变参数法薄壁机匣模拟件激光熔覆成形研究
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摘要
传统方法加工薄壁机匣组合件,工艺复杂、加工变形难控制、生产周期长,且支板与筒体之间采用焊接方法连接,薄壁结构焊接过程中易引起挠曲变形,影响机匣尺寸形状和整体性能。激光熔覆成形技术(Laser Cladding Forming, LCF)能够成形出具有功能特性的高致密复杂形状金属零件,可满足机匣工作的高性能要求。然而,开环控制和3轴数控条件下,采用固定优化LCF工艺参数组合熔覆成形薄壁机匣件,“2.5D”成形台阶效应不可避免且多层熔覆成形热累积效应严重,影响机匣斜坡结构形状精度及整体成形质量。将变参数法引入LCF工艺中,选择合适的工艺参数及其变化范围,有规律地改变参数,实现了对机匣整体熔覆成形质量的改善,具体工作及结果如下：
(1)分析机匣熔覆成形关键工艺,在此基础上设计变参数法机匣模拟件整体激光熔覆成形过程,深入分析变参数法成形过程原理知：近连续变送粉量成形可逼近于实时监测送粉量成形过程,从而减小机匣斜坡支板成形台阶效应,变激光功率和扫描速度成形可逼近于实时监测熔池成形过程,从而减小多层连续熔覆成形过程中的热累积效应,为后续变参数多层熔覆成形试验提供理论依据。
(2)深入研究稳定送粉状态下送粉量、激光功率及扫描速度对熔覆道几何尺寸和熔覆质量的影响规律,结果表明：送粉量范围0.5-2.5g/min,获得较好质量熔覆道；激光功率400W和送粉量2.0g/min组合有利于保证多层熔覆成形质量,每层Z轴提升量0.21mm；扫描速度500mm/min有利于保证成形制件综合性能；变送粉量法控制成形制件形状精度比较有效；最佳工艺参数组合熔覆成形获得致密、硬度580HV的熔覆道。
(3)针对机匣斜坡支板“2.5D”成形台阶效应问题,建立变厚度切片成形几何模型。0.5-2.5g/min内近连续增大送粉量,获得高度0.05-0.42mm近线性增大的单道单层熔覆层。采用Matlab仿真变厚度切片成形过程,规划正确扫描路径。通过变送粉量多层熔覆成形试验,成形出表面相对较光滑、形状较规则的斜坡薄壁件,有效减小了台阶效应。
(4)采用每层固定偏移0.05mm和0.026mm,分别获得了侧表面平整度较好的机匣内、外锥壳；选择直线形和圆弧形熔覆道扫描轨迹之间的较佳中心距0.67mm来搭接成形,实现了内、外锥壳与支板的良好连接。设计机匣整体成形激光扫描路径,每层变换成形起点,并改变Z轴提升量来配合变送粉量法成形,直接成形出具有规则斜坡和锥壳形状薄壁结构的机匣模拟件。采用变参数法和冷却等待法减小多层成形热累积效应,提高了机匣整体熔覆质量,结果表明：变参数法更有利于提高机匣整体成形几何尺寸精度。
The whole process is complex, difficult and of long period when manufacturing the aero-engine thin-walled casing with traditional methods. Besides, welding deformation is easily caused when web plates and conical shells are jointed by welding. As a result, not only geometrical precision but also properties of casing become bad. Technology of Laser cladding forming (LCF), which can flexibly manufacture metallic components with full metal density, functions and properties and specific geometry, can be used to manufacture the casing with high properties. However, under conditions of open-loop control and 3-axis CNC, stair-step effect is inevitable when "2.5D" forming process is performed and thermal cumulative effect is serious when multi-layer cladding process is carried out. So the formed ramp web plates of casing have bad geometrical precision and the casing has poor quality. The method with variable parameters is introduced into LCF. Proper parameters are selected and varied regularly in a good range. Consequently, geometrical precision and clad quality of the formed simulated casing is improved significantly. Study details are as followed:
(1) Key processes of forming thin-walled casing are analyzed and LCF of casing with variable parameters is designed. After deeply analyzing the process principle of forming with variable parameters, two key points are obtained. Process of varying powder feed rate approximately continuously can be considered as process closed-loop controlling powder feed rate so that stair-step effect can be reduced. On the other hand, process of varying laser power and scanning speed regularly can be considered as process closed-loop controlling melt pool so that thermal cumulative effect can be reduced. These two key points provide theoretical basis for the following experiment with variable parameters.
