Shop Solutions: Honing Scores with Machine Gunners
The classic Browning .50-caliber machine gun enjoys preferred status with American troops for many reasons, not the least of which that it is a straight shooter.
Part of the reason for that preference is the superior accuracy and easy cleaning that results from the bore geometry and surface finish of barrels made by UKbased Sabre Defence Industries. Since installing a Sunnen HTB tube hone from Sunnen Products Co. (St. Louis, MO) at its Nashville, TN plant, test fire groupings from sample barrels have tightened up nearly 100% over the Army's requirement.
"We have been making military .50-caliber barrels and guns since 1979, as well as commercial rifle barrels for various companies over the years," explains Charles Shearon, general manager of the Nashville plant, which was acquired by Sabre in late 2002. "The new owner, Guy Savage, planned to reposition our operation to be about 50/50 military and commercial," says Shearon.
The Nashville plant was to be a launch pad for US production of Sabre's XR15/16 rifles, a premium variant of the AR15/16 for the civilian and police markets. The start of the Iraq war in early 2003 changed that.
"We received military orders for our .50-caliber machine-gun barrels, 7.62-mm M60 machine gun barrels, M134 minigun barrels, and M6 weapons mount. The demand for .50-caliber barrels grew in the next few years from about 100 per month to 1200 per month and employment at the plant was ramped up from 15 to 85," says Shearon.
Sabre makes two variations of the 50-caliber barrel: the heavy barrel for the M2 Browning gun and a lighter, shorter version for the M3 aircraft machine gun. Both have a Stellite liner for the chamber throat and first few inches of rifling. The liner and a retainer for attaching the barrel to the receiver are both shrink-fit. The Stellite liner (75% cobalt and 25% chrome) withstands the intense heat and gas erosion of the initial discharge better than any ordnance steel.
The heavy barrel starts as a 45" (1143-mm) piece of bar stock 2.625" (66.7 mm) in diam, that weighs about 73 lb (33 kg). "For the heavy barrel we use MIL-S- 46047, a special alloy with extra vanadium to increase life," explains Shearon. The aircraft barrel is MIL-S-11595, which is also used on Sabre's commercial guns. Steel is bought by the mill run, cut by the mill, and heat-treated when received.
"We do some preliminary operations to prep it, then gun-drill the chamber end with a 0.75" [19-mm] diam hole about 11" [279-mm] deep. A temporary liner is then installed and the rest of the barrel is gundrilled with a 0.490" [12.45-mm] diam hole. We ream after drilling and have a hole size tolerance of ±0.001" [0.03 mm] at that point, but the next step is to stress relieve and that often changes the bore."
Honing allows Sabre to control final geometry and hole size of the bore to a fraction of the allowable MIL-Spec, which is helpful because of the small variations introduced later by button rifling and chrome plating.
Sabre had been using a manual lapping machine to finish bores, but the increase in military orders resulted in a bottleneck of work at that operation. "We consulted with Ron Williams, Sunnen's senior field engineer in our area, on how current technology could improve our processes," says Shearon.
The result was the installation of a Sunnen HTB-2000 tube hone system in early 2006. Equipped with Borazon CBN stones, a traveling steadyrest, and whip guide bushings, the PLC-controlled machine has an output of 10–12 barrels an hour compared to about one an hour with the old process.
"The load-sensing system on the machine automatically adjusts the stone feed for optimum stock removal without tool crashes, which reduces our labor and helps improve output," explains Garry Hogan, Sabre's plant manager. "More important to us is the automatic gaging system. The machine gages the bore after every stroke, allowing us to control hole size, roundness, and straightness to 0.0005" [0.013 mm] without operator intervention.
"Even after button rifling and plating, we are able to stay well below the MIL-Spec of ±0.004" [0.10 mm] on bore dimensions, which is quite a feat on a bore length of 33" [838 mm]. Tool life for the process varies with the amount of stock removal, which typically runs 0.002–0.004" [0.05–0.10 mm]," Hogan explains.
