Many years ago, when robots were introduced to the manufacturing arena, their mission was to relieve workers of the most dangerous and hazardous processes. Initially, these included manipulating parts from furnaces, presses, toxic solutions, and welding operations.
A typical Robot System integrated with a Machining Center…complete with safety fencing, monitoring and part queuing stations
Like any new process, robots were introduced with many skeptics. Non-believers thought the human process could not be replaced…and that robots were too cumbersome to do the job at hand. Also, many felt threatened by the use of robots as they were perceived as causing the elimination of someone’s job and not improving the overall workplace performance.
Over time, the use of robotics has expanded as manufacturers realized the benefits that they can bring to manufacturing processes. Today robots are commonplace in the assembly of automobiles and many of their components. The benefits of robots include the ability to work 24/7, reduced labor costs, repeatability of the process, reduction of accidents and scrap.
Presently, the use of robots is finding itself in operating rooms doing surgical procedures where accuracy is a must. In manufacturing, their use has expanded beyond assembly, to the machining operations where they are used for loading and unloading parts from lathes and machining centers. This has brought change and challenges to the way parts are fixtured and processed.
With the use of robotics comes different design requirements of the fixturing.
Fixtures now have to provide enough clearance to allow robot arms to manipulate the parts into the work nest and provide better chip evacuation. In addition, fixtures have to provide the ability to retain the parts in a free state prior to clamping and unclamping. Lastly, fixtures must have the capability of knowing when a part is not sitting properly in the work nest.
A Robot loading parts on to the Hydraulic Fixture within the work area of the Machining Center
To begin the process of the robot with the workholding fixture, the loading surface has to be designed with better chip evacuation and to be clean of any foreign material that would not allow the part to seat properly in the work nest. This may require an air or coolant source to remove chips or debris on the work area. In most cases the area is flooded with a coolant flush from the machine and then an air blast from the robot arm. Next the robot has to have the ability to load the part in the nest without the part falling out before it is being clamped. This requires a provision for some type of preload mechanism to hold the part in position for the clamping. This may be simple spring clips or a spring loaded low pressure clamp mechanism. Once the part is now in the preliminary load on the work nest, the final clamping of the part takes place with the robot retracted. However, confirmation of the part being located and properly clamped is required prior to the machining process. This is usually done with air sensing on the Locator Pads and/or Part Clamps. Basically, a low air pressure is forced through a small hole in the locator or clamp. If the part is located properly (thus blocking the air passage), it will signal an increase in air pressure which, in turn, signals to the machine control that the part is located properly. If the part is not seating properly, the air pressure will drop off and will signal an error in the process.
Adding to the intricacy of the fixture…
Providing the preliminary part locators and part sensing into the fixture design adds to the intricacy of the fixture. The hydraulic and air lines are normally internal to the base plates and work nests. This allows a cleaner fixture with better access and chip disposal. Hard piping is cheaper, but in the long run, takes up more space and tends to collect chips, and is susceptible to damage and leaks.
Once the machining is complete, the unload/load sequence of the robot is ready to complete the cycle. First the hydraulic clamping has to be disengaged allowing the parts to sit ready for unload. The machine control then initiates the coolant flush and the robot takes over the operation, grabbing each part and going through the load/unload sequence. This is a continued safe repeatable motion and timed process.
Today, as greater flexibility and quick changeover become the requirements to be competitive in manufacturing, the connection between Robots and the Fixtures will become much more sophisticated and an intricate part of the fixture design. Eventually, it is not that farfetched that a robot may become the fixture as well as the part handler.
Photos courtesy of Makino Production Machinery Group.