Carbide welding turning tool
Carbide welded turning tools are a common tool type in machining. They consist of a carbide insert welded to a conventional carbon steel shank. They combine the high wear resistance of carbide with the toughness of the steel shank and are widely used in turning a variety of materials, including steel, cast iron, and non-ferrous metals. Their simple structure, low cost, and versatility make them particularly suitable for small- and medium-volume production and complex machining operations. They are essential tools for both conventional and CNC lathes. Understanding the structural characteristics, welding process, sharpening requirements, and usage specifications of carbide welded turning tools is crucial for ensuring machining quality and increasing tool life.
The structure of a carbide welded turning tool consists of three parts: the blade, the shank, and the weld layer. The material selection for each component directly impacts tool performance. The blade is made of tungsten-cobalt (YG), tungsten-titanium-cobalt (YT), or general-purpose (YW) carbide. YG types (such as YG8 and YG6) are suitable for machining cast iron and non-ferrous metals, offering excellent toughness and impact resistance; YT types (such as YT15 and YT5) are suitable for machining steel, offering excellent wear resistance and red hardness; and YW types (such as YW1 and YW2) can machine steel, cast iron, and non-ferrous metals, offering high versatility. The shank is made of 45 or 50 steel, quenched and tempered (hardness 220-250 HBW) to ensure sufficient strength and rigidity. The cross-section of the shank is typically rectangular or round, with dimensions determined by the blade size and machining requirements. For example, a 30mm x 40mm rectangular shank is used for machining large-diameter workpieces. The welding layer is the key to connecting the blade and the shank. Copper-based or silver-based solder is used to firmly bond the blade and the shank through high-temperature melting. The thickness of the welding layer needs to be controlled at 0.1-0.2mm. Too thick will lead to a decrease in welding strength, and too thin will easily cause cracks.
The welding process is a core step in the manufacturing of carbide welded turning tools, directly impacting their lifespan and safety. Common welding methods include gas welding, arc welding, and induction welding. Gas welding uses an oxyacetylene flame to heat the tool at temperatures of 850-950°C. This makes it suitable for small-batch production and offers flexibility, but heating uniformity is poor. Arc welding uses the arc to melt the brazing material at high temperatures, resulting in rapid heating but easily overheating the blade. Induction welding utilizes electromagnetic induction heating, offering uniform temperatures, short heating times (10-30 seconds), and stable weld quality, making it suitable for large-scale production. Before welding, the blade and shank require pretreatment: the blade should be cleaned with gasoline to remove oil contamination. The welding area of the shank should be ground with a bevel (30°-45° angle) and coated with a flux (such as borax) to remove oxide film. The heating rate and holding time should be controlled during welding to prevent cracks in the blade caused by thermal stress. Low-temperature tempering (200-250°C for 1-2 hours) should be performed immediately after welding to eliminate welding stress and improve the tool’s impact resistance.
The quality of grinding for carbide welded turning tools significantly impacts cutting performance, ensuring a sharp cutting edge, accurate angles, and a smooth surface. Sharp grinding is performed on a grinding machine using a green silicon carbide grinding wheel (grit size 46#-60#) to grind the rake and flank faces of the blade, initially establishing the tool angle. Fine grinding is performed on a tool grinder using a diamond grinding wheel (grit size 100#-120#), ensuring a cutting edge straightness of ≤0.01mm and a surface roughness Ra ≤0.4μm. The grinding temperature must be controlled during grinding to prevent cracking due to overheating. Water mist cooling can be used, with the tool frequently immersed in water during the grinding process. Tool angles must be ground strictly according to design specifications. For external turning tools, the main rake angle should be 45°-90°, the rake angle 5°-15° (the larger value is used for steel machining, the smaller value is used for cast iron machining), the back angle 6°-10°, and the inclination angle -5°-5°. After sharpening, use a magnifying glass to check whether the cutting edge has defects such as chipping and notches. If so, use an oilstone to polish it to ensure that the cutting edge is intact.
Proper use of carbide welded turning tools is key to extending their lifespan. Appropriate cutting parameters should be selected based on the workpiece material and machining requirements. When machining steel, maintain a cutting speed of 80-150 m/min, a feed rate of 0.1-0.3 mm/r, and a depth of cut of 1-5 mm. When machining cast iron, maintain a cutting speed of 60-100 m/min, a feed rate of 0.15-0.4 mm/r, and a depth of cut of 2-6 mm. Before use, perform a test cut to observe the shape and color of the chips. Normal chips should be silvery white or light yellow. If they appear blue or black, the cutting speed is too high and requires adjustment. When installing the tool, ensure that the blade extension does not exceed 1.5 times the toolholder thickness to avoid vibration. The angle between the toolholder centerline and the workpiece axis must be consistent with the lead angle, with a deviation of ≤1°. Adequate cooling and lubrication are essential during the cutting process. Use extreme pressure emulsion for steel and kerosene or dry cutting for cast iron to prevent blade overheating and wear. When the cutting edge shows obvious wear (flank wear reaches 0.3-0.5mm), it needs to be re-sharpened to avoid increased wear and tear that may cause the blade to crack.
Common faults of carbide welded turning tools and their troubleshooting methods are crucial to ensuring processing quality. Blade chipping is mostly caused by excessive cutting force, poor welding quality, or unreasonable tool angles. Solutions include reducing cutting depth and feed rate, checking welding quality and re-welding, and adjusting rake angle and cutting edge inclination angle to increase tool toughness. Blade shedding is usually caused by insufficient welding strength, which requires re-welding and ensuring a uniform weld layer; rapid wear of the cutting edge may be due to excessive cutting parameters or poor cooling, so the cutting speed should be reduced and cooling should be increased. When chatter marks appear on the machined surface , the rigidity of the tool shank needs to be checked, and a tool shank with a larger cross-section should be replaced or the blade extension length should be shortened; if the surface roughness is out of tolerance, the tool needs to be re-sharpened to ensure a sharp cutting edge. By correctly selecting the tool type, standardizing the welding and sharpening processes, and using and maintaining it properly, the service life of carbide welded turning tools can be significantly extended, and processing efficiency and quality can be effectively guaranteed.
