J. Campos Rubio

State of the Art on Micromilling of Materials, a Review

The trend towards miniaturization has increased dramatically over the last decade, especially within the fields concerned with bioengineering, microelectronics, and aerospace. Micromilling is among the principal manufacturing processes which have allowed the development of components possessing micrometric dimensions, being used to the manufacture of both forming tools and the final product. The aim of this work is to present the principal aspects related to this technology, with emphasis on the work material requirements, tool materials and geometry, cutting forces and temperature, quality of the finished product, process modelling and monitoring and machine tool requirements. It can be noticed that size effect possesses a relevant role with regard to the selection of both work material (grain size) and tooling (edge radius). Low forces and temperature are recorded during micromilling, however, the specific cutting force may reach high values because of the ploughing effect observed as the uncut chip thickness is reduced. Finally, burr formation is the principal concern with regard to the quality of the finished part.

A study aimed at minimizing delamination during drilling of CFRP composites

The aim of this study is to present the methodology of Taguchi optimization technique for minimizing the delamination at the entrance of holes in high speed drilling of carbon fiber-reinforced plastics (CFRPs). The drilling process parameters evaluated are spindle speed, feed, and point angle. The experiments were performed as per Taguchi’s L27 orthogonal array using cemented carbide (K20) twist drills. The defects observed at the entrance of drilled holes of CFRP plates were measured and the delamination factor was computed for each trial of the orthogonal array. The analysis of means (ANOM) and analysis of variance (ANOVA) were employed to determine the optimal process parameter levels and to analyze the effect of parameters on delamination factor. The confirmation tests with the optimal levels of parameters were carried out to illustrate the effectiveness of Taguchi design. The optimization results indicate that point angle is the most significant factor followed by feed and spindle speed. The results also highlight the importance of employing the higher speeds to minimize the delamination defects.

Influence of Drill Point Angle in High Speed Drilling of Glass Fiber Reinforced Plastics

Drilling is one of the machining processes most widely applied to composite materials; nevertheless, these materials are prone to delaminate when subjected to stress concentration during machining operations. The damage induced by this operation may reduce the component performance drastically. The present study aims at high speed machining (HSM) to realize high performance drilling of glass fiber reinforced plastics (GFRP) with reduced delamination. The effects of feed rates, spindle speeds and the geometrical characteristics of the drill on the resulting delamination factor values are comparable regardless of the drill point angle used. A statistical model is proposed for use in predicting the delamination in drilling glass fiber reinforced plastic composites. The results proved that HSM is a technology capable of producing lower damage level in drilling of GFRP composites.

Statistical Analysis of Delamination in Drilling Glass Fiber-Reinforced Plastics (GFRP):

Fiber-reinforced composites are widely recognized for their superior mechanical properties and advantages for applications in aerospace, defence and transportation sectors. Delamination is a problem associated with drilling fiber-reinforced composite materials. In this work, the effects of feed speed, rotational speed and drill geometry on the resulting delamination factor are comparable in spite of the drill point angle used. A mathematical model is proposed to predict delamination in drilling glass fiber-reinforced plastic composites.

Surface roughness analysis in high-speed drilling of unreinforced and reinforced polyamides

In this work, surface roughness study in high-speed drilling of unreinforced polyamide (PA6) and reinforced polyamide with 30% of glass fibers (PA66 GF30) using cemented carbide (K20) tool has been carried out. The experiments were planned as per full factorial design of experiments. The effects of cutting speed and feed rate on centerline average surface roughness, maximum peak to valley height, and peak counts have been analyzed by developing response surface methodology based third-order mathematical models. The parametric analysis clearly indicates the influence of reinforced fiber on surface finish when high-speed cutting in drilling is used.

Effects of high speed in the drilling of glass whisker-reinforced polyamide composites (PA66 GF30): statistical analysis of the roughness parameters

Glass fiber-reinforced polyamides are promising materials especially for automotive applications, exhibiting high mechanical strength and stiffness. In order to achieve the required tolerances and surface quality, these materials must be subjected to machining operations. Drilling is one of the machining processes most widely applied to composite materials and, for this reason, this article is focused on the machinability of polyamide reinforced with glass whiskers for high speed drilling operation. A full factorial experimental design was carried out in order to identify the main effects and interaction between the factors feed speed, spindle speed and drill point angle on surface roughness (R a) and normalized peak count (Pc) responses. The work material (PA66-GF30 polyamide reinforced with 30% glass whiskers) was drilled using tungsten carbide (ISO grade K10) drills. The results indicated that the interaction between feed speed, spindle speed, and drill point angle presented a significant effect on the Ra response. In addition to that, the factor feed speed and the interaction between spindle speed and drill point angle significantly affected the peak count response.

Dimensional and Geometric Deviations Induced by Drilling of Polymeric Composite

Tool material, tool wear, and machining parameters drastically affect the quality of holes produced in polymeric composites and, therefore, the performance of the finished component. This article investigates the influence of the above-mentioned factors on thrust force, diameter, and roundness deviations on holes generated after drilling glass fiber reinforced epoxy resin. High speed steel and cemented carbide drills were tested as tool materials and the results indicated that the high speed steel drill presented severe wear after drilling 1000 holes, thus promoting high thrust force and roundness deviation values, in addition to hole diameter figures considerably smaller than the nominal value. On the other hand, after drilling 10,000 holes the carbide drill presented lower wear land and, consequently, lower thrust force values, producing holes with superior dimensional and geometric quality.

The influence of tool wear on delamination when drilling glass fibre reinforced epoxy composite with high speed steel and cemented carbide tools

This work is concerned with the machinability of a glass fibre reinforced epoxy composite when subjected to drilling at distinct cutting speeds and feed rates using high speed steel and tungsten carbide drills with similar geometries. The influence of tool material and machining parameters on tool wear and delamination were the principal aspects investigated. The results indicated that the high speed steel drill presented severe wear rates, which resulted in larger delamination areas after drilling 1000 holes, whereas the wear observed on the cemented carbide tool was negligible. Furthermore, the combination of tool wear with high cutting speed and low feed rate values resulted in an increase in the damaged area.

Optimization of Milling Parameters Employing Desirability Functions

The principal aim of this paper is to investigate the influence of tool material (one cermet and two coated carbide grades), cutting speed and feed rate on the machinability of hardened AISI H13 hot work steel, in order to identify the cutting conditions which lead to optimal performance. A multiple response optimization procedure based on tool life, surface roughness, milling forces and the machining time (required to produce a sample cavity) was employed. The results indicated that the TiCN‐TiN coated carbide and cermet presented similar results concerning the global optimum values for cutting speed and feed rate per tooth, outperforming the TiN‐TiCN‐Al2O3 coated carbide tool.