Haroldo Béria Campos

Influence of die semi-angle on mechanical properties of single and multiple pass drawn copper☆

Abstract Drawing is a metalworking process widely used in the manufacturing of cold worked bars, rod and wire. An important characteristic of the process is the die semi-angle (α), which influences the drawing forces, the lubrication in the process and also the mechanical properties of the final product. In this investigation, an experimental program was carried out in order to evaluate the influence of die semi-angle on the mechanical properties of round section annealed copper bars. Single passes involved drawings through dies with semi-angle of 1,23; 5; 10 and 24,5 deg. Molykote paste was used as lubricant and reductions in area were in the range of 2 to 31 %. In multiple passes total reduction of area was kept at a constant value of 30%, produced by two different drawing sequences: a first pass of 5% and a second pass of 25%; a first pass of 25% and a second pass of 5%. In both cases, the die semi-angle in the first pass was 4 deg. In the second pass the die semi-angle varied between 6 and 12 deg (First sequence), and 2 and 10 deg (second sequence). After drawing the samples were submitted to tensile testing in order to evaluate mechanical properties. The values of yield strength and ultimate tensile strength increase with increasing die semi-angle, while the values of percentage elongation decrease as α increases. For multiple passes, it was observed that die semi-angle in the second pass does not influence the values of yield strength, ultimate tensile strength and percentage elongation as markedly as it was observed in single pass drawing.

The influence of die semi-angle and of the coefficient of friction on the uniform tensile elongation of drawn copper bars

Abstract Cold drawing of bars leads to changes in the mechanical properties of the products. An increase in strength and a loss of ductility are usually observed. The tensile elongation for example, decreases as greater reductions in area in drawing are considered. Previous researche has shown that this is basically associated with a reduction in tensile uniform elongation. The present paper discusses the effect of die semi-angle and of the coefficient of friction on the decrease of this uniform elongation. It is shown that friction has no influence on the elongation, which is basically a function of die semi-angle and reduction in area.

Effect of reverse and cyclic shear on the work-hardening of AISI 430 stainless steel

Sheet metal forming commonly involves various processing steps leading to complex strain paths. The work hardening of the metal under these circumstances is different from that observed for monotonic straining. The effect of the strain path on the hardening of materials is usually studied through sequences of standard mechanical tests, and the shear test is especially well adapted to such studies in sheet forming. Shear straining covering Bauschinger and cyclic strain paths were used in the analysis of the hardening of AISI 430 stainless steel sheets. The tests were conducted at 0°RD, 45°RD, and 90°RD (Rolling Direction) and for three effective strain amplitudes. The results indicate that the material presents Bauschinger effects and strain hardening transients that are sensitive to the testing direction. In addition, the cyclic straining leads to an oscillating stress pattern for the forward and reverse shearing cycles, which depends on the deformation amplitude.

Effect of the Thermo-Mechanical Processing Characteristics on the Recrystallization of CuZn34 Brass

The effect of the temperature and the annealing time on the recrystallization characteristics of metals has been widely researched. However, the influence of the deformation history (involving changes in the strain path) on the recrystallization of metals is seldom studied. The aim of this paper was to investigate the effect of the mechanical loading sequence (monotonic and Bauschinger shearing tests), the amount of forward (effective strain of 0.10, 0.20, and 0.30) and reverse strain (effective strain of −0.35, −0.45, and −0.55), and the initial state (as-received and annealed) on the recrystallization kinetics of CuZn34 brass sheets. The softening caused by recrystallization is reduced as the forward and reverse strains applied during the Bauschinger shear tests are increased. For all investigated conditions, the data also revealed that the initial state and the amount of the reverse strain were the main variables on the recrystallization kinetics of CuZn34 brass.

Análise da formação de bandas de cisalhamento por meio de corpos-de-prova de tração especiais

The present study had as main purpose to analyze the formation of shear bands in metallic sheets of low-carbon steel (SAE 1006) submitted to uniaxial tension test. This verifi cation has been made through numerical analysis using the software Deform2D, and the performance of physical tests with the tension’s test specimen being notched with varied geometries. The fl ow curve and the anisotropy of the material used for the realization of numerical simulation have been designed. After this simulation, band formation analysis was performed using varios steps for each sample, and compared with the test specimen of the same formation with different geometrical notches. Finally, it was verifi ed that both the shear band formation and the fracture characteristics of the studied material are directly related with the geometrical shape of the notch.

Evaluation of the Work-Hardening of Brass Sheets Following Strain Path Changes

The strain paths followed by metals during sheet forming can be quite complex, especially when successive forming steps are involved. The work hardening of metals associated with these strain paths differs from that caused only by monotonic straining, such as simple tension or compression. It is important to have an adequate description of the work hardening of the material under processing, especially when numerical simulations of the forming are used. The experimental evaluation of the effect of strain path changes on the material work hardening is usually performed through tensile testing following the strain path changes. This technique, however, demands complex machining operations of the formed sheets and the imposed strain is severely limited by impending necking. The present paper utilizes simple shear as a tool for the determination of the work hardening of CuZn34 brass sheets following various strain path changes associated with combinations of different modes of deformation such as rolling, tension, cyclic and forward shears. The results indicate that the cyclic shearing delays the occurrence of plastic instabilities for brass previously tensioned, occurring the opposite for final monotonic shearing. These phenomena were correlated with the probable microstructural evolution of the CuZn34 brass.

The Evolution of Transversal Surface Defects in the Axisymmetric Drawing of Copper Bars

Surface defects are an inevitable characteristic of the raw material employed in the drawing of copper wires. These defects may cause problems in the processing of the material, both during the drawing down to wires and in the final manufacturing of artifacts with the produced wire. The literature reports few analyses covering the importance of these initial defects, as well as concerning their evolution or eventual healing during the drawing. The present paper presents such an analysis for a 12.7 mm diameter copper bar displaying artificial defects 1mm wide and 0.3mm deep. Low angle drawing led to the almost complete healing of the defect after three drawing passes with a 10% reduction of area each. The use of a high semi-angle die led to a completely different situation, where no such defect healing was observed.