Differential temperature push bending method and device for tube with small bending radius

A method for achieving differential temperature push bending for tube with small bending radius using a device comprising:

• a push bending die, cores, a filler and pushers, wherein the cores and the filler are both arranged in a curved bending chamber of the push bending die, an inlet of the push bending die is provided with a front guiding sleeve, an outlet end of the push bending die is provided with a rear guiding sleeve, an end of at an outer side of the bending chamber of the push bending die is provided with a heating rod, an end at an inner side of the curved bending chamber of the push bending die is provided with a cooling water channel, a first thermocouple is disposed near the heating rod, a second thermocouple is disposed near the cooling water channel, a first pusher in the front guiding sleeve abuts against the filler, and a second pusher in the rear guide sleeve abuts against the cores, the method comprising the steps of:
• step 1:
• blanking a tube blank, a length of the tube blank being larger than πD, chamfering a front end at a curved inner side of the tube blank at an oblique angle of 30° to 45°, chamfering a rear end of the curved inner side of the tube blank that is in contact with the first pusher at an oblique angle of 45° to 60°, then cutting and flattening a slope of a pushed end of the tube blank along a center line of the tube blank, and finally deburring two ends of the tube blank and cleaning the inner and outer sides of the tube blank;
• step 2:
• applying a lubricant to the tube blank, the lubricant being a high temperature resistant lubricant;
• step 3:
• filling the filler having a hardness of 80 to 85 A Shore hardness inside the pushed end of the tube blank, the filler being rubber cylindrical blocks, each of the rubber cylindrical blocks having a diameter that is 2 mm smaller than an inner diameter of the tube blank;
• step 4:
• energizing the heating rod, the heating rod heating the push bending die to a set temperature and keeping a temperature after heating constant, the set temperature being 200-400° C., and a variance of the temperature after heating being less than 2° C.;
• a deformation temperature of the tube blank being increased, so that a plasticity of an outer tube structure during a bending process is improved;
• step 5:
• injecting cooling water into the cooling water channel provided in the push bending die, heat inside the push bending die being taken away by a flow of the cooling water to lower a temperature inside the push bending die, and an initial water temperature of the cooling water being room temperature;
• step 6:
• after the first thermocouple and the second thermocouple detecting a differential temperature between an inner side and an outer side of the push bending die is 100-300° C., placing the tube blank in the push bending die, ensuring that the pushers and the cores are fixed in an initial position, increasing a thrust on a top of the core, providing an internal pressure in the tube blank by the fillers, forcing a material of the tube blank to flow towards a front groove, the tube blank moving forward at a constant speed by the thrust of the pusher, while the cores moving backwards, thus gradually completing the bending of tube blank with small bending radius for the tube blank;
• step 7:
• after the bending being completed, removing the lubricant on a surface of the tube blank.