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Study on isothermal precision forging technology for a cylindrical aluminium-alloy housing
Journal of Materials Processing Technology 72 (1997) 403 – 406
Study on isothermal precision forging technology for a cylindrical aluminium-alloy housing D.B. Shan *, Z. Wang, Y. Lu, K.M. Xue School of Materials Science and Engineering, Harbin Institute of Technology, PO Box 435, Harbin, Heilongjiang Pro6ince 150001, People’s Republic of China Received 12 November 1996
Abstract High-precision forging is becoming increasingly popular in modern plastic working. The effects of forging force, die chilling, residual stress and lubricant are significant in a hot precision forge. Producing aluminium-alloy precision forgings of reasonable complexity is a difficult operation. Temperature control within narrow ranges, high-accuracy dies and suitable forming methods are necessary in order to develop desirable microstructures, properties and the near-net shape of forgings. Therefore, isothermal forging is a prime method from the precision forming viewpoint. This paper presents details of isothermal precision forging technology for a cylindrical aluminium-alloy housing. © 1997 Elsevier Science S.A. Keywords: Isothermal precision forging; Aluminium alloy; Cylindrical housing
1. Introduction The cylindrical aluminium-alloy housing is a key part of a Z11 helicopter. Its raw material is 7075 aluminium alloy and the housing is a complex component with a high cylinder and a deep cavity. There is a flange at one side of the cylinder and four ears that are not located uniformly and symmetrically at the opposite side. The outer surface near to the ears can not be machined. The ears play an important part in bearing load, an intense force being exerted on them during the process of taking-off, flight and descent. It is therefore important that forging flow line is distributed along their geometric shape and there should not be phenomena of pierced fibre and folds, etc. In addition, the grain size is required to be homogeneous and small and the mechanical properties need to be superior. Moreover, not only is the complex-shape forging difficult to produce, but also it can not be removed easily from the dies after forging. A potential production method for the housing is based on isothermal precision forging and combined dies [1,2].
* Corresponding author. 0924-0136/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0 9 2 4 - 0 1 3 6 ( 9 7 ) 0 0 2 0 2 - 1
Isothermal precision forging is a new metal-forming process that has been developed only since the 1960s, which requires that its dies should be heated and kept to the same temperature as the workpiece when forging. The technology can effectively raise the level of metal plasticity and flow properties, improve the homogeneity of metal flow and decrease the deformation pressure on the material. Therefore, a forging of complicated shape, high dimension of accuracy and a well-distributed internal structure can be produced [3,4]. This paper deals mainly with the forming technology of isothermal precision forging and the design of the dies.
2. Experimental study on the cylindrical-housing forming process and the die device
2.1. Experimental study on the cylindrical-housing forming process The billet flow is complicated in the die cavity when forging the cylindrical housing, the forming process belonging to combined extrusion. Experimental dies were designed to research the forming process using 1:3 scale lead specimen on a 60 t material-test machine.
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D.B. Shan et al. / Journal of Materials Processing Technology 72 (1997) 403–406
Fig. 1. Experimental dies.
Two technological methods were employed in the experiments. (1) As shown in Fig. 1(a), punch 1 was used to press directly. At this time, the metal forming process is divided into two stages. Stage 1: From the beginning of pressing to the end of pressing, the billet contacts the upper surface of punch 1. In this stage the billet is divided into three parts: The first part fills the lower part of the cylindrical housing,which is equal to forward-extrusion deformation; the second part fills the four ears, which is equal to radial extrusion; and the third part fills the cylindrical wall and flange, which is equal to backward extrusion. The lower part will be completely filled in this stage. Stage 2: This takes place from the end of stage 1 to filling of the dies completely. In this stage the deformation is mainly backward extrusion and forging the flange, other deformation being much smaller. At this time, the billet under the punch has two flowing directions, one direction being to fill the four ears along the radius and the other flowing up along the axis (as shown in Fig. 1(a)). The flowing of the billet in the radial direction produces a great amount plastic forming because the area of the ears along the filling direction is becoming smaller, which makes the resistance along the radius increase sharpely. Therefore, the volume of metal flowing along the axis is larger and the volume of metal is too small to fill the four ears completely. Moreover, as the punch travels continuously, the contact area of the billet and the punch will grow constantly and the forging force will become increasingly greater. Thus the metal filling the ears suffers in creased resistance to flow and the ears can not be filled completely.
Fig. 2. Photograph of a lead specimen.
