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A study on cold forging process sequence design of terminal pins for high-voltage capacitors
Journal of Materials Processing Technology 187–188 (2007) 604–608
A study on cold forging process sequence design of terminal pins for high-voltage capacitors H.S. Kim ∗ School of Automotive, Industrial and Mechanical Engineering, Daegu University, 15 Naeri-ri, Jinryang-eub, Gyeongsan-si, Gyeongbuk-do 712-714, Republic of Korea
Abstract A terminal pin, which is a component of high-voltage capacitors, has a plate-shaped head section with a thickness of 0.8 mm. The current manufacturing process, in which the head section is welded on the body section, has yielded substantial deviations in part qualities such as dimensional accuracy, mechanical strength and electrical stability. In this paper, a cold forging process sequence was proposed in order to produce the terminal pin as one piece. The plate-shaped head section requires an upsetting in the lateral direction of a cylindrical billet, which is followed by a blanking process. However, with only designer’s intuition, it is difficult to predict precisely the deformed geometry obtained by the lateral upsetting process since metal flows along axial and lateral directions would occur simultaneously. Therefore, in this study, three dimensional finite element analyses were applied to the lateral upsetting process in order to determine the proper geometry of the initial billet. Once the geometry of the initial billet was determined, intermediate forging sequences were designed by applying the design guidelines of cold forging. Based on the proposed process sequence, a die set was manufactured and cold forging experiments were conducted. © 2006 Elsevier B.V. All rights reserved. Keywords: High-voltage capacitor; Terminal pin; Cold forging process sequence; Lateral upsetting
1. Introduction A high-voltage capacitor, which is one of the core components of electrical appliances generating high-frequency waves, has two or three terminal pins, as shown in Fig. 1. The terminal pin is made of AISI1010, which is a highly ductile material, and plating treatments with Cu-Ni-Sn of 6–12 m thickness are conducted after the forming processes. Although the material is the most suitable for cold forging processes, it is not easy to apply traditional cold forging process sequences due to its geometrical characteristics. As shown in Fig. 1, the terminal pin has a rectangular plate section with a thickness of 0.8 mm, which is indicated as ‘A’, and its geometry is more proper for sheet metal forming rather than cold forging. Therefore, terminal pins have been manufactured by using welding processes between cold forged sections and head. However, qualities of the parts such as dimensional accuracy, mechanical strength and electrical stability have shown substantial deviations according to the quality of the welding processes. As a matter of fact, the defect ratio of the current manufacturing pro-
∗
Tel.: +82 53 850 6683; fax: +82 53 850 6689. E-mail address: [email protected].
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.035
cess has been estimated roughly at 10% due to the imperfections of the welding processes. Moreover, considerable efforts and cost have been required for the welding process, which demands elaborate positioning of two parts and stable welding conditions. Therefore, in this investigation, a new cold forging process sequence to produce a terminal pin as one piece without welding processes was proposed to improve part qualities and process efficiencies. 2. Conceptual design of the process sequence Considering geometrical features, the terminal pin can be divided into four sections: body, neck, connector and head. Geometries of the neck and the connector sections were modified to eliminate welding processes. Assuming an initial billet has cylindrical geometry, which is the most general and economical geometry in cold forging processes, forming directions of the body and the neck sections would be parallel to the longitudinal axis of the cylinder since those sections have axi-symmetrical geometries. On the other hand, forming directions for the head and the connector sections should be perpendicular to the axial direction because the thin flat-shaped head section should be obtained by a side pressing. Therefore, in this paper, we classified the whole process sequence into two stages, preform forging
H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
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directions perpendicular to the longitudinal axis of the initial billet cylinder as shown in Fig. 2(b). More detailed examinations with design guidelines and determination of every dimension of intermediate forging should be conducted since the process sequence shown in Fig. 2 was planned with only the designer’s intuition. Most importantly, the diameter and length of the initial billet should be determined before detailed design of the process sequence. In addition, the head section of the preform, which is indicated as ‘C1’ in Fig. 2(b), should be designed appropriately in order to complete the following processes successfully since it would determine the geometries of the head section formed by the lateral upsetting, indicated as ‘C2’ in Fig. 2(b). 3. Preform geometry design 3.1. Investigation of preform geometry
Fig. 1. Drawing of a terminal pin for cold forging process sequence.
stage and final forging stage, according to the direction of applied forming loads. Fig. 2 shows the schematic diagram of the conceptually designed process sequence obtained by the designer’s experience and intuition [1,2]. As shown in these figures, the body and the neck sections were planned to be formed by a forward extrusion and an upsetting process during the preform forging stage. Once the preform forging stage was completed, the head section would be produced by applying four processes with forming
Fig. 2. Schematic diagram of the conceptually designed process sequence.
