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“If a drop of sweat gets in that vat of steel, we’re all goners.” That’s what a worker at the Yamaha Precision Propeller foundry in Indianapolis said in July 2019 as I watched a team of silver-suited workers pour blinding-hot, 3,000-degree stainless steel into a red-hot propeller mold.

As general manager Jonathon Burns walked me around the facility’s multiple buildings, the operation seemed particularly high-tech, especially given its annual production of more than 60,000 propellers. Automated wax casting machines, a robotic prop-dipping arm, and computer-controlled prop-polishing and prop-tuning equipment all added to the facility’s highly modernized feel.

Though the Indianapolis facility felt — and in many ways was — state of the art back then, it was reaching the limits of its capacity. That’s why, earlier that day, Yamaha broke ground on a $20 million, 55,000-square-foot foundry about 20 miles away in Greenfield, Ind. Built on 28 acres, the facility was expected to boost Yamaha’s propeller capacity by 67 percent with heavy automation, new processes and robotics — all to keep up with new and aftermarket demand, and to improve equipment as well as the overall space for employees.

Yamaha Precision Propeller’s $20 million, 50,000-square-foot foundry is one of only two stainless-steel propeller foundries in the U.S.

Yamaha Precision Propeller’s $20 million, 50,000-square-foot foundry is one of only two stainless-steel propeller foundries in the U.S.

A little more than three years later, the Greenfield foundry is a reality, humming along 24 hours a day, five days a week. It produces about 100,000 propellers a year, according to plant manager Batuhan Ak, who in August guided Soundings Trade Only through the foundry.

Ak began the tour by telling the backstory of Precision Propeller, which Jim Booe founded in 1969 in Indianapolis. (Booe’s son, Chris, still works for Yamaha.) Booe’s company initially provided propeller repair and tuning services out of a two-car garage. Around 1980, it expanded and began manufacturing its own Turbo-branded propellers for outboard OEMs, Ak says.

Yamaha purchased Booe’s Precision Propeller operation in 2008 and expanded the site piece by piece over eight years. It would eventually become the sole producer of all Yamaha stainless-steel propellers, and one of only two stainless-steel propeller foundries in the United States, according to Yamaha. Planning for the new foundry began in 2016. It was completed in late 2020 and reached full capacity in July 2021.

This wax propeller and hub assembly was produced in a computerized injection mold.

This wax propeller and hub assembly was produced in a computerized injection mold.

“It’s great to finally be firing on all cylinders in the Greenfield facility,” Ak said at the time in a press release. “Propellers are part of the integrated systems that boats need today, and the new facility gives us the opportunity to leverage more efficient manufacturing technologies that increase quality while decreasing manufacturing costs.”

Though the new facility boasts all sorts of high-tech manufacturing processes and equipment, the investment-casting process the company uses has been around for at least 5,000 years. “The process was originally used to craft jewelry,” Ak says, “but it’s been refined over thousands of years to produce everything from surgical equipment to turbine blades and all kinds of other precision metal parts.”

On the factory floor, metal shelves are filled with hundreds of wooden master patterns that are used to create aluminum injection molds for propeller blades. “Our engineers in the U.S. and Japan design the props, and these wood masters are used to fabricate the aluminum molds we inject the wax into,” Ak says. “The hub molds — the central part of the propeller — are machined directly out of aluminum from digital plans.”

The Greenfield foundry uses  65- and 150-pound furnaces brought from the Indianapolis facility to cast Sharrow propellers

The Greenfield foundry uses 65- and 150-pound furnaces brought from the Indianapolis facility to cast Sharrow propellers

A waxy, candle-like smell permeates the air near the starting point of the factory floor. This is where pink wax pellets are melted down and injected into computer-controlled molds to produce complete hub and propeller blade positives, and individual hub and blade parts. The single-piece, hub-and-blade wax positives require only a bit of scraping and cleaning up after they are released from the mold. However, the joining of individual blades to each hub is a different ballgame. “This is the artistic part of the process,” Ak says.

Here, I see a familiar face from my previous visit. Hilda Ramirez is attaching wax propeller blades to hubs with precise applications of heat from a soldering iron. It’s a job she’s done for nearly 25 years. Her muscle memory is so accurate that it’s difficult to imagine a robot doing it faster or with higher precision. She told me in 2019 that she could produce 90 to 100 prop-and-hub assemblies in a shift.

“There is already automation in this process with the one-piece wax hub and blade parts, but we still have models that require the blades be attached manually,” Ak says. “Hilda is not going anywhere anytime soon; this handwork will remain a part of the process in the future.”

