Wei Jun Liu

Influences of Processing Parameters on Dilution Ratio of Laser Cladding Layer during Laser Metal Deposition Shaping

Laser Metal Deposition Shaping (LMDS) is a state-of-the-art technology that combines rapid prototyping and laser processing. There are many factors affecting the quality, precision, microstructure and performance of LMDS-deposited parts. Among them, dilution ratio is a significant one since it is not only an important index to judge the laser cladding quality, but directly affects the interlayer bonding strength and performance quality of as-formed metal parts. Thus, the substantial LMDS experiments were performed to conclude the influence of processing parameters on dilution ratio of laser cladding layer. The results indicate that the influence degree of scanning speed is most significant, while that of laser power is relatively slight. In order to ensure the perfect forming quality and strong metallurgical bonding, it is necessary to choose suitable dilution ratio to accomplish the LMDS process.

Process Research on the Laser Rapid Manufacturing Technology

Laser additive direct deposition of metals is a new rapid manufacturing technology, which combines with computer aided design, laser cladding and rapid prototyping. The advanced technology can build fully-dense metal components directly from the information transferred from a computer file by depositing metal powders layer by layer with neither mould nor tool. Based on the theory of this technology, an experimental setup for laser rapid manufacturing process was developed. Through this state-of-the-art automated apparatus, some cladding experiments were performed to grasp the process features of laser rapid manufacturing technology. Finally, the columnar/equiaxed grain growth transition model is used to explain the morphology characteristic. Accordingly, the appropriate microstructure can be obtained by adjusting the processing parameters.

Experimental Study on Residual Stress in Titanium Alloy Laser Additive Manufacturing

The residual stress in laser additive manufacturing titanium alloy sample was measured using indentation stress measurement method. The residual stress variation formulas was fitted with the major process parameters such as laser power, scanning speed, the powder feed rate etc.. It was studied that the influence of processing layers and scanning corner on the specimen residual stress. The results show that the specimen residual stress increases first and then decreases with the increase of processing layers, and the maximum appears in the fiftieth layer, in addition, the residual stress in the side of corner sample is mainly pressure stress, the maximum appearing in the 150°scanning angle, the minimum appearing in the 120°scanning angle. Therefore, it can reduce the overall sample residual stress effectively by an obtuse angle scanning trajectory.

Effects of Processing Parameters on Powder Utilization Ratio during Laser Metal Deposition Shaping

The Laser Metal Deposition Shaping (LMDS) process involves injecting metallic powder into a molten pool created by a high power industrial laser. As the laser traverses across the substrate in a layer-by-layer fashion, a fully dense metal is left in its path. A few processing parameters involved with the LMDS include the laser power, traverse speed, powder feeding rate, and gas flow rate, etc, which affect many factors of LMDS technology. Among them, the powder utilization ratio is an important one because it directly determines the build rate and build height per layer. Due to some objective reasons, the powder utilization ratio is far less than 100%. In order to ensure the stability of LMDS technology, it is necessary to investigate the match between powder utilization ratio and build rate and forming efficiency, and grasp the influence rules of processing parameters on powder utilization ratio. Accordingly, the related experiments were performed with the varied laser power, scanning speed and powder feeding rate. The results prove that the powder utilization ratio is a varied value, and affected by the processing parameters. Consequently, the relative ideal parameter match should be chosen in accordance with the specific circumstances during the LMDS technology, thus ensuring the better powder utilization ratio and promoting the forming efficiency and economic benefit.

