hile titanium parts and equipment are in strong demand due to their extremely high strength-to-weight ratio, it is well known that they’re also difficult to machine. This is of particular note in the aerospace industry where strong but lightweight parts make a critical difference in the success of aircraft development and performance. To address this dilemma, the National Institute of Standards and Technology (NIST; Gaithersburg, MD) funded a three-year $2 million research project with the intent to reshape the future of cutting titanium and other difficult-to-machine, high-temperature alloys.
Project leader REALLCO (Rockford Engineering Associates LLC; Rockford, IL) developed the Super-Stiff Vibration-Free Machine (SSVF Machine), which is currently cutting titanium at Dial Machine Inc. (Rockford, IL), one of the project contributors. Advanced technologies in the SSVF, have produced a 50–150% increase in tool life and material removal rates for various high-temperature alloys over current state-of-the-art systems. It also is cutting titanium at 50% faster cutting speeds with excellent surface finish and maintaining very high accuracy.
The SSVF machine is structurally an order of magnitude stiffer than conventional milling machines. As many know, current methods and machining parameters for cutting titanium are derived from experience based on light-duty general-purpose machines. They aren’t ideally suited for machining titanium, because of much higher cutting forces per unit of power consumed. Insufficient machine stiffness to withstand higher forces is compensated by taking lighter cuts, resulting in lower productivity and increased heat retention in the tool. As a result, premature tool failure and higher wear and tear of the machine commonly occur in machining titanium. Heavy-duty general-purpose machines are more suitable, but they, too, have limitations unless their structural stiffness is adequate for the spindle power, and the spindle rotational speed is matched with the torque requirements for cutting titanium.
REALLCO first considered the two critical trouble spots related to cutting tool failure in machining titanium: sensitivity to thermal stresses and impact of vibration on the cutting edge. The new machine combines the use of MDR (membrane dual restrictor) hydrostatics for way guidance throughout the machine; linear motors; the use of Heidenhain absolute linear encoders right near the critical points; and an ultra-high-pressure coolant system. This patent-pending combination alleviates the high amount of vibration and heat issues seen when cutting titanium that often lead to catastrophic cutter failure and/or excessive machine tool wear.
"The SSVF Machine provides a unique machining environment that advances the understanding of machining techniques related to high-temperature alloys and other super hard materials," says Kanwar Singh, one of the three partners of REALLCO and a 40-year veteran of Ingersoll Milling Machine Co. Co-partners John Hurd and John Osborn together add another approximately 80 years of machine-tool experience to the team.
"NIST’s criterion in this project is that the resulting technology would have a positive impact on the national economy through improved manufacturing techniques, with an associated impact on job creation," explains Singh. "And in completing this, we now see that super-hard space-age materials can be machined much more efficiently and at lower overall cost, which should well change the way this industry thinks and works."
"Working with a limited budget for these three years had its challenges," explains REALLCO’s chief design engineer, Mark Tingley, "so we are particularly grateful to the companies like Heidenhain that contributed its expertise, services, and free components to further the cause of advanced machining.
"With the use of linear motors and the donated Heidenhain LC 183 absolute linear scales on the X, Y and Z axes of the SSVF, we have been able to design for exceptionally high position loop gains on our axes," Tingley says. The Heidenhain encoders are positioned such that no compliance exists between the load and the reader head of the encoder. Proximity of the encoders to the load was chosen to minimize compliance outside of the position control loop. Since all loads and compliance are within the positioning loop, it is necessary to eliminate structural compliance to have a very high servo gain. Because the linear scales have a high-resolution serial output, no additional interface was required which enabled REALLCO to install them right at these critical points in tight spaces and interface directly to the control. "This gives us the ability to run an exceptionally stiff and accurate machine, perfect for titanium cutting," Tingley adds.
Tingley says that the use of absolute linear scales for motor commutation was important, and that the SSVF Machine is now achieving position loop gains of 10 mm/min/micron. The SSVF Machine is able to circular interpolate a 25-mm diam circle at 200 mm/min within a total error of 1.1 µm, including reversal errors at transition points. This compares to position loop gains of 0.5–1.5 mm/min in most machine tools and geometric error of 10-25µm. "We have never seen performance this good," adds Hurd. "If we didn’t have the high resolution in the Heidenhain scales, we couldn’t achieve these high gains with the linear-motor system. This really is an enabling technology."
