Describe the 3 types of defects that occur in ultrasonic add

Describe the 3 types of defects that occur in ultrasonic additive manufacturing and how to reduce the occurrence of each.

Solution

The most common defects in ultrasonic additive manufacturing made parts are voids.

3 types of defects -

TYPE 1

These defects are the voids along layer/layer interfaces due to foil surface roughness and/or insufficient input energy. Since the metal surfaces have not bonded, oxide layers are not damaged and removed, and can be observed. Type-1 defects typically have a flat upper surface and a rounded lower surface.

TYPE 2

These defects are damaged areas, also at the layer/layer interface that are created when excess energy input during ultrasonic additive manufacturing results in the breaking of previously formed bonds. Since bonding has occurred, oxide layer has been disturbed and are difficult to locate. Type-2 defects thus have a different morphology than type-1 defects as the represent voids where the interface has been torn apart after bonding, rather than regions which have never bonded.

TYPE 3

These type of defects are found between adjacent foils within a layer. Type-3 defects are the physical gaps between adjacent metal foils.

REDUCE THE OCCURRENCE OF THE DEFECTS :-

Process Parameter optimization (including optimization of width settings) to minimize Type-3 defects is the most effective means to increase bond strength. With optimized parameters Type-1 and Type-3 defects are minimized and Type-2 defects do not occur.

Type-1 defects can be reduced by surface machining a small amount of metal (10 micro meter or the largest roughness observed at the uppermost deposited surface) after depositing each layer. Post process heat treatment can also be used to significantly reduce all types of defects.

The degradation of part mechanical properties due to type-3 defects can be reduced by designed arrangement of successive layers. Successive layers in a ultrasonic additive manufacturing part can be arranged so that 50% overlap across layers is obtained.