Shop Solutions: VTC Helps Crush Rising Mineral Demand
Telsmith Inc. (Mequon, WI), a manufacturer of crushers and screens for mineral and aggregate processors in the booming global mining industry, needed to find ways to substantially increase its production.
The company chose to reorganize its factory based on Lean manufacturing principles as one aspect of its multipronged approach. Another was maximizing spindle utilization on all its machine tools, starting with two new machine tools.
Telsmith produces parts for equipment that can handle more than 1000 tons of material per hour. The company required a vertical turning center (VTC) able to machine parts as large as 82" (2.1-m) diam, 54" (1372- mm) tall, and weighing nearly 9500 lb (4.3 t). On some parts the company is removing more than 45% of the material. Part materials include cast iron and 4140 steel forgings.
To achieve the metal removal required, Telsmith chose a VTC 2500 from MAG Giddings & Lewis (Fond du Lac, WI) with a turning capacity of 2.7-m diam, a table with a load capacity of 98,000 kg, and a 75-kW drive. Power of the drive was also a key buying criterion in making the selection, it should be noted.
The company more than doubled its crusher production last year, with the same level of manpower, and is experiencing cycle time improvements of 53–80%.
To optimize programs and operations, an extensive runoff of parts was conducted at the MAG Giddings & Lewis manufacturing facility. Michael Wier, Telsmith CNC programmer, with the assistance of G&L runoff technicians and programmers, spent four weeks refining programs for four parts. "We want to be on the cutting edge. So we decided that if we were going to spend the money for a quality machine, we’d better spend the time to get the most from it," Wier explains.
Working with newly written code and using macros supplied by G&L programmers, the Telsmith team, which also included programmer Dave Worzalla and operator Jim Kaczororski, was able to fine-tune eight part programs. Many manual operations were automated, taking advantage of all of the machine's capabilities. "The great thing about the run-off process at G&L, was that we had everyone we needed right there. That kept us on pace," says Wier. "The runoff was worth the effort. We had confidence in the machine and our programs when we finished."
Working in EdgeCam software to handle the variables makes the program updates that an operator has to input easier and less prone to mistakes. For example, to change the approach distance for a tapping cycle in the part program, the operator looks for the variable "SDIS" listed prior to the cycle and edits the value. (See sidebar.) Without the use of the variable, the operator must be familiar enough with the cycles to identify the correct input to the cycle call. Some cycles have as many as 17 different variables. Depth, retract position, and reference plane are examples of other actions or values where variables are used. "The development of the variables may take us longer initially, but anytime we can remove the potential for error, we feel it's time well spent," Wier notes.
Automating processes wherever possible was another objective when writing the programs for the Telsmith parts. Probing—both tool and part probing—is used extensively. Applying a process that G&L employs in its factory, Telsmith uses the part probe to automatically correct tool offsets. After a semifinish cut is taken, the part probe is used to measure the workpiece. The dimensions are compared to what the completed part dimensions should be. Offsets are updated and the finish cut is taken. This produces a better quality, moreaccurate part. The alternative of manual measurement and manual input of the offsets is more time consuming and open to human error.
The VTC has a live spindle that makes it possible to mill, drill, and tap, in addition to performing turning operations. A C-axis, 360,000 position, full-contouring table is supplied with the live spindle, and is useful for operations such as precision bolt-hole patterns.
The VTC's right-angle head gives Telsmith the capability of doing live spindle operations on the sides of the part without refixturing. With the right angle head, Telsmith mills back-thread leads on external threaded parts, drills radial holes in cast parts from the inside, and taps the same holes from the outside.
Much of Telsmith's runoff code was either used in the Giddings & Lewis machine shop or comes from the experience of the G&L runoff and programming personnel. One feature that G&L uses and was able to share with Telsmith is the code to rotate bolt-hole patterns and threads. With the VTC in the transmit mode during milling operations, it is possible to rotate the work plane to align features such as bolt-hole patterns and threaded holes on the workpiece. Without this function, it would be difficult, if not impossible, to precisely fixture and align the features manually.
The VTC 2500 is able to adjust spindle speed while threading. This means that there is no loss of the thread lead, and the operator may tune the threading operation. Most machines will lock out any speed adjustment, making it difficult to pick up the same lead should the threading operation be stopped for any reason.
"We have capabilities with this machine that we didn't have before," Wier says. "We're able to do surface milling and profiling because of the spindle horsepower and speed. Our metal removal rates are up to 85 in.3 (1393 cm3) for milling and over 150 in.3 (2458 cm3) for turning." The G&L has full X-axis travel left and right of center, which allows cutting from both sides and probing diameters rather than radii. "We save on tooling by being able to cut with the reverse spindle, and it saves space in our tool magazine. I don't know why anyone would buy a vertical lathe that didn't have the ability to cut from both sides," Wier says.