The crosshatch pattern that honing leaves on the bore surface aids in rifling the barrel by maintaining a consistent lubricant film. To create the rifling, a 0.517" (13.1-mm) carbide button is pushed through the bore, which is 0.503" (12.8 mm) at this stage. The button has the rifling form in high relief on it, and is rotated at the correct twist rate. Lands on the button engrave the grooves in the bore.
"The very round hole we get with the hone helps prevent high and low spots in the rifling, and keeps the grooves concentric with the bore, all of which aid accuracy," Hogan adds, "We're unique in the business in that we make our own buttons, too, which gives better control of our quality."
Surface finish of the bore coming off the hone is about 20 µin. Ra and drops into the low teens after button rifling, significantly exceeding the MIL-SPEC of 63 µin. This helps maximize muzzle velocity and makes it harder for metal and powder fouling to get a toehold, so cleaning is easier.
"In the precision rifle-shooting community, the sweet spot for surface finish is considered 10–20 µin.," Hogan explains. "Though it seems contradictory, a smoother surface actually increases surface contact and friction with the bullet jacket, causing increased copper fouling," he explains.
After contouring the exterior of the barrel, the bore is chrome-plated to a thickness of 0.0013–0.0020" (0.03–0.05 mm). "One of the reasons we run such tight tolerances off the hone is because we lose some tolerance in the plating process," Hogan explains. "The platers are excellent and seldom vary more than 0.0005" [0.013 mm], but if they do, we already have some margin for error to work with."
The Stellite liner starts as a casting, which Sabre gun-drills and reams, then sends to a third party for honing. "This supplier has never scrapped a part, so it's a good system that we're not going to fix," Hogan adds. With the barrel induction-heated and an alignment gage in place, the Stellite liner is pressed into the barrel's chamber so that its lands and grooves line up perfectly with those of the barrel.
Every barrel is then fired with a high-pressure test round and examined with a Sunnen magnetic particle inspection system. "We're required to test fire a certain number of barrels from each lot for accuracy," Shearon says. "The army's spec calls for a 10-round burst to hit within an 8" [203-mm] circle at 100' [30.5 m]. We've always been able to hit 7" [178 mm], but since we started honing we're hitting 4" [102 mm]."
"We're lucky to be able to interact with users of our products," says Shearon. "At a recent armor-war fighting symposium at Fort Knox, we had several tank gunners tell us that they knew as soon as they shot a fifty if it was a Sabre barrel or not. If it wasn't, they found one of ours and installed it. We're sure our commercial rifles will earn the same loyalty, too, as we ramp up production and get the word out," Shearon concludes.
VMC Speeds Gear Reducer Production
Contract manufacturers have a way of evolving into specialties that suit their particular machining capabilities and expertise.
Sometimes a success in one industry can prove capabilities that can be applied to other industries. It's not always possible to predict where business will come from, but one thing is certain, dedication to quality manufacturing is high on the list of things that will result in continued growth and success in the long run.
When Maybar Manufacturing Co. (Franklin, WI) was looking to increase its capacity, adding a new VMC to the job shop resulted in a 30% improvement in throughput in parts manufactured without changing anything else.
Maybar was established in 1951 as a family-owned and operated business. Founded by Edward Majcher, Ervin Bartczak, and Walter Majcher, the company grew steadily from its roots in the heart of Milwaukee through successive expansions that culminated in the opening of a 16,500 ft2 (1533 m2) facility in Franklin Business Park in 2001.
Through the late eighties and early nineties, Maybar experienced significant growth in the production of speed reducers and related drive components that are used mainly in the food-processing industry. Maybar designs and manufactures food-processing equipment that makes softserve ice cream and milk shakes around the world, among many other food products.
Manufacturing speed reducers and related products accounts for most of Maybar's business, but true to its beginnings Maybar is still a job shop with a small percentage of its current business consisting of jobshop work machining aluminum, alloy steel, and stainless steel for a select list of customers.
