When two or more letters appear together and you hear each sound that each consonant would normally make, the combination is called a blend. For instance, the word blend has two consonant blends: bl, for which you hear the sounds for both b and l, and nd, for which you hear the sounds for both n and d.
Digraphs: 2 letters that make one sound.
In the world "fang", the sound of the letters "ang" are welded together. Rather than pronouncing each letter, this group of letters create a singular sound that cannot be broken into its individual components of the letters "A," "N" and "G." This is a welded sound--one that helps define the sound of a word as the letters work together rather than individually.