Why does the product need aging? How to perform aging without aging room?

Conventional communication products need to be aging, especially metal products.     
If it is an active product, it can generate heat by itself, such as a commonly used base station. Nowadays, self-aging is more popular. By turning on the power, it can heat itself for aging without external temperature control.
Aging largely eliminates residual stress. The stress relief we often mention is to eliminate residual stress.

1.What is residual stress?

Residual stress refers to the stress system that exists in the object to maintain self-phase balance when no external force is applied to the object. It is a kind of inherent stress or internal stress.

When the external load is removed, the remaining stress inside the workpiece is the residual stress.

Residual stress is caused by uneven volume changes in the internal structure of the metal. The external factors come from hot working and cold working.

The workpiece with residual stress is in an unstable state, and its internal structure has a strong tendency to return to a stable state without internal stress.

The shape of the workpiece gradually changes (such as warping deformation) and loses its original accuracy. If the workpiece with residual stress is assembled into the machine, the accuracy of the whole machine will be damaged due to its deformation in use.



2. The source of residual stress

The external force deforms the part, and the work done by the external force that causes the plastic deformation is stored in the part due to the deformation of the internal material of the part. When the external force is eliminated, the energy of uneven stress will be released, causing the parts to slowly deform, that is, the residual stress will do work until all the energy is released.

In mechanical manufacturing, various processes often produce residual stress. However, if in essence, the cause of residual stress can be attributed to:

(1) Residual stress caused by machining

(2) Residual stress caused by uneven temperature

There are two main reasons for this kind of residual stress:

The first is local thermoplastic deformation due to uneven temperature;

The second is local plastic deformation due to uneven volume expansion caused by phase change.

(3) Residual stress caused by component dimensional tolerances.

In welding, riveting, and screw connection, there are often tolerance problems. For example, the butt steel plates must be pulled together when the hull sections are butted. These combined structures are pulled together by external forces. When the external forces are removed, the entire system will have residual stress.

This kind of stress is generally a structural stress, and in most cases it is in an elastic state.

3. The influence of residual stress on mechanical parts

(1) Cause changes in the size and shape of objects.

When there is residual stress in a deformed object, the object will produce corresponding elastic deformation or lattice distortion.

If the residual stress disappears or its balance is broken for some reason, the corresponding deformation will also change, causing the size and shape of the object to change.

(2) Shorten the service life of parts.

Because the residual stresses are in balance with each other, when an object with residual stress is loaded, the working stress of some parts of the object is the sum of the stress caused by the external force and the residual stress, and some parts are the difference. This will cause uneven distribution of stress in the object.

At this time, when the working stress reaches the yield strength of the material, the object will undergo plastic deformation; when the fracture strength of the material is reached, the object will fracture, thereby shortening the service life of the part.

(3) Reduce the plasticity and impact toughness of the metal.

When the object with residual stress continues to undergo plastic processing, the existence of the residual stress can strengthen the uneven distribution of stress and deformation in the object, so that the deformation resistance of the metal increases and the plasticity decreases.

(4) Reduce the corrosion resistance and fatigue strength of metals.

Due to the residual stress inside the part, it is in a high-energy state, and it is easy to chemically interact with the oxidizing medium, causing corrosion, that is, stress corrosion, which reduces the corrosion resistance of the part. The residual stress also changes the stress on the surface of the material under load. Distribution, reduce fatigue strength.

4. Measures and methods to reduce and eliminate residual stress

Hammering

Use a steel hammer to hammer the part where the residual stress of the workpiece is concentrated, so that the metal surface of the workpiece that is hammered is subjected to the compressive stress of the hammer, and local plastic deformation occurs, thereby reducing the peak value of the residual stress, improving and equalizing the original residual stress of the workpiece Distribution to avoid brittle damage of the workpiece.

This method is particularly suitable for welding parts, and it is widely used in welding processing occasions, and it is not used much for stamping parts.

Vibration aging

The use of proprietary equipment makes the workpiece resonate under the periodic external force of the special equipment, so that the microstructure grains inside the workpiece slip and intragranular twinning, thereby reducing the peak of residual stress, improving and balancing the original residual stress of the workpiece Distribution.

This method can eliminate about 50% of the residual stress or reduce about 50% of the peak value of the residual stress within one hour. It is one of the most common methods used. It has high processing efficiency and cost saving, but the biggest disadvantage is that it cannot completely eliminate the workpiece. The accumulated residual stress.

Heat treatment aging

It is a traditional method of eliminating residual stress, also known as artificial aging. It uses heat treatment facilities to slowly and uniformly heat the workpiece from room temperature to about 600°C, and keep it at this temperature for 4-8h, then slowly cool the temperature to below 120°C, and then cool it out of the furnace to room temperature.

This method has a very good effect of eliminating residual stress, and the elimination speed is fast and sufficient. It is one of the most practical methods so far.

Natural aging

It is to place the workpiece outdoors, let it be "wind, meal and dew", release and eliminate residual stress during the static process.
This method is not suitable for industrialized mass-produced products.

However, for the key components of high-value and high-precision equipment, artificial aging + natural aging is more common.

Method of stress relief in machining

After cutting, some treatment measures can be taken to adjust the residual stress of the machined surface. Surface strengthening treatment is currently one of the more commonly used methods.

The surface strengthening treatment process is a process in which cold extrusion of the surface of the part causes it to undergo cold plastic deformation, thereby improving its surface hardness and strength, and forming a residual compressive stress on the surface.