Charles Clarke says Siemens PLM Software has broken new ground with its Turbomachinery Milling module in NX 7.
By Charles Clarke, Ph.D.
CAD/CAM technology has progressed to a point where functions that were once considered advanced, like 5-axis NC programming, are now much more commonplace. However, technology advancements allow software vendors to push further into more specialist areas and provide higher levels of value to their customers. The result is new CAD/CAM extension applications (often referred to as add-ons) that address specific requirements in specific industries with a high degree of precision and performance. These add-on applications reduce the need to use specialist, stand-alone applications that operate outside of standard company PLM systems.
An example of these new applications is the NX Turbomachinery Milling module that Siemens PLM Software has introduced to their line-up of part manufacturing solutions in NX 7. The new software has been developed very closely with key customers. It is a market that Siemens PLM dominates from a generic CAD/CAM perspective with companies like Pratt and Whitney, GE Aircraft Engines, Rolls-Royce and many of the major aircraft and power generation engine manufacturers and suppliers being significant customers for Siemens. Also in-house divisions like Siemens Power Generation are significant users of the software.
Once upon a time these ‘industry specific’ solutions were regarded merely as re-packaging exercises of standard functionality often used to breathe new life into a ‘tired’ brand. Not the case these days.
The latest turbine systems offer high levels of efficiency in many applications from power generation to aircraft propulsion. However, machining multi-bladed turbine discs or blisks or impellers puts extra demands on the NC programming needed to drive the kind of advanced multiaxis machine tool used for this work. Although many CAM vendors choose these demanding components to illustrate their 5-axis software, the real tests come in productive programming. Unfortunately in many cases standard 5-axis software is not just multi-axis, it’s also intended to be multipurpose. Typically generic 5-axis CAM software does not offer the special operations designed especially for easy and effective programming of turbomachinery components.
For some time the specialist task of programming and machining the more complex turbine blades, blisks and impeller type components has been achieved using specialist machine tools and NC programming software provided either with the machine tool, or purchased separately from a very specialist software vendor. For many companies this is not an ideal solution, at least from the software perspective, as they would rather use an application that is consistent with the rest of their operations. Apart from having to deal with multiple vendors, and deal with data transfer or translation, it’s also a data management and revision control issue. For larger companies it’s a concern that such ‘one off’ applications tend to reside outside the Product Data Management (PDM) system adding to the cost of effective data management. In addition, these unique and specialist packages can be very expensive to buy and maintain separately.
New Generation Software
With the latest release of NX, Siemens has introduced a specialized extension application for their established NX CAM software that is totally focused on the machining of turbomachinery components, including blisks and impellers, propellers or any other multi-bladed rotational parts. A key objective of the new NX Turbomachinery software is to allow users to do this complex programming as easily as possible. The system provides purpose-built options that put the user in the context of turbomachinery. The idea is to simply select the geometry and tell the software the kinds of blades you are interested in and the operation you need. You then press the ‘go’ button and the system will come back with completely gouge-free, collision-free tool paths for the entire component with no further editing or modifications required.
With generic software it would probably take hours to generate a tool path just between two blades with a splitter. With NX Turbomachinery Milling it takes about 2 minutes. The closest analogy I can find for this kind of approach is that it’s a bit like knowledge-based engineering where you can develop complex components or systems just by specifying performance criteria to preprogrammed systems for creating the components.
Because all manufacturers tend to do things differently, the idea with NX Turbomachinery Milling was to keep the blade machining module as flexible as possible. There are some CAM software applications where you can only machine between the blades as long as the blades are straight. If the blades curve from the shroud to the hub, the system won’t be able to machine them. There are no such restrictions in NX CAM. On some impellers there are smaller blades called splitters in-between the main impeller blades. Some systems won’t even allow you to specify any splitters, and generally even the most powerful ones stop at one splitter. You can specify as many as six splitters in NX.
One area where the Siemens application appears to offer a particular advantage over some other systems is in rest milling. The NX software manages an active or “in-process” model of the work-piece so that the system knows what has been machined and what material is left. When material is left by a larger cutter between the base of a splitter blade and a main blade, NX CAM is able to target this uncut material directly with the click of a button. This saves programming effort, and leads to much more efficient machining.
Other CAM systems are very specific about the kinds of 3D geometry that can be used as the basis for NC programming in these complex parts. Finding and fixing problems with the CAD data can be a tedious and time consuming task. A big time saver with the new NX software is that it does not require you to resolve these geometric issues in the model before programming. NX CAM works directly with this imported geometry to create clean tool paths without the typical fixing and remodelling, saving hours of model preparation time prior to NC programming.
The Value of a Full CAD-CAM Solution
Another significant advantage of the NX solution is that the CAM software is a part of a complete suite of applications that can be used in manufacturing engineering where everything is connected back to a common part model. With NX, the NC programmer has access to a full NX CAD tool box that enables the creation of a 3D model from a drawing if needed. Because of the consistent model approach, if geometry is updated then the dependent data, such as the NX CAM tool path or the NX CMM inspection programs, is updated too. You can use exactly the same CAD functions to model everything else you will need to complete the process from tools and fixtures to a complete 3D model of the machine tool with full kinematics needed for machining simulation.
Given the number of demo examples of CAM systems showing simulations of their 5-axis software applied to impeller type parts you might think that any CAM package could be used to program these complex parts. While the availability of multi-axis CAM software has increased enormously over the last five years, there is still a big difference across the available packages in what can be achieved once you put the demo away. This difference is greater once established systems such as NX CAM (formerly Unigraphics CAM) move into really focused applications such as turbomachinery milling.
This new release takes Siemens into a new level of capability. As always there is more that could be added; Siemens says they have more specialized functions coming. They expect to add an out-of-the-box especially designed fillet machining for blades rather than have you use the standard fillet machining options that come with NX CAM today. §
Charles Clarke, Ph.D., is a Cambashi Senior Associate. His recent experience has been in European strategic marketing, market research, and application product specification. Cambashi is a global strategic IT advisory firm specializing in industry analysis, industry issues training, and market research for engineering, manufacturing, construction, and related industries. Cambashi Ltd., 52 Mawson Road, Cambridge, CB1 2HY, United Kingdom. +44 (0) 1223 460439 or fax +44 (0) 1223 461055. www.cambashi.com.