HOT LINE: +86-510-80628100The pillar is a key component of the four pillar hydraulic press. The column not only needs to support the upper beam and oil cylinder to withstand working tension, but also plays a guiding role for the slider and bears the lateral load during operation. Therefore, the column components should not only have high dimensional accuracy, but also have high requirements for surface wear resistance.
The four column hydraulic press column is a typical slender shaft component with a length to diameter ratio of 26.2. The machining process of this component is: cutting → rough machining → surface quenching → threading → grinding. In the production and manufacturing process, it is often difficult to precision process qualified products, and sometimes even lead to the scrapping of workpieces.
Control difficulties
A comprehensive analysis of the quality problems that have occurred reveals that the main difficulty lies in the difficulty of effectively controlling the amount of quenching deformation and determining how much precision machining allowance to leave before quenching. In actual production, it is generally adopted to leave a large finishing allowance (up to 3mm) during rough machining. This will result in a large amount of precision machining allowance and high surface hardness of the quenched column, leading to a considerable amount of grinding work, directly affecting the production cycle and generating significant costs. Moreover, most of the hardened layer will be ground away, and the initial design effect will not be achieved.
Deformation analysis
According to the principle of surface quenching, the quenching process of the column is analyzed, and it is found that the main reasons for the large deformation of the column after intermediate frequency quenching are:
(1) Before quenching, during the preparation of the column, due to significant deformation of some raw materials, the workpiece underwent cold correction, but the corrected workpiece did not undergo stress relief treatment;
(2) Due to the relatively large size of the workpiece and the lack of pre heat treatment for tissue preparation, the matrix structure and properties of the workpiece fluctuate greatly, especially for forged steel parts. Insufficient post forging heat treatment results in less removal of the rough machining layer of the workpiece's raw materials, leading to uneven surface tissue composition;
(3) The quenching design is unreasonable. During the quenching process, improper selection of heating equipment and the absence of reasonable process parameters through process experiments can increase thermal deformation.
Solution
(1) During the manufacturing process, cold correction should be minimized as much as possible, and columns that have undergone cold correction should undergo additional stress relief treatment. Fixed procurement channels for raw materials, try to purchase products from large factories to ensure stable quality. Select appropriate heating equipment and conduct process experiments. Based on the technical requirements of raw materials, original structures, and columns, select and formulate reasonable process parameters to reduce thermal factors. During the quenching process, while meeting technical requirements, increase the heating frequency and output power, increase the surface area specific power, reduce the heat penetration depth, and decrease the heat capacity ratio of the workpiece. This will result in the formation of high-pressure stress distribution on the surface of the column after quenching due to the refinement of austenite grains, the fragmentation of fine structures, and the expansion of quenched tissues. This can effectively improve the quenching hardness, enhance the workpiece's resistance to bite wear and fatigue wear, and reduce the tendency for deformation and cracking of the workpiece.
(2) From the above analysis, it can be seen that the factors affecting the quenching deformation of the column are relatively complex, and the quenching deformation is difficult to accurately control. Further analysis of the external structure of the column workpiece reveals that only the middle section of the column requires quenching, while the two ends of the workpiece do not require quenching. Therefore, during rough machining before quenching, the workpiece can be processed into a "dumbbell shaped" shape with coarse ends and fine middle, leaving more machining allowance at both ends. In subsequent machining, the quenched section in the middle of the workpiece can be used as a machining alignment reference to reprocess the center hole. This can reduce the length of the calibration error interval, make the alignment work simpler and easier, greatly improve production efficiency, and do not increase workload. Only the machining amount at both ends is moved from the rough machining process to the precision machining process. This can further ensure the manufacturing qualification rate of the columns.
