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Shop Solutions: Milling Tools More Than Tough Enough

           

       

Conventional wisdom holds that round inserts are good for rough milling because of their stronger geometry. But a tripling of edge life and a 3-to-1 reduction in cutter count on a tough, cast steel milling job at Harrison Steel Castings Co. (Attica, IN) proves there are always exceptions to every rule.An integrated foundry, Harrison achieved the productivity gain using tangential milling. In this technique, pioneered by Ingersoll Cutting Tools (Rockford, IL) in the 1960s, the inserts lie flat around the cutter's periphery. Re-orienting the inserts aligns the stronger insert axis with the main cutting-force vector. Ingersoll's latest iteration of tangential milling is the S-Max, which covers face milling, slab milling, and slotting applications.

 Harrison Steel was rough- and finish-milling two large mounting pads on a 1½-ton (1350-kg) bulldozer frame. Each pad measures 500 in.2 (0.3 m2) and requires milling of about 5/8" (16 mm) of material. As always with steel castings, the first pass is tough because of the inevitable surface oxides and inclusions.        

The company face-mills the frames in three roughing and two finishing passes on a Mazak Versatech V-60 vertical CNC mill. Rough and semifinish milling took place at speed of 400 sfm (122 m/min) and feed of 13.25 ipm (336 mm/min) at a 0.25" (6.4-mm) depth of cut. Finish milling parameters were speed of 480 sfm (146 m/min), feed of 24.2 ipm (615 mm/min), and 0.025" (0.64-mm) depth of cut. The roughing cutter was a 6" (152-mm), eight-insert face mill using button inserts. Total cycle time averaged one hour, split evenly between rough/semifinish and finish milling.

"This job was always high on our list of problematic jobs," says Process Control Coordinator J.D. Gray. "Whenever a tool salesman comes in looking for a trial with a new cutter, we put it on this job for two reasons. First, we wanted to fix the job; second, we'd get a quick assessment of the new cutter. The job has wrecked a lot of cutters."

In fact, the company averaged one wrecked cutter or blown pocket per week milling the frames. At $900 a pop, replacing cutters got expensive, not to mention the safety hazard from cutter shrapnel. And every time a cutter pocket was replaced, the toolsetter had to go through a sequence for the entire cutter, to bring all the round inserts into identical position with respect to datum.

In January, Harrison tried the S-Max MaxLine face mill, with tangential insert orientation, large rectangular inserts, and a 45º lead angle. Gray loaded it on the Mazak for the usual trial run, using the original machining parameters. The first roughing pass went fine despite the surface scale on the workpiece. So did the second, and then the semifinish and finish passes--all with the same edge.

Gray and colleagues Eric Dismore and Mike Bossaer decided to immediately adopt the new cutter for roughing cuts almost immediately. Since the changeover, Harrison has run scores of the parts. Edges during the roughing cuts have always lasted at least one full part, and some have lasted for three or four parts. There have been no damaged seat pockets or wrecked cutters. "We're still running the same cutter used in the test," Bossaer says. "The edges were good enough after roughing to be used again and the cutter needs no toolsetting after indexing."

More recently, Harrison decided to use the cutters for semifinish and finish cuts, adjusting feeds and speeds. This reduced cutter inventory requirements, and Gray says "the process is so secure that we don't have to stock nearly as many spares in case of tool wrecks."

"So far we haven't tinkered with machining parameters, but from the condition of the cutting edges after use, clearly we'll be able to ramp things up," Bossaer says.           

 

Lathes Fit Shop's Niche

                      

"We really don't produce anything. We just change it," explains Don Nicholson, owner of Advanced Secondaries Inc. (Cleveland). For the past 30 years, the company has carved out a niche turning standard screw-machine or cold-headed parts into specials.

Advanced Secondaries modifies parts using primarily drilling and tapping with automated drilling heads and turning operations. "Most of our business is for the cold-heading and fastener supply industry that use mild steels," says Nicholson. "Somebody sells a fastener or a box of fasteners, but needs something special done to them. Whether it's a hole in the shank, or the knurl on the allen capscrew turned off for a smooth finish, we'll do it."

