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Set the Standard. Then, Surpass It

March 19, 2012
Mercury Marine is turning and hobbing on the same machine, continuing a long practice of technical innovation and maintaining its standards for product quality and durability.
A sea of completed pinion driveshafts. Note the quality of the tapered splines.

Carl Kiekhaefer was a young engineer, just out of college when he bought a dying outboard-motor manufacturing company in Cedarburg, Wis., with financial help from his father. His plan was to produce magnetic separators to supply the dairy industry.

The asset sale included 300 defective outboards that had been rejected by Montgomery Ward, the mail-order retailer. Kiekhaefer needed cash to keep his new business running, so with a small crew he rebuilt the motors and sold them back to Montgomery Ward. The engines performed so well that the buyer placed an order for 500 more. Soon a second firm asked him to design and build an alternate-firing twin-cylinder outboard motor — and the Kiekhaefer Corporation was in business.

Outboards weren't new in 1940, but neither were they reliable. Working on his own designs for his fledgling business, Kiekhaefer developed features for quick, powerful, dependable boating power: a rubber water pump rotor that tolerates sand, silt, and vegetation; a one-piece streamline housing that protects driveshaft, waterline, and exhaust from exposure to the elements; and a reed valve induction system. All these were part of a new vision for outboards.

At Mercury Marine in Fond du Lac, Wisc., Kurt Lefeber’s Okuma LB3000 EX BB MYW800 (M spindle with live tools; Y-axis with 5 in. of travel; W subspindle; 800 mm bed) is equipped with a Westec overhead gantry for loading and unloading shafts.

Kiekhaefer called his machines “Mercury,” after the speedy messenger of the Roman gods. At the 1940 New York Boat Show, he displayed his engines for the first time, in a homemade trade show booth, and booked orders for more than 16,000 motors. The marine industry changed forever.

Shortly after WWII the Kiekhaefer Corp. expanded operations to the former Corium Dairy Farm in Fond du Lac, Wis., which housed its manufacturing, service and support, while administration and engineering remained at the Cedarburg facility. More than 70 years later, Mercury Marine, the largest division of the Brunswick Corp., has manufacturing, service and support facilities around the world and the best dealer-distributor network in the industry.

The technology behind the principle — Mercury Marine has not maintained its industry leadership position without constant innovation, foresight, and by adopting superior technology. These principles are easy to recognize at Plant 4 in Fond du Lac, where process engineers Bill Cusick and Kurt Lefeber are producing high volumes of drive and propeller shafts for outboard and stern drive marine propulsion applications.

“Plant 4 is some 220,000 sq. ft and employs 220 or more,” Lefeber explained. “It’s 70 years old, and the plant is where the original Corium barn used to be, specifically at the north end of the plant. It’s where Kiekhaefer settled manufacturing operations after moving up from Cedarburg. There must be 15 to 20 Okumas in here of various types and vintages.”

A close-up view of the hobbed pinion spline. It is a short spline (3/4 in.) that rises up to a taper, at which point the pinion gear is mounted.

“The shafts are 4820 or 8620 steel,” Cusick says, “and in the case of the propeller shaft, we’re turning and hobbing 630 stainless for corrosion resistance. The way that we used to make these shafts involved a multiple-step process: Turning on a lathe, dropping the shaft out, taking it to a WWII-era, dedicated Barber Coleman hobbing machine (with very time-consuming, labor-intensive set-ups), cutting the spline, then removing the part to a grinding operation. It used to take three minutes just in turning alone. Now, I’m doing turning and hobbing on one machine in 3 min., 40 sec. So, this new Okuma technology with the WTO hob assembly is doing away with some dedicated hobbing. We’re getting similar throughput and excellent quality, with one machine performing the operations of two older machines.”

Lefeber is running an Okuma LB3000 EX BB MYW800 (M spindle with live tools; Y-axis with 5 in. of travel; W subspindle; 800-mm bed.) It’s equipped with a Westec overhead gantry for loading and unloading shafts. He’s hobbing splines for driveshafts in the subspindle, and completes shafts in 3 to 4 min.

“In the main spindle we start with a blank that has been carburized,” Lefeber says. “We turn some of that carburizing off, giving greater definition to the part shape. We rough and finish one end and then transfer the shaft to the subspindle, where it’s roughed, finished, center drilled, and hobbed.”

Okuma has designed a particular method of transferring the shaft from the main to the subspindle. There’s a pneumatic pusher system inside the main spindle, so when the gantry places a raw piece into the spindle, it goes to a backstop. In the backstop is an air cylinder with a piston. When the first operation is finished and the operator wants to transfer the shaft to the subspindle, an M Code in the control (an auxiliary M function) fires the air cylinder, which pushes the shaft out of the main and transfers it to the subspindle. With a long part and a small chuck, you’d have to move the part by a series of pulls by the subspindle. With this arrangement, the air cylinder handles the transfer to the subspindle.

Okuma has advanced the practice of hobbing in a turning center, in particular via its machine control developments. One of these is “Autoretract,” a function that allows the operator to retract the hob out of the cut without damaging the hob or the splines.

