Better bandsawing technology

Manufacturing Engineering, Feb 2001 by Harris, Doug

Today's automated sawing system reduces the cost per cut

The strong economy of the 1990s challenged saw builders to produce more capable machines with better reliability at a competitive price. Today's saw manufacturers have responded with innovations like double-column saws that provide a heavier and more rigid cutting platform, barfeeds with sophisticated top clamping, bidirectional wising that allows easier cutting of mill bundles, and more stringent requirements for length tolerances.

Customers want fully hydraulic saws with fullstroking vises, hydraulically powered guide arms, sensors that display blade deviation, digital band speed readouts, digital feed rate displays, and pushbutton blade-speed settings. A recent innovation is the double-column bandsaw with an angled blade entry (cant) that reduces blade pinching, allows a more uniform chip, and increases blade life by reducing total band load. A 1.5 deg tilt to the blade entry angle was an immediate success among users. The increase in the speed of cutting structurals and bundles was dramatic, and significantly boosts production while reducing cost per cut.

The construction industry drove development of bandsaws with a 9 deg blade entry angle to cut large wide-flange beams. Internal stresses, created during the manufacture of wide flange, can cause pinching as the cut relieves residual stress. Specifically developed for wide-flange material, the 9 deg cant and wideset blades nearly eliminate the pinching problem.

Canted blades also reduce the total number of teeth in the cut, which allows blades to be used to their fullest capability. In the past, older horizontal and vertical-blade bandsaws often had either too many or too few teeth in the cut, so blade teeth were often stripped or broken. Blades never got dull; they were destroyed. Today's 9 deg blade cant allows blades to wear out gradually over the course of a long, useful life.

Barfeed systems have made quantum leaps from the old positive stop 24" (610mm) feed, to today's 144" (3.7-m) barfeeds. These systems are positioned by computers to tighter tolerances than ever before. When a shorter barfeed is used, tolerance build-up occurs because multiple strokes are required to feed stock. Longer barfeeds that use continuous feedback systems can drastically improve length consistency and speed of index for long parts.

Remnant lengths were also drastically reduced from perhaps 24" in the 1970s to as little as 3" (76 mm) today by split wising and interlocking wising techniques. Load capacities have also increased. Mill bundles weighing more than 12,000 lb (5450 kg) are common on today's larger bandsaw systems.

Improved blade and bandsaw technology place high demands on total accuracy, since the output from a bandsaw often goes directly to a robotic welding machine, which will have no tolerance at all for out-of-tolerance parts. Newer, faster, computer-driven barfeeds with special sensors and drive systems are more reliable, smoother, and more accurate than ever before.

Equipment manufacturers in industries as diverse as rapid transit, agricultural equipment, rail, aircraft, and commercial trailer forced the development of the 144" digital barfeed designed to hold exceedingly tight tolerances. These new feeds, equipped with bidirectional vises and improved top clamps, combine with double-column, 9 cant blade bandsaws with capacities reaching 25" (635 mm) vertical by 50" (1.3 m) horizontal to create high-performance sawing packages.

Some systems have powered lifting rollers to speed material to and from the saw. To improve productivity, many companies are purchasing material handling systems that include side loading and off-loading conveyors.

To process hard-to-cut aerospace materials such as Hastelloy, titanium, and Inconel, saws had to become heavier and bigger. Larger-diameter band wheels were necessary to put less stress on the blade. Guide arms and saw arms became heavier and larger to dampen vibration and withstand blade tensions as high as 50,000 psi (345 MPa). In addition, larger gearboxes were necessary to run these larger units.

Because the carbide-tipped bandsaw blades needed to cut these materials are very unforgiving, computer control systems have to maintain positive command of the cutting operation. When cutting work-hardening materials such as Inconel, it's necessary to maintain constant chip load. Today's computer-controlled traverse systems provide the cutting control that makes using carbide blades, even when cutting exotic materials, much more efficient and cost-effective.

Since the carbide blade is more heat-resistant than bimetal and can withstand much higher feed pressures than a tool-steel blade, band speed can be much higher. More durable than bimetal, a carbide blade retains its sharpness longer than a steel blade, and produces a better surface finish than cutting with bimetal. This improved finish allows cut-to-length tolerances to be held even tighter to reduce or eliminate downstream machining operations.