Maria Luisa Garcia-Romeu

A system based on machined volumes to reduce the number of route sheets in process planning

The paper focuses on the problem of choosing the manufacturing route in metal removal processes, which is very important for the Computer Aided Process Planning (CAPP) systems.A method consisting in establishing groups of precedence between machine operations has been proposed, in order to reduce the number of possible routes. This reduction is based on the elimination of the routes which are not technologically possible, despite being mathematically computable.A wide range of parts has been evaluated, using group technology for choosing the representative cases. For the different parts, the mathematically possible routes have been generated. Graph Theory has been used to determine the precedence between operations.The application of this method permits to reduce considerably the number of possibilities that must be computed, and therefore, the route sheet is obtained more quickly and the computational resources are used more efficiently.

Polymer incremental sheet forming process: Temperature analysis using response surface methodology

ABSTRACT To reduce costs associated with the manufacturing of customized products, several innovative forming processes have been developed. Incremental sheet forming (ISF) is one of these new technologies, becoming, in the past decade, more interesting for the academic and industrial community. The influence of main process parameters, namely, tool diameter, spindle speed, feed rate, and step down, is studied in depth in this paper. The maximum temperature achieved during the forming process of a truncated pyramid frustum with a circular generatrix using three nonbiocompatible and two biocompatible polymer materials is measured. Box–Behnken design of experiments and the response surface methodology have been utilized to statistically analyze the results and to provide models able to predict the maximum temperatures.

Breast Cancer Stem Cell Culture and Enrichment Using Poly(ε-Caprolactone) Scaffolds.

The cancer stem cell (CSC) population displays self-renewal capabilities, resistance to conventional therapies, and a tendency to post-treatment recurrence. Increasing knowledge about CSCs’ phenotype and functions is needed to investigate new therapeutic strategies against the CSC population. Here, poly(ε-caprolactone) (PCL), a biocompatible polymer free of toxic dye, has been used to fabricate scaffolds, solid structures suitable for 3D cancer cell culture. It has been reported that scaffold cell culture enhances the CSCs population. A RepRap BCN3D+ printer and 3 mm PCL wire were used to fabricate circular scaffolds. PCL design and fabrication parameters were first determined and then optimized considering several measurable variables of the resulting scaffolds. MCF7 breast carcinoma cell line was used to assess scaffolds adequacy for 3D cell culture. To evaluate CSC enrichment, the Mammosphere Forming Index (MFI) was performed in 2D and 3D MCF7 cultures. Results showed that the 60° scaffolds were more suitable for 3D culture than the 45° and 90° ones. Moreover, 3D culture experiments, in adherent and non-adherent conditions, showed a significant increase in MFI compared to 2D cultures (control). Thus, 3D cell culture with PCL scaffolds could be useful to improve cancer cell culture and enrich the CSCs population.

On the Rule of Mixtures for Predicting Stress-Softening and Residual Strain Effects in Biological Tissues and Biocompatible Materials

In this work, we use the rule of mixtures to develop an equivalent material model in which the total strain energy density is split into the isotropic part related to the matrix component and the anisotropic energy contribution related to the fiber effects. For the isotropic energy part, we select the amended non-Gaussian strain energy density model, while the energy fiber effects are added by considering the equivalent anisotropic volumetric fraction contribution, as well as the isotropized representation form of the eight-chain energy model that accounts for the material anisotropic effects. Furthermore, our proposed material model uses a phenomenological non-monotonous softening function that predicts stress softening effects and has an energy term, derived from the pseudo-elasticity theory, that accounts for residual strain deformations. The model’s theoretical predictions are compared with experimental data collected from human vaginal tissues, mice skin, poly(glycolide-co-caprolactone) (PGC25 3-0) and polypropylene suture materials and tracheal and brain human tissues. In all cases examined here, our equivalent material model closely follows stress-softening and residual strain effects exhibited by experimental data.

A functional methodology on the manufacturing of customized polymeric cranial prostheses from CAT using SPIF

Purpose This paper aims to propose a functional methodology to produce cranial prostheses in polymeric sheet. Within the scope of rapid prototyping technologies, the single-point incremental forming (SPIF) process is used to demonstrate its capabilities to perform customized medical parts. Design/methodology/approach The methodology starts processing a patient’s computerized axial tomography (CAT) and follows with a computer-aided design and manufacture (CAD/CAM) procedure, which finally permits the successful manufacturing of a customized prosthesis for a specific cranial area. Findings The formability of a series of polymeric sheets is determined and the most restrictive material among them is selected for the fabrication of a specific partial cranial prosthesis following the required geometry. The final strain state at the outer surface of the prosthesis is analysed, showing the high potential of SPIF in manufacturing individualized cranial prostheses from polymeric sheet. Originality/value This paper proposes a complete methodology to design and manufacture polymer customized cranial prostheses from patients’ CATs using the novel SPIF technology. This is an application of a new class of materials to the manufacturing of medical prostheses by SPIF, which to this purpose has been mainly making use of metallic materials so far. Despite the use of polymers to this application is still to be validated from a medical point of view, transparent prostheses can already be of great interest in medical or engineering schools for teaching and research purposes.

