Shop Solutions: Cutter Wins Over Shop's Ferrous Machining
When setting out to reduce machining costs, contract manufacturers might consider tackling the highest-volume jobs first with a new milling cutter. The results may be surprising and affect the entire enterprise.
That strategy paid off for General Manufacturing Inc. (GMI; Elk Grove Village, IL), which had retooled a 20,000-piece-per-year milling job on cast-iron pump parts. Running 20/6 in a new 65,000 ft2 (6039-m2) facility, the company specializes in largescale work for transportation and oil-patch equipment.
Using a new milling tool, the Evo-Tec milling cutter from Ingersoll Cutting Tools (Rockford, IL), generated savings at a rate of more than a quarter of a million dollars a year for GMI. Based on that initial success, the company standardized on the same milling cutter for dozens of other jobs.
The GMI retooling represents one of the first US applications for the Evo-Tec milling cutter and one of the most challenging. It involves a family of cast-iron volutes for centrifugal pumps that require five-axis contouring, square-shoulder milling, plus holemaking and counterboring by ID interpolation.
Because of the volume, manufacturing engineer John Temple strove to complete all these operations with a single tool in order to minimize dead machine time for tool changes. GMI got to the new level of output for the volutes in two main steps.
"Initially we ran with the ceramic tool for good edge life in a five-axis cast-iron job," explains Temple. "We wanted to complete it with a single tool and a single chucking, and minimize stoppages for tool changes or indexing. Ceramics are supposedly the insert of choice for this application."
Starting with a four-flute square-shoulder cutter with triangular ceramic inserts running on a Kia 630 full four-axis HMC, the best result GMI could get was 2.5 pieces/hr without excessive edge failure. Next, a five-flute cutter with carbide inserts achieved slightly better output but with "horrible edge life," according to machinist Mike Weber.
GMI settled on a 1.25" (6.35-mm) four-flute, zero rake, square-shoulder mill with triangular ceramic inserts in a radial orientation. Running it at 40 ipm (1 m/min) 0.150" DOC (38 mm) and 1400 fpm (427 m/min) yielded a finished part every 24 min, with a cutting edge lasting a 10-hr shift. "We were satisfied with the throughput rate but concerned with the high insert cost, since ceramic inserts are so expensive," he explains.
Next GMI tested a five-flute cutter of the same size and conventional radial insert orientation, but with coated-carbide inserts and positive rake. This didn't work at all. In fact it slowed the operation down. The best they could do was 40 ipm (1 m/min) and 0.150" (38 mm) DOC, with surface speed reduced to 850 fpm (259 m/min) to avoid overheating. Each piece took about 40 min, and wore out the edges much more frequently despite the lower speed.
Temple was considering going back to the ceramics when he asked Ingersoll's Jeff Clear for ideas during one of their regular walk-throughs. Clear suggested trying the then-new Evo-Tec cutter of the same diameter, and brought one in for a test. Temple was dubious about carbide on cast iron, especially after his latest experience, but figured he had nothing to lose. The Evo-Tec mill has a completely different geometry from anything GMI had tried before. It would be a drop-in replacement with no change required in the basic process or fixturing. Just slip it into the magazine, ramp up the settings, and let it rip.
"It was a drop-in replacement," Clear says. "We wouldn't even have to change any datum settings, just the feeds, speeds, and depths of cut."
The selected Evo-Tec cutter had only three flutes, leaving plenty of room to clear chips generated at higher feed rates. Inserts were square, yielding four edges each and, of course, oriented tangentially. Temple and Clear dropped the Evo-Tec into its slot in the tool changer magazine, then spent about two hours juggling with settings. Finally they settled on 80 ipm (2 m/min), 0.150" DOC (38 mm), and 1100 fpm (335 m/min). This nearly doubled throughput, to 4.5pc pieces/hr, with no sign of edge failure.
Edge life improved by four to one. "At that rate, we had a potential $250,000 annualized saving in machining time on that 20,000 pieces/yr job," says Temple.
