Ultrasonic mems cutting tool

However, research activities in the area have been increasing in the current decade. Micro-USM as one of the nontraditional manufacturing processes finds its main advantage in machining nonconductive, hard, and brittle materials and capability of generating surface free of thermal damage. Table 1 presents a comparison between different micromachining techniques.

The micro-USM process, as observed from the table, can be compared to almost all other micromachining processes. This process has the edge over the highly competitive LIGA process as far as 3D profile machining is concerned apart from applicable to a broad range of work materials. Ultrasonic machining is a relatively old machining technique whose basis was laid way back in and was patented by L. Balamuth in It is a technology that has attained a recognized status in manufacturing technology and found increasing applications in industries including aerospace, optics, and automotive [ 20 ].

The first USM tools, mostly mounted on the bodies of drilling and milling machines, had been built by By , independent USM tools of various types were commercialised and came into regular production for a variety of applications [ 21 ].

The first attempt of downsizing macro-USM for micromachining was conducted by Masuzawa of Tokyo University in the mid s [ 22 ]. The micro-USM is used for machining hard and brittle materials.

Typical workpiece materials being machined in previous experimental investigations include glass, silicon, and alumina [ 23 , 24 ]. However, the downsizing for micromachining requires a microsized tool or tool feature , smaller amplitude, and microsized abrasive particles. Figure 1 illustrates a basic setup of a micro-USM process.

The set up primarily consists of a tool system and slurry supply unit. The tool is mechanically vibrated at an ultrasonic frequency and amplitude of few micrometers.

The abrasive slurry, a mixture of irregular-shaped fine abrasive particles usually, in the range of 0. As the vibrating tool head hits the free abrasives in the slurry, they attain momentum and impact upon the target workpiece location.

A localized fatigue stress is developed in the impact zone owing to continued impact, and microchipping occurs resulting in material removal. Moreover, a small amount of material removal might also be contributed by the mechanical abrasion of the hard microabrasives. Further, implosion of the gas bubbles, also called cavitation, can play a key role in material removal at microlevel.

Although water is usually preferred as the slurry medium, there exists a possibility that the chemical impurities present in the slurry medium can selectively cause instantaneous degradation of the work material resulting in loss of material.

A continuous flow of slurry flushes away the debris from the machining zone and refills the gap with fresh slurry.

Thus, based on the understanding of macro-USM research, the contributing mechanisms in case of micro-USM can be summarized into four categories: i microchipping by impact of the free moving abrasive particles, ii mechanical abrasion by the abrasive particles against the workpiece surface, iii cavitation effects in liquid agitated by ultrasonic vibration, iv chemical actions associated with the liquid being employed.

The variants in micro-USM can be categorised as shown in Figure 2. While Figure 2 a presents a classification based on the machine tool characteristics, Figure 2 b shows some variations in the micro-USM according to different tool heads used. A simple cylindrical tool was used, and the vibration was given to the microtool. As USM is associated with a major drawback of tool wear, this kind of tooling causes continuous shortening of tool length and, therefore, imposes obstacles in maintaining consistent vibration amplitude at the tool tip.

The vibration amplitude varies at different locations along the tool axis, and tool wear changes the location of the tool tip causing the inconsistency. Applying ultrasonic vibration to the workpiece has been found to be preferable because it eliminates the influence of tool wear on the vibration amplitude of tool tip in case of applying vibration to the tool.

Furthermore, the vibrated workpiece may help in stirring the abrasive slurry during machining to increase the efficiency of abrasive particles around the machining zone and remove debris [ 26 ].

Rotary ultrasonic machining RUM , as indicated in Figure 2 a , is one of the cost-effective and hybrid machining processes available for drilling holes. It merges the material removal mechanisms of diamond grinding and USM, resulting in higher material removal rate MRR than that obtained by either diamond grinding or USM [ 27 ]. Figure 3 presents a schematic illustration of RUM.

The hollow tool can be given a rotary motion as well as it can vibrate. But this makes the design very unwieldy. Hence, an attempt has been made to study the material removal rate when the workpiece is rotated in rotary USM mode. However, owing to the rotation of the workpiece there will be sliding and rolling contacts between the abrasive grains and workpiece, as well as impacts and indentation of the abrasive particle with the workpiece at ultrasonic frequency.

