Hybrid Rapid Prototyping Research Articles

Development of a hybrid rapid prototyping system using low-cost fused deposition modeling and five-axis machining

Currently, two major processes are being used to produce prototypes, namely machining and rapid prototyping. Machining is generally more accurate and precise, but it is difficult to produce objects with certain complicated features. In contrast, rapid prototyping can produce objects with complicated features, which allows materials to be used more efficiently. However, due to the uneven shrinkage and residual stresses within rapid prototyping products, their accuracy is usually uncertain. This study attempts to integrate these two manufacturing processes and develop a hybrid rapid prototyping system in order to overcome the disadvantages associated with each process and to develop new applications. Fused deposition modeling (FDM) was used as the rapid prototyping process in this work. A spindle and a low-cost FDM extruder were designed to be placed on each end of a rotary axis in a five-axis machine tool. The proposed design allows the rotation of the axis on the five-axis machine to switch between machining and FDM, thus achieving the advantage of reducing costs for extra actuators without sacrificing working space. The case studies demonstrated that the proposed hybrid system can build FDM objects without using support materials and produce FDM parts with metal embedded to increase the stiffness. The system can also conduct five-axis machining on a completed FDM part or trim the freeform surface fabricated by FDM to achieve more accurate dimensions or better surface finish.

Bony defect repair in rabbit using hybrid rapid prototyping polylactic-co-glycolic acid/β-tricalciumphosphate collagen I/apatite scaffold and bone marrow mesenchymal stem cells

Background:In bone tissue engineering, extracellular matrix exerts critical influence on cellular interaction with porous biomaterial and the apatite playing an important role in the bonding process of biomaterial to bone tissue. The aim of this study was to observe the therapeutic effects of hybrid rapid prototyping (RP) scaffolds comprising polylactic-co-glycolic acid (PLGA), β-tricalciumphosphate (β-TCP), collagen I and apatite (PLGA/β-TCP-collagen I/apatite) on segmental bone defects in conjunction with combination with bone marrow mesenchymal stem cells (BMSCs).Materials and Methods:BMSCs were seeded into the hybrid RP scaffolds to repair 15 mm defect in the radius of rabbits. Radiograph, microcomputed tomography and histology were used to evaluate new bone formation.Results:Radiographic analysis done from 12 to 36 weeks postoperative period demonstrated that new bone formed at the radial defect site and continues to increase until the medullary cavity is recanalized and remodelling is complete. The bone defect remained unconnected in the original RP scaffolds (PLGA/β-TCP) during the whole study. Histological observations conformed to the radiographic images. In hybrid RP scaffold group, woven bone united the radial defect at 12 weeks and consecutively remodeled into lamellar bone 24 weeks postoperation and finally matured into cortical bone with normal marrow cavity after another 12 weeks. No bone formation but connective tissue has been detected in RP scaffold at the same time.Conclusion:Collagen I/apatite sponge composite coating could improve new bone formation in vivo. The hybrid RP scaffold of PLGA/β-TCP skeleton with collagen I/apatite sponge composite coating is a promising candidate for bone tissue engineering.

Review on CNC-Rapid Prototyping

This article reviewed developments of Computerized Numerical Control (CNC) technology in rapid prototyping process. Rapid prototyping (RP) can be classified into three major groups; subtractive, additive and virtual. CNC rapid prototyping is grouped under the subtractive category which involves material removal from the workpiece that is larger than the final part. Richard Wysk established the use of CNC machines for rapid prototyping using sets of 2½-D tool paths from various orientations about a rotary axis to machine parts without refixturing. Since then, there are few developments on this process mainly aimed to optimized the operation and increase the process capabilities to stand equal with common additive type of RP. These developments include the integration between machining and deposition process (hybrid RP), adoption of RP to the conventional machine and optimization of the CNC rapid prototyping process based on controlled parameters. The article ended by concluding that the CNC rapid prototyping research area has a vast space for improvement as in the conventional machining processes. Further developments and findings will enhance the usage of this method and minimize the limitation of current approach in building a prototype.

Effect of Moulding Sand Properties on Cost Effective Hybrid Rapid Casting Solution for Zinc Alloy

The purpose of the present experimental investigations is to study the effect of moulding sand properties on reducing the shell wall thickness of mould cavity for cost effective, hybrid rapid casting solution of zinc alloy. Starting from the identification of component/benchmark, technological prototypes were produced, with three different moulding sands (dry, green and molasses), at different shell wall thickness of mould cavity using hybrid rapid prototyping technique (combination of three dimensional printing and conventional sand casting). Measurements on the coordinate measuring machine helped in calculating the dimensional tolerances of the castings produced. Some important mechanical properties were also compared to verify the suitability of the castings. The study suggested that for the shell thickness, having value less than the recommended one is more suitable from dimensional accuracy and economic point of view, for all three moulding sands. Further best shell wall thickness of the mould cavity for different moulding sands, for the selected component/benchmark has been highlighted for rapid casting solution of zinc alloy.

