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Information Sheets
Work Handling
In every case, laser processing requires movement of the laser focus relative to the workpiece either while processing, for example in seam welding, or between processing one part and the next as in making a single spot weld per part. Virtually every way of establishing relative movement has been used in the history of laser processing. This note excludes the common case where the laser focus is moved (see Beam Delivery), although many of the considerations are the same.
Where continuous movement is required, as in seam welding or cutting, it is most common for this to be done under some form of computer control. This enables synchronisation of events on the laser, for example opening the process control shutter, turning on a shield gas or changing the power level, with the position of the work. The movement may be by means of rotary and linear translators or a robot is commonly employed.
Where point to point movement is employed the same choices may be made as for continuous movement. In other instances cam, solenoid or air-operated devices are used. It is common to use dial plates and mechanical indexers, often with vibratory bowl feeders when the parts are small.
For continuous path work, the control must permit a surface feedrate to be maintained constant, often to ±5%, whilst keeping the work surface perpendicular to the laser axis at the focal point. This can be challenging for complex 3D parts, particularly when the manipulator is a robot. The control must also synchronise on/off events to the work ACTUAL position as opposed to commanded position, even though these events may take finite time as a valve or shutter changes state.
All of the usual issues of repeatability and accuracy apply where parts are loaded into a holder and where the working point is not in the plane of guiding elements of the manipulator. If relevant experience is not available in-house, success demands that appropriate expertise is invoked, for example from the supplier. In any case, an awareness of the relevant machine tool inspection standards is a great help. Help may be obtained from the companies that test and calibrate machine tools ( See Measurement).
Particular problems arise where the parts to be processed are not dimensionally repeatable; this may well necessitate the application of a gauging or vision approach to correcting the program. (See Measurement). An advantage to this approach is that it can be used for in-process or post-process inspection of critical dimensions. Another effective solution, where the parts are flexible, can be to use powered tooling that compels the part to be in the designed place and shape.
When choosing the work handling system or its components, it is often more important to pay attention to acceleration than to maximum speed, particularly if the system is required to make many short point to point moves or to interpolate small radii. It is vital to consider the consequences of a power of drive failure occurring on a vertical axis or while traversing at high speed, both for the safety of the machine and workpiece, and for the safety of the setter.
The debris produced by laser processing can be extremely hard and abrasive. Means must be adopted to prevent such dust and swarf from entering motion or measuring systems. It is also essential to provide means for cleaning that do not expose the operator to risk from these materials. This is best considered early in the work handling design stage along with the issues of fume extraction and protection from laser light.
Chemical/fire/explosion hazards must also be considered as the debris may be combustible and the atmosphere strongly oxidising. These factors may limit the types or rating of motors used, and, once again, should be considered at the same time as the fume extraction provisions.
Safety guidance may be found at the Safety Section.