Final answer:
A k-factor is used in Solidworks for sheet metal parts to calculate the flat pattern by considering bending behavior.
Step-by-step explanation:
The type of part that uses a k-factor in Solidworks is a sheet metal part. The k-factor is a value that represents the ratio of the neutral axis' location to the material thickness in sheet metal forming. It is used to calculate the flat pattern of a sheet metal part, taking into account the material's bending behavior.