Laser Cladding Forming Of The Simulated Thin-walled Casing With Variable Parameters

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.