Hence better material removal has been claimed [ 28 ]. Two major requirements for micro-RUM are the microsized abrasive bonded tool and a machining system capable of applying very small load on the microtool with necessary feedback and control mechanisms.

Some of the disadvantages of the EDM, ECM, and other nonconventional machining processes were overcome by ultrasonic assistance in the form of hybridisation Figure 2 a.

Thus, ultrasonic machining was combined with EDM and abrasive flow machining AFM to achieve better yield [ 17 — 19 , 29 ]. Nowadays, ultrasonic vibrations are being used successfully to enhance machining capability of micro-EDM to handle titanium alloys [ 30 ].

It has been found in microhole machining of titanium plate that microultrasonic vibration lapping enhances the precision of microholes drilled by micro-electrodischarge machining. Further, USM assisted turning is claimed to reduce machining time, workpiece residual stresses, and strain hardening and improve workpiece surface quality and tool life compared to conventional turning [ 31 ].

Mode I consists of a solid or hollow cylindrical tool which is easy to fabricate and widely used in various applications of micro-USM. Figure 4 illustrates the mode I tool. In mode II, microfeatures are fabricated on the tool bottom. A unique benefit of this type of micro-USM is to realize a parallel production of many identical simple features. The tool is silver brazed with the tool head and not touching the workpiece. Figure 5 shows the microfeature developed on the tool itself and a gang drill.

In order to minimize tool wear, tools should be constructed from relatively ductile materials such as stainless steel, brass, and mild steel. Curodeau et al. The proposed tool was successfully investigated for micromachining and micropolishing for tool steel surface. The machine tools for USM range from small, tabletop-sized units to large-capacity machine tools. All USM machines share common subsystems regardless of the physical size or power.

The most important of these subsystems are the power supply, transducer, tool holder, tool, and abrasives [ 35 ]. In the case of USM transducer, electrical energy is converted into mechanical motion. With a conventional generator system, the tool and horn are set up and mechanically tuned by adjusting their dimensions to achieve resonance.

They can also accommodate any small error in setup and tool wear, giving minimum acoustic energy loss and very small heat generation.

The power supply depends on the size of the transducer. Two different types of transducers used for USM work on two different principles of operation-piezoelectric and magnetostrictive. Piezoelectric transducers generate mechanical motion through the piezoelectric effect using certain materials such as quartz or lead zirconate.

Magnetostrictive transducers are usually constructed from a laminated stack of nickel or nickel alloy sheets. Extensive research work has been carried out for macro-USM regarding material removal, tool wear, dimensional accuracy, and surface quality [ 37 — 39 ]. However, only a few publications have focussed on the ways of yielding optimal micro-USM performance measures in terms of high material removal rate MRR , low tool wear rate, and satisfactory surface quality.

The main task of process improvement for micro-USM is to economically machine a microfeature with required surface topography, minimal surface damage, good surface finish, high-dimensional accuracy, and acceptable material removal rate. The parametric relationship for micro-USM is complicated due to the involvement of numerous factors and related parameters that could affect the process outputs.

The possible parameters in micro-USM can be illustrated in a fishbone diagram as shown in Figure 6. The type and size of abrasive particle affect the machining rate significantly.

The machining rate increases with the size of abrasives. The machining speed increases with an increase in the average static load; however, it decreases with the increase of the average static load beyond a certain value. The debris accumulation in the working area leads to a part of the static load consumed in impacting the debris instead of removing the material from the workpiece, resulting in a lower machining efficiency [ 40 , 41 ].

The rotation of the tool improves the machining speed significantly as shown in Figure 7. The tool rotation helps in the debris removal and, therefore, increases the machining speed. The drilling speed, however, was reported to be rising with increase in the machining load as that for a single tool does while using cemented carbide tools.

In contrast, it decreases as the oscillation amplitude increases [ 34 ]. The effects of oscillation amplitude and machining load on drilling speed and tool wear ratio, as reported by Egashira et al. In USM, the grains hit the tip of the vibrating tool and tend to erode it. Thus, tool wear is an important variable for micro-USM, affecting the machining speed and the hole accuracy.