Fig. 3. Schematic diagram of the cylindrical housing dies. 1, upper backing plate; 2, clamp plate; 3, male die; 4, movable bushing; 5, clamp plate; 6, heater; 7, female die bushing; 8, combined female die; 9, heater; 10, lower backing plate; 11 – 12, bolt; 13-lower punch.
Fig. 2(a) is a photograph of a lead specimen. The grids of the four ears has been changed seriously and great plastic deformation has been produced: this is identical with the above analysis. It appears that it is not suitable to adopt this technological method to form the housing. (2) Considering the shortcoming of the first method, the authors designed the second technological method (as shown in Fig. 1(b)). First, punch 2 is employed for pressing, which effects extrusion deformation (mainly radial extrusion deformation) to fill the four ears and the lower part. Then punch 1 is employed to backward extrude and forge the flange. Because of the use of punch 2, die filling can be effectively improved. Fig. 2(b) is a photograph of a lead specimen. It appears that the ears and flange have been filled completely. Therefore, the technological method is feasible.
Fig. 4. Photograph of the cylindrical housing.
D.B. Shan et al. / Journal of Materials Processing Technology 72 (1997) 403–406
405
Table 1 The mechanical properties of the housing
Requirement Test result Requirement Test result
Testing direction
sb (MPa)
s0.2 (MPa)
d (%)
Hardness (HB)
Longitudinal Longitudinal Transverse Transverse
]455 507 ]403 475
]385 427.4 ]365 406.4
]6 10.9 ]2.5 5.21
]130 150 — —
From the above analysis, it can be seen that the forming process of the cylindrical housing is complex, the amount of plastic deformation is great and dies must be changed many times during the operation. Thus, the component should be forged at least several times when using conventional practices. Therefore, it is necessary for the cylindrical housing to be produced by isothermal forging.
2.2. Die de6ice In order to carry out the isothermal forging and remove the forging from the dies smoothly, a combined female die and a reasonable heating device should be employed. Fig. 3 is a schematic diagram of the dies. The structure of the female die is the key to die design. For the convenience of the forging being removed from the dies and the dies being machined, a combined female die with four pieces is designed, the parting planes of which are located in the middle of the ears along the axis. Each piece of the female die is combined by four key slots, the female die and its bush are designed to be conical so that the forging can be removed easily from the die and the combined female die can be joined together tightly. In the thesis of [2], a resistance heating device is described, which is installed at the bush of the female die, so that the temperature can be measured and controlled automatically.
Fig. 5. Metallograph of the 7075 aluminium alloy ( ×500).
minium-alloy materials especially have a pronounced tendency to adhere to the dies at high temperature. Therefore, there are many defects on the forging surface. Consequently, the second forging should be carried out after dipping and pneumatic chipping. A fairly
3. The forming technological test of isothermal precision forging The forming test using the second method was carried out on a 50 MN hydraulic press. The dies were pre-heated to the alminium alloy forging temperature of 460 9 10°C and kept at the same temperature during forging. The billets were heated according to the aluminium alloy heating specification. Colloidal graphite mixed with water was employed as lubricant. The results of the test show that the ears and flange can be filled completely at the pressure of 12 MN with a press-holding time of 5 min. However, the deformation of the billet is great during the process of forming, the newly-produced surface is increased and alu-
Fig. 6. Photograph of the macrostructure.
D.B. Shan et al. / Journal of Materials Processing Technology 72 (1997) 403–406
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well filled forging (shown in Fig. 4) with a good surface can be produced at a pressure of 9 MN with a pressholding time of 3 min. Table 1 lists the test results of the mechanical properties of the forged component, which exceed all the demands. Fig. 5 shows that the grain size is homogeneous and small. Fig. 6 shows that there are no defects such as pierced fibre and folds and the grain-flow patterns follow the contour of the forging. The above results indicate isothermal precision forging technology is reliable.
4. Conclusions (1) Forgings containing deep cavities and big bosses can be produced by isothermal precision forging technology, the forging is close to final contours, so that little or no machining is required.
.
(2) The structure of the combined female die is reasonable and ensures that the forging can be removed easily from the dies and that forgings with high quality can be produced. (3) The cylindrical aluminium-alloy housings produced by isothermal precision forging technology fulfill quality requirements.
References [1] D.B. Shan, Z. Wang, Y. Lu, J. Harbin Inst. Technol. 28 (1996) 97 – 101. [2] D.B. Shan, PhD Thesis, Harbin Institute of Technology, 1996. [3] T. Altan, F.W. Boulger, J.R. Becker, N. Akgerman, H.J. Henning, Forging Equipment, Materials and Practices, Air Force Materials Laboratory, 1973. [4] K.M. Kulkarni, N.M. Parikh, T. Watmough, J. Inst. Met. 100 (1972) 146 – 151.
