capabilities is crucial in this situation. Welding together smaller sheets may not always be the optimal solution, especially when focusing on aesthetics in a project.
The thickness of sheet metals is specified in millimeters all around the world. But in the US it is commonly specified by a traditional, non-linear measure known as a gauge, the larger the gauge number the thinner the metal.
The most commonly used steel sheet metal ranges from 30 to about 7 gauges. The gauge differs between ferrous and non-ferrous metals. In non-ferrous material such as copper, the thickness is measured in ounces, representing the weight of copper. Pieces of sheet metals are expected to maintain uniform thickness for ideal results when put to work.
Hot-Rolled and Cold-Rolled Sheet Metals
The two ways of producing sheet metals include hot and cold rolling. Research has shown that sheets and plates are hot rolled for cost-efficiency purposes. In the process of construction steels, the cold rolling process only goes up to 3mm. For stainless steel, the hot rolling process starts from 3mm and covers the sheet with cold rolling, i.e., up to 6mm.
Engineers should be able to differentiate these two processes for precision purposes. The cold rolled steels are preferred as the final dimension can be controlled. However, in hot rolled steels, the size and shape might change after cooling, leading to slight shrinks.
Sheet Metal Forming Process
The various methods of forming sheet metal include bending, curling, decambering, deep drawing, expanding, hydroforming, incremental sheet forming, ironing, laser cutting, photochemical machining, punching, rolling, press brake forming, and wheeling.
Bending
The forming process of metal involves bending sheet metal into the desired shape using bending stress. This process, known as bending, prevents plastic deformation and prevents the metal from regaining its former shape. The most common form of bending is V-bending, where a V-shaped die and a punch press together to create parts like flanges and corrugations. Edge bending is another common method for flange bending.
Curling
Curling is a process of forming a circular ring at the edge of a metal sheet to make it safer for handling. The initial edge is rolled into the formed circle, unlike in a tear-shaped hem. Curling can be classified into off-centre and on-centre rolls, with off-centre rolls having the center above the sheet level and on-centre rolls having the center at the same level.
Decambering
Decambering is a process used to remove camber from a sheet of metal, particularly in strip-shaped parts, by flattening the edges to remove the horizontal bend. The force is applied on the deformed edge, pushing it into a straight form, typically on limited length sections.
Deep Drawing
Deep drawing is a sheet metal forming process that involves changing a sheet’s shape in multiple stages using dies. The depth of the formed shape exceeds the original sheet’s diameter, making it considered deep drawing. This process converts sheets into various shapes like fuel tanks, sinks, and automobile parts, primarily used for large-batch production.
Expanding
The metal-forming process involves cutting and stretching a sheet of metal through perforating scissors, creating a structurally advantageous diamond-shaped mesh. This process is commonly used for manufacturing fences, catwalks, platforms, and grating, resulting in self-draining, strong products that support weight. The process prevents larger particles from passing, preserving the original metal’s strength, and is ideal for applications requiring air or liquid passage, while retaining the original metal’s strength.
HydroForming
Hydroforming is a method of shaping metal sheets into desired shapes using high-pressure fluid instead of a punch. This process is suitable for creating complex parts in a shorter time, is cheaper, and requires less work. It is compatible with various materials like stainless steel, aluminium, carbon steel, brass, and precious metals, and can form unconventional shapes without matching dies.
Incremental Sheet Forming
Incremental sheet forming is a metalworking process that forms a desired shape in low volumes using incremental steps. This method allows for quick changes to the product without much hassle, using a single-point sphere. Unlike deep drawing, it doesn’t require separate punches and dies, offering flexibility and similar results to deep drawing.
Ironing
The ironing process is a deep drawing process used to reduce the thickness of sheet metal in specific areas, ensuring uniform wall thickness. This process is crucial in manufacturing products like soda cans, where the walls need to be thinned to a predetermined thickness. Typically, multiple ironing processes with different dies are required to achieve the desired thickness in aluminium soda cans.
Laser Cutting
CNC machines are increasingly being utilized for laser cutting, a process that produces an extremely smooth finish on sheets. This precise and flexible method allows for easy changes in the required shape, enabling the creation of extremely complex pieces from metal sheets. This versatile tool is increasingly being utilized in sheet metal cutting applications.
