Abstract: The special dieless drawing technique and the mathematical model of dieless drawing speed for big inch tapered square pipes were established. The key processing parameters were determined based on our systematically researching and analyzing on the deformation mechanism of dielss drawing for big inch tapered square pipes. The dieless drawing technique and equipments were simple and for the tapered square pipe dieless forming， one dieless production procedure can replace all the forming procedure in the general. It completed the deformation heat treatment simultaneously during the dieless drawing process， which enhanced the overall performance of the products. The method is suitable especially for the variable section pipes with high strength， high friction and low plasticity. The experimental study showed that ideal tapered square pipes can be drawn by the dieless drawing technique and the size precision and surface quality of products are super compared with the bend welded steel pipes. The relative errors of tapered square pipes between the model calculation results and the experiment results are less than 78%， which indicated that the dieless drawing technique is with great practical value.

Key words: big inch tapered square pipes, dieless drawing, special forming methods, technique parameters, drawing speed mathematical models