The objective of the lateral upsetting is to make the head section of the preform thin and flat-shaped by compressing an initial billet along the side direction so that it makes it possible to apply the following blanking process. In general, one of the most serious defects of the blanking process is a formation of excessive burrs at sheared surfaces, which can damage dies of the following processes and deteriorate the flatness of the head section. Therefore, in this study, a blank holder was installed to the die set in order to suppress the burr formations. However, the blank holder would have little effect on reducing the burr formations unless an adequate amount of area of the preform head section were backed up. Fig. 3 shows the predicted geometries of the head section before and after the blanking process and ‘F’ and ‘G’ indicate the width of the region pressed by a blank holder, defined as blank-held length in this paper. In general, it is recommended that the blank-held length be over 1–1.5 times the thickness of the blank for shearing processes such as blanking or piercing [3,4]. Compared with general sheet metal forming processes, however, width and length of the head section of the terminal pin are relatively small considering the thickness of the head section. Moreover, it was predicted that effects of the blank holding would be reduced since side edges of the blank would have bulged profiles, which are indicated as ‘E1’ and ‘E2’ in Fig. 3. Therefore, in this study, it was decided that the blank-held length
Fig. 3. Predicted geometry of the head section deformed by lateral upsetting process.
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H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
‘E1’ of the terminal pin should be larger than that of general sheet metal parts and the value was set up as two times the thickness of the head section, which was 1.6 mm. In the case of ‘E2’ shown in Fig. 3, it is desirable that the blank-held length should be specified as a larger value since the arc length of ‘E2’ was smaller than that of ‘E1’ and only one side of the head section would be backed up by the blank holder. Therefore, in this study, the blank-held length along the ‘E2’ side was determined as four times the thickness of the head section, which was 3.2 mm. As shown in Fig. 1, width and length of the head section of the final part are 6.3 and 11.0 mm, respectively. Therefore, the width of the head section to be formed by the lateral upsetting process could be calculated as 9.5 mm, the sum of the final head width and the blank-held length of both sides. However, the head length obtained by the blanking process should be decreased from the final dimension since chamfering, which is the next process of the blanking, would elongate the head section. Taking into account the volume constancy of the head section, the elongated length at the chamfering process was calculated as 0.15 mm so that the head length right after the blanking should be 10.85 mm. Therefore, the target length of the head section at the lateral upsetting process should be 14.05 mm, which is the sum of the head length obtained by the blanking process and the blank-held length of ‘E2’ side. 3.2. Finite element analysis of lateral upsetting Three dimensional finite element analyses of the lateral upsetting were conducted in order to determine the proper values of the length and diameter of the initial billet to satisfy the target geometry of the preform. In this study, CAMPform-3D [5], which is a rigid-viscoplastic FEM code, was used for the analysis. Fig. 4 shows the geometrical models of die and billet used for FE analysis and only a quarter model was considered in this study due to the symmetrical characteristics of the process. The friction constant between die and billet was set up as 0.16 considering the lubricating conditions of the phosphate coating with oil and the stress–strain relation of the material, AISI1010, was as follows [2]. σ¯ = 713.1¯ε0.22 (MPa)
(1)
In order to determine the proper head geometry of the preform which can achieve the target dimensions described in the previous section, repeated FE analyses were required with many combinations of the billet diameter and the upset length, indicated as ‘D’ and ‘H’ in Fig. 4. Therefore, the range of initial billet diameters to be considered was narrowed down by applying the design rules of forward extrusion and upsetting. The forward extrusion ratio is defined as Eq. (2) and it is recommended that the value be limited to 75% for AISI1010 [1]. D2 − D2 A 0 − A1 × 100% = 0 2 1 × 100% A0 D0
(2)
where, A0 and A1 are cross-sectional areas and D0 and D1 represent diameters before and after an extrusion process, respectively. Therefore, in this study, the maximum value of the initial billet diameter was calculated as 4.0 mm with the forward extrusion ratio of 75% since the diameter of the extruded body section was 2.0 mm as shown in Fig. 1 and Fig. 2(a). A design rule of upsetting process was employed for determining the minimum value of the initial billet diameter. In general, the maximum value of an upsetting ratio, which is the ratio of diameters after and before an upsetting process, is limited to 2.5 due to the possible occurrence of ductile fractures [1]. As shown in Fig. 2(a), the neck section with a diameter of 7.5 mm would be obtained by an upsetting process so that the minimum value of possible billet diameters was calculated as 3.0 mm. In general, iron mills produce steel coils in diameter increments of 0.1 mm within the previously determined possible billet diameter range of 3.0–4.0 mm. Therefore, 11 diameters such as 3.0, 3.1, 3.2, etc. were selected as candidates for FE analyses. For the upset length, 13 cases were chosen ranging from 8.0 to 14.0 mm with an increment of 0.5 mm. In total, the number of possible combinations to be considered at FE analysis of the lateral upsetting process was 143. By applying several times of CAE analyses with a simple searching method, it was found that an initial billet with diameter of 3.4 mm and upset length of 11.0 mm yielded the most similar deformed geometry to the target. Fig. 5 shows the deformed geometries obtained by three dimensional FE analysis for the final case and the predicted width and length of the head section
Fig. 4. FE analysis model for lateral upsetting process.
