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Principles Of Enhanced Heat Transfer

Abstract This study presents an experimental investigation to improve Selective Laser Melting (SLM) regarding aspects such as surface roughness, density, precision and micro machining capability by employing secondary processes such as Selective Laser Erosion (SLE) and laser re-melting. SLM is a layered additive manufacturing technique for the direct fabrication of functional parts by fusing together metal powder particles. Laser re-melting, applied after each layer or only on the top surfaces, is used to improve the roughness and density while SLE, a subtractive process, is combined with SLM to improve the precision and micro machining capability.

Manufacturing by Combining Selective Laser Melting and Selective Laser Erosion / Laser Re-melting (Productie door het combineren van selectief laser smelten en selectief laser eroderen / laser hersmelten)

Hydroforming is a relatively new metal forming process with many advantages over traditional cold forming processes including the ability to create more complicated components with fewer operations. For certain geometries, hydroforming technology permits the creation of parts that are lighter weight, have stiffer properties, are cheaper to produce and can be manufactured from fewer blanks which produces less material waste. This paper provides a detailed survey of the hydroforming literature of both established and emerging processes in a single taxonomy. Recently reported innovations in hydroforming processes (which are incorporated in the taxonomy) are also detailed and classified in terms of “technology readiness level”. The paper concludes with a discussion on the future of hydroforming including the current state of the art techniques, the research directions, and the process advantages to make predictions about emerging hydroforming technologies.

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A state of the art review of hydroforming technology: its applications, research areas, history and future in manufacturing

Adding carbon black (CB) particles to elastomeric polymers is essential to the successful industrial use of rubber in many applications, and the mechanical reinforcing effect of CB in rubber has been studied for nearly 100 years. Despite these many decades of investigations, the origin of stiffness enhancement of elastomers from incorporating nanometer-scale CB particles is still debated. It is not universally accepted whether the interactions between polymer chains and CB surfaces are purely physical adsorption or whether some polymer–particle chemical bonds are also introduced in the process of mixing and curing the CB-filled rubber compounds. We review key experimental observations of rubber reinforced with CB, including the finding that heat treatment of CB can greatly reduce the filler reinforcement effect in rubber. The details of the particle morphology and surface chemistry are described to give insights into the nature of the CB–elastomer interfaces. This is followed by a discussion of rubber processing effects, the influence of CB on crosslinking, and various chemical modification approaches that have been employed to improve polymer–filler interactions and reinforcement. Finally, we contrast various models that have been proposed for rationalizing the CB reinforcement of elastomers.

https://www.mdpi.com/2073-4360/13/4/538/pdf

Nature of Carbon Black Reinforcement of Rubber: Perspective on the Original Polymer Nanocomposite

Flocculation plays an important role in reinforcement of silica filled rubber compounds, even if coupling agents are applied. It is well known that silica tends to flocculate during the early stages of vulcanization, when no dense rubber network has been formed yet. In the present study, flocculation was monitored by following the change in storage modulus at low strain, the so-called Payne effect, using a RPA2000 dynamic mechanical tester. The kinetic parameters: the rate constant and the activation energy of the silica flocculation were calculated according to the well-known Arrhenius equation. On basis of the value of the activation energy obtained for flocculation, it can be concluded that the silica flocculation is a purely physical phenomenon. Bound rubber measurements were also done in order to estimate the interfacial interaction layer between silica and polymer resulting from the coupling agent. The silica flocculation rate decreases with increasing interfacial interaction layer on the s...

Flocculation in Silica Reinforced Rubber Compounds

The directed energy deposition (DED) process can directly build full-density, high-performance, complex metal parts by melting metal powder with laser scanning. Functionally graded properties are characterized by gradual property variations over the volume according to the designed pattern. This study investigated the functionally graded properties obtained from DED of titanium powder. The formation of titanium nitride in the laser-melted layer has a strong potential to increase the hardness of the titanium alloy. Thus, the hardness of the deposited part was controlled by changing the concentration of nitrogen in the shielding gas. Furthermore, the effect of laser surface remelting on the deposited layer was investigated to control the surface qualities of the part, such as the roughness, hardness, and surface colour. From the analysis, a functionally graded part having variable hardness was obtained on a trial basis, and the proposed method is shown to be feasible with a high degree of reliability.

Functionally graded properties in directed-energy-deposition titanium parts

To produce highly functional tubular parts with locally different properties, tailor welded tubes (TWTs), which are made by tube-to-tube welding of tubes having different thicknesses or mechanical properties, are hydroformed. Notwithstanding the numerous applications of TWT hydroforming processes, TWT presents some disadvantages and considerable risk owing to the presence of a weld seam. This study proposes and characterizes the tailor layered tube (TLT) hydroforming process, which can fabricate hollow tubular parts with dissimilar thicknesses by using TLTs without welding. The proposed TLT hydroforming process was implemented and characterized both numerically and experimentally to validate its feasibility. The optimal loading path to prevent defects including insufficient bulging and wrinkle were analytically determined and verified by experiments. The deformation behaviors of TLT were also characterized at various processing parameters. The results demonstrate that the proposed TLT hydroforming process can be a feasible alternative for achieving tailored properties even with dissimilar thicknesses, with high reliability.

Tailor layered tube hydroforming for fabricating tubular parts with dissimilar thickness

The deformation characteristics of Al-Cu double layered sheet during rolling with various process parameters were studied by both a physical modeling technique and the finite element method. Physical modeling and the finite element method are complementary, due to their different advantages and limitations. Physical modeling simulates metal forming operations by using a model workpiece under conditions similar to those in actual production. The deformation characteristics of double layered sheet during rolling were also simulated using a commercial finite element code, FORGE™. The effects of process parameters, such as total reduction ratio, initial thickness ratio and differential speed ratio on the rolling characteristics were the primary focus of the investigation. In addition, an analytical model for double layered sheet rolling is also proposed with the use of a force-thickness diagram. From the results, the effect of the process parameters on the rolling of the Al-Cu double layered sheet has been determined.

Sang Wook Han

Papers

Functionally graded properties in directed-energy-deposition titanium parts

Tailor layered tube hydroforming for fabricating tubular parts with dissimilar thickness

Deformation analysis for cold rolling of Al-Cu double layered sheet by physical modeling and finite element method

Characterization of the longitudinal bow during flexible roll forming of steel sheets

Manufacturing of tailor-rolled blanks with thickness variations in both the longitudinal and latitudinal directions