Preform Geometry Research Articles

Interlayer-free laser coating of AISI H11 tool steel for H11/Cu composite material

Copper-based materials in combination with steels are of great interest for various applications in industry, such as tool manufacture, due to their high thermal conductivity. Additive manufacturing (AM) is beneficial for both tailored part geometry and customized material design. With laser-based AM, the copper-steel interface is highly prone to cracking. This study investigates a strategy of laser coating AISI H11 tool steel for a composite material consisting of AISI H11 tool steel and copper (H11/Cu) without using Ni-based interlayers. As an austenite stabilizing element, Ni dilution in H11 could lead to soft retained austenite, impeding wear resistance. The approach in this work employed presintering of tool steel powder to generate a porous H11 preform. Laser-based directed energy deposition (DED-LB/M) was used for coating H11 tool steel on the porous H11 preform followed by copper infiltration of the preform. The investigation of the effects of the main processing parameters: laser power, feed rate, and powder mass flow on the weld track geometry, clearly revealed different mechanisms when coating the porous preform compared to the conventional substrate. Defects at the coating/substrate interface such as cold crack formation were successfully avoided by adjusting the process parameters and process sequence. The developed processing strategy may in the future combine material extrusion of metals (MEX/M) and DED-LB/M to allow for intricate preform geometries and to generate H11 coatings on H11/Cu, respectively.

Improvement of the Technology of Precision Forging of Connecting Rod-Type Forgings in a Multiple System, in the Aspect of the Possibilities of Process Robotization by Means of Numerical Modeling.

The study refers to the application of numerical modeling for the improvement of the currently realized precision forging technology performed on a hammer to produce connecting rod forgings in a triple system through the development of an additional rolling pass to be used before the roughing operation as well as preparation of the charge to be held by the robot's grippers in order to implement future process robotization. The studies included an analysis of the present forging technology together with the dimension-shape requirements for the forgings, which constituted the basis for the construction and development of a thermo-mechanical numerical model as well as the design of the tool construction with the consideration of the additional rolling pass with the use of the calculation package Forge 3.0 NxT. The following stage of research was the realization of multi-variant numerical simulations of the newly developed forging process with the consideration of robotization, as a result of which the following were obtained: proper filling of the tool impressions (including the roller's impression) by the deformed material, the temperature distributions for the forging and the tools as well as plastic deformations (considering the thermally activated phenomena), changes in the grain size as well as the forging force and energy courses. The obtained results were verified under industrial conditions and correlated with respect to the forgings obtained in the technology applied so far. The achieved results of technological tests confirmed that the changes introduced into the tool construction and the preform geometry reduced the diameter, and thus also the volume, of the charge as well as provided a possibility of implementing robotization and automatization of the forging process in the future. The obtained results showed that the introduction of an additional rolling blank resulted in a reduction in forging forces and energy by 30% while reducing the hammer blow by one. Attempts to implement robotization into the process were successful and did not adversely affect the geometry or quality of forgings, increasing production efficiency.

Bayesian Optimal Experimental Design for Race Tracking in Resin Transfer Moulding

A Bayesian inference formulation is applied to the Resin Transfer Moulding process to estimate bulk permeability and race-tracking effects using measured values of pressure at discrete sensor locations throughout a preform. The algorithm quantifies uncertainty in both the permeability and race-tracking effects, which decreases when more sensors are used or the preform geometry is less complex. We show that this approach becomes less reliable with a smaller resin exit vent. Numerical experiments show that the formulation can accurately predict race-tracking effects with few measurements. A Bayesian A-optimality formulation is used to develop a method for producing optimal sensor locations that reduce the uncertainty in the permeability and race-tracking estimates the most. This method is applied to two numerical examples which show that optimal designs reduce uncertainty by up to an order of magnitude compared to a random design.

