Deciding whether to convert manual or semiautomatic arc welding stations over to robotic welding is typically driven by the payback or return on investment achieved through labor savings. But labor savings do not comprise the total anticipated savings, which are generated from a variety of other process-related areas.
The decision to convert manual or semiautomatic arc welding stations over to robotic welding is most often driven by the payback or return on investment achieved through labor savings.
Though direct-labor savings from the welding operation alone does not comprise the total anticipated savings in labor, it is a major contributor. Additional savings come from reduced consumable use due to improved consistency in weld size and length, fewer repair welds, less post-weld cleanup, reduced floor space, reduced recruiting and training of welders, and improved efficiency of material flow.
To perform a cost-justification analysis for installing a robotic welding system, a shop manager should compare current welding labor costs to anticipated savings for performing the same weld manually and robotically. By timing the current manual process, then using the formulas and worksheet as shown in Table 1, the potential savings become transparent, as does the required part volume required to achieve a two-year payback on your investment.
For example, let’s examine the costs to weld a three-component assembly semi-automatically by the gas metal arc process with .045 in wire. The operator deposits three 8 in long welds at a welding speed of 30 ipm, or 16 seconds per weld. Welding the assembly by robot, assume a two-station cell with fixed worktables; welding speed at 35 ipm or 14 seconds per weld. Let’s assume the capital investment in the robotic welding system is $60,000.
Reference Table 1 for the typical cycle times that are applied to these process elements:
(1) Load-unload performed at one station while the robot welds at the other station.
(2) Time required to lift torch, raise and lower hood, and start weld.
(3) Typical time, based on robot acceleration, motion, and deceleration specifications; will vary based on the size of the assembly and the robot arm purchased.
(4) Robot welding speed typically outpaces that of manual welding.
(5) With stationary tables, rather than indexing tables, any motion between the two tables occurs during welding. When using indexing turntables, indexing time will range from three seconds for a high-speed servo-driven table to 20 seconds for a large ferris wheel setup.
(6) Operating efficiency, or up-time, based on industry averages, accounting for work-breaks and slowdowns experienced by welders.
(7) Total time divided by operating efficiency.
(8) Based on national average of labor and overhead of $30.00 per hour.
With a cost savings of $.36 per weldment, the required number of parts to payback the estimated $60,000 cost of the robotic welding cell comes to 166,667 units. Therefore to achieve a two-year payback, assuming a 50-week work year of five days per week, a fabricator would have to weld 333 assemblies per day.
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