CH715701B1 - Laser additive manufacturing system comprising a laser metal coating system and a synchronized laser polishing system. - Google Patents

Abstract

The invention relates to an additive manufacturing system which comprises a laser metal coating system and a laser polishing system. The laser metal coating system includes a z-axis movement system that includes a coaxial powder feed laser head (2), a rotatable processing platform (3), and an X-Y-axis cross slide connection platform (4). The laser polishing system includes a laser head (1). The powder feed laser head (2) and the laser head (1) of the laser polishing system are arranged in parallel along the Z-axis of the movement system. The cross slide connection platform of the X-Y-axis comprises an X-axis movement platform and a Y-axis movement platform, each of which can be driven by AC motors for a horizontal movement in the X and Y directions. The rotatable processing platform (3) is mounted on the Y-axis movement platform of the compound slide connection platform (4). The rotatable processing platform (3) comprises a support platform rotating about the X axis and a chuck rotating about the Z axis, each of which can be controlled by AC servo motors. The X-axis movement platform is installed directly below the two parallel laser heads (1), (2). The layers applied with the powder feed laser head (2) can be polished with the laser head of the laser polishing machine after each coating step, so that the surface roughness of the layers can be effectively reduced.

Description

Field of invention

The invention relates to the technical field of laser additive manufacturing systems, in particular to a synchronous laser polishing system based on the existing laser additive manufacturing.

Background of the invention

Laser Additive Manufacturing (LAM) is one of the most promising advanced manufacturing technologies, also known as three-dimensional (3D) printing. The parts are manufactured layer by layer so that it is the best solution for manufacturing a near-net-shape component. Not only is it used in the aerospace, power generation and biological medicine sectors, but it is also of very important strategic importance for the development-oriented manufacturing industry.

According to the various types of powder supply, LAM includes the laser metal plating process (LMD), which is characterized by the synchronous powder supply and the selective laser melting process (SLM), characterized by a powder bed. Among other things, the LMD process is combined with traditional turning or milling technology in order to fully exploit the advantages of various materials. In this way, an overall high performance is achieved with low costs for processing and manufacturing metal parts.

However, the dynamic properties of the temperature distribution and the solidification behavior of the molten bath during LMD technology have a direct influence on the microstructure and the mechanical properties. In particular, the fast melting and solidification speed of LMD means that the gas in the melt pool does not have enough overflow time and forms pores during the solidification process. High temperatures lead to splashes in the weld pool, so that the splash powder particles adhere to the sediment layer, which leads to poor interlayer bonding and large interlayer infusion defects. This not only creates a lateral step effect with poor accuracy and higher surface roughness, but also the stress concentration at the edge of the pores is often the crack initiation point, which limits the further practical application of the LMD technology.

As a new machining method, laser polishing (LP) has many advantages such as non-contact, micro-selective, precise or high-precision fine crystal hardening, environmental protection and high efficiency, which can increase the corrosion and fatigue resistance of various materials. It melts a thin surface layer again with a laser beam and then smooths the surface roughness by using the surface tension and gravity in the weld pool.

Recently, scientists at home and abroad have used LP technology to improve the surface accuracy of AM components and reduce their surface roughness. Yingchun Guan, et al. (Beihang University, China) investigated the microstructure and properties of laser-polished titanium alloys and nickel-based superalloys and reduced the surface roughness to less than 0.2 µm. E. Yasa and J-P. Kruth (University of Leuven, Belgium) used LP to reduce the surface porosity and roughness of AM 316L parts. S. Marimuthu, et al. (Coventry University, Great Britain) examined the influence of different LP parameters (scan speed, laser power, overlap rate, etc.) on the surface quality of AM Ti-6A1-4V B. Rosa, et al. (Institutde Recherche en Communications et Cybernetique de Nantes, France) examined the LP in 316L parts. D. Bhaduri, et al. (University of Birmingham, UK) used different laser energy densities to study the surface roughness of AM parts. Hong Kong Polytechnic University examined the LP in AM surface on Ti6A14V, Nickel 625 and CoCr alloy.

