Why Do Machine Tools Need To Relieve Stress?

In the machine tool industry, there's a notion that machines need stress relief, especially high-precision ones. Why is it necessary? How long does it take? Let's delve into these questions.

What is Stress?

When an object deforms due to external factors like force, humidity, or temperature changes, internal forces develop within the object to counteract these factors and restore the object to its original shape.

The stress that machine tools need to release is called mechanical stress, generated during thermal forming. As high-precision machining requires accuracy down to micrometers or nanometers, any deformation caused by internal stress during casting is unacceptable. Therefore, stress relief is essential to ensure machine tool accuracy and stability.

How Long Does Stress Release Take?

Stress in machine tools is typically relieved through static rest, but the duration varies widely. Various sources suggest anywhere from a few months to several years, depending on factors such as the metal component, volume, and shape.

It's crucial to consider the specific environment for stress relief; extreme conditions aren't necessarily the most effective. With advancing technology, methods for stress relief have diversified, reducing the time required.

How to Release Stress?

While static rest was once prevalent, it's now less favored due to its lengthy duration and high cost. Modern methods include shot peening, vibration, and roller pressing. Shot peening involves bombarding the surface with pellets to induce residual compressive stress. Vibration uses resonant frequencies to eliminate stress, while roller pressing applies pressure to the surface.

Additionally, stress can be relieved through techniques like thermal aging, explosive methods, thermal shock aging, and ultrasonic aging.