Ultrasonic 

Metal-Weld Anvils

The basic process of welding metals together with ultrasonic vibrations involves vibrating one item at ultrasonic frequencies relative to a second item that is held stationary. When this process occurs, the two parts are pressed together with a moderate force. The weld anvil serves two purposes in this process. First, the anvil must grip and hold one of the components stationary relative to the ultrasonic vibrations. Second, the anvil is the static component of the clamping mechanism that applies the squeezing force to the weldment.

It is crucial to the success of the weld cycle that the anvil be mounted in such a way that it remains stationary relative to the ultrasonic vibrations. The shear forces generated during a weld cycle can be surprisingly significant. If the anvil design or mounting allows any movement, the efficiency of the weld cycle is diminished.

The anvil has a weld pattern machined into its surface. This pattern, which is used for gripping, is similar to that of the horn, with high ridges and low valleys. The ridges and valleys can either have sharp points (teeth) or radiused edges (waves) and can also be machined as straight serrations or on an angle to produce individual peaks (knurls). As the weld cycle starts, the anvil weld pattern seats into the lower weldment component and prevents it from vibrating. This ensures the relative motion of the ultrasonic energy is focused to the weldment interface and not dissipated elsewhere. 

The second function of the anvil is to provide a stationary, opposing force for the clamp pressures, which are generated by the welder and that squeeze the weldment during the weld cycle. 

While choosing an alloy for an ultrasonic metal weld anvil, consideration must be given to the alloys suitability for ultrasonic tooling, and for the particular application. Steel alloys that are high in vanadium may be good for some applications but detrimental to others. Also, due to elevated temperatures obtained with some applications, an anvil may need to be manufactured using an alloy designed specifically to withstand higher levels of thermal stress. 

Another consideration is the heat treat characteristics of an alloy. Anvils made from very hard metals do not necessarily equate to longer tool life. Generally, as hardness is increased, a metal becomes more brittle. Anvils made from brittle metals will crack and break prior to wearing down from use. There are several alloys that can be used for anvils and the specific metal used is usually determined by the application. Anvils are heat treated to exact specifications and undergo specialized surface treatments that aid in maximizing tool life.