Preform geometry determination for a connecting rod forging by CEL model in Abaqus™

AbstractForging is a widely used manufacturing process, and its design and modeling are important to reducing production costs, increasing die lifespan, and improving the mechanical properties of the final product. In this study, the forging process of a connecting rod was modeled using 3D coupled Eulerian Lagrangian (CEL) analysis by FEM. The methodology adopted achieved to determine a preform geometry that reduces final flash and forging load, while ensuring complete filling of the stamp. Starting from the final geometry, the final die was designed. After the first result for an approximately 27% of flash, the material distribution was adjusted decreasing it at the regions where the flash was too large. After an iterative method was applied to determine better preform, a proposal was found that reduced forging force by approximately 42% and the percentage of flash volume by 64% in comparison with the first one. A final flash of about 10% is considered a good objective to reach. Lower values may cause many iterations, not a significant difference in forging loads, the risk of an unfilled die, and complex preform geometries.

High‐fidelity modeling of the braiding process for generating the realistic mesostructure of preforms in braided composites

AbstractAn accurate method for modeling the braided preforms is vital for the mesoscopic performance analysis of tubular composites. This study proposed a high‐fidelity virtual braiding model for the general braiding process, which further considers the fiber‐level deformation of the yarns during the braiding process to generate the realistic mesostructure of preforms in tubular composites. The method uses the digital element approach previously proposed for weaving processes to model the braiding yarn. The whole braiding process, including the deposition zone and convergence zone, is incorporated into the model to account for the effect of interaction in these zones on the preform mesostructure. Two braiding processes were simulated with the proposed virtual braiding method. The simulated geometry of the braided preforms and the yarn paths in the convergence zone agree well with the reported experimental results. To facilitate the performance analysis of braided composite structures, further automated generation of solid cell instances based on the obtained braided preforms was studied. Importantly, this work could reduce the considerable effort required for characterizing the mesostructure via the costly micro‐CT scans for braided composites, and the generated geometry of the braided preform is more precise than the widely used highly idealized models.

A framework for hybrid manufacturing cost minimization and preform design

This paper describes preform design optimization in hybrid additive-subtractive manufacturing. In hybrid manufacturing, the question of what form and what geometry the additive preform should take has largely been a matter of intuition and experience, or trial and error. The choice of a more optimal preform depends on the target parameters, such as stiffness, cost, or lead time. We demonstrate a framework for preform optimization using static stiffness, and then the combined cost of additive and subtractive manufacturing, while respecting stable cutting conditions for the tool-part combination. The procedure is illustrated by comparing three preform geometries for a thin wall.

Hybrid manufacturing of Invar mold for carbon fiber layup using structured light scanning

This paper describes coordinate system definition and transfer for five-axis machining of additively-manufactured preforms. In this method, a set of fiducials are attached to the temporarily attached to the part, and their location relative to the preform geometry is calibrated using a structured light scanner. Those fiducials can then be measured in the machine tool to determine the location and orientation of the part. The method is demonstrated by finish-machining a carbon fiber layup mold from an additively manufactured Invar preform. In addition to showing the coordinate transfer methods necessary to machine the part, several key challenges with machining additively-manufactured preforms are discussed and potential solutions are proposed. Unfortunately, the final part was ultimately unusable due to porosity inside the part left from the additive process. Future work will remanufacture this part while taking steps to avoid porosity and other challenges encountered.

Chaining of Compaction with Flow Simulations to Predict the Filling Behavior in Resin Transfer Molding Processes

Closed mold injection processes such as resin transfer molding have an increasing importance for manufacturing high quality carbon fiber reinforced parts at high production rates. One major challenge during this process is to avoid resin rich corners, which are a result of a non-uniform compaction of the preform in the tool. The objective of this work is to predict compaction defects in the preform and their effects on the filling behavior. We use numerical compaction simulations to calculate the preform geometry after tool closing, which is subsequently transferred into the infiltration simulation to model the filling behavior. Additionally, the fiber volume content and the material orientations are transferred from the mechanical simulation. Areas in the tool, which are not filled by the reinforcement, are modelled as flow channels with high permeability. The achieved results prove the significant influence of the compaction state on the filling behavior. The novel method supports the design of RTM tools and helps to optimize the manufacturing process.