Maybar's manufacturing capability includes a full line of CNC equipment for producing dimensionally critical custom-machined parts like speed reducers. The company is able to take parallel shaft speed reducers with options like heat-treated helical gear sets and radial ball or tapered roller bearings from concept through production. It also produces pulleys, couplings, and drive shafts for input or output ends of the speed reducer.
"When we looked for ways to increase our capacity to meet growing demand, we began looking at the machining centers that were available," says Timothy S. Bartczak, Maybar president. In the past, Maybar had been using Hitachi Seiki machining centers, but with Hitachi Seikis no longer available, the company needed to explore other machine options.
"We were looking for speed as well as reliability in a VMC that would fit into our manufacturing cell configuration or operate as a standalone machine," Bartczak says. Machines priced at both ends of the spectrum—from less expensive to more expensive—were evaluated. Maybar wanted to invest in a machine with the best overall value for the long term.
The company finally selected the Ultra ZV5000 VMC from NTC America Corp. (Novi, MI). Advantages of the selection are twofold and include both machine capabilities and NTC's experience with its automotive customer base.
"The main reasons we chose the ZV5000 were the speed and NTC's extensive automotive experience," says Bartczak. "The rapid-traverse rates are much faster than anything else we looked at." While Maybar doesn't do automotive manufacturing, Bartczak says the fact that NTC's machines are used heavily in the automotive industry proves the capabilities, durability, and longevity of the machines.
"If NTC's machines can fulfill the needs of the automotive industry, they can certainly meet the needs of Maybar," says Bartczak, adding that other benefits of the ZV5000 include excellent rigidity, easy access to the spindle, and low maintenance. "The way the spindle is set up—you don't have to tear apart the whole machine to get to it," he points out.
The NTC ZV5000 VMC has the ability to machine a wide variety of parts, but it is being used by Maybar as part of a cell to machine aluminum die castings for the gear reducers that go into food-processing equipment.
The Ultra ZV5000 VMC is able to produce near-net shape parts in medium-to-high-production lot sizes with a CAT-40 taper tool shank, and a 25-hp (18.6-kW) spindle with 12,000-rpm maximum speed. Axis travels are 44 x 22 x 22" (1117 x 559 x 559 mm) X,Y,Z and traverse rates are 2362 ipm (60 m/min) for the X, Y axes and 1653 ipm (42 m/min) for the Z axis. The ATC has a capacity of 25 tools.
"By incorporating the ZV5000 into our shop without changing anything else, not upgrading any tooling and using all existing programs, we have seen an improvement of 30% in our parts manufacturing. In the near future, we expect to see even better results when we upgrade our tooling and fixturing," Bartczak says.
Press Delivers Precision Straightening
The rapid increase in the use of embedded PCs for industrial control systems is a natural outgrowth of designers' interest in building machines with enough flexibility to adapt to constantly changing requirements.
Windows PCs can do more than just implement a human-to-machine interface (HMI) or perform simple data acquisition. Windows PCs are capable of implementing reliable real-time control when augmented with a tightly-coupled real-time software environment.
Eitel Presses Inc. (Orwigsburg, PA) has migrated its control system from being purely PLC-based to incorporate a Windows-based platform. The migration was driven in part by the fact that some of the mathematical calculations couldn't be done efficiently by PLCs. What was needed was more general-purpose computational element in its system architecture, which Eitel developed and refers to internally as ORCA (Open Reliable Control Architecture).
High-speed mathematical computation is required to make the partstraightening cycle times fast and precise. Eitel's presses provide precision straightening for heat-treated metal parts to the automotive industry. Parts such as valves, crankshafts, pinions, and axles are typically out of alignment when they exit the heat-treatment process. Eitel equipment straightens these parts to tolerances as tight as 20µm, with a repeatability of measurement equal to 2µm or better.