As a result of that success last October, GMI quickly standardized on the Evo-Tec for all face and square-shoulder milling on ferrous metals in their shop. "So far on these other jobs, enterprise-wide we'll easily double the savings on the volute job," Temple projects, "and we're not done yet."
The Evo-Tec tool combines five tooling innovations into a single tool.
- In tangential milling, the insert is oriented tangentially, rather than radially, which presents the insert's strongest cross section to the main cutting force vector. It also makes possible a stronger cutter body since seat pockets are shallower, leaving more metal to absorb the cutting forces.
"Tangential cutters by themselves are not new, but when combined with other innovations in this cutter, they can move milling efficiency a huge step ahead," says Ingersoll's Clear. "They not only handle higher cutting forces and a wider range of work, including limited ramping and contouring, but reduce cutting forces as well."
- The helical cutting edge (slightly curved, not straight-sided) reduces cutting forces two ways. Rather than slamming into the work like a chisel, the helical shape eases the insert's cutting edge into the work, like scissors cutting paper. Moreover the helical curve enables a more positive presentation angle than has been possible in tangential cutters.
- The edge is supported by a hefty heel, which is the extended radius that trails and supports the cutting edge. This makes it possible to achieve higher positive rake without weakening the cutting edge.
- The seat design improves cutting geometry in two ways: 1) Flat lands, rather than points, increase the contact area; 2) The seat-pocket angle directs cutting forces in order to drive the insert into the pocket and hold it in place, not pull it out. At the same time, it increases the positive rake to promote more of a cleaving rather than scraping.
- Finally, advanced coatings protect the insert substrate from overheating, a principal cause of insert failure.
"The long and short of it is, the coating handles the heat and the geometry handles the pressure," explains Clear.
Probing Shapes NASCAR Cup Chase
When the owner of your race team is a three-time winner of the NASCAR championship series, as well as a three-time Super Bowl winning coach, you might expect that no stone would be left unturned in achieving excellence in performance, either on the track or in the machine shop.
For Joe Gibbs Racing (JGR; Huntersville, NC), teamwork is the key to success in the NASCAR Sprint Cup and Nationwide racing seasons. Its teams depend on the highest performing chassis and engine parts in their race cars. JGR's leading drivers include Denny Hamlin in the #11 Fedex Toyota Camry, Kyle Busch in the #18 M&M's Toyota Camry, and Joey Logano in the #20 Home Depot Toyota Camry.
JGR operates a 10,000 ft2 (929 m2) machine shop and quality control department equipped with the latest machine tools. Equipment includes 14 Doosan CNC mills and four CNC lathes, a Mitsubishi lasercutting machine, a Mitsubishi waterjet, two Mitsubishi wire EDMs, and one Mitsubishi sinker EDM. There are 21 machine operators, three NC programmers, two manufacturing engineers, and a six-person quality control department.
Installing advanced probing and noncontact laser systems from Blum LMT (Erlanger, KY) for tool setting and workpiece measurement has enabled JGR to reduce downtime, increase green light machining time, reduce scrap rates, and improve the manufacturing quality of its high-performance chassis and engine racing parts.
"We run a typical job-shop manufacturing operation," explains Kelly Collins, shop manager. "We set up and run between 60 and 65 jobs a week, some short run, others longer depending on the volume of parts needed. These parts range from internal and external engine components all the way to driveline and suspension parts."
One difference, of course, is that the engine and chassis parts and components that the JGR shop produces must meet the stringent requirements of NASCAR before they are even allowed on the track for a race on the next weekend during the Sprint Cup and Nationwide race seasons.
"Like most manufacturing companies, we have a master production schedule and build schedule, so there is a need for foresight in our planning and capacity in our shop, especially on the engine side," Collins says. "We know well in advance what we need to make and when we need to make it, how many engines we'll need, and when we will need them," says Collins. JGR also has to make unexpected short runs of some parts, sometimes just days before a race.
