the lifting fork frames — Fig. 1. The six-axis Arc Mate 120 iC series belongs to the electric servo-driven family of robots designed for precise, highspeed welding and cutting (Refs. 6, 8–10). The basic technical parameters for the welding robot are given in Table 3. Measuring the Production Time The time for manufacturing a frame for lifting forks with SMAW was measured in the first phase of the experiment. The time was measured in a manual welding workstation and was divided into the main production time and associate production time. Production time was defined as the time required for making a single product or part. Associate time is that consumed by the operations not directly related to the production process, e.g., replacement of welding wires, weld nozzle cleaning, and transport of parts from one workplace to another (e.g., from the welding shop to the paint shop). The resulting time is the arithmetic average of all measured times in one welding workstation. Figure 2 shows the proportion of initial time for manufacturing operations of the frame for lifting forks. Design and implementation of solutions were carried out in the second phase of the experiment. Despite several efforts, utilization of the original design did not reach the required tolerance of ±0.5 mm. Therefore, design changes that would provide the required precision were proposed. Since the original part was unsatisfactory in terms of structure, the technical drawing was redesigned using Roboguide 8 Weld Pro software. The old frame design did not meet the precision requirement for the initial positions of so-called zero points. Construction of the weldment was intricate, consisting of a high number of parts with 45-deg bends in some cases — Fig. 3. The objective of testing was to eliminate all deficiencies in the program. A welding technologist was consulted regarding any incorrect welding parameters. The change in the frame design was performed in Autodesk Inventor ®. The bearing plate of the fixture, lower girder frame, and upper girder frame were not changed, as these parts are not supposed to have a significant effect during robotic welding. The left quick-clamping device, the right quick-clamping device, fixture plate, middle beam, and frame side plate were reshaped. The upper beam, upper bearing girders, and a grid were completely removed from the original design. The main flange along with the upper beam and upper bearers were replaced with side plates and the upper frame. The design drawing for the lifting fork frame after the design changes is shown in Fig. 4. The operating program was written in Roboguide 8 Weld Pro software. Before programming and simulation, it was necessary to configure the visualization software. Simulation of the operation program was started after performing configuration and settings of all welding parameters, inserting the points and setting the trajectory for the welding gun. In cases of collision of the frame with the welding gun, the points where the collision occurred were adjusted. Upon successful completion of simulation, the program was prepared for implementation in the robotized workplace. Figure 5 shows the welding robot in Roboguide during the weld simulation. The implemented solutions were tested in the last phase of the experi- 56 WELDING JOURNAL / MARCH 2016 Fig. 2 — Graph showing the proportion of initial time for manufacturing operations of the frame for lifting forks. Fig. 3 — The original technical drawing of the lifting fork frame.
Welding Journal | March 2016
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