A study on influences of some process parameters on cold drawing of ferrous wires

Transcription

1 Indian Journal of Engineering & Materials Sciences Vol. 19, August 2012, pp A study on influences of some process parameters on cold drawing of ferrous wires Cem S Çetinarslan* Department of Mechanical Engineering, Faculty of Engineering and Architecture, Trakya University, Edirne, Turkey Received 21 March 2012; accepted 31 May 2012 Wire drawing process involves pulling metal wire road through a die by means of a tensile force applied to exit side of die. This paper is an experimental study that presents influences of some parameters like deformation (total reduction) ratio and drawing speed on cold drawing of ferrous wires. Wire drawing method is applied to C45, C63, C65 and C70 s for different deformation ratios and different drawing velocities. Subsequently, these process influences are considered by means of tensile and torsion tests. With these investigations, it can be simply observed that the deformation ratio and drawing speed parameters clearly affect tensile and torsion strength (number of twist) of ferrous s. In addition to these observations, from the results of experiments it can be concluded that C content is also effective on tensile and torsion strength of steel wires. ly, tensile strength and twist number values are obtained for C45, C65 and C70 wire as functions of drawing speed and deformation (total reduction) ratio by using the statistical analysis from the experimental data. Keywords: Wire drawing, Deformation (reduction) ratio, Drawing speed, Tensile test, Torsion test Wire drawing has an important role in plastic deformation process. It is a manufacturing method used to reduce the diameter of wires by pulling the wire through a die. In conventional wire drawing operations, the wire road is pulled through a conical aperture called a die to reduce its diameter 1. Generally, wire rod (semi product of wire) is made from plain carbon steel. Ferrous wires are used as a semi product at electrical wiring, ropes (rope wires are usually made of pearlitic iron and they have high-tensile property), cables, structural components, springs, nails, spokes, musical instruments, electrodes and paper clips 2. In general, drawing is known as a cold working process due to the fact that it is performed at a room temperature. Sometimes it may be performed at elevated temperatures for large wires to reduce applied forces. Several studies about wire drawing processes have been carried out. Vega et al. 3 have studied the effect of the process variables such as semi die angle and reduction in area, and the coefficient of friction on the drawing force value. Their results clearly indicate that friction has significant effects on the drawing force which decrease with the decrease of area reduction. The optimum die angle for wire drawing is assumed * cemc@trakya.edu.tr, cemcetinarslan@yahoo.com to be obtained when the plastic strain distribution across the diameter of the wire becomes uniform. Yilmaz 4 investigated the failure of the steel wires that occurred during production or service. On the other hand, Murakawa et al. 5 concluded that the drawing method utilizing the DLC (diamond-like carbon)- coated roller die and the transverse ultrasonicvibration drawing using a DLC-coated bisected die are effective in realizing semidry and dry drawing for aluminium s. With their study, the improvement of surface precision of the drawn wire and reduction of drawing resistance were realized by applying DLC coating to dies. Influence of main process parameters (wire yieldstress S, the cross-sectional area reduction R e and die half angle α) on shape quality and area fraction in round to hexagonal composite wire drawing were investigated by Norasethasopon 6. This study shows the R e and S strongly influence the shape quality however the R e, and S slightly influence change in area fraction of the core. The change in area fraction of core, which equals to zero, was obtained at a value of α and this α value increased as the S increased. Furthermore, it was clearly seen that the R e, and S strongly influenced drawing stress and the R e and S influenced optimal die-half-angle directly, strongly, inversely and respectively. L o and L u present an

