John O. Milewski

Directed light fabrication of a solid metal hemisphere using 5-axis powder deposition

Abstract Directed light fabrication (DLF) is a direct metal deposition process that fuses metal powders, delivered by gas into the focal zone of a high-powered laser beam, to form a fully-dense metal deposit. Computer-based design and numerical controls are used in conjunction with the metal deposition process to guide the formation of 3D parts. This study demonstrates the ability to directly fabricate complex shapes using a 5-axis DLF machine. As an example, the production of a hemispherical shape is described, with the associated fabrication case study, metallographic examination and part characterization. The deposition of fully-dense stainless-steel components is achieved in all orientations, from horizontal to vertical, and dimensional comparisons between the DLF-deposited shape and the original part definition, illustrates that near-net shape tolerance levels are attainable within a 0.1 mm envelope. The single-step production of fully-dense, near-net shaped, 3D metal parts directly from a computer model is achieved without the use of forming dies, tooling or machining. As a result, significant process flexibility over conventional processing capabilities are recognized, with potentially lower productions costs and higher quality components.

Heat transfer and fluid flow during electron beam welding of 21Cr?6Ni?9Mn steel and Ti?6Al?4V alloy

Electron beam welding (EBW) of two important engineering alloys, Ti–6Al–4V and 21Cr–6Ni–9Mn, was studied experimentally and theoretically. The temperatures at several monitoring locations in the specimens were measured as a function of time during welding and the cross-sections of the welds were examined by optical microscopy. The theoretical research involved numerical simulation of heat transfer and fluid flow during EBW. The model output included temperature and velocity fields, fusion zone geometry and temperature versus time results. The numerically computed fusion zone geometry and the temperature versus time plots were compared with the corresponding experimentally determined values for each weld. Both the experimental and the modelling results were compared with the corresponding results for the keyhole mode laser beam welding (LBW).Both experimental and modelling results demonstrate that the fusion zone size in Ti–6Al–4V alloy was larger than that of the 21Cr–6Ni–9Mn stainless steel during both the electron beam and laser welding. Higher boiling point and lower solid state thermal conductivity of Ti–6Al–4V contributed to higher peak temperatures in Ti–6Al–4V welds compared with 21Cr–6Ni–9Mn stainless steel welds. In the EBW of both the alloys, there were significant velocities of liquid metal along the keyhole wall driven by the Marangoni convection. In contrast, during LBW, the velocities along the keyhole wall were negligible. Convective heat transfer was important in the transport of heat in the weld pool during both the laser and the EBW. The computed keyhole wall temperatures during EBW at low pressures were lower than those during the LBW at atmospheric pressure for identical heat input.

Weld pool flows during initial stages of keyhole formation in laser welding

Weld pool transport phenomena during the transition from conduction-mode laser spot welding to keyhole laser spot welding of titanium were studied by numerical simulation. A range of laser powers were simulated and temperature dependent evaporation recoil pressure and cooling were applied as boundary conditions on the weld pool surface. Simulation results predicted a complex time-varying flow pattern during weld pool development. The surface-normal flow at the weld pool centre oscillated between upwards and downwards during the simulation time due to interaction of competing effects of evaporation recoil and surface tension pressures and laser heating and evaporation cooling. The results show that the laser weld pool flow dynamics play a key role during the transition from conduction-mode laser welding to keyhole welding.

DEVELOPMENT OF A NEAR NET SHAPE PROCESSING METHOD FOR RHENIUM USING DIRECTED LIGHT FABRICATION

Abstract Directed Light Fabrication (DLF) is a direct metal deposition process that fuses gas delivered powder, in the focal zone of a high powered laser beam to form fully fused near net shaped components. The near net shape processing of rhenium and refractory metals is currently in development and may offer significant cost savings compared with conventional processing. A full y associative 3D design through manufacturing model is presented for the application of DLF for the fabrication of a near net shaped nozzle part. This study describes the ability to move from a parametric 3D model integrated into a manufacturing model, creating a control file which can run on the DLF machine to produce a near net shaped metal component. Examples of DLF deposited rheniurn and iridium show a continuously solidified microstructure in rod and tube shapes. Entrapped porosity indicates the required direction for continued process development. These results demonstrate a new methodology for fabricating complex near net ...

