Deformations on the ship sections during fabrication: cause and remedies

During fabrication process, material deformations are likely to occur due to various factors such as heat during steel cutting, welding induced deformations, lifting and turning of ship sections, temporary stiffening and other possible modifications of ship sections. Lifting induced deformations is one of the major causes of deformations that highly affect the production cost and quality. The aim of this thesis is to outline the main causes of deformations that occur in ship sections during fabrication and to analyse in detail the lifting and turning operations of one ship section using the Finite Element Method (FEM). A strength check using the FEM has been performed on the selected ship section to investigate the deformations and stresses in two different cases with three different loading conditions. First, the section has been analysed without temporary stiffening in three load scenarios: lifting before turning, worst-case scenario during turning and lifting after turning. Similarly, the second case study has been analysed but with the temporary stiffening added according to the lifting plan. Various influencing parameters that determine the lifting plan has been investigated such as the sling angle which directly affects the deformation characteristics. It is observed that the addition of temporary stiffening is essential to minimize the deformations and to maintain the stress levels below the yield point.

Machinability evaluation of titanium alloy Ti-6Al-4V obtained by EBM for functional part at medical application

The potential and advantages revealed by the application of 3D manufacturing techniques such as Electron Beam Melting (EBM) in the production of medical devices such as orthopaedic implants are increasing manly in custom made devices. However, the use of milling and turning operations are indispensable on surfaces where surface finish and dimensional accuracy have more demanding requirements. This work aims to evaluate the machinability of titanium alloy test samples submitted to turning operations, to obtain the geometry of a functional cone of the modular component of the hip prosthesis. The differences in cutting forces and surface finish obtained in the turning tests are compared between a wrought Ti-6Al-4V test sample and three obtained by EBM with different thicknesses. To perform the tests, a constant cutting speed of 60m/min was used, feed of 0.1 and 0.2mm/rev and ap of 0.15mm. The cutting forces were measured for each test, also the roughness was measured in the form of Ra, Rt and RzD in each test sample. From the results obtained, EBM test samples presented higher roughness values and lower resulting cutting forces. In both materials, the effect of feed rate is visible. When machining a cone, the passive force and the cutting force become the most influential forces. Generally, when the feed rate value was doubled, the resulting machining forces value increased up to about 50% for both types of materials and the Ra value to approximately 200%. The EBM technology as used form medical devices allow good quality surfaces as the wrought titanium alloy.

INVESTIGATION OF THE METHOD OF THERMAL FRICTION TURN-MILLING OF HIGH STRENGTH MATERIALS

An analysis of the state of the matter of the manufacture of parts such as bodies of revolution has shown that there is a problem of turning processing by turning large, long parts, connected with increasing productivity and processing quality, as well as reducing the costs of turning operations. To solve this problem, the authors propose a resource-saving combined method for treating external cylindrical surfaces by thermal friction turn-milling. Experimental studies were performed on the processing of the outer cylindrical surface using a special friction cutter made of non-instrumental material. The results showed that with thermal friction turn-milling, it is possible to achieve Ra = 1,0 mcm. The process of chip formation was also investigated and the formation of a retarded layer was established, which protects the surface of the friction cutter from wear. Optimum values of cutting conditions for processing by thermal friction turn-milling of steel 30HGSA.

Prospects for the application of the product life cycle system by means of the planned preventive maintenance module on the example of aviation and agricultural components

The paper describes an approach to the development of a functional software module within the subsystem of planning, rationing, preventive, routine maintenance, with the functions of accounting for the time of turning operations in the manufacture of machine parts for various purposes, in the general technological chain of the software complex of interacting ERP/MRP/CAD/CAM/CAE technologies of the enterprise, including forecasting both the time of resource operation and the production of necessary components, in order to support manufactured aviation, agricultural and other products throughout the life cycle.

INVESTIGATION OF WIPER INSERTS EFFECTS IN TURNING AND MILLING PROCESSES

The surface roughness is a crucial factor in machining methods. The most effective factors on surface roughness are feed rate and tool nose radius. Due to the many advantages of wiper (multi-nose radius) inserts, their importance and use has been increasing recently. The purpose of this paper is to investigate the effect of wiper inserts on surface roughness and tool wear. In this study, conventional inserts and wiper inserts were experimentally compared separately in milling and turning operations. Compared to conventional inserts, the surface roughness values obtained using wiper inserts improved by 33% in turning operations and approximately 40% in milling operations. It was observed that the production time in the turning process was reduced by about 25% in the case of using wiper inserts compared to the use of conventional inserts. In milling, this ratio was determined to be approximately 43% due to the fact that it has multiple cutting edge. It has been observed that the use of wiper inserts in machining methods creates a significant time and cost saving advantage.

Turning of Additively Manufactured Ti6Al4V: Effect of the Highly Oriented Microstructure on the Surface Integrity

Additive manufacturing processes induce a high orientation in the microstructure of the printed part due to the strong thermal gradients developed during the process caused by the highly concentrated heat source that is used to melt the metal powder layer-by-layer. The resulting microstructural anisotropy may have an effect on the post-processing operations such as machining ones. This paper investigates the influence of the anisotropy in turning operations carried out on laser powder bed fused Ti6Al4V parts manufactured with different scanning strategies. The machinability under both transverse and cylindrical turning operations was assessed in terms of surface integrity, considering both surface and sub-surface aspects. The effect of the different cooling conditions, that is flood and cryogenic ones, was studied as well. The outcomes showed that the microstructural anisotropy had a remarkable effect on the machining operations and that the cryogenic cooling enhanced the effect of the anisotropy in determining the surface integrity.