When JGR looked for a better way to maximize the performance of its machining operations, it asked several suppliers how they managed their tool setting and quality-control issues. Their suppliers recommended the non-contact laser-control systems and contact probes from Blum LMT for tool setting, breakage detection, and workpiece measurement.
"At JGR we have a continuous drive to get improved parts to the race track that will give us a competitive advantage over the other NASCAR teams. Our old-school technology for setting tools and locating the workpiece inside the machine involved using 1-2-3 blocks and edge finders to accomplish the tasks. After machining, using hand tools, operators unclamped parts and took them to the quality department to verify features on our Zeiss and Starrett CMMs," Collins explains.
"Under the old way of doing things, we experienced a lot of downtime removing parts from fixtures for inspection and refixturing, and then manually entering tool and work offsets for remachining. Also, we were generating an unacceptable amount of scrap resulting from blend-line issues caused by imprecise tool heights, and wasting time on the shop floor by manually entering tool and work offsets into the machine controls," says Collins.
Searching for hidden machining capacity, JGR began its research into available probing and tool setting sources. Their objective was to get more out of their machines, reduce scrap rate, increase green-light machining time, and improve quality procedures. "Our investigation confirmed the suppliers' recommendation. Blum's devices were easy to use, accurate, and supported by good service," says Collins. "We brought in a probe and a tool setter so that the operators could see what the tools could do for them." There was some initial reluctance on the part of machinists to use the new technology, but after working with the Blum equipment, they now try to figure out new and creative ways to use it.
Operator Steve Larocque was one of the first operators to use the Blum equipment on a trial basis. "I run a Doosan VMC with a fourth/fifthaxis rotary table, a Blum TC50 probe, and a Laser Control NT. We load programs that tell what to measure and the Blum software automatically puts in correct offsets, eliminating potential errors while manually inputting data. The TC50 probe has also helped on certain jobs where we had to stop the program to edge-find," says Larocque. "The probe checks them and automatically adjusts offsets. We also use fixed probe programs, which are inserted into our part programs so that they run automatically. We can run part after part, and the probe will come out on its own and readjust our offsets."
Setting tools with either the Z-Nano contact probe or the laser eliminated problems caused by inaccurately produced blend lines in longer runs of parts with multiple tools. Setting tools by hand with the 1-2-3 block depends on operator feel, and there can be differences from operator to operator. "Now that all of the tools are set with a laser or the Z-Nano, everything is going to have the correct height offset," says Larocque.
JGR has seen a reduction in setup times in terms of locating stock in the machine by using the probes to more accurately locate the parts and set zeros in the control. "We estimate we have reduced setup time by 30% by using Blum technology, and reduced our level of non-value-added quality control tasks by approximately 20%, because we can now do a portion of our QC effort in the CNC mills," says Collins.
"Not only can our programmers put instructions in our programs to use Blum tools, but our machinists can also program the probes or tool setters at the machine by themselves. Blum also provided custom programming for several of our parts, and training was not an issue. Whenever we needed support, whether over the phone or in person, Blum was quick to respond," says Collins.
"The probing accuracy of Blum was within 0.00015" [0.0038 mm] of our Zeiss CMM. This level of accuracy enables us to perform in-themachine quality control checks," Collins says. The Z-Nano, for example, has half-micron repeatability, and is used by JGR in both the hard-wired and wireless versions. The laser has a shutter system that protects the optics and creates a higher quality focused beam. The result is better tool-to-tool accuracy, while an integrated tool air blast ensures reliable and repeatable measurements eliminating blend lines.
"We don't have blend issues on the first piece anymore, and with no need for manual entry of offsets, we get more green-light time and have fewer opportunities for typos being entered," says Collins.
"We have the ability to check for broken tools with the Z-Nano or laser. In the past, a broken tool would cascade into scrapped parts because we would normally not discover the problem until parts were destroyed. Many times, multiple tools would break before we realized there was a problem. Blum's tool-breakage detection stops the machine automatically when a broken tool is detected. We no longer have to re-run multiple tools in order to solve a broken-tool problem, and our scrap rate has decreased by 90% on issues caused by broken tools. Tool-breakage detection also gives us the ability to run unattended and lights out, which means free capacity," Collins says.
