Why do machine tool castings need aging treatment?

Aging treatment of machine tool castings is an important part of the casting process. It aims to eliminate the residual stress inside the castings through a series of measures, stabilize their size and structure, and thus improve the mechanical properties and service life of the castings. The following is a detailed analysis of aging treatment of machine tool castings:

1. Purpose of aging treatment

1. Eliminate residual stress：During the cooling process of castings, thermal stress and structural stress will be generated due to the uneven cooling speed of different parts. Aging treatment can release or homogenize these stresses through natural or artificial methods to avoid deformation or cracking of castings during use.
2. Stable size and organization: Aging treatment can cause subtle changes in the internal structure of the casting, such as grain refinement, phase change, etc., thereby improving the dimensional stability and organizational uniformity of the casting.
3. Improve mechanical properties: Through aging treatment, the strength, hardness, toughness and other mechanical properties of castings can be significantly improved to meet higher usage requirements.

2. Methods of aging treatment

1. Natural aging:
   • Definition: Place the casting in a natural environment, and gradually release the residual stress inside the casting through temperature fluctuations such as day and night temperature differences and seasonal changes.
   • Features: It takes a long time, but the cost is low, and it is suitable for occasions where time is not a big requirement.
2. Artificial aging:
   • Definition: By artificially controlling the heating temperature, holding time and other conditions, the release of residual stress inside the casting and the transformation of the organizational structure can be accelerated.
   • Classification:
     • Heat aging: Put the casting into the heating furnace, heat it to a certain temperature and keep it warm for a period of time, and then cool it with the furnace. This method can significantly shorten the aging cycle, but attention needs to be paid to controlling the heating temperature and holding time to avoid cracks or deformation of the casting.
     • Vibration Stress Relief：Use vibration equipment to apply a certain frequency of vibration to the casting, so that the residual stress inside the casting can be released during the vibration process. This method does not require heating, has a short cycle and high efficiency.

3. Precautions for aging treatment

1. Preprocessing: Before aging treatment, the casting needs to be cleaned, detoxified and preheated to ensure that the surface of the casting is clean and internal impurities are removed.
2. Control conditions: For artificial aging treatment, conditions such as heating temperature, holding time and cooling speed must be strictly controlled to obtain the ideal aging effect.
3. Deformation calibration：After aging treatment, the casting may be deformed to a certain extent. Therefore, a calibration process is required to restore the casting to the size and shape required by the design.
4. Quality Check: After the aging treatment is completed, the casting needs to be inspected for quality to ensure that it meets the design requirements and usage standards.