Monday, December 10, 2012

Taming Multi-Blade Parts With Expert CAM Software

Multi-Blade Parts = Multi Problems
Multi-bladed parts are difficult to machine because orientation of the tool must be continually adjusted to reach all the surfaces that require machining. Programming of a complex multi-blade part, even with full-featured CAM software, must be done thoughtfully and carefully to avoid crashes and ruining an expensive part. It is common for programming to take a couple days.

Multi-blade parts come in a variety of shapes and sizes, but there is a significant amount of similarity in the way they are machined.


One approach blade manufacturers have relied on is the 3:2 programming technique in which the part is rotated to a new angle and then a 3-axis program is used to clear out as much material as possible from that orientation. Then the part is moved to a new position and more material is cleared. These programs are tedious to write, and they result in very long machining cycles because there are many overlaps where the tool is doing nothing but air cutting.

Some blade manufacturers have sidestepped this problem by opting not to manufacture the blade out of a mono material but instead to manufacture blade segments and assemble them into a special manifold. This can result in a heftier design; however the problem of machining hard to access material is substituted for the problem of aligning and balancing blade components in a multi-blade assembly.
Programming of a complex multi-blade part, even with full-featured CAM software, must be done thoughtfully and carefully to avoid crashes and ruining an expensive part. It was common for programming to take a couple days, but Blade Expert drastically reduces programming time of complex shapes.


Less is More
Multi-blade parts come in a variety of shapes and sizes, but there is a significant amount of similarity in the way they are machined. The workflow is almost always the same:
  • Rough out excess material between the blades
  • Semi-finish the blades
  • Finish the blades
  • Finish the base
The initial iteration of our blade program made it possible to apply this one workflow process to an enormous variety of multi-bladed parts. All the user was required to do is identify the features on the part as prompted. There were no additional requirements to create geometry, as the interface is intuitive. After bringing in the blade model, the user was prompted for basic information about how he or she wanted the 5-axis blade manufacturing process to function:
  • Selection of the tool, holder and tooling related data
  • Choosing the cut pattern
  • Selecting the Tool Axis control method
  • Setting the collision avoidance method
  • Setting the tool movement method for non-cutting gap motions
Programs for these models were created in Blade Expert and then their operation was simulated using Vericut software. The user could visualize all of the complex machine movements with the program’s computer simulation. This simple process reduced what would have taken two days with conventional programming techniques down to an hour!

Benchmarking
We evaluated the expert blade program by dipping into a library of blade models that had been collected over decades. Once we had worked our way through our own library of nasty blades, we also began benchmarking the expert blade program against blade models sent to us by several 5-axis machine tool builders. By the time this simulation process was finished, the program was tested on more than 50 different blade designs.

Now the product was ready for more aggressive live testing. We created the part from our model and then manufactured it on 5-axis equipment in our own machine shop. Based on the results of these experiments, we developed a list of refinements that would improve the quality, safety, and ease of use of this manufacturing process. For example, cutting material from the leading and trailing edges of the blades requires precise control of tool movements within confined spaces. This called for the creation of special algorithms that would insert additional points and tool vectors to refine control of tool movements around the edges. The program knows where these edges are and assigns the additional points and vectors automatically. Another important activity during this period was developing post processor modifications so that the expert blade programming would work cleanly with a wide range of 5-axis manufacturing systems.