Reaching New Depths And Greater Accuracy

Just when you thought high speed machining or hard milling would steal the best applications from ram-type elertrical discharge machines, linear motor technology is taking "sinker EDM" to levels unattainable with any other metal removal process.

Mike Province, the vice president of Clarich Mold (Westchester, Illinois) had planned to take a vacation over the Christmas holiday but that was not going to happen. He needed to burn one more mold on his CNC ram-type (sinker) EDM. The electrode, about 4 inches wide by 6 inches long, had complex geometry and deep ribs. Instead of using those four vacation days, Mike got stuck at the shop "babysitting" the EDM process--constantly adjusting the cutting conditions and the flushing ports. Almost a year later that same job came through the door again, only this time, Mr. Province burned the job on his new EDM with linear motors. Instead of spending four days burning the mold, he spent only 15 hours. The new machine completed the job faster because it did not require any special flushing setups.

Adapting linear motors on machine tools has created a lot of interest in the last few years. This interest was apparent at Chicago's International Manufacturing Technology Show in September 2000. Several major machine builders including Cincinnati Machine, Mazak and Sodick unveiled various types of machines with linear motor drive units. Other manufacturers of servomotors or control units such as Fanuc, Mitsubishi Electric, Yaskawa and Siemens also displayed linear motor technology.

Linear motors are not a new invention. Rather, they are an innovative adaptation of an existing technology. It is, in fact, the very same technology that propels roller coasters and bullet trains to record speeds in Japan. What makes the current linear motor units so intriguing is their entry into mainstream machining operations. Many industry observers believe that linear motors will have a dramatic impact on the design of machine tool axis motion, outmoding the present technology much like CNC did to control systems a few years ago.

Linear motors are rather simple. On a CNC ram EDM, two series of magnetic plates are mounted on the Z-axis quill, along with fixed magnetic coils on each side of the axis. The basic components of a linear motor are shown in Figure l. A linear scale with very fine resolution is mounted to the Z-axis quill in order to detect axis movement location. As the control signals the Z axis destination, electrical current is introduced into the copper coils, which are adjacent to the magnet plates. The resulting difference in polarity between the plates propels them in opposite directions. Because the one set of plates is fixed, the other set is driven rapidly along its path. The more current that is introduced, the faster the moving axis will travel. The Z axis can travel more than 1,400 ipm, or nearly 22 times faster than a traditional ballscrew equipped EDM.

No Backlash

With conventional motors, before any movement is realized, the electrical motion (rotation) must be converted into mechanical (linear) motion through the use of belts, gearboxes or ballscrews. All of these conversions introduce issues of mass, inertia, backlash, lag-time, overshoot, friction and heat. Even in the case of direct-drive systems (where the motor-shaft is mounted directly to the ballscrew), it must first overcome the mass, inertia and friction of the ballscrew mechanism before it encounters the mass, inertia and friction of the table and the workpiece weight. Then of course, to stop this motion, the same amount of time and energy is required. With linear motors, most of these issues are reduced or eliminated because no conversion from rotational to linear motion takes place.

Although a linear drive produces less torque at low speed than conventional drive systems do, EDM machines don't have high-torque, high-load requirements as chip cutting machines do. Therefore, this characteristic is not an issue for EDM. Because EDM is a non-contact machining process, it is a perfect fit for linear motor technology. Unlike machining centers that take advantage of the table speeds of linear motors, EDM uses linear technology's speed for the Z axis (ram stroke) in order to create its own flushing capability. EDM also uses the speed of linear motors to react to changes in the spark gap. Linear motor EDMs will excel in difficult-to-flush applications.

Retrofit Increases Productivity And Reduces Capital Outlay

Monitor Aerospace Corporation of Amityville, New York, is a producer of aerospace structural components for companies such as The Boeing Company. The company invested heavily in the 1970s in large expensive machinery, but more than 20 years later these aging machines were no longer keeping up with productivity demands. The older controls on these machines had limited functionality, and operators had to continuously tweak the machines to compensate for wear. Moreover, maintenance costs were soaring and downtime was increasing.