2 222 INDIAN J. ENG. MATER. SCI., AUGUST 2012 advanced approach for the design of wire drawing dies based on a prescribed strain-rate variation for strain rate sensitive s. The analysis, incorporating the yield criterion and the velocity field with the die angularity, can give an accurate prediction of the die shape 7. A model has been presented for the prediction of fatigue strength of two different eutectoid steel wires, one of them being zinc coated, used in ropeway applications by Beretta and Boniardi 2. Pass schedule of wire drawing process to prevent delamination for high strength steel cord wire were studied by Lee et al. 8 The applied drawing process reduced the diameter of the wire from to mm, and consisted of nine passes. Languillaume et al. 9 performed tensile tests on heavily cold drawn and annealed pearlitic steel wires, on which wire drawing induced a partial dissolution of the cementite phase. Several studies were performed about torsion test of steel wires and bars. Fragmentation of as-drawn pearlitic steel wires during torsion tests were the ones investigated by Goes et al. 10. The effects of degrees of deformations, ranging from 5 to 30% reductions on the mechanical properties of cold drawn mild steel rods were experimentally investigated by Alawode and Adeyemi 11. In addition to these, influence of torsion deformation on microstructure of cold-drawn pearlitic steel wire was investigated by Mossbauer spectroscopy and the evolution of the pearlitic steel wires microstructure were discussed as a function of applied deformation nature 12. The aim of this paper is to investigate the influences of process parameters (deformation-total reduction-ratio, drawing speed) on the wire properties at wire drawing process. These parameters have a major influence over the properties of cold drawing ferrous wires. Experimental Procedures Wire drawing process Wire rod (raw) s are C45, C63 and C70. Additionally, two different types of C65 were taken from two different industrial companies. Chemical compositions of s are given in Table 1. Firstly, mechanical surface cleaning was applied to remove oxide layer on wires. Following this process orderly chemical pickling, washing, lime bath and drying processes were applied. And then the drawing process is initiated at room temperature. Figure 1 shows the drawing die (matrix) with soap box. Wire firstly passes along the soap box and then Table 1 Chemical composition of wire rod (raw) s Material Diameter %C %Mn %Si %P %S C45 Ø C63 Ø C65-A Ø C65-B Ø C70 Ø Fig. 1 Drawing die with soap box and wire wrapping block

3 CETINARSLAN: COLD DRAWING OF FERROUS WIRES 223 Fig. 2 Drawing die (matrix) (a) pressure die with tip and (b) normal die (matrix) Table 2 Series of dies for each type at drawing process Material C45 C63 - C65 C63 - C65 - C70 C70 Passes number Ø1.30 Ø1.45 dia Ø1.80 dia Ø2.00 Ø2.10 Ø2.20 Ø2.38 Ø through a die (matrix). The reduction of the diameter of a metal rod or wire is acquired by pulling it through a die (Fig. 2). The working region of steel dies is typically conical and made of W carbide. The die angle is 12 and this die is cooled by water as shown at Fig. 1. A series of dies are used to obtain the final wire diameter. Table 2 shows the series of dies in general. Reduction area ratios (A) were determined for a decrease in each diameter by following equation: A = [(D 2 inlet D 2 outlet) / D 2 inlet] 100 (1) Table 2 shows the series of dies. The high-speed drawing of high carbon content steel wires is also usually conducted at room temperature employing a number of passes or reductions through several dies 8. ly, end products are wrapped on a block (Fig. 1). There are some studies in literature about the effect of drawing speed and deformation ratio: The influence of drawing speed on properties of multiphase steel is known as a TRIP (transformation induced plasticity) steel wires 13. Additionally, the effect of total reduction ratio on wire breaks in Cu fine wiredrawing was also studied 14. Considering these works, my study is about the wire drawing process that was carried out at various drawing velocities at the final die and in various deformation-total reduction-ratios to investigate the speed and reduction ratio effects on

4 224 INDIAN J. ENG. MATER. SCI., AUGUST 2012 mechanical specifications of wires. These velocities are related with the end products; namely outlet velocities are at the final die. Preparations for the tests Experiments were carried out by using tensile and torsion test machines at room temperature. C45, C63, C65-A, C65-B and C70 wires (end products) were used as the test s that were subjected to tensile and torsion tests for determining the tensile strengths (N/mm 2 ) and numbers of twist. In order to determine the tensile strength, tensile test equipment which has 3 metric tons capacity with a ram (lower jaw) speed of 10 mm/min was used. Furthermore, the torsion test machine has 0.75 kw power with 1400 rpm. The number of revolutions of a specific length of wire, twisted on its own axis in one direction until rupture, was counted to determine the torsion characteristics of the tested wires 15. Results and Discussion Tensile test results This part of the study is about tensile properties of the wires. These tests were applied to five different wires which were drawn with different drawing velocities and reduction ratios for each group. Different C contents, reduction ratio and passes number are the reasons why distinct drawing velocities applied. Five experiments were carried out and average value of each observed parameters were pointed in diagrams. Reduction ratios were chosen higher for wires that have lower C content due to the fact that increasing C content causes brittleness and thus makes plastic deformation much more difficult. Reducing the carbon content increases ductility, malleability and elongation of steel. However, reducing the carbon content also dramatically reduces ultimate tensile strength of steel. From Fig. 3, it is observed that tensile strength values of C45 specimens increase with increasing drawing speed; moreover, increasing reduction r atio causes an increase in tensile strength. C63 and C65 specimens (A and B type) show similar tendencies with close and reasonable experimental errors which are shown in Figs 4-6. There are reasonable differences in stress values of A and B and therefore it can be easily observed that B values are a bit higher than A. As it can be seen from Table 2, chemical compounds of these s show some differences from each other (in view of % Mn, Si, P and S). Also, it is observed from Fig. 9 that tensile strength values of C70 Fig. 3 Tensile strength values versus drawing speeds for C45 Fig. 5 Tensile strength values versus drawing speeds for C65-A Fig. 4 Tensile strength values versus drawing speeds for C63 Fig. 6 Tensile strength values versus drawing speeds for C65-B

