Sheet metal is an important and popular component of modern manufacturing. It is used in domestic appliances, cookware, car doors, door handles, and more sophisticated machine parts. The art of creating these parts, components, and assemblies using sheet metal is known as sheet metal fabrication. This process consists of techniques or methods such as cutting, forming, joining, assembling, and finishing to achieve the desired component.
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Sheet metal forming is one of the most essential fabrication processes. It involves deforming the metal without adding or removing material. This article covers all you need to know about sheet metal forming, its definitions, a detailed explanation of its processes, and the considerations before using forming for your project.
Sheet metal forming is a fabrication process that involves the reshaping of sheet metals into a part of the desired geometry by applying forces such as tension and compression. This transformative sheet metal manufacturing process is carried out and completed without cutting or boring any part, maintaining its mass. Sheet metal forming is one of the most important processes in the modern fabrication of parts and components. Through the forming process, the metals' plastic characteristic allows the metals to be deformed into different desired shapes while still maintaining their structure and integrity. The process employs techniques like bending, stretching, and pressing to create components with high precision.
Sheet metal forming is ubiquitous in manufacturing because of the favourable properties of materials like steel, aluminium, brass, and copper, which combine strength and malleability. These characteristics enable the creation of lightweight yet durable parts suitable for various uses. Additionally, the process is typically cost-effective, particularly for simple designs and standard sizes, compared to alternatives like forging or metal stamping. The choice of forming methods depends on factors such as the metal type, design complexity, and production volume. High tooling and labour costs often make it more efficient for large-scale production, where economies of scale can be achieved. Techniques such as punching, press braking, rolling, and extrusion rely on the plasticity of metals to shape them while maintaining structural integrity.
Material selection in sheet metal forming is a critical decision that directly impacts the final product's manufacturability, functionality, and durability. The choice of material must align with the application, mechanical properties, and environmental conditions. Below are the materials commonly used in sheet metal forming, their properties, and applications:
Sheet metal forming involves shaping metal sheets into desired geometries without removing material. This process involves several different techniques that achieve widely varying shapes. Each sheet metal forming process involves specialised procedures and machinery.
Bending is one of the most popular metal sheet forming processes. It is done by applying force along the straight axis of the sheet metal, making it bend at an angle. This operation is performed without cutting or punching material, preserving the volume and typically maintaining the sheet's thickness. Bending is usually carried out by a machine called a press brake. It can be operated automatically or manually and is available in sizes 20-200 tons, matching the application. The press brake comprises an upper tool called the punch and a lower one called the die, between which the metal sheet is placed. The angle of the bend is determined by how deep the punch forces the metal sheet into the die. Bending applications include the fabrication of brackets, enclosures, automotive components, and various architectural features.
This sheet metal forming process has various techniques. It can be categorised into several types based on the technique and equipment used:
Rolling is a metal forming process in which a flat sheet continually passes through a series of roll stations. Each station contains paired roller dies, progressively shaping the sheet into the desired profile.
The process helps form complex cross-sectional geometries with high dimensional accuracy. Rolling is mainly used to manufacture roofing panels, structural beams, and storage shelves. types of Rolling Processes:
Curling adds a hollow, smooth, circular roll to the edges of sheet metal, eliminating roughness and sharpness. This process is carried out by feeding the sheets into machines that slowly roll and bend those edges into smooth shapes. Curling not only enhances edge strength but also improves safety and usability. It is commonly applied to parts requiring tubular or rolled edges, such as door frames, can edges, or decorative trims.
This sheet metal forming process involves forcing and compressing the metal through a die to create long pieces with uniform cross-sections. It can be performed using hot or cold methods and is versatile in producing components with complex profiles, including window frames, automotive trim, and lightweight structural components. Variations of this sheet metal forming process include:
This sheet metal forming process generally produces large volumes of identical metal components. It is a very close, effective, and high-speed process. For this process, sheet metals, called blanks, are loaded into a stamping press, where a tool and die interface exert force to reshape the material into the intended form. Stamping processes can be executed as independent operations or combined with other sheet metal forming methods, allowing them to be effective for short and long production cycles. Stamping presses with capacities that can handle up to 400 tons can produce components as thin as 0.005 inches while maintaining tolerances.
