By John Boucher, President, Thermocarbon, Inc., Casselberry, Florida
Reprinted from Microelectronic Manufacturing and Testing May & June, 1986
Effective cooling of the diamond blade at the point of contact with the material being processed is essential for any diamond cutting/ grinding application. Yet, cooling is one of the more overlooked conditions in the system.
The starting point for an efficient cooling system is the supply nozzle configuration which directs the coolant medium. Dual nozzle arrangements have significant advantages over most single nozzle designs in supplying coolant to the critical areas of the diamond blade during the cutting operation. Coolant must be directed at the blade/material interface as well as the leading edge of the blade. The coolant, after leaving this initial contact point, should follow along both sides and the extreme outside edge of the blade in such a manner that it will create intimate contact with these blade surfaces.
Proper workpiece position for efficient cooling.
A single-nozzle and dual-nozzle cooling
A single nozzle will satisfy the directional requirements but will fail to create intimate contact with the blade along its sides. The single stream of coolant, directed at the cutting interface, is split by the diamond blade into two separate streams and deflected away from the sides of the blade. The resulting decrease in cooling efficiency is characterized by more edge chipping damage when processing brittle materials, shorter blade life, and erosion on the sides of the diamond blade, which will cause uneven cuts.
The addition of side rails that direct a separate coolant supply to both sides of the blade is an attempt to compensate for the shortcomings of a single nozzle design. The problem is that the additional coolant supply interferes with the primary front supply, creating a non-directional and turbulent flow around the cutting edge of the blade so that each stream will favor increased efficiency in removing the debris developed during the cutting process. However, if the velocity of coolant supplied by the side rails is set to a point at which it will not interfere with the primary coolant stream, it will act as a wash due to the constant supply of flood coolant to the surface of the material being cut. This feature is worthwhile for surface-sensitive materials.
Dual nozzles provide two separate streams of coolant to the cutting interface, and at an angle to the cutting edge of the blade so that each stream will favor one side of the diamond blade after providing the necessary coolant to the leading edge. This approach provides the necessary coolant to all of the critical areas of the cutting blade, with no loss of the directional flow required for removing the debris generated during cutting.
Dual coolant nozzles meet the necessary criteria for the dicing/slicing of a wide variety of applications. A resinbonded blade is shown cutting through 0.165-in (4.191-mm) sapphire in one pass.
Main requirements for coolant nozzles
An extremely important step in setting the direction of the coolant flow is to ensure that the six-o-clock position of the blade is being supplied with adequate coolant in addition to the already mentioned guidelines. Coolant nozzles must provide a full and airless flow of coolant. Additionally, the nozzles should be installed in close proximity to the blade in order to prevent excessive pressure drop of the supply and to ensure that no air will become entrapped in the coolant stream prior to contact with the blade/ material interface.
Recirculating coolant systems require efficient filtering to remove the particles generated during cutting. These systems may incorporate cartridge, centrifugal, or cascade type filtering methods, and must be selected to fit the applications. Excessive particles suspended in the coolant medium will retard the heat transfer properties of the coolant, and cause surface damage to sensitive workpiece materials. Once the proper system has been installed, it must be maintained relative to the rate at which the volume of material is removed from the workpiece, in order to ensure consistent and reliable performance.
Coolant temperatures have a pronounced effect on blade life and cut quality in diamond 7 grinding technology. Test results indicate that coolant temperatures above 80° F (27° C) should be avoided, while temperatures of 50° F (10° C) or less dramatically improve cutting performance. Refrigeration of the coolant medium is easily adapted to most recirculating systems and is highly recommended.
The requirements of the variable dicing system components discussed thus far are basic and mandatory for successful diamond grinding in any application. Once the awareness factor of these variables is realized and made a part of the system building process, only then should the major components be procured. It is at that time that operational control functions, ergonomics, and the degree of automation of the dicing/slicing machine become a part of the final buying decision. These functions, as a part of the interacting variable components which make up the total system, warrant equal and due investigation.