Process design and control in cold rotary forging of non-rotary gear parts

https://doi.org/10.1016/j.jmatprotec.2014.05.003Get rights and content

Highlights

  • An accurate design method of the non-rotary upper die is presented based on the geometrical and kinematic relationship between the upper die and upper profile of parts.

  • A calculation method is presented to obtain the trajectory of any point in the upper die and thus the interference judgment between the upper die and upper profile of parts is achieved.

  • The metal flow and geometrical accuracy of the non-rotary upper profile of parts can be effectively controlled through optimizing the process parameters.

  • The process design and control method presented in this paper is valid and cold rotary forging can be used to manufacture the parts with non-rotary upper and lower profiles.

Abstract

This paper is aimed to investigate the process design and control method in cold rotary forging of parts with non-rotary upper and lower profiles. Using the analytical and FE simulation methods, three critical technological problems in the cold rotary forging process of this kind of parts are resolved reasonably. The first one is that an accurate design method of the non-rotary upper die is presented based on the geometrical and kinematic relationship between the upper die and upper profile of parts. The second one is that the interference judgment between the upper die and upper profile of parts can be achieved by analytically obtaining the trajectory of any point in the upper die. The third one is that the metal flow and geometrical accuracy of the non-rotary upper profile of parts can be effectively controlled through optimizing the process parameters. On the basis of the above research, the cold rotary forging process of a typical gear part, both the upper and lower profiles of which are non-rotary, is investigated numerically and experimentally. The results indicate that the desirable geometrical accuracy of the non-rotary upper profile of the gear part can be obtained, which verifies that the process design and control method presented in this paper is valid and cold rotary forging can thus be used to manufacture the parts with non-rotary upper and lower profiles.

Introduction

Cold rotary forging is an advanced but complicated incremental metal forming technology which is widely used to manufacture mechanical parts such as disks, rings, flanges and gears. A typical cold rotary forging process is illustrated in Fig. 1. During the process, the conical upper die with an inclination angle γ continuously oscillates around the vertical machine axis at a constant rotational speed n. Simultaneously, the non-rotating lower die feeds toward the workpiece vertically at a feed rate v. Under the action of the two dies, the workpiece produces the incremental plastic deformation. Compared with conventional forging, cold rotary forging has many advantages such as lower level of noise and vibration, uniform quality, smooth surface, close tolerance and considerable savings in energy and materials cost. Owing to these significant advantages, cold rotary forging technology has been attracting more and more applications in many industry fields such as automobile, machine tool, electrical equipment, cutting tool and hardware.

By now, many studies have been carried out on the cold rotary forging process. Marciniak (1970) developed an eccentric mechanism, i.e. two eccentric sleeves, for driving the upper die in cold rotary forging press. Using the experimental method, Appleton and Slater (1973) studied the effect of the upper platen configuration on the rotary forging process. Hawkyard et al. (1977) and Pei et al. (1982) measured the pressure distribution in the rotary forging process. Standring et al. (1980) studied the plastic deformation during the indentation phase of rotary forging through the metallographic observation. Nakane et al. (1982) experimentally revealed the deformation behavior in simultaneous backward extrusion-upsetting by rotary forging. Zhou et al. (1992) analyzed the defects caused in the forming process of rotary forged parts and presented the preventive methods. Kalinowska-Ozgowicz et al. (1997) experimentally studied the deformation laws in rotary forging of an oxygen cylinder web. Canta et al. (1998) carried out the experiment to analyze the load and energy in the rotary forging process. Wang et al. (2005) adopted the photo-plastic experimental method to study the deformation laws in rotary forging of a ring workpiece. Using the upper bound method, Zhang (1984), Oudin et al. (1985) and Choi et al. (1997) calculated the force and energy during the rotary forging process. Oh and Choi (1997) proposed a theoretical criterion to explain the center thinning in the rotary forging process of a circular plate. Since cold rotary forging is a complicated incremental metal forming process which integrates these features of three-dimensional (3D) metal flow, incremental plastic deformation, asymmetry, time varying, non-steady-state and high nonlinearity, several researchers have also attempted to use the increasingly popular FE method to analyze the cold rotary forging process in an effort to obtain an in-depth understanding of this process. Wang and Zhao (1999) developed a 3D rigid-plastic FE code to analyze the cold rotary forging process of a ring workpiece. Yuan et al. (1998) studied the cold rotary forging process of the knuckle pin using the 3D rigid-plastic FE software DEFORM. Liu et al. (2004) used the same software to investigate the inhomogeneous deformation characteristics in the cold rotary forging process of a cylinder. Sheu and Yu (2008) investigated the cold rotary forging process of a hollow-ring gear with a toothed collar numerically. Nowak et al. (2008) and Montoya et al. (2008) used the FE method to compare the rotary forging with conventional forging. Han and Hua (2009) adopted the elastic-plastic dynamic explicit FE method to study the deformation characteristics in the cold rotary forging process of a ring workpiece. Using the same method, Han and Hua (2011) predicted the contact pressure, slip distance and wear in cold rotary forging. Deng et al. (2011) simulated the cold rotary forging process of a spur bevel gear and optimized the workpiece geometry. Merklein et al. (2012) numerically investigated the cold rotary forging process of tailored blanks from sheet metal and revealed the effect of the process parameters on the part geometry and properties. Grosman et al. (2012) presented a new rotary forging process based on the small incremental deformation realized by a series of thin anvils and investigated the effectiveness of the process numerically. Samołyk (2013) achieved the simulation of the complex rocking motion of the upper die in cold rotary forging of an AlMgSi alloy bevel gear.