H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
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Fig. 5. Deformed geometries obtained by 3D FE analysis with compression ratios of 23, 46, 77 and 100%.
were 9.49 and 14.17 mm, respectively, compared to the target values of 9.5 and 14.05 mm. According to the FE analysis results, the diameter of the head section of the preform was determined directly as 3.4 mm. However, the upset length of 11.0 mm should be added to the length of the connector section, which was 3.0 mm as shown in Fig. 2, to match the length of the head section of the preform. Therefore, the diameter and the length of the head section of the preform were determined as 3.4 and 14.0 mm, respectively. 3.3. Cold forging experiments Once the head geometry of the preform was determined, the intermediate forging processes were designed easily with minor changes for the conceptual design as shown in Fig. 2. Based on the designed process sequence, a die set was manufactured and cold forging experiments were conducted. The intermediate forgings obtained by experiments of the preform forging stage and the final forging stage are shown in Fig. 6(a) and (b), respectively. As shown in these figures, by using the proposed cold forging process sequence, the head and the body section could be produced as one piece without any defects. In addition, inspections for the required specifications were conducted to the 100 randomly extracted samples in order to estimate the quality of the produced terminal pin. The results of the inspections indicate that the produced parts satisfied all properties of the specification as shown in Table 1. Moreover, it is expected that a considerable cost reduction could be obtained by using the proposed process sequence due to elimination of the welding process which was the main cause of defects of the previous manufacturing method. Table 1 Required specifications and the inspection results Properties
Specifications
Results
Straightness Vertical strength Capacitance Dielectric loss
Below 0.03 mm Above 15 kgf 500 pF ± 25% Below 1.0%
Maximum 0.012 mm Minimum 18.4 kgf 430.7–552.8 pF Maximum 0.35%
Fig. 6. Cold forged products obtained by experiments.
4. Conclusions In this study, a cold forging process sequence was developed to produce a terminal pin, which had been manufactured by using a welding process between the head and the body section, as one piece. With its geometrical characteristics, general cold forging process design rules could not be applied directly since volume removal processes such as blanking and piercing were required. Therefore, three dimensional FE analysis and design rules of sheet metal forming processes were employed in order to complement the traditional process design techniques of cold forging. In addition, cold forging experiments were conducted in order to verify the proposed process sequence and it was found that the obtained products satisfied all required specifications of a terminal pin. Finally, the qualities of terminal pins
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H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
and work efficiencies could be improved significantly by using the proposed process sequence which eliminated the welding processes. Acknowledgements This research was supported by the Daegu University Research Grant 2006 and the author wish to thank Prof. Y.T. Im in KAIST for permission of using CAMPform3D, which is a three dimensional rigid-viscoplastic FEM code for metal forming processes.
References [1] National Machinery Company, Part Shape Development and Tool Design for Multidie Cold Forming, Item 743A, Tiffin, Ohio, 1981. [2] H.S. Kim, Y.T. Im, An expert system for cold forging process design based on a depth-first search, J. Mater. Process. Technol. 95 (1999) 262–274. [3] D.F. Eary, E.A. Reed, Techniques of Pressworking Sheet Metal, PrenticeHall, New Jersey, 1974. [4] K. Lange, Handbook of Metal Forming, McGraw-Hill, New York, 1985. [5] J.S. Cheon, S.Y. Kim, Y.T. Im, Three dimensional bulk metal forming simulations under a PC cluster environment, J. Mater. Process. Technol. 140 (2003) 36–42.
