There has been a saying in the machine tool industry that the machine tool needs to release the stress, and the higher the precision of the machine tool, the more attention should be paid to the stress release. So, why release the stress? If so, how long will it take? How to release the stress is good and so on a series of questions about the machine tool stress, don’t worry, and with the article slowly.
▌ What is the stress?
When an object is deformed due to external factors (stress, humidity, temperature field changes, etc.), the internal forces of the interaction between the parts of the object are generated to resist the effect of the external factors, and try to make the object recover from the position after deformation to the position before deformation.
The stress released by the machine tool is called mechanical stress, which is produced in the hot forming process of the bed and other components. Because the high precision machining accuracy of the machine tool needs to reach micron or even nanometer level, the deformation error caused by the internal stress in the casting is unacceptable, so the machine tool needs to release the stress.
In short, the related components of the machine tool will produce stress during the hot processing, which will lead to certain deformation of the components, and this deformation will affect the accuracy of the machine tool, so the higher the precision of the machine tool, the more need to release the stress, so as to ensure the accuracy and stability of the machine tool.
▌ How long does it take to release the stress of the machine tool?
In order to release the stress, some machine tool manufacturers will sink the castings into the sea or bury them in the ground. This method is called natural aging.
How long will the stress of machine tool be released?
When searching for information on the Internet, people are dazzled by all kinds of answers, ranging from a few months to seven or eight years old. After consulting some professional papers, the answer is that according to the different metal components, and considering the volume, shape and other factors, the stress release will take several months to several years.
▌ How to release stress?
After months to years of wind and sun exposure and seasonal temperature changes, the components are repeatedly subjected to repeated temperature stress, resulting in relaxation of residual stress and stable dimensional accuracy
Vibratory stress relief
Through vibration, a small amount of plastic deformation occurs in the material, so that the internal stress of the material is relaxed and reduced, which can be divided into sub resonance aging, modal broadband aging, spectrum harmonic aging and spectrum harmonic positioning aging
Thermal aging is to put the workpiece into the thermal aging furnace for heat treatment, slowly and evenly heat it from room temperature to about 550 ℃, keep it for 8 hours, and then strictly control the cooling rate to below 150 ℃
Due to the disadvantages of high time cost and wide land occupation, natural aging is adopted less and less by manufacturers. With the progress of technology, there are more and more methods to release stress, and the time is shorter and shorter.
Generally speaking, high-precision machine tools will use marble and other materials that are not easy to produce stress to make the bed. And the machine tools using metal materials will also use shot peening, vibration, rolling and other methods to remove stress.
Shot peening is to bombard the surface of workpiece and implant residual compressive stress; Vibration is to eliminate stress by resonance between vibrator and workpiece; Rolling is through some rolling tools to apply pressure to the surface of the workpiece to achieve the purpose of stress relief.
In addition, the stress can be eliminated by thermal aging, explosion, thermal shock aging and acoustic aging.
Compared with the above mentioned aging methods, VSR is more suitable for stress release of machine tools. Vibratory stress relief (VSR) is to eliminate or homogenize the residual stress of metal structure after casting, forging, welding and cutting. It transfers energy to the workpiece by applying a certain magnitude and frequency exciting force to the workpiece, which makes the workpiece produce micro or macro plastic strain to homogenize and eliminate the residual stress.