Metal Forming Process Explained: Guide

Metal forming is a process in which metals are deformed plastically to achieve the desired geometry. It is broadly classified as bulk forming, sheet metal forming, and powder metal forming. Owing to its versatility, it is widely used in various industries, including automotive, aerospace, construction, and more. 

This article provides a detailed guide about metal forming by going through its classification, applications, and different tools used for metal forming.

MellowPine is reader-supported. When you buy through links on my site, I may earn an affiliate commission at no extra cost to you.

What is Metal Forming? Explained

The metal forming process involves using greater forces than the metal's yield strength to permanently shape and alter its physical and chemical properties.

It exploits the plasticity of metals to produce strong, durable, and reliable metal products. 

This method has various advantages over other metalworking methods, including enhanced mechanical qualities, faster manufacturing rate, and minimal wastage of raw materials, making it a vital manufacturing process.

However, metal forming is a broad term that includes several techniques, each of which has its own merits and demerits.

Therefore, it is essential to learn about different forming processes to select the best fit for your application.

Metal forming techniques are broadly classified into two main categories: cold forming and hot forming.

Cold forming is carried out below the recrystallization temperature of the metal and is preferred for easy handling, a good surface finish, enhanced strength, and hardness in the product.

Whereas hot forming involves heating the workpiece to a temperature between the material's recrystallization temperature and melting point. 

Hot forming yields products of enhanced ductility, lesser porosity, greater homogeneity, and less energy expenditure.

However, it may be necessary to perform hot forming to achieve specific shapes or properties or to work with brittle or hard materials at room temperature. 

Metal forming is the preferable metal processing technique for metals with a low melting point, good ductility, and malleability.

Various heat treatment processes like annealing, carburizing, tempering, and normalizing help alter these properties to make the material more formable, out of which annealing provides the best ductility.

Metals, such as steel, aluminum, copper, brass, and bronze, are more suitable for forming than others, due to their mechanical properties.

Types of Metal Forming Techniques

Apart from hot and cold forming, these techniques can further be classified based on their optimal use cases.

Bulk Metal Forming

Bulk metal forming techniques are suitable for industrial applications where a high volume of similar products is required with good tolerance and surface finish.

Casting

In the process of casting, metals are molten and poured into molds having cavities of desired shapes and then allowed to solidify. 

This allows it to be used for producing parts with intricate patterns, which otherwise can be difficult to produce by other metalworking techniques.

If your application demands cost efficiency, mass production, complex patterns, exotic alloys, and higher product customization, casting is the way to go.

DIY and small-scale casting generally involves using temporary molds that are destroyed after casting.

On the other hand, techniques such as gravity die casting use reusable metallic molds to save time and increase productivity.

As a result, the casting process applies to both small and large-sized projects, making it suitable for industrial and DIY applications.

Generally, aluminum casting is preferable for DIY applications due to its low melting point.

Forging

Forging is a manufacturing process that involves using compressive forces to shape the metal. A hammer or die is used to deliver these compressive forces. 

There are broadly three types of forging methods based on working temperature: cold, warm, and hot forging. 

When comparing forging against other metalworking techniques, it produces comparatively stronger parts with denser and uniform microstructure, which enhances their reliability.

The process of forging requires less secondary processing and yields products of enhanced tensile strength, shear strength, creep resistance, structural integrity, and better reliability overall.

Like casting, forging is extensively used in industrial as well as DIY projects.

However, when comparing forging against machining operations, forged parts have better strength and provide better reliability.

Drop forging is one of the most commonly used forging techniques in various industries for applications such as the forging of steel workpieces.

Extrusion

In extrusion, a hot or cold metal is forced through a die of the desired cross-section, which causes the extruded metal to acquire the shape of the die as it moves through the cavity. 

This allows for considerable deformation since it generates compressive and shear stresses without tearing the metal.

It also requires a lower tooling cost and yields better strength and hardness.

The extrusion process produces bar-like and tubular objects with hollow designs or complex cross-sections.

Since extrusion is very demanding in terms of process control, it is more suitable for industrial applications.

Drawing

Drawing is a forming process in which metals are stretched to desired lengths by applying tensile forces.

It resembles extrusion except that in drawing, the metal is pulled rather than pushed under tension.

The products obtained using drawing display a well-polished surface, enhanced mechanical properties, and accurate, consistent dimensions.

Metal drawing is mainly employed for creating cylindrical, cup-shaped, and thin-walled products.