Effect of Work Piece Dimensions on Cost Effective Hybrid Rapid Casting Solution for Aluminium Alloy

The purpose of the present experimental investigations is to study the effect of work piece dimensions on reducing the shell wall thickness of mould cavity for cost effective, hybrid rapid casting solution of aluminum alloy. Starting from the identification of component/benchmark, technological prototypes with three different work piece dimensions (volume/ weight) were produced, at different shell wall thickness of mould cavity using hybrid rapid prototyping technique (combination of three dimensional printing and conventional sand casting). Measurements on the coordinate measuring machine helped in calculating the dimensional tolerances of the castings produced. Some important mechanical properties were also compared to verify the suitability of the castings. The study suggested that the shell wall thickness, having value less than the recommended one is more suitable from dimensional accuracy and economic point of view, for all three work piece dimensions (volume/ weight). Further best shell wall thickness of the mould cavity for different work piece dimensions of the selected benchmark has been highlighted for rapid casting solution of aluminum alloy.

Concave edge-based part decomposition for hybrid rapid prototyping

As one of the solutions to the limitations of the current layered manufacturing, hybrid rapid prototyping systems that perform both machining and deposition are being introduced. In the hybrid rapid prototyping, a part of a complicated shape is realized by adding layers of a simpler shape, each of which is obtained by machining a sheet of constant thickness from its top and bottom surfaces. Thus it is desired to decompose a given part into the minimum number of layers while guaranteeing each layer to be fabricated from the given sheets using a 3-axis milling machine. To satisfy these requirements, a concave edge-based approach is proposed to decompose a part into layers by considering the tool accessibility, the total number of layers, and the allowable sheet thickness. In this approach, for a given build-up direction, the undercut edges, which cause a part to be inaccessible by a tool, are extracted and classified into two types and eliminated in two decomposition steps.

Improvement of surface finish by staircase machining in fused deposition modeling

A semi-empirical model for evaluation of surface roughness of a layered manufactured part by fused deposition modeling is presented. Surface roughness resulting due to staircase effect in rapid prototyped parts is one of the major problems. Even though there have been some attempts to improve the surface finish of the rapid prototyped components, the drawback of those attempts is the accessibility of certain areas of the prototyped component. An attempt is made to address this problem using a simple material removal method namely hot cutter machining (HCM). A fractional factorial design of experiments, with two levels and four process parameters, is adopted to understand the effect of various process variables. ANOVA is used to find the significance index for process variables, and confidence level for the statistical model developed for the surface roughness of hot cutter machined surface. It is concluded that the proposed machining method is able to produce surface finish of the order of 0.3 μm with 87% confidence level. This machining process provides a key for development of a hybrid rapid prototyping system, which will have features of both layer-by-layer machining and deposition simultaneously, in order to achieve improved surface finish and functionality of RP parts.

Determination of optimal build orientation for hybrid rapid-prototyping

To overcome the limitations of the layered manufacturing process, hybrid rapid-prototyping systems that allow material removal and deposition are being introduced. This approach should benefit from the advantages of conventional layered manufacturing and traditional CNC machining processes. To realize these advantages, however, an intelligent process plan must be generated. In the hybrid rapid-prototyping process, a part is decomposed into thick-layered 3D shapes, such that each layer can be machined and stacked easily. When each layer is generated from the part’s shape, the build orientation is an important factor to be considered, because it greatly influences the lead-time, the machining accuracy, and the number of tool-accessible features in each setup. In this paper, an algorithm to determine the build orientation is described. It considers the deposition process attributes and the machining process attributes simultaneously.

Hybrid rapid prototyping system using machining and deposition

Many rapid prototyping (RP) systems are commercially available, and others are introduced daily. RP has proven to be an effective tool for dramatically reducing the time and expense involved in the realization of a new products and for overcoming the bottlenecks of existing manufacturing processes. However, its fields of application are currently saturated, and the emphasis has moved towards using RP for short-run manufacture. The current need is for a technique that will produce finished parts of the required quality in the shortest possible time, and which meet this need, the focus now falls on improvements in production speed, accuracy, variety of materials, and cost. For these practical reasons, we concentrated on a new form of hybrid-RP system, which performs both deposition and machining in a single station. Our proposed system meets the requirements of material deposition (RP) and material removal (CNC) at the process planning and manufacturing level. We believe that this new production system, which incorporates a combined RP concept, offers an optimum manufacturing solution by adopting the advantages of the RP and CNC systems. In this paper, we describe the system architecture and the fabrication process in detail and present the framework of the process planning system and the concepts of the geometric algorithms involved in developing such an environment.

Development of New Rapid Prototyping System Performing both Deposition and Machining (II)

The necessity of using rapid prototyping(RP) for short-run manufacturing is continuously driving a development of a cost-effective technique that will produce completely-finished quality parts in a very short time. To meet these demands, the improvements in production speed, accuracy, materials, aid cost are crucial. Thus, a new hybrid-RP system performing both deposition and in a station is proposed. For the new hybrid RP process to maintain the same degree of process automation as in currently available processes like SLA or FDNI, a sophisticated process planning system is developed. In the process planner, CAD models(STEP AP203) are partitioned into 3D manufacturable volumes called 'Ueposition feature segment(DFS) after features called machining feature segmenf'(MFS) are extracted from the initial CAD model. Once MFS and DFS are identified, the process planner arranges them into a chain of processes and automatically generates information for each DFS and MFS. The goal of this paper is to present a framework for a process planning system for hybrid RP processes and to outline the geometric algorithms involved in developing such an environmentnvironment