However, these LP of AM parts are mostly concentrated in the plane or the inclined plane, and the structure is relatively simple. Although K.C. Yung, et al. (Hong Kong Polytechnic University) performed LP on the concave surfaces of AM CoCr alloy parts, this study was laser polished after the AM parts were completed, which does not allow for a one-step machining mode in which AM and laser polishing are performed simultaneously. In addition, the LMD process is widely used to shape complex parts such as Self-supporting structures with large curvatures and curved inner / outer wall parts with a high depth-to-diameter ratio, which is often limited by the travel range of the polishing platform. As a result, the laser beam cannot reach the specified position during laser polishing, so that the optimal polishing parameters cannot be achieved. Although some foreign scientists adjust the angle of incidence of the laser beam by adjusting the scanning galvanometer, the scanning range of this type of angle of incidence is limited and can only reach ± 10 °. It should be noted that research into laser polishing as a cantilever having a structure with a large curvature and curved inner / outer wall parts with a high depth-to-diameter ratio is seriously insufficient.

Therefore, the development of a synchronized laser polishing machine based on the existing LAM with high polishing efficiency, high degree of automation, environmental protection, which improves the surface accuracy of complex LMD parts, can constitute a one-step laser polishing process, which has become an urgent problem for scientific researchers.

Summary

It is the object of the invention to provide a laser additive manufacturing system comprising a laser metal coating system (LMD) and a synchronous laser polishing system that covers the surface and the side area of the first layer, the second layer, the third layer, etc., or the N -th layer can polish at the same time as AM forming. And it forms a one-step machining mode where AM and laser polishing can be done at the same time. Not only can it solve the problem of large-area polishing of AM parts with a large curvature of the cantilever structure, but also the problem of the laser incidence angle for curved inner / outer wall parts with high depth-to-diameter ratio. Depending on the polishing of the individual deposition layers, the problem of powder splash and adhesion during the LMD deposition is effectively improved, which forms a good basis for the deposition of the next layer and effectively reduces the surface roughness of the finished LMD parts.

The invention relates to a laser additive manufacturing system comprising a laser metal coating system (LMD) and a synchronous laser polishing system. wherein the laser metal plating system comprises a Z-axis movement system, a rotatable processing platform, and an X-Y-axis compound slide connection platform, the Z-axis movement system including a coaxial powder feed laser head of an LMD system, the laser polishing system including a laser head of laser polishing; wherein the positions of the powder supply laser head and the laser head of laser polishing are arranged in parallel and along the z-axis, controlled by a laser metal plating system and a laser polishing system, respectively; wherein the rotatable processing platform, which is mounted on the cross slide connection platform of the XY-axis, with a support platform rotating around the X-axis and a chuck rotating around the z-axis, each controllable by two AC servo motors, and the one on the support platform installed lining; wherein the XY axis compound slide connection platform, an X axis movement platform, an AC servo motor that drives the horizontal movement of the X axis, a Y axis movement platform and an AC servo motor that drives the horizontal movement of the Y axis , includes; wherein the X-axis moving platform is installed directly below the two parallel laser heads, and the Y-axis moving platform is installed on the X-axis moving platform, and the rotary processing platform is installed on the Y-axis moving platform. Compared to the prior art, the invention has the following advantages: <tb> (1) <SEP> The invention combines the existing laser metal plating technology (LMD) with laser polishing technology, which covers the surface and side area of the first layer, the second layer, the third layer, etc., and the Nth layer, respectively can polish at the same time as the AM deformation. Not only can it solve the large area polishing problem with AM parts with large cantilever structure curvature, but also the laser incidence angle problem with curved inner / outer wall parts with high depth-to-diameter ratios. <tb> (2) <SEP> The invention effectively improves the problem of powder splatter and adhesion during LMD coating by polishing each coating layer, which forms a good basis for coating the next layer and improves the surface roughness of the finished LMD- Parts effectively reduced. <tb> (3) <SEP> The invention has a simple structure, high polishing efficiency, high degree of automation, environmental protection, which can reduce surface roughness and realize repetitive machining of a large area on complex LMD components, and it is easy to perform a to realize industrial application.

Brief description of the drawings

[0011] <tb> <SEP> Figure 1 is a schematic representation of the overall structure of the invention; <tb> <SEP> Figure 2 is a schematic representation of the rotatable machining platform of the invention; <tb> <SEP> Figure 3 is a structural diagram of the X-Y axis compound slide connection platform of the invention; <tb> <SEP> Figure 4 is a schematic representation of the polishing process of the invention; <tb> <SEP> Figure 5 is a schematic representation of metal parts having a cantilever structure with a large curvature; <tb> <SEP> Figure 6 is a schematic diagram of the inner / outer wall portions of the curved surface with high aspect ratio.