Recently, a customer asked Advanced to make changes to 5000 bolts per week. Workers fixtured the workpiece and drilled it using an automated drill head. But excessive runout was an issue, and operators had to locate the part correctly for subsequent tapping and countersinking operations.

Looking to minimize potential quality problems, Nicholson purchased an OmniTurn GT-Jr. lathe made by Richlin Machinery Inc. (Farmingdale, NY). The gang-tooled lathe can handle up to eight tools. Precision linear guides and ground, zero-backlash ballscrews allow rapids and machining feed rates of 300 ipm (7.6 m/min). Other features include a composite frame casting, cast-iron headstock, 5-hp (3.7-kW) spindle, and PC-based control.

Cycle time on the lathe was a bit longer than the previous process, but parts come off the machine complete and require no secondary operations. "Improved quality more than justifies having a longer cycle time," Nicholson says.

According to Nicholson, the old process required a setup man standing by to deal with crashes or tool breaks. "And, after a crash or broken tool, the fixture or the drill head could move," he says. "Then everything's off center, and the parts are scrap until we can get the drill head or fixture set up properly. With the OmniTurn, if a drill breaks--and it will happen--you replace it, and as long as you know there were no major problems, you're right back producing parts again." The turning process holds runout of 0.001 - 0.003" (0.025 - 0.076 mm) TIR on the cold-headed parts, he adds.

The lathe worked so well for Advanced Secondaries that Nicholson eventually bought three others. Two of them are placed in a workcell tended by one operator, essentially doubling output with no increase in labor costs.Nicholson also says purchasing the additional machines helps his company stay competitive and take care of customers with large jobs or rush orders. "It was either buy the machines or have customers say, 'We can't send it to Advanced, because they take too long to produce it,'" he explains. "Now when these rush jobs hit my desk at a moment's notice, I have some flexibility to produce them without getting my customers upset."                  

 

Robots Speed 'Cycle Frame Welding'

                       

The all-aluminum frame and engine design of the new K 1200 S sport bike from BMW Motorcycle Works (Berlin) posed challenges to the company's traditional manufacturing process.

Composed of cast, extruded, and hydroformed parts of varying sizes and contours, the frame must be built to tight tolerances to accommodate the engine as a stressed component further down the production line-quite a challenge, given aluminum's tendency to distort during welding. Because the frame is also a design element, visible welds had to look good. And, of course, cycle time and financial metrics had to be met or exceeded.


 

Welding robots in action, and a worker removes a completed motorcycle frame from the robotic welding cell.
 

To achieve all these goals, BMW chose Cloos Schweisstechnik GmbH (Haiger, Germany) to design, build, validate, and install a compact manufacturing cell at its Spandau (Germany) Works. The cell houses two complete robotic welding systems in a 8 X 6 m footprint. Components include: two Cloos Romat 320 six-axis articulated-arm robots, two Cloos Rotrol II central processing units with 12 digital servo drives each, and two Cloos Quinto SD microprocessor-controlled welding power sources.

BMW engineers initially planned to use high-speed MIG welding for seams which would not be visible on the finished motorcycle, and TIG welding with cold wire for visible welds. But Cloos engineers were able to control the MIG welding process precisely enough to allow MIG welding even of exposed joints, cutting manufacturing time and eliminating tool changes. As a result, welding cycle time for a completed frame is 12 minutes.

A joint development effort between BMW and Cloos engineers spawned the two-stage joining process, which requires front and rear sections to be assembled separately and then welded together to complete a frame. The process starts when an operator loads frame components on a programmable dual-station positioner designed to precisely locate and clamp the components without tack welding. Eliminating tacking cut out a production step and minimized possible thermal distortion.

The fixture consists of an indexing table and two rotatable/tilting workpiece mountings inclined at 10º. The incline makes it easier for the operator to insert the frame components and facilitates workpiece positioning, allowing welding of most seams in gravity position, which is preferred for aluminum.