Laser Powder Deposition of a Near Net Shape Injection Mold Core — A Case Study

Abstract Directed Light Fabrication (DLF) is a direct deposition process that fuses metal powder, in the focal zone of a laser beam, to form fully fused near net shaped components. A fully associative 3D design-through-manufacturing model is presented as a case study for the fabrication of a near net shaped injection mold core part. This study evaluates the ability to move from a parametric 3D model, integrated into a manufacturing model, to creating a control file used to produce a component using a nickel base alloy. Evaluation of the efficiency, quality, attributes and limitations of the process is reported. A high degree of accuracy for large feature location was obtained but improvements in surface finish and the dimensional accuracy of small features are required to fully realize benefits of this technology. The competing benefits of deposition accuracy and manufacturing time are discussed in terms of computerized numerical control code generation.

Measurement and Simulation of Residual Strain in a Laser Welded Titanium Ring

Elastic residual strains were measured in a laser welded commercially pure titanium ring using a non-destructive neutron diffraction technique in order to determine the resolution of this method for the characterization of small laser welds. In addition, these measurements were used to validate calculations made using residual strain data obtained from simulation of the residual stress near the weld. The measured strains were in good agreement with the simulated results.

Ferrite Scanning Microscope Based on Magnetic Tunnel Junction Sensor

We have developed a scanning magnetic microscope (SMM) based on a magnetic tunneling junction (MTJ) magnetoresistive (MR) sensor. The microscope is based on commercially available components employing two sets of scanning stages and a MTJ sensor. Spatial resolution and noise sensitivity were investigated using two MTJ sensors, one having high spatial resolution and the other low noise but coarser spatial resolution. We present measurements of magnetic field images from ferrite concentration calibration standards and a stainless steel welded specimen both imaged using a magnetoresistive scanning microscope. A sensitivity of ~ 10 μT/FN was obtained from standards with defined ferrite numbers (FN). This microscope represents a new powerful tool for the characterization and investigations of delta ferrite concentrations in stainless steel welded samples.

Additive Manufacturing of Metals

Springer Series In Materials Science Band 258 By John O Milewski ADDITIVE MANUFACTURING OF METALS THE TECHNOLOGY. ADDITIVE MANUFACTURING OF METALS THE TECHNOLOGY. METALS 3D PRINTING CLOSING THE COST GAP AND GETTING TO. NEW RESEARCH PUSHES BOUNDARIES IN METALS PRINTING GT AIR. SWEDISH ARENA FOR ADDITIVE MANUFACTURING OF METALS SWERIM. ADDITIVE MANUFACTURING OF METALS BY JOHN O MILEWSKI. ADDITIVE MANUFACTURING OF METALS FROM FUNDAMENTAL. ADDITIVE MANUFACTURING OF METALS FROM FUNDAMENTAL. ADDITIVE MANUFACTURING OF METALS FROM FUNDAMENTAL. METAL ADDITIVE MANUFACTURING ADDITIVE LAYER. ADDITIVE MANUFACTURING OF METALS FROM FUNDAMENTAL. ADDITIVE MANUFACTURING OF METALS FROM FUNDAMENTAL. WHAT IS METAL ADDITIVE MANUFACTURING RENISHAW. ADDITIVE MANUFACTURING OF

Trends in AM, Government, Industry, Research, Business

In this chapter, we identify current trends in government sponsored programs, universities, industry, and private enterprise, technology development, and adoption. Taking a higher level view we predict how the technology will connect these sectors and where we will see the greatest impact in the next 5 years. 3D printing and AM technology have been in development for at least the past two decades with the hard work of science and engineering being done at universities, national labs, and within corporate research labs. Advanced manufacturing has seen large investments on the order of billions of dollars driving a higher level of activity and high profile of media attention. The global impact of additive manufacturing is gaining momentum with high levels of funding seen at the government, university, and major corporation levels. Emerging economies are seeing the advantages of developing AM capabilities without the burden of historical infrastructures and as a potential means to leap frog the development of costly infrastructure or creating an advanced manufacturing infrastructure well suited to regional needs. Business, commerce, intellectual property, global, and social issues are discussed and reference leading national and global intelligence reports. The author concludes with a summary of the trends and destinations of highest impact for AM metal technology.

Building, Post-Processing, and Inspecting

The build cycle of an AM part can be broken down into prebuild operations, the actual build, post-processing, and inspection. This chapter provides the reader with a typical scope and sequence of operations and considerations associated with these operations. This knowledge is useful for those users considering the purchase and establishment of an AM system capability as well as those utilizing service providers. Knowledge of post-processing and finishing operations is critical to the design process and plays a critical role in subsequent design or process improvements. Operations such as powder recycling, heat treatment, hot isostatic pressing, machining, and surface finishing are discussed as well as the application of nondestructive and destructive evaluation and defect detection as applied to AM metal parts. Ongoing efforts within industry to draft standards and certify AM produced part are described.