Analysis of single-operation cold forging of a hollow ball from a tubular billet

A bare AISI420J2 punch often suffers from severe adhesion of metallic titanium as well as titanium oxide debris particles in dry, cold forging of biomedical titanium alloys. This punch was plasma-carburized at 673 K for 14.4 ks to harden it up to 1200 HV on average and to achieve carbon supersaturation in the carburized layer. This plasma-carburized punch was employed in the cold, dry forging of a pure titanium wire into a flat plate while reducing the thickness by 70%. The contact interface width approached the forged workpiece width with increasing the reduction ratio. This smaller bulging deformation reveals that the workpiece is upset by homogeneous plastic flow with a lower friction coefficient. This low-friction and anti-galling forging process was sustained by an in situ solid lubrication mechanism. Unbound free carbon was isolated from the carbon-supersaturated AISI420J2 matrix and deposited as a thin tribofilm to protect the contact interface from mass transfer of metallic titanium.

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Cold Forging Effect on the Microstructure of Motorbike Shock Absorbers Fabricated by Tube Forming in a Closed Die

Applied Sciences ◽

10.3390/app11052142 ◽

2021 ◽

Vol 11 (5) ◽

pp. 2142

Author(s):

Trung-Kien Le ◽

Tuan-Anh Bui

Keyword(s):

Material Flow ◽

Cold Forging ◽

Technological Parameters ◽

Forming Process ◽

Tube Forming ◽

Shock Absorbers ◽

Thin Walled Tube ◽

Thin Walled ◽

Quality Of Products ◽

Forming Defects

Motorbike shock absorbers made with a closed die employ a tube-forming process that is more sensitive than that of a solid billet, because the tube is usually too thin-walled to conserve material. During tube forming, defects such as folding and cracking occur due to unstable tube forming and abnormal material flow. It is therefore essential to understand the relationship between the appearance of defects and the number of forming steps to optimize technological parameters. Based on both finite element method (FEM) simulations and microstructural observations, we demonstrate the important role of the number and methodology of the forming steps on the material flow, defects, and metal fiber anisotropy of motorbike shock absorbers formed from a thin-walled tube. We find limits of the thickness and height ratios of the tube that must be held in order to avoid defects. Our study provides an important guide to workpiece and processing design that can improve the forming quality of products using tube forming.

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Multi-Stage Cold Forging Process for Manufacturing a High-Strength One-Body Input Shaft

Materials ◽

10.3390/ma14030532 ◽

2021 ◽

Vol 14 (3) ◽

pp. 532

Author(s):

A Jo ◽

Myeong Jeong ◽

Sang Lee ◽

Young Moon ◽

Sun Hwang

Keyword(s):

High Strength ◽

Microstructural Characterization ◽

Fatigue Tests ◽

Machining Process ◽

Cold Forging ◽

Element Analysis ◽

Forging Process ◽

Input Shaft ◽

Multi Stage ◽

The One

A multi-stage cold forging process was developed and complemented with finite element analysis (FEA) to manufacture a high-strength one-body input shaft with a long length body and no separate parts. FEA showed that the one-body input shaft was manufactured without any defects or fractures. Experiments, such as tensile, hardness, torsion, and fatigue tests, and microstructural characterization, were performed to compare the properties of the input shaft produced by the proposed method with those produced using the machining process. The ultimate tensile strength showed a 50% increase and the torque showed a 100 Nm increase, confirming that the input shaft manufactured using the proposed process is superior to that processed using the machining process. Thus, this study provides a proof-of-concept for the design and development of a multi-stage cold forging process to manufacture a one-body input shaft with improved mechanical properties and material recovery rate.

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Nanofiber-Mâché Hollow Ball Mimicking the Three-Dimensional Structure of a Cyst

Polymers ◽

10.3390/polym13142273 ◽

2021 ◽

Vol 13 (14) ◽

pp. 2273

Author(s):

Wan-Ying Huang ◽

Norichika Hashimoto ◽

Ryuhei Kitai ◽

Shin-ichiro Suye ◽

Satoshi Fujita

Keyword(s):

Three Dimensional ◽

Hollow Structure ◽

Dimensional Structure ◽

The Novel ◽

Fibrous Scaffold ◽

Hydrogel Beads ◽

Inner Surface ◽

Intracranial Epidermoid ◽

Hollow Ball

The occasional malignant transformation of intracranial epidermoid cysts into squamous cell carcinomas remains poorly understood; the development of an in vitro cyst model is urgently needed. For this purpose, we designed a hollow nanofiber sphere, the “nanofiber-mâché ball.” This hollow structure was fabricated by electrospinning nanofiber onto alginate hydrogel beads followed by dissolving the beads. A ball with approximately 230 mm3 inner volume provided a fibrous geometry mimicking the topography of the extracellular matrix. Two ducts located on opposite sides provided a route to exchange nutrients and waste. This resulted in a concentration gradient that induced oriented migration, in which seeded cells adhered randomly to the inner surface, formed a highly oriented structure, and then secreted a dense web of collagen fibrils. Circumferentially aligned fibers on the internal interface between the duct and hollow ball inhibited cells from migrating out of the interior, similar to a fish bottle trap. This structure helped to form an adepithelial layer on the inner surface. The novel nanofiber-mâché technique, using a millimeter-sized hollow fibrous scaffold, is excellently suited to investigating cyst physiology.

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