CAD/CAM Developments: What is Required?
By Jeff Jaje
Business Development Manager
The aerospace industry has always been an early adopter of CAD/CAM technologies for designing and manufacturing of the components necessary for its industry. Milling of aerospace components, while sharing similarities to milling of other parts, also presents its own set of unique challenges, often related to the intended use and long-term safety requirements of those components.
Because of this, many CAD/CAM developers collaborate with engineers from the aerospace industry when determining future development directions. Often, what is requested is not new cutterpath algorithms, but rather complementary functions to make existing functions work more reliably and efficiently.
Large Parts: It has become necessary for CAM systems used in aerospace applications to utilize an internal database capable of working with large data sets. Aerospace parts with curved details, such as an airfoil, are often tessellated so that point-to-point CNC output can be generated. Tighter the tolerance used during tessellation, the more points generated. It is not uncommon for CNC files for large parts to have tens of millions of individual CNC points defined in them.
Calculating these large parts can be time consuming: Fortunately, new developments in CAM have shortened these calculation times. CPUs and workstations with multicore technology have replaced older workstations. Additionally, CAM developers have implemented multithreading into their algorithms, allowing for faster calculations.
With some aerospace parts, you have a very large part with slight curvature, such as an airfoil. This presents a challenge in the finish of the part, where one may see the use of tessellations. Although using tighter tolerances is beneficial due to the large curvature of the part, it may not be enough. Some CAM systems also utilize a “Maximum Segment Length,” such that no two points in an NC file will be more than a set distance apart regardless of the tolerance, and additional points will be placed on the 3D data as needed to fill in the gaps.
Accurate Stock Representations: During the milling process, there are often multiple operations performed prior to the completion of the final part. Maintaining an accurate representation of the remaining stock, before, after and during cutter-path calculations is important for reliable milling.
Knowing stock thicknesses during calculations in a dynamic environment allows CAM algorithms to create more efficient cutterpaths. It also allows cutterpaths to consider the cutter load and make adjustments as necessary. Creating trochoidal, or similar adaptive movements is necessary to maintaining the cutter load. Accurate stock representations are necessary for the collision checking process, not just the tool, but for the toolholder and machine tool.
Machine Simulations: Although the aerospace industry was an early adopter of five-axis technology, enhancements to this technology have improved the CAM process. Previously, third-party programs have been used to accurately simulate the five-axis cutterpaths to ensure there were no collisions or catastrophic events with the machine tool, tooling, and part. Machine simulation and collision checking has since been integrated into the CAM software—allowing programmers to fine-tune their five-axis programs without changing software products. This ensures programmers are using the shortest tool lengths possible, and the stiffest tool and toolholder combinations allowed. This minimizes tool deflection, which allows for faster cutting speeds, allowing programmers to optimize their toolpaths for cutter forces and chip loads.
3D Printing: While the scope of this article was CAM focused, we would be remiss to not mention the growth of 3D printing in the aerospace industry.
Besides its use in prototyping, there are 3D-printed parts used in production airplanes. The Boeing 787 currently has approximately 30 different parts that are manufactured through 3D printing. These parts in use are in noncritical areas, however, it has been stated by the major aerospace manufacturers that they would like to see this technology evolve into creating structural parts.
When this happens, many 3D-printed parts may still need some form of milling, drilling, tapping or grinding to bring them to a finished state. It will become important for CAD/CAM software to work with 3D printing software and algorithms, allowing these parts to be created seamlessly through a hybrid of 3D printing and milling operations. ✈
This article was first published in the 2013 edition of the Aerospace & Defense Manufacturing Yearbook.
Published Date : 12/9/2013