Cutting, Drilling or Milling Robots Applications
Cutting, Drilling and Milling robots are the most common robot manufacturing applications for removing material.
More and more we are finding industrial robots being used to perform milling and trimming operations where in the past particularly in the case of milling these were traditionally carried out by CNC machines.
There are two major advantages of using a six-axis robot:
- The first the ratio – “envelope against price” is low. In other words, it is possible to mill big things for not too much money.
- The second is the ability of the robot to mill from different directions including undercutting. By adding an external axis to the robot to provide a rotating turntable or positioner this allows milling most complex shapes.
Main Factors for Milling Robots
We must, however, mention at this stage the two considerations to take into account with robotic milling and to a lesser degree trimming:
Firstly, the accuracy of milling operations carried out from a program created via an offline source. Basically, there is a difference between jogging the robot by eye using the teach pendant and saving a position compared to generating the position offline.
If we use the teach pendant then we are asking the robot when it runs the program to go back to the position that we just saved. If so, we are working with the “repeatability” of the robot, typically around +/- 0.15mm. In the case of an offline program, the position has been calculated mathematically from a datum point and we are expecting the robot to move mechanically to that point. In this respect, we are working with the “accuracy” of the robot, typically around +/- 1.0mm.
The ability of the robot to accurately move to a calculated point from an offline source will also bring in the tolerances involved from teaching the TCP or tool centre point. Also, the definition of the local coordinate system, and the tolerance of the placing of the part (in the case of trimming or stock in the case of milling) on the fixture.
Secondly, we must consider the rigidity of the robot, compared to a CNC machine. In this instance, the robot is going to be less rigid as the mechanical construction is very different. It might have some deflection particularly when the robot is stretched right out. All this means that the robot cannot generate high cutting forces, so we don’t normally consider robots for milling hard materials like steel etc.
Main Elements of Robot Arm Cell
Having talked about the advantages and some main factors to take into account let’s have a look at the main elements that make up the majority of robot arm milling cells.
Firstly, we have the six-axis robot itself. Considerations here are for payload, envelope and rigidity. These usually point to a largish robot where the payload will invariably be much greater than the weight of the spindle that will be carrying out the cutting. However, it will be both the envelope and rigidity aspect that will point to the robot choice rather than payload. Because the tool paths will be created offline and no doubt consist of a large number of points reaching into the hundreds of thousands it must be borne in mind that the controller needs the capacity to hold large programs, reaching as much as 20 or 30 megabytes for large milling projects.
Allied with the robot we must consider if you require an external axis. The need to re-orientate the stock will largely dictate the need of this axis. It allows the robot to work behind or to the side of the stock rather than having the robot “reaching”. Thereby, allowing the robot to work in a more rigid configuration of its axes.
Fitted to the robot will be some form of spindle to work the cutter. Invariably this will incorporate a tool changer to allow the use of different cutters through the milling operations. The automatic exchange of the cutters takes place as part of the cutting program sequence. The spindle will need to be of sufficient power to work the largest cutter envisaged. Allied with the spindle will be an inverter to vary the cutter rotation speeds. The cutter speed will be under the control of the robot controller usually via an analogue output cabled to the inverter speed input.
Milling Tool Rack
The position to mount the tool rack is near the robot but out of the work area. Invariably it will have plastic forks to hold each of the cutters in their respective tool holders. Also, a switch wired to the robot to indicate that a tool holder is present in the rack. When a tool change is called for the robot will come over to the tool rack to exchange tools.
Robot Safety Panel
It is essential to install a safety panel with cell control pushbuttons to control the complete cell. This panel is electrically connected to the robot controller. The panel will include the safety relays for the two safety circuits for both the robot and spindle. One circuit will be for the Estops, these will stop the robot in all modes. Then, the other will be for the cell access and this will stop the robot and spindle whenever the robot is in Auto mode.
This mounting table for the parts or material needs to be very flat and well-fixed to provide a good reference when setting up the robot. Next, it is important to teach a coordinate system as a reference for the parts or stock placed on this table and later for transfer to the offline programming package.
Robot Milling Guarding
The cell will need some form of guarding which will form a room or enclosure to make sure that nobody is present whilst the robot is working in automatic. The guarding or room enclosure will have any access points protected by a two-channel safety system. It is important to integrate the system into the safety panel. Please bear in mind that the guarding or room enclosure would need to take into account the possibility of a tool burst.
Lastly, we would normally have some form of offline programming package to generate the milling paths from CAD data. This software runs on a laptop or PC separate from the robot. There are many different offline CAD-CAM packages available and the robots will work with all of them.
Milling Cell Package
Phoenix can help you to choose the right robot arm milling cell based on your requirements, part fixtures, safety components or any other tailored equipment for the automation. Additionally, we work with all robot manufacturers such as ABB, KUKA, FANUC, and others.
Contact us for a free consultation, if you require world-class customer support before and after the installation of the robot.
Technical Datasheet Milling Robot Cell with Pricing (Standard Cell Pricing Without or With Turntable)
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