How to Reduce The Deformation of Heat Treatment Process
The heat treatment process is an important means to obtain excellent performance of various metal materials. Sometime, reasonable choice material and various machining processes can’t meet the requirements of the mechanical properties, physical properties and chemical properties of metal parts. At this time, the heat treatment process is crucial to them.
Even though the heat treatment process has so many advantages, but it also inevitably produces more or less deformation in the machining process, and this is must be avoided in mechanical processing. But how to balance and maintain these two relationships? Today, we will introduce 4 ways to reduce the deformation of heat treatment as much as possible.
Below are main points to reduce and avoid deformation of heat treatment process
Temperature measurement and control
In fact, there are many forms of heat treatment process applied in industry, and their basic processes are the thermal processes which are composed of three stages: heating, heat preservation and cooling. In the whole heat treatment process, we need to use all kinds of heating furnace, since metal heat treatment was done in the heating furnace. (such as annealing, quenching and tempering etc). Therefore, temperature measurement is an important parameter measurement of heat treatment. If the temperature measurement is not accurate, the heat treatment process specification can’t be implemented correctly, resulting in the product quality decline or even scrapped. So temperature measurement and control are crucial to the heat-treatment process and also the key factor affecting the deformation.
Reasonable cooling method
After metal quenching, the cooling process is also important to factor affection to the deformation of metal parts. Hot oil quenching deformation is small than a cold one, so generally temperature control in the 100+/-20 ℃. The cooling capacity of oil is also critical to deformation. In addition to this, the stirring method and speed of quenching will also affect the deformation. When metal heat treatment cools faster, the more uneven the cooling, the greater the stress, and the greater the deformation of the die. Of course, we can use the pre-cooling method to reduce the deformation on the premise of ensuring the hardness of the mold; and we also can use fractional cooling quenching to reduce the thermal stress and tissue stress of metal to reduce the deformation. For many high degrees of complexity or precision workpiece, using isothermal quenching can significantly reduce the deformation of metal parts.
Reasonable the structure of metal
- After metal heat treatment, the thin part is always cold fast than the thick one in the cooling process. In the case of meeting the actual production needs, the thickness of the workpiece should be minimized and the section of the parts should be uniform, so as to reduce the distortion and cracking tendency of the stress concentration in the transition zone.
- The workpiece should keep the structure symmetry with the material composition and organization to reduce the deformation caused by the uneven cooling
- The workpiece should avoid sharp cornets, groove and so on, and the round angle transition should be made at the thickness of the workpiece and the steps.
- Minimize the structural asymmetry of holes and grooves in the workpiece.
Reasonable clamping way and fixture
In order to make uniform cooling of the heating workpiece, as usual, we need to choose a reasonable clamping way and fixture to reduce the uneven thermal stress and organizational stress, thus to reduce the deformation of metal parts.
When the heat treatment is the final process of the workpiece process, the allowable value of the heat treatment distortion should meet the size of the workpiece specified in the drawings, and the distortion quantity shall be determined according to the machining dimension. Therefore, we should pre-modification of the size according to the distortion rule of the workpiece, so the heat treatment distortion is within the qualified range.
When heat treatment is an intermediate process of the workpiece process, the processing allowance before heat treatment should be regarded as the sum of machining allowance and heat treatment distortion. Usually, machining allowance is easy to determine, heat treatment due to the influence factors are more & complex, so for machining to set aside enough machining allowance, the other all can be used as heat treatment distortion quantity is allowed. The machining after heat treatment, we can use the anti-deformation, shrinkage end bulking hole to improve the deformation pass rate after quenching according to the deformation rule of the workpiece.
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