Machining with robots
Machining with robots
Keywords: Computer aided design, Robotics
CADCAM developer Delcam has linked with industrial-robot manufacturer KUKA to develop machining by robot. The companies believe that robots could provide a low-cost alternative to machine tools for many large-scale manufacturing operations carried out on softer materials (Plates 2 and 3).
Until now, machining by robot has been limited to a small number of specialist production operations. The complexity of the programming has been the main barrier. While “teach and learn” methods have seen some success, these can only be used when duplicating an existing part and not when creating a new component. Also, the time taken to produce the toolpaths means that this approach is only practical for a longer production runs. However,developments undertaken recently in Delcam's PowerMILL machining software and in KUKA's control systems have made it far easier to program robots directly from CAD data, for a much wider range of applications.
Plate 2Simulation of robot machining with Delcam software
Plate 3Robots are ideal for machining softer materials to sub-millimetre tolerances
This ability to program from CAD duplicates the process used to generate toolpaths for machine tools and so make it much easier to take advantage of the benefits offered by robots. Firstly, the cost of installing a robot is far less than the price of a large machine tool with a similar working envelope. Secondly, the flexibility of the robot's arm means that even complex operations can be carried out in a single set-up, so cutting production times and reducing the number of fixtures needed.
The benefits of using robots are not limited to large and complex parts since one system can mill a number of parts stationed around it from a single position. For longer runs of parts, the robot can also load and remove each component before and after machining in many cases.
For additional travel capability the KUKA robot can be mounted on a linear rail. This can either give the capability to work on a single larger part, such as a boat hull, or to produce an even larger number of smaller components in one series of operations.
While robots do offer advantages, it is equally important to be aware of the limitations. The first is that no robot currently available has the rigidity to machine harder materials, such as tool steels or the more exotic compounds used in the aerospace industry. The second is the limited accuracy, which is in the range of tenths of a millimetre, compared to the micron-level accuracy available from machine tools. However, while the robot cannot match the tolerances possible with a machine tool, it can often be more than adequate, especially for components that might be several metres in length and for those where a smooth finish is more important than precise dimensions.
The ability to program robots on the same way as machine tools has resulted from a joint development programme between Delcam and KUKA to develop easy-to-use routines within Delcam's PowerMILL CAM software. These routines can quickly generate programs for robots that allow smooth machining of large components.
Both companies believe that trimming of composites could provide a perfect application for the new technique. This need arises because, with composite components, there will often be some flash from the moulding operation that needs to be removed before assembly, for example, into an aircraft structure. Indeed at the 2004 MACH exhibition, Delcam demonstrated the finishing by robot of a composite wing spar test section supplied by Airbus.
The first stage in the process demonstrated was to probe the part with a Krypton's metrology system fitted with Delcam's PowerINSPECT software to reverse engineer the shape of the component as it had been manufactured. The material to be removed can be identified by comparing the resulting model with the required shape as defined in the master CAD design.
The trimming toolpaths can then be created within PowerMILL to develop the robot paths completely “off-line”. The KUKA robot undertakes the trimming of the spar section, with online compensation using a Krypton camera to compensate for variances between the nominal CAD world and the physical reality.
The trimming is normally done just with swarf cuts along the edges of the component. For the purposes of the demonstration, the robot also machined the Delcam and Airbus logos into the cross-section of the spar test section.
Finally, the Krypton probe is used again with PowerINSPECT to confirm that the trimming operation has removed the correct amount of material to leave a component that conforms exactly to its CAD model.
This demonstration confirmed the potential that exists for robots in the composites industry. As stated already, robots cannot match the precision of machine tools. However, in cases where tolerances of tenths of a millimetre are acceptable, they offer a very cost- effective alternative.
For more information, please contact: Delcam plc, Small Heath Business Park,Birmingham, B10 0HJ, UK, web site: www.delcam.com
