There has always been a saying in the machine tool industry that machine tools need to undergo stress release. The higher the precision of the machine tool, the more attention must be paid to stress relief.
But why is stress release necessary?
How long does it take to release stress, and what is the process for achieving it?
Don’t worry about these questions related to machine tool stress – all you need to do is read this article carefully.
What is stress?
When an object is deformed due to external factors such as force, humidity, or changes in temperature, internal forces are generated. These forces interact between various parts of the object to resist the effects of the external factor and attempt to restore the object from its deformed position to its original position before the deformation occurred.
The stresses generated during the thermoforming process of the bed and other components of the machine are known as mechanical stresses, which need to be released.
The machine requires high precision, with micron or even nanometer accuracy, and any deformation error caused by internal stress in the casting is unacceptable. Hence, stress relief is necessary.
In simple terms, during thermal machining, stresses are generated in the relevant components of the machine, which can result in deformations that may negatively impact the machine’s accuracy.
Therefore, the more precise the machine, the greater the need for stress relief to ensure its accuracy and stability.
How long does it take for a machine to be released from stress?
As we all know, machines are generally used to alleviate stress through stationary means.
I have heard that in the past, some machine tool manufacturers would submerge or bury castings at the bottom of the sea to fully relieve stress. However, this statement cannot be quantified and is for reference only.
The duration required to release machine stress varies greatly, as there are a plethora of answers available online, ranging from a few months to as long as seven or eight years.
After consulting some professional papers, my conclusion is that the duration of stress relief depends on various factors such as the metal components, volume, shape, and other factors. It can range from several months to several years.
It is important to note that the stress relief environment should be chosen based on the specific conditions of the component. The best results are typically achieved in controlled environments and not outdoors or in extreme conditions.
With the advancement of technology, there are now various methods of stress relief available that are quicker and more efficient than traditional methods.
How to release stress?
As mentioned earlier, immobilization used to be a method for stress release. However, this approach is now becoming less common due to its time-consuming and expensive nature for machine tool manufacturers.
Thanks to technological advancements, there are now numerous stress release methods that are faster and more cost-effective.
It’s worth noting that stress release is typically performed before assembly. After assembly, the entire machine is typically left standing for around 10 to 20 days, as instructed by the manufacturer, to complete the process.
We will discuss specific stress release methods shortly.
High-precision machine tools are typically made of materials such as marble that are not susceptible to stress. However, even machines that use metal materials now utilize methods such as shot blasting, vibration, and rolling to remove stress.
Shot blasting involves blasting the surface of the workpiece with pellets, thereby implanting residual compressive stress. Vibration eliminates stress through resonance between the vibrator and workpiece, while rolling removes stress by applying pressure to the surface of the workpiece using a number of rolling tools.
In addition to these methods, stress can also be eliminated through thermal aging, explosion, thermal shock aging, acoustic aging, and various other techniques. Of these aging methods, vibration aging is considered the most suitable for stress relief in machine tools.
Vibration aging involves using mechanical resonance methods to eliminate or equalize the residual stresses generated by the metal structure after casting, forging, welding, and cutting during mechanical processing. It transfers energy to the workpiece by exerting an excitation force of a certain size and frequency, causing the workpiece to undergo micro or macro plastic strain to homogenize and eliminate residual stress.