Shop Solutions: VTC Cuts Crane Delivery Times
Delivery time is usually critical when a pedestal crane is needed for construction or repair of a dock, bridge, offshore oil rig, or other structures in coastal waters. However, batch-type manufacturing processes used to control costs tend to prolong lead times.
For example, engineers at Elevating Boats LLC (EBI; Braithwaite, LA) developed processes based on machining batches of 10 - 12 upper and lower crane pedestals. While reducing machine breakdown and setup costs, batch machining led to long lead times for delivery.
The parts were being machined on older vertical lathes with relatively few tools, which limited the number of tools available for a particular job. Different parts often required loading of new tools, and tool changes included manual loading of tool and fixture offsets, increasing the potential for error. Fewer tools also led to premature tool wear, lack of repeatability, and longer machining cycle times.
That all changed when the company purchased a VTC 60 vertical turning center (VTC) from Giddings & Lewis (Fond du Lac, WI). The machine quickly reduced breakdown, setup, and machining cycle times by up to 57%. With lower setup times, EBI has abandoned batch processing in favor of machining parts as needed or in kits, resulting in faster deliveries and reduced inventories.
"The VTC 60 gives us more flexibility in machining the pedestals for our C10, C20, and C30 cranes," says machine shop manager Ronald Ricouard. "We can machine an upper and lower pedestal and send it off to assembly or painting with minimal breakdown and setup time. We don't have to machine in lots of 10 before sending them to the next process. The VTC allows us to get cranes to our customers faster."
EBI uses the machine to process very large parts, such as a 40 X 38" (1 X 0.9-m) plate made of ASTM A 588 steel. The part requires facing, boring of an 11" (279-mm) diam hole, and drilling of a series of holes. Other parts include rings forged from 4130 alloy steel with hardness of 340 HB.
Shop-floor personnel use a 40-ton (36-t) capacity overhead crane to move the large parts into and out of the VTC's 60" (1.5-m) hydraulic chuck. Modified to accept an additional set of boring mill jaws, the standard three-jaw chuck/table allows EBI to make either three or four-jaw setups--the latter are often useful for rectangular or square parts.
The machine also features a 20-position tool disk, which reduces time spent loading and unloading tools. "On the other machines, we sometimes had to use the same tool for roughing and finishing," Ricouard recalls. "This meant running at lower feed rates to minimize tool wear and maintain smooth surface finishes. With the VTC 60, we can do roughing with one tool and use another tool for the semifinish and finish cuts. This reduces tool wear and saves time changing inserts."
Using an automatic probe to capture tool offsets and load them directly into the CNC is faster than manual data entry and reduces the opportunity for errors, he adds. "In some machines, you have to make a number of calculations," Ricouard says. "With the VTC 60, we put the tool in, it touches the probe, and the machine automatically calculates the tool tip position and location in the disk."
EBI uses the probe for process control and other applications as well. For example, it can be used to level the rail, making sure it is parallel to the table. If a part requires multiple holes, the probe can be used to find the existing holes' position and determine where remaining holes will be drilled. "The probe makes it very easy to locate holes in relation to existing holes," Ricouard says. "We can also determine where the part is located or measure the part for accuracy."
EBI uses its G&L VTC 60 vertical turning machine to process large plates, forgings, and other crane components. The machine includes a spindle probe for tool offsets and part location/inspection.
The machine's 40-hp (30-kW) live spindle enables milling, drilling, and tapping to reduce secondary operations and improve accuracy. According to Ricouard, a rectangular plate that is faced, bored, and drilled is machined complete using the live spindle. In the past, the part was faced and bored on a horizontal lathe, then transferred to a mill for perimeter milling and drilling of multiple holes.
An example of the VTC's accuracy and repeatability is a forged 4130 steel ring 10.5" (267 mm) thick which requires drilling of 64, 17/32" (13.5-mm) diam holes. "Through-spindle coolant gets the chips out of the way, and we drill the holes half way--to 5.3" [134 mm] deep," Ricouard explains. "Then we flip the ring over, position it in the fixture, and drill from the other side. The holes are matched perfectly, so we can insert a bolt and it goes all the way through. We did this at 2300 rpm and 18 ipm [455 mm/min]. Operators couldn't believe it."
The machine features a Z-axis ram extension that facilitates deep boring operations, and a programmable rail that accommodates parts of varying heights and minimizes ram extension. "We had our machine built with an extended height of 96" [2.4 m] under the rail to fit larger parts," Ricouard says. "We can use one program for the upper and lower pedestal of our C30 crane, and automatically program the rail to move up or down when we change from the lower to the upper part. The setup maintains accuracy, and we don't have to adjust offsets to machine the two parts accurately."
Sound Waves Measure Part Quality
For the past year, Capstan Atlantic (Wrentham, MA) has been using sound waves for nondestructive testing of its powder metal (P/M) automotive components.
