CIM blends lasers into automated manufacturing.
An advantage of mixing lasers and CIM relates to the flexibility of high-power lasers, ie., they're the only tools that can efficiently perform cutting, welding, trimming, and surface heat treating.
Automated laser processing
Sophistication of automated laser materials processing is increasing steadily. CNC parts handling now is used widely to achieve necessary process consistency. Also, the recent emphasis is more on controlled motions of the beam, and less on part or material motion. As a result, larger, more complex part geometries can be handled.
To this end, lasers increasingly are being integrated into robotic systems. For high-power laser systems, a rectilinear or gantry robot is preferred. The perpendicular motion axes permit beam tracking with a minimum number of mirrors in an open optical path, which is desirable for multi-kilowatt lasers. Large-scale manufacturing is performed with a gantry robot laser processing cell, Figure 1.
Articulated-arm robots also are being interfaced with materials processing lasers. For these systems, a passive beam delivery channel usually is employed. Here, the robot acts as a positioner for the laser processing head, which can deliver up to 1.5 kW to a workpiece surface. Smaller lasers also are being mounted directly to robots, simplifying beam handling to the end effector. These systems are capable of working with more complex part geometries and orientations, Figure 2.
Although combining lasers and robotics greatly increases processing flexibility, it doesn't necessarily advance development of CAD/CAM laser processing, a precursor to CIM. To date, robotic involvement consists of merely repeating "taught" patterns; the capacity of robots to operate on the basis of programs generated off-line is limited. Implementing robotic function into flexible work cells, however, soon will lead to that capability.
CAD/CAM laser systems
Use of lasers with CAD/CAM involves consideration of fundamental differences between an intense thermal-energy source and a mechanical one.
First, the laser mechanism doesn't contact the work material. Thus, tool wear, and subsequent tool changing and sharpening are obviated. Further, low mechanical forces on the workpiece mean fixturing needs are less restrictive--in some cases, part clamping is eliminated.
Another major difference between laser processing and other methods concerns process control. Successful laser metalworking requires accurate deposition of laser energy on workpiece surfaces. Since the beam is moving across a surface, travel speed must be controlled precisely. In mechanical machining, positioning accuracy is more important than speed control; the reverse is true for most laser metalworking.
There's a tradeoff in CNC systems between positional accuracy and maximum controlled speed attainable with hardware. CNC machining often is engineered to emphasize positional accuracy. With lasers, position increments usually need to be increased so process speeds can increase as well.
The most powerful reason to integrate laser systems into the automated factory concerns process flexibility. The goal is to combine a full-function CAD system, multi-axis CNC or robot systems, and one or more lasers to perform multiple operations. High-power lasers are required for continuous welding and/or surface heat treating. Therefore, most development is taking place with multi-kilowatt CO.sub.2 lasers. However, to our knowledge, there's no production facility currently implementing fully flexible CAD/CAM with lasers.
Such systems are being developed at large application and development laboratories such as the MITI flexible manufacturing demonstration facility in Japan, Westinghouse Electric's 25 kW laser laboratory in California, and the US Navy/FMC metalworking laser center in Minnesota.
Related developments also are underway at Battelle's laboratories in Ohio and Frankfurt, Germany; at IITRI in Chicago; with the Ferranti/Cullham Lab venture in Great Britain; and at Fiat Motor Co in Italy. These large-scale programs are charged with developing systems and processes in laser metalworking, and only have limited production responsibilities, if any.
While this work has significant long-term potential in manufacturing, near-term prospects are less favorable. The processes are still in development, and integration of various novel technologies isn't complete. Moreover, there isn't a standard framework from which compatible new systems and software can be developed. The combination of high development costs and large capital expenses will limit implementation on the factory floor.
Family of parts
Opposite maximum flexibility, is the family of parts approach. In a family of parts driven CAD/CAM system, hardware must be defined with respect to motion axes, operating parameter space, speed ranges, and possible part geometries. Graphics displays and laser processing subroutines are preprogrammed.
An operator designs new parts by selecting options from electronic forms in the control program. The graphics display and NC part programs follow directly from the options chosen by the operator. In this manner, an operator designs and produces custom parts without detailed knowledge of programming, or even laser processing.
An example is the laser cutting system implemented by a US circular saw blade manufacturer. Here, a 750 W CO.sub.2 laser is engineered to cut flat plates up to 6-mm thick.
The design stage consists of selecting saw-blade dimensions and characteristics from screen forms. The resulting blade design is displayed on the screen or plotted to produce a drawing. Design data also serves as the part program.
A variety of tooth geometries and blade sizes are possible. Several patented blade design features are produced on the system. Although the laser cutter originally was procured to expand the company's existing line of stamped saw blades, it's now used for more than 70 percent of total production, Figure 3.
Even though some process flexibility is sacrificed compared to fully flexible systems, a family of parts CAD/CAM system is faster, easier to operate, and more cost effective than more sophisticated approaches.
Because tasks are better defined, hardware can be matched efficiently to the work. Also, users don't have to pay for unused capability, which makes it easier to justify a family of parts system.
CIM-based laser materials processing is expected to benefit from several continuing improvements in systems hardware. One area receiving significant attention is the downsizing of high-power lasers. The newer units are smaller and weigh less than older systems with equivalent power. This makes it easier to integrate new lasers into workcells.
Although lasers are now usually stationary and mounted relatively far from workpieces, they soon will be mounted directly to the process hardware. This will promote laser robotics.
Another advancement in cavity excitation provides nearly a two-fold increase in electrical efficiency for CO.sub.2 lasers--from about 8 percent total efficiency to 15 percent. Increased efficiency translates directly to smaller lasers for a given power level, less waste heat and lower cooling requirements, lower operating costs per kWhr, and ultimately reduced capital costs.
As various laser processes develop, related databases will accumulate also. They will be used to compile routines to transform part designs into part programs. Successful CAD/CAM laser processes will require consistent hardware and optics operated with reliable process information derived from databases.
In addition, control and translation software is as important as laser hardware. Creation of new design and process-control programs must be supplemented by linking software already in use. One difficulty is lack of software standards and protocols.
A graphics standard has emerged in the CAD community for interchanging design files, which should help. The Initial Graphics Exchange Specifications (IGES) is being accepted by more system suppliers and is expanding to cover more data types, such as finite element meshes and solid models. This trend will likely include CAM software compatibility with IGES.
In addition to a lack of general software standards, incompatibilities arise because machine-tool builders, CAD/CAM software developers, robot makers, and laser manufacturers have operated independently. This clearly is changing as machine-tool builders integrate higher technologies into their products through acquisitions and joint ventures.
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|Title Annotation:||computer-integrated manufacturing|
|Author:||Tucker, T.R.; Billhardt, C.F.|
|Publication:||Tooling & Production|
|Date:||Mar 1, 1985|
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