"That setup, coupled with the exclusive highly damped hydrostatic bearing guidance systems that we have on the axes and the stiffness of the structure, has resulted in some exceptionally good cutting conditions for titanium," Tingley says. Singh also points out that the concept of "infinite" to "negative" stiffness in the hydrostatic way bearings has been employed for the first time in a machine tool, and that the SSVF Machine is now working with titanium cutting speeds close to 100 m/min vs. the current industry benchmark of 40–50 m/min, while maintaining a 30-min or more tool life.
The spindle used on the SSVF has also been specially designed as part of this NIST project, and includes hydrostatic bearings to deter vibration propagation from the cut to the machine structure and a Heidenhain ERA 4000 series angle encoder. The spindle is powered by a high-torque/low-speed torque motor.
"With this combination, we are able to achieve exceptional dynamic contouring accuracy, as well as contribute to the higher machine stiffness levels," adds Tingley, who says that the SSVF Machine is showing a stiffness of 2.2 million lb/in at the spindle face, compared to that of conventional machines that show between 50,000–250,000 lb/in. This is important since vibration-induced impact loading causes the micro-thermal fissures on the cutting edge to propagate faster. This then develops into cracks and results in premature tool failure.
Tingley also explains that high-temperature alloys have a higher melting-point temperature than the melting point of conventional cutting tool materials and are poor conductors of heat. Heat generated in the cut is conducted into the cutting material more than into the alloy or the chip. Consequently, the surface speed (sfm) of the cutting tool must be kept low enough so that the heat generated in the cut doesn’t raise the temperature to the melting point of the cutting material. In order to increase speed and productivity, the SSVF Machine utilizes high-pressure coolant up to 3000 psi (20.68 MPa) and precision placement of coolant nozzles in the cutting tool to penetrate the area of chip formation and carry the heat away from the cutting tool insert more efficiently.
The SSVF Machine is also showing usefulness for many other hard-to-machine, high-temperature materials like nickel alloys and stainless. It is also said to be suitable for machining advanced technical ceramics. Basic applications could include aerospace components, armor, dies, and medical implants. ME
For more information on Rockford Engineering Associates LLC, call 815-316-6377; on Heidenhain Corp. go to www.heidenhain.us, or call 847-490-1191.
Advanced CAM Puts It All Together
Over the last five years, GCM (Union City, CA) has enjoyed substantial growth supplying a demanding high-tech customer base with high-quality custom-manufactured components and assemblies. The company’s strategy for building and capturing business is to expand the range of services offered to customers so that projects can be completed economically on a fast turn basis with little, if any, outsourcing required. Advanced CAM capabilities are credited with assuring efficient manufacturing for complete assemblies at GCM, making fast fast-turn delivery possible.
GCM is a preferred supplier to OEMs in the aerospace, biotechnology, data communications, industrial, medical, security, semiconductor, and transportation industries. The company’s 90,000 ft2 (8361-m2) facility is equipped to provide customers with a high value-added mix of services that encompasses pallet-based CNC machining, sheetmetal work, and electromechanical integration. In addition, GCM offers a number of cost-competitive specialties from laser cutting, plating, punch press, plastic forming, and welding on the materials side, to development and supply-chain management on the product-distribution side.
At the core of GCM’s manufacturing capabilities are two Mazak pallet-based Palletech manufacturing cells, with seven four-axis HMCs, and one five-axis system supporting a total of 80 pallets. The five-axis machining cell will soon be upgraded with an additional machine and more pallets.
"There are a lot of parts continually moving through our system, explains Tim Senf, programming/engineering manager for GCM. "At the hub of our CNC manufacturing operations, the five CAM programmers in my department rely on advanced capabilities in Mastercam X5 CAM software from CNC Software Inc. [Tolland, CT] to make sure our manufacturing processes come together as they should and to make sure the company’s core manufacturing investment in Mazak CNC manufacturing cells is fully utilized."
