What classification is used to describe welds made without filler material?

The classification referred to in the question describes welds made without the addition of filler material, which is accurately identified as fusion welds. In a fusion weld, the base metal is heated to its melting point, causing it to fuse together, and this process does not involve adding any additional material. This method is often used for its efficiency and the strong joint it provides, relying solely on the base materials themselves.

In contrast, the other classifications involve the use of filler material or different configurations. For instance, fillet welds, butt welds, and groove welds may have components where the filler material is utilized to achieve desired joint characteristics or fill gaps between the base metals. Each of these weld types serves specific purposes in joining metals, but they typically do not align with the criteria of being performed without filler material, which is the defining characteristic of fusion welds.