A device for clamping at least two components for use in friction stir welding supports the components and holds the components in place using a plurality of channels placed under vacuum for clamping of the components during friction stir welding. Both sides of a welding backup plate may have a mounting device including the vacuum channels, for example. The mounting device may have a contoured support surface for supporting components with a simple or complex surface curvature, allowing the same device to be rapidly configured to a plurality of component types with varying surface curvatures.