July 11, 2006
Today metal tube sawing technology is light-years ahead of where it was just five years ago. Sawing machine and saw blade advancements—Special-purpose CNC tube-sawing machines, Dynamic ball-screw feed systems, Automatic Blade-changing, Carbide-tipped blades, blade coatings, Thin-kerf Blades, segmented saw Blades, optimize tube cutting.
Today metal tube sawing technology is light-years ahead of where it was just five years ago. A better understanding of the cutting process has led to advancements in sawing machine and saw blade technology that optimize tube cutting.
Many tube fabricators are unaware of how the latest sawing machines, blades, and technology are applicable to their current applications and how they can save in cost.
The optimal tube cut is achieved by using the blade characteristics—material, coating, diameter, thickness, number of teeth, and tooth profile—and machine variables—cutting speed and feed rate—that are most suitable for the tube material, diameter, and wall thickness.
The blade rotation speed, saw blade feed rate, and the number of teeth on the saw blade are the three most important variables to determine accurately before sawing literally anything.
These variables are even more critical—and difficult to determine—when sawing tubes with a circular saw because the saw blade encounters different amounts of material, depending on which part of the tube it is cutting. A tube has three different planes: the top, mostly horizontal area; the sides, which are mostly vertical; and the bottom of the tube, which is also mostly horizontal and is the longest cut length.
The blade rotation speedis determined by material hardness. Generally, hard materials are cut slower than softer materials.
The number of teethon the saw blade is determined by calculating the longest cut length based on the tube's outside diameter and wall thickness.
The feed rateis a result of the number of teeth in the cut during a specified amount of time and the amount of work each tooth is capable of doing.
Adjusting these variables can result in surprising production and blade life increases while costing little or nothing to implement.
Many tube cutting fabricators have been able to recoup the cost of their new tube sawing equipment in a short time because of the savings they have been able to realize.
Special-purpose CNC tube sawing machines, combined with the latest generation of saw blades and application technology, provide the best of all worlds—high precision and cut quality at high outputs.
Dynamic ball-screw feed systems produce variable feed rates (based on which part of the tube is being cut) to achieve constant volume removal. The resulting slow-fast-slow pace decreases the total time required to cut a tube.
High throughput rates—up to 8,000 parts per hour—can be attained with these machines.
Integrated systems that not only saw but also chamfer, thread, deburr, measure, wash, dry, and package the tube eliminate the cost of performing these secondary operations in separate steps.
Automatic Blade Changing. CNC tube sawing machines with automatic blade-changing capabilities select the blade type and cutting parameters automatically for the tube being cut. This enhances flexibility and short- and medium-run capabilities.
Blade Coatings. In the early '90s a revolutionary metal tube sawing development was the introduction of titanium nitride (TiN) coating. This coating on high-speed steel cold saw blades increased surface hardness, reduced friction, lowered heat conductivity, increased oxidation temperature, and reduced formation of buildup on the cutting edge. The resulting speed and feed increases, as well as blade life increases, substantially reduced the cost per cut.
The high-performance coatings of today, made of titanium carbonitride (TiCN), or titanium aluminum nitride (TiAlN), are applied in up to 1,000 microlayers. The coatings can increase surface hardness up to 3,200 Vickers hardness and decrease the friction coefficient to as low as 1.5.
These high-performance coatings can substantially reduce sawing costs by increasing blade life over that of standard (vapor-treated) black-oxide cold saw blades.
The cost effectiveness of these coatings can be evaluated by considering how long the blade lasts and taking the lower sharpening cost into account.
Thin-kerf Blades. Better understanding of the sawing process and problems associated with sawing tubes (such as deformation and spinning of the tubes in the sawing machine vise) have led to the development of increasingly thinner-kerf saw blades (seeFigure 1). Thin-kerf technology has reduced cutting times, increased blade life, and, in some cases, decreased scrap rates.
Thin-kerf blades are ground flat, then tapered on the outer rim. This allows the kerf and blade to be thinner than blades that are taper-ground from the outside rim toward the center hole of the blade.
Instead of being taper-ground from the outside rim toward the center hole of the blade, the blade is first ground flat and then tapered on the outer rim. This allows the kerf to be as thin as possible and creates a much thinner saw blade that can be engineered to specific applications. The hub can be strengthened for stability under high cutting forces and adjusted larger or smaller for the requirements of the job. As a result, machine and part vibration are reduced, allowing higher feed rates. The narrower blade may even result in material savings on large quantities of short tubes.
Carbide-tipped Blades. Historically, high-speed steel saw blades were the only option available to improve tube cutting results with circular cold saws. As tube fabricators respond to demands to fabricate tubes constructed of exotic materials and materials that are cheaper, harder, and more difficult to cut than in the past, saw blade technology is changing to help them meet those demands.
New sawing machines with fast-turning capabilities allow the use of carbide-tipped saw blades to cut advanced materials effectively. The increased blade rotation speed that the carbide-tipped blades allow accelerates the speed at which tubes can be cut.
Currently carbide-tipped blades provide excellent cut finish quality and long blade life. While these blades are very application-specific, they are increasingly being engineered for broader tube cutting applications.
Saw Blade Repair. Saw blade repair also has improved recently. The latest grinding equipment can produce noticeably improved saw blades. Rigid, CNC grinding machines using cubic boron nitride (CBN) abrasives have strong cooling systems that can produce a consistent grind finish. These machines optimize the grinding process by attending to every variable.
For example, the programmable forward speed feature slows the grinding process exactly where the grind finish of the saw blade is critical for blade life longevity. By reducing thermal stress at the cutting edge and producing a burr-free, mirror surface, the machine allows chips to pass the cutting edge without creating the friction that shortens blade life.
Additional advancements in blade repair technology are direct-drive motors and coolants. Direct-drive motors eliminate belt vibration. New coolants match blade temperature to reduce blade expansion and contraction during the sharpening process. These two improvements allow the production of a concentric, high-pitch (distance from cutting edge to cutting edge), precision saw blade that has a uniform chip load on each tooth. Each tooth is exactly where it should be—evenly spaced, within the same circumference as the one before it and the one behind it. In addition, the blade wears evenly for long blade life. As a result, the saw vibrates less and can cut faster.
Tube performance, quality, and cost effectiveness—and the systems used to manufacture them—are more crucial today than ever before. The relationship that exists between tube manufacturers and their suppliers is important so that both can profit from technology advancements and establish an industry that can cut the tubes of tomorrow more cost-effectively.
Craig Ridge is president of Kinkelder Cutting Solutions Inc., firstname.lastname@example.org, www.kinkelder.nl.
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