A lot of change has occurred since Senf began working with GCM in 2007. The company was still using the previous generation of Mastercam software, and he was asked to work with his staff of five programmers to transition smoothly into the Windows-based X-series. He was also tasked with identifying and implementing advanced capabilities of the software that would have a significant impact on manufacturing productivity. Mastercam’s Work Coordinate System (WCS) was implemented first to substantially improve programming and manufacturing consistency and productivity.
CAM programmers get involved in numerous transform and rotate manipulations as they align an imported CAD model to the various tool planes required for assigning toolpaths. The Work Coordinate System allows users to orient the part model in the programming environment only once, rather than each time a new view of the part or a different tool plane is required. This makes it easy to program everything from the same machine coordinates and define work planes that allow users to flip through various views in the same alignment at the click of a mouse, saving programming time.
"As a group, we are getting better at using the WCS. We share tips and tricks amongst ourselves. It’s a means to create a coordinate system on your part without having to do a transform/rotate to manipulate the part around. Instead of manipulating the part, you manipulate the coordinate system. You just click on the part and define your work plane by geometry. Set your zero point on the part where you want it, save it, and from then on you are going," Senf explains.
Recently, GCM selected Solid Edge as its standard corporate design software. Today, when programmers import Solid Edge files into Mastercam, a model has already been created in the same coordinate system that will be used for machining, so all alignments take place in a minute or two. When design changes occur, and these happen frequently, it’s a simple matter to overlay the new model—in blue over the old one in red—so areas where toolpaths need to be modified are readily apparent. This is also a fast way to pick up mistakes and communicate with the customer if something has been mistakenly added or removed from the new model.
GMC has a maintenance license for Mastercam so that technical support is always available from either the local reseller or the factory, and upgrades to the software are provided at no additional cost. Upgrades are important because they frequently allow GCM to improve its manufacturing productivity and consistency. When an upgrade is released, Senf reviews the documentation and discusses the potential benefits of the upgrade with the local reseller, Sierra Cad/Cam Inc. (Browns Valley, CA). Typically, the new upgrade is installed within two to four weeks of its release, after Senf is comfortable with reports from other users as relayed on the eMasterecam forum.
Dynamic Milling, a new feature released with Mastercam X4 , is typical of the impact a new software release can have on a company’s productivity. This "self-aware" 2-D pocketing toolpath protects the tool and machine by generating intelligent motion according to what material is coming up ahead to keep the load on the tool as consistent as possible, and always within safe limits. This approach allows GCM to pocket at exceptionally high speeds but with minute stepovers, using the full flute of the tool instead of just the tip.
"We can run a ¾" [19-mm] end mill full depth of cut in steel at 180 ipm [4.6m/min]. When you use the full flute at a 20% depth of cut, the tool lasts a long time in steel. You aren’t necessarily doubling your cycle time, but you are definitely improving the stability of the process, because you aren’t dealing with busted tools and excessive tool wear. There is also less wear on the machine, because of the high-speed low-entry force and because there is much less linear travel compared to conventional roughing toolpaths. I also believe this approach is reducing the machining stresses on our parts," Senf says.
By far the biggest impact Dynamic Milling has had on GCM is the magnitude of improvement in tool life. "Instead of using just 20% of the tool, we can use the full flute and that makes a huge difference," Senf says. The results are that tool costs have been reduced, but more important, up-time was increased for the company’s CNC machining cells. "We do a lot of small batch size runs and deliver on a daily or weekly basis so our customers can keep their part inventories down. We need to keep our equipment fully utilized on a 24/7 basis and tool management is a big part of that. Our Mazaks have excellent tool-management features. With those features and Dynamic Milling, we almost rarely have to stop production for an unplanned tool change due to wear or breakage and the tools themselves last at least 50% longer. These factors reduce tool-related overhead tremendously," Senf says.
One of the reasons why GCM chose Mastercam was the software’s ability to transfer files and data to other electronic systems within the manufacturing process. Virtually no adjustments had to be made within Mastercam when Solid Edge CAD models were integrated into the CNC manufacturing workflow. Within the last six months, GCM has taken advantage of Mastercam’s open architecture to integrate 100% simulation and verification of five-axis toolpaths using Vericut from CGTech Corp. (Irvine, CA).
