Net Shape Parts Research Articles

Thixoforming of Aluminum A201- Expectations and Fulfilment

Thixoforming as a Semi-Solid Metal Processing (SSM) route is a near net shape forming of metals in the semi-solid state, i.e. within the freezing or melting range between the fully solid and fully liquid states. Aluminum A201 is a copper containing casting alloy with additional small quantities of magnesium, silicon and silver. Although this alloy is difficult to cast, it has a particularly high response to age-hardening and therefore offers mechanical properties close to the wrought 2014 alloy. Alloy development experiments carried out at the University of Sheffield on A201 alloy have shown that feedstock of this alloy can be produced having uniform non-dendritic microstructures amenable to thixoforming, exhibits thixotropic properties under these conditions, can be shaped into complex near net-shape parts and develops impressive mechanical properties after appropriate heat treatment. A201 aluminum alloy billets when thixoformed in the semi-solid state and heat treated with a T7 followed by T6 treatment before being mechanically tested, have exhibited properties approaching those of wrought 2000 series aluminum alloys. Here follows a review of work done to date on shaping the A201 aluminum alloy in the semi-solid state, describing the hopes, expectations and fulfilment of researchers in the field.

A high strength low alloy steel fabricated by direct laser deposition

Direct laser metal deposition (DLMD) can produce near net shape parts by layer-by-layer deposition of metallic powders. In the present study, DLMD was used to fabricate a high strength low alloy (HSLA) steel. The characteristics of the microstructure and mechanical properties of the as-built HSLA were characterized using optical microscopy, electron back-scatter diffraction (EBSD), transmission electron microscopy, and tensile test machine respectively. It was found that the optimized parameters ensured a high quality of the built samples. The as-built HSLA steel was mainly composed of α-Fe (Ferrite) phase with a trace of C6Cr23 and Fe3C phases. TEM result proved the formation of martensite phase. Most grain boundaries misorientation angles were low-angle grain boundary which elevated the strengthening effect. Tensile strength, yield strength, and elongation of the as-deposited HSLA were comparable with other high-performance alloy steels. The present results show the potential of DLMD for the fabrication of a HSLA with excellent mechanical properties.

Kesan Pembentukan Tikso terhadap Mikrostruktur dan Sifat Mekanik Aloi Al-Si-Cu-Mg

Forming of metals in their semi-solid state is one of the options for producing near net shape parts. It can produce a strong and highly reliable product. Al-Si-Cu-Mg casting alloy is commonly used in automotive engine components which is now widely used in the semi-solid processing. The main physical properties of the aluminium alloy and alloying element content such as silicon, copper and magnesium, plays an important role in determining the mechanical properties of the alloy. In this paper, the effect of the formation process of Al-Si-Cu-Mg permanent die casting alloy and the thixoforming process has been investigated towards the evolution of microstructure and mechanical properties. Compound phases, shapes and morphology of the two processes were compared. The porosity effect was examined at permanent die castings and thixoforming process. The result of image analysis showed significant change of the thixoforming process of α-aluminum solid phase structure in spherical shape. Size and morphology, as well as the uniformity of the silicon eutectic phases and intermetallic compound distributions of Al2Cu, Al5Fe Si and Al15(Mn,Fe)3Si2 changed due to the compression during thixoforming process. Thixoforming process of the Al-Si-Cu-Mg alloy exhibit the lowest percentage and microporosity area thus proved that porosity issue significantly reduced during the aluminium alloy solidification process in thixoforming process . The tensile properties of thixoformed alloy improved significantly with its ultimate tensile strength, yield strength, and elongation to fracture at 193MPa, 163MPa and 1.6%,respectively.

Automated post machining process planning for a new hybrid manufacturing method of additive manufacturing and rapid machining

PurposeThe purpose of this paper is to present a new method for automated post machining process planning for a hybrid manufacturing process. The manufacturing process is expected to generate complex functional parts by taking advantage of free form surface creation from additive manufacturing and high-quality surface finishing from CNC milling.Design/methodology/approachThe hybrid process starts with additive manufacturing to generate a near net shape part with pre-defined machining allowances on surfaces requiring high quality surface or tight tolerances, along with integrated fixture geometry. The next step is to conduct automated machining process planning to determine critical parameters such as setup angle, tool selection, depth, tool containment, and consequently, the NC code to machine the part.FindingsThis method is shown to be a feasible solution for rapidly creating functional parts. The tests have been conducted to validate the method developed in this paper.Originality/valueThis paper introduces a new automated post machining process planning method for integrating additive manufacturing with a rapid milling process.

