There is a set of guide blocks on the independent walking platform of the CNC double-column vertical lathe. The end and end of the guide blocks are connected in a straight line and connected to the column, which is equivalent to two rolling guide rails. The walking platform is raised or lowered by rolling the rollers along the guide blocks. The guide block is made of 45 steel, and the hardness of the two rolling surfaces of the guide block is required to be 52-57HRC. For this purpose, a medium frequency heating furnace is used for quenching heat treatment. However, affected by various factors, the guide block is prone to distortion and cracking defects. Today, this article will briefly tell you about the causes and preventive measures of distortion and cracking defects.
(1) Problems with distortion and cracking of guide blocks (rolling guide rails)
1) Since the 12 countersunk holes in the original design are only 5mm away from the side, if these holes are processed before quenching, stress distortion will increase and even cracking will occur; when reprocessed after quenching, the surface hardness of the counterbore will increase and Difficult to process.
2) Both ends and sides of the quenching surface of the guide block form right angles. During quenching and heating, it is easy to overheat and cause cracking, melting, and distortion. The combined guide rail is a rolling guide rail, and no gaps or soft materials with low hardness are allowed between the guide rails district.
(2) Process flow. Forging, normalizing, straightening, stress relief, machining, medium frequency induction quenching, straightening and tempering.
(3) Heat treatment process
1) Normalizing, straightening, and stress relief. Normalizing treatment is performed after forging to refine the grain structure, increase the dimensional stability of the workpiece, and reduce distortion and cracking tendencies in subsequent medium-frequency induction quenching. For forgings with bending distortion >2mm after normalizing, straighten to ≤2mm, and stress relief treatment is required after straightening.
2) Medium frequency induction hardening specifications
①Preparation work. Prepare the flat sensor, contour block, and flat quenching sample, start the equipment, adjust the sensor water spray pressure to make the water spray uniform, and control the water pressure at 0.2MPa.
②Debugging. According to the quenching area of the workpiece and the equipment capacity, the length of the inductor can be improved to perform induction quenching on the surfaces of 2 or 3 workpieces at the same time. Adjust the output voltage, current, moving speed, gap between the sensor and the workpiece and other parameters on the profiling test block to meet the quenching needs.
③Quenching. Since both sides of the workpiece are not chamfered, align the workpiece and mark it, adjust the gap between the sensor and the workpiece, use a wooden pad to raise the sensor by 2mm at the starting point, and move it 2mm to the right. The sensor does not heat the sharp corners, but heats 2mm next to the sharp corners. Use heat transfer to heat the sharp corners to the quenching temperature, pull out the wooden pad, and the sensor will restore the original adjustment gap. At this time, water can be sprayed for cooling, and the equipment can be started for continuous quenching. When the preheating circle has passed the terminal, stop the induction heating. At this time, the terminal temperature has been heated to 860-880°C. Continue to walk and spray water to complete the end quenching.
3) Turn over the workpiece, align it according to the mark, repeat the above process, and complete the quenching on the other side.
4) Tempering. The heating temperature is 200°C.
(4) Inspection results
The hardness of the two rolling surfaces of the guide block is 53-55HRC, there are no cracks or burns at the sharp corners, there is no quenching soft zone, and the distortion also meets the requirements.
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GS-ZP-1200
