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Aerospace Machining uses Full CAD/CAM/CAE CNC Capability

Jim Lorincz
By Jim Lorincz Contributing Editor, SME Media
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A reverse thrust component for jet engines being machined on a DMG Mori DMU 65 with Siemens 840D sl CNC. Cycle 800 allows the DMU 65 to define a rotated working plane in space, commonly known as “3+2 programming.”

DMG Mori (Hoffman Estates, IL) delivers manufacturing technologies to aerospace OEMs and production shops supported by a package of CAD/CAM/CNC hardware, software, and engineering services from Siemens Industry Inc. (Elk Grove Village, IL) for  aerospace machining. A long-time partner with Siemens, DMG Mori builds a variety of conventional chip-cutting and ultrasonic machining centers.

For the aerospace industry, great care and planning in the aerospace machining process are required to achieve desired accuracies and overall production efficiencies. Typical components produced include those made from lightweight but hard materials, such as titanium and related alloys as well as aluminum workpieces, where substantial volumes of material removal occurs. Due to long cycle times and other high raw material costs, the machining of such components is challenging.

Two recent applications illustrate how DMG Mori was able to turn to Siemens to improve part production, including reduction of design-to-part protocols, aerospace machining time, tool life, surface finish, dimensional accuracies and overall production efficiencies.

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An aerospace impeller fan machined on the DMU 50 in partnership with Siemens’ CAD-CAM-CNC hardware, software and engineering services. With limited clearance between blades, this piece is only possible with full five-axis machining.

In the first instance, a reverse thrust component for a jet engine was to be made from Ti Gal-4-V, a material often used in aerospace owing to its elastic stiffness. Starting from the CAD file, the Siemens PLM (product lifecycle management) team ran the program through its NX CAM with a VoluMill add-on feature that calculates maximum material removal rates. The user-defined events (UDE) feature inside the NX program allows check boxes for triggering post-processor references for coolant pressure, amplitude, ultrasonic generator settings, and more. This avoids manual programming and, as a result, reduced the program transition time from as long as two days to approximately 30 minutes.

Once the program was ready for the control, the features of the Sinumerik 840D sl CNC allowed a more streamlined simulation of the actual cutting path. The 3D quick-set compressor feature provides a parametric itemized data file for all path motions, thereby eliminating collisions and ensuring the optimum toolpath, in conjunction with the NC kernel and PLC on the machine tool.

As Randy Pearson, technical applications center manager for Siemens observed: “This feature is a huge time saver for our customer, as the test ball and probe in the spindle mechanism can be run at any point in the cycle, testing the actual machine kinematics at any time. The procedure can also be automated to run on the table at prescribed time intervals.”

The high-speed machining feature is highlighted by Cycle 800, a static plane transformation that allows a five-axis machine to define a rotated working plane in space. It is commonly known in the industry as 3+2 programming. The cycle converts the actual workpiece zero and tool offsets to refer to the rotated surface. Of note here, the cycle accommodates particular machine kinematics and positions the physical axes normal to the working plane. This is referenced as TRAORI or transformation orientation.

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A DMG employee showcasing the DMU 50 with Siemens’ 840D sl CNC. The features of the 840D allow a streamlined simulation of the actual cutting path.

Meanwhile, the Sinumerik CNC Operate user interface on the machine allows the operator to perform integrated tool management and information management functions, all transportable on a USB or network connection.

In the simulation, the loading and fixturing of the workpiece are performed virtually in NX CAM, which also calculates a consistent chip load, critical in these large material removal applications. The simulation further verifies the tool length at every cutting section and the program is finalized for the machine to begin. It is literally like working with a “Digital Twin” of the machine.

During production, this process yielded a 2.25 times improvement in tool life on this very hard material, according to Luke Ivaska, national product manager for DMG Mori. “With the combination of NX CAM, plus the Sinumerik 840D sl on the machine and all it could do, we had some initial challenges, as most software programs are purpose-built CAM packages that allow quick and easy use by anyone. They have significant limitations, however, as the software drives the toolpath and the operator has very little control. With NX CAM and Sinumerik, we have a lot more input on the creation of the toolpath. I have yet to find a problem I could not solve with NX.” As a result, the finished part is run in 4½ hours with a surface finish improvement from 62.5 Ra to 35 Ra, due to the ultrasonic actor.

In the second example, a conventional chip-cutting five-axis machining center, the entry-level DMU 50 is utilized to cut a 7″ (177.8-mm) diameter × 2″ (50.8-mm) high block of 6061 aluminum into an impeller fan for the aerospace industry, with more than 90% material removal achieved. The same NX CAM software began this process chain, with the initial benefit of considerable time savings in the five-axis setup and comprehensive G-code simulation and verification in a single system.

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The DMU 50 machining an impeller fan designed for aerospace. The finished part is run in 7-1/2 hours.

Because of the bladed structure of this impeller fan component, only a 0.5 clearance between the part and the toolholder was allowable during machining. Simulation with NX CAM prevented collision of tool and part. DMG Mori engineering looked to another long-time tooling partner, Haimer, and its slim line holder to provide a viable solution for this application. Meanwhile, the interpolated tool axis and section views were run on NX CAM to verify the operation of the tool in the tight workspace.

In the Sinumerik 840D sl, the same 3D quick-set compressor feature ensured the proper toolpath, while the high-speed machining setup and Cycle 800 were again utilized for this project. Sinumerik Operate, the CNC’s graphical user interface, affords the end user’s operator and manufacturing engineering personnel access to production conditions, including all roughing and finishing data in plain text, plus all five-axis transformation orientation data logged for restart after any interruption and manual restart.

The variable streamline operation of the machine tool combines with an interpolated vector to produce a smoother finish when machining blade surfaces in a single toolpath. The machine transitions from square-to-round machining and then the extreme angle paths needed to accurately machine the blade internals. The single blade fin portion of the program was automatically captured, so a step-and-repeat program could be built-up.

The simulation of each blade fin cutting path was done on both the NX CAM and the CNC programs. This vectored program is transportable to any machine with comparable results, according to Randy Pearson and Matthias Leinberger, PLM director of business development for Siemens, who commented, “Precisely because the machine kinematics are knowable, this program, once created, can be transferred onto multiple machines within the same facility or run by shops around the world, all tied together by the control. There is total continuity between the operations, the data capture protocol, and feedback received for production analysis.”

Both these projects were performed using the new CELOS onboard the DMG Mori machines. CELOS facilitates interaction between operator and machine in these applications. It has numerous apps to enable instant call-up of actual conditions, full data comparison through a link to CAD and CAM products, plus full interface to the customer company’s ERP system for logging and analysis, with in-process remote adjustment. In the case of these aerospace customers, interactive communication to a global production network is also provided.

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