Highly porous Fe-2wt%P alloy produced by plasma assisted debinding and sintering of injection-molded parts

Metal Injection Molding is a well-known powder metallurgy technology, which allows net-shaped parts to be produced with a high degree of automation and reduced costs in large-scale production. However, shape retention during sintering of porous parts remains a challenge. The present study demonstrates that plasma assisted debinding and sintering of injection-molded parts is a promising route for manufacturing highly porous Fe-P-based parts, improving porosity amount and dimensional accuracy, avoiding surface distortion of injection-molded parts while decreasing processing time. In this study, the effect of plasma sintering was analyzed regarding dimensional accuracy, porosity, phase composition and microstructure of highly porous Fe-2wt%P parts.

Anisotropy of nickel-based superalloy K418 fabricated by selective laser melting

Selective laser melting (SLM) is a promising additive manufacturing (AM) technology for fabricating the near net-shaped parts by selectively melting and solidifying a thin powder layer with a high-intensity laser beam according to the CAD data for arbitrary components. In this work, Ni-based superalloy K418 samples were fabricated by selective laser melting (SLM). To evaluate the anisotropic mechanical behavior of the SLM processed K418 samples with layer-by-layer melting, the samples were manufactured parallel (transverse specimens) and vertical (longitudinal specimens) to the building direction on the substrate. The microstructural anisotropy analysis was performed by optical microscopy (OM) and scanning electron microscopy (SEM). Electron backscatter diffraction (EBSD) analysis was used to identify their crystallographic preferred orientation (texture) and to correlate the anisotropy of the mechanical strength with the texture of the material. The results showed that the transverse specimens had slightly higher yield strength, but much significantly higher ductility than that of the transverse specimens with the elongated columnar grains along the building direction.

From Powder to Solid: The Material Evolution of Ti-6Al-4V during Laser Metal Deposition

The additive manufacturing of titanium parts by laser metal deposition (LMD) offers a promising alternative to conventional machining of aviation parts. The technology enables the production of near net shape parts with higher deposition rates than powder bed-based processes. Ti-6Al-4V powder is fed directly into a high-power laser beam in order to form a deposition track on the underlying material. For three dimensional parts several tracks are stacked on top of each other. In this paper the material evolution from powder to a solid wall during LMD is investigated. Powder properties as well as the microstructure in deposited structures are thoroughly described and analyzed. The gained knowledge provides a deeper process comprehension and is an important step towards high-quality additive manufacturing of Ti-6Al-4V. At first, the influence of powder particle size on the LMD process is quantified by creating two powder fractions with different sieving procedures. The used material is recycled Ti-6Al-4V powder from a powder bed-based AM process with particle sizes up to 150 µm. The powder is characterized according to current standards; apparent density, tap density and the flowability are determined as well as the particle size distribution. Additionally, the particle morphology is analyzed using electron beam microscopy. In order to link the powder properties to the LMD process and to identify impact factors to the feeding behavior the mass flow of both powder fractions is measured. Secondly, walls are manufactured with the characterized powder and the resulting microstructure is analyzed. Because of the layer-wise deposition and the resultant periodic heat input each layer experiences several thermal cycles. As a result various solid phase transformations occur during the deposition of consecutive tracks. In addition the thermal boundary conditions change with increasing wall height and a heterogeneous microstructure is observed. It consists of non-equilibrium phases (martensitic or massive α) and α+β lamellae. Based on an existing numerical model the thermal history of each layer is estimated and an explanation is presented for the complex sequence of solid phase transformations in each area of the structure.

