In the field of precision mechanical engineering, mechanical rolling is one of the best techniques for improving the surface properties of materials. This process, based on the controlled application of pressure through specific tools, allows for the achievement of smooth, hard, and resistant surfaces, which are essential for numerous industrial applications.
In this article, we will explore in detail what mechanical rolling is, how it works, and what its main advantages are.
What is Mechanical Rolling and What is it Used For?
Mechanical rolling has ancient origins, dating back to rudimentary metalworking techniques used since antiquity. However, the true development of this technique occurred in the 20th century with the introduction of more advanced machinery and a scientific understanding of plastic deformation phenomena.
In the 1950s and 1960s, the automotive and aerospace industries began to exploit mechanical rolling to improve the durability and performance of critical components.
As previously mentioned, mechanical rolling is a surface working process that uses specific tools to enhance the physical characteristics of metal surfaces.
This method involves applying controlled pressure through rollers or similar tools that plastically deform the material's surface without removing any part of it. The result is a smoother, harder, and more resistant surface, with a significant reduction in micro-imperfections and residual stresses.
The basic principles of mechanical rolling are founded on controlled plastic deformation, which induces surface compression.
Advantages and Benefits of Mechanical Rolling
Mechanical rolling offers numerous advantages to metal components. Among the main ones are:
- Increase in Surface Hardness: The plastic deformation process creates a compressive layer that makes the surface harder and more resistant to impacts. Higher surface hardness is essential for components that must withstand high loads and extreme working conditions, reducing wear and prolonging the service life of the part.
- Reduction of Friction: Mechanical rolling also improves the tribological properties of materials, reducing friction between contacting surfaces. The reduction in surface roughness allows for better lubrication and more uniform contact, decreasing wear and heat generation.
- Improved Fatigue Resistance: The fatigue resistance of mechanical components is significantly improved thanks to mechanical rolling. The process induces a state of surface compression that counteracts the action of tensile forces, which are primarily responsible for the propagation of fatigue cracks. This effect increases the material's ability to withstand repeated load cycles, preventing the formation of cracks and premature failures.
- Other Benefits: Besides the main advantages, mechanical rolling ensures a better aesthetic finish, greater corrosion resistance, and a reduction in residual stresses.
How Mechanical Rolling Works
The rolling process is based on the application of a compressive force on the surface of the component, using specific rollers or tools.
The Key Steps in the Mechanical Thread Rolling Process are as follows:
- Component Preparation: before starting the processing, it is essential to properly prepare the component. The surface must be clean and free of contaminants to ensure uniform application of pressure.
- Selection of the Roller or Tool: the choice of the appropriate roller or tool depends on the specifications of the component and the treatment objectives. Rollers can vary in size, shape, and material to suit different application needs.
- Setting Processing Parameters: processing parameters such as pressure, speed, and duration of the process must be precisely set. These parameters directly influence the surface quality and the effectiveness of rolling.
- Execution of Rolling: during execution, the roller is applied to the surface of the component with controlled compressive force. The movement can be linear or rotational, depending on the type of machine and the component being processed.
- Quality Control and Verification: after rolling, the component undergoes rigorous quality control to verify that the surface has reached the desired specifications. Measuring instruments are used to evaluate hardness, roughness, and other surface characteristics.
Tools and Machinery Used
Mechanical rolling requires specialised tools and machinery to ensure the precision and efficiency of the process.
Below is a brief description of the main tools used:
- Rolling Tools: these are the primary tools used in this process. They can be made from various materials such as hardened steel or tungsten carbide, depending on the specific process requirements and the type of material to be treated. Rollers can come in various shapes, including cylindrical, spherical, or conical, to adapt to different component geometries.
- Manual Rolling Machines: used for small productions or custom operations, these machines allow the operator to manually control the pressure and movement of the roller. They are ideal for high-precision work on unique components or prototypes.
- CNC Rolling Machines: numerically controlled (CNC) machines represent the pinnacle of advanced technology for mechanical rolling. These machines use control software to program and automate the process, ensuring high precision and consistency among the produced parts. They are particularly suitable for large-volume productions and complex components.
- Hydraulic Rolling Machines: these machines use hydraulic power to apply high and constant pressures during the rolling process. They are ideal for processing hard materials and large components.
- Advanced Technologies: real-time monitoring systems, self-regulating rollers, and virtual simulation software to optimize the process and ensure superior results.
Process Parameters
As seen above, mechanical rolling is influenced by several parameters that determine the quality of the end result. Optimisation of the parameters is fundamental to guarantee high quality results and meet the required technical specifications.
Below we see the characteristics of the main parameters and their impact:
- Pressure: determines the depth and intensity of plastic deformation on the surface. Optimal pressure is essential to improve hardness and resistance without damaging the material.
- Speed: the speed of the roller movement affects the heating of the material and the efficiency of the process. It must be calibrated to avoid overheating and ensure uniform deformation.
- Temperature: although often performed at room temperature, rolling can vary in temperature to suit the material's specifications. Accurate control is necessary to maintain the material's properties.
Types of Mechanical Rolling
Mechanical rolling comprises several techniques with specific applications and advantages.
These include:
- Surface Rolling: Treats the outer surface of components, improving hardness, reducing roughness, and increasing wear resistance. Used for shafts, axles, bearings, and gears, it is ideal for smooth and durable surfaces, mainly in the automotive and aerospace industries.
- Cold Rolling: Performed at room temperature, plastically deforms the material, improving hardness and resistance without altering the metallurgical structure. Used for screws, bolts, crankshafts, and structural parts, it is useful in the automotive and aerospace industries for precision and surface quality.
- Internal Rolling: Used to treat the internal surfaces of cylinders and tubes, this technique requires special tools to access and apply pressure inside the component.
- Hot Rolling: Involves heating the material before rolling, facilitating plastic deformation and further improving surface characteristics.