Surface finishing processes, such as fine milling, grinding, burnishing, polishing, lapping, and diamond turning, play an important role in the final fabrication stage to improve the surface finish of molds, optical components, and some semiconductor components. The different kinds of polishing machine tools or processes, mainly including the ultraprecision freeform polishing machine, ultrasonic-vibration-assisted polishing, hydrodynamic polishing, abrasive fluid jet polishing, robot-assisted polishing, laser polishing, and sequential ball burnishing and ball polishing, etc., have been discussed in [
1]. The main application areas of ultraprecision plane or freeform surface polishing are the fabrication of high-precision optics, artificial orthopedic joints, wafers of semiconductor applications, and precision molds for different kinds of materials. Ultrasonic-vibration assisted polishing processes have been applied to different materials, such as the BK7 or K9 optical glasses, aluminum ceramic, 4H–SiC wafers, sapphire, monocrystalline silicon, Inconel 718 nickel-based alloy, and STAVAX mold steel, etc., to improve the surface roughness of the workpieces. The modeling and analysis of the material removal rate and predictive and experimental research on the polishing slurry consumption model of ultrasonic-vibration-assisted polishing of optical glass BK7 have been presented in [
2,
3]. The modeling and prediction of the generated local surface profile for ultrasonic-vibration-assisted polishing of optical glass BK7 has been reported in [
4]. The predictive modeling and experimental study of the polishing force of ultrasonic-vibration-assisted polishing of K9 optical glass has been reported in [
5]. The material removal profile prediction and experimental validation for obliquely axial ultrasonic-vibration-assisted polishing of K9 optical glass has been investigated in [
6]. The effect of ultrasonic-vibration-assisted polishing on the surface properties of alumina ceramic has been investigated in [
7]. For the surface finish of 4H–SiC wafers, an efficient and slurryless ultrasonic-vibration-assisted electrochemical mechanical polishing has been proposed in [
8]. The effects of ultrasonic amplitude on sapphire ultrasonic-vibration-assisted chemical mechanical polishing has been investigated by experimental and CFD methods [
9]. The effect of ultrasonic vibration polishing on the surface quality and material removal rate of monocrystalline silicon has been analyzed in [
10]. The ultrasonic-vibration-assisted polishing of Inconel 718 has been studied in [
11,
12], in which the material removal rate was improved and the surface roughness and average standard deviation of the roughness values significantly reduced. Ultrasonic-vibration-assisted magnetic compound fluid polishing has been developed for the final finishing of acrylic plate in [
13]. Using an ultrasonic-vibration-assisted polishing machine, the ultraprecision finishing of a microaspheric surface was possible [
14,
15]. Four different types of CBN particles used to polish STAVAX mold steel on a three-axis machining center, using ultrasonic-vibration-assisted polishing, yielded a better surface finish [
16].
The ball burnishing process has been applied to perform the prefinishing process for ball polishing to improve the surface roughness of the mold steel [
17]. Using the sequential ball burnishing and ball polishing process, the surface roughness of a workpiece can be improved sequentially from about 1.0 μm to 0.020 μm on average [
18]. To reduce the volumetric wear of the polishing ball, a vibration-assisted polishing device for the workpiece, activated by a piezoelectric actuator, was designed and fabricated in [
19]; however, the developed device was not suitable for integration with an automated production due to taking up too much space.
With the development of an ultrasonic tool with holder type BT40 that can be integrated into the tool magazine, the automated ultrasonic-vibration-assisted polishing on a machining center is possible, as shown in
Figure 1. According to the literature survey, the optimal ultrasonic-vibration-assisted ball polishing parameters for STAVAX mold steel on a five-axis machining center, such as the vibration amplitude, working frequency, spindle speed, abrasive grain size, slurry concentration, depth of penetration, etc., have not been studied.
The aim of this study was mainly to determine the optimal combination of the ultrasonic-vibration-assisted ball polishing parameters on a machining center and to investigate the tool wear of the polishing ball. The property of the adopted material, STAVAX stainless mold steel, the experimental setup of the ultrasonic-vibration-assisted ball polishing system on a five-axis machining center, and Taguchi’s method for determining the optimal plane spherical polishing parameters are introduced in
Section 2. The optimal combination of the ultrasonic-vibration-assisted ball polishing parameters for a plane surface, the ANOVA analysis and discussion on the dominant ultrasonic-vibration-assisted ball polishing factors for plane surfaces, the volumetric wear of the polishing ball, and the application to the surface finishing of an aspherical lens carrier are reported in
Section 3. The main results of this study are summarized in conclusion.