Robotic arms dip wax positives into ceramic slurries, and silica sand and zircon flour baths to form hard molds into which molten stainless steel will be poured.

Robotic arms dip wax positives into ceramic slurries, and silica sand and zircon flour baths to form hard molds into which molten stainless steel will be poured.

The next stop on the line is where workers apply a soft, wax-like compound called “goop” to the places where the prop blades intercept the hub. Using heated tools and plastic scrapers, workers apply the goop at each propeller root, then shape it into a smooth radius at each junction. “This is a very critical part of the process,” Ak says. “Any mistake in creating the wax positives will hurt production down the line and result in scrap. So these people are very important to the end quality of each propeller.”

Scrap is a big deal in any investment-casting operation. While defective castings are to be expected — and can ultimately be remelted to form new props — having too much scrap in the process reduces the line’s efficiency and results in higher production costs. “Our ultimate goal is to be below 2.5 percent of net sales in scrap,” Ak says. We are not there yet today but are actively making progress toward achieving that target. After just our first year running the new automated pour line, we are less than 5 percent, which is considered in the top percentile of foundries within the investment-casting industry.”

A worker transfers a rack of molds into a steam oven.

A worker transfers a rack of molds into a steam oven.

On the other side of the room, another member of the wax team is attaching pour cups to the propeller hubs. These fixtures aid in the metal-pouring process, acting as a funnel for the molten stainless steel. They also add strength to the final mold, forming a gripping point used in the casting process.

Once workers have completed the wax positives and added pour cups, each one goes through a three-step cleaning process. A worker places each wax piece on a metal rod that swirls the parts in a solution for a set amount of time before hanging them on a metal rack that holds five wax castings.

Computerized jigs are used to precisely tune finished propellers.

Computerized jigs are used to precisely tune finished propellers.

For now, the manufacturing processes and machinery are all much the same as they were in Indianapolis three years ago, but “that’s about to change very quickly,” Ak says. “You probably remember this dipping cell, right?”

In this fenced-in cell, a robotic arm reaches over to a line of racks, each loaded with five wax propeller positives. The arm picks up one rack at a time, and dips and swirls it in a yellow ceramic slurry. It then lifts the wax pieces from the cauldron, spins them around for approximately 30 seconds to shed excess slurry, and twirls them in a rotating drum filled with a wind-driven blizzard of silica sand. Zircon flour is used in later dipping sequences. This is the first step in a process that creates a hard ceramic propeller mold, into which 3,000-degree stainless steel will ultimately be poured.

“This piece of equipment came over from the Indianapolis facility,” Ak says. “Now you’ll see the automation we’ve created in this new facility responsible for the huge increase in our output.”

Props fresh out of the mold require multiple rounds of finishing before they are ready to ship.

Props fresh out of the mold require multiple rounds of finishing before they are ready to ship.

At this point in the old facility, the ceramic molds would be rolled on carts by hand to various drying and dipping stations scattered among the plant’s multiple buildings. In Greenfield, a robotic arm places each rack onto a moving track that leads to three additional dipping cells.

“These are the last three dip-and-dry stations,” Ak says. “Each dipping cell uses a robotic arm to dip and coat each rack of prop molds before placing it into a 72-degree drying room where fans expedite drying. The shortest drying time required between dips is an hour; the longest drying step takes 12 hours. It depends on the slurry and whether it’s silica sand or zircon flour added in the previous step.”

Ak says that drying may seem mundane, but it’s a critical step in the process. “Any moisture caught between subsequent mold layers will turn into steam and crack the mold. Automating this process speeds things up and ensures proper drying between each slurry dip and coating. Dialing this in has been one of the keys to increasing production. It takes about one day to create each mold. Now, we’re simply doing it on a much larger scale.”

Props fresh out of the mold require multiple rounds of finishing before they are ready to ship.

Props fresh out of the mold require multiple rounds of finishing before they are ready to ship.

The molds, now hard, yellow shells, come out of the last drying room and enter a markedly hotter and visually stimulating part of the Greenfield factory: the foundry. Past an automatic overhead metal door — and through a sudden, 25-degree burst in temperature — the prop molds are placed on racks in a huge, pressurized steam oven that melts the wax away from inside. “This creates a void where metal will be poured,” Ak says. “Any residual wax will be burned away in another process down the line.”

