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简体中文 Sheet metal forming refers to a category of manufacturing processes that induce plastic deformation in metal sheets through external forces, molds, or energy fields without significantly changing the sheet thickness, thereby achieving predetermined shapes, dimensions, and performance. As a key branch of plastic working, sheet metal forming primarily processes thin metal sheets (such as steel, aluminum, copper, and titanium alloys) and is one of the most widely used and efficient forming methods in modern manufacturing. Based on existing research, this paper reviews the mechanisms, common and advanced technologies, and material applications of sheet metal forming, analyzes its applications across multiple industries, evaluates current challenges, and proposes future research directions, aiming to enhance the understanding of the role of sheet metal forming in modern manufacturing.
Historical Development of Sheet Metal Forming Technology
The use of sheet metal forming technology can be traced back to early civilizations, when people developed methods to improve tools and armor. Since then, during the Middle Ages, the production of custom metal parts and manual hammering and folding techniques advanced. Subsequently, numerous progress has been made in this field, especially after the introduction of mechanization during the Industrial Revolution.
The improvement in production efficiency drove the development of advanced automation technologies in the 20th century. In recent years, the integration of Computer-Aided Design (CAD), Computer-Aided Manufacturing (CAM), and advanced materials has brought significant transformations to the sheet metal forming industry, which is increasingly adopting more efficient technologies.
Basic Mechanisms of Sheet Metal Forming
Elastic and Plastic Deformation
In sheet metal forming, elastic deformation is a reversible shape change that occurs when the stress on the material is below the yield strength. The stress-strain relationship typically follows Hooke’s Law (linear relationship), and the material can fully recover its original shape after unloading. When the stress exceeds the yield strength, the material enters the plastic deformation stage, where a large number of dislocations begin to slip, resulting in irreversible permanent deformation—this is the core stage of realizing sheet metal forming.
Strain Hardening and Anisotropy
Strain hardening (also known as work hardening) is a phenomenon in which the dislocation density increases and entangles during the plastic deformation of metals, leading to increased material strength and decreased plasticity. In sheet metal forming, moderate strain hardening can enhance the local strength of formed parts and avoid excessive deformation, but excessive hardening may cause cracking risks. Therefore, it is necessary to regulate the hardening degree through process parameters such as blank holder force and lubrication conditions.
Anisotropy originates from the preferred grain orientation formed during the sheet rolling process, manifesting as significant differences in yield strength and plasticity in different directions. For example, the formability of low-carbon steel sheets is usually better in the rolling direction than in the transverse direction.
Fracture Mechanics in Sheet Metal Forming
The core of fracture mechanics is to reveal the laws of crack initiation and propagation in materials under load, thereby determining the forming limit and avoiding component failure. In sheet metal forming, fracture is mainly divided into two categories: ductile fracture (accompanied by extensive plastic deformation, cracks initiated by void coalescence) and brittle fracture (almost no plastic deformation, cracks propagating along grain boundaries or cleavage planes).
Stress concentration, strain path, and material microstructure are the core factors affecting fracture, while temperature and strain rate further change the fracture toughness of materials. For instance, high strain rates in high-speed stamping can increase material strength but also reduce plasticity, increasing the risk of brittle fracture.
Common Sheet Metal Forming Processes
Stamping
Stamping is one of the most basic and widely used sheet metal forming processes. It exerts instantaneous pressure on metal sheets through molds to achieve various forming operations such as cutting, bending, and deep drawing. The core process involves feeding the sheet into a stamping press and completing continuous or single-step forming with different molds such as progressive dies, transfer dies, or deep drawing dies. Common materials include steel alloys, aluminum alloys, and copper alloys, which possess both good plasticity and mechanical strength, making them suitable for high-speed mass production.
The prominent advantages of stamping lie in high processing efficiency and stable dimensional accuracy, especially suitable for large-scale manufacturing scenarios such as automotive body panels and electronic device housings. However, the design and manufacturing costs of molds are relatively high, and there are strict requirements on the forming limit of materials—for example, stamping of high-strength steel is prone to cracking risks. Currently, the application of intelligent mold design combined with finite element simulation and servo stamping technology is continuously improving the forming quality and process adaptability of stamping.
Deep Drawing
Deep drawing is a process that transforms flat sheets into hollow rotating bodies or complex curved parts through molds, and it is a core technology for manufacturing complex thin-walled components such as automotive fuel tanks and aero-engine casings. Its typical process includes blanking, first deep drawing, multiple deep drawing, and final trimming. Wrinkle, tearing, and other defects are avoided by controlling blank holder force, lubrication conditions, and mold fillet radius.
Aluminum and low-carbon steel are the most commonly used materials in deep drawing processes. Aluminum alloys are highly favored in the aerospace field due to their light weight and high plasticity, while low-carbon steel dominates the production of automotive parts with its cost advantage. The core challenges of this process lie in springback control and wall thickness uniformity. In recent years, the development of adaptive blank holder force systems and warm deep drawing technology has significantly improved the forming success rate of complex parts.