Stamping sheet metal is widely used in mass production of parts. It is valued by many industries for its efficiency, consistency, and ability to produce complex geometries with tight tolerances. This process plays a crucial role in modern manufacturing, whether for small intricate components such as steel plates and door handles or large structural parts like car doors and machine parts.
Ironing achieves uniform wall thickness in components by passing the metal through a narrow clearance between a punch and a die. Commonly used in producing beverage cans and containers, this process enhances strength and reduces weight without compromising volume.
In this process, the metal sheet is stretched by a highly pressurised fluid over a die to create curved or hollow forms. It's especially effective with malleable metals such as aluminium, producing strong structural components while preserving the material's original qualities. The procedure involves securing a metal sheet over a die and sealing it within a hydraulic chamber. The metal is pressed into the die by pumping fluid at high pressure to achieve its final shape.
Hydroforming can efficiently produce parts with consistent thickness and minimal scrap, leading to cost-effective solutions for complex designs in sectors like automotive, medical, and aerospace. However, the initial costs for hydroforming machinery and die creation can be significant.
Spin forming is also called the sheet metal forming process, which is utilised to form rotationally symmetric parts by pressing a rotating sheet metal blank against a tool called the mandrel using rollers. It is used for cookware, satellite dishes, and musical instruments. This process has two spinning methods, namely;
Deep drawing stretches sheet metal into deep, cup-shaped components. The process uses a punch and die and is suitable for producing parts with a depth greater than half their diameter. The deep drawing process involves several key components: a blank, a blank holder, a punch, and a die. The blank is a pre-cut piece of sheet metal, usually in the shape of a disc or rectangle, intended for forming into a final part. The blank holder secures the blank over a die with a cavity shaped like the final product. A punch then moves downwards, stretching the material into the die cavity.
Hydraulic systems typically power this punch to exert sufficient force on the blank. Both the die and punch undergo wear due to the pressure exerted during the process, which is why they are constructed from durable materials like tool steel or carbon steel. Applications include automotive panels, kitchen sinks, and beverage cans.
The sheet metal is stretched and bent over a die, forming wide contour parts. Stretch forming stretches and bends sheet metal over a die to create large, contoured parts. Stretch forming is a stretch press process where a metal sheet is clamped along its edges by gripping jaws. These jaws are connected to a carriage that uses pneumatic or hydraulic power to stretch the metal sheet. A solid, contoured tool known as a forming die acts as a mould for the sheet. Typically, stretch presses are designed vertically; the form die is positioned on a table that rises to press against the sheet, causing it to deform under tension. There are also horizontal stretch presses, where the form die is mounted sideways, and the sheet is pulled around it. It is commonly used in aerospace for fabricating aircraft skins and in automotive industries for door and roof panels.
Several key parameters influence the quality, precision, and efficiency of sheet metal forming processes. Understanding and controlling these factors is essential for achieving optimal part performance, minimising defects, and ensuring cost-effective manufacturing.
The K-Factor determines how much steel material is displaced after bending. High K-factor values show that much material is stretched in the bend area. During bending, the outer layers of the sheet stretch while the inner layers compress. The neutral axis is the point where no stretching or compression occurs.
The K-Factor varies depending on the material type, thickness, and bend radius and is crucial for producing accurate and consistent angular bends.
Formula; K=tT
Where;
t = Distance from the inner bend surface to the neutral axis
T = Sheet thickness
Typical K-Factor Values:
The bend radius is the inside radius of a bend. It helps determine the amount of bending stress exerted on the material, the chances of cracking (in harder materials), and the springback effect after bending. Smaller bend radii lead to higher stress concentrations. Mild steel can have small bend radii, but brittle materials must have wider bend radii to avoid failure.
This consideration is critical for effective sheet metal welding after forming. Bend Radius recommendation (as a multiple of thickness, T):
Bend deduction is the length lost as a result of the curve, whereas bend allowance is the extra length of material required in the flat pattern to accommodate the bend. Both elements are essential to guarantee that the part's final dimensions are precise and that the necessary tolerances are fulfilled. These values can be found using various charts and algorithms based on bend characteristics and material parameters.
