Ultrasonic Spindle Research Articles

Development of a High-Speed Precision Ultrasonic-Assisted Spindle for Ultra-Precision Optical Mold Machining.

Ultrasonic vibration-assisted grinding is a critical method for machining ultra-hard optical molds. However, current ultrasonic-assisted grinding spindles, as essential foundational equipment, face limitations in maintaining ultra-high rotational speed, high precision, and a compact structure during ultrasonic operation. This study presents a novel ultra-precision ultrasonic-assisted high-speed aerostatic spindle for grinding ultra-hard optical molds, developed through theoretical calculations, FEM, and CFD simulations. The spindle features a simple and compact design (φ60 mm outer diameter × 194 mm length), operates at an ultrasonic frequency of 41.23 kHz, and is driven by an impulse turbine providing torque up to 50.4 N•mm, achieving speeds exceeding 40,000 r/min. Aerostatic bearings provide axial and radial load capacities of 89 N and 220 N, respectively. The results demonstrate that the proposed high-speed precision ultrasonic spindle exhibits both feasibility and potential for practical application.

Cryogenic and ultrasonic-assisted micro-drilling of printed circuit boards using high-frequency-amplitude spindle

Printed circuit boards (PCBs) are key components in computers, 5G, 6G, and other wireless communication devices. On the other hand, the manufacture of micro-holes in PCBs faces severe challenges. Conventional micro-drilling methods often encounter challenges such as poor surface quality and limited tool life. To overcome these issues, a novel micro-drilling method called cryogenic and ultrasonic-assisted micro-drilling (CUAMD) has been developed. This study compared four drilling methods to investigate the benefits of cryogenic and ultrasonic-assisted drilling in hybrid machining processes: conventional micro-drilling (CMD), cryogenic-assisted micro-drilling (CAMD), ultrasonic-assisted micro-drilling (UAMD), and cryogenic and ultrasonic-assisted micro-drilling (CUAMD). The experimental results unequivocally indicate that the utilization of cryogenic-assisted drilling leads to a significant reduction in cutting heat during the machining process. This not only contributes to an improvement in machining accuracy but also exerts a positive influence on tool life and surface morphology. Ultrasonic-assisted drilling separates chips into smaller volumes through high-frequency-vibration, effectively reducing the cutting forces. The high frequency of 38.25 kHz and high amplitude vibration of 5.16 μm of the ultrasonic spindle induced vibrations on the drill bit. Liquid nitrogen with a pressure and temperature of 28 kPa and − 196 °C, respectively, was used in the cryogenic-assisted method. The superior machining performance of the CUAMD approach was evaluated by comparing it to various methods, including cutting forces, tool flank wear, entrance/exit hole morphology, and chip formation. The CUAMD method avoids chip entanglement, suppresses burrs, and reduces the maximum cutting force, maximum torque, and exit hole damage factor Fd by 47.7 %, 56.1 %, and 42.5 %, respectively, compared with CMD.

드릴링 가공을 위한 초음파 유닛 설계

With the development of new alloys and composites, existing drilling techniques have technical constraints for machining difficult-to-cut materials. To overcome these constraints, researchers have developed various drilling methods, including ultrasonic-assisted drilling (UAD). An ultrasonic spindle with a 30 kHz resonant frequency was designed to apply UAD to hole processing. The resonance frequency and vibration mode were predicted using the finite element method (FEM), and a vibration nodal plane was selected. The resonance frequency and impedance characteristics of the ultrasonic spindle were determined using an impedance analyzer, and an error of approximately 1.9% was predicted using the FEM. Next, the vibration characteristics of the ultrasonic spindle were analyzed using a laser displacement system. The vibration displacement tests showed amplitudes of 39.7 and 0.5 μm at the end of the drilling tool and the nodal plane, respectively. The design validity of the manufactured ultrasonic spindle was demonstrated based on experimental drilling results.