With the new VTC 2500 running three shifts, six-days-a-week, work from three other machines was moved to the machine because of its efficiency. Since the VTC installation in October 2007, 16 additional parts have been added. "Our goal is to machine 100% in-house even as business continues to grow," says Dennis Van Asten, manufacturing manager.
In its initial cost justification for the machine, Telsmith looked for a payback of five years. They now expect the machine to pay for itself in less than two years. "A lot of credit goes to the programming efforts and the machine capabilities," Van Asten comments. "The live tooling for milling, and tool probing all play a big part. The macros keep it all working together." Equally important was the company support. "Management gave us the time and resources to accomplish the improvements, and our operators are working with us using new methods that they were not accustomed to initially. Efficiencies are improving as they become more experienced and confident," adds Van Asten.
Telsmith's arsenal of machines includes, among others, a machine purchased from another MAG company. The MAG Cincinnati FTV 1050 VMC features X, Y, Z travels of 2540 x 1005 x 800 mm and table capacity of 8000 kg. The FTV has supplied the capacity and ability to finish parts complete that has reduced a large backlog of outsourced parts. The goal was to have all parts in-house and on-time by August 2008. Dave Worzalla, a Telsmith CNC programmer, is writing the programs for the MAG Cincinnati machine with the same automation and cycle-time reduction objectives. "Our experience with G&L and their machine is definitely our benchmark," Wier concludes.
Time To Upgrade That VMC
Votaw Precision Technologies (Santa Fe Springs, CA) has been making critical parts for aerospace projects for 45 years. It has grown from a startup in the owner's garage to a 240,000 ft2 (22,297 m2) facility, employing 130 people.
Votaw Precision's current job list contains some of the most notable and important aerospace and defense projects, including the Mars Land Rover, the Aries 1 rocket, Raptor fighter planes, and various satellites, among others, according to Richard Roy, Votaw maintenance manager.
"We are a go-to source for these types of projects because our equipment can handle them," says Roy. A case in point was a five-axis VMC that the company bought several years ago. The previously owned, but almost-new VMC, was at Votaw less than a year when Votaw discovered that the company needed to tighten its tolerances to meet customers' needs. It was critical that its accuracies and tolerance be on spec.
"We ran this used machine on many projects, and time and time again saw that it wasn't as accurate as we expected, and just wasn't holding tolerances," says Roy. "We had to repeatedly do time-intensive adjustments. Important parts could not be done on this expensive machine."
When it was purchased, the measurement feedback system of the VMC consisted of rotary encoders on the ballscrews. "Sometime after we started using this VMC, it began to have problems holding tolerances, so we did some testing ourselves," says Roy. "We found the machine was experiencing cyclic error on one axis, a mechanical error we believed originated in the ballscrew and rotary encoders. That error was then being transferred to the accuracy, or should I say inaccuracy of one of our axes. That was unacceptable. Even our adjustments didn't meet expectations."
That was when the staff at Votaw knew it was time for some assistance. "We looked for outside help and received conflicting advice," explains Roy. One of Votaw's outside vendors said there was nothing they could do, and even advised the company against doing a linear-scale upgrade, because they didn't believe it would be effective. Roy adds, "And they sold linear scales themselves!" They couldn't have been more wrong.
"We ultimately went with the advice of A Tech Authority (Chino, CA). The company recommended installing linear scales from Heidenhain Corp. [Schaumburg, IL] on our VMC. That turned out to be the right decision." Adding linear scales to the VMC allowed key parts to be produced, with confidence, to the tolerances and specifications required.
The five-axis milling VMC is employed to serve a wide range of projects that require contour machining of flight components for aerospace, and precision-engineered parts for industrial customers. The machine features a moving table, X, Y, Z axis travels of 8 x 15 x 3' (2.4 x 4.8 x 0.9 m), and A and B tilting axes. It is currently working a schedule of 16–20 hr/day, 5½ days per week.
Luckily for Votaw, A Tech Authority, considered to be scale experts, was prepared to do the job. "Unfortunately, it is not uncommon for some machine-tool equipment distributors to fail to understand the full benefit of a linear upgrade," says Craig D'Ambrosio, owner of A Tech Authority.
Roy adds, "You know, I believe that the top machines in the industry all come with linear scales already on them. I also believe that, even if there are mechanical problems with the machine, it will be negated by good quality scales. Linear scales truly are the best way to achieve the best accuracy."