Formula:
Where:
θ = Bend angle (in radians)
R = Inside bend radius
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K = K-Factor
T = Material thickness
Springback is the tendency for a material to partially return to its original shape after removing the bending force. The amount of springback can depend on the material properties, the bend angle, and the degree of plastic deformation. Springback affects the final part dimensions and must be compensated for during forming.
Manufacturers often compensate with an intentional over-bend during the forming process, which requires a deep understanding of the material's behaviour . Factors affecting springback include:
Die clearance is the gap between the punch and die during the Sheet Metal Forming processes. Not enough clearance can lead to excessive stress and damage, while too much can cause poor edge quality and increased scrap rates. To get the required results, die clearance must be adjusted according to the thickness and qualities of the material.
Formula: for (C):
C=P-D2
Where:
C = Die Clearance
P = Punch diameter
D = Die opening diameter
Die Clearance Recommendation:
Holding time is the duration over which pressure is maintained on the material during the sheet metal forming operations. This period allows the material to adapt to the shape of the die and can significantly influence properties such as surface finish and dimensional accuracy. Optimising holding time can improve the effectiveness of the forming process, reduce defects, and enhance overall product quality. Holding time is particularly important in deep drawing to improve material flow, reduce tearing, coining, and embossing to enhance accuracy and detail, and in hot forming processes to transform uniform grain structure.
When considering the sheet metal forming process, you have to consider several key factors that would affect the process's efficiency and the quality of the final product. A clear understanding of these factors is essential for optimising the process. Geomiq meticulously implements these considerations, ensuring we deliver top sheet metal fabrication services. Join us on the path to better, faster and stronger innovation.
The properties of the material directly impact its behaviour during the forming process. Important considerations include:
Ductile materials such as copper, aluminium, and low-carbon steel are more suitable for sheet metal forming as they can undergo significant deformation without cracking. Meanwhile, brittle materials require other specialised techniques to be adequately fabricated to avoid failure.
The orientation of the metal's grains affects its strength and formability. Note the grain direction before you start the forming process. Working along the grain direction increases the risk of cracking, while working across or at an angle to the grains ensures better performance.
Proper heat-treated materials offer improved ductility and reduced residual stress, making them easier to form. However, hardened or cold-worked metals may require higher forming forces and careful handling.
The dimensions of the sheet metal to be formed are crucial in determining the sheet metal formation.
Thicker sheets need more force during forming, potentially limiting the complexity of shapes. Therefore, consider using other techniques if you are working with thicker-sized parts. Thinner sheets are easier to shape but are more prone to tearing, wrinkling, or distortion.
Larger sheets pose challenges for uniform deformation, consistent force application, and handling, often requiring specialised equipment.
Parts with a high aspect ratio may experience uneven deformation or localised thinning, necessitating additional design or process adjustments to mitigate defects.
Effective management of the applied forces during formation is necessary to maintain the material's integrity and prevent defects:
The design of the sheet is an important factor in determining how best to go about the sheet metal forming. Taking into account these considerations would ensure reduced defects and increased cost efficiency. Key design aspects include:
Sheet metal forming is a versatile manufacturing process used across various industries to create precise, durable, and functional components. Selecting the right material, process, and parameters is crucial for achieving optimal performance while minimising defects and production costs. Factors such as material ductility, grain direction, heat treatment, and geometric considerations significantly impact formability and final part quality.
By carefully evaluating load-bearing capabilities and design constraints, manufacturers can enhance efficiency, reduce waste, and improve structural integrity. A well-optimised sheet metal forming process ensures high-quality results, making it a reliable solution for modern engineering and production needs.
Forming is usually carried out with special electronically controlled machines such as presses, bending machines and steam hammers. In accordance with the integrated tool, many of them are suitable for multiple manufacturing processes. The most common materials used in sheet metal forming are steel, copper, aluminum, aluminum alloys and copper alloys (wrought alloys). A distinction is made according to
In addition, there are also special processes for sheet metal forming such as press hardening and flexforming. For sheet metal forming, level sheets are usually used, which are usually machined by cold forming. Three-dimensional and large, heavy blanks are modified using massive forming. Cold or hot forming is used in this process. Manufacturing processes commonly used for this are bending, rolling, impact extrusion and extrusion.