Gary Kahrau, director of manufacturing engineering, and Chris Nagowski, facilities manager, had a dilemma. They needed to address the machines' performance problems, but they did not have access to the enormous capital outlay necessary to replace them. Mechanically the machines were in fairly good condition, so they decided to explore retrofitting the machines with new controls as a solution to their problem. They knew that new controls would provide more flexible functionality, higher reliability and less downtime, but they also hoped that newer error compensation capabilities would help make up for some of the machines' wear related tolerance problems.

As Mr. Kahrau and Mr. Nagowski explored their retrofit options, their first task was to decide on a control. They wanted a control that would give them ease-of-use, high reliability, and sophisticated capabilities such as five-axis movements and advanced error compensation. Just as importantly, however, they wanted an open control that they could integrate into their existing plant system architecture and that would be poised for integration with undefined systems of the future.

Traditional controls offered the motion and compensation sophistication they were looking for but did not offer the flexibility and integration capabilities they wanted. On the other hand, purely PC-based controls, which offered the integration and operator flexibility they wanted, did not offer the motion sophistication they needed.

As their search went on, Mr. Kahrau and Mr. Nagowski spoke with CNC Engineering, Inc. (Enfield, Connecticut) and learned about CNC Engineering's PC-based Open Vision HMI system for the GE Fanuc series of controls. This system provides a hybrid solution that ties together a flexible and powerful PC-based front-end with the motion and compensation capabilities of a GE Fanuc control. Based on GE Fanuc's HSSB, and using an industrial PC for the operator interface, Open Vision HMI provides access to all of the control's native functions through intuitive touch screen menus. And, since the operator interface is on a PC running Windows NT, custom screens and options are readily available, and advanced network and system connectivity is fully supported.

The first machine Monitor decided to retrofit was a three-axis Cincinnati Bridgemill. This was a sound machine, but the X-axis gearboxes were worn, and the machine was not holding tolerances well. Rebuilding the gearboxes would be an expensive undertaking, and Mr. Kahrau and Mr. Nagowski thought that this expense could be avoided by applying some of the advanced error compensation functions available in a newer control. Working with CNC Engineering, a specification was developed for the control. For this application, Monitor decided to use a GE Fanuc 15MB control with CNC Engineering's standard Open Vision HMI Software. (The front-end software would run under Windows NT Workstation, and the PC initially would be connected to Monitor's Local Area Network via a standard Ethernet topography.) Since the GE Fanuc control had many options that might help compensate for the worn gear boxes, it was decided to add compensation features one at a time and perform accuracy tests after each feature was implemented to quantify the results.

Monitor has tight production schedules, and it could not spare the machine for the protracted period of time associated with a full in-field retrofit. CNC Engineering's CPR (Certified Pre-assembled Retrofit) package solved this problem. Under the CPR program, engineering and design specifications were worked out in advance during an initial site visit. During the site visit, detailed measurements were taken of the machine, and new component placement was finalized. The engineers at CNC Engineering spent considerable time working with Monitor to specify the optimum operators' pendant for the application. In this case, the original operator console was removed, freeing up a large amount of floor space, and a new three joint operator pendant was designed for maximum operator convenience. With the information from the site visit the entire retrofit package was engineered, designed and assembled at CNC Engineering's facility. During the engineering and assembly phase all necessary electrical schematics, cable lis ts, panel layouts, mechanical prints and ladder programs were developed. The exact equipment that was to be installed at Monitor was then assembled, wired and powered up. All parameters were loaded into the control, and the entire package was then tested exactly as it would be on the machine--right down to servomotors with their custom length servo cables. Once testing was finalized, the package was shipped to Monitor for field installation. For this machine the installation took 3 weeks.

Techno trucks: Roush racing

I'n a western suburb of Detroit, the Roush Racing NASCAR Craftsman Truck teams have been busy all winter preparing for the 1999 season opener in Homestead, Florida. The snow-shrouded shop could be mistaken for any other factory in a row of commercial buildings that line the service drive of a major expressway leading into downtown Detroit. But inside lies one of the most organized and complete shops in racing.

