Robotics Case Studies
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Robots Speed up Flashlight Assembly, Cut Costs
DENSO Robotics Posted 11/13/2008SureFire LLC, located in Fountain Valley, Calif., is a manufacturer of professional-grade, high-intensity flashlights. The extra-rugged, extra powerful flashlights are used in a variety of demanding applications.
Although much of the flashlight assembly process was already automated or semiautomated, the company, which has a continuing program of finding ways to streamline its manufacturing operations and increase their efficiency, began implementing articulated robots to replace its existing hard automation equipment, as well as to integrate and automate previously semiautomated lean cells.
The robots have had several benefits, including: (1) dramatically reduced operator labor; (2) higher output; (3) more consistent quality, resulting in reduced scrap and rework; (4) reduced usage of valuable factory floor space; (5) greater manufacturing flexibility; (6) built-in R&D capability and (7) faster ROI than hard-automation equipment.
As of now, the company has installed two robot cells; several more are being planned. In the first cell, a DENSO VS-Series six-axis articulated robot picks up flashlight and mounting-rail parts from a conveyor belt and presents them to a laser. The laser engraves the parts on up to four sides with serial numbers and other information. After engraving, the robot places the parts onto an outgoing conveyor.
Previously, an indexing table was used, with stationary fixturing that required an operator to load and unload the parts multiple times, once for each side to be engraved. Now, however, the robot, with its articulated wrist, presents each side of a part in turn to face the engraving laser, so the operator has to load and unload the parts only once.
With less setup, less manual part handling and a more constant output flow, one operator can run multiple machines. In addition, the robot’s versatile gripper can handle a variety of different parts, eliminating the time and cost required to produce fixtures. Cycle time is now only 24 seconds, compared with 48 seconds before, boosting output by 100 percent.
In the second cell, another DENSO six-axis articulated robot, equipped with a three-function gripper, assembles flashlight tail-cap units, consisting of a tail cap, retainer ring, spring holder, spring and drive stud. Here, a single robot performs multiple functions formerly carried out by five different operators, each at a separate station, plus an additional operator to load and unload parts.
To begin the assembly sequence, the robot picks up a drive stud from the drive-stud dispenser and places it into a spring holder. The robot then picks up a tail cap and takes it to a glue dispenser, which places glue onto the interior threads of the cap. Next the robot inserts a retainer ring into the cap and presents it to a screwdriving machine, which tightens the ring in the cap. The robot then inserts a drive stud, spring holder and spring into the cap assembly and presents the assembly to a press, which fits the spring into the spring holder. Finally, the robot removes the completed assembly from the press and places it into a parts box on an outgoing pneumatic shuttle.
The new cell takes up much less floor space than the several semiautomated stations previously used, and can be run by just a single operator—the same one who runs the first cell—drastically reducing labor costs. Having only one operator also makes it easier to pinpoint and correct sources of error. In addition, cycle times have been cut in half, from 76 seconds to 38 seconds, doubling output.
Even though the cell is compact, the design is flexible enough to accommodate a second robot, which would bring the cycle time down to approximately 20–25 seconds, essentially doubling production output again. Also, the current robot uses only 120 degrees of its total 340-degree work envelope. This leaves 220 degrees of work envelope behind the robot available for R&D activities, eliminating the cost of building a dedicated R&D cell, or for future assembly operations should the need arise.
So far, all the integration and construction of these robot cells has been done in-house at SureFire, with most parts fabricated in the company’s own machine shop. Daniel Fischer, SureFire’s vice president of assembly operations, who has a degree in automation engineering and previous automation experience, said, “In-house integration isn’t for everyone, of course, but for us it had a lot of advantages. The robots themselves were easy to set up and program, especially using DENSO’s 3-D offline simulation software. And naturally we saved a considerable amount of money by designing and building our own cells. ROI is pretty fast this way—running two shifts, it’s only a little over a year.
“But more importantly, by using ‘concurrent engineering,’ we were able to do things in stages, so that we had practically no downtime, which also translates to a substantial cost savings,” Fischer said. “Having our own machine shop also makes it very convenient to get minor changes done whenever we need them, without having to do drawings.”