Press forming is an essential metalworking technique in the modern manufacturing industry.
This methodology allows simple metal sheets (plates) to be transformed into complex and structural components, which are indispensable in numerous sectors.
In this article we will look at how the press-bending process works, analyzing the mechanical principles behind it, the different technologies used and the recent innovations that are revolutionizing the sector.
Metal Bending: What is it and How Does it Work?
Press forming is a metal forming technique that allows sheets of metal to be bent into precise shapes and defined angles using press brakes. The technique is distinguished by its ability to create complex metal components required in various areas of the manufacturing industry, such as automotive, aeronautics and construction.
The press-bending process begins with the positioning of the metal sheet between two parts of a die: the lower die and the upper punch.
The punch moves downwards with controlled force and pushes the metal into the die, which has a shape complementary to the desired profile. During this process, the metal undergoes plastic deformation, changing shape permanently without being cut or assembled with other parts.
Pressing uses advanced technology to improve precision and efficiency.
Presses can be manual, where the operator directly controls the bending process, or CNC (Computer Numerical Control), which allow detailed programming of bending operations. CNC presses, in particular, are able to handle complex tasks with high precision due to their programmability, offering repeatability and high quality in finished parts.
Parameters such as bending force,bending angle, punch speed and metal type are essential in determining the quality of the final component. Careful control over the above factors reduces the risk of defects such as cracks or unwanted deformations.
The Mechanical Principles of Press Bending
Press-forming is based on the principles of plastic deformation, a mechanical phenomenon through which a material (in this case, a metal) is forced beyond its elastic limit but without reaching the breaking point, thus allowing it to acquire a new permanent shape.
The phenomenon is fundamental in metalworking to produce parts with precise angles and complex configurations.
When a metal is subjected to stress, it initially undergoes elastic deformation, which is reversible.
If the stress is removed at this stage, the metal returns to its original shape.
However, if the stress exceeds a certain limit, known as the yield stress, the material enters the plastic deformation phase. And it is here that press-forming shapes the metal, creating permanent deformation.
Critical Factors in the Pressing Process
As previously mentioned, the bending process is influenced by various mechanical factors:
- Bending force: the amount of force applied directly influences the depth and angle of the bend. Insufficient force may not properly deform the metal, while excessive force may cause damage or unwanted deformation.
- Bendingangle: the angle at which the punch presses on the metal determines the sharpness of the bend. Sharper angles require greater precision to avoid excessive stresses that could lead to breakage.
- Type of metal and thickness: different metals and thicknesses react differently to bending due to their intrinsic mechanical properties, such as hardness and ductility. The choice of metal and its pre-bending heat treatment can significantly influence the quality of the process and the final product.
Pressing Machinery
Bending machines represent the technological heart of the bending process, essential for transforming engineering theories and technical drawings into real metal components.
Press Bending Machines can vary greatly in terms of technical specifications, capacities and levels of automation, each adaptable to specific production requirements.
The main types of Bending Press es include:
- Manual presses: these are the most basic versions of presses and require intensive manual operations. They are suitable for machine Workhops that produce low volumes or work with one-off parts. Their simplicity makes them economically advantageous for small companies or for prototype production.
- Hydraulic presses: use hydraulic force to bend metals, offering more precision and control than manual presses. They are preferred for machining operations that require repeated bending with high precision.
- Pneumatic presses: operate on a similar principle to hydraulic presses but use compressed air. They are generally faster than hydraulic presses but can be less powerful, ideal for thinner metals or less intensive operations.
- Servo-electric presses: these are presses that use servo-controlled electric motors for even greater bending control. They are highly energy efficient and offer extreme precision, suitable for applications where tight tolerances are required.
Worthy of special mention are CNC (Computer Numerical Control) presses, which have revolutionized bending due to their ability to precisely programme and control every aspect of the bending process.
CNC presses can be programmed to perform complex sequences, allowing:
- Automatic multiple bends: with a single setting, the machine can perform complex sets of bends.
- Repeatability: each part is bent with the same accuracy, reducing the margin of error and increasing production consistency.
- Efficiency: production speed is greatly increased, essential for large batches.
Material Selection and Work Preparation
The selection of the right material and its correct preparation are crucial steps in the press-bending process, as they influence the quality of the end product and the efficiency and safety of the production process.
The selection of the appropriate material for press-bending depends on several factors, including material strength, ductility, sheet thickness and the complexity of the component to be manufactured.
Commonly used materials include:
- Steel: very versatile, available in different alloys and degrees of hardness, suitable for various industrial applications.
- Aluminium: light and strong, ideal for applications where weight is a critical factor, such as in the automotive and aeronautics sectors.
- Stainless steel: known for its resistance to corrosion and rust, used in environments exposed to harsh conditions or for the manufacture of products requiring high hygiene standards.
- Copper and its alloys: commonly used for its excellent electrical and thermal conductivity, ideal for electrical components.
Before starting the bending process, it is essential to carry out a number of preparations to ensure that the material and the machine are ready for production:
- Cleaning: the metal sheets must be cleaned to remove oil, grease, dust or other impurities that could affect the quality of the bending.
- Lubrication: the application of a suitable lubricant reduces friction between the metal and the bending tools, facilitating the process and finishing of the product.
- Tool calibration: it must be ensured that all tools and equipment, including punches and dies, are correctly calibrated and in good condition. This is essential to maintain accuracy during bending.