The company uses resonant acoustic method (RAM) NDT for automated 100% inspection of a variety of automotive structural parts, including precision gears for powertrain applications. Customers include domestic US automakers and Japanese transplant facilities.
Capstan Atlantic's 100,000 ft2 (9300 m2) production facility employs 230 people and houses a complex process that begins with an iron-based P/M alloy. The powder blends are pressed to varying densities depending on application requirements, then newly formed gears are sintered in 65' (20-m) long continuous-belt furnaces at temperatures above 2000ºF (1100ºC). The process is robust, but customers still require 100% inspection of parts for structural integrity.
Before investing in RAM NDT technology supplied by The Modal Shop Inc. (Cincinnati), Capstan Atlantic used a nondestructive torque test. But the method was subject to operator interpretation, it was slow and expensive, and it didn't guarantee 100% conformance. "Our previous method tested around 40 - 50 parts an hour," recalls VP of Engineering Rich Slattery. "Now, the RAM NDT unit tests 600 - 700 parts per hour, and when I go home at the end of the day I know every single gear produced on our line has been thoroughly and completely tested.
"It's hard to put a price tag on that, but it's easy to figure the consequences involved in a field failure. That's every manufacturer's worst nightmare."
After an initial learning curve, Capstan Atlantic personnel found the RAM NDT system relatively easy to use. The technology works on a principle analogous to that of a bell or tuning fork. When you strike either instrument, it vibrates, emitting a sound. An instrument that rings true produces a consistent sound, and this consistency reveals the structural integrity of the instrument.
In RAM NDT, the test piece is struck by a small anvil and emits a natural frequency as part of its structural response. This unique and measurable signature is then compared to signatures from both good and bad product. If a gear is cracked, is not fully densified, or misses other characteristics of a structurally sound product, the flaw will be exposed when its signature deviates from that of a good product.
The unit tests the part for external and internal flaws and provides an objective, quantitative analysis that eliminates operator errors. A dynamic sensor captures sound, and a high-speed analog/digital converter translates the sound into measurable data which is then compared to predefined data. In effect, RAM NDT listens to the structural response of a part and evaluates it against the statistical variation from a control set of good parts in order to screen defects.
"We've incorporated RAM NDT technology right on our assembly line," says Slattery. "components pass through it right before packaging. Any product that doesn't pass inspection is removed from the line automatically. And gears that pass inspection are immediately packaged and shipped."
According to Slattery, the system saves the company $0.33 on each gear produced over the previous method. Because Capstan Atlantic ships approximately 5000 gears a day, that amounts to savings of $1660 per day. And, by eliminating the need for a specially trained operator, it also reduces personnel costs.
Finally, the captured data provided feedback that contributed to other quality improvements. "The unit has enabled us to recognize things about our process and make improvements upstream that have increased our product yield by reducing process variation," Slattery concludes.
End Mills Slash Machining Time
Despite some initial skepticism, Steve Seebold, owner of Seebold Engineering (Santa Ana, CA), decided to follow the manufacturer's recommended feeds and speeds for a new end mill he was trying. The result: machining time slashed by more than 50%, and a six-fold increase in tool life.
Launched in 1986, Seebold Engineering machines military parts for helicopters, and out-drive components for large radio controlled (RC) boats that can move over the water at speeds to 120 mph (190 kph). Most of the boat parts are 6061 and 7075 aluminum alloy, while military parts may be machined from stainless steel, Inconel, titanium, or aluminum alloys. Lot sizes generally run from one to 50 parts.
Always looking for ways to increase productivity and decrease tooling costs, Seebold sent away for a sample of a WhisperKut end mill from Dura-Mill Inc. (Malta, NY). He stored it away until he got in a job he knew posed special machining challenges.
Seebold had machined the component, a 17-4 PH stainless window frame for a military vehicle, before. He knew that coated solid-carbide end mills were good for about 1.5 parts before they needed replacement, and the job took 14 hr to rough and finish.
He called Dura-Mill to get some information on how to run the end mill for this application. "I talked to them, and I felt the feed and speeds they recommended were way too fast," Seebold recalls. "But I figured, 'Hey, it's your end mill.' So I ran it the way they told me."
Machining time on the 21.5 X 12.5 X 7/8" (545 X 318 X 22-mm) component dropped from 14 to 6 hr. "I ran the 1/2" [12.7-mm], three-flute end mill at 1600 rpm at 6 ipm [150 mm/min], 0.350" [8.9-mm] depth of cut, full cutter width, and I roughed and finished with the same tool," says Seebold.
The tool not only cut his machining time, but it machined four parts with minimal wear. "I would burn up my old cutter at 1100 rpm with the same feed and depth of cut," Seebold says. "I'd get about a part and a half at this spindle speed. The WhisperKut ran four pieces inside and out, along with doing the roughing and finishing. I've never done that before with any end mill." After Seebold purchased more of the tools, he discovered they worked well on all his work materials.
