Ultrasonic Processing Techniques

Fabrics and films used in the nonwoven, medical, filtration, textile and packaging industries can be processed using ultrasonic energy. Several of the common techniques applied are ultrasonic rotary/continuous bonding, ultrasonic slitting, plunge and traversing.

Rotary/Continuous Ultrasonic Bonding

Ultrasonic bonding assembles two or more layers of materials by passing them between a vibrating horn and a rotary drum (often referred to as an anvil). The figure below illustrates ultrasonic bonding. The rotary drum is usually made from hardened steel and has a pattern of raised areas machined into it.  The high frequency mechanical motion of the vibrating horn and the compressive force between the horn and the rotary drum create frictional heat at the point where the horn contacts the material(s). The frictional heat bonds the material together only at the horn/material contact points. This gives the bonded material a high degree of softness, breathability and absorption. These are the exact same properties which are critical for hospital gowns, sterile garments, diapers and other applications used in the medical industry and clean room environments.

Ultrasonic bonding requires far less energy than thermal bonding which uses heated rotary drums to bond materials together. As a result, ultrasonic bonding is economical and requires no consumables, adhesives or mechanical fasteners.

Ultrasonic Slitting

When a thermoplastic material is slit ultrasonically, its edges are also sealed. Sealing the edges of a woven fabric is beneficial because the yarns are prevented from unraveling and the smooth, beveled edges prevent buildup of the roll material. When two or more layers are ultrasonically slit together, the layers will become joined. The strength of the bond is determined by the material and anvil geometry.

Many factors influence the speed at which fabric can be ultrasonically slit. Some of the parameters are the geometry of the cutting wheel (anvil), the material composition, material weight and thickness.

Plunge Mode

In the plunge method, the material remains in a fixed location and is periodically contacted by the horn. The horn operates perpendicular to the material that is on the anvil. The horn can also be used to cut and seal. Typical plunge applications include but are not limited to:

Traversing Mode

With the traversing method, the material remains stationary and the horn and anvil move across it. Typical applications for this method are cutting materials to length as shown in the photo, and splicing rolls together.

Thermoplastics Used

The fabrics and films best suited to ultrasonic processing contain thermoplastic materials with similar melting temperatures and compatible molecular structure. These materials have many of the following characteristics:

Polyester is considered to be a good material for ultrasonic applications. However ultrasonics can produce strong, neat stitches in both Nylon 6 and Nylon 6/6. Most polyolefins (Polypropylene and Polyethylene) also have good ultrasonic welding characteristics and are one of the lightest weight materials. Characteristics of the most common thermoplastics and their typical fabric and film uses are listed below in order of preference.

Fabric Types and Films

Fabrics are classified into five categories as listed here; Films however have only one category.

Weldability

Many factors influence the weldability of the various fabric and film types. Please send in your material to our laboratory for free feasibility testing.

The process of ultrasonic metal welding uses high-frequency vibrations. Ultrasonic metal welding works by placing the parts to be welded on the anvil.

Next, force is applied to the parts. Then the upper part is vibrated back and forth with the ultrasonic horn.

This causes the parts to rub together. The ultrasonic energy disperses oxide film layers (cleaning the surface) and results in the mixing of metal atoms, without melting the metals. The activated metal atoms join each other, causing a true metallurgical bond.

Ultrasonic metal welding is sometimes called "cold welding" because it works without melting the metals. It cleans and welds at temperatures lower than the melting point of the metals. It most commonly joins nonferrous metals, but can also be used with others, such as when welding aluminum to ceramics.