Incorporating Windows PC control in Eitel's Automatic Mechanical Straighteners has reduced straightening time for camshafts to 10 sec compared with 20 sec with PLC-only controlled machines. In addition to calculating the straightening algorithm, the Windows PC implements the HMI, rotates the parts being straightened, and hosts a data collection card that obtains dimensional measurements on the parts during the straightening process. The Windows PC also handles communication with a conventional PLC in the system for controlling general machine I/O functions, such as activating solenoids for parts transfer.
The only reluctance that Eitel had in adopting a Windows PC for the critical control element in their system was their concern for system reliability. At the time, PCs had the reputation of being prone to software crashes, Eitel wanted a software environment that was demonstrably robust.
After evaluating multiple PCbased software alternatives for managing control and data-acquisition functions, Eitel chose the VLC package from Steeplechase, a division of Phoenix Contact (Ann Arbor, MI). Using Steeplechase VLC, Eitel's designers quickly implemented a flowchart design to control servo drives and facilitate data collection from the data acquisition card.
The INtime real-time kernel underlying the VLC software is a realtime OS provided by TenAsys Corp. (Beaverton, OR). It works in parallel alongside Windows. INtime ensures that the time-critical elements of an application like servicing the data acquisition card and performing Eitel-specific straightening algorithms always have priority over non-timecritical Windows processes like HMI and enterprise networking.
With the help of TenAsys engineers, Phoenix Contact developed a means by which OEMs can extend Steeplechase VLC with custom realtime PLC function blocks. These custom function blocks, created with the Steeplechase C-Toolkit and a standard Visual Studio compiler, execute on INtime and expand the functions and features available in the Steeplechase VLC programming environment.
Eitel engineers were able to develop custom code for Steeplechase VLC to run on the INtime RTOS. The Eitel real-time code manages the complex action of reading and processing information from the data-acquisition card before it is passed back to Steeplechase VLC to control Eitel's straightening press. This flexibility of the INtime RTOS allows Eitel to create a fast and precise control system that can be programmed by their end users.
Steeplechase VLC also controls two press servomotors through a PC motion-control card. Servo drives power the straightening function and rotation of the part for measurement. They also provide encoder feedback for the straightening algorithm. Standard motion-control function blocks provided with VLC, combined with function blocks developed by Eitel, form the system's core elements.
During application development, designers can view the values of variables in real-time as VLC programs are being debugged. Eitel's customers also have the ability to modify VLC programs to make application-specific changes themselves—giving Eitel an advantage over competing "black box" systems that require vendor support for modifications.
After straightening, information about each part, deflection before and after and the cycle time required to correct, are stored on the PC's hard drive. Additional information is collected that can help the customer troubleshoot upstream processes that affect the straightness of the part. The customer can use this information to improve his process, thus yielding better quality parts and improved cycle times. Some applications, such as those involving the straightening of aircraft parts, require that such information be archived.
"Due in large part to the reliable VLC/INtime software environment, the AMS system has proven to be fast, quiet, and environmentally friendly," says Karl Klemsche, Eitel vice president. "We are now building machines around the second generation of the ORCA architecture." This new generation incorporates adaptive controls that adjust the straightening stroke infinitely based on the measured deflection before straightening.
Other benefits include plotting thermal infrared (TIR) imaging curves and surface geometry, multilingual HMIs (including Japanese), and automatic flaw detection systems.
Machining Springs, Wire Forms Near-Dry
Near-dry machining on a CNC wire-forming operation has produced substantial benefits, including cost savings and a better and safer working environment for employees of a supplier of custom springs and wire forms.
Located in the Chicago area, Master Spring & Wire Form Co. (River Grove, IL) specializes in small-to-medium quantity orders of one to 500,000 custom precision springs and wire forms, delivering them in short lead times to various industries.
Master Spring & Wire Form was founded in 1945 by Emil Burda, who worked as a foreman and setup man at a large spring manufacturing plant. Burda was unhappy at the way the smaller orders were handled so he decided to found his own company, starting with a homemade coiling machine. Burda liked to say, "We can do the possible quickly. The impossible might take a little longer."
