Ultrasonic horns are metal devices that amplify the vibration amplitude of ultrasonic transducers – boosters and then transfer the acoustic energy to the plastic parts being welded. They are widely used for various applications involving solid or liquid media, such as welding, cutting, homogenization, sono-chemistry, etc. In this blog post, we will discuss the factors that affect the choice of material for making ultrasonic horns utilized in plastic welding, and the advantages and disadvantages of different materials.

The main factors that determine the suitability of a material for making ultrasonic horns are:

• Fatigue strength: The ability of the material to withstand repeated stress cycles without breaking. This is important because ultrasonic horns vibrate at high frequencies and amplitudes, which can cause fatigue failure over time.
• Acoustic properties: The speed of sound and acoustic impedance of the material. These affect the resonance frequency and efficiency of the horn. Ideally, the material should have a high speed of sound and a high acoustic impedance to match the transducer and booster.
• Surface hardness: The resistance of the material to abrasion and wear. This is important for applications that involve contact with hard or abrasive materials, such as metal insertion, glass-filled parts, or plunge cutting that will cause wear to the tooling.

Based on these factors, three common materials are used for making ultrasonic horns: titanium, aluminum, and steel. Let’s compare their pros and cons:

• Titanium: Titanium is the preferred choice of material for making ultrasonic horns because of its good fatigue strength, excellent acoustic properties, and good surface hardness. Titanium horns can be coated with materials like carbide, nickel, or TIN for applications that require high amplitude and a harder surface. However, titanium is an expensive material and not always readily available in a convenient range of sizes. Horns up to 6.0 inches in diameter or 3.5 inches in width and/or length (for rectangular or block horns) are commonly manufactured from titanium.
• Aluminum: Aluminum has excellent acoustic properties, which makes it suitable for making large horns over 6.0 inches in diameter or 12.0 inches in width. It is a lower-cost material, readily available in a wide range of raw material sizes, and easy to machine. Therefore, it is a good choice for making prototype horns or horns that require complex machining. However, aluminum has poor surface hardness and moderate fatigue strength, which can make it unsuitable for long-term, high-wear production applications. Aluminum horns can be coated or plated with materials like chrome or nickel, to help alleviate these problems.
• Steel: Steel can be heat-treated for a wear-resistant surface, which makes it well suited for applications that cause severe wear, such as metal insertion, welding glass-filled parts, and plunge cutting applications. Due to its hardness, steel horns are more brittle and are usually used for low amplitude applications.

In conclusion, choosing the right material for making ultrasonic horns depends on several factors, such as the size, shape, frequency, amplitude, and application of the horn. The dimensions in this blog are mostly representative of 20kHz tooling. It is best to consult with an expert before selecting a material for your specific application. If you have any questions or need advice on choosing the right material for your ultrasonic horn, please contact us today!