5 CETINARSLAN: COLD DRAWING OF FERROUS WIRES 225 specimens increase with an increasing drawing speed and reduction ratio. In addition to these results, it is understood that difference of C content is effective on tensile strength as it can be seen from Figs 3 to 7. Furthermore, it is observed that the tensile strength of C70 specimens decrease slightly due to relatively lower reduction ratios (lover work hardening). The tensile strength increases gradually as the drawing speed increases and as the reduction ratio goes up 13. It is a known fact that increasing reduction or deformation ratio causes an increase in strain hardening and as a result of this yield stress of s also increases. Strain hardening (workhardening) is the process of making a metal harder and stronger through plastic deformation. When a metal is plastically deformed, dislocations move and additional dislocations are generated. The more dislocations within a, the more they will interact and become pinned or tangled. This will result in a decrease in the mobility of the dislocations and a strengthening of the. Torsion test results This part of the study is about the torsion properties of the wires. These tests were carried out to five groups of wire s which were drawn with different drawing velocities and different reduction ratios for each group. In this test, number of twist of a definite length of wire was counted until rupture. Five experiment tests were carried out and average values are calculated. Reduction ratios were chosen higher for wires which have lower C content since increasing C content causes brittleness and thus make plastic deformation much more difficult. From Fig. 8, it is observed that number of twist of C45 specimen decreases with increasing drawing speed and also we can find out that increasing reduction ratio affects (increases) the torsion strength. C63 specimens show similar tendencies with close and reasonable experimental errors (Fig. 9). Also, it is observed that the number of twist (torsion strength) of C63 specimens decreases slightly for all reduction ratios by increasing drawing speed. C65 specimens (A and B) show similar characteristics shown in Figs 10 and 11. There is a reasonable difference between stress value of A and B. Torsion strength value of C70 specimens shows similar characteristic (Fig. 12). Furthermore, it is observed that the twist number of C70 specimens decreases slightly because of respectively lower reduction ratios. The torsion strength (number of twist) decreases gradually as the drawing speed increases and as the reduction ratio decreases 15. It is a fact that, increasing reduction or deformation ratio causes an increase in strain hardening and as a result of this torsion strength of s increases. As tensile strength, torsion strength is increased with strain deformation too. ly, tensile strength and twist number values were obtained for C45, C65-B and C70 wire as functions of drawing speed and deformation (total reduction) ratio by using the statistical analysis from the experimental data. Regression analysis was performed by employing the non-linear Bivariate Quadratic Regression Method. The resulting equation is also given below for the case of tensile strength and twist number: f(ϑ,r)=a1+a2 ϑ+a3 R+A4 ϑ 2 +A5 R 2 +A6 ϑ R (2) Fig. 7 Tensile strength values versus drawing speeds for C70 Fig. 8 Number of twist values versus drawing speeds for C45 Fig. 9 Number of twist values versus drawing speeds for C63

