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Adding Value and Functionality to the Precision Machining Process

Wed, 01/14/2009 - 9:25am
Patrick Laughter
In their efforts to optimize processes in order to more efficiently move product out to the market, medical device manufacturers need to be consistently reviewing their SOP to see if enhancements can be made. Automation is one option that some OEMs have examined. This article provides a brief overview of the advantages that can be realized by adding robots to a precision machining process.

Patrick Laughter is a regional engineering sales manager with DENSO Robotics. He can be reached at 937-475-7034 or patrick_laughter@denso-diam.com.

As medical device manufacturers continue to look for ways to reduce process inefficiencies in their precision machining operations, they are increasingly turning to the use of robots, which are well suited to tending CNC lathes.

Besides feeding and removing parts, robots can perform additional, secondary operations. For both machine tending as well as secondary operations, robots provide significant value-added benefits, such as lower cycle times and higher quality. By eliminating operator error and other human variables, robots can also greatly help to reduce the time and cost of process validation, an especially important consideration in medical device manufacturing.

Traditionally, manufacturers have automated or semiautomated their CNC lathes through the use of bar feeders. These units feed bar stock, typically in 12-foot lengths, into the lathe. Once the part has been machined, the lathe cuts it off from the bar stock, letting it drop into a bin or other container.

For many applications, bar feeders have significant drawbacks. First, they can only be used with round or hexagonal stock, most often 2.5 inches or smaller in diameter. This usually eliminates parts that have a larger diameter, require oblong or otherwise odd-shaped stock, consist of a casting, or have already been partially machined.

Six-axis articulated robots can streamline a precision machining process by performing secondary operations in addition to machine tending.
In addition, bar feeders are necessarily large, taking up valuable factory floor space and, like all hard tooling, they have limited functionality. Also, if the parts are delicate and easily damaged, as is often the case with medical devices, letting them fall into a parts container may be unacceptable. For such applications, filling the container with heavy oil allows the parts to sink slowly to the bottom and protects them from damaging each other. This requires additional setup and cleaning steps, however.

Robots provide a flexible, efficient alternative to bar feeders. One of their major advantages is their small footprint, which saves valuable factory floor space. In some cases, with a dust- and mistproof configuration to protect them from flying debris and cutting fluids, they can be mounted inside the CNC machine itself, saving even more space. They can also be mounted externally on a moving track, either on the floor or overhead, allowing a single robot to tend two or more machines.

In a machining operation, the robot's basic tasks are to pick up a part from a pallet or incoming conveyor, place it into the lathe's chuck, remove it when it is done and place it in a parts bin or on an outgoing conveyor. Although robots operate at high speeds, their precise, controlled movements let them handle delicate parts with care. After the part is machined, the robot can carry out secondary operations, such as inspection, deburring, polishing or other surface finishing, packaging into trays or boxes, etc.

In addition, if a robot is equipped with vision, it can pick from randomly arranged parts of different sizes, shapes, and colors. It can also communicate to the lathe which part to run, allowing small-lot and mixed production to be performed automatically, without changeovers.

For CNC machine-tending, six-axis articulated robots are the usual choice. Four-axis Cartesian robots can also be used, but the two additional axes of six-axis robots give them much greater flexibility in performing complex secondary operations. Also, even though four-axis robots are generally faster than six-axis robots, the six-axis robots are still very fast, and for most CNC machine-tending applications, the difference in speed between the two types is usually not a factor.

Online
For additional information on the technologies and products discussed in this article, see MDT online at www.mdtmag.com or DENSO Robotics at www.densorobotics.com.
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