Effects of Cutting Angle on Kerf width and Edge Shape in the Hotwire Cutting of EPS Foam for the Case of Single-Sloped Cutting for VLM-s Process

The dimensional accuracy and global roughness between successive layers of VLM-s, which is a new rapid prototyping process using hotwire cutter and EPS foam, depend significantly on the operating parameters of hotwire cutter. In the present study, the effect of cutting angle on the kerf width and edge shape in hotwire cutting of EPS foam for the case of single-sloped cutting with one cutting angle was investigated. Through single-sloped cutting tests, the modified relationship between kerf width and effective heat input, considering the effect of the cutting angle, and the relationship between the melted area and the cutting angle were obtained. In order to investigate the effect of cutting angles on the thermal field in EPS foam, transient heat transfer analyses using single-sloped volumetric heat flux model and locally-conformed mesh were performed. Through the comparison between experimental and numerical results, it was shown that the proposed analysis model is needed to estimate the three-dimensional temperature distribution of the EPS foam for the case of single-sloped hotwire cutting

Surface Reconstruction for Cutting Path Generation on VLM-Slicer

A new rapid prototyping process, Variable Lamination Manufacturing using a 4-axis-controlled hotwire cutter and expandable polystyrene foam sheet as a laminating material of the part (VLM-S), has been developed to reduce building time and to improve the surface finish of parts. The objective of this study is to reconstruct the surface of the original 3D CAD model in order to generate mid-slice data using the advancing front technique. The generation of 3D layers by a 4 axis-controlled hot-wire cutter requires a completely different procedure to generate toolpath data unlike the conventional RP CAD systems. The cutting path data for VLM-S are created by VLM-Slicer, which is a special CAD/CAM software with automatic generation of 3D toolpath. For the conventional sheet type system like LOM, the STL file would be sliced into 2D data only. However, because of using the thick layers and a sloping edge with the firstorder approximation between the top and bottom layers, VLM-Slicer requires surface reconstruction, mid-slice, and the toolpath data generation as well as 2D slicing. Surface reconstruction demands the connection between the two neighboring cross-sectional contours using the triangular facets. VLM-S employs thick layers with finite thickness, so that surface reconstruction is necessary to obtain a sloping angle of a side surface and the point data at a half of the sheet thickness. In the process of the toolpath data generation the surface reconstruction algorithm is expected to minimize the error between the ruled surface and the original parts.

Investigation into development of post-processing system to improve geometrical conformity of VLM-ST_{ST} parts for the detail shape

Surface finishing is still indispensable for most rapid prototyping (RP) processes because of the inherent stair-stepped surface and shrinkage of the parts. These problems can be minimized in the $VLM-_ST$ Process, because it uses expandable polystyrene foam sheets, each of which has a thickness of3.9 mm and a linear-interpolated side slope. The use of thick layers, however, limits the process capability of constructing fine details. This study focuses on the design of post-processing tool for fine details of $VLM-_ST$ parts and investigation of thermal characteristics during EPS foam cutting using the post-processing tool. To calculate the heat flux from the tool into the foam sheet, the tool was modeled as a heat source of radiation for finite element analysis. Results of the analysis agreed well with those of the experiment

Investigation into Net-Shape Manufacturing of Three- Dimensional Parts using VLM-SP and Its Applied Technology

The integration of Rapid prototyping (RP) and Rapid Tooling (RT) has the potential for rapid net shaping of thee-dimensional parts, which have a geometrical complexity. In this study, a new R)P process, (VLM-SP), was proposed to manufacture net shapes of three-dimensional prototypes and it was shown that VLM-SP is an effective and economic process through the comparison of building time, building cost and dimensional accuracy for the test parts with the commercial RP processes ; LOM and FDM. In addition, the metal parts, which are a spanner shape and a clover punch, were produced by the plaster casting as one of RT using the prototypes of VLM-SP

Development of Shape Refining Process of VLM-ST Parts Using Noncontacting Hot Tool

In most RP processes, the inherent stair-stepped surfaces and shrinkage-induced warping of the parts require post processing such as surface finishing. To minimize such defects, VLM-ST, a newly developed RP process, employs a 3.9mm thick expandable polystyrene (EPS) foam sheet and a hot wire to contour it to have slant linear-interpolated sides. The use of relatively thick sheets for layers, however, limits the process capability of constructing fine details, especially smaller than the layer thickness. This study is focused on the development of a post processing method for fine details of VLM-ST parts. The post-processing tool was designed to meet all the requirements for the desirable post processing. It adopted a hot wire as a means of melting the EPS foam sheet. Various basic experiments on the post processing were carried out to obtain the optimal process conditions. The dominant process parameters such as the radiated heat input, the tool speed, and the gap between the tool tip and the foam sheet (tool height) were considered in the experiments. The effectiveness of the developed post-processing method for forming or engraving fine details on the VLM-ST parts has been thus demonstrated. The experiments on engraving several sets of letters, such as CANESM, 人間, and 한국과학기술원, on the EPS foam sheet were carried out. In addition, a flowery shape was engraved on a three-dimensionally curved surface of a pottery-shape VLM-ST part

발포 폴리스티렌 폼을 이용한 가변 적층 쾌속 조형 공정 개발에 관한 연구

학위논문(박사) - 한국과학기술원 : 기계공학전공, 2002.8, [ xxiv, 199 p. ]Rapid prototyping (RP) technologies have been widely used to reduce the lead-time and development cost of new products. Most of the developed thin-layered RP technologies have disadvantage due to their working principles: large building time, stair-stepped surface of a part and additional time consuming post-processing. In addition, it requires high cost to install, operate and maintain the RP apparatuses. The thick-layered RP technologies employ mostly very thick layers thicker than 10 mm, expensive cutting systems and fully manual or extremely large automatic manipulation systems. Hence, a new effective RP process is needed for RP technology innovation of RP and to meet the needs of the RP market. In the present work, a new effective rapid prototyping process, Variable Lamination Manufacturing Process using expandable polystyrene foam (VLM-S), has been developed to improve building efficiency including a building time and cost, to extend capabilities of the current RP technology toward the fabrication of practical parts covering the volumetric range from small-and-medium size and to medium-and-large size, to minimize the post-processing, and its equipment cost. In addition, thermal characteristics of hotwire cutting for expandable polystyrene foam (EPS) is investigated to improve the quality of parts and to estimate the optimal cutting conditions. VLM-S process has several advantageous features such as thick layers with a thickness of less than 4 mm, sloping surfaces with the first order approximation between top and bottom surfaces of each layer, the concept of unit shape layer (USL) and unit shape part (USP), and a building sequence in that it performs stacking and bonding after cutting. The thick layer and the sloping surfaces have reduced the building speed, while maintaining the dimensional accuracy in a reasonable range. Using the concept of USL and USP, the problems of cutting for a multiply connected domain have been overcome. The majority...한국과학기술원 : 기계공학전공

Investigation into effect of cutting angle on the thermal characteristics in the linear heat cutting of EPS foam

During the hotwire cutting of EPS foam sheet, the dimensional accuracy and part quality of the cut par are highly dependent upon the thermal field in the EPS. The thermal field is determined by operating parameters such as heat input, cutting speed and cutting angle. The objective of this study is to investigate into the influence of cutting angle on the kerfwidth and part quality of the cut part in hotwire cutting of EPS foam using the experiments and the numerical analysis in the case of a single sloped cutting. In order to estimate an accurate temperature field, the transient thermal analysis using a moving coordinate system and the sloped heat flux model is carried out. From the results of the experiments and the analysis, it has been found that the effect of cutting angle on the kerfwidth and the melted area at the edge are 0.1 mm and 0.11 m㎡ respectively. The results of the experiments show that the surface roughness is not appreciably influenced by the cutting angle

Investigation of Thermal Characteristics and Skeleton Size Effects to improve Dimensional Accuracy of Variable Lamination Manufacturing by using EPS Foam

Rapid Prototyping(RP) techniques have unique characteristics according to their working principle: the stair-stepped surface of a part due to layer-by-layer stacking, low building speed, and additional post-processing to improve surface roughness. A new RP process, Variable Lamination Manufacturing by using expandable polystyrene foam(VLM-S), has been developed to overcome the unfavorable characteristics. The objective of this study is to investigate the thermal characteristics and skeleton size effects as the hotwire cuts EPS foam sheet in order to improve dimensional accuracy of the parts, which is produced by VLM-S. Empirical and analytical approaches are performed to find the relationship between cutting speed and heat input, and the relationship between maximum available cutting speed and heat input. In addition, empirical approaches are carried out to find the relationship between cutting error and skeleton size, and cutting deviation and skeleton size. Based on these results, the optimal hotwire cutting condition and available minimum skeleton size are derived. The outcomes of this study are reflecting in the enhancement of VLM-S input data generation S/W