The requirements of heavy machinery make drawing more suitable for industrial use.

Rolling

In the process of rolling, a metal slab or plate is fed to a pair of heavy rotating rolls.

The rotating rolls draw the metal through them. As the metal moves between the rolls, it is subjected to elongation and thickness reduction.

This process is repeated until the workpiece attains the desired cross-sectional profile.

The thickness of the resulting sheet metal can be precisely controlled by adjusting the roll gap, the roll speed, and the amount of force applied to the metal.

The products obtained through this method have high tensile strengths, repeatable tolerances, favorable grain structures, and minimal scrap.

Rolling is extensively used to manufacture products with constant cross-sections throughout their lengths, such as rings, bars, plates, and sheets.

Apart from that, special rollers with the desired die cavity can be used to roll the metal into the required shape without the need for further operations.

Rolling is better suited for industrial applications due to the requirement of complex machinery.

Sizing

Sizing is a manufacturing process usually employed to alter the size of the workpiece.

In this process, the metal is subjected to a squeezing force to manipulate its thickness.

The application of a larger force over a short span makes this process cost-effective and allows for very accurate dimensions and excellent surface quality. 

Since sizing is mainly employed for manipulating specific regions in existing components, it is more suitable for industrial use.

Sheet Metal Forming

Deep Drawing

In this process, a sheet metal blank is made into a concave or cup shape using the mechanical force of a sheet metal tool, called a punch die.

The sheet metal blank is held firmly in place on the female die by a blank holder as the male punch die presses into the sheet metal, causing the sheet to conform to the cavity's shape.

Deep drawing is typically used when the metal being drawn has high ductility, allowing it to be stretched without breaking. 

The process of deep drawing is a cost-effective method for producing high-volume, high-quality parts with complex patterns, consistent dimensions, and enhanced surface finishes.

This method is extensively used in industries and can also be employed for DIY projects.

Punching and Blanking

In punching and blanking, die punches are used to cut metal sheets along closed outlines, such as holes.

The difference between punching and blanking lies in the workpiece that is attained after the process.

If the material cut from the sheet is the workpiece, the process is referred to as blanking, whereas if the material left after removing the blank from the sheet is the workpiece, the process is known as punching.

Punching is a fast and accurate method for producing a large number of holes in sheet metal, and blanking allows for the creation of complex patterns and layouts.

Both methods are suited for DIY as well as industrial projects.

Another similar technique is known as piercing. It is similar to punching, except that the holes made are extremely small, and involve no or minimal material removal.

It uses the same machinery and is employed to cut off desired geometrical shapes from the metal.

Shearing

Sheet metal shearing is a cutting process in which certain parts of metal sheets are removed by the application of shearing forces.

The metal sheet is properly positioned between the upper and lower blades of a shearing machine. Then the upper blade is forced downwards, resulting in the cut.

Shearing is often used as a finishing process to remove unwanted scrap from the workpieces.

The machines used for shearing are of many types, including hydraulic, pneumatic, or electric, making shearing possible for industrial and small-sized DIY projects.

Embossing

In embossing, a raised or recessed pattern is created into a metal sheet by pressing it against a die of the desired shape.

This method is usually employed to make visually appealing products.

Metal sheets with embossed patterns are typically used to decorate objects like lanterns, windows, and utensils.

Embossing is extensively used in DIY projects due to simpler tool requirements.

Bending

Bending involves using press brakes, folding machines, or similar machine presses to create angle bends in the metal sheet along a straight axis. 

In this process, a punch pushes against the sheet metal, causing it to bend around a die, which acts as a form and causes minimal residual stress.

It can be used to create a variety of features in sheet metal, including flanges, folds, and corners.

Spin Forming

Also called spinning, it is a manufacturing process in which flat circular sheets are transformed into axially symmetric hollow shells.

It is carried out by placing the workpiece on a rotating chuck and using a pressing tool to carve it into the desired shape.

Spinning is suitable for manufacturing concentric and axially symmetric articles such as flower pots, ashtrays, oxygen cylinders, and utensils.

In comparison to stamping, spinning is more economical for small- and medium-scale production, making it suitable for DIY use.

Powder Metal Forming

Powder forming is a new kind of forming technique that is gaining popularity in modern industries. 

It is a manufacturing process involving the use of powdered metal to create parts with specific shapes and properties. 