A study on cold forging process sequence design of terminal pins for high-voltage capacitors H.S. Kim ∗ School of Automotive, Industrial and Mechanical Engineering, Daegu University, 15 Naeri-ri, Jinryang-eub, Gyeongsan-si, Gyeongbuk-do 712-714, Republic of Korea
Abstract A terminal pin, which is a component of high-voltage capacitors, has a plate-shaped head section with a thickness of 0.8 mm. The current manufacturing process, in which the head section is welded on the body section, has yielded substantial deviations in part qualities such as dimensional accuracy, mechanical strength and electrical stability. In this paper, a cold forging process sequence was proposed in order to produce the terminal pin as one piece. The plate-shaped head section requires an upsetting in the lateral direction of a cylindrical billet, which is followed by a blanking process. However, with only designer’s intuition, it is difficult to predict precisely the deformed geometry obtained by the lateral upsetting process since metal flows along axial and lateral directions would occur simultaneously. Therefore, in this study, three dimensional finite element analyses were applied to the lateral upsetting process in order to determine the proper geometry of the initial billet. Once the geometry of the initial billet was determined, intermediate forging sequences were designed by applying the design guidelines of cold forging. Based on the proposed process sequence, a die set was manufactured and cold forging experiments were conducted. © 2006 Elsevier B.V. All rights reserved. Keywords: High-voltage capacitor; Terminal pin; Cold forging process sequence; Lateral upsetting
1. Introduction A high-voltage capacitor, which is one of the core components of electrical appliances generating high-frequency waves, has two or three terminal pins, as shown in Fig. 1. The terminal pin is made of AISI1010, which is a highly ductile material, and plating treatments with Cu-Ni-Sn of 6–12 m thickness are conducted after the forming processes. Although the material is the most suitable for cold forging processes, it is not easy to apply traditional cold forging process sequences due to its geometrical characteristics. As shown in Fig. 1, the terminal pin has a rectangular plate section with a thickness of 0.8 mm, which is indicated as ‘A’, and its geometry is more proper for sheet metal forming rather than cold forging. Therefore, terminal pins have been manufactured by using welding processes between cold forged sections and head. However, qualities of the parts such as dimensional accuracy, mechanical strength and electrical stability have shown substantial deviations according to the quality of the welding processes. As a matter of fact, the defect ratio of the current manufacturing pro-
∗
Tel.: +82 53 850 6683; fax: +82 53 850 6689. E-mail address: [email protected].
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.035
cess has been estimated roughly at 10% due to the imperfections of the welding processes. Moreover, considerable efforts and cost have been required for the welding process, which demands elaborate positioning of two parts and stable welding conditions. Therefore, in this investigation, a new cold forging process sequence to produce a terminal pin as one piece without welding processes was proposed to improve part qualities and process efficiencies. 2. Conceptual design of the process sequence Considering geometrical features, the terminal pin can be divided into four sections: body, neck, connector and head. Geometries of the neck and the connector sections were modified to eliminate welding processes. Assuming an initial billet has cylindrical geometry, which is the most general and economical geometry in cold forging processes, forming directions of the body and the neck sections would be parallel to the longitudinal axis of the cylinder since those sections have axi-symmetrical geometries. On the other hand, forming directions for the head and the connector sections should be perpendicular to the axial direction because the thin flat-shaped head section should be obtained by a side pressing. Therefore, in this paper, we classified the whole process sequence into two stages, preform forging
H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
605
directions perpendicular to the longitudinal axis of the initial billet cylinder as shown in Fig. 2(b). More detailed examinations with design guidelines and determination of every dimension of intermediate forging should be conducted since the process sequence shown in Fig. 2 was planned with only the designer’s intuition. Most importantly, the diameter and length of the initial billet should be determined before detailed design of the process sequence. In addition, the head section of the preform, which is indicated as ‘C1’ in Fig. 2(b), should be designed appropriately in order to complete the following processes successfully since it would determine the geometries of the head section formed by the lateral upsetting, indicated as ‘C2’ in Fig. 2(b). 3. Preform geometry design 3.1. Investigation of preform geometry
Fig. 1. Drawing of a terminal pin for cold forging process sequence.
stage and final forging stage, according to the direction of applied forming loads. Fig. 2 shows the schematic diagram of the conceptually designed process sequence obtained by the designer’s experience and intuition [1,2]. As shown in these figures, the body and the neck sections were planned to be formed by a forward extrusion and an upsetting process during the preform forging stage. Once the preform forging stage was completed, the head section would be produced by applying four processes with forming
Fig. 2. Schematic diagram of the conceptually designed process sequence.
