Fixed, rail or gantry robot: which one fits your part
What part size a fixed robot covers, when a rail is needed, when to hang it, and what 8 and 9-axis configurations are for.
The question is not how many axes the robot has, but how big the largest part you will weld is. With that, the configuration is chosen: fixed robot with table or positioner, robot on a rail, robot hanging from a carriage, or 8 and 9-axis gantries.
Fixed robot with table or positioner (6 axes)
With a robot of about 2 m reach, the welding area reaches roughly 1,200 mm wide by 2,000 mm long, and the two dimensions limit each other. A one or two-axis positioner turns the part to weld flat and allows taller parts. It is the most compact option for supports, brackets and medium assemblies.
Robot on a floor rail (7 axes)
The robot travels on a rail beside the part. The width it covers is still about 1,200 mm, but the rail sets the length: it suits beams, long profiles or several stations in a row, loading one while another is welded.
Robot hanging from a carriage (7 axes)
With the robot inverted on a carriage that travels along the part, the usable width grows: up to about 2,200 mm with a 2 m robot and about 1,300 mm with a 1.4 m one. The rail sets the length again. It is the typical configuration for chassis, frames and built-up beams welded from above.
8 and 9-axis gantries
When the part is wide and long, the robot hangs from a gantry that moves in two or three directions (X, Y and Z). The axis travel defines the work area, so it is sized to order: columns, panels, bridges and large structures.
The usable area is smaller than the reach
Catalog reach is how far the wrist goes, not how far it welds well. The torch needs a correct angle, the laser has to scan the joint first, and collisions with the part must be avoided. That is why the figures above are references: the final configuration is confirmed by simulating the largest part.
