Welcome to Jiangsu Sai Neng Machinery Technology Co., Ltd. [official website]]
Telephone:0519-88611708 E-mail:sainengjx@163.com
10
2022
-
01
The principle and application of deep cryogenic treatment of molds.
Post-processing of molds, including grinding and electrical machining, generates localized high heat on the processed surface, which can lead to changes in the surface structure of the mold. The formation of primary martensite on the surface increases the brittleness of the mold surface and pits, reducing the mold's fatigue resistance while also decreasing its wear resistance. Excessive grinding and discharge can also lead to surface cracks.
Post-processing of molds, including grinding and electrical processing, generates localized high heat on the processed surface, which leads to changes in the surface structure of the mold. The primary martensite formed on the surface increases the brittleness of the mold surface and pits, reducing the mold's fatigue resistance while also decreasing its wear resistance. Excessive grinding and discharge can also lead to surface cracks.
Quenched austenite cannot completely transform into martensite at room temperature. For example, residual austenite in D2 material cannot transform to 20% after normal quenching, but during tempering below 350°, the amount of residual austenite remains almost unchanged. However, during post-processing and use of molds, such as electrical discharge machining and grinding in high-speed stamping, it is easy for residual austenite to further transform, leading to decreased impact resistance due to the brittleness of primary martensite. Additionally, due to the different volume ratios of martensite and austenite, the instability of residual austenite can lead to reduced hole diameter perpendicularity and loss of WEDM positioning accuracy, resulting in line clamping and changes in mold precision during use and storage.
The influence of residual stress: The residual stress from quenching molds comes from two aspects: one is structural stress caused by martensitic phase transformation; the other is volumetric stress caused by uneven heating and cooling. These two types of residual stress are generally tensile stresses. The presence of residual tensile stress reduces the actual load-bearing capacity of the mold, that is, its fatigue life. The existence of residual stress easily alters the dimensions of molds when subjected to external forces. At the same time, stress redistribution generated during mold processing often makes it difficult to achieve processing precision; in severe cases, it can even cause mold cracking.
Mechanism of deep cryogenic treatment and ultra-deep cryogenic treatment: During quenching, materials transform from austenite to martensite. Due to the larger volume of martensite, it becomes increasingly difficult for austenite to transform into martensite, creating significant compressive stresses within the material that lead to transformation failure. Residual austenite refers to this change at room temperature. The volume of martensite will shrink; if there is a sharp drop in temperature during transformation conditions, its surrounding compressive stresses will decrease, allowing for further transformation of residual austenite—this is the mechanism behind deep cryogenic treatment. Generally speaking, after room temperature quenching, D2 material retains 20% austenite; at -196°, this amount drops to 2-4%, while at -80°, it retains 10%.
The effects of deep cryogenic treatment are as follows: 1. Almost all residual austenite transforms into martensite; thus increasing mold hardness; 2. Residual stress is greatly reduced; 3. Wear resistance improves; 4. Enhances WEDM processing performance by reducing verticality deviation in rough-cut hole diameters with good precision stability—large or thin workpieces can be cut without clamping wires; 5. Linear dimensional changes in molds caused by temperature variations are reduced by two-thirds compared to conventional treatments—beneficial for maintaining high-precision mold dimensions; 6. The service life of stamping notches is significantly extended while reducing overall usage costs for molds.
Mold
Next article
Next article
Contact Us
Address: Xingchen Industrial Park, Hengshanqiao Town, Changzhou City, Jiangsu Province
Telephone:0519-88611708
Fax: 0519-88611508
E-mail:sainengjx@163.com
Website:www.sainengjx.com
Mobile Web