Computational analysis of copper electrodeposition into a porous preform

Electroplating of metals into a porous preform with conductive walls is relevant in the fabrication of structural composites, fuel cells and batteries, and microelectronics. Electrodeposition process parameters, such as direct current or pulsed current, electric potential, and electrolyte concentration, as well as preform geometry, have important implications in the process outcomes including the filling process and the percentage of the infiltrated volume. Although electroplating into a vertical interconnect access (with nonconductive walls) for microelectronic applications has been extensively studied, the "flow-through" electroplating into a channel geometry with conducive walls has not been previously investigated. Here, copper infiltration into a such channel has been investigated using computational analysis for the first time. The effects of the inlet flow velocity, potential, electrolyte concentration, and microchannel geometry are systematically studied to quantify their influence on the electrodeposition rate, uniformity of the deposition front, and the infiltrated area within the channel. Computational results revealed that the unfilled area can be reduced to lower than 1% with a low applied potential, a high electrolyte concentration, and no inflow velocity. The results can be used to guide experiments involving electroplating metals into porous preforms toward reliable and reproducible manufacturing processes.

Microstructural and infiltration properties of woven preforms during chemical vapor infiltration

AbstractInterface‐resolved direct numerical simulations (DNSs) of chemical vapor infiltration (CVI) have been performed over a range of furnace‐operating conditions (Thiele moduli) and for practical woven preform geometries. A level‐set method is used to resolve the geometry of the initial preform at tow scale. The interface between the vapor and solid phase is then evolved in time through the entire CVI densification cycle, fully resolving the time‐varying topology between the two phases. In contrast to previous level‐set methods for CVI simulation, the physical reaction and diffusion processes govern the level‐set movement in the current approach. The surface deposition kinetics is described by the usual one‐step model. In this paper, the DNS data are used to study the evolving porosity, surface‐to‐volume ratio, and flow infiltration properties (permeability and effective diffusivities). Comparisons are made to popularly‐assumed structure functions and the standard, Kozeny–Carmen porous media model commonly employed in modeled CFD simulations of CVI. The virtual DNS experiments reveal a Thiele modulus and preform geometry (fabric layup) dependence which the existing microstructural and infiltration models are not able to describe throughout the entire densification process. The DNS‐based, woven geometry‐specific correlations can be applied directly to mean‐field, furnace‐scale CFD simulations.

Experience of QFormDirect software implementation for preform impressions design in hot closed die forging

The paper presents the method and the software QFormDirect developed for preform impressions design in hot closed die forging. The program allows automated creation of the preform geometry and the dies, which significantly reduces the occurrence of metal flow defects in a finished forged part. Verifying the developed preform dies is carried out by finite element simulation in the QForm software. Several industrial case studies that prove the proposed method and the effectiveness of the developed software are presented.

Chemical vapor infiltration of additively manufactured preforms: Pore‐resolved simulations and experimental validation

AbstractThe densification of additively manufactured porous preforms by chemical vapor infiltration (CVI) is studied using pore‐resolved simulations and experiments. Experimentally, 3D printed silicon carbide (SiC) preforms are subject to CVI synthesis using methyltrichlorosilane (MTS) precursor to obtain high purity SiC/SiC composites. Optical images of the cross sections of the processed preforms are analyzed to obtain the spatial porosity distribution. The numerical method is based on a level set formulation to capture the spatial distribution and time evolution of the pore scale microstructural characteristics. The coupled transport and kinetic effects are represented using a dimensionless Thiele modulus. Simulations are initialized using representative synthetic preform geometries comprising of packed particles based on the size distribution of the powder used for 3D printing. The simulation results are validated against the experimental observations in terms of total density and the distribution of residual porosity. The densification characteristics, porosity classification, concentration profiles, and structure functions are analyzed as functions of processing temperature and Thiele modulus.

A parameterised and integrated modelling method for plain-weave composite preform of a component with complex geometry

The mesoscopic model of fibre-reinforced composites can provide key geometric and material related information for predicting the mechanical properties of composite components. In this study, an approach to build a mesoscale preform of a plain-weave composite component with complex geometry was established. This was achieved via parameterisation and integration - with a set of parameters, related to the preform geometry, and a macroscopic geometrical model, of the composite component, as the inputs. In this method, tow centrelines were simulated as sinusoids in curvilinear coordinates. A simplified model of the tow section is proposed at the mesoscale. Based on this method, the geometry of the plain-weave preform at the mesoscale can be obtained integrally according to the macroscopic shape of the component input. The credibility of this proposed method was verified with similar microscopic observations and experiments conducted in other studies. The applicability of this approach to a more complex component was also investigated. Finally, a characteristic layer was established to analyse the material aperiodicity in a complex component.