Force Modeling in Single Point Incremental Forming of Variable Wall Angle Components

Prediction of forming forces in Incremental Sheet Forming (ISF) is specially important in the case of using adapted machinery not designed for the process. Moreover, forming force is an important indicator that can be monitored on-line and utilized for real time process control. Besides experimentation, simulations based on the Finite Element Method (FEM) have been utilized as a reliable source of process force data. Nevertheless, the long solution times required to simulate ISF renders difficult its inclusion into a process optimization chain. In consequence, models that predict the forces required to manufacture simple parts have appeared. This work begins with a review of forming force models available for Single Point Incremental Forming (SPIF). Then, an equation recently proposed in the literature is compared with published experimental results of SPIF under different working conditions. The same data is employed to verify our own FEM simulations. Finally, the above-mentioned formula and FEM simulation were applied to predict the forming force of Variable Wall Angle (VWA) geometries where available force information is limited. Besides the applicability assessment of the equation, results will supplement a future experimental campaign focused in modeling geometries of intermediate complexity level by means of Computational Intelligence methods.

Single-Point Incremental Forming of Two Biocompatible Polymers: An Insight into Their Thermal and Structural Properties

Sheets of polycaprolactone (PCL) and ultra-high molecular weight polyethylene (UHMWPE) were fabricated and shaped by the Single-Point Incremental Forming process (SPIF). The performance of these biocompatible polymers in SPIF was assessed through the variation of four main parameters: the diameter of the forming tool, the spindle speed, the feed rate, and the step size based on a Box–Behnken design of experiments of four variables and three levels. The design of experiments allowed us to identify the parameters that most affect the forming of PCL and UHMWPE. The study was completed by means of a deep characterization of the thermal and structural properties of both polymers. These properties were correlated to the performance of the polymers observed in SPIF, and it was found that the polymer chains are oriented as a consequence of the SPIF processing. Moreover, by X-ray diffraction it was proved that polymer chains behave differently on each surface of the fabricated parts, since the chains on the surface in contact with the forming tool are oriented horizontally, while on the opposite surface they are oriented in the vertical direction. The unit cell of UHMWPE is distorted, passing from an orthorhombic cell to a monoclinic due to the slippage between crystallites. This slippage between crystallites was observed in both PCL and UHMWPE, and was identified as an alpha star thermal transition located in the rubbery region between the glass transition and the melting point of each polymer.

Evaluating Material Constitutive Equations for the Simulation of Incremental Sheet Forming Applied to Form Thermoplastic Materials

Incremental Sheet Forming (ISF) is able to produce highly customized products at a reasonable manufacturing cost and it has gain importance in the last years, becoming the focus of interest for many researchers and institutions. Some recent publications have revealed an increasing interest in forming thermoplastic materials. There is a tremendous amount of effort put in developing a model that may describe the equilibrium hysteresis and rate-dependence of thermoplastic materials in ISF. This paper will present a brief review of the most common constitutive equations that are able to model the behaviour of glassy polymers. It will be shown that by using a small number of material parameters defined in the Marlow model, it is possible to accurately predict experimental data collected on samples of PVC subjected to simple uniaxial test performed at room temperature. Additionally, some parts have been formed with ISF in order to verify whether the material is incompressible or not. It can be concluded that Marlow model might be used in future work to model the ISF manufacturing process.

Input Parameters Determination for Predicting Ram Speed and Billet Temperature for the First Billet

The aim of this paper is to present the results of the first step of a defined methodology for the neural network tool development. That first step is to studying the variables that have influence on extrusion process, especially in those that affect billet temperature and extrusion speed. In order to determine those parameters, a preliminary analysis was conducted with experimental data from real industry. Then, a multiple regression analysis was carried out to define which parameters will be the inputs of the neural network prediction tool.

Process Parameter Effects on Biocompatible Thermoplastic Sheets Produced by Incremental Forming

There has been increasing interest in the processes that enable part customization and small-batch production in recent years. The prosthetic sector, in which biocompatible materials are used, is one of the areas that requires these types of processes; Incremental Sheet Forming (ISF) technology can meet these requirements. However, the biocompatible thermoplastic polymers formed by this technology have not yet been tested. Hence, the aim of this paper is to cover this gap in our knowledge by analyzing the effects of process parameters on the ISF process with the aim of optimizing these parameters before the actual production of, in this case, customized prostheses. Tests with polycaprolactone (PCL) and ultra-high molecular weight polyethylene (UHMWPE) were performed. Maximum force, surface roughness and maximum depth were statistically analyzed by means of response surface methodology and survival analysis. Spindle speed and tool diameter were shown to be the most influential process parameters in terms of maximum forming force and surface roughness for both materials. In contrast, survival analysis applied to maximum depth showed a greater influence of tool diameter in PCL sheets and a greater influence of spindle speed in the case of UHMWPE.