Building bridges

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by Kip Hanson

The Problem: Additional business calls for higher production efficiency
The Solution: An investment in five axis plasma cutting technology

Nova Scotia fabricator reduces processing time with integrated beveling capability

If your bridge needs fixing, give Cherubini Metal Works Ltd. a call. As a member of the Cherubini group of companies, this Dartmouth, NS, company is well-equipped to fabricate a new double-tee or deck slab, bathtub girder or three plate girders. With 18,000 sq m (200,000 sq ft) of production space, an assembly bay boasting 14 m (47 ft) under the hook, and 420 employees across the Cherubini Group as a whole, there’s little this company can’t handle.

Cherubini doesn’t stop at bridges, however. Vice president of operations Steve England points to a number of massive projects the company has worked on in recent years—half a dozen wellhead protection structures for Encana’s Deep Panuke Project, a 400-tonne, 15 m tall subsea turbine base, 4000 tonnes of structural steel components for the Shearwater Airbase hangar expansion, and many more. “Business is good. Aside from all the bridge projects we’re doing, there’s a lot of structural and energy-related work.”

To meet its customers’ increasing demands, Cherubini made the decision in early 2013 to purchase additional cutting machines for the fabrication department. The request for proposal was placed and, after comparing the relative merits of five equipment brands, the company chose a pair of Avenger 2 cutting systems from ESAB Welding & Cutting Products, Mississauga, ON.

“The pricing was comparable to other brands, and ESAB’s equipment is a standard in the industry,” says England. “We use a lot of the company’s welders and consumable products on our bridge fabrication.” Cherubini’s familiarity with ESAB played a part in the selection process, and the machines were installed several months later.

Plasma cutting is nothing new to Cherubini—according to England, they’ve been doing it for over 25 years. The ESAB machines, however, were the company’s first experience with five axis. “This is certainly an update for us. We can now do plasma cutting to 50 mm (2 in.) thick, around twice what we can do with our old plasma machines. And before the new machines, we were cutting all of our bevels by hand with a radiograph. The five axis heads on the ESAB machines provide consistent and accurate bevels—the result is not only greater efficiency, but higher weld quality and a lower rejection rate.”

Now a permanent landmark located on the waterfront in downtown Halifax, Cherubini fabricated and installed 1,200 tons of structural steel, cupola spires and pedways.JP Dillon agrees. As ESAB’s regional sales manager, cutting systems, Dillon can cite numerous points to consider when shopping for a cutting system, starting with the machine controller. “When you do bevel cutting, it’s important to have built-in angle and geometry compensation. This means when you look at the program code, it’s easy to see that you’re cutting a 10 ft by 6 ft rectangle with a 30° bevel down both sides. You can read it plain as day. Without this compensation, the program might read 10.316 ft x 6.195 ft, and any adjustments to the bevel requires tweaking of the machine program. With our controller, the parts are always programmed to the actual part dimensions.”

According to Dillon, ESAB equipment has process intelligence embedded into the machine. “We have plasma and oxy-fuel in the same machine, as well as multiple heads, at least one of which has five axis capabilities. There are many process variables to consider, most of which are dealt with by the controller—the operator doesn’t have to be an expert to successfully run this equipment.”

Beveling capability was a big factor in Cherubini’s decision, but so too was productivity. Dillon says modern plasma cutters can cut 25.4 mm (1 in.) thick plate at 2,032 mm (80 in.) per minute; by comparison, oxy-fuel cuts that same steel only one-fourth as fast. But since Cherubini equipped its machines with four oxy-fuel heads, it can cut multiple parts simultaneously, and still have a precision plasma head available for cutting and beveling when needed.

“These machines offer the best of both worlds,” says Dillon. “Get four or five torches going and you’re producing the same amount of parts as plasma but with a process that costs less to run. Consider that a single plasma head runs around $10 an hour all-in. With gas, the fuel costs are a little higher, but consumable life is significantly longer, and the only electricity you use is to drive the table. So even with multiple heads, oxy-fuel is almost always less expensive than plasma.”

To program the Avengers, Cherubini purchased ESAB’s Columbus programming software, a CAD/CAM system designed specifically for this type of equipment. The software does far more than spit out G-code, though—part nesting, plate management, job control and complex beveling capabilities, together with a number of programming wizards are included. “The learning curve wasn’t too bad,” Cherubini’s England explains. “ESAB sent two guys out to set up the machine, train the operators and teach them how to use the software. It was pretty painless.”

Aside from programming the machine, Cherubini uses the Columbus software to track its remnant material. “Picture a sheet of 350WT or A709 Grade 50 steel measuring 8 ft by 40 ft,” England says. “We’ll load up the software with whatever parts are needed and nest it all into one program, then email it to the controller. Once the parts have been cut, the system tracks the leftover material and actually assigns a drop number so we can put it back into our inventory. Just last week we were able to use one of those drops for a small rush job that came in.”

England says they keep the machines pretty busy with bridgework, most recently on the Strandherd-Armstrong Bridge, which opened in early July and crosses the Rideau River to connect Strandherd Drive in Barrhaven and Earl Armstrong Road in Riverside South. Other notable projects done on the ESAB equipment include Cherubini’s work on coal-fired power generation for DTE Energy and others. “We’ve used the new machines to cut the steel for a number of duct sections shipped to Detroit Edison and Riley Power. Each measures roughly 9 m x 9 m (30 ft wide and 30 ft tall) with big baffle plates inside to direct air flow. They function in much the same way as the furnace ducting in your house.”

When complete, the ducts are loaded onto a barge and sent to the site for installation. In fact, this last point is probably England’s only complaint, although it’s not about the equipment. “To maximize efficiency, we do as much as possible in the fabrication shop, then splice and bolt it all together in the field. But when you’re designing bridges, you can only go so wide and so long because of the roads in Nova Scotia. Probably the biggest unit we’ve ever delivered was 48 m (160 ft) long.”

Until the province decides to widen the roads, it looks like Cherubini will have to make do with the undeniably robust capabilities of its ESAB cutting system. It’s a nice problem to have. “ESAB has been very quick to help us with any questions, and we’ve been able to keep the equipment quite busy. Overall, we’re very happy.” SMT

Kip Hanson is a contributing editor.

Cherubini Metal Works Ltdherubini Metal Works Ltd

ESAB Welding & Cutting Products

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