Mastercam’s built-in simulation features, Backplot and Verify, had always worked well for GCM, but the complexity of five-axis machining spurred the company to opt for 100% verification using the third-party software. The two software products are seamlessly integrated via Mastercam’s C-Hook technology. The Vericut interface resides within Mastercam but operates independently, so a programmer can be creating toolpaths for one program while he is verifying another.
"With Vericut in Mastercam, you bring in the actual part model and overlay the machining onto the model. You can see if you missed anything or if there will be some sort of tool or holder interference with the part or machine. Now our programs are even more accurate—ready to go out of the box. That doesn’t mean we aren’t out on the shop floor. There are always issues, but there are fewer of them and they are generally smaller," Senf explains.
Advanced simulation capabilities have given GCM more confidence in its ability to keep parts moving through the system with five-axis machining. Most of these parts are not 3-D, but the five-axis system allows the tool to reach more of the part so that more parts can be manufactured with a single setup. To make the most of this system, it’s necessary to fit as many parts as possible on the fixture. "Programmers do this quickly using Mastercam’s transform feature (Xform) to move duplicates of parts to different positions on the fixture. It’s almost like cutting and pasting," says Senf. This is a real time-saver, especially when "the bottom line for all this electronic integration is pushing higher volumes of parts through CNC manufacturing equipment in ever decreasing batch sizes," Senf concludes. ME
For more information on Mastercam/CNC Software Inc.,
go to www.mastercam.com, or phone 860-875-5006.
Honing In On Bottom Line Profit
Sometimes the best way to ensure a job is done right is to do it yourself, especially when doing so adds to the bottom line and trims turnaround time. Those benefits, as well as greater ability to salvage damaged cylinders, a higher-quality finished product, and increased worker safety, are the reasons why Air Hydro Power (Louisville, KY) acquired a HTA horizontal tube hone from Sunnen Products Co. (St. Louis, MO) to repair and recondition hydraulic cylinders. Adding the HTA to its repair shop machine tool lineup allowed Air Hydro to bring previously farmed-out honing work back in-house, helping it regain control of job turnaround times and save the company thousands of dollars in outsourcing costs.
Air Hydro Power started in 1961 in the founder’s basement, but quickly established itself as a major player in hydraulics by becoming the third Vickers distributor in the US in 1965. Acquisition of Marlatt Controls in 1983 added pneumatics. In 1998, the company was purchased by its current owners, Dick Beaven, Thomas McGuire, and Matthew Ott. The acquisition of Premier Hydraulic Services the same year added a repair facility now known as Air Hydro Repair Division.
When Air Hydro Power’s Perry Goldstein assumed leadership of the repair division in 2007, in-house honing capability consisted of hand honing with a ½" (12.7-mm) chuck Milwaukee drill. "Hand honing was physically demanding and a little tricky," says Goldstein, Air Hydro’s director of value-added services. "If someone accidentally hit the reverse switch while adjusting the hone, the stones would bite the tube and rotate the drill, which is not good if you’re the one standing next to it." Other factors, such as inability to maintain constant stone pressure and having to deal with blind bores, relegated Air Hydro’s in-house honing to low-end tasks such as taking out light scratches, deglazing, or polishing.
"Correctly honing a tube, maintaining accurate diameter, and keeping all the taper out are really difficult to do by hand," says Goldstein. As a result, parts requiring more significant material removal had to be sent out at significant cost. Outsourcing also took out some control of meeting delivery dates, putting Air Hydro at the mercy of its honing subcontractors. "There were times when sending parts out-of-house came back to bite us," says Goldstein. "A third party may not have the same sense of urgency we do. We’ll work all night and do everything we can to deliver parts on time, because we have ultimate accountability to our customers. Bringing the HTA on board gave us more control of projects and the ability to deliver when we promise."