Kinematic analysis and process stability of ultrasonic-assisted drilling

Regarding drilling, ultrasonic-assistance enables various potentials such as less tool wear, enhanced chip breaking and burr reduction. Although there are many technological studies verifying these advantages, no theory for process behaviour, design and parameter evaluation is available. Thus, this paper presents a kinematic analysis of the interaction between tool and workpiece to contribute to overall process understanding. Specific process scenarios are classified and characteristic parameters for the evaluation and design of ultrasonic-assisted drilling are determined. In addition, experimental investigations based on the developed process model are carried out analysing chip shape, bore surface and process stability acquired by acoustic measurements. The kinematic analysis shows the classification of ultrasonic-assisted drilling according to continuous and intermitted cutting conditions. In addition, the superposition of ultrasonic vibrations causes a modulation of uncut chip thickness related to the ratio of ultrasonic frequency and spindle speed. In general, experimental results show that ultrasonic-assisted drilling is leading to shorter chips. While using parameters for intermitted cutting conditions needle chips occur. At the same time, intermitted cutting conditions induce process instabilities identified using the acoustic measurement approach.

Development of Ultrasonic Vibration Assisted Micro Electrochemical Discharge Machining Tool

Background: The fabrication of microstructures with high machining quality is always difficult when it is concerned with non-conductive hard and brittle materials such as glass and engineering ceramics. It is reported in related papers and patents that Electrochemical Discharge Machining (ECDM) process is a good choice for machining non-conductive, hard and brittle materials. However, the machining performance of ECDM process, especially in the aspect of geometric accuracy and surface quality, needs to be greatly improved. Objective: The purpose of this study was to improve the machining quality of conventional ECDM process by introducing ultrasonic vibration to ECDM process, develop an Ultrasonic Vibration Assisted Micro Electrochemical Discharge Machining (UAECDM) tool, and investigate the improvements of the machining performance by means of comparative experiments. Methods: Firstly, the machining principle of UAECDM was investigated, and the effects of ultrasonic vibration are discussed with the analysis of the micro process. Secondly, the hardware system, which consists of a machine tool body, XY and Z axes, an ultrasonic spindle system and motion control system, was established; and the software system was developed based on the analysis of the overall workflow of the machining process. Finally, comparative experiments, including ECDM drilling, UAECDM drilling, ECDM milling and UAECDM milling, were carried out to reveal the improvements of the machining quality. Results: In the UAECDM group, a micro-hole with the inlet diameter of 133.2µm as well as the 3 × 3 array of micro holes was fabricated on the glass workpiece with 300µm thickness, and a microgroove with the width of 119.2µm was successfully milled on the glass workpiece. It is shown in both microscopic photographs and optical measurements that the microstructures fabricated by UAECDM have better machining quality compared with similar microstructures fabricated by ECDM. Conclusion: Based on comparative experiments and discussions of the results, it has been proved that the machine tool can meet the requirement of the ultrasonic vibration-assisted micro electrochemical discharge machining and can improve the geometric accuracy and surface quality significantly.

A study on the effect of main process parameters of rotary ultrasonic machining for drilling BK7 glass

BK7 glass is an important engineering material with extensive applications in high-quality and precision transmissive optical components. However, BK7 glass is considered to be a difficult-to-cut material due to its high brittleness and nonconductivity. This article presents the use of rotary ultrasonic machining process for drilling holes in BK7 glass. No previous reports have been found in the literature to experimentally investigate the response of the BK7 glass to rotary ultrasonic drilling. The experimental investigations take into account the effect of the key rotary ultrasonic machining input parameters including the ultrasonic power, spindle speed and feed rate on the output responses of cutting force, exit chipping, surface roughness, hole cylindricity and overcut errors, and surface integrity. The results show that the input parameters within the current ranges can significantly affect the quality of the drilled holes. Moreover, the selected level of any input parameter has the ability to significantly affect the influence of the other input parameters on the output responses. Through proper selection of input parameters, holes could be drilled in BK7 glass with less fractured topography, low surface roughness (1.32 µm), low exit chipping size (0.85), and very low cylindricity (3 µm) and overcut (73.6 µm) errors.