Votaw specifically requested the implementation of high-precision linear scales from Heidenhain to be used for replacing the measurement systems on the X, Y, Z axes. A Tech Authority obtained two Heidenhain LS 100 series linear scales (of varying lengths) and one LB 382 scale to do the job. Both of these sealed linear scales are accurate and characterized by high tolerance to vibration.
Once the plans were made and the components were delivered onsite, it took the A Tech Authority technicians only a couple of days to complete the job.
"You know, we have a customer here that purchased probably half-a-million-dollar machine entrusting us to drill 50 or 60 holes in it, and basically give the machine a new sense of balance. We realized that and worked hard to do the job as needed," explains Bill Ritter of A Tech Authority.
A Tech Authority's technicians mounted the scales and ran cables so that it looked like an OEM install, explains D'Ambrosio. "When the cables were plugged into the control, the new measurement system on the VMC was ready to go."
Votaw regularly does laser calibrations on its working machines and this was no exception. After the linear upgrade retrofit was completed, the laser calibrations showed success. "The cyclic error had disappeared," says Roy. "And overall, where the accuracy had been ±0.0005" [0.013 mm] on the three axes, it had now dropped down to ±0.0002" [0.005 mm]. That is an increase of 150% in accuracy," Roy says.
Votaw's upgraded VMC was put back into production and has been running its schedule ever since. "Our machine has been made extremely accurate since the retrofit," says Roy, adding that just over the last year, it has also produced parts for the 787 Dreamliner and the Joint Strike Fighter. "Even our operator who works on this particular machine, and who originally was not convinced that a linear upgrade would fix the problem, was pleased after the job and exclaimed "What a difference!"
Fixturing Leads To Efficient Machining
Dana Cox, the owner of Automated Manufacturing, a small but highly productive shop in Chatsworth, CA, draws on his past experience as an engineer at Haas Automation Inc. (Oxnard, CA) as he runs his business.
When the opportunity surfaced to bid against an army of larger shops for a big lock-parts contract, Cox knew exactly how to make his small operation competitive. The key to keeping costs down on this high-volume, three-op job was to design a set of special fixtures that would speed the work and guarantee accuracy by allowing his machines to do their jobs with as little operator intervention as possible.
"CNC, by its nature, is very accurate," asserts Cox. "With good fixturing, you only have to measure a couple of critical things. By using probes for that, you pretty much eliminate operator error, and if you keep a tight rein on the few things that are all-important, the machine will carry through on everything else."
In this case, "keeping a tight rein" meant fabricating a pair of precision, cast-iron fixture plates, each with capscrew hold downs able to clamp 168 stainless parts per load. Cox made one plate for the first operation, and an equally complex second plate for op two. Mounting space for the third operation was split between the two big fixtures.
"I organized the tightest possible arrangement," Cox explains. "There was a right-hand and a left-hand part, so I did them as pairs, and it worked out really well." The precision of the fixtures ensured the accuracy of the machining, and allowed Cox to routinely turn out 700 parts per day for nearly seven months. "I was able to do the work very costeffectively. That's why I won the bid." And for a person passionate about efficiency, he reveals, "That was really the perfect job."
Today, Cox makes and markets his own line of products, high-performance cylinder heads for motocross bikes. They are assemblies comprising a separate outer shell and a number of various-sized combustion-chamber domes that fit inside.
"Instead of having only one compression ratio to work with, riders can easily change their combustion chambers to match the engine's performance to the riding conditions," Cox explains. They can configure their bikes with high compression for competition, or with lower compression for general riding using less-expensive fuel.
Cox produces more than 40 different versions of these precision parts to accommodate the wide assortment of bike manufacturers, engine sizes, and compression ratios, with each dome mating perfectly to its matching shell. Because they are consumer products, these precision machined assemblies must be produced cost-effectively to be profitable.
Fixtures and probe systems play a major role, but in a slightly different way. Because a wider range of parts are being machined in smaller quantities, a lot of the efficiency comes from the product design. Cox designed each head assembly to exploit the capabilities of a specific machine: a Haas VF-3APC with an integral pallet changer.
Cox believes that it makes a lot of sense for a small shop to take this approach, which he calls crazy-efficient. "It has proven to be a very cost-effective product. That's one of the big advantages you get when the designer has a manufacturing background."
Mounting billets into simple vise fixtures atop the VF-3APC's pallets allows the shop to load and machine a lot of parts in a short period of time. Although the undemanding vises allow an operator to keep the machine producing at top capacity, they can't be relied on to ensure the consistent accuracy that a slower-loading, bolton fixture would guarantee—especially during the heavy cuts demanded by aggressive machining.