Iterative hybrid manufacture of a titanium alloy component

This paper describes an iterative hybrid (additive + subtractive) manufacturing approach for a titanium alloy (Ti6Al4V) part using a laser hotwire directed energy deposition system (LHWDED) and a traditional four-axis milling machine tool. The term iterative hybrid manufacturing is used to described hybrid manufacturing where the additive and subtractive operations occur in multiple stages rather than sequentially. It is currently common to produce an entire part by sequential hybrid manufacturing by additively manufacturing (AM) an entire preform geometry that then requires post processing by another machine tool to create final part features. By contrast, a part produced by iterative hybrid manufacturing (IHM) does not produce the entire preform geometry in a single AM process. Instead, a portion of the entire preform geometry is manufactured by an AM process, then that portion is transferred to another machine tool which creates features in that portion, and then that machined portion is transferred back to the AM machine to complete another AM process. There is no limit to the number of iterations that an IHM process can have. IHM offers several advantages over sequential hybrid manufacturing such as the use of shorter and stiffer subtractive tooling, better access to part geometries that require subtractive processes, and the separation of the AM heat source from the subtractive machine tool. A titanium alloy demonstration part was successfully manufactured by IHM with three iterations using a shared pallet system between the AM machine tool and the subtractive machine tool.11Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Compaction, nesting and image based permeability analysis of multi-layer dry preforms by computed tomography (CT)

Textile preforms have a multi-scale hierarchy of fibres, tows and plies; geometry at each scale influences the manufacturing processes, the permeability of the textile to resin as well as the mechanical properties of the finished laminate. High-fidelity structural models for textile composites require accurate non-idealised tow geometry as well as changes to this geometry during processing. This paper presents a CT-based experimental technique for capturing the realistic meso-scale geometry of individual tows in a 2D fabric layer and the nesting or ply shifting between fabric layers in a multi-layer stack during a simulated consolidation process. An in-situ compression loading mechanism has been implemented in order to capture multi-layer preform geometry. Inter-tow and inter-ply void geometry has been captured in 3D due to high x-ray contrast between the fibres and the air. The degree of ply nesting and the connectivity between adjacent voids have been assessed at each stage of the compaction process. An image-based flow analysis has been performed on the extracted 3D realistic void geometry and the effect of layer nesting on resin flow has been evaluated. Image-based prediction of permeability values have been in good agreement with experimental values found in the literature when normalised as a function of fibre volume fractions.

Effect of preform design on forging load and effective stress during closed die hot forging process of pin

In hot forging process the design of preform is very important to minimize the forging load and effective stress to improve the die life and quality of components. In this paper three preforms have been designed with the rule of volume constancy for the pin’s head which are forged under 150 ton friction screw press. The forging load and effective stress have been analyzed by finite element analysis. The effects of preform volume and length to diameter ratio of preform geometry have been also analyzed and validated experimentally.

Metamodelling of the Correlations of Preform and Part Performance for Preform Optimisation in Sheet Moulding Compound Processing

In the design of parts consisting of long-fibre-reinforced Sheet Moulding Compounds (SMC), the potential for the optimisation of processing parameters and geometrical design is limited due to the high number of interdependent variables. One of the influences on fibre orientations and therefore mechanical part performance is the initial filling state of the compression moulding tool, which is defined by the geometry and positioning of the SMC preform. In the past, response surface methodology and linear regression analysis were successfully used for a simulation-based optimisation of rectangular preform size and position in regard to a part performance parameter. However, the computational demand of these increase exponentially with an increase in the number of design variables, such as in the case of more complex preform geometries. In this paper, these restrictions are addressed with a novel approach for metamodelling the correlation of preform and the resulting mechanical part performance. The approach is applied to predicting the maximum absolute deflection of a plate geometry under bending load. For metamodelling, multiple neural networks (NN) are trained on a dataset obtained by process and structural simulation. Based on the discretisation of the plate geometry used in these simulation procedures, the binary initial filling states (completely filled/empty) of each element are used as inputs of the NNs. Outputs of the NNs are combined by ensemble modelling to form the metamodel. The metamodel allows an accurate prediction of maximum deflection; subsequent validation of the metamodel shows differences in predicted and simulated maximum deflection ranging from 0.26% to 2.67%. Subsequently, the metamodel is evaluated using a mutation algorithm for finding a preform that reduces the maximum deflection.