4D printing of net shape parts made from Ni-Mn-Ga magnetic shape-memory alloys

This work investigates an additive manufacturing route of producing functional net shaped parts from pre-alloyed magnetic shape-memory Ni-Mn-Ga powders. Three types of Ni-Mn-Ga powders were used in this investigation: spark eroded in liquid nitrogen (LN2), spark eroded in liquid argon (LAr), and ball milled (BM). Additive manufacturing via powder bed binder jetting, also known as 3D printing (3DP), was used in this research due to both relatively easy control of part porosity and the possibility to obtain complex shaped parts from Ni-Mn-Ga alloys. The four-dimension (4D) is created by the predictable change in 3D printed part configuration over time as the result of shape-memory functionality. Binder jetting of Ni-Mn-Ga powders followed by curing and sintering proved successful in producing net shaped porous structures (spring-like, 3-D hierarchical lattice structures, etc.) with good mechanical strength. Parts with porosities between 24.08% and 73.43% have been obtained by using powders with distinct morphologies. The printed Ni-Mn-Ga parts undergo reversible martensitic transformation during heating and cooling, which is a prerequisite for the shape-memory behavior. Thermo-magneto-mechanical trained 3D printed parts obtained from ball milled Ni-Mn-Ga powders showed reversible magnetic-field-induced strains (MFISs) of up to 0.01%. The additive manufacturing is a viable technology in solving the design issues of functional parts made of Ni-Mn-Ga magnetic shape-memory alloys (MSMA).

Evolutionary-based optimization strategy in a hybrid manufactured process using LMD

We investigate a hybrid manufacturing strategy combining laser metal deposition (LMD), and milling or turning. LMD is an additive manufacturing process, which can be used for surface cladding, repair, and 3D build-up of parts. One of its advantages is the creation of near net-shape parts on variable ground geometries.The strategy focusses on manufacturing a part by choosing the appropriate wrought material with the remaining volume being added by LMD to minimize used resources and manufacturing time. This is done by adapting an evolutionary algorithm that varies the size, orientation, and position of wrought material with respect to the remaining volume.

Prediction of fracture in cold forging with modified Cockcroft-Latham criterion

Cold forging technology provides production of net shape parts that required very little or no further machining. Meanwhile one of the technological problems of the cold forging is fracture of the workpiece during production. This is especially important when using less ductile high strength materials or technological schemes that require significant deformation. The use of reliable fracture criteria implemented in metal forming software can help predict possible cracks and find ways to avoid them. There are many criteria that can be used for this task, for example, Gurson and its modifications, Johnson-Cook, Wierzbicki and Cockcroft-Latham. The latter one is the most widely used due to its simplicity since only the first principal component of stress is required for calculation. On the other hand, in this simple form, it does not take into consideration the influence of the stress state and the path of plastic deformation. In the presented work, a comparative analysis of different criteria has been done to find out the relations among them and a modified Cockcroft-Latham criterion of fracture has been proposed. It considers both the influence of the normalized first principal stress and the influence of the stress state scheme. A new approximation of the surface of critical plasticity has also been proposed that considers the limit values of the normalized average stress. The modified Cockcroft-Latham criterion was programmed as a subroutine in QForm metal forming simulation software and it has shown good accuracy in tests for different practical cold forming processes.

Additive manufacturing of compositionally gradient metal-ceramic structures: Stainless steel to vanadium carbide

Processing of hard, refractory ceramic coatings in a metal matrix is challenging due to various factors including delamination or cracking due to large material property differences at the interphase, and non-uniform distribution due to improper mixing. These issues can be reduced or even eliminated if the coating had a gradual change in material properties from the surface to the inside. Additive manufacturing is now being looked at to accomplish compositional control beyond the ability to produce net shape parts for repair as well as adding functionality. In this study, laser engineered net shaping (LENS™) was used to manufacture compositionally gradient structures of vanadium carbide (VC) and stainless steel 304 (SS304). Compositions ranging from 5 to 100wt% of VC were mixed with SS304. The internal stress from the carbides significantly increased the hardness and wear resistance of the coatings. The 100%VC outer layer increased the hardness by 1450HV and lowered the wear rate by 95% compared to SS304 substrate.

Enhanced mechanical properties of additively manufactured bulk metallic glasses produced through laser foil printing from continuous sheetmetal feedstock

Metal additive manufacturing (AM) is a rapidly growing field aimed to produce high-performance net-shaped parts. Therefore, bulk metallic glasses (BMGs), known for their superlative mechanical properties, are of remarkable interest for integration with AM technology. In this study, we pioneer the utilization of commercially available BMG sheetmetal as feedstock for AM, using laser foil printing (LFP) technology. LFP and traditional casting were used to produce samples for four-point bending and Vickers hardness measurements to rigorously compare the mechanical performance of samples resulting from these two fabrication techniques. Through LFP, fully amorphous BMG samples with dimensions larger than the critical casting thickness of the same master alloy were successfully made, while exhibiting high yield strength and toughness in bending. This work exemplifies a potential method to fabricate high-value BMG commercial parts, like gears or mechanisms, where the parts are conventionally machined after printing, and greatly benefit from utilizing novel materials.

