Modeling and Optimization of Ultrasonic Machining Process Using a Novel Evolutionary Algorithm

Introduction

The technological advancement and introduction of newer materials in the manufacturing field put a challenging task in front of researchers. Mostly, these new materials have high strength, hardness and toughness properties and that make them difficult to machine by conventional techniques. Furthermore, whenever there is a need for complex and intricate shaped products, non-conventional manufacturing techniques are really suitable. Removal of unwanted material from the workpiece is one of the usual practice in all the manufacturing industries. Conventional machining processes like turning, drilling, milling, etc. show poor results as the workpiece is harder than the tool material. Thus, it is necessary to replace and to supplement the existing process with the novel machining concepts. Ultrasonic machining (USM) is one of the non-conventional mechanical material removal processes which uses high-frequency ultrasonic vibration. The other types of non-conventional mechanical machining processes are electric discharge machining (EDM), wire electric discharge machining (WEDM), electric chemical machining (ECM) and abrasive jet machining (AJM). The applications of EDM, WEDM and ECM processes are only limited to the electrically conductive materials. But USM is a widely used and versatile technique in the semiconductor industries for machining of both conducting and non-conducting materials with great accuracy. Thus, the hard and brittle materials which have low ductility properties and high hardness above 40 HRC like glass, ceramics, nickel and titanium alloys, etc. can be easily machined. However, the major hindrance to this process is the low material removal rate.

USM process works at a typical operating frequency of 20-40 kHz. This high-frequency electrical energy is produced by the ultrasonic generator. The piezoelectric or magnetostrictive transducer converts this high-frequency electrical energy to the mechanical vibration with some amplitude. But, this amplitude of vibration is not sufficient for machining purpose. Thus, a booster is generally used to amplify this amplitude. The ultrasonic energy transferred to the abrasive particles by a horn/tool. This tool is vibrated in a specific direction which is usually perpendicular to the workpiece surface. The abrasive slurry flows on the workpiece surface and underneath of the tool tip. The repetitive hammering of the tool tip on the abrasive particles of the slurry lead to the brittle fracture of the workpiece and the formation of a cavity precisely similar to the shape of the tool. Gradually, the tool is advanced in the direction of vibration until a through hole is produced. Figure 1 illustrates the schematic diagram of ultrasonic machining process on the brittle material. The beautifulness of the whole process is that there are no metallurgical and chemical composition changes during machining.

Figure 1.

Schematic representation of USM setup