Graphical method for determining of limit and permissible values of drawing and friction coefficients, stress, drawing angle and delta-criterion for shape of plastic deformation zone

The maximum and permissible values of the coefficients of drawing and friction, the Delta criterion of the shape of the deformation center, the index of the deformed state, the angle and drawing stress are determined graphically for different models of hardening and values of the anti-tension stress. For the determination, cartesian graphs were used, on the ordinate axis of which the desired indicators are located, and on the abscissa axis the values of the I.L. Per lin safety factor obtained by varying the extraction coefficient. The permissible values of the drawing coefficient and drawing stress decrease with the growth of the safety factor of I.L. Perlin. The dependence of the limit and permissible values of the Delta criterion for the optimal value of the drawing angle on the deformation parameters and the harden ing model is shown. The maximum and permissible values of the coefficient of friction are higher at the optimal value of the drawing angle. For the first time, the possibility of increasing the limit value of the coefficient of friction from the action of anti-gravity is established. The limit and permissible values of the coefficient of friction decrease with the increase in the value of the coefficient of drawing and increase with the increase in the coefficient of hardening k. Curves for the dependences of the safety factor, the stress state indicator and the absolute safety margin Zap on the value of the drawing angle fix small and large values of the limit drawing angle on the abscissa axis. Small limit values of the drawing angle do not differ significantly in value for different values of the drawing and hardening coefficients, in contrast to large limit values of the angle. The action of counter-gravity increases the small limit angles and decreases the large limit angles. Determination of the limit and permissible values of the coefficients of drawing and friction, the Delta criterion, stress and drawing angle contributes to the rational choice of modes of deformation of the wire (bar).

Effect of deformation hardening intensity, contact friction and back tension on indicators of wire drawing process

Dependences on the hardening factor for the drawing stress, the safety factor of I.L. Perlin and the stress state indicator V.L. Kolmogorov at different values of the drawing angle, coefficient of friction and stress of back tension are presented. For the first time, the nature of the dependences for the limiting and permissible values of delta-criterion is shown for the shape of the deformation zone of round solid profile on the coefficients of friction, hardening and safety factor and the back tension stresses. The limiting and permissible values of the delta-criterion increase from increase in the coefficients of friction and safety factor, the back tension stress and decrease from increase in the hardening coefficient. It is shown that for small values of the criterion ∆ < 1.5, the drawing stress can be higher than the yield point at the die output. As result, the wire material may be destroyed and the drawing process cannot be realized. Assessment of the change degree in the limiting and permissible values of the elongation coefficient and delta-criterion is carried out with increase in the friction coefficient from 0.05 to 0.15, the back tension from 0 to 85 MPa, the safety factor from 1.0 to 1.4, the hardening coefficient from 0 to k.

Deformation Behavior Causing Excessive Thinning of Outer Diameter of Micro Metal Tubes in Hollow Sinking

The deformation behavior of microtubes during hollow sinking was investigated to clarify the mechanism of the excessive thinning of their outer diameters. Stainless-steel, copper, and aluminum alloy tubes were drawn without an inner tool to evaluate the effect of Lankford values on outer diameter reduction. Drawing stress and stress-strain curves were obtained to evaluate the yielding behavior during hollow sinking. The observed yielding behavior indicated that the final outer diameter of the drawn tube was always smaller than the die diameter due to the uniaxial tensile deformation starting from the die approach end even though the drawing stress was in the elastic range. The results of a loading-unloading tensile test demonstrated that the strain remained even after unloading. Therefore, the outer diameter is considered to become smaller than the die diameter during hollow sinking due to microscopic yielding at any Lankford value. Furthermore, the outer diameter becomes smaller than the die diameter as the Lankford value increases, as theorized. As the drawing stress decreases or the apparent elastic modulus of the stress-strain curve increases, the outer diameter seems to approach the die diameter during unloading, which is caused by the elastic recovery outside the microscopic yielding region.

