During diamond saw blade welding, temperature control is crucial for preventing thermal damage to the diamond. Diamond is prone to graphitization at high temperatures (typically starting above 700°C), resulting in a sudden drop in hardness and structural collapse. Excessive temperatures or localized overheating during welding can directly damage the integrity of the diamond particles. Therefore, through a comprehensive approach involving process design, equipment selection, and operational specifications, the welding temperature must be strictly controlled within the diamond's tolerance range while ensuring weld strength.
The choice of welding method directly impacts temperature control accuracy. Laser welding, due to its concentrated energy and minimal heat-affected zone, is the preferred method for high-end diamond saw blades. It uses a high-energy laser beam to instantly melt the substrate and blade material, allowing welding times to be controlled in milliseconds, significantly reducing heat transfer to the diamond particles. In contrast, high-frequency brazing, while less expensive, relies on induction heating coils to transmit energy, resulting in a longer heat transfer path and requiring optimized current frequency and heating time to control temperature distribution. Flame brazing, however, is difficult to precisely control the flame temperature and is therefore only suitable for rough machining diamond saw blades that are more tolerant of thermal damage.
Establishing a temperature monitoring system is key to avoiding thermal damage. In practice, infrared thermometers or thermocouples should be used to monitor the temperature of the welding area in real time, focusing on temperature changes at the interface between the diamond particles and the weld. When the temperature approaches the critical point of diamond graphitization, welding parameters should be adjusted immediately or heating should be suspended. For example, in high-frequency brazing, a segmented heating strategy can be implemented, with a pause of several seconds after each heating step to promote heat diffusion and avoid localized temperature accumulation. For laser welding, precise control of laser power density and scanning speed is required to ensure a uniform and consistent molten pool temperature.
Compatibility of welding materials is crucial for temperature control. The selection of brazing filler metals requires a balance between melting point and thermal expansion coefficient. Low-melting-point filler metals (such as silver-based filler metals) can lower the welding temperature, but wettability with the substrate and tool tip materials must be ensured. High-melting-point filler metals, while improving weld strength, may increase the risk of thermal damage. Furthermore, the addition of active elements (such as titanium) to the filler metal can improve interfacial bonding with the diamond and reduce localized overheating caused by interfacial defects. For the base material, selecting alloys with excellent thermal conductivity (such as copper-based alloys) can accelerate heat dissipation and reduce the heat exposure time of the diamond particles.
A coordinated design of the preheating and cooling processes can further mitigate thermal shock. Preheating can reduce the temperature difference between the base and the blade, reducing thermal stress during welding. However, the preheating temperature must be strictly controlled below 200°C to prevent premature oxidation of the diamond. A staged cooling method should be used during the cooling phase: after welding, the blade is first cooled naturally to approximately 300°C, followed by accelerated cooling with forced air or water. For thick-section diamond saw blades, heat dissipation grooves or embedded heat conducting sheets can be added to the back of the base to enhance heat transfer efficiency.
The design of the welding fixture must balance positioning accuracy and thermal management. The fixture should be made of a material with a low thermal expansion coefficient (such as Invar) to prevent deformation that could cause the welding position to shift. Furthermore, the fixture should provide heat dissipation channels to prevent heat accumulation at the contact surface. For laser welding, the fixture should also have a light-absorbing coating to reduce potential damage to the equipment from laser reflection.
The operator's skill level directly affects the effectiveness of temperature control. Training should strengthen understanding of the relationship between welding parameters (such as current, voltage, and scanning speed) and temperature, and enhance the ability to identify abnormal temperatures through case analysis. For example, abnormal sparking or a darkening of the weld during welding may indicate excessive temperatures, necessitating immediate shutdown and inspection.
Quality inspection should integrate nondestructive testing (NDT) with performance testing. NDT (such as X-ray or ultrasonic testing) can reveal cracks or pores within welds, while microhardness testing and diamond grain integrity assessment can directly assess the extent of thermal damage. For diamond saw blades used in critical applications, simulated cutting tests should also be conducted to verify their stability under high-temperature conditions.
