A Comprehensive Guide to Ultrasonic Machining

Ultrasonic machining (USM) is an advanced machining process that uses the power of high-frequency mechanical vibrations to remove material from a workpiece.

By applying ultrasonic vibrations (typically in the range of 20 kHz to 50 kHz), ultrasonic machining provides exceptional precision and efficiency in shaping and machining a wide range of materials, including hard and brittle substances.

This unique technology uses an abrasive slurry or particles introduced between a vibrating tool (called a sonotrode) and the workpiece, causing localized wear and material removal.

This blog will dive into all the important information related to ultrasonic machining, how it works, applications, advantages and disadvantages.

1.Ultrasonic Machining

Ultrasonic machining (USM) uses ultrasonic vibrations and an abrasive slurry to erode material from a workpiece. This non-thermal machining process excels in machining complex and brittle materials while maintaining structural integrity.

USM can be used to create complex shapes in semiconductors, ceramics, and jewelry that may not be met by conventional methods.

2.What is Ultrasonic Machining?

Ultrasonic machining is a non-traditional machining process that uses abrasive particles to remove material from a workpiece. In this method, the tool does not directly strike the workpiece, but instead introduces abrasive particles between the workpieces.

These hard abrasive particles are able to produce impact erosion on the workpiece material, similar to the way impact is used. The process involves the use of ductile tool materials to prevent brittle fracture during hammering, thereby achieving precise material removal and fine machining of complex components.

3.Ultrasonic machining parts

Ultrasonic machining consists of several basic parts that work together to achieve precise material removal:

1) Power supply

The power supply, also known as a high-frequency generator or electronic oscillator, converts standard electrical energy into high-frequency electrical energy, generally at a frequency of 20-40kHz, with a small vibration amplitude in the micron range.

2) Speed ​​converter

The speed converter or horn amplifies and focuses the vibration of the sensor to an intensity suitable for driving the tool during the cutting operation. It is made of hard, non-magnetic and easy-to-machine materials such as K-Monel, metallic bronze or mild steel.

3) Tool

The tool is made of ductile material and uses abrasive particles to hammer or impact to remove material from the workpiece. Wear resistance and fatigue resistance of the tool are critical because the ultrasonic frequency increases the hammering rate, thereby increasing the material removal rate.

4) Abrasive slurry

A slurry of abrasive particles is applied between the tool and the workpiece to facilitate material removal. Abrasives, such as boron carbide or silicon carbide, are hard and rigid, ensuring efficient machining. Fresh abrasives are continuously supplied via a water jet to maintain optimal machining efficiency.

5) Electromechanical sensor

The transducer converts electrical energy into mechanical vibrations, transmitting a low-amplitude, high-frequency signal to the tool. There are two types of transducers used: piezoelectric transducers and magnetostrictive transducers.

6) Sanding gun

The abrasive gun delivers abrasive slurry to the machining site through a water medium, ensuring a continuous supply of fresh abrasive at a controlled pressure. The water jet also removes debris and broken abrasives from the machining process.

7) Workpiece

Ultrasonic machining is well suited for machining brittle, non-conductive materials, such as engineering ceramics, without introducing thermal damage or residual stresses. The process is able to precisely machine complex 3D shapes on the workpiece.

4.How Ultrasonic Machining Works

Ultrasonic machining works by maintaining a 0.25 mm gap between a ductile tool and the workpiece, with a slurry of abrasive particles injected between the two.

As the tool moves downward, the embedded abrasive hammers the workpiece, effectively removing material. The slurry helps flush material from the machining area, ensuring a clean result and allowing the creation of straight holes with a slightly tapered tool.

In ultrasonic machining, varying certain parameters can affect the material removal rate (MRR). Increasing the viscosity of the carrier fluid causes the MRR to decrease because flushing is less efficient. Increasing the frequency causes the MRR to increase because more impacts occur per unit time.