The objective of the lateral upsetting is to make the head section of the preform thin and flat-shaped by compressing an initial billet along the side direction so that it makes it possible to apply the following blanking process. In general, one of the most serious defects of the blanking process is a formation of excessive burrs at sheared surfaces, which can damage dies of the following processes and deteriorate the flatness of the head section. Therefore, in this study, a blank holder was installed to the die set in order to suppress the burr formations. However, the blank holder would have little effect on reducing the burr formations unless an adequate amount of area of the preform head section were backed up. Fig. 3 shows the predicted geometries of the head section before and after the blanking process and ‘F’ and ‘G’ indicate the width of the region pressed by a blank holder, defined as blank-held length in this paper. In general, it is recommended that the blank-held length be over 1–1.5 times the thickness of the blank for shearing processes such as blanking or piercing [3,4]. Compared with general sheet metal forming processes, however, width and length of the head section of the terminal pin are relatively small considering the thickness of the head section. Moreover, it was predicted that effects of the blank holding would be reduced since side edges of the blank would have bulged profiles, which are indicated as ‘E1’ and ‘E2’ in Fig. 3. Therefore, in this study, it was decided that the blank-held length
Fig. 3. Predicted geometry of the head section deformed by lateral upsetting process.
606
H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
‘E1’ of the terminal pin should be larger than that of general sheet metal parts and the value was set up as two times the thickness of the head section, which was 1.6 mm. In the case of ‘E2’ shown in Fig. 3, it is desirable that the blank-held length should be specified as a larger value since the arc length of ‘E2’ was smaller than that of ‘E1’ and only one side of the head section would be backed up by the blank holder. Therefore, in this study, the blank-held length along the ‘E2’ side was determined as four times the thickness of the head section, which was 3.2 mm. As shown in Fig. 1, width and length of the head section of the final part are 6.3 and 11.0 mm, respectively. Therefore, the width of the head section to be formed by the lateral upsetting process could be calculated as 9.5 mm, the sum of the final head width and the blank-held length of both sides. However, the head length obtained by the blanking process should be decreased from the final dimension since chamfering, which is the next process of the blanking, would elongate the head section. Taking into account the volume constancy of the head section, the elongated length at the chamfering process was calculated as 0.15 mm so that the head length right after the blanking should be 10.85 mm. Therefore, the target length of the head section at the lateral upsetting process should be 14.05 mm, which is the sum of the head length obtained by the blanking process and the blank-held length of ‘E2’ side. 3.2. Finite element analysis of lateral upsetting Three dimensional finite element analyses of the lateral upsetting were conducted in order to determine the proper values of the length and diameter of the initial billet to satisfy the target geometry of the preform. In this study, CAMPform-3D [5], which is a rigid-viscoplastic FEM code, was used for the analysis. Fig. 4 shows the geometrical models of die and billet used for FE analysis and only a quarter model was considered in this study due to the symmetrical characteristics of the process. The friction constant between die and billet was set up as 0.16 considering the lubricating conditions of the phosphate coating with oil and the stress–strain relation of the material, AISI1010, was as follows [2]. σ¯ = 713.1¯ε0.22 (MPa)
(1)
In order to determine the proper head geometry of the preform which can achieve the target dimensions described in the previous section, repeated FE analyses were required with many combinations of the billet diameter and the upset length, indicated as ‘D’ and ‘H’ in Fig. 4. Therefore, the range of initial billet diameters to be considered was narrowed down by applying the design rules of forward extrusion and upsetting. The forward extrusion ratio is defined as Eq. (2) and it is recommended that the value be limited to 75% for AISI1010 [1]. D2 − D2 A 0 − A1 × 100% = 0 2 1 × 100% A0 D0
(2)
where, A0 and A1 are cross-sectional areas and D0 and D1 represent diameters before and after an extrusion process, respectively. Therefore, in this study, the maximum value of the initial billet diameter was calculated as 4.0 mm with the forward extrusion ratio of 75% since the diameter of the extruded body section was 2.0 mm as shown in Fig. 1 and Fig. 2(a). A design rule of upsetting process was employed for determining the minimum value of the initial billet diameter. In general, the maximum value of an upsetting ratio, which is the ratio of diameters after and before an upsetting process, is limited to 2.5 due to the possible occurrence of ductile fractures [1]. As shown in Fig. 2(a), the neck section with a diameter of 7.5 mm would be obtained by an upsetting process so that the minimum value of possible billet diameters was calculated as 3.0 mm. In general, iron mills produce steel coils in diameter increments of 0.1 mm within the previously determined possible billet diameter range of 3.0–4.0 mm. Therefore, 11 diameters such as 3.0, 3.1, 3.2, etc. were selected as candidates for FE analyses. For the upset length, 13 cases were chosen ranging from 8.0 to 14.0 mm with an increment of 0.5 mm. In total, the number of possible combinations to be considered at FE analysis of the lateral upsetting process was 143. By applying several times of CAE analyses with a simple searching method, it was found that an initial billet with diameter of 3.4 mm and upset length of 11.0 mm yielded the most similar deformed geometry to the target. Fig. 5 shows the deformed geometries obtained by three dimensional FE analysis for the final case and the predicted width and length of the head section
Fig. 4. FE analysis model for lateral upsetting process.