“The spline I’m hobbing is only about 3/4 in. long,” Lefeber continued, “but we’re hobbing into a taper. The spline follows a diameter for 0.400,” but then it goes into a taper another 0.350.” This is the shaft that transfers power from the crankshaft to the gear case. The taper is the point where the pinion gear is mounted. The pinion gear drives the gear case for forward and reverse gears. This pinion spline needs to have a low run-out, and it’s absolutely critical to the driving application.

“The previous cell process had the blanks machined on a twin spindle LT10 Okuma lathe (without live tooling,)” he recalled. “Then, the machined shafts would be manually transferred to a Gleason P60 hobbing machine that was dedicated to cutting the splines. The new LB3000 EX BB MYW800 was purchased for additional flexibility, and as a backup for the cell. Now, a single operator runs both the existing LT10/P60 machines and the new Okuma lathe. I’m getting an additional 75% of output in the cell without an increase in manpower.”

One of Cusick’s Okumas, an LB3000 EX, is a bar-fed machine with the Okuma ballscrew-driven, programmable tailstock, which is very convenient when working with shafts of varying lengths. “We’re two-axis turning these shafts, ‘green‘ or rough turning,” Cusick said, “after which the parts catcher extends and we cut off the shaft. We’re not doing any hobbing on this machine.”

However, Cusick has four other LB3000 EX BB MY1000s. These are 1,000-mm bed machines and he’s turning and hobbing between centers. Propeller shafts come off the machine at approximately 3 min., 40 sec.

“We’re turning the shaft and then cutting the splines that drive the propeller,” Cusick said. “Basically, the shaft has an alloy steel section friction-welded to a stainless steel section. The stainless is in bar stock condition, and we turn the shaft down, starting with the stainless, crossing over the friction weld and onto the alloy steel section. Then, we hob a spline that’s about 2-1/8-in. long into the stainless section of the shaft.

The turned shafts go to a cell with a dedicated Gleason P60 hobbing machine that cuts the splines. The first LB3000 EX was acquired to back-up for this cell. Now, a single operator runs both machines, so throughput is about 75% greater than with the former arrangement, and the new machine replaced two older machines.

“The hobbing unit is mounted on the tool turret and driven by the M spindle,” he detailed. “The Y-axis allows us to shift the hob like a typical dedicated machine, moving the hob back and forth across the cutter to equalize wear.”

Letting the control hob it — Okuma has made significant progress for hobbing in a turning center, much of this centered on the machine control. One that’s particularly notable is Autoretract. With this function, if there is any problem with the hob, if you hear something that doesn’t sound quite right, you push the Stop button and the Autoretract system will retract the hob out of the cut, without damaging the hob or the splines.

Further, with other machines, an operator has to time the C-axis spindle with the hob itself, which is rotating. He has to keep the timing of the two just right, or he won’t have a straight spline; he may leave a bit of a corkscrew or turn in the spline.

Because Okuma builds its own drives, no tuning is needed. Other machines must have the drive spindle on the turret for the hobbing unit tuned to the C-axis, and that relationship has to be calibrated to get the right timing for each one.

At Mercury Marine, the propeller shafts presented an interesting challenge. The front of the prop shaft is stainless steel and the back is an alloy steel. As noted, these materials are joined by a friction weld at the center of the shaft. These are smaller shafts, 1 in. to 1-1/4 in. in diameter, and fairly long. If the operator is turning the center of the shaft across the friction weld between the chuck and the tailstock, there may be some chatter. Okuma developed a machine-control function to eliminate chatter, called “spindle-speed variation.”

This bar-fed LB3000 EX machine with the Okuma ballscrew-driven, programmable tailstock is very convenient when working with shafts of varying lengths. “We’re two-axis turning these shafts, ‘green‘ or rough turning,” Bill Cusick said, “after which the parts catcher extends and we cut the shaft off. We’re not doing any hobbing on this machine.

For example, if the machine is turning at 1,000 rpm, the operator can use spindle-speed variation to increase the speed by 20 rpm or reduce it by 20 rpm for the duration of 1/10 of a second. The result is a winding sine wave-type action. This takes out the chatter completely when the operator is turning between the alloy steel and the stainless steel at the friction weld. He can listen to the spindle as it varies in rpm, up and down, eliminating chatter in tasks like Mercury Marine’s longer propeller shafts.

WTO, hob-meister — Matt Mayer, national sales manager for precision toolholder developer WTO Inc., recalled how in-process hobbing on the Okuma LB3000 EX machines developed. “This story goes way back to February 2005, and I was approached by the Okuma distributor at that time about an application where Mercury Marine was trying to hob the splines on the propeller and driveshafts for the outboard motors. Their goal was to drop the completed shafts off a lathe or turning center, versus sending the turned shafts out for second and third operations on an offline hobbing machine.

“So, we were asked to develop a hobbing unit for the Okuma machine,” Mayer said. “At the time their Okuma machines had VDI turrets, a tooling system that mounts on the face of the turret and uses a prismatic wedge clamp to secure the tool into the tool pocket.”