Reconstruction of meso-structure and numerical simulations of the mechanical behavior of three-dimensional four-directional braided ceramic matrix composites

Textile-reinforced ceramic matrix composites are key structural materials for aerospace applications. In this paper, the influence of meso-structure and damage mechanisms on mechanical behavior of three-dimensional (3D) four-directional braided SiC/SiC composites is systematically investigated by using numerical simulations. First, periodic preform geometry model, also known as representative volume element (RVE), is reconstructed by using micro-computational tomography (μ-CT). Then, two damage mechanics models are employed to establish non-linear behavior of tows and matrix. Moreover, cohesive model is introduced to represent tow/tow and tow/matrix delamination behavior. It is noteworthy that homogenized tow model is derived from micromechanical model on fiber scale. Finally, macro stress-strain and failure behaviors of 3D braided SiC/SiC composites are simulated by meso-scale finite element analysis. Numerically simulated tensile modulus and strength of 3D braided SiC/SiC composites are compared with experimental results, exhibiting good consistency. Numerical simulations revealed failure mechanism and confirmed that, in addition to globally evolved damage process under tensile load, meso-scale preform caused stress concentration and subsequent local rupture behavior. Current research shows that reconstructed textile model realistically describes tensile mechanical behavior and damage evolution of 3D braided SiC/SiC composites.

An investigation on deformation mechanism of non-standard gear teeth forming in the hot impression forging of multicore cable cutter

On this study, a hot forging process in making non-standard gear will be experimentally as well as numerically researched and verified by simulation. The purpose of the research is to look for the crucial station of the finishing forging process and also to realize the particular non-standard gear teeth forming within the closed die hot impression forging associated with multicore cable cutter and replace the traditionally investment casting and open die forging counterparts. Furthermore, in order to make certain realize the non-standard gear teeth forming, the novel extrusion-forging teeth forming (EFT) approach is proposed and simulated from the commercially obtainable finite element software Qform 3D, the procedure parameters on the non-standard gear teeth forming are methodically analyzed and also carefully in contrast to experimental research. Based on consequents of the simulations, the distributions associated with forming, stress, strain, and temperature have been obtained to describe the microscopic phenomena. Accuracy from the numerical models have been verified by comparing with experimental dimensions. The proposed modified geometry from the forged preform has been finally proposed to to attain a similar forming situation while decreasing manufacturing expenses. The the extrusion-forging ratio (Rx=AxAm) and the fractional reduction in area (rx=1-AmAx) of the proposed EFT method can be calculated as R2 = 1.38 and r2 = 0.28 respectively for the modified geometry of preform 2. We expect that this advancement can provide a valuable and useful technical reference for the forging customized gears associated with any geometry.

Concept and validation of an active cooling technique to mitigate heat accumulation in WAAM

This work aimed at introducing and exploring the potential of a thermal management technique, named as near-immersion active cooling (NIAC), to mitigate heat accumulation in Wire + Arc Additive Manufacturing (WAAM). According to this technique concept, the preform is deposited inside a work tank that is filled with water, whose level rises while the metal layers are deposited. For validation of the NIAC technique, Al5Mg single-pass multi-layer linear walls were deposited by the CMT® process under different thermal management approaches. During depositions, the temperature history of the preforms was measured. Porosity was assessed as a means of analyzing the potential negative effect of the water cooling in the NIAC technique. The preform geometry and mechanical properties were also assessed. The results showed that the NIAC technique was efficient to mitigate heat accumulation in WAAM of aluminum. The temperature of the preforms was kept low independently of its height. There was no measurable increase in porosity with the water cooling. In addition, the wall width was virtually constant, and the anisotropy of mechanical properties tends to be reduced, characterizing a preform quality improvement. Thus, the NIAC technique offers an efficient and low-cost thermal management approach to mitigate heat accumulation in WAAM and, consequently, also to cope with the deleterious issues related to such emerging alternative of additive manufacturing.