Fundamental investigation of gyro finishing experimental investigation of contact force between cylindrical workpiece and abrasive media under dry condition
Introduction
Smoothing of surface roughness is a significant process in manufacturing because rough surfaces result in low performance of friction, wear, and corrosion. Hence, various finishing methods have been developed to improve surface roughness [1]. Mass finishing can improve the surface roughness of several workpieces via relative motion against free abrasive media in a container. The relative motion between the workpiece and the abrasive media is caused by the motion of the container. Because the abrasive media moves along the workpiece surface, the process has a unique character that it is easy to smooth a workpiece surface with a complex shape. Thus, this process is used to manufacture various products, such as mechanical parts, medical items, glasses, and cutting tools [2].
To achieve better productivity for each product, various types of mass finishing processes have been developed [3]. Fig. 1 shows schematic illustrations of major mass finishing processes. Rotary barrel finishing shown in Fig. 1 (a) is a typical process. The container in which several workpieces are present with free abrasive media, is positioned horizontally and rotated around its principal axis. The container rotation causes motion of the workpieces and abrasive media in the container, and the workpieces are finished when they stream downward. Centrifugal barrel finishing is the process whereby the containers rotate around their principal axis and also exhibit revolutions as shown in Fig. 1 (b). The centrifugal force caused by the revolution prevents adhering of the workpieces to the container wall under high rotation speed conditions and increases the force acting on the workpieces. Thus, its productivity is much higher than the rotary barrel finishing. Centrifugal disk finishing shown in Fig. 1 (c) is the process where the bottom disk rotates. The workpieces and the abrasive media near the bottom disk move spirally to the fixed outer wall, and they move upward along the wall. Then, they stream down to the inner direction of the bottom disk. The workpieces are mainly finished when they move upward because of high pressure caused by centrifugal force, and hence, its process time is shorter than the rotary barrel finishing. The relative motion is caused by the vibration of the container in the vibratory finishing process as shown in Fig. 1 (d). The container supported by springs is shaken by the vibrator in the process, and the workpieces and the abrasive media are applied in a spiral motion around the circumferential direction of the container. Because the motion of the workpieces and the abrasive media is not faster than that in the other processes, larger workpieces are applicable in the process. In these major processes, workpieces are contained in the container without any fixtures. Hence, they are advantageous in that several workpieces can be finished simultaneously. However, they have a disadvantage that large workpieces are not applicable because the damages caused by the contact to the other workpieces become serious in the case that the workpiece is large. In addition, their process controllability is low, so that it is hard to add other advanced functions.
Gyro finishing, shown in Fig. 2, is a type of mass finishing process that has different characteristics described later. In the process, the filled abrasive media container is positioned vertically and rotated around its principal axis; the workpieces are held by fixtures from the outside. Hence, the workpiece does not move freely in the container. Thus, it is difficult to finish a large number of workpieces simultaneously, but larger workpieces are applicable in the process than vibratory finishing. Therefore, the process is used in a smoothing process of large gears [4,5]. Moreover, its process controllability is considered not low because the finishing performance can be controlled by optimizing the process conditions, such as the workpiece position and motion of the workpiece and the container. Thus, the process is expected to be an excellent finishing process of a workpiece with a complex shape. However, its fundamental understanding is few, and the development of new techniques or optimization of the process condition is hindered by a lack of understanding of the process.