Photochemical Machining
Photochemical machining is an extremely precise and cost-effective method for creating sheet metal parts. It uses controlled corrosion to create a smooth finish, utilizing a photoresist and an etchant. This method, developed in the 60s, is ideal for mass production and can easily accommodate changes. It is used for creating extremely fine meshes, apertures, flexible heating elements, metal gaskets, electrical contacts, and jewelry, offering a smooth finish similar to laser cutting.
Punching
Punching is a common technique for cutting holes in sheet metal, involving a punch and a punching die. The material is pressed between the two, and shearing force is applied to cut a hole in the sheet. This process is relatively inexpensive and can be used for strip and sheet metal. It is recommended that the hole diameter is greater than the material’s thickness, especially for sturdy alloys, to ensure accurate results.
Rolling
Hot rolling is a process used to reduce the thickness of sheet metals by passing them through a set of rolls. The temperature of the process, typically around 1400 degrees Fahrenheit, can achieve a thickness of 1/16th of an inch to 5/16th of an inch. Cold rolling, on the other hand, is carried out at room temperature, washed with acid, and heat treated for a better finish.
Press Brake Forming
Press Brake Forming involves forming a long sheet of metal around a straight axis through the material, creating a ‘V’, ‘U’, or channel-shaped material. Precision bending is challenging, requiring careful consideration of material properties, press, and tooling. This process is suitable for both large and small parts, with thickness up to 25mm and lengths up to 6 meters. However, it requires careful tooling and material properties to achieve the desired springback.
Wheeling
The English wheel is a crucial tool in the forming process of flat metal sheets into required shapes. This method requires skilled labor and is expensive, making it unsuitable for mass production. It is primarily used for low-volume customized parts, car prototypes, and aircraft. The shape is produced in stages, with operators comparing the formed piece with the reference shape, requiring different wheels and directions.
Sheet Metal Tools
Below are the tools used in sheet and other metal fabrication processes to carry out operations like shearing, blanking, shaping, punching, etc.
Angle grinder: an angle grinder is used to cut, sharpen, sand, grind and cut different types of metals. It is also known as a disc grinder or side grinder.
Throatless shear: This is used to make straight, curved, and irregular cuts on sheet metals with ease and accuracy.
Corner notcher: These sheet metal cutting tools are used on different types of sheet metals. It is powered hydraulically.
Planishing hammer: Planishing hammers are used as sheet metal tools to flatten, finely shape, straighten, and smoothen sheet surfaces.
Flange and punch tool: The punching tools are used on sheet metals to create holes around the material’s edges.
Shrinker and stretcher: These sheet metal tools function the same as it is primarily used to form curves on sheet metals.
Cleco fasteners: Cleco is temporary fasteners that are used to hold sheet metals and other parts like frames or stiffeners together.
Sheet Metal Processing Tools
Bending tools: Sheet metal bending tools are tools and equipment used for the bending operation. Here are some bending tools and equipment used for the process:
Bench top budget brakes: These tools consist of a wide bench at the top with an upper and lower fixed beam. the bending equipment forms a radius using the upper beam of the bench-top sheet metal brake.
Bracket makers: This is another great piece of tools for bending sheet metals. It helps to create brackets of many shapes and specifications using the 90-degree tools and radius tools.
Related: What is Steel? its Properties and Raw Materials
Sheet Metal Forming Tools
Shrinker stretchers: It is one of the most used and common forming tools, used to shape materials. The operation does not require the need of heating, cutting, or welding and smooth radius curves can be formed with ease. Well, the primary purpose of these sheet metal tools is for making inside curves. This is achieved when the metal is shrunk on one side.
Shearing tools: Shearing tools allow a straight cutting on a material, done to make angled cuts. But generally, shearing is used to make cuts that are parallel to the existing edge.
Throatless hand shears: It is used on a heavy steel frame as it is designed with no throat. Due to the arched top blade, the tools cut smoothly.
Rotary shears: This tool for the sheet metal forming process is a bit more flexible than the hand shear. It is used to cut almost all types of shapes as its cutter can be adjustable and it contains a ratcheting head.
Here are some other important types of tool used in sheet metal fabrication:
- Steel Rule
- Snips
- Scriber
- Burring Tool
- Half Round Stake
- Hand Stake
- Divider
- Trammel Points
- Grooving Stake
- Files
- Centre Punch
- Mallet
- Prick Punch
- Ball Pean Hammer
- Raising Hammer
- Taper Stake