Automated Defect Recognition as a Critical Element of a Three Dimensional X-ray Computed Tomography Imaging-Based Smart Non-Destructive Testing Technique in Additive Manufacturing of Near Net-Shape Parts

In this paper, a state of the art automated defect recognition (ADR) system is presented that was developed specifically for Non-Destructive Testing (NDT) of powder metallurgy (PM) parts using three dimensional X-ray Computed Tomography (CT) imaging, towards enabling online quality assurance and enhanced integrity confidence. PM parts exhibit typical defects such as microscopic cracks, porosity, and voids, internal to components that without an effective detection system, limit the growth of industrial applications. Compared to typical testing methods (e.g., destructive such as metallography that is based on sampling, cutting, and polishing of parts), CT provides full coverage of defect detection. This paper establishes the importance and advantages of an automated NDT system for the PM industry applications with particular emphasis on image processing procedures for defect recognition. Moreover, the article describes how to establish a reference library based on real 3D X-ray CT images of net-shape parts. The paper follows the development of the ADR system from processing 2D image slices of a measured 3D X-ray image to processing the complete 3D X-ray image as a whole. The introduced technique is successfully integrated into an automated in-line quality control system highly sought by major industry sectors in Oil and Gas, Automotive, and Aerospace.

Functionally Graded Stainless Steel Fabricated by Direct Laser Deposition: Anisotropy of Mechanical Properties and Hardness

Direct laser metal deposition is a kind of advanced rapid manufacturing technology, which can produce near net shape parts by depositing metal powders layer by layer. This study demonstrates fabrication, the anisotropy of mechanical properties and hardness of a graded steel. The characteristics of constituent phases, microstructure, mechanical anisotropy, and microhardness were investigated using electron backscatter diffraction, optical microscopy, tensile test machine, and microhardness tester. It was found that the graded steel is dense and free of cracks. The crystal structures of the as-built samples evolved in three grades from fcc structures to fcc + bcc structures and then to bcc + fcc structures. Samples in x and z directions showed obvious mechanical anisotropy. The samples machined in x direction showed higher strength and lower elongation than those machined in z direction due to the presence of lack-of-fusion pores and the higher metallurgical bonding between layers in the x direction. The microhardness of the as-built samples increased along the cross section from the substrate (159.7 HV) to the top surface (545.4 HV).

Trend of DED type Additive Manufacturing Technology for Titanium

Titanium is an important material used throughout the aerospace, power generation, and medical industries with its high specific strength and excellent corrosion resistance. In recent years, the use of net shape parts has become possible due to the progress of the additive manufacturing process. In this paper, we investigated the characteristics of titanium applied in the directed energy deposition(DED) process in various additive manufacturing processes and tried to search for recent trends. Among titanium materials, CP Ti and Ti-6Al-4V alloy are the most widely used, and most of them are supplied in powder or wire forms. By using these materials, it can be melted by a heat source such as laser, electron beam, arc, plasma, etc., and it is possible to determine the additive speed according to the size and precision of a desired part. The DED process is being developed in a large-scale and complex system because it has the advantage of building large and repairing parts. Compared with advanced countries in the world, the domestic aerospace industry has not been yet developed, but it is expected to grow together with the development of additive manufacturing processes. Key words: Titanium, Additive manufacturing, DED(Directed Energy Deposition), Coaxial powder deposition

Design for Wire + Arc Additive Manufacture: design rules and build orientation selection

ABSTRACTWire + Arc Additive Manufacture (WAAM) is an additive manufacturing technology that can produce near net-shape parts layer by layer in an automated manner using welding technology controlled by a robot or CNC machine. WAAM has been shown to produce parts with good structural integrity in a range of materials including titanium, steel and aluminium and has the potential to produce high value structural parts at lower cost with much less waste material and shorter lead times that conventional manufacturing processes.This paper provides an initial set of design rules for WAAM and presents a methodology for build orientation selection for WAAM parts. The paper begins with a comparison between the design requirements and capabilities of WAAM and other additive manufacturing technologies, design guidelines for WAAM are then presented based on experimental work. A methodology to select the most appropriate build orientation for WAAM parts is then presented using a multi attribute decision matrix approach to compare different design alternatives. Two aerospace case study parts are provided to illustrate the methodology.

