- THE MAGAZINE
Truing ultra-thin diamond blades to their original cross-sectional shape is a crucial step in achieving repeatable and precise part geometries in diamond sawing processes. An important aspect of truing is eliminating the effect of the diamond blade "hammering" the work piece, which is caused when the diamond blade "runs out," or becomes misaligned relative to the machine spindle axis. Out-of-round conditions lead to inconsistent blade performance and cut quality, rapid blade wear, premature abrasive particle pullout and, in extreme cases, blade failure or breakage.
In most machining operations, the operator must regularly stop the slicing or slotting process to manually true the diamond wheel using abrasive cup truers or brake-controlled truing devices. This is a time-consuming process that limits a company's production efficiency.
One precision slicing and slotting machine* was designed to overcome this problem by incorporating an in-process blade truing device that automatically maintains the rotational integrity of both single- and multiple-blade adaptations. When used in conjunction with a non-contact blade height detector, the on-line truing device can be CNC-programmed for unattended machine operation.
Benefits of On-Line TruingDiamond blade sawing is typically categorized as "ultra-thin" when the cutting widths are less than 0.012 in. (0.3 mm) or when the cutting ratios are greater than 15:1 (blade thickness to blade exposure values). A seldom-understood behavior of ultra-thin slicing and slotting processes is the diamond blade's tendency to "wander" due to insufficient diamond particle exposure or a worn and irregular-shaped cutting face. It is generally believed that self-dressing blades, such as the softer phenolic resin bonds, will continually break down to expose new and sharp diamonds from the cutting face. However, this is not the case in ultra-thin applications, primarily because the tangential loads are not high enough to break down the bond material around the diamond particle. As a result, manufacturers of ultra-thin products-such as read/write rigid disk heads and miniature electronic components-must regularly true their diamond blades or risk quality problems.
The on-line truing system is an air-driven abrading device that automatically returns worn and tapered diamond/CBN blades to their original square profile. The system is impervious to flood coolant water and is designed to provide higher performance and reliability than either abrasive cup truers or brake-controlled truing devices.
An on-line truing system also provides a number of other benefits. For example, since operators no longer have to remove the blade assembly from the saw, alignment and cut placement errors-including blade and hub assembly run out, vibration and imbalance-are avoided. Additionally, as long as the truing wheel's abrasive material type, grit size and bond hardness have been carefully selected, on-line truing can effectively expose the diamond particles from the bond material, thereby combining the truing and dressing steps into one operation. (The machine supplier can guide companies in the abrasive selection process.) The system is ideally suited for diamond and CBN resins, as well as metal and nickel bond structures, from 2 to 8 in. in diameter.
On-line truing also eliminates the blade-to-blade variation often found on multiple diamond blade gang assemblies. For precision, full-depth slotting operations, properly trued blades ensure that each blade is penetrating the work piece in harmony with the others while preventing the pull effect that comes from the greater diameter of a leading blade.
Using an on-line truing system on tape-frame-mounted applications enables the cross-sectional shape of the blade cutting face to be maintained-a key to ensuring accurate depth-of-cut control and reduced cutting forces. Most mounting tapes are no more than 0.005 in. thick, requiring the diamond blade to be set approximately 0.002 in. below the work piece. As the cutting face becomes worn or tapered, the cut wall loses its perpendicularity while taking on the worn or rounded shape of the blade. Additionally, the cutting forces substantially increase due to the higher axial loads generated by the rounded corners of the blade, and this increases the potential for material damage. With an on-line truing system, the operator can set the machine to automatically true the blade as often as needed to reestablish a square cutting face and ensure lower cutting forces.
An on-line truing system can also be used with a CNC-programmable, non-contact blade height detector.** This device measures the blade height for a given slicing or slotting operation, stores the measurement in its memory, and then automatically controls the blade height in relationship to various sawing operations without operator assistance. Whenever the system's LED thru-beam is penetrated by the blade's outer diameter, the machine automatically establishes a new Z-axis zero coordinate value in the cutting cycle program. Blade breakage and chipping resulting from the operator trying to manually determine the point at which the blade's outer diameter meets the top of the work piece are eliminated with this process-controlling feature.
Ensuring Cutting AccuracyWith the continued development of ultra-thin cutting processes, controlling and maintaining the cross-sectional integrity of the blade cutting face is imperative to ensure high-quality results. On-line truing offers an economical solution to achieving repeatable and accurate part geometry in full-depth slicing operations, enabling manufacturers to more easily achieve a final net shape in ceramics, glass, rare earth magnets and composite materials.
For more information:For more information about the on-line truing system, contact Manufacturing Technology Inc., 2226 Goodyear Ave., Ventura, CA 93003; (805) 644-9681; fax (805) 644-3541; e-mail firstname.lastname@example.org; or visit http://www.mtionline.com.
References:*The NSX-250i precision slicing machine, manufactured and supplied by MTI, Ventura, Calif.
**Supplied by MTI.