The names of the components in the figures are as follows: <tb> <SEP> 1- laser head of laser polishing; 2- LMD coaxial powder feed laser head; 3-turnable processing platform; 4- X-Y axis cross slide connection platform; 31-AC servo motor to control the rotation of the support platform; 32- support platform; 33 chuck; 34 AC servo motor to control the rotation of the chuck; 41 Y-axis motion platform; 42 X-axis motion platform; 43 AC servo motor for driving the Y axis; 44- AC servo motor for driving the X axis; 5- A metal part with a large bend of the cantilever structure; 6- metal substrate; 7- The inner / outer wall parts with curved surface with high depth to diameter ratio.

Description of the preferred embodiments

In order to better understand the content of the invention, the technical idea of the invention is combined with the accompanying drawings and specific embodiments in order to describe them in detail. The examples mentioned serve only to illustrate the invention and not to define the scope of protection of the invention.

This embodiment takes the machining of metal parts with a large curvature of a cantilevered structure (5) and a curved inner / outer wall part with a high depth-to-diameter ratio (7) as examples. Laser metal plating technology (LMD) is combined with laser polishing technology, and the working process is as follows: <tb> <SEP> First, a suitable metal substrate (6) is selected to be installed on the chuck (33), and the focal length of the coaxial powder delivery laser head (2) on LMD is adjusted so that it simultaneously hits the metal substrate (6) aims as shown in Fig. After selecting the appropriate overlap rate and scanning pattern, the LMD system and the synchronous powder feed system are started to perform the AM molding and the molding process is carried out under an inert protective gas. During the process of AM forming, the AC servo motor (43) and the AC servo motor (44) can control the Y-axis and the X-axis synchronously, respectively, to realize the horizontal movement of the rotary processing platform (3) and the Ensure effective implementation of each separation path. Second, when the first layer is finished, the LMD system and the synchronous powder feed system are suspended. Then the AC servo motor (44) is started to drive the X-axis moving platform (42) so that the rotating machining platform (3) and the Y-axis moving platform (41) move directly under the laser-polished laser head (1) as shown in Fig. 4. At this time, the laser polishing laser head (1) is adjusted to find the appropriate focal length, and the appropriate laser polishing parameters are selected. In addition, the first deposition layer is polished under an inert protective gas. Third, when the polishing is completed, the laser polishing system is suspended and the AC servo motor (44) started to drive the X-axis moving platform (42) so that the rotating processing platform (3) and the Y-axis moving platform ( 41) can be moved directly under the coaxial powder feed laser head (2) from LMD.

The second coating layer is thereby achieved. After the alternating cycle, the synchronous shaping of LMD and laser polishing is finally realized. When polishing the curved side surface of a metal part (5) with a large curvature or the curved inner / outer surface part (7) with a high depth-to-diameter ratio, the polishing angle of the LMD parts can be adjusted by driving the rotation angle of the support platform (32) or the Chuck (33) can be adjusted by driving the AC servo motor (31) and the AC servo motor (34), so that the respective deposition layer can be polished precisely until the entire part is machined.

Claims (1)

1. Laser additive manufacturing system comprising a laser metal coating system and a synchronous laser polishing system, wherein the laser metal coating system comprises a movement system of the Z-axis, a rotatable processing platform and a compound slide connection platform (4) of the X-Y-axis, wherein the movement system of the Z-axis comprises a coaxial powder feed laser head (2), wherein the laser polishing system comprises a laser head (1) for laser polishing; wherein the powder feed laser head (2) and the laser head (1) for laser polishing are arranged in parallel and along the z-axis of the movement system, wherein the rotatable processing platform (3) is mounted on the Kretizschlitten-connecting platform (4) of the X-Y axes, and comprises a support platform (32) rotating about the X axis on which a A chuck (33) rotating around the z-axis is installed, each of which can be controlled by AC servo motors, wherein the cross slide connecting platform (4) of the XY-axes is an X-axis moving platform with an AC servo motor that drives the horizontal movement of the X-axis, and a Y-axis moving platform with an AC servo motor that makes the horizontal movement the Y-axis drives includes; wherein the X-axis moving platform is installed directly below the two parallel laser heads, and the Y-axis moving platform is installed on the X-axis moving platform, and the rotating processing platform is installed on the Y-axis moving platform.