Spline shafts are the most common slender shaft parts in various machine tools. During the operation of the machine tool, the spline shaft has to bear huge friction, so it wears out quickly. In order to meet the needs of work, many manufacturers use ultrasonic induction heating power to heat treat spline shafts, with good results. Today, we will take the CNC machine tool ball spline shaft as an example to briefly introduce its heat treatment process.
The material of the CNC machine tool ball spline shaft is 55CrMn steel. Heat treatment technical requirements: the arc quenching hardness of the three pairs of raceways is 58-62HRC, and the full-length radial circular runout is ≤0.15mm.
(1) Process flow. The hot-rolled steel blank-normalizing-roughing-stress relief treatment-half finishing-super-audio induction quenching-straightening-low-temperature tempering-fine grinding.
(2) Heat treatment process
1) Normalize the fire. The heating temperature is 800-820℃, the holding time is 2h, and it is cooled in still air. Since the ball spline shaft does not bear much force, normalizing treatment can meet the performance requirements. After normalizing, blanks with radial circular runout >1mm should be cold-pressed and straightened to make their radial circular runout <0.5mm. The blanks that have been straightened by cold pressing must be stress relieved in time.
2) Stress relief treatment. An ultrasonic induction heating power supply is used for stress relief treatment, and the heating temperature is 600-650°C. After stress relief treatment, workpieces with radial circular runout >0.5mm should be cold pressed and straightened, and then stress relief treatment should be performed.
3) Super audio frequency induction quenching. A vertical ultrasonic induction quenching machine tool is used to continuously quench the arcs of the three pairs of raceways. A magnet is installed on the arc surface of the sensor to ensure that the arc surface of the spline shaft is hardened. The sensor is formed by bending a flat pure copper tube. Except for the depth of the hardened layer on the raceway surface ≥1.5mm, other parts should not be heated or hardened as much as possible to reduce the bending distortion of the spline shaft.
The quality of the spline shaft processed by the ultrasonic induction quenching process is easier to control, but due to the special cross-sectional shape of the spline shaft, the inductor is not easy to bend. If the distance between the surface of the spline shaft and the sensor is small, sparks will easily occur and the spline shaft will be burned. On the contrary, if the distance is large, the heat-affected zone will expand and bending distortion will easily occur. In this regard, after bending the sensor, a layer of enamel powder can be sprayed on the surface, melted after heating at 930°C, and solidified on the surface of the sensor after air cooling. After ultrasonic induction quenching, the radial circular runout of the entire length should be controlled to ≤0.15mm.
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GS-ZP-1200