Similarly, increasing the amplitude increases the MRR by enhancing the momentum of the abrasive. The amplitude of the vibrations can vary from 5 to 75 µm, while the frequency ranges from 19 to 25 kHz.

In addition, the MRR can be affected by adjusting the concentration and size of the abrasive. The higher the abrasive concentration, the greater the impact force and the higher the MRR, until collisions between the abrasive particles cause momentum loss, which reduces the MRR. Likewise, increasing the size of the abrasive results in a larger impact area, but beyond a certain size the momentum of the abrasive is reduced.

In terms of material removal rate, it is important to note that ultrasonic machining (USM) is somewhere between electrochemical machining (ECM) and electrical discharge machining (EDM).

5.Applications of Ultrasonic Machining

Ultrasonic machining is widely used in various industries due to its unique capabilities:

1. Machining of non-conductive ceramics: Ultrasonic machining excels at machining non-conductive ceramics, making it ideal for precision molding and complex designs of ceramic parts.
2. Machining of brittle materials: Materials with high scrap rates, especially brittle substances, can be effectively machined using ultrasonic machining, ensuring minimal material waste and precise results.
3. Drawing, punching and blanking dies: The process is used to manufacture dies used in drawing, punching and blanking operations, achieving accuracy and consistency in die production.
4. Dental applications: Ultrasonic machining enables dentists to drill holes of any shape in teeth without causing pain, providing a precise and painless dental treatment experience.
5. Quartz, Glass and Ceramics Grinding: It is used for precision grinding of materials such as quartz, glass and ceramics, ensuring high-quality surface finish and dimensional accuracy.
6. Cutting Industrial Diamonds: Ultrasonic machining is used to cut industrial diamonds, making precise and intricate cuts to these precious and hard materials.
7. Mold Manufacturing: The process is also used to make molds for various applications, such as molds for casting, embossing and molding operations.

6.Advantages of Ultrasonic Machining

Ultrasonic machining has several advantages that make it the first choice for specific applications:

1. Processing of brittle, non-conductive, hard and fragile materials: Ultrasonic machining excels at processing brittle, non-conductive, hard and fragile substances, providing precise molding and material removal.
2. Almost no heat is generated: Since there is no heat generation, the physical changes caused by ultrasonic machining in the workpiece are minimal, ensuring that the material properties and dimensional stability are maintained.
3. Suitable for non-metallic materials: Materials with poor conductivity cannot be effectively processed by EDM and ECM, but can be easily processed using ultrasonic machining.
4. Burr-free and deformation-free process: Ultrasonic machining can achieve burr-free and deformation-free machining, resulting in a clean and precise finished surface.
5. Compatibility with other technologies: Ultrasonic machining can be combined with other advanced technologies such as EDM, ECG and ECM to enhance the capabilities and versatility of the material removal process.
6. Noiseless operation: Ultrasonic machining is silent during operation and is suitable for applications that require low noise levels.
7. User-friendly equipment: The equipment used in ultrasonic machining can be operated by skilled and unskilled operators, making it easy to use and more widely applicable.
8. High surface finish and precision: The process provides excellent surface finish and high precision, ensuring the production of precise and complex-shaped parts.

7.Disadvantages of ultrasonic machining

Despite its advantages, ultrasonic machining also has certain limitations:

1. Low material removal rate: Compared with some traditional machining methods, the material removal rate of ultrasonic machining is relatively low, making it less suitable for high-volume material removal applications.
2. High energy demand: The process requires a relatively high energy input for the cutting operation, which affects the overall efficiency and operating costs.
3. Difficulty in machining soft materials: Soft materials are easily deformed and damaged under the strong impact of abrasive particles, so they face challenges in ultrasonic machining.
4. Limited deep hole machining: Drilling deep holes can be challenging in ultrasonic machining because the movement of the slurry is restricted, which may hinder effective material removal.
5. High tool wear rate: The presence of abrasive particles in the slurry will lead to increased tool wear, shorten tool life and require more frequent tool changes.