In the manufacturing field of industrial high-voltage motors (10kV and above), the motor housing serves as the load-bearing substrate for the stator core. The tolerance of the stop diameter, the perpendicularity of the end face to the axis, and the cylindricity of the bearing chamber directly affect the stability of the motor operation (the national standard GB/T 1993-1993 requires that the tolerance of the stop diameter be IT7 level, the perpendicularity be ≤ 0.05mm/m, and the cylindricity of the bearing chamber be ≤ 0.008mm). A large industrial motor manufacturer is facing a traditional process bottleneck when processing the motor housing of Φ 300-600mm ductile iron (QT500-7): it needs to go through three processes: "horizontal lathe rough turning outer circle → vertical boring machine precision boring bearing chamber → rocker arm drilling machine processing installation hole". Multiple clamping causes the coaxiality between the stopper and the bearing chamber to exceed 0.1-0.15mm, and the vibration intensity during motor operation exceeds 1.8mm/s (qualified value ≤ 1.1mm/s), with a single piece processing cycle of up to 75 minutes; At the same time, the intermittent impact generated during the cutting of ductile iron results in a lifespan of only 40-50 pieces/blade for hard alloy cutting tools, and the cost of a single motor casing cutting tool exceeds 50 yuan.
Customer usage scenarios
To overcome this dilemma, the company has introduced the Kede CNC VTC70 CNC vertical lathe and established an exclusive manufacturing system for motor housings that combines heavy-duty rigid machining with a single clamping process. The equipment adopts an integral aviation grade cast iron bed body (with a casting wall thickness of 90mm), which has undergone dual stress relief of "natural aging for 12 months+vibration aging for 72 hours", combined with four point support static pressure guide rails (bearing capacity ≥ 50kN), and optimized structural rigidity through finite element analysis. The radial cutting stiffness reaches 35kN/mm, which can stably withstand the 22kN radial impact load during ductile iron cutting; Equipped with FNK CNC system and grating ruler full closed-loop control (resolution of 0.05 μ m), it achieves ± 0.007mm positioning accuracy and ± 0.01mm repeated positioning accuracy, accurately matching the H6 level tolerance requirements of the bearing chamber. In response to the intermittent cutting characteristics of ductile iron, the equipment is equipped with a high-power spindle (45kW) and a dual high-pressure cooling system (internal cooling pressure of 1.2MPa, external cooling flow rate of 40L/min), combined with ultra-fine grain WC Co alloy cutting tools (adding NbC reinforcement phase, impact toughness ≥ 15MPa · m ¹/²), effectively suppressing tool chipping.
Motor shell clamping
In terms of technological innovation, the equipment has achieved dual breakthroughs in "process integration+heavy-duty stable cutting" for motor housing processing: integrating a Φ 800mm four jaw linkage hydraulic chuck (clamping force up to 150kN), an 8-station servo turret (tool change time of 1.6 seconds), and a radial power tool head (output torque of 350N · m), it can complete the motor housing outer circle precision turning (tolerance IT6 level), bearing chamber precision boring (cylindricity ≤ 0.006mm), stop forming (diameter tolerance ± 0.015mm), end face milling (flatness ≤ 0.03mm), and 20-24 installation hole drilling and tapping (positional tolerance ≤ 0.1mm) in one go. In response to the difficulty of coaxiality control, we innovatively adopt the "benchmark integrated processing method": taking the inner holes of the motor housing at both ends as the positioning benchmark, real-time processing data is collected through an on machine measurement system (measurement accuracy ± 0.001mm), dynamically compensating for the trace deformation caused by the weight of the workpiece, so that the coaxiality between the stopper and the bearing chamber is stably controlled at ≤ 0.04mm. For complex structures such as heat dissipation ribs, the equipment uses Y-axis and C-axis linkage interpolation to achieve one-time forming of three-dimensional surfaces, avoiding the tool marks caused by traditional process transfer.
The implementation results fully comply with the standards of industrial high-voltage motors: the single piece processing cycle has been compressed from 75 minutes to 42 minutes, and the daily production capacity has been increased from 120 sets to 220 sets; The cylindricity of the motor housing bearing chamber is ≤ 0.006mm, the coaxiality between the stopper and the bearing chamber is ≤ 0.04mm, and the perpendicularity of the end face to the axis is ≤ 0.03mm/m, fully meeting the requirements of GB/T 1993-1993 "Cooling Methods for Rotating Electrical Machines" and IEC 60034-1 standards; The vibration intensity during motor operation decreased from 1.8mm/s to 0.8mm/s, and the vibration exceedance rate decreased from 22% to 1.5%; The tool life has been extended by 60% (up to 65-80 pieces/blade) due to impact resistant design, and the cost of a single motor casing tool has been reduced to 32 yuan; The intelligent diagnostic system equipped on the equipment can monitor the spindle vibration acceleration (sampling frequency 1kHz) and cutting force fluctuations in real time. Combined with a tool wear prediction model, the comprehensive utilization rate of the equipment has increased from 76% to 93%, and the annual downtime has been reduced by 480 hours.
VTC70 solves the contradiction between 'heavy-duty machining and precision control' of our high-voltage electrical casing. The chief engineer of the company stated, 'Our 20MW high-voltage motor has not only passed CE certification, but also meets the requirement of 100000 hours of fault free operation for equipment in key fields such as nuclear power plants and large-scale chemical industries. This provides us with core competitiveness for exploring high-end markets.'. This case confirms that the CNC vertical lathe has become a key equipment for breaking through quality and efficiency bottlenecks in the field of industrial high-voltage electrical casing manufacturing through the deep collaboration of "heavy-duty structure design+process integration innovation+intelligent precision control".
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