Ultrasonic Machining(USM)

NON Conventional machining

1. ULTRASONIC MACHINING(USM) BISHAL DAS(BT14ME001) DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY MIZORAM 1

2. CONTENTS WORKING SCHEMATIC DIAGRAM MECHANISMS COMPONENTS ADVANTAGES DISADVANTAGES APPLICATIONS 2

3. WORKING It is a mechanical material removal processes, used to erode material in the form of fine holes and cavities in hard or brittle work pieces. It uses firm tools, vibrations of high frequency and a suitable abrasive slurry-mix The USM process is suitable for machining brittle materials such as:glass,ceramics and semiconductors ,for increasingly complex operations to provide intricate s hapes and work piece profiles. The cutting is actually performed by the abrasive particles which are suspended in the slurry(fluid) USM accomplishes the material removal through the abrading action of the grit-loaded slurry which is kept circulated between the tool and the work piece 3

4. Schematic Diagram Ultrasonic material removal process Ultrasonic machine 4

5. WORKING Small amplitudes and high frequency of vibration are given to the tool, typically in the range of (10-20)µm at 20 -40 kHz. The hard abrasive particles in the slurry are accelerated towards work piece surface by the oscillating action of the tool through repeated impacts . The work piece shape and dimensional accuracy is directly dependent on the geometry of the tool. In this process, high frequency electrical energy is converted into mechanical vibration through a transducer. The high frequency vibrations are transmitted to the abrasive particles in the slurry via an energy focusing device or horn/tool assembly A re-circulating pump forces abrasive ,suspended in a liquid medium, between the vibrating tool face and the work piece The tool shaped like the cavity to be produced, oscillates at amplitude of about 0.013 to 0.062 mm at 19 to 40 kHz(cycles per second) 5

6. Mechanism of Material Removal Although the USM process is commercially used since many decades the exact details of mechanism leading to the removal of fine materials is yet to be understood well. The main mechanism responsible for the material removal in USM are : MECHANICAL ABRASION : This occurs due to the hammering effect of the abrasive particles on work piece through the tool. IMPACT : The freely moving particles impact with a certain velocity on the work piece resulting in micro chipping. EROSION : Due to cavitation's effect of the abrasive slurry, erosion of the work surface occurs. CHEMICAL : Due to the fluid employed chemical effect can come into consideration. 6

7. ULTRASONIC MACHINE The basic ultrasonic equipment consists of the following elements: A generator for high frequency oscillations(Ultrasonic generator ): generator transmits electrical power to the transducer which creates energy impulses in the ultrasonic range i.e. 18-20kHz An acoustic head consisting of transducer and trunk(shank) and Tool and abrasive slurry elements 7

8. The Acoustic Head This is the HEART of the whole equipment and consists of two parts : The transducer which converts the high frequency output of the generator into linear vibrations and The trunk which mechanically amplifies the linear vibrations The shape of the tool holder is cylindrical or conical, or a modified cone which helps in magnifying the tool tip vibrations. Its function is to increase the tool vibration amplitude and to match the vibrator to the acoustic load. Therefore it must be constructed of a material with good acoustic properties and be highly resistant to fatigue cracking . Monel and titanium have good acoustic properties and are often used together with stainless steel, which is cheaper. 8

9. The tool The tool is designed to provide the maximum amplitude of vibration at the free end The selection of the tool material is very important as the tool tip is subjected to vibration and it must not fail due to wear. The shape of the tool, mechanical properties of the material used in tool making are some of the other parameters that may effect the USM process performance significantly Tool material should be tough and ductile. Low carbon steels and stainless steels give good performance. Tools are usually 25 mm long ; its size is equal to the hole size minus twice the size of abrasives. Mass of tool should be minimum possible so that it does not absorb the ultrasonic energy. It is important to realize that finishing or polishing operations on the tools are sometimes necessary because their surface finish will be reproduced in the work piece. Tool and tool holder are often attached by silver brazing. 9

10. Abrasives common types of abrasive - boron carbide (B 4 C) good in general, but expensive - silicon carbide (SiC) glass, germanium, ceramics - corundum (Al 2 O 3 ) - diamond (used for rubies , etc.) - boron silicon-carbide (10% more abrasive than B 4 C) liquid - water most common - benzene - glycerol - oils - high viscosity decreases MMR 10

11. ADVANTAGES Machining any material regardless of their thermal conductivity USM is suitable for precise machining of brittle materials It does not produce any thermal, chemical or any abnormal surfaces Can drill circular or non-circular holes in very hard materials Less stress-concentration because of its n on-thermal characteristics 11

12. DISADVANTAGES/LIMITATION OF USM Soft materials like lead and plastics are not suitable for machining by the USM process, since they tend to absorb the abrasive particles rather than chip under their impact. The USM process consumes higher power and has lower material removal rates(3-15mm 3 /min) compared to traditional fabrication processes. The holes produced in USM have a tendency to break out at the bottom owing to the static load and high amplitudes. While producing deeper holes through USM method, there is ineffective slurry circulation leading to presence of a fewer active grains under the tool face.Due to this, the bottom surfaces of blind holes tend to become slightly concave. 12

13. APPLICATIONS USM process is used in machining hard and brittle metallic alloys, semiconductors ,glass,ceramics,carbides,etc In machining of advanced ceramics for applications in auto-engines components In machining, wire drawing, punching or blanking of small dies Drilling,grinding,profiling,coining ,piercing of dies welding operations on all materials which can be treated suitably by abrasives. Used for machining round, square, irregular shaped holes and surface impressions. 13

14. Various work samples machined by USM 1- The first picture on the left is a plastic sample that has inner grooves that are machined using USM. 2- The Second picture (in the middle is a plastic sample that has complex details on the surface 3- The third picture is a coin with the grooving done by USM 14 1 2 3

15. Thank you 15