Don't tell Jack Roush that NASCAR teams must be located in the Carolinas to be competitive. The Roush truck teams have been extremely successful operating right out of Michigan, thank you, with third and eighth place overall standings in the 1998 series, almost identical to 1997. And don't tell Roush he has to purchase his chassis, engines or other components from someone in the South. If it can be done at all, it can be done well by Roush Racing.

Perhaps this formula has been the secret to the success of Roush's NASCAR teams over the last few years. (Roush Racing campaigns five Winston Cup and two Busch Grand National cars, in addition to the trucks.)

Part of the credit, however, must be given to the vast amount of technology used in this operation. Everywhere I looked I saw laptop computers used for reference and data recording. Nothing is left to human memory or the possibility of miscommunication.

The Teams

The two truck teams consist of the No. 50 Grainger Ford, driven by Greg Biffle, and the No. 99 Exide Battery Ford, now piloted by Mike Bliss for 1999.

I was given a shop tour by Matt Chambers, Crew Chief for the No. 99 truck and Randy Goss, Crew Chief for the No. 50 truck. I asked them what it was like, working in close proximity to another team.

"The two teams eat their lunches together and share information and communication. It keeps everybody together," said Goss. "It's an advantage."

"Randy and I work together closely, comparing notes and finding out what works and what doesn't," Chambers added. "It saves us a lot of time." Chambers prefers working in the NASCAR Truck Series rather than the Winston Cup or Busch Grand National cars. He's been on Winston Cup and Grand National teams and thinks the trucks are the best, "especially here with Roush. This is the best team I've been on," he continued, "and I find it's a lot of fun. In Winston Cup, there's tremendous pressure to please sponsors. We know we still have to make them happy,' but the pressure doesn't seem as bad in the Truck Series. We're also very fortunate to have great sponsors, as well as great ownership."

"We still have fun," Goss chimed in. "We race hard and take it seriously, but we still enjoy ourselves. Plus, when we leave home, we know we've got a chance to win. Some teams can't say that, and it takes all the fun out of it."

The huge facility is large enough to house both teams, with plenty of space for several built-up trucks, plus the offices and fabricating and storage areas. There's even a "wall" area for practicing pit stops. Each team has bays to work on five or six trucks that are in various stages of completion. Located in the fabricating area is a machine shop, a shop where oil pans and coolers are made, a shop for making headers, a chassis-building section and a shop to create the steel body shells. Outside, the transport trucks for each team wait to be loaded for the trip to Homestead.

Technology Abounds

I visited with Kevin Caparella, an experienced shock man who builds the shock absorbers for both teams. He creates a computer profile of each track on the schedule, compares it to last year's results and prebuilds the shocks for each truck accordingly. Caparella says short tracks with higher banks, like Bristol, create his biggest problems, because "a lot is happening in a short distance"-lots of bumps and turns. He then prepares several sets of shocks for each of the two trucks, which can then be fine-tuned at the track during testing and qualifying.

Caparella logs the mileage of each component and records the changes on his laptop computer. He inspects the shocks after every race and rebuilds them after three races. He uses a dynamometer that's specially made for testing and proofing the shocks before returning them to action. Again, the dynamics of each shock are recorded on his laptop for later reference.

Brian Hoye builds the transmissions and differentials for the truck teams. He has 22 Jerico four-speed gearboxes in his inventory and prebuilds several boxes prior to each race. Hoye usually prepares a tranny and two spare boxes for each truck, while the parts truck hauls two extra units, just in case. Having eight transmissions for the two trucks gives him the flexibility to rebuild quickly at the track to suit the driver's needs.

