Byung Min Kim

Flexural Stiffness and Stresses in Nickel-Titanium Rotary Files for Various Pitch and Cross-sectional Geometries

INTRODUCTION Shape is the main determinant of mechanical performance for nickel-titanium rotary instruments. This study evaluated how pitch and cross-sectional geometry affected flexural stiffness and stresses. METHODS Finite element models of rotary instruments with 4 cross-sectional geometries (triangle, slender-rectangle, rectangle, square) and 3 pitches (5-, 10-, 15-threads) were created, featuring superelastic nickel-titanium properties. All models had the same length, taper, and external peripheral radius; cross-sectional area and/or center-core area varied. The clamped shaft was rotated axially, while the tip was deflected 5 mm. Flexural stiffness and maximum von Mises stresses were calculated. RESULTS Stiffness and maximum stress decreased with decreasing pitch (increasing threads). Doubling or tripling the threads for the triangular or rectangular cross sections decreased the stiffness and stress 6% and 12%, respectively; square cross sections were less affected (1% and 3% decrease, respectively). Square cross sections (higher cross-sectional and center-core areas) had higher stiffness and stresses than other models with same deflection. Rectangular and triangular models with the same center-core areas had similar stresses, but the rectangular model was 30%-40% stiffer. The slender-rectangle had the smallest center-core area and the lowest stiffness and stresses. Both rectangular cross sections caused stiffness and stress variations with rotation angle (13% for slender-rectangle); larger pitch caused more variation. CONCLUSIONS Under the same tip deflection (simulating canal curvature), flexural stiffness and stress correlated with center-core area. Increasing pitch increased flexural stiffness and stresses.

A compact and practical CAD system for blanking or piercing of irregular-shaped sheet metal products and stator and rotor parts

This paper describes the development of a computer-aided design of blanking and piercing for irregular-shaped sheet metal products and stator and rotor parts. An approach to the compact and practical CAD system is based on the knowledge-based rules. Knowledge for the CAD system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. The system has been written in AutoLISP on the AutoCAD with a personal computer and is composed of six main modules, which are input and shape treatment, production feasibility check, blank layout, strip layout, die layout, and drawing edit module. Based on knowledge-based rules, the system, STRTDES, is designed by considering several factors, such as complexities of blank geometry and punch profile, availability of press equipment and standard parts, utilization ratio which minimizes the scrap in a single or a pairwise operation, bridge width, grain orientation and design requirements which maximize the strength of the part when subsequent bending is involved. Therefore, this system can carry out a die design for each process which is obtained from the results of an automated blank layout drawing with the best utilization ratio for the irregular shape of the product, which was successful in the production feasibility check module, and those of an automated strip layout drawing. It can then generate part drawings and the assembly drawing of the die set in graphic form. The developed system provides its efficiency and effectiveness for blank layout, strip layout, and die layout of irregular-shaped sheet metal products and stator and rotor parts.

An integrated CAD system for the blanking of irregular-shaped sheet metal products

Abstract This paper describes research work into developing computer-aided design for the blanking and piercing of irregularly-shaped sheet metal products. This approach to an integrated CAD system is based on knowledge-based rules. Knowledge for the CAD system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. The system has been written in Auto LISP on the AutoCAD system with a personal computer. The system is composed of six main modules: input and shape treatment, production feasibility check, blank layout, strip layout, die layout and drawing edit module. Based on the knowledge-based rules, the system, STRTDES1, is designed by considering several factors, such as the complexities of the blank geometry and the punch profiles and the availability of press equipment and standard parts. This system can therefore carry out a die design for each process that is obtained from the results of an automated process-planning system and generate part drawings and the assembly drawing of the die set in graphic form. The developed system provides powerful capabilities for the process planning and dies design of irregularly-shaped products.

Uniform superhydrophobic surfaces using micro/nano complex structures formed spontaneously by a simple and cost-effective nonlithographic process based on anodic aluminum oxide technology

This paper presents a uniform micro/nano double-roughened superhydrophobic surface with a high static contact angle (CA) and low contact angle hysteresis (CAH). The proposed micro/nano complex structured surfaces were self-fabricated simply and efficiently using a very simple and low-cost nonlithographic sequential process, which consists of aluminum (Al) sputtering, anodization of the Al layer and pore widening, without specific equipment and additional subsequent processes. The wetting properties of the fabricated surfaces were characterized by measuring the static CAs and the CAHs after plasma polymerized fluorocarbon coating with a low surface energy. The measured static CA and CAH were 154 ± 2.3° and 5.7 ± 0.8°, respectively, showing that the fabricated double-roughened surfaces exhibit superhydrophobic behaviors clearly. In addition, the proposed double-scaled surfaces at a wafer-level exhibited uniform superhydrophobic behaviors across the wafer with an apparent CA and CAH of 153.9 ± 0.8° and 4.9 ± 1.3°, respectively.

