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NC in aerospace.

As CAD/CAM evolves, it is becoming commonplace for software vendors to provide enhancements to their basic NC programming package. These enhancements tailor the basic NC software to specific applications such as turning, milling, grinding, etc. Numerical Control Computer Sciences (NCCS) has taken the process one step further in its release of NCL Version 8.1.

NCL is a full-featured CAD/CAM program used for a variety of 2 1/2, 3, 4, and 5 axis milling applications. However, Version 8.1 incorporates advanced routines for creating NC programs specifically for complex turbine blades. NCCS says that optimizing its standard milling software enables the product to be more efficient and effective while machining turbine blades, which are common in products such as steam turbines, gas turbine compressors, and jet engines. Considering that, it's not hard to understand why NCCS counts Boeing, Bombardier, Deutsche Aerospace, Lockheed, McDonnell Douglas, Northrop, Rockwell, and other aerospace companies amongst its users.

Lockheed, for example, has installed NCL in both its Missile Systems Div (MSD) and the Space Systems Div (SSD). Lockheed is running NCL on Silicon Graphics workstations as well as its mainframes in conjunction with CADAM, CATIA, Pro/Engineer, and SDRC's I-DEAS software.

Version 8.1 provides users such as Lockheed with a variety of features that solve problems that are unique to the NC milling of turbine blade configurations. Included are such features as:

* The ability to do four- and five-axis lead angle milling using flat, bull nose, and ball end mills.

* A variety of tool path options such as "spiral" cutting. This creates a continuous path around the blade's surface (convex, concave, and the leading and trailing edges). As the cutter moves along the surface, it will constantly "spiral" along the blade-stacking axis, thus never making an abrupt stepover. This is sometimes referred to as "orange peeling."

* A lead angle can be specified or modified by a minimum clearance distance at the heel of the tool. A heel clearance distance, unlike a fixed lead angle, provides for the minimum tilt angle at all times. A smaller lead angle results in an increased effective cutter radius. This allows for few passes and, therefore, reduces machining time.

* Special options have been incorporated for milling the root and tip platform sections of the blade. These options include continuous path five-axis flank milling of complex platform geometry. When using a four-axis machine, form tools such as bell or wheel cutters can be used to reach "closed" platform surfaces. These surfaces are impossible to reach using standard end mills if the machine tool lacks a fifth axis.

All current projects are not available in the form of a 3D model. In such a case, the model is interpreted from traditional blueprints and created using the modeling capabilities of NCL or NCLCADD. The Space Div is currently working on systems integration issues directed at providing a tight coupling between I-DEAS and NCL for model transfer.

Currently, CL files from NCL are sent to the mainframe for post-processing. However, the Missile Systems Div is presently configuring post-processors for each of its machines. Post-processing will then be done locally, and the mainframe will be used for model retrieval, archiving, and distribution of NC programs.
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Title Annotation:Machining Control & Software; numerical controlled programs
Publication:Tooling & Production
Date:Mar 1, 1993
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