Eight-axis CNC turn/mill machines—EMCO Maier, booth A-8540 - Turning Equipment - advertisement - Brief Article

The Hyperturn 645/665MCplus, an eight-axis CNC turning-milling machine with Y and B axes is said to feature an crgonomically designed work area with straight chip drop, fully covered guideways and optimum lighting. According to the company, both dynamic spindles are powered by integrated spindle motors with synchronization and have a wide speed range, high torque and high drive power. The main spindle also has a bar capacity with a maximum diameter of 45/65 mm. The 12-station, upper tool turret Y axis and B axis (Quickmill or Powermill) have 12 driven tools and are for use on both spindles. The lower tool turret, which is also used on both spindles, features VDI quick-change system, 12 driven tools and alignment-free toolholders. The machine's control is a Sinumerik 840D with LCD color monitor.

This B-axis configuration of the Hyperturn QuickMill allows the upper turret to swivel to any position within a 45-degree arc. The combination of axial holder, radial holder and 45-degree holder can reach any angle within a 180-degree range. Its tool-change time is 0.14 second.In the configuration of the Hyperturn Powermill, a milling spindle with hollow-shaft motor takes the place of the upper turret. The B axis travels 210 degrees. The tool carrier is a 24-tool station magazine with Capto-C4 holders (48-tool stations optional). The Y axis of the machine is designed to divide the cutting forces over two guide planes. The result, the company says, is rigidity for all turning and milling operations. Travel of [+ or -]50 mm permits off-center milling and drilling. The company will show examples of its machine tool line. Some additional models on display include the Hyperturn 690 and Emcoturn 325-II.

CNC needs CNC support - computer numerical control machines

Outdated secondary-operation machines were strangling the productivity of a Chicago-area screw machine shop's impressive battery of CNC screw machines. Now, CNC drilling and tapping machines and turning centers are providing secondary machining efficiency that has raised the firm's performance to a level few competitors can match.

When you drive past the building, with its concave front and narrow, close-set, floor-to-ceiling windows, you would guess an insurance firm, or an engineering or architectural firm, or perhaps an association office. In fact, the distinctive exterior pictured in Figure 1 houses the operations of General Automation, Inc., one of the most impressive screw machine shops in the country.

General Automation specializes in, among other things, Swiss screw machine parts, that is, workpieces with high length-to-diameter ratios. The firm produces them on numerous Swiss-type cam automatic screw machines, arranged like spokes on large wheels, bar feeds toward the center. (The arrangement makes the most efficient use of floor space and makes it easier for the operators to load the machines and tend their operation.)

Although cam-operated screw machines have been around for generations, they remain a very competitive method for producing workpieces in large quantities. They can produce workpieces in less time (a shorter cycle) than by most other methods.Screw machine shops are aware of the advantages of CNC screw machines; many have one or two in order to remain competitive on prototype work, short run jobs, and jobs where fast turnaround and/or high quality are critical. However, few shops are in a position to invest in enough CNC screw machines to comprise a separate department.

General Automation is one of the few. The firm operates some 63 Nomura CNC Swiss-type screw machines--the largest concentration of such machines in the U.S. The CNC Swiss-type screw machine offers a number of advantages over the older cam automatic screw machine. As its name implies, the cam automatic's cutting tool movements are controlled by a set of cams specially made for the workpiece being produced.

The CNC screw machine needs no cams. Tool movements are automatically determined by data from the dimensions of the part, fed into the machine's CNC unit. The workpiece can be programmed on the CNC right at the machine. Or, as is more often the case, the program can be prepared on a programming system located off the shop floor, and loaded in the machine's control when required. The control's "memory" is capable of storing dozens of workpiece programs; preparing the CNC screw machine to produce a different workpiece simply involves calling up the program for the next job, minimizing machine downtime between jobs.

Because CNC machine tools handle job change-overs much faster than manual or automatic machines, they are usually thought of as "short-run machines." By contrast, cam automatics, which are noted for their very rapid cycle times, are considered "production machines," ideal for producing large quantities of workpieces over long periods of time.

However, General Automation's CNC screw machines are faster than its cam automatics, so the company benefits not only from fast, easy machine setups, but from fast workpiece cycle times as well. According to General Automation president Max Starr, the CNC Swiss-type machines are frequently the most economical choice for complex workpieces, regardless of the length of the run.

Other advantages of the CNC screw machines are their greater accuracy and piece-to-piece consistency. Both are important to today's product manufacturers who demand parts machined to finer dimensional tolerances--and that those parts be within tight statistical process control parameters.