"When the dome is fitted inside the head, a critical differential in thickness must be maintained," says Cox. Post-inspecting each part and rejecting even a small number, however, would wipe out all the efficiency gained with the quick-loading pallet system.
The simple solution would be to reduce the feed rate to lessen the chance of parts shifting in the fixture. Cox's solution was to design the parts with enough extra material to allow an additional "re-dress" pass if the machine's automatic-probing system finds it is necessary.
"Probes measure the differential during the operation. If it's off, they call up two tools which remachine the surface to correct it. This not only compensates for shifting after mounting, it also eliminates any operator loading errors. We're pushing it hard for maximum efficiency, yet the VF-3 holds the height differential within 10µm," says Cox. "I don't worry about quality, because all the critical dimensions are measured and corrected by the machine."
Production never stops. "The beauty of the pallet-changer system," says Cox, "is that, with the probing and fast setup, you can run the machine with the spindle turning all day long. The operator loads parts up front, and the spindle never stops working. His only job is to make sure the machine is constantly running; it's much easier to monitor that way. When the spindle stops for a guy to change parts, you've lost a lot of time there."
Cox uses carefully conceived fixtures and probe routines on all his equipment. "I don't know how an operator can run a machine efficiently without them," he asserts. "And it's not crazy to design your parts efficiently by reducing critical measurements to an absolute minimum. You still have to pay attention to what you're doing, but with this approach, and a little forethought, you don't have to worry about a lot of other things. You can let the machine take care of that."
VTC System Takes Scooters for a Soft Ride
Piaggio & C S.p.A. (Pontedera, Italy), the largest manufacturer of two-wheelers in Europe, can trace its multifaceted business in manufacturing motor scooters and professional and commercial three and four-wheel vehicles to the design of the famous Vespa motor scooter in 1946.
To date, more than 16 million Vespa motor scooters have been sold worldwide, and that number may even be much higher, as the parent company doesn't know the exact figure due to many franchises that are held and copies that are made. The brands of high-performance motor scooters/cycles under the Piaggio corporate banner have also proliferated. They include Piaggio, Vespa, Derbi Aprilia, Gilera, and Moto Guzzi.
Emag Group (Salach, Germany) was selected to supply a complete system to Piaggio for machining motorcycle crankshafts used in the motor scooters. In its systems approach, Emag has set out on a somewhat unconventional path in the machining of motorcycle crankshafts by adopting vertical shaft-turning machines. It has been much more common to employ a horizontal concept in crankshaft machining.
In the case of the Piaggio project, Emag crankshaft specialists made its case for the VTC concept by pointing out that the system would be flexible and able to produce a number of crankshaft variants. It would have a small footprint, owing to its vertical design, and all dimensions would be within a tolerance of 1.67 Cmk or better.
Markus Woitsch, Emag chief of production, explains: "Emag has been successful with employment of vertical turning machines for chucked components since 1992. Now customers are asking more frequently for their shaft-type components also to be machined vertically. We can see clear advantages in this concept, and have been able to prove the manufacturing process on our VTC vertical shaft turning center, where we successfully applied it to crankshafts."
The requirement was for 80,000 crankshafts annually with flexibility and component quality topping the list of demands. The production line now turns out eight crankshaft variants in hardened and tempered, microalloyed ACF steel 38MnVs6, whereby all dimensions are subject to a tolerance of 1.67 Cmk.
To achieve this specification, the machining process has been split into different operations. The components are cut to length, centered, and premachined in OP 10 + OP 20 on a VTC 250 DUO ED. Apart from three turrets and the main spindle, this machine also features a separate clamping station. Once the first turret has gripped the raw part and conveyed it from loading to clamping station, both its ends are machined. For the machining of the front and rear ends of the shaft, the turret accommodates up to four live tools each (with power ratings of 38 kW and maximum speed of 3000 rpm).
When the end-machining process is complete, the second turret conveys the workpiece to the second station, where it is clamped in the main spindle chuck and steadied by the tailstock. As many as 11 tools in the second and third turrets then machine the workpiece in four axes. The main spindle, with its power rating of 38 kW, a torque of max 250 Nm, and maximum speeds to 5000 rpm, in conjunction with maximum direct-drive feed rates of 40 m/min, guarantee the dynamic machining of the component at short idle times.
"In fact, the turrets ensure that all the VTCs load themselves," says Woitsch. "The function makes every VTC shaft turning center a manufacturing system that can be adjusted to suit individual machining requirements. It requires no further automation."