If the sheet metal forming is classified according to the load on the workpiece, more processes are available. In the case of tensile compression forming (DIN ), simultaneous pressure and tensile loads are carried out with different effective directions. The most important subgroup is deep drawing. In this process, flat sheets are drawn into hollow shapes to produce hollow bodies such as cans, helmets and body parts. In the case of tensile forming (DIN ), sheets are extended and hollow bodies expanded by tensile stress. Bending (DIN ) is mainly performed by bending. Swivel bending uses a rotating movement of the clamped tool, free bending uses a straight movement of the clamped tool. In rolling, metal forming is performed by rotating rollers.
For shear forming (forming due to mainly shear stress, DIN ), the tool performs either a turning motion or a straight motion. The twisting is used for the production of propellers and drills, the shifting is used to manufacture cranks. Press forming (DIN ) is carried out, for example, as rolling (sheet and plate production) or free forming (free-form forging). Depending on the sheet metal forming process used, the shape change is achieved either by special tool movements (bending) or by creating the later shape in the tool as negative (die forging, rolling).
Sheet metal forming is ideal for mass production. However, the shape is not completely precisely extracted from the blank. To obtain the fitting finished part, the workpiece must be reprocessed, for example, by grinding. Most sheet metal forming processes achieve an accuracy between IT16 and IT12. Precision processes even enable an accuracy of IT8 or IT6. The so-called flexforming (fluid cell forming) is a particularly cost-effective, fast and versatile method of sheet metal forming. It is therefore used for small series production and for the development of prototypes. Fluid cell presses are used to manufacture components for the aviation industry, the automotive industry and their suppliers.
The sheets to be machined have thicknesses from 0.1 mm to more than 16 mm. The low-maintenance and user-friendly special presses enable a particularly good pressure control on small workpieces and a significant reduction in manual finishing. Some of the high-speed fluid cell presses produce up to 120 parts per hour. Using flexforming, even complex geometries with low tolerances and flawless surface can be produced with a single die.
Compared to cutting processes, metal forming offers the advantage that the material is optimally utilized: There is no metal waste left. In addition, the workpiece has a grain flow that is suitable for use. At identical mass, this results in drawing parts and other components of high strength and load capacity. In milling, on the other hand, the grain flow is prone to stress because milling creates many tiny notches in the component. Forming tools are only profitable for large series production. Milling can already be implemented at low cost for individual parts and small series.
Cold forming is performed below the recrystallization temperature. During warm forming, the respective workpiece is heated to a temperature that is also lower than the recrystallization temperature (600 to 950 °C). The hot forming is done by heating the material, so that the recrystallization temperature is exceeded.
Cold forming makes the material more solid, allowing it to be machined more precisely. The special fiber structure ensures that the finished part withstands a high mechanical stress and is therefore optimally suited for the production of safety-relevant components in the aircraft and automotive industry. Warm forming combines the advantages of both methods. It is used to manufacture forged parts made of steel alloys for which cold forming is not an option. The forged parts have low dimensional tolerances, a homogeneous material surface, only slight scaling and sometimes even more demanding geometries.
Hot forming (hot forging) is a very energy-consuming method that is suitable for forming various metals. This forming technique results in temperatures between °C (steel alloys) and °C (iron). These temperatures cause a rough surface. Material shrinkage occurs after the workpiece has cooled down. The workpiece does not necessarily have to be heated for hot forming. Depending on the metal, even room temperature can be sufficient.
When sheet metal is bent, the force is applied uniformly linear or selectively. The degree of deformation depends on the degree of this bending moment. Embossing machines, round bending machines and press brakes enable different types of bending. In the press brake, the tool presses down on the metal sheet with a certain force. At the contact point, an equally strong force is applied in the opposite direction. The couple must work so strongly that the sheet metal is permanently altered afterwards. To do this, the industrial user must know to what extent the given metallic material can be subjected to load and how it behaves in the event of force. For permanent deformation, the force applied must exceed the range of elastic deformation.
The material composition and tensile strength also play a role. The latter must also not be exceeded to prevent damage to the material. To calculate the required pressing force, the edging length must be known. The edging length increases proportionally to the bending length. In addition, the material thickness, the bending angle and the rolling direction are required. Larger material thicknesses generally require larger bending radii. If the tool does not reach the minimum bending radius, the workpiece can break, its outside can crack and wrinkles in the inside can result.