A novel flexible tool with rotary ultrasonic spindle for fine grinding of tungsten carbide

Tungsten carbide is a typical difficult-to-cut material by conventional machining processes. In this paper, a novel design of flexible abrasives tool combined with a rotary ultrasonic machining (RUM) spindle is conducted to reduce the labor force significantly. The newly designed flexibility of tool-tip is aimed at preventing overcutting from the CNC grinding. The grinding conditions with resulted surface morphology of the tungsten steel were investigated through Taguchi design of experiment and ANOVA analysis. The machining capability of the novel flexible tool is compared with conventional tools through specific grinding paths under proper operational conditions.

Ultrasonic-Assisted Incremental Microforming of Thin Shell Pyramids of Metallic Foil

Single point incremental forming is used for rapid prototyping of sheet metal parts. This forming technology was applied to the fabrication of thin shell micropyramids of aluminum, stainless steel, and titanium foils. A single point tool used had a tip radius of 0.1 mm or 0.01 mm. An ultrasonic spindle with axial vibration was implemented for improving the shape accuracy of micropyramids formed on 5–12 micrometers-thick aluminum, stainless steel, and titanium foils. The formability was also investigated by comparing the forming limits of micropyramids of aluminum foil formed with and without ultrasonic vibration. The shapes of pyramids incrementally formed were truncated pyramids, twisted pyramids, stepwise pyramids, and star pyramids about 1 mm in size. A much smaller truncated pyramid was formed only for titanium foil for qualitative investigation of the size reduction on forming accuracy. It was found that the ultrasonic vibration improved the shape accuracy of the formed pyramids. In addition, laser heating increased the forming limit of aluminum foil and it is more effective when both the ultrasonic vibration and laser heating are applied.

Ultrasonic assisted electrolytic grinding of titanium alloy Ti-6Al-4V

Aiming at the development of a novel grinding technology for the high efficient machining of difficult to machine materials such as titanium alloy Ti-6Al-4V, an ultrasonic assisted electrolytic grinding (UAEG) method was proposed. Firstly, an experimental apparatus was constructed by installing an electrolytic mechanism on an existing 3D CNC machine tool attached with an ultrasonic spindle. Then, after the performance test has been carried out for the constructed apparatus, UAEG experiments of Ti-6Al-4V specimen were conducted on the apparatus to investigate the effects of the ultrasonic vibration of grinding wheel and the electrolytic phenomenon on the grinding force and the work surface quality. The experimental results indicate that the ultrasonic assisted electrolytic grinding is greatly beneficial to the decrease in grinding force and the improvement in the work surface quality compared to conventional grinding.

Ultrasonic assisted electrolytic grinding of titanium alloy Ti-6Al-4V

Aiming at the development of a novel grinding technology for the high efficient machining of difficult to machine materials such as titanium alloy Ti-6Al-4V, an ultrasonic assisted electrolytic grinding (UAEG) method was proposed. Firstly, an experimental apparatus was constructed by installing an electrolytic mechanism on an existing 3D CNC machine tool attached with an ultrasonic spindle. Then, after the performance test has been carried out for the constructed apparatus, UAEG experiments of Ti-6Al-4V specimen were conducted on the apparatus to investigate the effects of the ultrasonic vibration of grinding wheel and the electrolytic phenomenon on the grinding force and the work surface quality. The experimental results indicate that the ultrasonic assisted electrolytic grinding is greatly beneficial to the decrease in grinding force and the improvement in the work surface quality compared to conventional grinding.

Ultrasonic motorized spindle with hydrostatic bearings

Ultrasonic and acoustic axial spindle oscillations improve the productivity and product quality in machining, reduce the cutting forces, and increase the tool life in the grinding, milling, and boring of structural components, including those made from materials that are hard to machine. Industrial prototypes of motorized spindles with axial spindle oscillations have been developed by specialists at Siberian Federal University and AO NPP Radiosvyaz and patented in Russia. These spindle units include contactless hydrostatic bearings, a resonant-frequency generator (a piezo generator for ultrasonic spindles and a hydromechanical generator for acoustic spindles), and a local concentrator for the spindle’s longitudinal intrinsic waves.