Another big advantage of the CNC screw machines--important to any job shop concerned about controlling costs--is that operator responsibilities are reduced to monitoring the machines and keeping their bar feeds filled. This enables General Automation to use less skilled operators at lower hourly rates.

Plugging into STEP NC - Emphasis: CNC - CAM software firms offer programs for CNC machines

CAM software companies are offering software programs that allow their users to read STEP-NC files info their existing CAM software to generate the tool path and output for specific CNC machines. These "plugins" make many of the benefits of STEP-NC available to the average machine shop today.

The concept behind STEP NC is simple. It enables a product model database to serve as direct input to a CNC machine tool. No separate files of tool paths. No G or M codes. No post processors.

This is a radically different approach to CNC programming. It has far-reaching implications for the emerging possibilities of "e-manufacturing." Recent developments, however, promise to make it easier for CNC machine shops to make the transition to this technology Without scrapping existing machine tool and CNC programming technology, shops now have a way to implement key aspects of STEP-NC.

Several leading CAM software companies have made it possible for STEP NC files to be used with their own software. This makes their users ready to participate in supply chains that are turning to global data exchange standards to streamline the flow of digital information over the Internet. According to STEP Tools, Inc. (Troy, New York), a leading supplier of STEP software toolsets for application software developers, design firms and manufacturing companies, STEP NC offers significant savings to machine shops and their customers. The company estimates that, by fully implementing STEP NC, machine shops can reduce the time it takes to get jobs onto their machines by 35 percent if they can seamlessly read the 3D product geometry and manufacturing instructions of their customers. Likewise, original equipment manufacturers can reduce the time they spend preparing data for their suppliers by as much as 75 percent if they can seamlessly share the design and manufacturing data in their databases.

STEP Tools also estimates that STEP NC will reduce machining time for small- to mid-sized job lots by as much as 50 percent because STEP NC compliant CNC units will be capable of optimizing speeds and feeds with very little intervention from CNC programmers or machine operators. This factor could make it easier and safer to program high speed and five-axis machines, the company says, making it more likely that they will be used for small- to mid-sized job lots.

STEP NC In A Nutshell

STEP NC is an extension to STEP, the STandard for the Exchange of Product model data. STEP is the international standard that specifies a neutral data format for digital information about a product. STEP allows this data to be shared and exchanged among different and otherwise incompatible computer platforms. STEP NC standardizes how information about CNC machining can be added to parts represented in the STEP product model.

By using STEP NC to capture instructions on what steps to follow for machining the part, the "producability" of this part would not be affected by the availability a certain brand of control unit, programming system or post processor. Figure 1 compares the key features of STEP NC to current conventional approaches to creating CNC machine tool input.

If equipped with a STEP NC compliant CNC, any suitable machine tool could be designated to make the part. Because a product model database can be made accessible through the Internet, this designated machine tool could be linked to this global network virtually anywhere on earth. For manufacturing enterprises participating in a highly competitive global supply chain, this kind of flexibility is crucial. With the Internet acting as a global DNC system, the world becomes one big job shop.

Step Rather Than Leap

The availability of STEP NC software plug-ins for CAM software puts STEP NC within the reach of many shops. Currently, plug-ins are available for Gibbs CAM from Gibbs and Associates (Moorpark, California) and for Mastercam from CNC Software (Tolland, Connecticut). A plug-in for Esprit from DP Technology(Camarillo, California) will be completed soon. With these plugins (or "add-ins," as they are also called), a shop can take in a customer's STEP NC files and produce parts on existing CNC equipment.

A full implementation of STEP NC would involve equipping machine tools with CNCs customized with special software. This software enables the CNC to interpret the STEPNC data directly and use the information to machine the part without a conventional G-code program. This software is currently under development.

Machine tools with PC-based open architecture control systems may be able to install this software to upgrade to STEP NC compatibility rather effectively. The conventional input/output (I/O) structure and the servo system of the CNC machine do not need to be modified under STEP NC.