Effect of Drawing Pass on Softening or Plasticizing of Q235 Steel Bar during Electrochemical Cold Drawing

In this work, the effect of drawing pass on the surface layer softening or plasticizing of Q235 steel bar during electrochemical cold drawing (ECD) was studied, as well as cold drawing in air (DIA) for comparison. The results indicate that the softening or plasticizing degree gradually decreases with increasing drawing pass. The reason for this should be that dislocations generated in surface layer are only partially overflowed from the surface in the form of additional dislocation flux. The general dislocation density thereby gradually increases with the increase in drawing pass, resulting in the increase in the work hardening degree of the surface layer, and thus, the drawing stress. In this case, the texture orientation of the bar surface layer is gradually enhanced. In contrast, the dislocation density, and thus the work hardening degree of DIA bar, are higher than those of the ECD partner, resulting in larger drawing stress. ECD can obtain a product with excellent comprehensive mechanical properties compared with DIA, and there are no cracks on the fracture surface of ECD bar drawn for at least seven passes.

Nature of relationship between simple and integrated indicators of stressed state, safety margin and effi ciency of wire forming

The combined criterion, which includes forming effectiveness indicator and the I.L. Perlin’s safety margin is proposed. Interdependencies for different criteria for the shape of the deformation zone are given. Suggested indicators for assessing of the shape of plastic deformation zone are simpler than delta criterion used in the foreing theory of drawing. For different hardening models, the results for the calculation of the axial stress, the absolute safety margin, the I.L. Perlin’s wire safety margin, V.L. Kolmogorov’s stress state indicator stress state indicator and the proposed criteria for assessing of the forming effectiveness when drawing round solid profile depending on the drawing coefficient, drawing angle and criteria for the shape of the plastic deformation zone. In the plastic deformation zone with equal average yield strength, the equality of the strain indicators of the wire is not ensured if hardening curves of material are different. In particular, when the drawing coefficient ensures equal yield strength for different hardening curves and is equal to the initial yield strength, the drawing stress is more at more convex shape of the hardening curve. At the optimum drawging angle, when the minimum axial stress, the maximum values of the safety margin indicators and the proposed criteria for the forming effectiveness and the minimum stress state indicator are observed. Equal minimum values of the drawing stress when varying the drawing angle, the length of the plastic deformation zone or other criteria. The nature of the relationship between the stress state indicators, the safety margin and the forming effectiveness is shown. With different hardening models of lines for the relationship of the I.L. Perlin’s safety margin and V.L. Kolmogorov’s stress state indicator are located along one curve, as are the lines for the relationship between the dimensionless axial stress and the stress state indicator. With the strain parameters, when the drawing stress under the action of back tension is less than this stress in the absence of back tension, the safety margin and the new combined forming effectiveness indicator are more under the action of back tension. This is possible with intensive hardening of the wire material in the draft of drawing, reduced drawing angles and increased values of drawing and friction coefficients. Different values of strain indicators of steel 12Kh18N10T wire after quenching and annealing are shown.

Effect evaluation of back tension on stability of drawing stress of wire blank

The fi rst derivatives of the axial stress of wire drawing are calculated by the coeffi cients of drawing friction and strain hardening. Decrease of the derivatives with increase in back-pull stress is shown, which indicates the feasibility of using back-pull drawing mills to stabilize drawing power and reduce fatigue wear of the dies working surface.