Tool wear tends to increase when harder and coarser abrasive grains are used [ 25 ]. When tools of very small dimensions are used, the static load needs to be small to avoid breakage of the tool.

The populous tool materials such as stainless steel and thoriated tungsten in conventional USM are not suitable in micro-USM because of their large wear. Also, tool wear increases remarkably with a decrease in tool diameter [ 22 , 43 ]. The tool wear ratio is defined as the ratio of the tool wear length to the hole depth. The tool wear ratio for cemented carbide tools varies widely and is influenced by the machining load or oscillation amplitude as illustrated in Figure 8 [ 34 ].

Some studies on possible effect of tool geometries on machining rate and tool life were also carried out by the present authors. Measurements of machining rate and tool wear ratio as a function of drilling depth were performed using hollow and solid tools.

The experiments were carried out in a stationary Sonic-Mill machine AP with a power output of W. The static load applied on the horn was taken in the range of g to g throughout the trials. Figure 9 illustrates the variations in the observed machining rate MR as a function of the static load for the two types of tool.

In both types of tool used, the overall machining rate increases with an increase in the static load. Increase in static load means increasing the pressure on the abrasive grains and eventually on the workpiece, resulting in an increase of machining rate.

However, the machining rate decreases with the increase in static load differently for the two types of tool. Decrease in MR with increasing static load is explained by the insufficiency in recycling abrasive particles at the machining interface because of accumulation of the debris.

The recycling capacity affects the hammering and impact actions of the abrasive particles in the working gap. Also, the MR is more in case of hollow tool with the varying static load. This is because of the necessary contact area between the tool and abrasives and correspondingly between abrasives and the workpiece.

In case of hollow tool, material is removed by the border of the tool only whereas in case of a solid tool, the whole lower edge is involved in machining.

The design of a tool must be such that it should machine as little of the workpiece material as necessary. The importance of tool head area can also be seen from the accompanying scanning electron micrograph SEM images in Figure 9. Higher straying abrasive action is seen with the solid tool, while the hollow tool provides a more focused cutting zone, although at the cost of higher tool wear.

Thus, further studies in this direction would be needed to obtain optimal machining conditions. Figure 10 illustrates the tool wear ratio of different types of tool used. The observed higher tool wear ratio in case of hollow tool is attributed to reduced contact area. As the contact area is less for a constant load, the stress produced will be more which results in easy and quick work hardening of the tool tip.

This leads to an induced brittleness on the tool tip causing a favourable condition to be eroded by the deflected abrasives. In addition, the problem of debris accumulation also causes the crack generation and material removal from the tool, leading to the more tool wear. The type and size of abrasive particle affect the surface finish and it increases as the size of abrasive increases.

Egashira et al. Theoretically, the surface roughness is small when small particles are used because of the small crater generated. However, because of debris accumulation, the surface roughness generated by small abrasive particles can be larger than that of big particles. If abrasive particles of small size are used, particles get embedded in the workpiece or in the tool under the static load and may stay in their original craters without moving to other locations during several cycles of vibration.

The thickness of accumulated debris in the working area reaches the exposed height of abrasive particles in a short time, resulting in the debris involved in machining. This leads to a change in the abrasive particle distribution and movement, which may increase the surface roughness. When large abrasive particles are used, more debris is removed from working area and the abrasive particles easily move to new locations by the vibration because of the large number of impacts [ 40 , 41 ].

Surface roughness, out-of-roundness and taper ratio are three important parameters for evaluating microhole quality [ 22 , 43 ]. Rotating the tool not only decreases the severity of protrusions along the machining path, but also improves machining speed as observed by Kuriyagawa et al.

The geometrical capabilities of micro-USM have been verified by machining microfeatures such as blind or through holes, slots, and 3D cavities. Ultrasonic machining has a limitation in its application to micromachining because there are problems in fixing microtools to the machine and maintaining high precision. Accordingly, a technique was proposed for micro-USM by applying on-the-machine tool fabrication by wire electrodischarge grinding WEDG. Figure 11 shows a triangular and square hole made on silicon using WEDG method, as reported by Egashira et al.

A machine was developed at FEMTO-ST institute, France for producing electronic components based on piezoelectric quartz crystals for ultraprecise processing on 2-in. The drilling was performed four times and a total of 64 holes could be fabricated with an oscillation amplitude of 0.