There were a couple of problems with that, he elaborated. First, the 40-mm interface to secure the tool into the pocket wasn’t rigid enough for heavy splining. Also, the axis needed to rotate the hob around the center line would require a massive, very complex head. To match that up with 40-mm connection proved impractical at the time. When Okuma introduced the LB3000 EX series of machines three to four years ago, with a peripherally mounted turret having a bolt-on interface and a very large diameter pilot hole in the turret — 60 mm, versus 40 mm — it presented a more rigid interface to secure the hobbing unit. The peripherally mounted turret lends itself better to rotating the head around the X-axis plane, which is needed for generating splines or gears.

Mercury Marine operates four other Okuma LB3000 EX BB MY1000s. These are 1,000-mm bed machines, and he hobs the shafts between centers. The hob cuts the spline, using the Y-axis and the full length of the hob. Propeller shafts come off the machine in approximately 3 min., 40 sec.

“So, we went ahead with the development of the gear hobbing unit,” Mayer said. “It’s made out of billet steel, which is critical because it needs a lot of rigidity in the head. It’s gear-driven and has either a 1:1 gear ratio or a 2:1-ratio torque increaser unit. The Okuma LB3000 EX, in addition to having a larger, more rigid interface, now has more horsepower and torque to be able to generate these cuts.

“Mercury is hobbing the propeller shafts out of stainless steel to avoid corrosion from salt water,” Mayer indicated. “Stainless steel is fairly hard to cut, and this cutting process generates of lot of tool pressure and cutting forces on the machine. The LB3000 EX machines handle these forces very well. As a matter of fact, when we did the sample pieces, Mercury was pleased that we were getting near-ground finishes.

“We’ve even designed two special heads for them to accept their Barber Coleman-style hob arbors,” he recalled. “One of the characteristics of our head is the ability to ‘quick change’ the hob. So, you can leave the head set up in the machine, remove an arbor support, and pull out the entire arbor and hob assembly. Thus, you can change cutters without messing with the orientation of the head or having to remove the head from the machine. You simply remove the arbor support, slide the assembly out, make the cutter changes, slide back the assembly, replace the arbor support, and you’re back into cutting very quickly. Once you get the angular orientation of the head set, you really don’t want to mess with it.”

Mercury has some splines with diameters so small that they have to incorporate the hob into the arbor as one piece. WTO developed a special head to accept that hob arbor, which is the same hob arbor design as Mercury’s 60-year old Barber Coleman machines. So, Mercury is able to use the same tooling in the WTO head its had in house for decades — a big cost saver.

A group of finished propeller shafts. Note the smooth transition from stainless steel, crossing over the friction weld, to alloy steel.

Mercury is dropping off these parts complete, except for hardening and grinding after hardening. Other manufacturers have used this technology, but Mercury is the first to use it in a high volume, mass production operation.

Morris Midwest is a Milwaukee-based distributor for both WTO and Okuma, and has been very well involved in the Mercury project through its Morris Midwest Tech Center — especially in the efforts to ‘prove out’ the head and the process.

“We do a lot of up front work before we ever sell a machine,” said Morris Midwest sales and applications engineer Mark Krzewinski. “It’s a process, and we bring together all the project people involved — Mercury, Morris Midwest and Okuma — and look at the part and process, and develop a process, in this case bringing the expertise of WTO to bear to achieve in-process shaft hobbing on Okuma’s LB3000 EX series.”

The goal was better product quality, and higher throughput. Always in the background of these projects is an awareness of the declining numbers and capabilitis of people coming into the machining professions. So global manufacturers need partnerships, according to Krzewinski, … “someone to rely on, from engineering, design, manufacturing, sales and service, someone who can really take the ball and run.”

A propeller shaft being hobbed by the WTO Inc. hob. The hobbing unit is mounted to the tool turret and driven by the M spindle. The Y-axis allows Mercury Marine to shift the hob like a typical dedicated machine, moving the hob back and forth across the cutter to equalize wear.

Kurt Lefeber recalled that five or six years ago he looked outside the Mercury Marine organization for a solution to the shaft turning problem. “We had some manufacturers do some test cuts,” he reported, but “the quality wasn’t there, the cycle time wasn’t there, and the capability really wasn’t there, … so we decided not to pursue it.

“The Okuma machines have the rigidity to do the hobbing work, and that goes for the WTO unit as well,” he said recently. “It’s got to be able to hold the hob cutter. Previous styles of hobbing units held the cutter with the standard single-mounted cutter where the hob end was not supported. WTO allows support on both ends of the cutter. Cutter life is better, spline quality is better than we were getting on the dedicated hobbing machines, and the hobs last longer. For example, I’m running 1,200 pieces on a cutter that’s about 1 in. in diameter and 2 in. long.”

Bill Cusick added: “Because there aren’t many people turning and hobbing in the same machine — which is new to just about everybody — there isn’t a lot of knowledge out there as to which is the best coolant for this application. So, we’re doing a little bit of testing on that, too. Which is to be expected when you’re running a very successful, complex process that few are attempting because they haven’t drawn on the right suppliers with the right technology. As a result we’ve set the standard, and are surpassing it.”

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