(2) Under the condition that metal powders are fed in stable state, influences of powder feed rate, scanning speed and laser power on clad dimensions and quality are deeply investigated. Results show that range of powder feed rate 0.5-2.5g/min achieves clad layers with good clad quality; good parameters combination of laser power 400W and powder feed rate 2.0g/min is appropriate for multi-layer cladding and Z-increment value is also determined to be 0.21mm; scanning speed 500mm/min makes the formed sample with good combination property; to improve geometrical precision of the formed sample, the method with variable powder feed rate is more effective than with variable scanning speed; clad layer with dense structure and micro-hardness 580HV is achieved by the good parameters combination.
(3) To prevent stair-step effect when layered forming ramp web plates of casing with 2.5D slices, a geometrical model forming with variable thickness slices is developed. While powder feed rate is varied at a calculated step approximately continuously, a single clad layer with height increasing near linearly to clad length is obtained. Clad height increases from 0.05mm to 0.42mm with powder feed rate varying from 0.5g/min to 2.5g/min. Correct scanning paths are planed by simulating the process forming with variable thickness slices through Matlab program. Using clad layer of variable height and the obtained scanning path, a relatively smooth ramp thin wall is formed by multi-layer cladding experiments. Result shows the method with variable powder feed rate reduces stair-step effect significantly.
(4) By offsetting fixed values of 0.05mm and 0.026mm every layer, inner and outer conical shells of casing are formed with good side surface smoothness respectively. By overlapping linear and circular clad layers and selecting center distances between linear and circular scanning tracks to be 0.67mm, joints of web plates and conical shells are formed with good properties and precision. Scanning path for forming the integral casing is designed. Starting point is changed every layer and Z-increment value is varied to match the method with variable powder feed rate. Consequently, the simulated thin-walled casing is directly formed with uniform ramp and conical thin-walled structures. Method with variable parameters and self-cooling are both used to reduce thermal cumulative effect and clad quality of the formed casing is improved significantly. Results also show that the method with variable parameters is more effective to improve geometrical precision of the formed casing.
(1)分析机匣熔覆成形关键工艺,在此基础上设计变参数法机匣模拟件整体激光熔覆成形过程,深入分析变参数法成形过程原理知：近连续变送粉量成形可逼近于实时监测送粉量成形过程,从而减小机匣斜坡支板成形台阶效应,变激光功率和扫描速度成形可逼近于实时监测熔池成形过程,从而减小多层连续熔覆成形过程中的热累积效应,为后续变参数多层熔覆成形试验提供理论依据。
(2)深入研究稳定送粉状态下送粉量、激光功率及扫描速度对熔覆道几何尺寸和熔覆质量的影响规律,结果表明：送粉量范围0.5-2.5g/min,获得较好质量熔覆道；激光功率400W和送粉量2.0g/min组合有利于保证多层熔覆成形质量,每层Z轴提升量0.21mm；扫描速度500mm/min有利于保证成形制件综合性能；变送粉量法控制成形制件形状精度比较有效；最佳工艺参数组合熔覆成形获得致密、硬度580HV的熔覆道。
(3)针对机匣斜坡支板“2.5D”成形台阶效应问题,建立变厚度切片成形几何模型。0.5-2.5g/min内近连续增大送粉量,获得高度0.05-0.42mm近线性增大的单道单层熔覆层。采用Matlab仿真变厚度切片成形过程,规划正确扫描路径。通过变送粉量多层熔覆成形试验,成形出表面相对较光滑、形状较规则的斜坡薄壁件,有效减小了台阶效应。
(4)采用每层固定偏移0.05mm和0.026mm,分别获得了侧表面平整度较好的机匣内、外锥壳；选择直线形和圆弧形熔覆道扫描轨迹之间的较佳中心距0.67mm来搭接成形,实现了内、外锥壳与支板的良好连接。设计机匣整体成形激光扫描路径,每层变换成形起点,并改变Z轴提升量来配合变送粉量法成形,直接成形出具有规则斜坡和锥壳形状薄壁结构的机匣模拟件。采用变参数法和冷却等待法减小多层成形热累积效应,提高了机匣整体熔覆质量,结果表明：变参数法更有利于提高机匣整体成形几何尺寸精度。