Laser Metal Deposition Shaping System for Direct Fabrication of Parts

The fabrication of metal parts is the backbone of the modern manufacturing industry. Laser forming is the combination of five common technologies: lasers, rapid prototyping (RP), computer-aided design (CAD), computer-aided manufacturing (CAM), and powder metallurgy. The resulting process creates part by focusing an industrial laser beam on the surface of processing workpiece to create a molten pool of metal. A small stream of powdered alloy is then injected into the molten pool to build up the part gradually. By moving the laser beam back and forth and tracing out a pattern determined by a CAD, the solid metal part is fabricated line by line, one layer at a time. By this method, a material having a very fine microstructure due to rapid solidification process can be produced. In the present work, a type of direct laser deposition process, called Laser Metal Deposition Shaping (LMDS), has been employed and developed to fabricate metal parts. The LMDS apparatus consists of four primary components: energy supply system, motion control system, powder delivery system, and computer control system. These components have their specified functions, but work in association with each other.

Model of End Milling Force Based on Undeformed Chip Surface with NURBS in Peripheral Milling

A new cutting force model for peripheral milling is presented based-on a developed algorithm for instantaneous undeformed chip surface with NURBS. To decrease the number of the differential element, the contact cutting edges of end-milling cutter with the part and the chip thickness curve are represented by NURBS helix, and the instantaneous undeformed chip is constructed as a ruled surface with the two curves. The cutting force generated by the edge contact length and the uncut chip area. Using the cutting coefficients from Budak[1] , the cutting-force model verified by simulation. The simulation results indicate that new cutting-force model predict the cutting forces in peripheral milling accurately.

Realtime Measurement of Temperature Field during Direct Laser Deposition Shaping

Direct laser deposition shaping is a state-of-the-art rapid prototyping technology. It can directly fabricate metal parts layer-by-layer without any die, mold, fixture and intermediate, just driven by the laminated CAD model. Accordingly, how to improve the quality of as-formed parts becomes an urgent issue in this research field. It is well known that as for the hot working, the heat history can generate enormous influence on the microstructure and mechanical properties of the parts. Due to the large quantity of heat introduced by laser fabrication process, it is necessary to build a temperature measuring platform to realtime monitor and control the temperature field in the laser fabrication process. As a result, such platform was created to communicate with computer by the temperature data collecting module and interface standard converting module, and achieved the temperature acquisition in the serial communication process through the Microsoft programming software. The experimental result proves the validity of the platform, which can provide effective boundary condition and experimental verification for the numerical simulation. In addition, the desirable temperature distribution can be obtained through the realtime process monitoring and effective parameter adjusting.

Measurement of Internal Residual Stress of the Laser Rapid Forming Parts by Incremental-Step Hole Drilling Method

In order to study the residual stress distribution in the titanium alloy laser rapid forming parts, the incremental-step hole drilling method is improved. Choose a calibration sample which has the same material as the test sample to conduct internal residual stress measurement by incremental-step hole drilling method. Conduct stress-release heat treatment (insulation 4 hours in 750 centigrade, furnace cooling) to the calibration sample before the measurement to uniform the internal stress. Calculate calibration compensation coefficient according to the calibration sample stress measurement result, and use the compensation coefficient to compensate the stress measurement result of the laser rapid forming sample. This method improves the reliability of internal residual stress measurement by incremental-step hole drilling method. Then use this method to measure the stress of laser rapid forming sample. The result shows that both the residual stress in the X direction and the Y direction is larger when the depth ranges from 1 mm to 3 mm. When the depth is greater than 3 mm, the residual stress decreases gradually with the hole depth increasing. The maximum value in the X direction is 147.13 MPa, and the maximum value in the Y direction is 236.32 MPa.

Research on Conceptual Design of Laser Shock Processing Equipment

In order to develop the laser shock processing equipment, the technical features and the design requirements are analysis. The concept scheme of laser shock processing equipment is built and the functions are defined. The technology and specifications is discussed relating to the concept scheme.

Concept Exploration on the Design Requirements and Design Scheme of Laser Shock Processing Equipment

In order to development the laser shock processing equipment, the technical features and process demand are analysis. The design requirements about laser shock processing equipment are discussed in detail by the methods of use case analysis and sequence diagram. Functional framework and technology architecture are put forward for the development of laser shock processing equipment. Finally, the equipment structure concept is given which is described for the future equipment design.