Development of a novel 2D rotary ultrasonic texturing technique for fabricating tailored structures

Microgrooves, microdimples, or hierarchical surfaces comprising these structures are highly required in many industrial fields for their functional performances. In the present research, a novel two-dimensional (2D) rotary ultrasonic texturing (RUT) technique is developed for efficiently fabricating these precision surface structures. A rotary ultrasonic spindle that can generate circular vibration on the horizontal plane perpendicular to the spindle axis was designed and manufactured for carrying out the 2D RUT processes. The spindle structure and the texturing principle are introduced. Surface generation mechanisms are mathematically analyzed and experimentally verified. A diamond tool with geometrically defined cutting edge was designed and manufactured for carrying out the surface texturing experiments. Different types of nearly burr-free textured surfaces composing of periodic grooves from several micrometers to tens of micrometers were successfully fabricated, and their textural features coincide well with the theoretical prediction. Material removal mechanisms, tools design principles, and machinable structures of the new 2D RUT technique are discussed.

Comparison on gas bubble and pulse trains of deep-cavity electrical discharge machining with/without rotary ultrasonic assistance

Fundamental observation of bubbles and debris in deep-cavity electrical discharge machining (EDM) with an ultrasonic spindle aimed at achieving higher machining efficiency is proposed and compared. Various discharge pulse trains for EDM, rotary EDM (R-EDM), ultrasonic vibration-assisted EDM (UA-EDM), and rotary ultrasonic EDM (RU-EDM) are investigated. Their effects on the removal efficiency, machining stability, and the tool wear rate are studied as well. It is found that EDM in deep cavity is actually discharged in the gas bubble most of the time except the short period at the very beginning stage. The main bubble at EDM tool jumping is maintained with a constant volume. And, the volume results in the boundary height of the bubble at the next EDM stroke. In which, ultrasonic vibration of sufficient strength was found to split main bubble quickly and improve the material removal rate at about 49 % through much higher frequency of pulse trains. Appended with rotation, the rotary ultrasonic vibration EDM can improve the tool wear rate but reduces the MRR in compared with conventional EDM.

S1320205 超音波スピンドル援用によるCFRPの穴あけ加工に関する研究([S132-02]先進切削加工技術(2))

CFRP (Carbon fiber Reinforced Plastics) is recently used as structure components in the aviation and automobile industry due to its excellent properties, such as specific strength, stiffness and so on. A great number of rivet holes are necessarily drilled out in the airplane manufacturing. CFRP is, however, difficult-to-cut material because that hard carbon fibers cause to rapid tool wear. Ultrasonic vibration cutting is cutting method that tool will be vibrated ultrasonically and used to cutting. Major merit is reducing the thrust force and tool lifetime elongation. In this study, aims to investigate about the effects of ultrasonic vibration assisted drilling on CFRP plates with ball-nose end mill. 40 kHz ultrasonic spindle is attached on the conventional 3-axis machining center. Cutting conditions of cutting speed and feed rate are optimized value by previous research which was experimented without vibration conventional drilling, and the experiment was performed and investigated. As the result, width of tool flank wear is reduced 20%. On the ultrasonic vibration drilling, hole diameter reduction becomes small because tool vibrated to radial direction. After tool head passed bottom surface, tool vibration becomes large. Thrust force vibrated large and becomes minas values. The minus thrust force becomes cause to reducing delamination of exit side, and increasing entry side delamination.

Rotary Ultrasonic Machining of Sapphire: Feasibility Study and Designed Experiments

Sapphire, widely used in high-speed integrated-circuit chips, thin-film substrates, and various electronic components, is regarded as one of the most difficult to cut materials owing to its great hardness and low fracture toughness. Rotary ultrasonic machining (RUM) has been regarded as an effective processing method for hard and brittle materials. In this paper, RUM process is introduced into the drilling of sapphire for the first time. The feasibility to machine sapphire using RUM is studied. Moreover, results of a designed experimental study into RUM of sapphire are presented to discuss the main effects as well as interaction effects of process parameters (ultrasonic power, spindle speed, and feedrate) on outputs. The process outputs investigated include cutting force and edge chipping size.