The Development of Lead-Free Sliding Contacts Based on Bronze-Graphite Composites through Powder Injection Moulding

Sliding electrical contacts are traditionally produced by conventional compacting technologies. Employing the powder injection moulding process (PIM) as a new manufacturing method can offer several advantages such as the fabrication of complex net-shaped parts, cost-effectiveness and high volume productions. The PIM process route consists of the following steps: powder processing, compounding, injection molding, debinding and sintering. A two-stage process consisting of solvent debinding and thermal debinding is often used to remove the moulding binder. In the present paper, the suitability of the powder metallurgical processes: mechanical alloying and powder mixing for the preparation of bronze-graphite powder mixtures for the compounding and injection moulding of sliding contacts is discussed. The use of a suitable binder is of central importance for the preparation of injection-moldable feedstocks. For this purpose, two commercial ready-to-use binder systems were utilized and evaluated. The essential challenge of the process route is to optimize all parameters of the subprocesses to achieve a damage-free debinding and sintering of the injection-moulded parts. First results on the influence of the graphite content, the binder fraction, the debinding and sintering parameters are presented and discussed.

Characterization of the anisotropic properties for laser metal deposited Ti-6Al-4 V

Laser metal deposition (LMD) connected with milling processes offers the opportunity for an efficient, resource conserving manufacturing for large structural components made from Ti-6Al-4 V. Conventional manufacturing routes for example in the aerospace industry come along with up to 95% of the waste material that has to be machined from the bulk material. LMD is an additive manufacturing process building parts based on nozzle-fed powder by laser solidification. This technology offers unique advantages for the production of near net-shape parts. In contrast to the powder bed-based technologies, it also provides a higher productivity rate. Today, LMD lacks reproducible process strategies manufacturing large parts in narrow tolerances and predictable microstructural properties. The building height of a single layer and the geometrical shape of a three-dimensional shaped part alter progressively with increasing part dimensions, consecutively leading to a higher effort in the manufacturing-process development for such parts. To reduce this effort, in this paper, first the actual state of the anisotropic properties is investigated for LMD-manufactured parts to obtain thorough knowledge of the process and shape-related dependencies with the quality aims. A preliminary experimental investigation of the shape and process-dependent properties such as the microstructure (chemistry changes and grain sizes), mechanical properties (hardness), and geometry (tolerances) is conducted. Based on these results, an in-depth study with optimized parameter sets is carried out to identify the linkage between geometry, process parameters, and the quality criteria of the part, using methods such as light microscopy, inductively coupled plasma-mass spectrometry, Vickers hardness, coordinate measuring, and laser scanning microscopy. For this purpose, representative shaped specimens are manufactured with the LMD-process through different optimized process strategies. The results give the opportunity to evaluate the impact of process parameter changes and the shape on the part quality such as mechanical properties, surface quality, and element loss. This is achieved through identifying the relationship between the input and the output factors from the experimental study, and their importance for part quality is assessed. It is shown that the complex correlation between the process parameters, the part geometry, and the resulting quality can be controlled with suitable process design in LMD-manufacturing of Ti-6Al-4 V parts. Finally, based on the summarized results, an outlook is given on tolerances for different quality aims.

Overview on Additive Manufacturing Technologies

This paper provides an overview on the main additive manufacturing/3D printing technologies suitable for many satellite applications and, in particular, radio-frequency components. In fact, nowadays they have become capable of producing complex net-shaped or nearly net-shaped parts in materials that can be directly used as functional parts, including polymers, metals, ceramics, and composites. These technologies represent the solution for low-volume, high-value, and highly complex parts and products.

Influence of the Direct Metal Laser Sintering Process on the Fatigue Behavior of the Ti6Al4V Alloy

Direct Metal Laser Sintering (DMLS) is additive manufacturing (AM) process that can produce near net shape parts from metal powders such as titanium alloys. DMLS is a layer by layer additive manufacturing technique based on high power fiber laser that creates solid layers from loose powder material and joins them in an additive manner. The specific DMLS process conditions, lead to a specific and complex microstructure and to mechanical properties that show a degree of directionality. It was found that microstructural characteristics are related to the building process parameters. The aim of this work is to evaluate the fatigue performance of the Ti6Al4V alloy depending on the process parameters, building orientations and post-process heat treatment.