From its founder, Master Spring inherited his pride in the company's ability to solve tough spring and wire form problems that larger companies often choose not to quote. Its reputation for fast service on small-to-medium quantity orders grew, and the company became a natural choice as a supplier to the local pinball and gaming industry.
"The industry has changed a lot since I joined in 1999," explains Steve Skolozynski, the founder's grandson and Master Spring's general manager. "With all the pressures on manufacturing caused by competition from Chinese companies, a lot of our larger competitors are being hurt. Most of the jobs we get can't be exported to China, either because they are low volume or they require fast delivery," says Skolozynski.
"More and more customers are looking at lean manufacturing, a trend that helps Master Spring as our customers try to eliminate stock and select suppliers with the ability to meet short lead times," he says.
Master Spring manufactures wire forms with a wire diameter from 0.008 to 0.500" (0.20–12.7 mm). The company offers secondary operations such as thread, chamfer, swage, drill, tap, machine, and weld. The company will also take care of any finishing required, such as plate, passivation, stress relieve, heat treat, shot peen, and tumble.
To improve productivity, cut costs, and improve workers safety, Master Spring addressed the two main challenges it faced in using a water-soluble flood coolant system: cost of the cutters and cost of any machine downtime.
Using flood coolant, Master Spring had to change the cutter every 4000 or 5000 parts. Another issue concerned the press. If the part isn't lubricated enough, the press will be dry and will stick to the part. The operators had to fill oil every day, requiring them to constantly watch oil levels. Using coolant made the process messy, and chips would clog the coolant. Finally, the coolant equipment took a lot of floor space. There was a drum on the back and a big circulation pump.
Master Spring began to look at alternatives to this coolant system and in particular at the Accu-Lube system of near-dry machining from ITW ROCOL North America (Glenview, IL). Accu-Lube applicators carry the lubricant to the cutting edge in exact quantities, preventing heat build-up and improving performance. Lubricant is carried by air, eliminating atomizing and misting.
An Accu-Lube two-nozzle aluminum pump applicator with an on/off valve was installed on an AccuForm Modular 3DX CNC wire-bending machine from AIM Inc. (Addison, IL) with circular cutter that cuts into the wire. The on/off switch allows the flow of lubricant to be regulated manually, an advantage when the operator is setting up an application. Once the operator was comfortable with the flow of lubricants, the Accu-Lube applicator was upgraded to a system with an electric solenoid where the lubricant is applied automatically when the machine is on.
At first, the setup man didn't like near-dry machining. He was very concerned that he could not see the coolant, that the part was no longer flooded. He questioned how the Accu-Lube system was going to be better, how it would save money, and how it would increase cutter life.
Once the Accu-Lube applicator was set up properly to go right on the cutting edge of the tool with enough lubricant, the operator began to see the benefits. He is now a main supporter in getting the Accu-Lube system installed on other machines in the plant.
"The benefits didn't take long to be seen and quantified," says Skolozynski. "Since we started using the Accu-Lube system, we have quadrupled the life of the cutter and the life of the die. We have a much cleaner environment without spills, and operator's hands and floors are cleaner. We are looking forward to eliminating flood coolant wherever we can in the plant in favor of near-dry machining.
Edge Prep Drives Axle-Plant Production
With a reputation for manufacturing some of the strongest and quietest automobile axle assemblies, the Getrag Axle Plant in Newton, NC, has shown remarkable growth driven by the plant's ability to produce high-quality products at a competitive price.
Since 1999, production has increased from 68 axle assemblies per day to 1800 per day. The plant supplies high-end products for an expanding set of vehicles, including General Motors' Corvettes and Cadillacs and DaimlerChrysler's PT Pacifica.
At the heart of Getrag's axle assembly there are ring and pinion gears which are produced using a gear-generating process that cuts all the gears dry. The dry process results in significant savings in the purchase and disposal costs of coolants, but places extra demands on their tooling, causing premature tool failure.
Getrag recognized the need to extend the life of the carbide blades to minimize this downtime, to achieve higher utilization of its expensive geargenerating equipment, and to reduce unproductive labor activity spent regrinding tools.
