Spot Welding in the Automotive Industry with Offline Programming
Car manufacturing has been one of the key drivers in the technical development of industrial robots as the preci- sion handling of spot-welding guns was one of the first breakthrough use cases (Fig。 54。12) body-in-white (i。 e。, unpainted car body) assembly is mostly done by robots, very much in contrast to the final assembly which is
Fig。 54。15 A robot-guided tool for handling and processing limb
material, in this case a self-adhesive seal for car bodies
dominated by manual work。 Demands for faster cycle times have led to a concurrent and coordinated motion of the spot-welding gun and robot: the robot continues to move while the weld gun is simultaneously rotated about the electrode axis during welding [54。43]。
Most of a spot welding robot’s programming is done using offline programming (OLP) packages (Fig。 54。13。 A library of robots, devices, and ad- vanced CAD capabilities helps plan, program, vi- sualize, and optimize layouts and complete produc- tion cycles under assumed manufacturing conditions。 Robot programs can be generated and downloaded to robots workcells。 A critical step is the calibration
Fig。54。16a,b Design of the KUKA iiwa: (a) Shape and (b) integra- tion of joint mechatronics
of the robot workcell with respect to the simula- tions [54。44]。
Arc Welding in Metal Construction
Normally steel constructions are designed using CAD programs that offer functions for GMAW-task defi- nitions such as welding parameters, multipass seams, weld beads sequencing, etc。 This information may be used for automatically generating welding robot pro- grams, even in the case of lot-size one jobs。
As an example, the generation principle of a weld- ing robot program is depicted in Fig。 54。14。 Large- scale trusses of up to 15 m for large halls are welded- to-measure。 The robot program is generated from the CAD drawing with process relevant information。 Work- piece tolerances for example, induced by placing the steel components into the fixtures, by bending of the material under its own weight are compensated through active measurement。 The robot-mounted sensor locates the weld seam by laser-based vision for shifting the generated programs in such a way that they match the actual weld seams。 This calibration is automatically performed if expected and actual bead locations are within a range of ˙2:5 cm。
54。4。3 Assembly
Assembly in manufacturing describes the combination of subsystems or components to systems of a higher complexity through joining。 Assembly in manufactur- ing comprises four process groups: joining, handling, controlling, and auxiliary processes (cleaning, adjust- ment, marking, etc。) [54。45]。 The composition of these four functions may vary depending on batch size, product, and throughput: from assembly workcells to high-throughput assembly lines。 Assembly processes form up to 80% of a product’s manufacturing cost and this is where the greatest competitive advantage can be gained [54。46]。 Therefore, optimization in as- sembly includes tightly interweaved aspects: Design
Table 54。2 Assembly subprocesses or modules and their implementation on the KUKA LBR iiwa
Assembly
subprocess
Characterization Principle
search: search module which supports several search motions or search strategies
peg in hole: execution of
Search motion type examples:
● Linear
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