Study on isothermal precision forging technology for a cylindrical aluminium-alloy housing D.B. Shan *, Z. Wang, Y. Lu, K.M. Xue School of Materials Science and Engineering, Harbin Institute of Technology, PO Box 435, Harbin, Heilongjiang Pro6ince 150001, People’s Republic of China Received 12 November 1996
Abstract High-precision forging is becoming increasingly popular in modern plastic working. The effects of forging force, die chilling, residual stress and lubricant are significant in a hot precision forge. Producing aluminium-alloy precision forgings of reasonable complexity is a difficult operation. Temperature control within narrow ranges, high-accuracy dies and suitable forming methods are necessary in order to develop desirable microstructures, properties and the near-net shape of forgings. Therefore, isothermal forging is a prime method from the precision forming viewpoint. This paper presents details of isothermal precision forging technology for a cylindrical aluminium-alloy housing. © 1997 Elsevier Science S.A. Keywords: Isothermal precision forging; Aluminium alloy; Cylindrical housing
1. Introduction The cylindrical aluminium-alloy housing is a key part of a Z11 helicopter. Its raw material is 7075 aluminium alloy and the housing is a complex component with a high cylinder and a deep cavity. There is a flange at one side of the cylinder and four ears that are not located uniformly and symmetrically at the opposite side. The outer surface near to the ears can not be machined. The ears play an important part in bearing load, an intense force being exerted on them during the process of taking-off, flight and descent. It is therefore important that forging flow line is distributed along their geometric shape and there should not be phenomena of pierced fibre and folds, etc. In addition, the grain size is required to be homogeneous and small and the mechanical properties need to be superior. Moreover, not only is the complex-shape forging difficult to produce, but also it can not be removed easily from the dies after forging. A potential production method for the housing is based on isothermal precision forging and combined dies [1,2].
* Corresponding author. 0924-0136/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0 9 2 4 - 0 1 3 6 ( 9 7 ) 0 0 2 0 2 - 1
Isothermal precision forging is a new metal-forming process that has been developed only since the 1960s, which requires that its dies should be heated and kept to the same temperature as the workpiece when forging. The technology can effectively raise the level of metal plasticity and flow properties, improve the homogeneity of metal flow and decrease the deformation pressure on the material. Therefore, a forging of complicated shape, high dimension of accuracy and a well-distributed internal structure can be produced [3,4]. This paper deals mainly with the forming technology of isothermal precision forging and the design of the dies.
2. Experimental study on the cylindrical-housing forming process and the die device
2.1. Experimental study on the cylindrical-housing forming process The billet flow is complicated in the die cavity when forging the cylindrical housing, the forming process belonging to combined extrusion. Experimental dies were designed to research the forming process using 1:3 scale lead specimen on a 60 t material-test machine.
404
D.B. Shan et al. / Journal of Materials Processing Technology 72 (1997) 403–406
Fig. 1. Experimental dies.
Two technological methods were employed in the experiments. (1) As shown in Fig. 1(a), punch 1 was used to press directly. At this time, the metal forming process is divided into two stages. Stage 1: From the beginning of pressing to the end of pressing, the billet contacts the upper surface of punch 1. In this stage the billet is divided into three parts: The first part fills the lower part of the cylindrical housing,which is equal to forward-extrusion deformation; the second part fills the four ears, which is equal to radial extrusion; and the third part fills the cylindrical wall and flange, which is equal to backward extrusion. The lower part will be completely filled in this stage. Stage 2: This takes place from the end of stage 1 to filling of the dies completely. In this stage the deformation is mainly backward extrusion and forging the flange, other deformation being much smaller. At this time, the billet under the punch has two flowing directions, one direction being to fill the four ears along the radius and the other flowing up along the axis (as shown in Fig. 1(a)). The flowing of the billet in the radial direction produces a great amount plastic forming because the area of the ears along the filling direction is becoming smaller, which makes the resistance along the radius increase sharpely. Therefore, the volume of metal flowing along the axis is larger and the volume of metal is too small to fill the four ears completely. Moreover, as the punch travels continuously, the contact area of the billet and the punch will grow constantly and the forging force will become increasingly greater. Thus the metal filling the ears suffers in creased resistance to flow and the ears can not be filled completely.
Fig. 2. Photograph of a lead specimen.
Fig. 3. Schematic diagram of the cylindrical housing dies. 1, upper backing plate; 2, clamp plate; 3, male die; 4, movable bushing; 5, clamp plate; 6, heater; 7, female die bushing; 8, combined female die; 9, heater; 10, lower backing plate; 11 – 12, bolt; 13-lower punch.