الانحناء
Bending is a process that bends sheets into a predetermined angle or curvature along a specific axis using a bending machine or folder. Common forms include air bending, bottom bending, and coining bending. Air bending achieves flexible forming through point contact between the mold and the sheet, suitable for small-batch and multi-variety production; bottom bending and coining bending obtain higher precision angles through full contact with the mold.
Material properties, sheet thickness, and mold geometric parameters are the key factors determining bending quality. Among them, springback effect is the most important process challenge—materials will produce angular springback after unloading, which usually needs to be corrected by compensating the mold angle or increasing the over-bending amount. With the popularization of CNC bending machines and robot-assisted bending technology, the automation level and forming precision of the bending process have been greatly improved, widely used in fields such as home appliance frames and steel structure connectors.
Stretch Forming
Stretch forming is a process that achieves complex curved surface forming by applying tension to both ends of the sheet and combining with mold bending. It is particularly suitable for large-size thin-walled parts such as skins and ribs in the aerospace field. This process eliminates residual stress inside the sheet through pre-stretching and then combines with bending forming, which can effectively reduce springback and improve the surface quality and mechanical properties of parts.
Aluminum and titanium alloys are the main materials for stretch forming. Titanium alloys are indispensable in aero-engine components due to their high strength and corrosion resistance, but they need to be formed at high temperatures to improve plasticity. The advantage of stretch forming lies in the ability to achieve integrated forming, reducing subsequent welding processes, but it has extremely high requirements on the tension control precision of equipment. Currently, closed-loop control systems based on real-time feedback and digital twin technology are further optimizing its process stability.
Hydroforming
Hydroforming is a sheet metal forming process that uses high-pressure fluid (usually oil or water) as the force transmission medium to fit the sheet into the mold for forming. It is divided into two categories: single-sided hydroforming (such as water bulging) and double-sided hydroforming (such as rubber pad forming). Compared with traditional stamping, it can manufacture more complex hollow parts with fewer processes, higher material utilization rate, and lighter part weight, thus having significant advantages in the manufacture of automotive chassis components and aerospace ducts.
The core challenges of this process are high mold costs and difficult process control under high pressure, especially strict requirements on the forming limit and wall thickness uniformity of materials. In recent years, the progress of ultra-high pressure hydraulic systems and adaptive pressure control technology has gradually expanded its application to the forming of complex components of high-strength steel and aluminum alloys. In the future, composite mold technology combined with additive manufacturing is expected to further reduce costs.
Roll Forming
Roll forming is a continuous bending operation used to process metal sheets into desired profiles. The main purpose of this process is to manufacture long strip products with uniform cross-sections. The process usually includes material feeding, bending, and cutting, through which complex shapes can be produced efficiently.
Suitable materials for this process include steel, aluminum, and copper. Compared with other forming processes, roll forming has advantages in material waste and precision, making it highly attractive. Its typical applications include automotive parts and structural components. In design, the thickness of the material and the geometry of the profile are crucial. With technological advancements, production efficiency has been improved, but these advancements are limited by mold costs and material knowledge.
Advanced Technologies in Sheet Metal Forming
Incremental Sheet Forming (ISF)
ISF is a flexible die-less/simple die sheet metal forming technology. It achieves cumulative forming by performing local and gradual plastic deformation on the sheet along a preset path through a numerically controlled spherical tool. According to the support method, it is divided into single-point incremental forming (SPIF, suitable for simple curved surfaces) and two-point incremental forming (TPIF, suitable for complex precision parts).
Key parameters include tool path (helix, contour, etc.), step depth, tool diameter, and feed rate. The core advantage is that the mold cost is reduced significantly, and the rapid prototyping capability is prominent, making it suitable for the production of aerospace customized parts, automotive concept car parts, and medical personalized implants.
Currently, ISF faces challenges such as slow forming speed, easy generation of step textures on the surface, and prone to cracking in high-strength steel forming. In the future, it will develop towards robot automation, finite element path optimization, and integrated processes combined with 3D printing.
Superplastic Forming (SPF)
SPF is an advanced sheet metal forming technology that utilizes the superplasticity of materials (elongation exceeding 1000%) under specific conditions (temperature of 0.5-0.7 times the melting point, appropriate strain rate) to achieve large-deformation forming through gas pressure or molds.
Materials suitable for SPF need to meet the requirements of fine equiaxed grains and low flow stress, such as Ti-6Al-4V titanium alloy and 7075 aluminum alloy.
Its advantages include near-net forming, low material waste rate, and uniform mechanical properties of parts. It is widely used in aircraft titanium alloy skins, engine blades, and medical titanium alloy restorations.
Limitations include high cost of superplastic alloys, long forming cycle, and high requirements for temperature control precision. In recent years, through the development of new alloys, optimization of temperature-pressure coupling control, and SPF/DB (Diffusion Bonding) composite processes, the efficiency and application scope of SPF have been gradually improved.