The workpiece material was soda lime glass. Micro-USM with a single tool had so far been carried out on hard and brittle materials; however, it is time-consuming for drilling multiple holes, which is often a requirement for application of microholes. Thus, a micro-EDM has been used to drill parallel holes, which is later used to produce microcemented carbide multitool using reverse micro-EDM.

The fabricated multitool Figure 5 and the array of microholes machined by micro-USM are shown in Figure Because of this movement, the ultrasonic cutter can easily cut resin, rubber, nonwoven cloths, film, composite materials in which various products are superposed, and food. The ultrasonic cutter is composed of a "transducer" that generates vibration and an "oscillator" that drives the transducer. A piezoelectric element is used for the transducer. When voltage is applied, the piezoelectric element displaces the transducer by a few micrometers.

Periodically applying voltage generates vibration. Each object has its special frequency, by which the object is stable and easy to vibrate. By adding an external force that corresponds to that special frequency, a small force can obtain a large vibration.

This phenomenon is called resonance. In the ultrasonic cutter, the piezoelectric element generates a force that resonates the whole body, from the transducer to the blade tip, generating a large vibration at the tip. The oscillator periodically generates voltage to resonate and drive the transducer. Using a component of the ultrasonic cutter called the horn to ring the cross-sectional area, from the piezoelectric element to the blade tip, can obtain a larger vibration.

The NSK Nakanishi Sonic Cutter system is an excellent, low-cost system capable of cutting a wide variety of paper goods, plastics, leather, and woven materials. The Sonofile ultrasonic cutting systems utilize more powerful control units designed for heavier-duty and continuous-use cutting applications. Specifications vary according to the model. Ultrasonic cutters can also be used easily as a hand tool; click on the link to the YouTube video demonstration below. Compared to other separation processes ultrasonics stand out with high process speeds and immaculate cutting edges which can be sealed in the same process step.

The right cut for all types of plastic Especially impressive is the broad range of plastics which can be processed with our technology. From delicate foils with the smallest thickness, over highly elastic materials which require extremely sharp knifes, to hard and brittle materials.

With more than projects in over 60 countries Weber Ultrasonics advanced to one of the premier suppliers to system manufacturers of the most diverse industries. We always manufacture our Sonotrodes specifically for each customer and product employing FEM in the design process. Even complex shapes and punches can be designed this way. Based on the individual requirements, high-end materials like Titanium, Aluminum alloys and sintered steel will be used.

Speer tips, sickle blades, punches or cross Sonotrodes — we manufacture the blade with the right shape for each application. All of our Sonotrodes shine with their outstanding cutting depth giving you the right tool to cut towering cakes, bread or cheese wheels as well as other voluminous materials in one pass. Cross-Sonotrode for piercing We developed the Cross-Sonotrode to achieve cross cuts in one process step resulting in faster cycle times and higher precision.

Knife Sonotrodes The Lambda1 cutting Sonotrode with reduced node point allows the cutting of tall products. Sickle Blade Speer tips and sickle blades are being used for the continuous cutting or scoring of foils and dough. Weber Ultrasonics belongs to the world-wide leading suppliers of ultrasonic solutions and components for industrial use. We offer an extensive product portfolio of generators, boosters, converters, and sonotrodes for cutting with ultrasonics tuned to your individual requirements.

We are cooperating with more than 50 system manufacturers and technology leaders in wide range of industries, and incorporate their feedback into the development of our products. This is how we gathered valuable industry know-how and why we can say with confidence that we are able to support you in the development of your individual and tailored solutions.

System Integration, the Key to Success Our experienced and competent solution engineers have successfully completed over projects. Products which think ahead: Thinking Solutions 4. One of our newest innovations is the ultrasonic cutting system SonoTrans, a joint development with Hufschmied Zerspanungssysteme. The SonoTrans is able to cut demanding composite materials like fiberglass, carbon fiber, stacks and honeycomb structures cleanly and fast. Explore the benefits you can have with our solutions and products.

We are looking forward to developing the right solution together with you. Rubber, plastics or butter cream — almost any material can be separated efficiently with ultrasonics. Ultrasonic cutting already offers a solution for most tasks. This technology can be used in many different applications and can be separated into different application fields.