5-Axis Programming Made Simple(r)
Aerospace Dynamics International Inc. (ADI; Valencia, CA) is a $60 million prime contractor supporting aeronautics and aerospace OEMs. The company manufactures large components such as aircraft wing spars, bulkheads, and panels.
Due to their large size and critical applications, these parts can be difficult to machine. "Our parts are very large, and we must hold extremely close tolerances," explains NC programmer Brian Carlson. "Yet our customers are raising the bar higher and higher in terms of how soon they expect delivery."
In the past, ADI programmers used either an Automatically Programmed Tool (APT)-like NC programming language to code toolpath motion by hand, or an earlier-generation graphical CAM program. There were drawbacks to both methods.
Hand coding could achieve very precise toolpath motion even on high-speed, five-axis machines, but it was time-consuming. And, it was difficult for programmers to work on each other's projects. "They had to be dragged kicking and screaming to another's job," Carlson recalls. "Coding style differences had become a big problem."
The other method, using graphical CAM software, sped program creation somewhat but was still labor-intensive when used to create toolpaths for high-speed machines. It was also difficult to revise programs once they were generated.
Installation of seven seats of NX Machining CAM software from UGS (Plano, TX) gave ADI the combination of fast programming and complete motion control needed to meet tight delivery schedules. For jobs that require high-speed, five-axis machining, the software has become ADI's programming method of choice.
"The sequential mill function in NX Machining allows us to program any feed rate change, any stepover, looping passes, whatever we need," Carlson says. "NX Machining also makes it easy to modify existing programs. If a machining technique programmed in other CAM systems doesn't work, it can be a real bear to modify the code."
The ability to create complex toolpaths accurately saves ADI a great deal of time. An example is programming for ribs of a commercial airplane. Originally done with the APT-like language, the initial program took 400 hr to write. Subsequent programs in a series required about 260 hr of work.
When the company won a contract for similar ribs, Carlson decided to do programming in NX Machining. "The first program took 260 hr, the second took 190, and the third took 152," he says. "On the first program with NX Machining, we equaled the best we could do with all our experience in hand programming. On the last, we took more than 100 hours off the best time we had ever accomplished by hand."
Other programs for space shuttle fuel panels used to take 10 days per panel with hand coding. With NX Machining, one panel (the last in a series of six) was recently programmed in three days. "That was very fast, but all six were perfect to plan," Carlson says. "The motion was every bit as good as hand-written code."
Magnetic Chuck Boosts Blade Production
Like many contract manufacturers, Stonebridge Corp. (Worcester, MA) produces machined and welded parts in a wide variety of configurations and workpiece materials. Since acquiring Stonebridge in 1998, president and CEO Kerstin E. Forrester has modernized operations and adopted lean manufacturing techniques to increase productivity and improve the company's competitive position.
Since early 2002, Stonebridge has been working with a customer, HotBlades, to develop and manufacture a new, lightweight ice-hockey skate blade that is marketed throughout North America. Using 400-series magnetic stainless steel, a material that's considered tough to hold and machine with accuracy, Stonebridge produces the precision blades in various sizes. The blades are then sent to the customer for a proprietary composite overlay process that is said to result in blades that are 40% lighter and provide better acceleration and maneuverability than conventional skate blades.
Using a 5/16" (8-mm) end mill on a YCI Supermax-1 vertical machining center, operators mill ten skate blade "pockets" one side at a time from a 14 X 16" (355 X 405-mm) stainless sheet 0.125 - 0.134" (3.2 - 3.4 mm) thick. The sheet is then turned over to repeat the process on the reverse side.
Process engineer Tom Fannon says the machine setup involved manually clamping the stainless sheet to an aluminum plate and affixing multiple screws to firmly hold the sheet in position throughout the machining cycle. It was a time-consuming and tedious operation required for each new sheet and side, and accuracy was always a concern based on how tight and well the clamps and screws were applied. Operators produced about ten blades an hour, and 40 minutes of that time were needed to change over and position the setup on the next pallet.
Looking for alternative workholding solutions to trim setup costs and improve workflow, Fannon and his manufacturing team chose magnetic workholding. In February 2004, Stonebridge took delivery of a 16 X 32" (405 X 810-mm) TurboMill magnetic milling chuck supplied by the O.S. Walker Co. (Worcester). The chuck was installed with an integrated controller to facilitate rapid positioning, holding, and release of workpieces appropriate to the milling machine's CNC program.
Since installing the magnetic chuck, Stonebridge has realized a four-fold reduction in setup time, according to Fannon. Operators now manage multiple machines rather than just one.
The chuck's rigidity and vibration damping capability also more than doubled tool life. Before installing the magnetic milling chuck, Stonebridge could produce 20 to 25 complete skate blades before a tool change was required. After installation, part production increased to 50 to 60 complete blades per end mill.
This article was first published in the March 2005 edition of Manufacturing Engineering magazine.