Laser Forming (LF)
LF is a non-contact, die-less advanced sheet metal forming technology. It uses a high-energy laser beam to scan the sheet surface, generating uneven thermal expansion and cooling shrinkage through local temperature gradients, thereby forming residual stress to drive plastic deformation. According to the deformation mechanism, it is divided into temperature gradient forming (small-angle bending), buckling forming (large-curvature curved surfaces), and gas-assisted deep drawing forming (hollow parts).
The core advantages are high forming precision, strong flexibility (changing the scanning path to change the shape), and no surface scratches. It is suitable for aerospace titanium alloy skin straightening, micro-bending of electronic devices, and rapid prototyping of complex automotive parts.
Current challenges include slow processing speed, the need for surface treatment of high-reflectivity materials, easy cracking of high-strength steel, and difficulty in controlling the coupling of temperature and stress fields. In the future, the focus will be on high-power laser systems, numerical simulation parameter optimization, and robot-assisted 3D forming to promote the large-scale application of LF in high-end manufacturing.
Industrial Applications of Sheet Metal Forming
Automotive Industry
Sheet metal forming is a core process in automotive manufacturing, widely used in the production of key components such as body panels (stamping forming), chassis structural parts (hydroforming), and door frames (bending forming). Currently, the industry is transitioning towards lightweight and low-carbonization, with the application ratio of lightweight materials such as aluminum alloys and high-strength steel continuously increasing. Through processes such as deep drawing and roll forming, component weight is reduced, directly improving fuel efficiency and electric vehicle range.
Automated production lines (such as robotic stamping and CNC bending) have greatly improved production efficiency and dimensional consistency, while the application of finite element simulation technology has effectively solved the wrinkling and cracking problems in complex curved surface forming. Core challenges include the high-precision forming requirements of electric vehicle battery pack housings, the optimization of lightweight material forming processes, and the efficient recycling of waste sheet metal parts—all of which are driving the upgrading of sheet metal forming technology towards greenization and intelligence.
Aerospace Industry
The aerospace industry has extremely high requirements for the lightweight, high strength, and precision of components, and sheet metal forming plays an irreplaceable role here. Fuselage skins adopt stretch forming and laser forming technologies to ensure the accuracy of aerodynamic shapes; wing and empennage structural parts achieve near-net forming of complex curved surfaces through superplastic forming (SPF), significantly reducing material waste; engine ducts rely on hydroforming processes to obtain hollow structures with both high strength and lightweight.
The industry has strict requirements for forming tolerances and widely uses difficult-to-process materials such as titanium alloys and composite materials, which places extremely high requirements on the pressure control and temperature precision of forming equipment.
Future development directions focus on the development of forming processes for advanced materials, the large-scale application of flexible technologies such as incremental sheet forming, and the optimization of forming processes through digital twin technology to improve component reliability and service life.
Consumer Electronics Industry
The demand for sheet metal parts in consumer electronics focuses on housings, heat dissipation structures, and internal brackets, featuring small size, high precision, and strict appearance requirements. Aluminum alloys and magnesium alloys have become mainstream materials due to their light weight and easy processability. Through sheet metal forming processes such as stamping, bending, and laser forming, ultra-thin and special-shaped product housings (such as laptop bodies and mobile phone middle frames) are manufactured.
Precision forming technology ensures the assembly accuracy of sheet metal parts, while the coordination of surface treatment (such as anodizing and spraying) with forming processes not only meets aesthetic requirements but also improves wear resistance. In addition, the heat dissipation structures formed by sheet metal (such as stamped fins of heat sinks) can effectively improve the thermal management efficiency of electronic devices. Industry trends include customized forming (adapting to personalized product design), the application of recycled metals (responding to sustainable development), and technological breakthroughs in high-precision forming of micro sheet metal parts.
Construction and Structural Applications
The application of sheet metal forming in the construction field mainly focuses on long strip components and enclosure structures. Roll forming technology is used to produce purlins such as C-shaped steel and Z-shaped steel, while stamping and bending processes manufacture building curtain wall panels and roof color steel plates. Steel and aluminum alloys are the main materials, and their corrosion resistance, high strength, and easy processability make them suitable for various construction environments. Moreover, their lightweight characteristics simplify the construction and installation process.
The rise of prefabricated buildings has promoted the standardized production of sheet metal components. Through modular forming, rapid assembly of components is achieved, significantly shortening the construction cycle. At the same time, the recyclability of sheet metal materials and the application of environmental protection coating technology are in line with the green development concept of the construction industry.
Current development focuses include the forming optimization of sheet metal components for large-span spatial structures, the process adaptation of weather-resistant materials, and the customized production of sheet metal components through parametric design to meet diverse architectural shape needs.
استنتاج
In summary, sheet metal forming is currently at a crossroads of development. Advances in technology and metallurgy provide tremendous opportunities for enhancing process capabilities and expanding application scope. To address existing challenges and fully tap the potential of sheet metal forming in manufacturing, further interdisciplinary cooperation and innovation are required. The continuous evolution of sheet metal forming will continue to drive the progress of modern manufacturing towards higher efficiency, precision, and sustainability.
