An image-based methodology to establish correlations between porosity and cutting force in micromilling of porous titanium foams

Abstract

Porous titanium foam is now a standard material for various dental and orthopedic applications due to its light weight, high strength, and full biocompatibility properties. In practical biomedical applications, outer surface geometry and porosity topology significantly influence the adherence between implant and neighboring bone. New microfabrication technologies, such as micromilling and laser micromachining opened new technological possibilities for shape generation of this class of products. Besides typical geometric alterations, these manufacturing techniques enable a better control of the surface roughness that in turn affects to a large extent the friction between implant and surrounding bone tissue. This paper proposes an image analysis approach for optical investigation of the porosity that is tailored to the specifics of micromilling process, with emphasis on cutting force monitoring. According to this method, the area of porous material removed during micromilling operation is estimated from optical images of the micromachined surface, and then the percentage of solid material cut is calculated for each tool revolution. The employment of the aforementioned methodology in micromilling of the porous titanium foams revealed reasonable statistical correlations between porosity and cutting forces, especially when they were characterized by low-frequency variations. The developed procedure unlocks new opportunities in optimization of the implant surface micro-geometry, to be characterized by an increased roughness with minimal porosity closures in an attempt to maximize implant fixation through an appropriate level of bone ingrowth.

An investigation on the material removal mechanism, surface porosity, and surface integrity in ultrasonic vibration assisted turning of porous stainless steel 316L

“…9 The term pore filling in these cases is used to describe the irregular plowed surfaces. Tutunea-Fatan et al 12 and Fakhri et al 13 have shown that in micro processing of porous titanium foams (54% porosity), the large size of the pores in the workpiece (0.5–1.5 mm) and the small size of the cutting tool (less than 1 mm diameter) lead to discontinuity in the cutting process. The fine folds created in the material result in filling of the surface pores.…”

Experimental investigation of porous metal materials in high-speed micro-milling process

“…Titanium, ferrous alloys, and ceramic are used as the predominant porous materials in bone engineering and have received significant research attention. 13–16 Jasperson et al 13 compared micro-pin-fin and micromachining considering thermal–hydraulic performance and manufacturability. Shen and Brinson 14 studied the finite element modeling of porous titanium.…”

“…Microstructure-level machining modeling of ferrous alloys was investigated by Chuzhoy. 15 Abolghasemi Fakhri et al 16 used an image-based methodology to establish correlations between porosity and cutting force in micro-milling of porous titanium foams. Sharma et al 17 presented an experimental work on wire electrical discharge machining process which identifies the influence of process parameters that affect the cutting rate, dimensional shift, and surface roughness while machining of porous nickel–titanium (Ni40Ti60) alloy.…”

“…With the characteristics of high production efficiency and low cost, the micro-cutting technology is particularly suitable for porous metal materials. 9,10,16 Furthermore, in the micro-milling of porous materials, uneven stiffness distribution and poor machinability occur because of the anisotropy and non-continuity of the internal microstructure. The performances of cutting tools are closely related to surface quality.…”

“…In the micromachining process, the feed per tooth and axial cut depth are extremely small, thereby inducing larger micro-milling force per unit and producing a high cutting temperature per unit. 9,16 The machining parameters have a significant effect on cutting force, cutting temperature, cutting vibration, and surface quality. 22,23 Fakhri et al 24 revealed that the presence of a material discontinuity has a prevalent effect on cutting force variation in the case of micro-milling processes of porous titanium.…”