Papers by Keyword: Direct Metal Deposition (DMD)

Abstract: This paper presents an investigation on laser direct metal deposition of tool steel on copper alloy substrate both directly and using high nickel stainless steel as buffer layer. The bond strength between the clad and the substrate has been investigated. Tensile testing was employed to measure the bond strength. The characteristics of the fracture surfaces have also been analyzed. Bond strength measurement revealed that the ultimate tensile strength of the substrate material was higher compared to the bond strength between the clad and the substrate. In addition, the experimental result revealed that use of high nickel stainless steel reduced the bond strength with substrate. However, the bond strength measured in this experiment between laser cladded tool steel and copper alloy substrate was much higher compared to the bond strength between these two metals coated using other techniques.

Abstract: This paper presents an investigation on the microstructure and surface hardness of the parts fabricated by laser assisted Direct Metal Deposition (DMD) technology. A series of engineering metallic alloy powders were used in the DMD process to produce simple 3D geometric structures. The alloy powders investigated include: 316L stainless steel, 420 Stainless Steel, Stellite(R) 6, tool steel (H13), Cholmoloy (Ni Based alloy), and Aluminium Bronze. These were chosen due to their frequent application in engineering parts and components. The microstructure and hardness values have been compared to those of the wrought products (as annealed) as reported in the SAE standards, Heat treater’s guide to metals ASM international, and material data sheets supplied by the materials manufacturers. A significant difference is reported in both hardness and microstructure of the laser deposited samples compared to those of the wrought form.

Abstract: A Ti-47Al-2Cr-2Nb (at.%) material was fabricated using two laser-based methods, “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD), for potential uses in aircraft jet engines. Experiments were conducted under controlled atmosphere by changing the processing parameters. Optimal parameters were searched for this relatively low ductility material to prevent cracking due to built-up residual stresses during fast cooling. It was observed that these non-equilibrium cooling conditions were fast enough to generate ultra fine and metastable structures exhibiting high microhardness values. Post heat-treatments were successfully used to restore homogeneous lamellar or duplex microstructures and to relieve the residual stresses. A comparison of these two methods is provided in terms of powder requirements and of process parameters to achieve noncracked structures and fully dense materials.

Abstract: The technological parameters of laser direct metal deposition (DMD) were researched by DMD forming experiments using 2Cr13 powder. Fixing other parameters, the lower of laser power, the smaller the characteristic sizes of cladding layer are. Increasing of laser power, cladding height would firstly increase and then decrease, cladding width would firstly increase and then almost maintain constant, while cladding depth would gradually increase. When other parameters are invariable, with increasing of powder feeding speed, cladding height would increase, cladding width and cladding depth would decrease. When other parameters are invariable, cladding width, cladding height and cladding depth would decrease with the adding of scanning speed. The microstructure of single track cladding had three typical patterns, cellular dendritic, column dendritic and equiaxed crystal. The patterns depended on the temperature gradient and the solidification velocity. Under different technical parameters, the average hardness of specimens would change from 300HV0.2 to 550HV0.2.

Abstract: Functionally Graded Materials (FGMs) are composite materials that have continuous material variation along with geometry. This paper introduces a method for FEA-based design and layered manufacturing (LM) of FGMs. An FGM solid model is first created by referring to the libraries of primary materials and composition functions. The model is then discretized into an object model onto which appropriate material properties are mapped. Next, the object model is adaptively meshed and converted into an FE model. FEA using ANSYS is finally performed to estimate stress levels. This FEA-based design cycle is repeated until a satisfactory solution is obtained. The object model is then fed to the fabrication system where a process planning is performed to create instructions for LM machines. As a laser-based LM method, Direct Metal Deposition (DMD) at the University of Michigan is briefly described. A specific example (FGM pressure vessel) is shown to illustrate the entire FEA-based design and DMD fabrication cycle.