The lathe guide rail uses medium frequency induction heating equipment for quenching heat treatment, and the effect is good.

The C6127B lathe guide rail has a total length of 1520mm and the material is HT200. Heat treatment technical requirements: the hardness of the guide rail working surface after quenching is 48.5-56HRC, the depth of the hardened layer is ≥2.5mm, and the maximum distortion of the entire length (concave bend) is ≤0.40mm.

The cast iron bed guide rails used to use the contact resistance heating self-cooling quenching process. During production, it was found that the process performance of the guide rails after heat treatment was unstable, the hardness was uneven, and the distortion was large, making it difficult to meet the technical requirements. In order to solve the problem of guide rail distortion, we switched to medium frequency annealing equipment for quenching heat treatment, and the effect was good.

1) In order to eliminate casting and cold working stress and stabilize the structure to reduce guide rail distortion, thermal aging can be used. Usually the induction quenching distortion of the guide rail is concave in the middle. In order to control the final distortion of the guide rail within a small range, the reverse pre-deformation method is used to make the middle part of the guide rail convex by 0.40-0.50mm after fine planing. At the same time, reverse stress deformation is pre-loaded on the quenching machine tool, that is, the two ends of the guide rail are pressed, and the middle part is used to lift the guide rail, so that the total amount of reverse distortion in the middle part is convex by about 1.Omm. In this way, the entire length of the guide rail is concave ≤0.40mm after quenching, which meets the technical requirements.

2) Since the depth of medium-frequency induction heating reaches 3-6mm, the quenching stress and distortion are large, and cracks are easy to occur. Therefore, the selection and operation of process parameters should be strictly controlled. During induction heating, the induced current generated at the tip of the guide rail should be considered. Since the ring effect and sharp corner effect are strong in the inductor heating, the workpiece is easily overheated due to the concentration of induced current. In this regard, in addition to the profile design of the guide rail section, the general position gap of the sensor is 1.5-2mm, and the gap at the tip of the guide rail is 3-3.5mm, so that the induction heating tends to be uniform on the entire guide rail; the sensor spray The water hole diameter is φ1.5mm, the hole spacing is 4mm, the water spray hole angle is about 45°, and the cooling water temperature is about 50°C. The HT200 guide rail intermediate frequency should be quenched process parameters as shown in the table below.

(3) Effect. After testing, medium frequency induction heating equipment was used for quenching heat treatment. The temperature was (850±10)℃, the hardness of the guide rail was 48.5-50.OHRC, and the hardness after grinding was 54-55.5HRC, which met the technical requirements; the structure after quenching was qualified and the structure It is martensite + retained austenite + graphite + a small amount of cementite phosphorus eutectic, etc., which is equivalent to martensite structure level 4; the depth of the guide rail quenching layer is ≥ 2.5mm; the maximum distortion of the entire length of the guide rail after medium frequency induction quenching ( Concave curve) ≤0.40mm, there are no soft spots or soft belt defects on the guide rail surface, which fully meets the technical requirements of machine tool guide rails.