Apr 01,2026
Time-Time Processing and Size Stability of Molds
Time-Time Processing and Size Stability of Molds
Aging treatment, Dimensional stability, Stress relief, Heat treatment, Precision mold
For precision molds, size stability is one of the core indicators for measuring their quality. After a set of mold is finished manufacturing, if slight size drift occurs over time or with temperature changes, it will directly lead to the loss of product precision, or even mold depreciation. Time-effective processing is precisely the key process performed to eliminate residual stress within the mold and improve size stability.
Where do the residual stresses in the mold come from? Firstly, thermal and tissue stresses generated by uneven cooling during the heat treatment tempering process; secondly, plastic deformation stresses caused by cutting forces during mechanical processing (especially rough processing); and thirdly, thermal and phase transition stresses generated by abrasive processing. These residual stresses are in an imbalanced state inside the mold, and as time passes or temperature fluctuations, they will gradually be released and redistributed, causing the mold to deform at the micron level.
The basic principle of time-effective processing is to accelerate the release and redistribution of residual stress through heating and thermal conservation, thereby stabilizing mold tissues. Time-effective processing can be divided into natural time-effective, artificial time-effective, and deep cold processing, depending on the different processing temperatures.
Natural time effect is the oldest method, placing the mold outside for long periods of time (months or even years), allowing it to slowly release stress under natural temperature changes and vibration effects. This method has stable effects, but the cycle is too long to suit modern production rhythms.
The most commonly used method at present is the artificial time effect. Molds are heated to a certain temperature (usually below a return heat temperature of 30–50°C), kept warm for several hours to dozens of hours, and then slowly cooled. Warming can reduce the yielding strength of the material, making microplastic flow more likely to occur, thereby accelerating stress relaxation. The longer the time of heating, the more thoroughly the stress elimination is achieved. For precision molds, two or even three artificial time effects are usually performed to maximize size stability.
Vibration time effect is an efficient alternative method. By applying a transient load to the mold with an excitator, it generates resonance, which uses the resonance energy to promote the release of internal stress. Vibration time effect has a short processing time (typically 30 minutes to 1 hour), low energy consumption, and does not alter the material‘s gold phase tissue. It is especially suitable for large moldes and parts that are not suitable for heating.
Deep cold treatment (detailed in the previous section) not only stabilizes residual Oluvia but also eliminates some residual stress and improves size stability.
The timing of time-effective processing is equally important. Typically, the first artificial time-effective is performed after rough processing and before fine processing to eliminate the stresses generated by rough processing and thermal processing, laying a stable foundation for fine processing. After fine processing, for extremely precise molds, another cold time-effective can be performed to eliminate the surface stresses generated by fine processing. After electrical discharge machining, decompression is also recommended due to the tension in the discharge layer.
Effective validation of time-effective treatment can be achieved by detecting the size stability of the mold. Time-effective-treated mold is placed in a constant temperature environment, its key sizes are regularly measured, and changes in trends are observed. For high-precision mold, size changes should be controlled at the level of a few microns/year.
Time processing is not just a process, but also a commitment to the quality of the mold. It embodies the mold manufacturer‘s pursuit of long-term reliability. A fully time-treated mold can always maintain its initial accuracy through millions of injection cycles, providing a solid guarantee for customers‘ stable production.
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