Dedicated Fixture Eases Large-Part Clamping

While workholding is an important factor in virtually any machining application, properly locating and fixturing large, heavy parts can be especially challenging. In addition to posing difficulties with part change-over and setup, big workpieces are more likely to vibrate and more difficult to clamp rigidly for efficient, accurate machining.

As a supplier of clamps, fixtures, tombstones and other workholding products, Rockford, Illinois-based Advanced Machine & Engineering (AME) is all too familiar with the difficulties posed by large parts. The company recently designed a dedicated Amrok fixture to provide the clamping forces and reduced setup time required to win a job for the contract machining side of its business.

That job came from Weir Minerals North America, a Madison, Wisconsin-based manufacturer of large pumps for mining slurry applications. In addition to AME, the company initially contracted several other manufacturers to machine housings for pumps used to extract oil from the tar-sand fields of Alberta, Canada.

Measuring 108 by 108 inches and constructed of Class 40 iron castings, the parts require milling, drilling and boring operations. A full housing consists of two parts—a frame and cover section—each of which must be fixtured in two separate configurations to complete machining operations. Thus, a full housing assembly requires four separate setups. This is a substantial challenge considering each component weighs in at more than 5,000 pounds. Moreover, the enormous load and tooling masses involved cause issues with rigidity and vibration.

From the outset, AME was able to deliver the two to three pump sets per week required by Weir. However, with multiple, non-dedicated fixtures, setup took far too long for each part, resulting in much higher costs per pump set, the company says. Each change-over took anywhere between 6 and 8 hours, and clamping the pump housings was tedious at best. Meanwhile, less-than-optimal clamping forces adversely affected cycle time and tool life. AME needed to not only reduce the total setup and machining time, but also address operator safety concerns resulting from material-handling, strapping and clamp-positioning methods.

The solution was a dedicated Amrok fixture, which the company designed to hold each pump section for both setup configurations. The fixture, which measures 120 by 110 inches, features adjustable jacks that enabled proper support for the workpiece sections during cutting on a horizontal milling machine. Due in large part to these jacks, the fixture reduced setup times by more than 50 percent compared with the previous method. Improved locating and clamping also made milling and drilling operations more efficient, resulting in a 45-percent reduction in overall cycle time per pump set.

In addition, replacing multiple, separate fixtures with a single fixture enabled the company to more easily maintain and repeat the tight tolerances required for the job, while standardized lifting, locating and clamping methods enhanced operator safety. When the savings made possible by the new fixtures were passed on to Weir, the customer awarded the entire project exclusively to AME.