Research on spinning temperature control of thin walled tungsten tube
Tungsten has unique characteristics, which is an important material for high temperature heating body and high temperature heat insulation. Its brittleness brings great difficulties to its deep processing, especially in the spinning thinning process of P / M tungsten tube blank under multi-directional force, even if the tube blank with good deformation performance can be produced. Due to some improper process factors, tube billets with a deformation rate of more than 70% will be cracked during spinning. Aiming at the qualified billets with good spinnability, the temperature control problem in spinning process is mainly studied, and the solutions are put forward. The high temperature spinning of tungsten tube is successfully realized and improved.
1、Spinning method
The spinning test was carried out on 12t four column vertical three wheel spinning machine. The core die speed was n=145 r/min, feed ratio f = 0.5-0.7min/r, and the pass processing rate was 15% - 28%. The processing temperature was blank opening, 1000-1200°C close to the finished product 600-700°C, and the heating condition was 2 heating guns with oxygen and acetylene flame.
2、Influence of tube geometry design on temperature spinning
The geometric design of tube blank is one of the important factors for successful spinning of P / M tungsten tube. In the past, only sintering cost and spinning loss were considered, so the tube blank length was designed by the maximum multiple scale limit. In this experiment, two different lengths of tube blank, 55mm X 84.5mm X 1200mm and 55mm X 84.5mm X 1100 mm in diameter, were designed and compared, Results when the processing rate of L = 200 mm was 32% in the fourth pass, cracks appeared on the surface, and many micro cracks were found on the inner wall after demoulding. This situation was found in the repeated two branch billets, while the tube with L = 100 mm was successfully spun to the outer 55mm x 80.38mm x L250 mm, When spinning to the lower part, the surface of the deformation zone appears to be warm enough. In fact, the overall temperature, especially the core sticking temperature of the inner wall of the tube blank, fails to meet the required processing temperature requirements, resulting in microcracks on the inner wall of the tube, When the tube is spun to 30% ~ 40% thinning rate, the crack will not appear on the outer surface, but if the spinning continues, the inner wall crack will seriously damage the mandrel, and the gap between the inner diameter of the tube blank and the mandrel will also affect the control of the blooming temperature, The surface temperature of the first pass of tube billet preheating does not reflect the overall temperature of the mandrel and the tube blank. After the tube is taped to the core, it is lower than the deformation temperature required by the tube blank. If the internal and external temperatures can not reach the deformation temperature, the whole pipe will be broken after the first spinning. In order to prevent this, except that the inner diameter gap should not be greater than 0.8 mm during the forming of the tube blank, cracks will occur, The length of tube blank is designed according to the above mentioned, in order to control the temperature and smooth the bloom.
