Process chain simulation of laser powder bed fusion including heat treatment and surface hardening

Additive manufacturing (AM) has enabled the creation of geometrically complex parts for a range of industries. However, the nature of AM often requires multiple post processing techniques to be carried out to reach the desired material properties or required surface finish. This often involves heat treatment (HT), shot peening (SP) or laser shock peening (LSP). To date, hardly any process chain modelling has been carried out on manufacturing applications with AM. This investigation focuses on the finite element (FE) modelling of the complete manufacturing process chain of an AM impeller made of IN718, including the AM, HT, LSP and SP processes. The particular AM process applied to build the impeller is laser powder bed fusion (L-PBF). Each FE process is validated individually against experimental data before being applied to the impeller process chain. The validated data from each process is mapped to the next process in the chain to investigate the combined effects of manufacturing and post processing techniques. Results have shown that high tensile residual stresses induced by AM can be reduced by approximately 75% by applying HT. SP and LSP processes can further modify remaining tensile residual stresses after HT by inducing a layer of compressive stresses at the surface. In summary, this research work has demonstrated that the simulation of AM process chains using finite element techniques is sufficiently mature to support the product and process development of industrial AM components

Behaviour of a biocompatible titanium alloy during orthogonal micro-cutting employing green machining techniques

The sustainability of a process is the objective of modern industries aiming to reduce waste in production, since consumers require high quality and efficiency with fair price. Thus, a good understanding of the process should be its starting point. The manufacture of dental implants is an example in which waste reduction is important for the reduction of prices due to the demand for great quality and accuracy. This study observed the behaviour of sustainable micro-cutting applied to the Ti-6Al-7Nb titanium alloy, considering the ploughing effect on minimum quantity lubrication (MQL) and high-speed machining (HSM) conditions. When compared with dry condition and low-speed cutting in orthogonal micro-cutting, the use of HSM in dry cutting was more efficient than using MQL. The dry condition presented lower surface roughness, whilst the cooled/lubricated condition presented lower burr formation.publishe

An in-core grid index for transferring finite element data across dissimilar meshes

The simulation of a manufacturing process chain with the finite element method requires the selection of an appropriate finite element solver, element type and mesh density for each process of the chain. When the simulation results of one step are needed in a subsequent one, they have to be interpolated and transferred to another model. This paper presents an in-core grid index that can be created on a mesh represented by a list of nodes/elements. Finite element data can thus be transferred across different models in a process chain by mapping nodes or elements in indexed meshes. For each nodal or integration point of the target mesh, the index on the source mesh is searched for a specific node or element satisfying certain conditions, based on the mapping method. The underlying space of an indexed mesh is decomposed into a grid of variable-sized cells. The index allows local searches to be performed in a small subset of the cells, instead of linear searches in the entire mesh which are computationally expensive. This work focuses on the implementation and computational efficiency of indexing, searching and mapping. An experimental evaluation on medium-sized meshes suggests that the combination of index creation and mapping using the index is much faster than mapping through sequential searches

Chatter modelling in micro-milling by considering process nonlinearities

AbstractThis paper presents a new approach for chatter modelling in micro-milling. The model takes into account: the nonlinearity of the uncut chip thickness including the run-out effect; velocity dependent micro-milling cutting forces; the dynamics of the tool-holder-spindle assembly. The uncut chip thickness is determined after considering the full kinematics of the cutting tool including the run-out effect. The micro-milling cutting forces are determined by: (i) a finite element (FE) prediction of the cutting forces in orthogonal cutting at different cutting velocities and uncut chip thicknesses; (ii) describing the relationship between cutting forces, cutting velocities and uncut chip thicknesses into a nonlinear equation; (iii) incorporating the uncut chip thickness model into the relationship of the cutting forces as function of the cutting velocity and the uncut chip thickness. The modal dynamic parameters at the cutting tool tip are determined for the tool-holder-spindle assembly and used for solving the equation of motion. The micro-milling process is modelled as two degrees of freedom system where the modal dynamic parameters for the tool-holder-spindle assembly and the micro-milling cutting forces are considered. Due to nonlinearities in the micro-milling cutting forces, the equation of motion is integrated numerically in the time domain using the Runge–Kutta fourth order method. The displacements in the x and y directions are obtained for one revolution-per-tool. Statistical variances are then employed as a chatter detection criterion in the time-domain solution. Scanning electron microscope (SEM) inspection is carried out to observe potential chatter marks on the micro-milled AISI 4340 steel surfaces at different spindle speeds and depths of cut. The predicted stability lobes and the experimentally obtained stability limits resulted in satisfactory agreement. The influence of the run-out effect on the stability lobes at different feed rates was investigated, which demonstrated the capability of the developed chatter model to consider quantitatively the run-out phenomenon. The results showed that the stability limits decrease by increasing the run-out length

Fast mapping of finite element field variables between meshes with different densities and element types

yesIn the simulation of a chain of manufacturing processes, several finite element packages can be employed and for each process or package a different mesh density or element type may be the most suitable. Therefore, there is a need for transferring finite element analysis (FEA) data among packages and mapping it between meshes. This paper presents efficient algorithms for mapping FEA data between meshes with different densities and element types. An in-core spatial index is created on the mesh from which FEA data is transferred. The index is represented by a dynamic grid partitioning the underlying space from which nodes and elements are drawn into equal-sized cells. Buckets containing references to the nodes indexed are associated with the cells in a many-to-one correspondence. Such an index makes nearest neighbour searches of nodes and elements much faster than sequential scans. An experimental evaluation of the mapping techniques using the index is conducted. The algorithms have been implemented in the open source finite element data exchange system FEDES