Short tool life has a cost attached to it. "Our largest tool cost was carbide stick blades," says Tony Trimm, the engineer at Getrag responsible for gear cutting, "Improving tool life will reduce the downtime of our gear-generating machines."
"In one year we performed 1250 cutting head replacements, a procedure that costs about 40 minutes of production downtime, each and every time," Trimm points out.
The unproductive labor consisted of the effort to change out the blades as well as the effort to regrind the blades so that they could be reused. Because of the short life of the blades, the plant carried an inventory of carbide worth $160,000–$220,000. The most significant cost was the diminished utilization of gear-generating machines, each costing $600,000 to $1 million.
Getrag tried several possible approaches to extending the life of the blades. First they tried using many different grades of carbide and various coatings, without achieving much improvement. Next, the company tried several different honing techniques. Some produced good results with a 30–40% improvement in tool life, and then yielded some bad results when using the same method on a second application.
Getrag could not find a process that would give repeatable results, until mid-2005, when it found the Engineered Micro-Geometry (EMG) edge-preparation process developed by Conicity Technologies (Cresco, PA).
The EMG process uses dense silicon-carbide filament brushes applied with CNC control to consistently and precisely shape edges to tolerances of 0.0002" (0.005 mm), an order of magnitude more precise than most conventional honing methods. The EMG process is more consistent than conventional edge-prep methods, applying the same edge preparation to tool after tool. This is accomplished by the software in the system's CNC control, which manages all of the critical process variables.
The optimal microgeometry can be applied precisely according to the particular requirements of each cutting application. To determine the optimal edge preparation for Getrag's gear-generating application, Trimm worked closely with William Shaffer, executive vice president of Conicity Technologies and developer of the EMG technology.
"For our gear-generating application, Conicity determined that the optimal edge preparation is a slight radius, producing a good chip roll and making the tool cut more efficiently with less heat generated and less material trapped between the tool and the workpiece. This results in a smoother finish and less tool wear," explains Trimm.
Getrag outsourced the edge-preparation process to Conicity. "After consistently achieving a 50% increase in tool life for each subsequent batch of blades, we decided to purchase our own machine so that we could perform the EMG edge preparation inhouse," Trimm says.
The Getrag plant installed a Conicity GXM-50A edge-preparation system, with a capacity to hone 100 blades per hour. The GXM-50A was configured to take a tray of 100 blades directly from the grinding machine. Because of its small size, flexibility, and quick setup, the GXM-50A is able to reduce production costs, improve part quality, and shorten lead times.
"With the new edge-preparation process, our machine utilization has increased significantly," says Trimm, "and we will not need to buy and maintain as many gear-generating machines as our plant expands capacity, saving us millions of dollars in equipment costs."
The Newton plant is expected to increase production to 3000 axle assemblies per day, and the increased machine utilization means that the plant can produce this volume with two or three fewer gear-generating machines than would otherwise be required.
Trimm has also been able to lower costs by reducing labor for changing out blades, as well as regrinding and blade inspection. Moreover, carbide blade inventory and replacement costs have been reduced significantly.
Grinding Beyond Ordinary Limits
There are parts that seem to defy the application of process technology like grinding. They are too big, too long, nonround, and/or eccentric in shape. Too much stock has to be removed, or they are difficult-to-handle materials.
The key is to have the right grinding technology, something that Hommer Tool & Manufacturing Inc. (Arlington Hts. IL), which opened in 1983 to specialize in the production of round tooling and components as well as the fabrication of replacement tooling for the plastics injection-mold building industry, has done.
Since then, Hommer Tool has earned an impressive list of customers including Nypro, Inc., Courtesy Mold, Tech Mold and Baxter Laboratories. With annual revenues in excess of $5 million, a new state-of-the-art 12,000 ft2 (1115 m2) facility and 35-plus employees, the company continues to grow.
JR Hommer, vice president, admits that he's constantly looking for ways to make the company stand out from the competition. One way is by being able to do what others cannot do—or at least cannot do as competitively.