Fig. 2(a) is a photograph of a lead specimen. The grids of the four ears has been changed seriously and great plastic deformation has been produced: this is identical with the above analysis. It appears that it is not suitable to adopt this technological method to form the housing. (2) Considering the shortcoming of the first method, the authors designed the second technological method (as shown in Fig. 1(b)). First, punch 2 is employed for pressing, which effects extrusion deformation (mainly radial extrusion deformation) to fill the four ears and the lower part. Then punch 1 is employed to backward extrude and forge the flange. Because of the use of punch 2, die filling can be effectively improved. Fig. 2(b) is a photograph of a lead specimen. It appears that the ears and flange have been filled completely. Therefore, the technological method is feasible.
Fig. 4. Photograph of the cylindrical housing.
D.B. Shan et al. / Journal of Materials Processing Technology 72 (1997) 403–406
405
Table 1 The mechanical properties of the housing
Requirement Test result Requirement Test result
Testing direction
sb (MPa)
s0.2 (MPa)
d (%)
Hardness (HB)
Longitudinal Longitudinal Transverse Transverse
]455 507 ]403 475
]385 427.4 ]365 406.4
]6 10.9 ]2.5 5.21
]130 150 — —
From the above analysis, it can be seen that the forming process of the cylindrical housing is complex, the amount of plastic deformation is great and dies must be changed many times during the operation. Thus, the component should be forged at least several times when using conventional practices. Therefore, it is necessary for the cylindrical housing to be produced by isothermal forging.
2.2. Die de6ice In order to carry out the isothermal forging and remove the forging from the dies smoothly, a combined female die and a reasonable heating device should be employed. Fig. 3 is a schematic diagram of the dies. The structure of the female die is the key to die design. For the convenience of the forging being removed from the dies and the dies being machined, a combined female die with four pieces is designed, the parting planes of which are located in the middle of the ears along the axis. Each piece of the female die is combined by four key slots, the female die and its bush are designed to be conical so that the forging can be removed easily from the die and the combined female die can be joined together tightly. In the thesis of [2], a resistance heating device is described, which is installed at the bush of the female die, so that the temperature can be measured and controlled automatically.
Fig. 5. Metallograph of the 7075 aluminium alloy ( ×500).
minium-alloy materials especially have a pronounced tendency to adhere to the dies at high temperature. Therefore, there are many defects on the forging surface. Consequently, the second forging should be carried out after dipping and pneumatic chipping. A fairly
3. The forming technological test of isothermal precision forging The forming test using the second method was carried out on a 50 MN hydraulic press. The dies were pre-heated to the alminium alloy forging temperature of 460 9 10°C and kept at the same temperature during forging. The billets were heated according to the aluminium alloy heating specification. Colloidal graphite mixed with water was employed as lubricant. The results of the test show that the ears and flange can be filled completely at the pressure of 12 MN with a press-holding time of 5 min. However, the deformation of the billet is great during the process of forming, the newly-produced surface is increased and alu-
Fig. 6. Photograph of the macrostructure.
D.B. Shan et al. / Journal of Materials Processing Technology 72 (1997) 403–406
406
well filled forging (shown in Fig. 4) with a good surface can be produced at a pressure of 9 MN with a pressholding time of 3 min. Table 1 lists the test results of the mechanical properties of the forged component, which exceed all the demands. Fig. 5 shows that the grain size is homogeneous and small. Fig. 6 shows that there are no defects such as pierced fibre and folds and the grain-flow patterns follow the contour of the forging. The above results indicate isothermal precision forging technology is reliable.
4. Conclusions (1) Forgings containing deep cavities and big bosses can be produced by isothermal precision forging technology, the forging is close to final contours, so that little or no machining is required.
.
(2) The structure of the combined female die is reasonable and ensures that the forging can be removed easily from the dies and that forgings with high quality can be produced. (3) The cylindrical aluminium-alloy housings produced by isothermal precision forging technology fulfill quality requirements.
References [1] D.B. Shan, Z. Wang, Y. Lu, J. Harbin Inst. Technol. 28 (1996) 97 – 101. [2] D.B. Shan, PhD Thesis, Harbin Institute of Technology, 1996. [3] T. Altan, F.W. Boulger, J.R. Becker, N. Akgerman, H.J. Henning, Forging Equipment, Materials and Practices, Air Force Materials Laboratory, 1973. [4] K.M. Kulkarni, N.M. Parikh, T. Watmough, J. Inst. Met. 100 (1972) 146 – 151.