A Full CAD-CAM-CNC Sequence on a Five-Axis Machine

May 18, 2023
The task of processing a hard steel rock bit for oil-and-gas exploration shows the flexibility needed for optimal efficiency in machining precision parts.

Oil-and-gas exploration and processing demands a lot of heavy equipment and precision parts, and for machine shops supplying parts for machines and components, it’s critical to plan the machining processes in careful detail. Typically, they are large and heavy components, often with complex contours, making the machining time long and the tool life short.

The DMU 50 is an entry-level five-axis machining center from DMG Mori Seiki, a compact unit that delivers considerable strength for milling and turning, as the following example will detail. “It is a ‘David Handles Goliath-type’ of story,” according to Matthias Leinberger, the business development director for Siemens Digital Industries Software (formerly Siemens PLM.)

In one challenging incident, the DMG Mori machine was tasked with a 440-lbs., 8-in. diameter x 8-in. high workpiece made from 1045 grade steel, to be processed into a rock bit for oilfield exploration. The project also required fast changeover to produce the part from various metal materials, with all the associated tool changes and workpiece set-up variances. The customer, an upstream oil industry supplier, was trying to decide if the better path for this product was a single block of steel or a near-net-shape casting: Both high-speed roughing and then very precise, five-axis machining were required in this small footprint machine, which the customer had selected due to specific plant capacity utilization concerns, plus a desire for a flexible, reasonably priced and highly cost-effective machine tool.

DMG Mori Seiki turned to Siemens for assistance on this one. Because it offers a full array of machining process technology – CAD/CAD and CNC hardware, software and engineering services – Siemens is able to help improve part production by reducing design-to-part protocols, machining time, and tool life, and to improve surface finish, dimensional accuracies and overall production efficiencies.

Starting from the CAD file, the Siemens PLM team ran the program through its NX CAM process, eliminating the set-ups through full five-axis operation. The User Defined Events (UDEs) feature in the NX program allows simple check boxes for triggering post-processors’ references for coolant pressure, spindle speed settings, and more. This avoids manual programming and, as a result, for the rock bit production process it reduced the program transition time from as long as two days to approximately 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,” observed Chris Pollock, Siemens’ virtual technical applications center manager. “The procedure can also be automated to run on the table at prescribed time intervals.”

The high-speed machining feature is highlighted here by Cycle 800, which is a static plane transformation that allows a five-axis machine to define a rotated working plane in space. (This is commonly known in as 3+2 programming.) The cycle converts the actual workpiece zero and tool offsets to refer to the rotated surface. 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 Siemens CNC graphical user interface on the machine, allows the operator to perform various integrated tool-management and information-management functions, all transportable on a USB or network connection.

In the simulation, loading and fixturing of the workpiece is 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.

In production, this process also yielded a substantial improvement in tool life on this very heavy part over the three-hour, forty-five-minutes cycle time, according to DMG national product manager Luke Ivaska. “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,” Ivaska recalled.

In the CNC, the Sinumerik Operate affords the end-user’s operator and manufacturing engineering personnel full access to various 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.

Easy-to-use 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 intricate rock bit surfaces in a single toolpath. The machine seamlessly transitions from square-to-round machining, and then the extreme angle paths needed to accurately 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 – as if working with a digital twin of the machine.

This vectored program, it should be noted, is transportable to any machine and will deliver comparable results, according to Pollack and Leinberger.

“Precisely because the machine kinematics are knowable,” Leinberger detailed, “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.”

Pollack further noted that, in this application, the customer’s desire to change the materials used on successive runs could be easily 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, with in-process remote adjustments achievable.

For the oil-and-gas sector customer, interactive communication to a global production network is also provided, which allows the customer to run parallel production of different rock bits at locations around the world, with seamless data tracking and full production analysis.