The impact on operator morale has been positive. Their confidence level in the quality and accuracy of parts they produce has never been higher. "It snowballed from the first successful installation of the Blum probes and lasers, and nearly all of our machines now have the devices installed," says Collins.
CNC Switch Forges Time Saving
With automakers using more aluminum forgings for suspension systems to reduce weight and increase gas mileage, Kobe Aluminum Automotive Products LLC (KAAP; Bowling Green, KY) invested $80 million in its plant to produce forged aluminum automotive suspension components.
The company's primary customers are Nissan, GM, and Honda. To meet this demand, KAAP employs 180 people in its 108,000 ft2 (10,033-m2) Bowling Green plant. The company is a joint venture owned 60% by Kobe Steel, 25% by Mitsui, and 15% by Toyota Tsusho. In 2008, it installed its fourth forging press, increasing capacity to 280,000 pieces per month.
KAAP's greatest CNC programming challenges are closed forging dies. These dies are used to produce parts with geometry ranging from simple to complex shapes such as an 18" (457-mm) long link that is shaped somewhat like a baseball bat, tapering down over its length to meet a larger- diameter end. The end itself has a number of different radii that blend into each other.
The company normally roughs out the part on a Mazak FJV-3580 VMC and performs finishing operations on a Mazak Nexus VMC with a 25,000-rpm spindle. KAAP has a company policy of running all machining operations dry. This reduces the environmental impact of machining operations, and also helps avoid the potential for allergic reactions among employees.
Running dry makes machining operations more difficult, however. The CNC software that the company originally used was hard to learn and produced programs that took too long to run. "We were able to program these parts with the CNC software that we used in the past, although it was not very intuitive," explains Victor Steele, tooling shop manager for KAAP. "Roughing operations were relatively slow, because the tools spent much of their time cutting air," says Steele.
The most efficient way to rough out a forging die is to start with a large tool and use it to cut as much of the cavity as possible. Then you switch to the next size smaller tool, and again cut as much of the cavity as possible. The problem with KAAP's previous software was that each successive cutter traced the complete path of the part profile even if there was nothing for it to cut, either because the section had already been finished or because the cutter was too large.
"Switching to PowerMILL CNC software helped us reduce machining cycle times by 40%, primarily because its Offset Area Clear strategy's rest-machining capabilities greatly reduce air-cutting time," says Steele. "Its Optimized and Interleaved Constant Z finishing strategy has improved surface finish to the point that manual finishing has been reduced by 50%. PowerMILL is also easier to learn. New programmers can be trained in less than an hour."
Kobe Steel's Japanese operations had successfully programmed this type of part with PowerMILL and recommended that the KAAP try the CNC programming software. "One of Kobe Steel's programmers from Japan visited us and showed us how to use PowerMILL," says KAAP engineer David Taylor. "Despite his limited English, he was able to teach us to use the program without a great deal of difficulty. We liked the way the user interface is laid out." Later, KAAP programmers had two days of onsite instruction from a PowerMILL trainer. "As we got to know the software, we were impressed with the large number of machining strategies that it offers to help optimize cycle time and accuracy of machining operations," Taylor says.
KAAP's typical programming methods proceed as follows. The die geometry is normally defined in Siemens PLM NX CAD software. The geometry is imported as an IGES file into PowerMILL. The cavity geometry typically consists of a 3-D contoured surface, so it's defined as a single toolpath. The programmer clips the boundaries of the geometry to define the surfaces that need to be machined.
"We typically use the Offset Area Clear function for removing large volumes of metal in cavities," Taylor explains: "With this strategy, you select a tool and give it a stepover and stepdown value. You can also reference a toolpath or generatedstock model of the volume left from the previous tool. PowerMILL compares the material that is left on the workpiece with the geometry of the tool, and determines the areas of the part that the next tool is capable of cutting. The software then produces a toolpath that rapid traverses directly to the areas that can be cut by the tool, while skipping areas where there is nothing to do."
