Machining of alloy steel double-throw crankshaft
As a core component of internal combustion engines, compressors and other equipment, the turning quality of alloy steel double-throw crankshafts directly affects the operating accuracy and service life of the entire machine. Due to the high strength, high hardness and good wear resistance of alloy steel materials themselves, problems such as rapid tool wear, high surface roughness, and difficulty in controlling dimensional accuracy are prone to occur during the turning process. Therefore, a scientific and reasonable processing plan needs to be formulated. First of all, before turning, the blank must undergo strict quality inspection, including chemical composition analysis, mechanical property testing and appearance defect inspection to ensure that the blank material meets the design requirements. Blanks with internal cracks or inclusions should be removed in a timely manner to avoid safety hazards such as workpiece breakage during subsequent processing. At the same time, it is necessary to select appropriate lathe equipment based on the structural characteristics and dimensional accuracy requirements of the crankshaft. Generally, CNC lathes with high rigidity, high speed and high-precision feed system are preferred to meet the processing requirements of complex surfaces.
The selection of turning tools is a key step in the machining of alloy steel double-thrust crankshafts. Due to the high cutting resistance of alloy steel, ordinary high-speed steel tools are unable to withstand continuous cutting loads, so carbide tools or ceramic tools should be used. Among them, coated carbide tools are widely used in alloy steel turning due to their excellent wear resistance and heat resistance. The geometric parameters of the tool need to be optimized according to the machining process. For example, larger rake and clearance angles should be used for rough turning to reduce cutting forces and tool wear; while the rake and clearance angles need to be reduced for fine turning to increase tool rigidity and ensure the quality of the machined surface. In addition, cooling and lubrication of the tool are also crucial. A high-pressure cooling system should be used to spray cutting fluid directly into the cutting area. This not only reduces the cutting temperature, but also washes away the chips to prevent them from scratching the machined surface.
The double-throw crankshaft has an asymmetrical structure and a large eccentric mass. This easily generates centrifugal force during the turning process, causing workpiece vibration and affecting machining accuracy and surface quality. Therefore, effective clamping and balancing measures must be taken. In terms of clamping, a double-thimble positioning method combined with a steady rest can be used to ensure that the workpiece remains stable during rotation. For the machining of eccentric parts, the mass and position of the counterweight block must be determined through calculation to balance the centrifugal force. During the turning process, the cutting parameters should be adjusted gradually, starting with low speed and small feed rate, observing the vibration of the workpiece, and gradually increasing the parameters to the optimal state. At the same time, regularly check the wear of the tool and replace the tool in a timely manner to avoid aggravating the vibration of the workpiece due to tool wear.
The control of dimensional accuracy and form and position tolerances is the core goal of turning alloy steel double-throw crankshafts. Since the crankshaft’s journal, turn neck and other parts have high dimensional accuracy requirements, and there are strict form and position tolerance requirements such as coaxiality and parallelism between each part, multiple measurements and adjustments are required during the processing. An online measurement system can be used to monitor the processing dimensions of the workpiece in real time, and the feed rate can be automatically compensated by the CNC system to ensure that the dimensional accuracy is within the design range. For the control of form and position tolerances, the rotation accuracy of the lathe spindle and the straightness of the guide rails must be guaranteed, and the lathe must be maintained and calibrated regularly. After the fine turning process is completed, precision measuring tools must be used for comprehensive inspection, such as using a micrometer to measure the journal diameter and a dial indicator to detect radial runout, to ensure that all indicators meet the design requirements.
The surface treatment after turning has an important impact on the performance of the alloy steel double-throw crankshaft. Since the crankshaft needs to withstand alternating loads and friction and wear during operation, its surface needs to be strengthened, such as carburizing, nitriding, etc., to improve the surface hardness and wear resistance. Before surface treatment, the workpiece after turning needs to be cleaned to remove oil, chips and oxide scale on the surface to ensure the treatment effect. For parts that do not require surface treatment, effective protective measures should be taken to avoid excessive treatment. After the surface treatment is completed, the workpiece needs to be inspected for the second time to check whether indicators such as surface hardness and penetration layer depth meet the requirements. Finally, the crankshaft is cleaned and rust-proofed as a whole to prepare for subsequent assembly processes.
