Titanium alloys for their characteristics have acquired a prominent position in numerous industrial applications. Due to its properties, such as high resistance to corrosion, reduced density, high specific strength, and low Young’s modulus, titanium alloys became indispensable as a biomaterial with high use in medical devices, with special emphasis in the area of orthopedics. Problems associated with its manufacturing by conventional machining processes, such as milling, turning, and drilling are well known and studied. Its low thermal conductivity, high chemical reactivity, high hardness at high temperatures make it classified as difficult to machine material. Despite the already extensive knowledge about machining titanium alloys problems, and the constant technological development to overcome them, it is not yet possible to machine this material like other metals. This work is based on research and review papers from Scopus and Scholar from 2010 to 2020 and addresses the main issues related to the machining of titanium alloys used in medical devices manufacturing and current solutions adopted to solve them. From the research consulted it was possible to conclude that it is consensual that for milling, turning, and helical milling cutting speed can reach up to 100 m/min and up to 40 m/min in drilling. As for feed rate, up to 0.1 mm/tooth for milling and helical milling and up to 0.3 mm/rev for turning and 0.1 mm/rev for drilling. Also, that Minimum Quantity Lubrication is a valid and efficient solution to mitigate titanium alloys machining problems.

The material characterization regarding sheet metal formability is usually assessed by the forming limit curve (FLC). The FLC requires specialized and expensive equipment, several samples with different geometries, and can be a very time-consuming procedure for data treatment. Alternatively, the hole expansion test (HET) and the Erichsen Cupping Test (ECT) can be used for routine evaluations of sheet metal mechanical behavior. These formability tests require fewer quantities of material and easy specimen preparation with a fast analysis of results. The HET and ECT procedures provide a proper evaluation of sheet material stretch-flangeability, formability, strength, and ductility. In this work, we developed a low-cost mechanical device capable of performing the HET and ECT tests using a universal testing machine. The equipment is designed to meet the test parameters set by ISO 16630 (HET) and ISO 20482 (ECT) standards. In order to verify its functionality, tests were carried out with the dual-phase steels DP600 and DP780. The corresponding values determined for the hole expansion ratio and the Erichsen index provided reliable results in terms of the accuracy and repeatability of the proposed testing device.

CNC machining manufacturing is critical to the development of biomedical industries, especially orthopaedic implants. Understanding a material's machinability under different cutting conditions is essential for component design as well as for optimizing the machining process. Despite their widespread use in the biomedical industry, α + β-type titanium (Ti) alloys, such as Ti-6Al-4V and Ti-6Al-7Nb, are being replaced by β or near β-type Ti alloys like Ti-13Nb-13Zr Ti alloy due to issues associated with Vanadium and Aluminium toxicity and lower modulus of elasticity. By simulating the machining of a functional cone of the hip prosthesis femoral component, this work aims to investigate some aspects of the machinability of titanium alloys: Ti-6Al-4V, Ti-6Al-7Nb, and Ti-13Nb-alloy 13Zr. Cutting forces values were registered during the tests. Using correlative microscopy, machined surfaces were examined by measuring roughness and topographic examination. According to the results obtained, the new titanium alloy Ti-13Nb-13Zr alloy presents lower cutting forces and a worse surface finish for a lower feed rate. However, when the feed rate was increased to double the initial value, this alloy had the smallest increase in Ra, compared with the other alloys under test The effect of federate is highly significant in cutting forces and surface finish, with increases in cutting forces of 35%, 45% and 66% on cutting forces for Ti-13Nb-13Zr, Ti-6Al-4V and Ti-6Al-7Nb, respectively.

Hybrid manufacturing (HM) is a process that combines additive manufacturing (AM) and subtractive manufacturing (SM). It is becoming increasingly recognized as a solution capable of producing components of high geometric complexity, while at the same time ensuring the quality of the surface finish, rigour and geometric tolerance on functional surfaces. This work aims to study the surface finish quality of an orthopaedic hip resurfacing prosthesis obtained by HM. For this purpose, test samples of titanium alloy Ti-6Al-4V using two Power Bed Fusion (PBF) processes were manufactured, which were finished by turning and 5-axis milling. It was verified that, upon the machining tests, no differences in Ra and Rt were found between the various types of AM. Regarding the type of SM used, 5-axis milling provided lower roughness results with a consistent value of Ra = 0.6 µm. The use of segmented circle mills in 5-axis milling proved to be an asset in achieving a good surface finish. This work successfully validated the concept of HM to produce a medical device, namely, an orthopaedic hip prosthesis.As far as surface quality is concerned, it could be concluded that the optimal solution for this case study is 5-axis milling.