Need for Speed
Down in the Tiers, there's a serious need for speed
By Jim Destefani
It's a fact of life for Tier automotive suppliers: aggressive bids are a must to win new business, and continuing cost reductions will be required to maintain whatever margins you can squeeze out. This hyper-competitive environment puts a premium on tooling up to produce parts as efficiently as possible, and on retooling to meet automakers' ongoing demands for lower costs.
Complicating things is a wider variety of work materials than in the past. Work materials in automotive machining today range from the old standbys--cast irons and steels--to magnesium and aluminum alloys, high-strength/low-alloy steels, and all types of composites.
The complex and competitive nature of the automotive supply chain places a premium on application of the latest cutting tool technology. The following short application stories illustrate how some Tier suppliers are partnering with cutting-tool suppliers to gain an edge in this cut-throat business.
For a Tier supplier, survival can depend on developing a solid market niche. American Production Machining LLC (APM; Fraser, MI) found its place as the equivalent of dialing "9-1-1" for powertrain and chassis components. As much as 75% of the company's output is emergency work to cover customers' down equipment.
According to fixture/tooling manager Dennis Deaver, APM accomplishes new part setups, including programming, in 24 hours. Repeat jobs often take less than 6 hours. "A lot of our customers operate older production equipment that simply doesn't have the capacity of our newer machines," explains Deaver. "We can often take a lot of time out of the cycle using our own programs and tooling."
An example is a steel transmission turbine shaft that APM machines in a single chucking using two-turret, four-axis CNC lathes. The job runs using TP1000 coated carbide inserts from Seco-Carboloy (Warren, MI) for all turning operations. Designed for finishing and light roughing applications, the grade is said to combine good wear resistance and edge toughness that make it well suited for mass and large-batch production, including untended or dry machining applications.
The inserts enabled APM to increase speed and feed by 20% over the previous operation, to 1300 fpm (400 m/min) and 0.012 ipr (0.3 mm/rev), respectively. Alleviating a chip-control problem with the previous inserts also helped facilitate a 30% cycle time reduction from the previous process.
In another application, APM machines cast steel front output flange components in two stages, before and after heat treatment. Operations on the raw part--rough face and turn diameter, center drill, and machine front face and ID angle--are done in two chuckings on a CNC lathe. The parts have interruptions on both sides.
APM got the results it was looking for using Seco-Carboloy's TP2000 grade running dry over the interruptions at speed of 900 fpm (275 m/min) and feed of 0.011 ipr (0.28 mm/rev). The grade is designed to withstand very high temperatures, and can handle cutting of most steels and cast irons. On the steel front output flanges at APM, TP2000 provided a 50% increase in tool life compared with the previous coated grade.
Deaver believes using the latest insert grades often requires machines with sufficient horsepower to run them efficiently. "The newer machines we have in our plant allow us to make the most efficient use of the new, highly engineered, coated carbide cutting grades," he says. "In some applications, we're peaking the machine's horsepower rating, but only for a short duration. So, we're really getting the maximum utilization of our machines' capability, and that's good for APM's business."
Turnkey installations of machining technology are very popular among Tier auto suppliers, who are able to leave much of the process engineering to the selected suppliers of machine and cutting tool technology.
Cycle times are critical, and turnkey projects often involve automated material handling, gaging, and other operations. Keeping costs in line--and addressing customers' ergonomic, lean manufacturing, and other management concerns-places a premium on experience.
Gerotech Inc. (Flat Rock, MI) has experience in all aspects of automotive turnkey development, including process design, project management, programming, tooling, setup and installation, training, and pre-production runoffs. Like many turnkey technology suppliers, the company forms partnerships with its preferred suppliers, including cutting tool vendors.
Recently, the company worked on a multimillion-dollar turnkey for a Tier I automotive supplier. The parts were left- and right-hand steering knuckles, and expected annual output was 500,000 parts. Gerotech's proposed solution was a manufacturing cell using four horizontal machining centers and four lathes with automated material handling and in-process gaging.
One of the tougher machining operations on the part was straddle milling of the upper joint pads. Gerotech contacted Iscar Metals Inc. (Irving, TX), and tested the company's Tang-Mill straddle mill assembly at speed and feed in excess of 850 fpm and 26.5 ipm (260 m/min and 675 mm/min). The tool's positive-cutting tangential design left a superior finish and maintained good dimensional control.
For holemaking, Iscar supplied Chamdrill-Jet drills. Able to run at high speeds and feeds, the drills' combination of high-pressure, through-coolant capability and a solid, replaceable head resulted in a good surface finish that was used to locate downstream operations. The tools' design also allows changing on the machine, eliminating setup time.
Other Iscar tools were used in critical operations throughout the cell, including Bayo-T-Ream indexable carbide, coolant-through reamers that run at feed rates of more than 65 ipm (1650 mm/min). Consisting of an interchangeable carbide reaming head with a quick-change bayonet mechanism, the tool yielded a 95% decrease in cycle time over a solid-carbide competitor.
"The cycle-time reduction was just an added bonus," says Gerotech applications engineer Terry Kasper. "This reamer held ±1 µm during six months of testing, and requires virtually no setup time. This consistency allowed us to reduce in-process gaging, which was an inherently slow process, by 75%, and freed up time for value-added machining such as deburr operations."
