Weir Minerals North America, in Madison, Wis., manufactures large pumps for mining slurry applications. It needed a series of very large (108x108 in.) Class 40 iron castings machined for its pump housing fabrication, including milling, drilling and boring.  Each pump housing consists of a frame and cover section, and each required an A and B load — which meant four set-ups for a complete housing assembly.

The slurry pumps are used in Canada’s Athabasca tar sand fields, specifically for flue-gas desulfurization (FGD) in the process of extracting oil from the mineral sands. 

Weir Minerals presented its problem to Advanced Machine & Engineering Co. (AME), among several other contract manufacturers, to do the machining on these parts, approximately 2-3 sets per week.  Each housing section weighed well more than 5,000 lb., presenting substantial challenges for fixturing: rigidity was essential, but other critical considerations was the vibrational distortion from the enormous load and tooling masses involved in the milling, etc.   

Although AME started the job and began delivering the machined FGD pump sets on time, by using non-dedicated fixturing, set-up was taking far too long per part — which as AME v.p.-operations Steve Schubert explained, resulted in much higher costs per pump set. Changeover took as long as six to eight hours, each time.  Locating and clamping the pump housings was tedious, too, and the methods used raised safety concerns, both in materials handling, strapping and clamp positioning. 

Furthermore, clamping forces for the machining process were less than optimal, which had a negative effect on the manufacturing cycle time and the tool life.  AME recognized it needed to reduce the total set-up and machining time significantly, as well as improve operator safety.

“The challenge was to design a fixture that was within the weight limitations of our machine tool table,” Schubert detailed, “without compromising the structural integrity and rigidity of the fixture itself.” Too light a fixture would yield poor finishes, with out-of-tolerance dimensions, etc.

“We also needed a design that would allow for quick change of the workpiece,” he indicated, as we did not have a two-pallet machine. So, clever swing clamps were designed to ‘get out of the way’ so we could remove the completed part and put a new one on.

“Finally, but most important of all, we were extremely concerned with safety,” Schubert said. “We needed a fixture that would allow safe usage for the operator to climb onto repeatedly, as well as being secure enough to not allow one of these massive parts to fall off of the table.”

The solution to this challenge was a single, dedicated AMROK® fixture measuring 120x110 in. (WxH) to hold each GFD pump section for both A and B loads. It reduced set-up times to less than 50% of the previous method.