The influence of induction heating on the microstructure of A356 for semi-solid forging

Abstract Semi-solid forging is a compound forging technology to develop conventional forging process. Among the several steps of the semi-solid forging process, the heating step of the billet prior to semi-solid forging step is necessarily required to obtain a globular microstructure. For the forming operation to work properly, it is important to heat the billet uniformly for the uniformity of solid–liquid distribution and globular grain. It is also required to heat the billet as soon as possible. To satisfy these requirements, induction heating has been generally used for a long time. This paper presents a method to find the heating condition and the temperature distribution inside the billet with induction heating apparatus by comparing computer simulation with experiment for A356. The microstructure of the billet is also investigated by using a conventional parameter, i.e. the mean size of globules, in connection with the heating condition.

Effect of Tool Shape on Hole Clinching for CFRP with Steel and Aluminum Alloy Sheet

Use of light materials such as aluminum, magnesium and carbon fiber reinforced plastic (CFRP) has been increased to achieve the light-weight car body in automotive industry. For successful multi-material design of automotive body, the joining method for dissimilar materials is required to assemble the automotive components produced by various materials. Especially, hole clinching process is effective to fasten dissimilar materials without any additional joining element. In this study, effect of tool shape on the hole clinching is investigated by FE-analysis and experiments. The parameters related to clinching tool shape are punch diameter, punch corner radius and die depth. The geometrical interlocking is evaluated by the neck-thickness and undercut. Joint strength using single lap shear test is evaluated also to verify the effectiveness of hole clinching as automotive joints.

Determination of Die Design Rules for Semi-Solid Die Casting Process and Its Experimental Investigation

Die design rule for semi-solid die casting (SSDC) with A356 electromagnetic stirring (EMS) aluminum alloy, was proposed. The die design rule included inspection of machine, part requirements, parting line determination, sleeve, plunger, gating system, overflow, air vent, ejector pin, and heating line design. The specification of gating system, overflow, air vent, plunger tip, and sleeve suitable for respective part were regulated. Two steps die system of lower-positioned gate and three steps die system of center-positioned gate were manufactured for 4 automobile suspension parts, based on the die design rule. For the sound filling pattern and solidification behavior, injection speeds of 4 parts were summarized to the interval (from V1 to V4). As a result of observing the microstructure of 4 parts after T6 heat treatment, primary Al-α phase was globularized and fine Si particles were distributed around the grain boundary. The mechanical properties of 4 parts with T6 heat treatment were investigated and showed ultimate tensile strength (UTS) of 330 MPa, yield strength (YS) of 250 MPa, and elongation of 7.5% as average.

Process design and forming analysis of a permalloy shielding can for instrument clusters

Abstract This study shows the process design and forming analysis of a permalloy shielding can (PSC) that supports cross-coil movement (CCM) structurally and enables CCM gained by an electro magnetic property to indicate accurate information of a car. This study is particularly important, since the magnetic properties such as coercivity and permeability are quite sensitive to the strain and thickness of a PSC. The objective functions are strain and thickness deviation. The punch radius, die radius and blank holding force are considered as design parameters. An orthogonal array (OA) table and characteristics are applied to the neural network (NN) as training data. After training, the optimal and robust design parameters are selected. This study shows the correlation between the design methodology of NN and the statistical design of experiments (DOE) approach.

Microstructure and Hardness of Yb:YAG Disc Laser Surface Overlap Melted Cold Die Steel, STD11

이광현 * ·최성원 ** ·윤중길 ** ·오명환 ** ·김병민 *** ·강정윤 **,† * 한국기계연구원 부산레이저기술지원센터 ** 부산대학교 재료공학부 *** 부산대학교 기계공학부 Abstract Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70mm/sec, 2.8kW and 800um respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is 3~4μm, matrix is γ(Austenite) and dendrite boundary consists of γ and M7C3 of eutectic phase. This microstructure crystallizes from liquid to γ of primary crystal and residual liquid forms γ and M7C3 of eutectic phase by eutectic reaction at 1266 ﾟ C. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine M23C6 and coarse M7C3 that have 210Hv. Microstructures in the HAZ consist of fine M23C6 and coarse M7C3 like substrate. But, M23C6 increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of γ, M7C3 and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around γ and M7C3. Hardness is maximum 557Hv in the partial melted zone.

The Adhesion Evaluation of Thin Hard Coatings on Tool Steel with Nitride or Non-Nitride Layer Using the Scratch Test

The deposition of thin hard coating onto tool steel is done to improve the surface properties such as wear, corrosion. The adhesion strength between substrate and coating is one of important parameters in practical applications since coating failure affects the lifetime of tool directly. Scratch test with acoustic emission(AE) technique was performed to evaluate the adhesion strength qualitative by observing the friction load vs. the normal load curves, the acoustic emission signal generated by the damage of coatings and the scratch track using an optical microscope. In this study, the effect of substrate hardness on the adhesion strength was investigated by evaluating critical load and work of adhesion and observing AE signal and failure mode in scratch track using optical microscope. Coatings were individually deposited on six substrates by means of physical or chemical vapor deposition(PVD, CVD) process and TD process. The critical load of the substrates with nitride layer is higher than without nitride. Although high load causes higher stresses which make flaking occur in the coating-substrate interface, the work of adhesion of harder substrates is also high. Because harder substrates have small contact area causing lower the plastic deformation around stylus.