Milling is also an operation carried out on the VTC. The side and face-milling cutter is suspended vertically in the machining area of a VTC 250 F. It machines, in OP 30, the web and the pin bearings. The machine also carries out diverse drilling and reaming operations. It's here where Emag has been most successful with their vertical concept. Although the milling operation is highly chip-intensive, the vertical arrangement of the VTC ensures unhindered chip flow and prevents the build-up of chip clusters.
The only operation for which a horizontal machining concept has been employed is OP 40. "The HSC 800 is a special-purpose machine for deep-hole boring operations. As the machining of the oil holes, the stroke-relief bores, and the bores on the face calls for large boring tools, we had to fall back on this type of machine," Woitsch explains. Centric and eccentric finish-machining in the last two operations, OP 50 and OP 60, is again carried out on VTC 250s. And at the end of the production line, the system provides ready-to-install crankshafts.
The whole system was planned, built, installed at customer's works, and commissioned by Emag as the system supplier. The customer has thus only a single contact point, making processing of the project that much easier. "For all changes and alignments, and to answer all questions, there is only one person the customer needs to contact. All changes and alterations to the project are centrally managed and followed up," concludes Woitsch.
Toy Molds Are Child's Play For CNC
Geobra Brandstätter GmbH & Co. (Nuremberg, Germany) first introduced its toy-molding system in 1974. Today, the company manufactures thousands of parts and adds about 600 new individual Playmobil characters every year.
Creativity is key from development right through to production. It's also a common practice that the designers turn a creative hand to their three and five-axis DMG VMCs for the moldmaking process. If it is still the norm to program either offline or directly on the machine, then the Playmobil example shows that a combination of both provides a lot of latitude for creating and implementing new ideas.
The speed and flexibility of this process are enhanced by the onboard Sinumerik 840D CNC controls and ShopMill, the shop floor-oriented numerical control programming software, both from Siemens (Elk Grove Village, IL). Faster and more flexible workflow on the shop floor results from options for programming on the machine or offline. The end result is that the work load for offline programmers is lightened.
Parts are sketched, modeled, constructed, prototyped, and finally produced in an injection mold. Construction of molded parts and the complete tooling takes place in the same way as the construction of the item itself, using Pro/Engineer design programs. When offline programming is performed, NC programs are implemented using Work NC from Sescoi (Southfield, MI) and Esprit from DP Technology (Camarillo, CA) translation programs.
Programming is also done directly on the DMG machining centers, which are typically equipped with Sinumerik 840D or Sinumerik 810D controls, depending on the axes and complexity of motion control required. The shop-floor-oriented ShopMill programming software is installed on the Sinumerik 810D. This enables a trained operator to program simple contour modifications onto the machine, which lightens the load for offline programmers, and allows machining specialists to employ their own expertise.
Sinumerik controls are also being used in the design development department (prototype workshop). In principle, the individual parts are completed using virtual methods on an in-house CAD/CAM design system. Between these stages, however, models and prototypes are produced in hard foam or plastic. For this process, the developers have a separate machining center, the three-axis DMU 35 center with the Sinumerik 810D CNC control and programs that are also created using ShopMill.
"We introduced this combination about seven years ago and, in hindsight, this was a very good decision," says Michael Friedrich of the Playmobil development department. He explains: "ShopMill is simple to grasp and integrates into daily workflow without any problems." Siemens offers two versions of ShopMill—one for programming directly into the machine tool control, and another for offline PC format. The latter enables NC programs to be created on the desktop and, thereby, reduces machine downtime. This gives the shop's work schedule manager a decided advantage in determining machine-tool utilization schemes.
ShopMill allows operators to access CNC technology, and can be operated without a high degree of programming skill and without in-depth CNC knowledge (G-code). The standard way that operators look at the work sequence (setup, programming, and milling) is reproduced, and is supported through the user-friendly representation of the tasks and graphical help images.
Friedrich says that this protocol works well in the shop. "The software is very intuitive, and it guides you through everything. In theory, you can't actually go wrong, because ShopMill only offers the options that are specifically useful for each command." According to the operators, correct programs are produced in a very short time. Input can happen without documentation through the use of help screens.
Despite its simplicity, there are a large number of standard cycles available for processing and measuring tasks. For moldmaking, there is a text editor specifically for large NC programs and simple programming of moldmaking functions with a high-speed setting cycle. The simulation possibilities of the programs with genuine tool data facilitate process security. Intuitive user guidance reduces machine setup time, as well. All these features have led to Siemens controls and ShopMill "being very well established in our shop today," Friedrich concludes.
This article was first published in the July 2008 edition of Manufacturing Engineering magazine.
Published Date : 7/1/2008