6 226 INDIAN J. ENG. MATER. SCI., AUGUST 2012 Fig. 10 Number of twist values versus drawing speeds for C65-A Fig. 13 Tensile strength as a function of drawing speed and reduction ratio for C45 Fig. 11 Number of twist values versus drawing speeds for C65-B Fig. 12 Number of twist values versus drawing speeds for C70 Resulting equation is the same for tensile strength and twist number; however, coefficients are different as seen in Table 3. Figures show the variation of tensile strength and number of twist respectively as a function of drawing speed (ϑ) and reduction ratio (R). The increase of drawing speed and also increase of C content deteriorates plasticity properties of wires 13. Hence, lower drawing speeds were used wires that specially contain higher C content according to Figs C65-B wire give especially higher torsion values than C70 wire for same deformation ratios (Ø5.5- Ø2.20) and same drawing speed (9 m/s). High C content hardens a metal, thereby increasing flow stress, ultimate tensile stress, and yield stress and decreasing ductility and torsion strength 15. Fig. 14 Number of twist as a function of drawing speed and reduction ratio for C45 Fig. 15 Tensile strength as a function of drawing speed and reduction ratio for C65-B

7 CETINARSLAN: COLD DRAWING OF FERROUS WIRES 227 Table 3 Coefficient values for Eq. (2) C45 C65 C70 Coefficient Tensıle Twıst Tensıle Twıst Tensıle Twıst A A A A A A Fig. 16 Number of twist as a function of drawing speed and reduction ratio for C65-B Fig. 17 Tensile strength as a function of drawing speed and reduction ratio for C70 Conclusions The wire drawing process of steel wires has been studied experimentally. This study assists to the knowledge of some processes that affect tensile and torsion properties of drawn-steel wires which Fig. 18 Number of twist as a function of drawing speed and reduction ratio for C70 occurred during cold drawing process. Moreover, process parameters (deformation-total reduction-ratio, drawing speed) that have major influences on the wire drawing for five types of ferrous wire s are investigated. The following conclusion can be drawn from this study: (i) Drawing speed has a remarkable effect on mechanical properties (tensile and torsion strength) of wires 15. (ii) The experiments have shown that the tensile and torsion strength increase when reduction (deformation) ratio are increased. High reduction ratio causes maximum tensile strength and twist number (torsion strength) because of work (strain) hardening. Considerable difference at tensile strength and twist number (torsion strength) obtains by difference of considerable reduction ratios. (iii) C content is also effects tensile and torsion strength of steel wires but this effect is not as much as the drawing speed and reduction

8 228 INDIAN J. ENG. MATER. SCI., AUGUST 2012 ratio from the viewpoint of plastic deformation. It is well known that low carbon content produces better plastic deformation characteristics in drawing of steels. Higher reduction ratios were applied on C45 due to its lower C content, namely its ductility. Since higher C content causes brittleness which makes plastic deformation much more difficult, lower reduction ratios were chosen for wires that have higher C content. Maximum twist number (approximately twist of 68) and maximum reduction ratio (Ø5.50- Ø1.30) were obtained at minimum C content (C45). (iv) Regression analysis was performed by employing the non-linear Bivariate Quadratic Regression Method. Tensile strength and twist number values were obtained for C45, C65 and C70 wire as functions of drawing speed and deformation (total reduction) ratio. Acknowledgement The author would like to thank Mr. Uğur UZ for his help in experimental work and he is grateful to the Yilmar Steel Wire and Spring Company Bursa, Turkey, for the technical support in experimental processes. References 1 Tiernan P & Hillery M T, J Mater Process Technol, 10 (2008) Beretta S & Boniardi M, Int J Fatigue, 21 (1999) Vega G, Haddi A & Imad A, Mater Des, 30 (2009) Yilmaz M, J Mater Process Technol, 171 (2006) Murakawa M, Jin M & Hayashi M, Surf Coat Technol, (2004) Norasethasopon S, J Mater Process Technol, 203 (2008) Lo S-W & Lu Y-H, J Mater Process Technol, 123 (2002) Lee S K & Ko D C, Kim B M, Mater Des, 30, (2009) Languillaume J, Kapelski G & Baudelet B, Mater Lett, 33, (1997) Goes B, Martín-Meizoso A, Gil-Sevillano J, Lefever I & Aernoudt E, Eng Fract Mech, 60 (1998) Alawode A J & Adeyemi M B, J Mater Process Technol, 160(2) (2005) Cordier-Robert C, Forfert B, Bolle B, Fundenberger J-J & Tidu A, J Mater Sci, 43 (2008) Suliga M, Muskalski Z & Wiewiórowska S, J Achieve Mater Manuf Eng, 26(2) (2008) Cho H, Jo H-H, Lee S-G, Kim B-M & Kim Y-J, J Mater Process Technol, (2002) Su Y-Y & Shemenski R M, Mater Des, 31 (2010)