Ultrasonic machining can be used to generate a wide range of intricate features in advanced materials.
Figure 1. Square, round and odd-shaped thru-cuts in alumina.
Engineered ceramic materials exhibit a host of very attractive properties for today’s scientists, design engineers and R&D engineers. Properties of interest include high hardness, high thermal resistance, chemical inertness, tailored electrical conductivity, high strength-to-weight ratio and longer life expectancy. These characteristics make ceramic materials attractive for a variety of applications, including structural, semiconductor, microelectromechanical systems (MEMS), medical, defense, aerospace and electronics. Over the last two decades, the use of engineered ceramic materials in these types of applications has increased rapidly.
Designers, engineers and scientists continue to push the envelope in developing designs that harness the advantages of these materials and their properties. The machining of these materials-to evermore exacting requirements-remains technically challenging. Many of the applications demand intricate shapes, tighter tolerances and finer, more precise dimensions. In addition, minimal surface damage and very specific surface characteristics are critical in many end uses.
Conventional forming and sintering techniques are often not able to meet these demands. Diamond tool machining is limited in the number of feature shapes and sizes possible, and is also time consuming. Electrical discharge machining (EDM) offers a range of feature shapes and sizes, but it is only suitable for use on conductive materials. Since laser machining is a thermal process, heat-affected damage does occur and can have a negative impact on the end use, especially in high-reliability applications.
In contrast, ultrasonic machining (UM or USM) is a non-thermal, non-chemical and non-electrical machining process that leaves the chemical composition, material microstructure and physical properties of the workpiece unchanged. Sometimes referred to as ultrasonic impact grinding (UIG) or vibration cutting, the UM process can be used to generate a wide range of intricate features in advanced materials.
UM is a mechanical material removal process that can be used for machining both conductive and non-metallic materials with hardnesses of greater than 40 HRC (Rockwell Hardness measured in the C scale). The UM process can be used to machine precision micro-features, round and odd-shaped holes, blind cavities, and OD/ID features. Multiple features can be drilled simultaneously, often reducing the total machining time significantly (see Figure 1).
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