To program the link, KAAP programmers normally begin with a 125-mm shell mill cutter, then drop to an 80-mm shell mill cutter, then use 30, 20, 16, and 6-mm ballnose cutters respectively. The shell mills and 30-mm ballnose cutters use indexable inserts, while the smaller cutters are solid carbide. "PowerMILL's rest-machining capabilities save us a considerable amount of time, reducing cycle time by 40–45%," Taylor says. "It takes about 24 hr to machine a complete die, or about 2 hr to make a repair."
PowerMILL's advanced simulation capabilities provide fully integrated simulation and collision detection to ensure the CNC program is both safe and efficient, giving the operator extra confidence by predicting axis reversals and surface quality. The simulation process provides an opportunity to take a close look at the program that has been created up to that point. It often identifies problems such as crashes or opportunities for improvement. Then the programmer can easily change or reorder operations in order to prevent crashes or reduce cycle time.
"PowerMILL has helped us improve the efficiency of our machine shop operations." Steele concludes, "We've been able to reduce the time required to machine parts and also reduced hand-finishing time. The new software is also much easier to use, saving time in training new programmers."
Modular System Drills Pins
When you're a one-man operation, there's no passing the blame for poor performance. Tools and machines must perform according to expectations if customers are to be kept satisfied and your business is to grow.
Alben Engineering (Brisbane, Australia) is not only John Roberts' means of supporting his family, but it's named after them. Alben is a combination of his children's names Alexandra, Lara, and Ben.
Roberts started his company about two years ago with a machining center and two CNC lathes. He produces a mix of parts for various industries, such as flight boxes for aerospace customers, gearshift levers for automotive manufacturers, and complex parts for medical suppliers.
Earlier this year, drilling an induction-hardened pin made from high-alloy 4140 steel had been giving Roberts problems. To achieve a through-hole in a 300- mm pin on Roberts' equipment required drilling a 150-mm hole from each end. The rigidity and rpm capabilities of his CNC lathe were sufficient; the problem was that his indexable drill kept breaking off in the hole.
"It got to where this required constant supervision on my part," Roberts recalls. "You couldn't walk away from the job. If the drill breaks, you've got a big mess on your hands." Not to mention that at more than $100 (AUD) per drill, production costs escalate quickly.
When Roberts' tooling supplier suggested drilling pilot holes, adding time and operations to the job, Andrew Guy of Kennametal Australia in Queensland, suggested a test with the Kennametal KSEM modular drill system.
The modular KSEM system features steel drill bodies with a stable, four-wall pocket at the tip, where a Kennametal carbide insert specific to the job at hand provides the cutting edge. Hole depths of up to 10xD up to 40-mm drilling diam are standard.
The grade Andrew selected for the test was KC7315, a PVD-TiAIN-coated universal fine-grain grade with high wear-resistance at higher cutting speeds. "It's the first choice for alloyed and high-alloy steels, as well as cast iron," Guy says.
The test was performed at Alben Engineering on Alben equipment. It entailed running Roberts' original setup as a baseline, then with the KSEM system for comparison. With the cutting speed set at 70 m/min, spindle speed at 891 rpm, and feed speed of 267.3 mm/min, Roberts achieved one hole per edge, breaking two drills to produce one pin.
With the KSEM system and KC7315 insert grade, not only was Roberts able to drill a batch of 25 parts (50 holes) with only minimal wear on the cutting corners, he was able to increase his cutting speed to 95 m/min and feed speed to 363 mm/min. "We could have run the feed at an even greater speed, but we were getting pushback on the job due to the smooth surface," Andrew reports.
Where Roberts would have required 400 inserts per year under his old setup, eight Kennametal inserts would produce the same amount of parts at higher speeds. More importantly, Roberts' productivity is up, and the reliability of the new tooling allows Roberts to "get in and get the job done," in his words. At the end of the day, he says, "it solves the problem and solves it well."
This article was first published in the September 2009 edition of Manufacturing Engineering magazine.
Published Date : 9/1/2009