During welding, the fixture rotates the frame components in the gravity position while the power source optimizes arc width and depth. According to Cloos, the setup delivers good root formation even in square butt welds. The aluminum weld wire is held at constant temperature in a sealed chamber, while an argon-helium gas mixture is used for welding.

Each robot is independently controlled and programmed via a teach pendant. System memory can store and recall up to 20,000 parameters, and the multiprocessor system's short interpolation time is said to provide tight control of the robot's movement. Combined with an absolute position measuring system, the setup provides positioning repeatability of (less than symbol) 0.1 mm even at high speeds.

                    
           

 

Better Sawing Boosts Bottom Line

                       

ASKO (Homestead, PA) produces a wide range of specialty wear-resistant tooling and wear parts for steel mill rolling, slitting, side trimming, sawing, and shearing operations. The 75-year-old company's expertise in special tool materials, technology, and tooling application requirements has been developed by working directly with customers to understand what kind of products they need, and what product attributes work best for their applications.

ASKO buys steel in 12 - 14' (3.7 - 4.3-m) lengths, then cuts the materials according to job specifications. The company was having problems getting bulk steel sawed to the proper lengths quickly and efficiently enough to satisfy customer delivery demands and keep costs low.

"Our just-in-time inventory practices for raw materials necessitate the prompt application of material to production orders," explains Material Director Kurt Mihaly. "We have to cut several thousand parts per month to begin the manufacturing of our products."

Sawing was a production bottleneck using three older saw models, according to director of engineering Jim Kassan. "With the older models, sawing was a constraint," he says. "The saws were not fast or precise enough."       

When the company began looking for a solution to its sawing problems, cutting accuracy, repeatability, and throughput were the top priorities. "We put a lot of effort into the decision-making process," Kassan recalls. "Before making a final decision, we narrowed our selection to several different brands."

In December 2003, ASKO purchased two machines from Behringer Saws Inc. (Morgantown, PA) to replace its old trio of saws. The Behringer HBP-650/850A cuts solid materials up to 25.6" (650-mm) diam and rectangular shapes up to 33.4 X 25.6" (850 X 650 mm). The second machine, an HBP-530A, is constructed using heavy-duty guides and wheel bearings. Designed to cut solid materials up to 20.8" (530-mm) diam and rectangular shapes to 20.8 X 20.4" (530 X 520 mm), the machine is fully automated and requires no straps when bundle-cutting. Both saws have a cast-iron frame for long service life and good vibration dampening in the cut.

"We decided on two different models because the larger machine was not needed for all of our jobs," Kassan explains. "A portion of our cutting mix is up to 28" [710-mm] diam, but not all of it. The 530A could adequately handle cutting 16" [405-mm] or below, while the 650/850A could cut the remainder of the mix."

According to Kassan, the machines' twin-column construction was a driving force in the company's decision. "We wanted straight cuts at rapid surface speed, and the dual-column design really improved the machines' productivity, accuracy, and performance," he says. The machines' parallel down-feed design guarantees constant feed rates, and the horizontal band arrangement and hydraulically tensioned tungsten-carbide guides provide excellent blade support right up to the work material, he adds.

Faster cutting speeds have been a real benefit for ASKO, and Kassan says another advantage stems from the saws' ability to produce multiples while running untended. The machines are also providing greater precision, which enables sawing to near-finish sizes and reduces or eliminates rough machining downstream.

Sawing to near-finish size also results in material savings, which come in the form of more pieces per raw material length or less material removed by subsequent machining. Material savings are magnified by recent increases in steel prices.

Kassan sums up: "These saws have brought ASKO long-term savings," he says. "We've reduced costs overall. We've reduced our stock and improved automation. Our productivity increased by reducing material usage and scrap due to inaccurate cuts. Plus, we have the ability to move more jobs in the same amount of time."



This article was first published in the August 2005 edition of Manufacturing Engineering magazine. 


Published Date : 8/1/2005

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