Better Band Sawing Technology
Article By Doug Harris
Vice President, HE&M Inc.

Pryor, OK
The strong economy of the 1990’s 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, bar feeds with sophisticated top clamping, bi-directional vising that allows easier cutting of mill bundles, and more stringent requirements for length tolerances.

            Customers want fully hydraulics saws with full-stroking 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 band saw 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° 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 band saws with a 9° 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° cant and wide-set 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 band saws 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° blade cant allows blades to wear out gradually over the course of a long, useful life.

Bar Feed Systems have made quantum leaps from the old positive stop 24” (610-mm) feed, to today’s 144” (3.7-m) bar feeds.  These systems are positioned by computers to tighter tolerances than ever before.  When a shorter far feed is used, tolerance build-up occurs because multiple strokes are required to feed stock.  Longer bar feeds 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 1970’s to as little as 3” (76-mm) today by split vising and interlocking vising techniques.  Load capacities have also increased.  Mill bundles weighting more than 12,000 lbs (5450 kg) are common on today’s larger band saw systems.

            Improved blade and band saw technology place high demands on total accuracy, since the output from a band saw often goes directly to a robotic welding machine, which will have no tolerance at all for out-of-tolerance parts.  Newer, faster, computer-driven bar feeds with special sensors and rive 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 bar feed designed to hold exceedingly tight tolerances.  These new feed, equipped with bi-directional vises and improved top clamps, combine with double-column, 9° cant blade band saws 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 band saw 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 mi-metal and can withstand much higher feed pressures than a tool-steel blade, band speed can be much higher.  More durable than bi-metal, a carbide blade retains its sharpness longer than a steel blade, and produces a better surface finish than cutting with bi-metal.  This improved finish allows cut-to-length tolerances to be held even tighter to reduce or eliminate downstream machining operations.

            Carbide is good in compression but not in tension, so a carbide blade requires a soft exit from the cut to prevent damage.  The band saw controller automatically reduces force and rate near the very end of a cut to prevent the blade from exploding out of the cut, which would cause tooth damage.

            Carbide band saws are still a new technology.  Specially designed carbide band saws will revolutionize the saw industry just as carbide inserts revolutionized the machine tool industry in the 1980’s. 

Faster and more efficient cutting provides yet another challenge for the band saw manufacturer:  how to get material to the saw and how to remove it.  In times past, the saw was a manufacturing bottleneck.  In the coming decade, manufacturers and steel service centers will want to move material to the saw and away from the saw as quickly as possible.  Instead of a forklift or overhead crane waiting on a saw to finish a job, the saw will probably be waiting for someone to unload it.

            Soon, automatic loading and unloading tables may speed stock to the band saw, and move the saw’s output to the next manufacturing step.  Scrap will be automatically dumped into special bins, sorted for length, and placed into containers for later use.  Saw operators will be able to automatically determine the optimum use of bar stock, based on data entered at a control keyboard.

            Today’s computer-controlled traverse systems already provide a smooth and predictable blade break-in process.  After installing a new blade, the saw operator simply pushes a button on the console, and the computer automatically adjusts cutting forces to properly break in a new blade, substantially improving blade life.

            Saw computers will soon be communicating with warehouse inventory computers to determine which jobs run first, second, or third.  Ultimately, a bar code on material will contain information such as material type, hardness, traceability, source, final destination, and other information including quantity and length required.  The saw will automatically adjust itself to the proper feeds and speeds, lengths and quantity, and the material handling system will deliver the cut-to-length parts to the appropriate location.

            Service technicians will be able to plug their laptops or cellular telephones into a band saw’s computer to download information such as the saw’s service history, the number of cycles it has made, the number of hours the machines has been operated, and any glitches or faults the computer may have recorded.  Band saws can now be placed online, and diagnostics can be transmitted through the Internet.

            In just a few decades the band saw has changed from a back-shop necessity to a double-column saw with an 80 x 80” (2 x 2-m) capacity and a 4” (100-mm) blade.  Today only one thing is certain; somebody is still going to have to change the blade from time to time – and even that task may be automated in the not too distant future.