DMG Mori’s entry-level, compact DMU 50 five-axis machining center is producing an oil field rock bit from a 440 lb (199.5-kg) 1045 grade steel workpiece, 8″ (203-mm) diameter by 8″ (203-mm) high, for a major upstream oil industry supplier. The result using Siemens full CAD/CAM-CNC digital process chain was better tool life, a higher degree of accuracy, and overall production efficiencies.
The oil patch customer specified the need for fast changeover to produce the part from various metal materials and was trying to decide between a single block of steel or a near net shape casting. Both high-speed roughing and then five-axis machining were required in this small-footprint machine, which had been selected by the customer due to plant capacity utilization concerns, plus its desire for a flexible, cost-effective machine tool.
The machine builder turned to its longtime business partner, Siemens Industry Inc. (Elk Grove Village, IL) and its package of CAD/CAM-CNC hardware, software, and engineering services. Siemens helped the machine builder improve part production, including reduction of design-to-part protocols and improvements in machining time, tool life, surface finish, dimensional accuracy, and overall production efficiency. This scenario was particularly applicable in this case, as the production runs were expected to be low with short lead times.
Avoiding Manual Programming
Starting from the CAD file, the Siemens PLM team ran the program through its NX CAM process, eliminating the setups through full five-axis operation. The User Defined Events (UDEs) feature inside the NX program allows simple check boxes for triggering post-processor references for coolant pressure, spindle speed settings and more. This avoids manual programming and, as a result, reduced the program transition time from as long as two days to about 30 minutes.
Once the program was ready for the CNC, the features of that control 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 collision and ensuring the optimum toolpath, in conjunction with the NC kernel and PLC on the machine tool.
“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,” said Randy Pearson, technical applications center manager for Siemens. “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, which is a static plane transformation that allows a five-axis machine to define a rotated working plane in space, more commonly known 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.
Meanwhile, Sinumerik Operate, the CNC’s on-machine graphical user interface, allows the operator to perform integrated tool management and information management functions, all transportable via USB or network connection.
In the simulation, workpiece loading and fixturing are performed virtually in the NX CAM program, which also calculates a consistent chip load, critical in these large material removal applications. The simulation further verifies the tool length at all cutting sections and the program is finalized for the machine to begin.
Big Tool Life Improvement
In production, this process also yielded a substantial improvement in tool life on the very heavy part over a 3 ¾ hr cycle time, according to Luke Ivaska, DMG national product manager. “With the combination of the NX CAM software, plus the CNC 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 and Sinumerik CNC, 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.”
In the CNC, Sinumerik Operate affords full access to a variety of conditions in production, 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. Probing for work offsets is another advantage the builder and their customer enjoy with the CNC used on this machine. The operator is guided graphically for setting the workpiece zero, for example, while the tool length is automatically included in the calculation. With the Operate system, the difference between the position value in the machine coordinate system and workpiece coordinate system is saved in the active zero offset.
The variable streamline operation of the machine tool combines here with an interpolated vector to produce a smoother finish in the machining of the rock bit surfaces in a single tool path. The machine transitions from square-to-round machining and then to the extreme angle paths needed to machine the internal surfaces. A single bit portion of the program is automatically captured, so a step-and-repeat program can be built up. The simulation of each bit cutting path was done on both the NX CAM and the CNC programs, creating a “Digital Twin” of the machine.
The vectored program is transportable, 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, so there is total continuity between the operations, the data capture protocol and feedback received for production analysis.” Pearson further noted that, in this application, the customer’s desire to change the materials used on successive runs could be accommodated by the control, owing to its ability for on-the-fly adjustments, based on the orientation of the tool tip to the workpiece.
This project was accomplished, using CELOS onboard the DMG Mori machine. CELOS facilitates the total interaction between operator and machine, in this application, as 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. In the case of this oil-and-gas customer, interactive communication to a global production network was also provided, which allows the customer to run parallel production of different rock bits at locations around the world, with data tracking and production analysis.