Nearby, after the wax has largely been eliminated from the molds, a factory worker installs insulation collars around the pour cup section of each mold before lining each one up on a metal tray that holds many propeller molds. The fluffy white collar helps prevent mold cracking when handled by metal gripping tools used by human hands or robots.

Production splits at this point. To the left are a 1,800-degree oven and two induction furnaces brought over from the Indianapolis facility. During my visit, they were being used to produce propellers for Sharrow, which in April entered into an agreement with Yamaha to produce many different sizes of its uniquely shaped props.

This side of the foundry is particularly analog, requiring workers to manually move prop molds one rack at a time into a second oven, where they are heated to 1,800 degrees. Workers covered in protective silver suits manually pull molds from the oven and then place them under a 65- or 150-pound induction furnace loaded with 3,000-degree metal for filling. Props are poured in batches. When the furnaces are empty, the melting process starts again. Melt, pour, repeat.

“This was a bottleneck in our Indianapolis operation,” Ak says, “but it’s perfect for smaller-scale orders like the ones we get from Sharrow.”

On the right side of the foundry, which primarily produces Yamaha’s Saltwater Series and Reliance propellers, is another oven, but this one is automated. Racks of propeller molds are loaded into one end of the inferno and are mechanically moved toward the other until the molds reach a temperature of 1,800 degrees. This removes any residual wax and contaminants, and brings the mold to an ideal temperature for receiving molten metal.

Once heated to the proper temperature, an insulated robotic arm reaches into the oven, pulls out a propeller mold, and positions it in a sand-filled pan. It sits under a pot that automatically dispenses a precise amount of molten 15-5 stainless-steel alloy into each mold.

The most significant contributor to the efficiency of this new foundry is an automated 1.25-megawatt induction furnace. “With the old process, we had to add stainless-steel ingots and scrap to the furnace, wait for the metal to heat up to around 3,000 degrees, pour the metal, and then start the process all over again,” Ak says. “This furnace has a 4,000-pound reservoir that is always kept at 3,000 degrees. The metal then falls by way of gravity down to a pouring cup where each propeller is filled. The process is never held up by waiting for the metal to melt; this saves an extraordinary amount of time.”

After the propeller mold is filled, the pouring cup tilts upward, a metal drum is placed over the glowing-red mold, and an automated trackway slowly moves the whole assembly down the line to cool. The cans move toward a workstation where an employee uses a mechanical arm to remove the lid and lift the still-hot propeller casting toward a vibrating machine that breaks it loose from its ceramic shell. What comes out of the other end of the machine is a rough, dull-gray propeller casting that looks nothing like the shiny finished products that end up on new Yamaha outboards and dealers’ stock shelves.

The vibrating machine removes much of the ceramic coating, but an unacceptable amount of material is left behind in the prop’s nooks and crannies. The Greenfield plant employs a team of finishers who inspect and shot-blast each prop by hand to remove the contaminants. Props with casting defects that can’t be fixed are scrapped and put in a bin to be melted down and recast.

Free of casting contaminants, the props are loaded onto pallets and into a waiting tractor-trailer that carries them to the Indianapolis plant for last touches. “It takes a lot of work to turn these rough castings into the gorgeous, shiny propellers our customers expect,” Ak says, “so we are relying on the finishing staff and equipment we have in Indianapolis to get the propellers through to their final form.”

At the Indianapolis plant, props go through various ceramic media tumbling machines and other processes to shine them up before workers repair defects, further polish specific areas, grind leading edges, and tune the props using computer-aided jigs, hammers and anvils before they are approved for shipment to the company’s Kennesaw, Ga., headquarters.

“This is where our next expansion comes in,” Ak says. “We’ll eventually move our Indianapolis people and some manufacturing gear to a building that will be constructed next to the existing one in Greenfield. We expect that will get underway in two to three years.

“That’s where we see the opportunity for additional automation and manufacturing advances,” Ak adds. “The goal is not to replace employees but to employ automation in some of the dirtier and dangerous aspects of our operation so they can be used in other production areas. And, of course, continue to improve our production processes and build the best propellers for our customers.”

The company measures efficiency and return on Yamaha’s $20 million investment not only in terms of units, but also in terms of speed. “We’re not only producing 33,000 more propellers each year, which is significant, but we’re also making more props using less man-hours,” Ak says. “At the old plant, we were producing 1.9 propellers per man-hour. Here in Greenfield, that number is 2.2 … and we expect that metric to climb.”

Ak adds: “We can’t wait to get started on the next expansion.”

Progress never stops. I look forward to returning for an update in a few years. 

This article was originally published in the October 2022 issue.



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