The whole process is complex, difficult and of long period when manufacturing the aero-engine thin-walled casing with traditional methods. Besides, welding deformation is easily caused when web plates and conical shells are jointed by welding. As a result, not only geometrical precision but also properties of casing become bad. Technology of Laser cladding forming (LCF), which can flexibly manufacture metallic components with full metal density, functions and properties and specific geometry, can be used to manufacture the casing with high properties. However, under conditions of open-loop control and 3-axis CNC, stair-step effect is inevitable when "2.5D" forming process is performed and thermal cumulative effect is serious when multi-layer cladding process is carried out. So the formed ramp web plates of casing have bad geometrical precision and the casing has poor quality. The method with variable parameters is introduced into LCF. Proper parameters are selected and varied regularly in a good range. Consequently, geometrical precision and clad quality of the formed simulated casing is improved significantly. Study details are as followed:
(1) Key processes of forming thin-walled casing are analyzed and LCF of casing with variable parameters is designed. After deeply analyzing the process principle of forming with variable parameters, two key points are obtained. Process of varying powder feed rate approximately continuously can be considered as process closed-loop controlling powder feed rate so that stair-step effect can be reduced. On the other hand, process of varying laser power and scanning speed regularly can be considered as process closed-loop controlling melt pool so that thermal cumulative effect can be reduced. These two key points provide theoretical basis for the following experiment with variable parameters.
(2) Under the condition that metal powders are fed in stable state, influences of powder feed rate, scanning speed and laser power on clad dimensions and quality are deeply investigated. Results show that range of powder feed rate 0.5-2.5g/min achieves clad layers with good clad quality; good parameters combination of laser power 400W and powder feed rate 2.0g/min is appropriate for multi-layer cladding and Z-increment value is also determined to be 0.21mm; scanning speed 500mm/min makes the formed sample with good combination property; to improve geometrical precision of the formed sample, the method with variable powder feed rate is more effective than with variable scanning speed; clad layer with dense structure and micro-hardness 580HV is achieved by the good parameters combination.
(3) To prevent stair-step effect when layered forming ramp web plates of casing with 2.5D slices, a geometrical model forming with variable thickness slices is developed. While powder feed rate is varied at a calculated step approximately continuously, a single clad layer with height increasing near linearly to clad length is obtained. Clad height increases from 0.05mm to 0.42mm with powder feed rate varying from 0.5g/min to 2.5g/min. Correct scanning paths are planed by simulating the process forming with variable thickness slices through Matlab program. Using clad layer of variable height and the obtained scanning path, a relatively smooth ramp thin wall is formed by multi-layer cladding experiments. Result shows the method with variable powder feed rate reduces stair-step effect significantly.
(4) By offsetting fixed values of 0.05mm and 0.026mm every layer, inner and outer conical shells of casing are formed with good side surface smoothness respectively. By overlapping linear and circular clad layers and selecting center distances between linear and circular scanning tracks to be 0.67mm, joints of web plates and conical shells are formed with good properties and precision. Scanning path for forming the integral casing is designed. Starting point is changed every layer and Z-increment value is varied to match the method with variable powder feed rate. Consequently, the simulated thin-walled casing is directly formed with uniform ramp and conical thin-walled structures. Method with variable parameters and self-cooling are both used to reduce thermal cumulative effect and clad quality of the formed casing is improved significantly. Results also show that the method with variable parameters is more effective to improve geometrical precision of the formed casing.
引文
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