Summarily, one of the common characteristics of cold rotary forged parts described above is that the upper profile is rotary while the lower profile is non-rotary, as shown in Fig. 2(a). Generally, the simple rotary upper profile is formed by the upper die while the complicated non-rotary lower profile is formed by the lower die during the cold rotary forging process of this kind of parts. Because the upper die is a rotary cone (i.e. the generatrix of the upper die is constant) which matches with the rotary upper profile of parts, it can be easily designed as long as the generatrix of the rotary upper profile of parts is determined. Meanwhile, the contact between the upper die and rotary upper profile of parts is relatively simple and thus the metal flow and geometrical accuracy of the rotary upper profile can be easily controlled during the process. With the fast development of modern industries, some complicated mechanical parts, both the upper and lower profiles of which are non-rotary (shown in Fig. 2(b)), have more and more popular applications in the industries. In the cold rotary forging process of this kind of parts, the accurate forming of the non-rotary upper profile is the most critical. Through a comprehensive analysis, three critical technological problems need to be addressed in order to achieve the forming of the non-rotary upper and lower profiles. The first one is the design of the upper die. Because the upper die is a non-rotary cone (i.e. the generatrix of the upper die is varied) which has to strictly match with the non-rotary upper profile of parts at any time, it cannot be directly obtained by revolving the generatrix of the upper profile of parts (The generatrix of the upper profile of parts is varied) or by the Boolean operation between the upper die and upper profile of parts (The lower die can be directly obtained by the Boolean operation between the lower die and lower profile of parts). The second one is the interference judgment between the upper die and upper profile of parts. During the process, the upper die oscillates around the vertical machine axis and the trajectory of any point in the upper die cannot interfere with the upper profile of parts. Otherwise, the cold rotary forging process cannot be performed successfully. The third one is the control of the metal flow and geometrical accuracy of the non-rotary upper profile of parts. During the process, the upper die and non-rotary upper profile of parts produce the repeated spatial meshing motion and the contact boundary conditions between them are highly dynamic. Therefore, the metal flow of the non-rotary upper profile of parts is complicated and has to be controlled effectively so as to guarantee the geometrical accuracy.

By now, the studies on cold rotary forging of parts with non-rotary upper and lower profiles are scant. Therefore, this paper is aimed to investigate the process design and control method in cold rotary forging of parts with non-rotary upper and lower profiles. Using the analytical and FE simulation methods, three critical technological problems mentioned above are resolved reasonably. On the basis of the above research, the cold rotary forging process of a typical gear part, both the upper and lower profiles of which are non-rotary, is investigated numerically and experimentally. The results indicate that the process design and control method presented in this paper is valid.

Section snippets

Design method of the non-rotary upper die

To achieve the accurate design of the non-rotary upper die, the geometrical and kinematic relationship between the upper die and upper profile of the workpiece has to be investigated detailedly. Fig. 3 shows the schematic diagram of the geometrical and kinematic relationship between the upper die and upper profile of the workpiece. It is assumed that at the beginning and t time of the cold rotary forging process, the generatrix of the upper die OA and OB coincides with that of the upper profile

3D FE model of cold rotary forging of parts with non-rotary upper profile

To conveniently observe the metal flow and measure the final geometry of the non-rotary upper profile of parts, a non-rotary upper profile with a hemispherical indentation is chosen as the research objective in this study. The FE method is adopted to investigate its metal flow and geometrical accuracy variation laws. The 3D FE model developed in DEFORM-3D is shown in Fig. 7. It should be noted that one of the key modeling technologies is modeling the rocking motion of the upper die. In this

Metal flow and geometrical accuracy of the non-rotary upper profile with a hemispherical indentation

Different from conventional forging, besides the axial and radial flow, the metal in the workpiece also produces the circumferential flow in cold rotary forging owing to the rocking motion of the upper die, which is one of the main deformation characteristics of cold rotary forging. Fig. 10 shows the metal flow evolution of the non-rotary upper profile with a hemispherical indentation under different feed amount of the lower die. It can be seen from Fig. 10 that with increasing the feed amount

Conclusions

This paper investigates the process design and control method in cold rotary forging of parts with non-rotary upper and lower profiles. Using the analytical and FE simulation methods, three critical technological problems are resolved reasonably.

  • (1)

    An accurate design method of the non-rotary upper die is presented based on the geometrical and kinematic relationship between the upper die and upper profile of parts.

  • (2)

    A calculation method is presented to obtain the trajectory of any point in the upper

Acknowledgments

The authors would like to thank the National Natural Science Foundation of China (No. 51105287), Key Research and Development Project of New Product and New Technology of Hubei Province (No. 2012BAA08003), Innovative Research Team Development Program of Ministry of Education of China (No. IRT13087), High-end Talent Leading Program of Hubei Province (No. 2012-86) and China Postdoctoral Science Foundation (No. 2013M531750) for the support given to this research.

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