Retooling existing jobs to wring out a bit more productivity is a fact of life for Tier suppliers. Such an update allowed engineers at Metaldyne (Plymouth, MI) to double material removal rates in some operations and reduce tool inventories.
Originally tooled to run on a dedicated rotary transfer machine in a US plant, the job--machining steering knuckles at annual volume of 225,000 pairs--was relocated to a facility in Mexico at the customer's request. Rather than simply relocate or replicate the existing process, Metaldyne engineers chose to optimize the operation. The decision paid off in higher metal removal rates, lower tooling inventory and reconditioning expenses, longer tool life, and reduced cycle time resulting from "commonizing" the tooling--performing more operations with a single tool.
"Every time you 'commonize,' you not only eliminate a tool but also the dead cycle time to change it," explains process engineer Dave Borden. "You also remove one more paper trail in the supply chain." For example, a single drill with replaceable points and inserts drills, chamfers, and countersinks a hole in the new process. Previously, the job required three tools.
The new process runs on eight identical horizontal machining centers, which meet current cycle-time requirements and provide flexibility going forward. Qwik-Twist drills from Ingersoll Cutting Tools (Rockford, IL) replace solid carbide tools, reducing drill inventory and reconditioning costs by more than half. "Replaceable-point drills also give us a more secure process, less dependent on reconditioning turnaround cycles," Borden points out. "All we need is a box of replaceable points and inserts."
For milling operations, Ingersoll positive-rake cutters and double-positive V-Max inserts have increased material removal rates for milling by 30 - 100%. Straddle mills are one-piece monoblock designs, eliminating extra arbor length for spacers and collars and resulting in a more rigid setup. The one-piece, inherently balanced cutters run on stubby Cat 50 toolholders at higher speeds than previous tools without vibration.
Tool commonizing includes drill/chamfer/spotface in a single step with one tool, and face milling over five surfaces. The result is three tool stations saved and a 45-second reduction in overall cycle time. "True, commonizing requires special tools, which are more expensive," Borden says. "But since we run faster and need fewer of them, we come out ahead. And the savings in machining time far outweighed any difference in tooling cost anyway. On an annualized basis, tool commonizing on this job probably contributes about 30% of the total saving."
Metaldyne bypassed verification testing to cut weeks from the retooling project, but Borden got a few pleasant surprises when he began optimizing the new process. For example, penetration rates with the Qwik-Twist drills were at least double those of the previous solid-carbide tools. "We're drilling at 350 fpm and 0.020 ipr [107 m/min and 0.5 mm/rev], yet the drills last four times longer than before," says Borden. The drills feature a replaceable point that can be changed in about 20 seconds.
Monoblock cutters and double-positive inserts allow the HMCs to mill well-supported surfaces at 900 fpm/ 0.012 ipt (275 m/min/0.3 mm/tooth) chip load, about 30% faster than before. For less well-supported surfaces, Borden cuts back to speed of 600 fpm (180 m/min) and feed of 0.005 ipt (0.13 mm/tooth). Inserts are projected to last 2400 - 3000 pieces, a tool life increase of about 30%.
Some of Metaldyne's manufacturing processes use special tools, which many process engineers avoid as too expensive and too risky. But Borden points out that only milling cutters and drill bodies are specials--the inserts are off-the-shelf items. "And, specials are key to 'commonizing' the tooling, which is largely responsible for halving cycle times for the job," he says. "There are risks to specials, but the much larger risk is to lose competitiveness by not using the best of what's available."
Machining improvements can sometimes be gained by a process redesign, as in the previous story. Sometimes, they can result from something as simple as switching tools. Case in point: Eberle Engine (Augsburg, Germany), where operators found they could cut machining time for a diesel rocker arm shaft in half using Xtra-tec milling tools from Walter Waukesha (Waukesha, WI).
Eberle produces special components for diesel, gas, and hydraulic engines for customers around the world. Production of the tempered, heat-treatable steel rocker arm shafts involved milling to produce two faces at each end of the shaft. Milling time on the company's horizontal machining centers was 22 minutes per part.
Walter Xtra-tec F 4042 universal shoulder milling cutters use high-positive inserts to reduce power consumption and provide free cutting action. Recommended for roughing and finishing steels and cast irons, the 63-mm diam cutters produced solid gains in cycle time and tool life, reducing machining time to 11.5 minutes and doubling the life of previously used tools. Cutting speed increased from 330 to 490 fpm (100 - 150 m/min), and feed rate jumped from 5.98 to 14.92 ipm (150 - 450 mm/min) while maintaining good dimensional stability.
The productivity gains resulted not only from implementing the right individual components--indexable inserts, geometry, and grade--but from optimizing the overall system, according to CEO Karlheinz Eberle Jr. "What we dealt with here was a shaft--a round component which can't be clamped too tightly. We also faced a difficult edge, so the tool couldn't exceed a certain length." The Xtra-tec system allowed use of a tool length of 4.53" (115 mm)--able to reach the center of the pallet, but short enough not to compromise the stability needed to achieve good milling results, Eberle says.
This article was first published in the September 2004 edition of Manufacturing Engineering magazine.