Railroad axle manufacturing retrofit
Remanufacturing and updating a three-stage lathe was more beneficial than purchasing a new modern machine. Everything was already in place; it just needed updated drives, and hydraulic systems.
Wisconsin-based Euro Machinery Specialists recently remanufactured a 1960s vintage Snyder "Three-Stage" lathe machining line for work in the production of rail and locomotive axles. Owing to the change from hydraulic tracer to advanced computer numerical control (CNC), dc headstock to synchronized ac drive and hydraulic to ac-axes servo motion, the production of steel billets into hammer-forged finished axles was substantially improved for the end user.
According to Karl Engelke, Euro's vice president, "Standard Forged Products was looking for a significant productivity increase to bring the 'Three Stage' system back to OEM-level cycle times, due to punishment from many years of heavy-duty machining around the clock. Peak operating performance was originally about a four-minute cycle time for a completely machined axle, from start to finish. Over the years, cycle times dwindled and were more than seven minutes per axle, due to numerous mechanical and electrical problems. Therefore, this line was in need of a total overhaul and remanufacture.
Since the old iron was extremely durable, it was an ideal candidate for remanufacture, including the key motion control package, consisting of three CNCs, motors and drives at each lathe, plus a PLC and HMI as the master of the entire line." He noted that on all three machines, 4-inch diameter ball screws and bearing blocks capable of more than 44,000 lb of thrust were designed to replace the original hydraulic cylinders. The line required complete rebuilding of all headstocks and hydraulic chucks, replacement of most gears, shafts and Timken bearings. All new hydraulic and lubrication systems were designed and integrated. Other improvements were double-way wiper systems and special sheet metal to protect operators and machine components from heavy chips. In total, the entire project required more than 11,000 hours of labor.
In addition to the remanufacture of the three lathes, Euro re-engineered and provided an entirely new overhead gantry workpiece shuttle system. This automated system, having been converted from hydraulic to servo operation, performs barcode scanning and moves the initial raw forged axles into the roughing lathe "stage one" position for left and right journal section machining. Then, it transfers the workpieces in sequence to the next two machining stages for center-section roughing "stage two" and finish cut "stage three." The final step is to transfer and offload the completed workpieces to the holding area.
The turning line synchronizes left-head and right-head 150-hp motors for both stage one and stage two roughing lathes. The rough cut is on each tool block, multiple large-diameter button-nose cutting tools with high carbide content plunge into the forging at a minimum 0.5 inch depth of cut at approximately 0.200 inch-per-revolution. The high-carbon tool allows for extremely high tool pressure and resists high temperature which puts the heat into the chip, not into the cutting tool.
The challenge was to optimize the cutting process even further, thanks to the incredible power and torque from the headstock motors and newly designed large ball screws, gear reduction and servomotors versus the old hydraulics systems. Since the axle is hammer forged, the surface is extremely difficult to break and machine with any consistency; therefore, tool stability and extremely rigid machine components are absolutely critical to the integrity of the process.
In stage two, the center section of the axle is machined with an overall first finish pass made. Stage three involves the final finish pass with a single headstock 75-hp motor driving the workpiece. In operation, while the customer spec for the axle surface finish is 250 root-mean-square (RMS) surface finish, the line is currently holding 124 RMS consistently, Engelke noted. Every workpiece in process is subject to form gage and profilometer readers for accuracy. On an interesting note, two semi-trailers full of chips are produced by this line, every day.
Each stage's motion control is run by a CNC system with integrated metalworking operations. A mobile handheld terminal unit is provided at each station for easy setup and commissioning.
Dual-channel (X, Z and U, W) cutting paths in stage one necessitated the higher level CNC for motion control accuracy, according to Cary Ramthun, CNC programmer and controls engineer at Euro. He detailed the additional challenges of the line-control rebuild and the solution. "We were challenged by the large amounts of power and torque required to perform this machining operation in each of the three stages, plus the overhead gantry system and other materials handling devices all required precise integration."
Ramthun said, "Programmers from both companies worked with us to accomplish the final solution on this project." He mentioned the unique adaptive control feature on the CNC, which accommodates the out-of-roundness condition often found on hammer forgings. The Profinet coupler provided with the new CNC syncs the gantry and the machine stages in a series of "handshakes" with no hard wiring, only sub-network connections are required, plus full isolation of the networks. [Profinet is an industrial Ethernet protocol from PI North America.]
Engelke detailed the engineering required for the project presented considerable challenges, as well. "We were working with 1960s machinery built by a Snyder company that's no longer in business. We literally started by reverse engineering each individual machine component in our CAD system. Doing so allowed us to design, engineer and adapt new modern mechanical and servo driven solutions as well as provide the customer with complete, highly detailed machine documentation such as manuals with assembly drawings, spare parts lists, hydraulic, lubrication and electrical system schematics."
Engelke said the retrofit was a cooperative effort among the automation provider, Standard Forged Products, and Euro Machinery Specialists. The result was a better-than-new production line, which came about through the use of new modern motion control and CNC technologies, diverse talents cooperating together and a good deal of old-fashioned American ingenuity."
- John Meyer is manager, marketing communications, digital factory, motion control, machine tool systems, Siemens Industry Inc.; edited by Eric R. Eissler, editor-in-chief, Oil & Gas Engineering, email@example.com.
- Refurbishing older technology with new automation is viable.
- Working with other companies can provide better insight into solving an engineering challenge.
- CNC retrofits bring new life to old machinery.
What other re-engineered ideas could come from working on older equipment with other manufacturers?
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To watch a video of this line in operation visit: