Dong-Gyu Ahn

Integration of CAD/CAM/CAE/RP for the development of metal forming process

Abstract In order to reduce lead-time and investment cost for the development of metal forming processes, the technological fusion of VP&M (virtual prototyping and manufacturing) and PP&M (physical prototyping and manufacturing) with the concept of concurrent engineering is needed. In this paper, the technology integration of CAD/CAM/CAE, as a part of the practical VP&M methods, and rapid prototyping and manufacturing (RP&M), as a part of the practical PP&M methods, in metal forming is investigated in order to improve the efficiency of development of trial products and dies for metal forming processes. The technology integration does not necessarily require fabrication of conventional trial dies and parts including drawing, machining and final treatments. The technology integration can also consider the process characteristics such as geometrical complexity, effects of the process parameters, flow pattern of workpiece, deformation induced defects, etc., so that it could reduce the trial-and-error in the design stage. Hence, the technology integration enables a remarkable shortening of the lead-time for development of metal forming processes and investment cost for the period. The integrated technology is examined by case studies such as a spider forging, preform design of a rib-web part, extrusion of a triple-connected rectangular tubular section and underframe part for a railroad vehicle, and deep drawing of a clover punch. As a result of the studies, it was verified that the technology integration could be effectively applied to various metal forming processes and reduce remarkably the lead-time and cost of the process.

Investigation into thermal characteristics of linear hotwire cutting system for variable lamination manufacturing (VLM) process by using expandable polystyrene foam

The dimensional accuracy and efficiency of VLM-S, which is a new rapid prototyping process using hotwire cutter and expandable polystyrene (EPS) foam sheet, depends significantly on the thermal fields of EPS foam sheet when the hotwire cuts the sheet. The objective of this study is to investigate thermal effects of the hotwire cutting on the sheets and to find relationships between process parameters in order to obtain optimal conditions for hotwire cutting and improve dimensional accuracy of the process. Several experiments were performed to find the relationships between maximum cutting speed and heat input, and between cutting offset and heat input. Numerical analyses were carried out to investigate the influence of the cutting parameters on temperature distribution around the hotwire and to estimate the amount of the sheet melted away. Moreover, the size of the thermal front as the hotwire is about to lose its stiffness was predicted to propose the optimal cutting conditions. Based on the results, the optimal cutting conditions of the hotwire cutting system for cutting of an EPS foam sheet were found. In addition, the outcomes of the present study were reflected on the fabrication of a spanner shape and a clover punch shape.

Influence of cutting parameters on surface characteristics of cut section in cutting of Inconel 718 sheet using CW Nd:YAG laser

Recently, laser cutting technologies begin to use for manufacturing mechanical parts of Inconel super-alloy sheet due to difficulties of machining of the Inconel material as a results of its extremely tough nature. The objective of this work is to investigate the influence of cutting parameters on surface characteristics of the cut section in the cutting of Inconel 718 super-alloy sheet using CW Nd:YAG laser through laser cutting experiments. Normal cutting experiments were performed using a laser cutting system with six-axis controlled automatic robot and auto-tracking system of the focal distance. From the results of the experiments, the effects of the cutting parameters on the surface roughness, the striation formation and the microstructure of the cut section were examined. In addition, an optimal cutting condition, at which the surface roughness is minimized and both the delayed cutting phenomenon and the micro-cracking are not initiated, is estimated to improve both the part quality and the cutting efficiency.

A study on the influence of the sloped cutting angle on kerfwidth and part quality in the hotwire cutting of EPS foam for the VLM-s rapid prototyping process

The VLM-s rapid prototyping process employs hotwire cutting of an EPS foam sheet using a four-axis synchronized automatic hotwire cutter. The dimensional accuracy and the quality of the cut part are highly dependent on cutting parameters such as effective heat input, and cutting angle, etc. The objective of this study is to investigate the influence of cutting angle on the kerfwidth and the part quality in hotwire cutting of EPS foam for the case of the sloped cutting including single-sloped cutting with one cutting angle and generally sloped cutting with two cutting angles. Experiments are carried out to obtain the relationship between kerfwidth and effective heat input for each cutting angle, and to find the relationship between the melted area and the cutting angle for each effective heat input. In order to investigate the influence of cutting angle on temperature distribution in EPS foam, transient heat transfer analysis using the sloped heat flux model and the conformed mesh structure is carried out. Through comparison of the results of the experiment and the transient heat transfer analysis, it has been shown that the sloped heat flux with an elliptical cross-section and the conformed mesh structure are needed to estimate the three-dimensional temperature distribution in the EPS foam in the sloped hotwire cutting.

Development of transfer type variable lamination manufacturing (VLM-ST) process

Abstract RP technologies have been widely used to reduce the lead-time and development cost of new products. However, most of the developed RP technologies have disadvantageous characteristics, due to their working principle: a large building time, a stair-stepped surface of a part and additional post-processing. In addition, it requires a high cost to install, operate and maintain the RP apparatus. The objective of this paper is to propose a new rapid prototyping system, transfer type variable lamination manufacturing process using expandable polystyrene foam (VLM- st ), to overcome the disadvantages. VLM- st has various technical novelties such as a thick layer with thickness of less than 4 mm, a sloped surface with the first order approximation between the top and bottom surfaces of each layer, a stacking method using the pilot pin and building board, a concept of unit shape layer (USL), and a synchronized four-axis hotwire cutter with linear heat source and a parallelogram mechanism. In this paper, the characteristics and the key features of VLM- st are discussed. In order to investigate the applicability of the new RP process, various prototypes, such as an extruded shape, son-o-kong shape, a world-cup logo, and a human head shape, are manufactured by the prototype of the VLM- st apparatus. All shapes are manufactured within one hour. In addition, the efficiency of the new RP process is examined by comparing the world-cup logo shape and the human head shape with those of Laminated Object Manufacturing (LOM) from the viewpoint of geometrical conformity, total building time, building cost, and dimensional accuracy.

Rapid prototyping and reverse engineering application for orthopedic surgery planning

This paper describes rapid prototyping (RP) and reverse engineering (RE) application for orthopedic surgery planning to improve the efficiency and accuracy of the orthopedic surgery. Using the symmetrical characteristics of the human body, CAD data of undamaged bone of the injured area are generated from a mirror transformation of undamaged bone data for the uninjured area. The physical model before the injury is manufactured from Polyjet RP process. The surgical plan, including the selection of the proper implant, pre-forming of the implant and decision of fixation positions, etc., is determined by a physical simulation using the physical model. In order to examine the applicability and efficiency of the surgical planning technology, two case studies, such as a distal tibia comminuted fracture and an iliac wing fracture of pelvis, are carried out. From the results of the examination, it has been shown that the RP and RE can be applied to orthopedic surgical planning and can be an efficient surgical tool.

Influence of process parameters on drilling characteristics of Al 1050 sheet with thickness of 0.2 mm using pulsed Nd׃YAG laser

The object of this work is to investigate the influence of process parameters on drilling characteristics of an Al 1050 sheet with a thickness of 0.2 mm using a pulsed Nd:YAG laser through numerical analyses and experiments. By comparing the numerical analyses with the experiments, a proper numerical model was obtained. From the results of the numerical analyses and the experiments, the effects of process parameters on entrance diameters of drilled holes, shapes of the holes, taper angles of the holes and temperature distributions in the vicinity of the holes were examined quantitatively. In addition, the optimal drilling condition was estimated to improve the quality of the drilled holes.

Design of the Thermally Conductive Mould to Improve Cooling Characteristics of Injection Mould for a Mouse

Abstract The objective of present research work is to design the heat conductive mould to improve cooling characteristics of the injection mould for a mouse. In order to obtain the high cooling rate of the mould, a heat conductive mould with three different materials was designed. The materials of the base structure, the mid-layer and the molding part of the heat conductive mould were chosen as Cu-Ni alloy (Ampcoloy 940) to improve the heat conductivity of the mould, Ni-Cu alloy (Monel 400) to reduce a thermal stress, injection tool steel (P21), respectively. Through the three-dimensional transient heat transfer analysis and the thermal stress analysis, the effects of the geometrical arrangement of each material on the cooling characteristics and the thermal stress distribution were examined. From the results of the analyses, a proper design of the thermal conductive mould was obtained.기호설명  : 금형 재료 밀도k : 금형 재료 열전도도C p : 금형 재료 비열  : 금형 재료 열팽창 계수   : 마우스 인서트 단위 표면적당 투입열량m p : 마우스 커버 제품의 질량C

Bending behaviors of metallic sandwich plates with a sheared dimple core under simply supported loading

In this study, the bending responses of metallic sandwich plates with a sheared dimple core were investigated through the 3-point bending tests and dynamic plane bending tests. It was experimentally shown from the uniaxial tensile tests that the yield and tensile strengths of the brazed face sheet were weaker than those of the welded face sheet. A mild steel sheared dimple core was fabricated by the sectional forming process and then bonded with DP590 face sheets by multi-point resistance welding. Analysis for large deformation of a sandwich plate subject to 3-point bending was carried out, where frictional work was considered and a face sheet was treated as a rigid-plastic material based on Hollomon’s flow rule. Load—deflection curves and the deformed shapes of the finite element method computations and the experiments were efficiently predicted by the proposed analysis. The effect of frictional work on the peak load and energy absorption increases as the bending angle increases. The dynamic bending responses of the sandwich plates, such as the effect of a deformed shape, failure mode, energy absorption and absorption ratio were compared with those of a high-strength steel sheet. It was demonstrated that a bendable sandwich plate was stronger construction than a high-strength steel sheet under the tested conditions, despite the weight reduction and weaker properties.

Estimation of the Thickness and the Material Combination of the Thermal Stress Control Layer (TSCL) for the Stellite21 Hardfaced STD61 Hot Working Tool Steel Using Three-Dimensional Finite Element Analysis

The research on a thermal stress control layer (TSCL) begins to undertake to reduce residual stress and strain in the vicinity of the joined region between the hardfacing layer and the base part. The goal of this paper is to estimate the material combination and the thickness of TSCL for the Stellite21 hardfaced STD61 hot working tool steel via three-dimensional finite element analysis (FEA). TSCL is created by the combination of Stellite21 and STD61. The thickness of TSCL ranges from 0.5 mm to 1.5 mm. The influence of the material combination and the thickness of TSCL on temperature, thermal stress and thermal strain distributions of the hardfaced part have been investigated. The results of the investigation have been revealed that a proper material combination of TSCL is Stellite21 of 50 % and STD61 of 50 %, and its appropriate thickness is 1.0 mm.