In past literature, fundamental researches on gyro finishing have been few, although some fundamental researches on other mass finishing processes have been reported. In the mass finishing process, which includes gyro finishing, smoothing results from the relative motion between the workpiece and the abrasive media. Hence, the relative velocity and contact force between them are major concerns to understand the process. The motion of the workpiece and the abrasive media in rotary barrel finishing and centrifugal barrel finishing was observed through the transparent side wall, and it was summarized in a textbook [3]. In addition, their complex motion and relative velocity during the process in centrifugal barrel finishing and vibratory finishing were investigated by using the discrete element method [[6], [7], [8], [9]], which is a method to simulate behavior of powder and grains. Furthermore, the velocity of the abrasive media moving on the workpiece during gyro finishing was measured by X. Li et al. [10]. However, researches featuring the contact force are few. A. Yamamoto et al. measured contact pressure acting on the workpiece in the centrifugal barrel finishing by using pressure measurement film [11]. The pressure was confirmed to become larger when the media amount in the container was not full and the revolution speed was high. S. Wang et al. measured the normal force acting on a bottom surface of a cylindrical workpiece in vibratory finishing with a force-sensing device constructed in the workpiece [12]. A. Yabuki et al. then improved the device to measure the force not only for normal component but also for tangential components [13]. Furthermore, F. Hashimoto et al. measured the variation of the force during the process [14]. The force was confirmed to become large when the workpiece was at a lower position in the barrel, and this was caused by increasing the hydrostatic pressure. Y. Matsumoto et al. measured the force acting on the fixed workpiece in a centrifugal disc finishing machine with strain gauges attached to the fixture [15]. In the study, the force was confirmed to be increasing as the vertical position of the workpiece became lower, and the reason was guessed to be that the force was directly affected by the distance between the workpiece and the bottom disk because the movement of the abrasive media was applied by the disk.
As indicated by the researches featuring the contact force, factors affecting the contact force are different in each type of mass finishing process. Thus, it is necessary to investigate the force particularly in gyro finishing for its fundamental understanding. However, there is no related literature available on the contact force between the workpiece and the abrasive media in the process. Therefore, the contact force in gyro finishing is investigated experimentally in the present study. Though most of the workpieces finished in the process have complex shapes, a simple workpiece with a cylindrical shape was finished to obtain a basic understanding of the force. This is because it is considered quite difficult to discuss the force acting on the complex-shaped workpiece without basic understanding because of the complicated behavior of the abrasive media near the workpiece. The force was measured under various process conditions, such as workpiece position, amount of abrasive media in the container, and rotational speed of the container, in Chapter 2. Then, the factors affecting the contact force are discussed based on the abrasive media height in Chapter 3. Moreover, the variation of the surface roughness is investigated, and the effect of the contact force on the finishing performance in gyro finishing is investigated in Chapter 4.
Section snippets
Experimental setup and experimental conditions
Fig. 3 shows the experimental setup. A container with an inner diameter of 400 mm and a depth of 200 mm stands vertically and is rotated around its principal axis by a speed control motor with a belt. The container was filled with the abrasive media. This means that the container had no liquid, and the experiment was conducted under dry conditions. The abrasive media shape was spherical with a diameter of 1 mm, and its surface was filled with micro asperities. Although the abrasive media was
Investigation of abrasive media height above workpiece
As described in the previous chapter, the abrasive media height above the workpiece was indicated to be a significant factor affecting the contact force. In order to investigate its effect more detail, the height during the process was measured, and the actual abrasive media height above the workpiece was investigated in Investigation C. Table 2 lists the experimental conditions, and Fig. 10 shows the experimental setup. The height of the abrasive media was measured with a laser displacement
Variation of surface roughness under different contact force condition
The effect of the contact force on the finishing performance was investigated with the abrasive media for dry condition in this chapter. The abrasive media was a plastic-type media, and it wore well to maintain its finishing performance in dry condition. Its initial shape was a regular triangular prism with a height of 3 mm.
First, the contact force and the abrasive media height were measured with the media to confirm the effectiveness of the results in the previous chapters in Investigation D.
Conclusion
Gyro finishing is expected to be an excellent finishing process of a workpiece with a complex shape. In the present study, a fundamental investigation of the contact force between the workpiece and abrasive media in gyro finishing was conducted for its understanding. The contact force acting on a cylindrical workpiece, which was designated by simplifying a large gear, was measured under different conditions in workpiece position, amount of abrasive media, and rotational speed of the container.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was supported by JSPS KAKENHI Early-Career Scientists Grant Number 18K13668.
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