The AHP repair division services and repairs all brands of industrial and mobile hydraulic pumps, motors, valves, and cylinders. Work in the repair shop is primarily focused on refurbishing steel hydraulic cylinders used in construction equipment, material-handling equipment (forklift trucks, telehandlers, and lift-gates) and heavy industry (cranes, oil rigs, off-road vehicles). Approximately 80% of AHP’s repair work is done on cylinders 8" (203.2 mm) or smaller in diameter, however it has honing stone sets and holders that handle bores up to 18" (457.2 mm). "Our largest lathe has a 3' [0.91-m] swing and 15' [4.57-m] bed," says Goldstein. "But, most of our work is done on our 22" [559-mm] swing lathe. The HTA fits perfectly with our other equipment."
The Sunnen HTA tube honing system handles parts weighing up to 8000 lb (3629 kg) with ID ranges from 2.5 to 21" (63.5-533 mm). The HTA machine is available for 6 and 12' (2 and 4-m) part lengths. Air Hydro has the 12' (4-m) model. The HTA is designed for resurfacing and repair work where light-duty stock removal up to 0.030" (0.76 mm) is required.
Air Hydro’s HTA hone also gives the repair shop greater flexibility on how to approach a job, and has saved many cylinders from the scrap heap. "Having the hone in-house allows us to look at the size and complexity of each job and determine if it’s a repair or a replacement," says Goldstein. "Prior to the HTA, we’d rub a finger over the tube and determine the material removal to be 0.005" [0.13 mm], which means 0.01" [0.25 mm] off the diameter. That would require us to make a new piston, new seals, etc., and we were better off just making a new tube." What AHP discovered, however, is the grooves felt larger than they actually were due to the "finger test" reflecting raised material as well as missing material. "Now, we put that tube on the HTA, make a few passes and find that, once honed, the tube may be only 0.001" or 0.002" [0.03-0.05 mm] over tolerance and the seals can easily absorb 0.002" [0.05] so we save the tube."
The HTA also comes in handy when AHP builds a cylinder from scratch, which requires the tube to have a trunnion mounted. When the trunnion is welded on, the cylinder will distort and cause a tight spot. AHP hones the tube to eliminate the tight spot and allow the piston to pass. The shop also hones across all ports on the tube, improving the life of the seals and wear bands.
The HTA includes a Siemens drive and PLC control with touchscreen HMI for setting machine parameters such as stroke reversal point, spindle/stroking speed, and crosshatch angle calculation. The control features a load meter to determine areas of bore tightness, and provides the ability to dwell the tool in multiple areas to correct part geometry. A touchscreen-controlled hone provides a safer working environment and reduces operator fatigue. It also provides better quality parts by producing a controlled crosshatch pattern, which allows the honed surface to retain oil or grease, ensuring proper lubrication and ring seal of pistons in cylinders. "Having the hone in-house allows us to look at the size and complexity of each job and determine if it’s a repair or a replacement," says Goldstein.
Transition to the HTA was easy for AHP, because the machine uses the same Sunnen ANR tooling the shop was using to hand hone. The shop’s crew also appreciates how fast and easy the machine is to operate versus the old hand-honing method. "Generally, it takes us longer to set the machine up than to run it," says Goldstein. "We know how much material is removed for every minute the machine runs, so we calculate the surface area and set the time. Once we get it set, we can hit the go button, walk away for a few minutes, come back , measure and we’re done." The shop will run anywhere from two to 15 parts per day through the hone. "We’ve got it down to where we will stage the tubes by grouping like sizes, so we can run it without changing the setup," adds Goldstein.
On the business side of the equation, the HTA hone has delivered excellent return on investment. Goldstein cited an example of a large-bore, thin-walled steel cylinder that the company had outsourced due to the complexity of the honing operation required to get the part to spec. "This part is extremely hard to hone," says Goldstein. "The manufacturer would have to make three or four parts to get one to spec, and that makes for a very expensive part." Air Hydro developed special fixturing for the part and was able to hone it in-house with the HTA. "It took us some time to get the setup right," says Goldstein. "But, in the big picture we saved a lot of money."
The savings goes beyond eliminating third-party help. "When we were looking to justify the purchase, we considered not only the elimination of outsourced work, but also warranty claims that would have been written off. We’ve had the machine less than a year and it’s already paid for itself," Goldstein concludes. ME
For information from Sunnen Products Co. go to
www.sunnen.com, or phone 800-325-3670.
This article was first published in the October 2011 edition of Manufacturing Engineering magazine. Click here for PDF.