Surface Textures Fabrication on Zirconia Ceramics by 3D Ultrasonic Vibration Assisted Slant Feed Grinding

Zirconia (ZrO2) is a promising material in the field of prosthetic and implant dentistry. Surface grinding has been used for surface roughening of zirconia ceramics to increase the mechanical retention of ceramic/resin cement bonding. In the present study, a three-dimensional (3D) ultrasonic vibration spindle, which can generate three ultrasonic vibration modes referred to as longitudinal vibration, circular vibration and 3D hybrid vibration, was employed to machine zirconia ceramics by slant feed grinding for producing tailored rough surfaces. Different micro/nanosurface textures were generated successfully, proving that the ultrasonic vibration assisted slant feed grinding is a viable method to fabricate tailored rough surfaces composed of micro/nanostructures. The surface texturing procedure was mathematically studied, and the influence of grinding and vibration conditions on the textural features was also analyzed.

Ultrasonic Coring of Glass Disks Using Double Core Tool

Glass disks are used as substrates for the recording media in magnetic disk devices. To mass produce glass disks, a technology is required for machining glass (a material that is difficult to machine) with both high precision and high efficiency. Consequently, this study adopted a method that processes the inner- and outer-diameters simultaneously using a double core tool. In addition, the thrust force in coring process was also reduced using an ultrasonic spindle to apply ultrasonic vibration to the feed direction of the rotating tool. This resulted in high quality machining with less chipping. Furthermore, this study conducted experiments to compare the three methods of stabilizing the stack of glass substrates. As a result, it was found that the method using ultraviolet curable resin was able to limit the chipping to a smaller size.

Study of Ultrasonically Assisted Internal Grinding of Small Holes: Effect of Grain Size of cBN Grinding Wheel

This study aims to develop an ultrasonically assisted grinding technology for precision internal grinding of a small hole measuring several millimeters in diameter, such as those formed in a fuel injector for an automotive engine. In a previous work, an experimental apparatus mainly composed of an ultrasonic vibration spindle was designed and constructed, and grinding experiments were carried out. The previous investigation found that applying ultrasonic vibration to the wheel decreased the normal and tangential grinding forces, respectively, and improved the surface roughness in surface grinding. The purpose of this paper is to examine the effect of ultrasonic vibration on grinding force and surface roughness in internal grinding when the grain sizes of small cBN grinding wheel are changed. The experimental results indicate that applying ultrasonic vibration to the wheel decreases the normal and tangential grinding forces by more than 83 % and 80 %, respectively, and improves the surface roughness by as much as 62 % while the wheel grain size is changed. In addition, over the range of grinding conditions employed in this paper, the grain size as small as 3 µm can be used in ultrasonically assisted internal grinding.

Development of a new rotary ultrasonic spindle for precision ultrasonically assisted grinding

In our previous work, a new method for inducing a machine spindle to ultrasonically vibrate was proposed in which the axial ultrasonic vibration is excited by a fluctuating electromagnetic force applied to the spindle. The validity of this method was also confirmed experimentally. In this paper, focusing on the development of a new rotary ultrasonic spindle based on this new method, an actual ultrasonic spindle unit was designed and constructed in accordance with the previous work. The unit consists of an ultrasonic spindle, two rotary bearings and their housings for holding the spindle, eight electromagnets and their supporters for the generation of a fluctuating electromagnetic force, and a base plate. Its performance was also investigated experimentally for different exciting conditions. The results showed that an ultrasonic vibration with a sub-μm order amplitude is generated on the produced spindle and that the applied electromagnetic force affects the spindle performance significantly.

Effects of Grain Size and Concentration of Grinding Wheel in Ultrasonically Assisted Grinding

This study aims to develop an ultrasonically assisted grinding technology for precision internal grinding of a small hole measuring several millimeters in diameter, such as those formed in a fuel injector for an automotive engine. In a previous work, an experimental apparatus mainly composed of an ultrasonic vibration spindle was designed and constructed, and grinding experiments were carried out. The purpose of this paper is to examine the effect of ultrasonic vibration on grinding force and surface roughness when the grain size and concentration of small cBN grinding wheel are changed. The experimental results indicate that applying ultrasonic vibration to the wheel decreases the normal and tangential grinding forces by more than 50% and 78%, respectively, and improves the surface roughness by as much as 10% when the wheel grain size and concentration are changed. In addition, over the range of grinding conditions employed in this paper, the grain size as small as 5μm can be used in ultrasonically assisted grinding.