In powder metal forming, metal in the powdered form is mixed with a binding agent to create a feedstock. 

The feedstock is then pressed into the desired shape using a die or mold. 

Then, the part is sintered or heated to a high temperature, which causes the binder to burn off and the metal particles to fuse.

This minimizes material wastage and helps produce parts with tight tolerances, making it ideal for projects that require high dimensional accuracy.

There are several powder metal forming processes, including powder forging, powder extrusion, and powder injection molding.

Powder forging involves using a press or hammer to shape the feedstock into the desired shape.

This results in products with uniform density, higher performance, and enhanced mechanical properties.

In powder extrusion, the powdered metal is forced through a die or other shaped opening to create a continuous, solid shape.

This process produces a wide range of products, including tubes, rods, sheets, and other shapes.

Powder Injection Molding (PIM) is a manufacturing process in which the feedstock is injected into a mold using an injection molding machine, where it is subjected to heat and pressure.

The heat and pressure cause the binder to melt and bind the powder particles together, forming a solid, cohesive shape which is then cooled and removed from the mold.

PIM is used to make products that are air sensitive and display complex geometries.

Tools Used for Metal Forming

Presses

Presses come in various types, including mechanical, hydraulic, and pneumatic. They are used to apply pressure to the workpiece to shape it. 

These can be used to perform a wide range of metal forming operations, including punching, blanking, and other stampings, as they provide bending and shearing stresses.

They also come in various sizes and thus are well-suited for small-size DIY projects and large industrial applications.

Dies

A die is an essential metal-forming tool that is used to shape the workpiece under pressure.

Dies come in various shapes and sizes and are used in conjunction with presses to perform a wide range of metal-forming operations, including drawing, embossing, and extrusion.

The use of die is seen in almost every type of metalworking process and is suitable for DIY and industrial projects.

Benders

Benders are used to bend sheet metal, rods, and tubes into various shapes and angles.

Depending upon the raw material, various types of benders are employed, including manual benders, hydraulic benders, tube benders, and mechanical benders.

For example, a press brake is a bending tool used to bend or shape sheet metal or plate into V and U-shaped bends.

With the advent of technology, today, we can perform bending using special machines capable of automating the bending process.

A CNC bending machine uses a computer system to control the press brakes and produce the required bend in the workpiece.

CNC bending produces consistent bends and accurate dimensions in the workpiece. 

Applications of Metal Forming

Owing to its diverse techniques, metal forming is used in many industries to produce a wide range of products.

The use of forging is prominent in the industrial equipment industry and aerospace industry as it delivers products of enhanced strength, durability, and reliability.

Rolling is used in construction industries for creating ladders, railings, beams, bars, and other components of uniform cross-sections.

Extrusion is used in construction, automobiles, and electronic industries because it can yield products with complex hollow structures.

Casting is employed in agriculture, defense, and automotive industries as cast products can incorporate intricate patterns and are suitable for forming a wide range of alloys.

The process of casting alloys is known as alloy casting.

Metal stamping is well-suited in the industries of appliances, aircraft, hardware, and fasteners due to its capability of creating customized parts with minimal costs.

CNC bending is best suited for forming sheet metal to be used in aircraft and automobile industries because it provides high accuracy along with a smooth surface finish and good durability.

Final Thoughts

Although there are several forming processes for shaping metals, each method has merits and demerits, making it more suitable for specific applications.

Casting and deep drawing are suitable for producing identical components with complex designs.

Metal stamping is appropriate for creating consistent and cost-effective indents on your metal sheets.

Forging is best suited for making products with enhanced strength, less risk of failure under load, and better reliability.

It is also preferable to employ hot forming if you require enhanced ductility and malleability in your workpieces since higher temperatures enhance these properties.

Whereas cold forming is preferred for enhanced tensile strength, a good surface finish, and easy handling.

Frequently Asked Questions (FAQ)

What are the common defects that can occur during metal-forming processes?

Some common defects that can occur during the metal-forming processes include wrinkles, cracks, porosity, and warping. However, these can be easily reduced by using proper forming techniques and preventative measures.

How can the quality of the final product be improved in metal forming processes?

The quality of the final product in metal forming processes can be improved using proper material selection, the use of high-quality tools, and regular inspection of forming tools.

Are there any disadvantages of metal forming processes?

Yes, there are some disadvantages of the metal forming processes, such as the potential for residual stresses, the possibility of defects and imperfections, and the need for specialized equipment and expertise.