H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
607
Fig. 5. Deformed geometries obtained by 3D FE analysis with compression ratios of 23, 46, 77 and 100%.
were 9.49 and 14.17 mm, respectively, compared to the target values of 9.5 and 14.05 mm. According to the FE analysis results, the diameter of the head section of the preform was determined directly as 3.4 mm. However, the upset length of 11.0 mm should be added to the length of the connector section, which was 3.0 mm as shown in Fig. 2, to match the length of the head section of the preform. Therefore, the diameter and the length of the head section of the preform were determined as 3.4 and 14.0 mm, respectively. 3.3. Cold forging experiments Once the head geometry of the preform was determined, the intermediate forging processes were designed easily with minor changes for the conceptual design as shown in Fig. 2. Based on the designed process sequence, a die set was manufactured and cold forging experiments were conducted. The intermediate forgings obtained by experiments of the preform forging stage and the final forging stage are shown in Fig. 6(a) and (b), respectively. As shown in these figures, by using the proposed cold forging process sequence, the head and the body section could be produced as one piece without any defects. In addition, inspections for the required specifications were conducted to the 100 randomly extracted samples in order to estimate the quality of the produced terminal pin. The results of the inspections indicate that the produced parts satisfied all properties of the specification as shown in Table 1. Moreover, it is expected that a considerable cost reduction could be obtained by using the proposed process sequence due to elimination of the welding process which was the main cause of defects of the previous manufacturing method. Table 1 Required specifications and the inspection results Properties
Specifications
Results
Straightness Vertical strength Capacitance Dielectric loss
Below 0.03 mm Above 15 kgf 500 pF ± 25% Below 1.0%
Maximum 0.012 mm Minimum 18.4 kgf 430.7–552.8 pF Maximum 0.35%
Fig. 6. Cold forged products obtained by experiments.
4. Conclusions In this study, a cold forging process sequence was developed to produce a terminal pin, which had been manufactured by using a welding process between the head and the body section, as one piece. With its geometrical characteristics, general cold forging process design rules could not be applied directly since volume removal processes such as blanking and piercing were required. Therefore, three dimensional FE analysis and design rules of sheet metal forming processes were employed in order to complement the traditional process design techniques of cold forging. In addition, cold forging experiments were conducted in order to verify the proposed process sequence and it was found that the obtained products satisfied all required specifications of a terminal pin. Finally, the qualities of terminal pins
608
H.S. Kim / Journal of Materials Processing Technology 187–188 (2007) 604–608
and work efficiencies could be improved significantly by using the proposed process sequence which eliminated the welding processes. Acknowledgements This research was supported by the Daegu University Research Grant 2006 and the author wish to thank Prof. Y.T. Im in KAIST for permission of using CAMPform3D, which is a three dimensional rigid-viscoplastic FEM code for metal forming processes.
References [1] National Machinery Company, Part Shape Development and Tool Design for Multidie Cold Forming, Item 743A, Tiffin, Ohio, 1981. [2] H.S. Kim, Y.T. Im, An expert system for cold forging process design based on a depth-first search, J. Mater. Process. Technol. 95 (1999) 262–274. [3] D.F. Eary, E.A. Reed, Techniques of Pressworking Sheet Metal, PrenticeHall, New Jersey, 1974. [4] K. Lange, Handbook of Metal Forming, McGraw-Hill, New York, 1985. [5] J.S. Cheon, S.Y. Kim, Y.T. Im, Three dimensional bulk metal forming simulations under a PC cluster environment, J. Mater. Process. Technol. 140 (2003) 36–42.