Rick Skaja, operations manager, thinks for a moment before describing an application for Honda Motors of America's engine plant in Marysville, OH. "I've been a toolmaker for 25 years, and in all that time, I don't think I've seen anything like this," says Skaja. "At first, I thought: No way, not with the tolerances, the number of operations, the shapes, the wheel changes, the eccentricity."
The part is 26" (660-mm) long. The material is a mild steel, about RC 45, somewhat harder than H13 and, as Skaja says, pretty "gummy and prone to springing." The part is first turned, the flanged body is roughed on a mill, and a 0.315" (8-mm) diam hole is gun-drilled nearly the entire length of the part. There are some 12 grinding operations requiring five different wheel shapes—four nonround peripheral shapes and one round tapered shape. Grinding requires four setups and two double-wheel changes. Overall dimensional tolerances: 0.0002" (0.005 mm). Actual grinding time (excluding setup and wheel changes): just over six hours per part.
The solution was found in using a Studer S40cnc from United Grinding Technologies (UGT; Miamisburg, OH). The S40cnc was purchased initially because of its flexibility and ease of use. "The rationale was this. If I was going to make a considerable capital investment in new grinding technology, I wanted a machine that could do the entire job and that could be changed over quickly and easily programmed by our operators," Hommer explains.
Because the company runs multiple jobs during each shift, ease of programming was deemed an absolute necessity. With the Studer Pictogramming software, Hommer operators are able to perform a pictographic-based setup on a new job and have the machine producing new parts usually in less than an hour.
The Studer wheelhead configuration of the S40cnc has two OD wheels and a high-frequency ID spindle on an infinite B axis. With this configuration, a job that would have previously taken five separate operations could now be completed with one setup. This level of efficiency has more than doubled productivity on many jobs.
"We clamp it in the Studer with a custom two-jaw chuck, hold it on the milled surface, and hit the back face of the large diameter," Skaja says. "Then, centering off the milled flanged center surface, we reproduce the flats on the head. After this, we turn the part around and grind the area of the oblong closest to the end of the hole, so we can check wall thickness and concentricity. Then, we put in an offset center at the long tapered end of the part, and in a literal sense begin working backward. We figure out where the hole walks, put in the offset center, and start grinding again on the backside, this time between offset centers. What we're now doing at this point is grinding an eccentric, nonround shape between offset centers."
There are a number of precise radii (at least four over the length of the part) that require wheel reconfiguration or change. The radii range from 0.5 mm under the head of the part, to 8.5 mm at the junction between the oblong nonconcentric oval and the final tapered length, and a 3.0-mm radius at the end of the part.
About 60 mm down from the head of the part is the start of the oblong taper, which is basically a nonround oval shape except that it's tapered in two ways, across the flats and across the radii. "Even though we're grinding an eccentric, the part here is actually round due to the relationship of the centerline location at this point with respect to the part plane," Skaja explains.
If much of this appears pretty complex, that's because, according to Skaja, it is. "You should actually see this part run," he says. "The orchestration of head and slide movement—it's wild. And when we're done, we've ground off more than 3.75 lb [1.7 kg] of steel. Which is a lot of stock removal. More impressive, however, is that it's highly precise stock removal on a job many of us thought impossible." Skaja explains: "The finished part ends up in a die caster, which is about all I can say about its end-use application. But the part's grinding complexity really demanded that we put the Studer through its paces."
While programming the Studer S40cnc is routinely pretty easy, even on complex jobs, the Honda die casting part proved something else.
UGT, which had been asked to assist in resolving the issue, came up with a software upgrade at no additional charge. It's called a nonround eccentric traverse that, Skaja says, has made it all work. "Nonround eccentric traverse means that we can traverse across ovals and tapers while grinding nonround, eccentric shapes and running between offset centers. This software solution made the job possible. And the S40cnc makes producing it practical," Skaja says.
This article was first published in the December 2006 edition of Manufacturing Engineering magazine.
Published Date : 12/1/2006