INCREASE OF WIRE STRESS STABILITY DEPENDING ON ANTI-TENSION ACTION WHEN FRICTION COEFFICIENT IS INCONSTANT

The strain parameters instability causes variable axial stress during the drawing process. Contact friction specification varies in the shortest time and depends on many factors: homogeneity physico-mechanical properties of the processed material along the length of the pulled billet, quality of technological lubrication, stability of tension force of the billet at the entrance of deformation center and cooling intensity of the fiber, suction drums, washers, rollers, etc. To estimate the effect of friction coefficient on stability of drawing force (stress), first derivative with respect to friction coefficient in drawing equation is used. The first derivative dependence on drawing coefficient is constructed for different hardening models and deformation parameters. Action of anti-tension was investigated when drawing on stressed state of a circular continuous profile. Studies have been carried out for simulation models of hardening. In the course of study, it was proved that it is possible to estimate instability of stressed state by the first derivative with respect to magnitude, depending on friction coefficient of the equation that determines drawing stress. For different deformation parameters, the first derivative with respect to friction coefficient is calculated for the equation determining axial drawing stress. A decrease in magnitude of the derivative is shown with an increase in anti-tension, which indicates expediency of drawing with antitension to stabilize drawing force and to reduce fatigue wear of dies working surface. Calculations were performed for different values of friction coefficient for drawing under the conditions of presence and absence of drawing cylinder and slope angle of drawing cone to drawing axis, mechanical properties of the billet for drawing, and for various coefficients of its hardening. The stabilizing effect of drawing cylinder of dies on drawing stresses with an increased friction coefficient is shown. Instability of drawing stress from deviation of nominal value of friction coefficient depends on values of other strain parameters. In conditions of drawing cylinder presence and small amount of deformation in drawing path and smaller initial friction coefficient, change in its magnitude has a greater effect on stability of the stressed state. Increase in drawing stress stability positively affects quality of wire, operational stability of units and drawing-line elements, for example, due to decrease in fatigue wear of die working surfaces, drawing drums, bypass and straightening rollers. Drawing with anti-tension and the use of special drawing tools stabilize stress state in deformation zone.

The Analysis of Force Parameters in Drawing Process of High Carbon Steel Wires in Conventional and Hydrodynamic Dies

The paper analyzes force parameters in the process of multistage drawing of steel wires in conventional and hydrodynamic dies. The drawing process of the wire rod with a diameter of 5.5 mm for wires with a diameter of 1.70 mm was performed in 12 drafts with the usage of the multistage drawbench Koch KGT with the speed range of 5-25 m/s.Modern software of multistage drawbenches allows direct reading of many parameters during the drawing process, including drawing power. The force and drawing stress in each drafts were determined relying on experimental measurements. A complement to the research was a theoretical analysis of the drawing process. The results of the theoretical studies were compared to those obtained by experiment.The significant impact of the drawing speed on the force parameters of the drawing process in conventional and hydrodynamic dies was demonstrated. Depending on the real conditions of the drawing, ie. temperature, friction and lubrication, enhancing the drawing speed can result in both an increase and a decrease in drawing stress.

A study of ethylene vinyl alcohol copolymer fiber for the drawing process

This study investigates the effect of the drawing process of ethylene vinyl alcohol (EVOH) fibers on their physical properties. Three different ethylene contents, namely EV-32, EV-38 and EV-44, were used where the ethylene content has the order of EV-44 > EV-38 > EV-32. The result indicates that at the same drawing temperature and draw ratio, the online drawing stress of the fiber with high ethylene content is higher than that with low ethylene content. Moreover, the drawn EVOH fiber, at the drawing temperature of 80℃ and the draw ratio of 2.0, exhibits an optimal mechanical property. As the draw ratio increases, the online drawing stress, birefringence and initial modulus increase. Notably, unlike typical polymeric fibers, the glass transition temperature ( Tg) of the drawn EVOH fibers decreases with the draw ratio due to more water being absorbed by thinner fibers within the same number of samples. The draw ratio was found to have little effect on the melting temperature ( Tm). At the same draw ratio, the online drawing stress, birefringence, stress and initial modulus of the fiber EV-44, which has the highest ethylene content, is higher than those of EV-32 and EV-38. The creep strain of the drawn fibers EV-32 and EV-38 linearly increase with the drawing time when the applied stress maintains constant at 150 MPa, while an insignificant increase is observed for EV-44, suggesting that EV-44 is difficult to deform and has higher size stability. In the stress relaxation test, the elongation increases with the initial stress. At the same elongation percentage, the initial stress of the drawn fibers has the following trend: EV-44 > EV-38 > EV-32 and the stress relaxation time (τ) has the following trend: EV-44 > EV-38 > EV-32, indicating again that EV-44 is relatively difficult to deform during drawing. Finally, EV-44 fiber performed the best in the hot water resistance test.