A.M. Abrão

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.

Delamination in High Speed Drilling of Carbon Fiber Reinforced Plastic (CFRP)

When holes are produced on carbon fiber reinforced plastic (CFRP) laminates, in particular for the aerospace and automotive industries, special attention should be focused on as the machining parameters influencing the damage. In this study special drill bits and high-speed cutting (HSC) are used and compared with conventional cutting conditions. The digital image of the damage was conducted in order to analyze the delamination when two composite boards were drilled simultaneously. The experimental results indicated that the use of HSC in drilling is suitable to reduce the damages produced in CFRP with material removal rate increasing considerably.

The performance of cutting fluids when machining aluminium alloys

Purpose – The knowledge over the performance of cutting fluids when applied under different machining conditions (such as distinct work material and cutting parameters) is critical in order to improve the efficiency of most machining operations. This paper is concerned with the performance of cutting fluids employed under two distinct machining operations involving aluminium alloys: drilling of AA 1050‐O aluminium applying cutting fluid as a mist and turning of AA 6262‐T6 aluminium alloy using cutting fluids (as a flood) with distinct extreme pressure additives (chlorine, sulphur and phosphor).Design/methodology/approach – This work reports on a experimental study of the performance of cutting fluids when machining aluminium alloys.Findings – The results indicated an increase in the flow rate of the mist led to lower feed forces but higher torque, power consumption and specific cutting pressure in the drilling operation (AA 1050‐O aluminium). The surface finish was not drastically affected by the cutting ...

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.

Turning of hardened AISI 4340 steel using coated carbide inserts

Abstract The machining of hardened steels employing polycrystalline cubic boron nitride and ceramic tooling has been comprehensively investigated over the last 20 years; however, the development of newer cemented carbide grades has extended the use of this group of materials to the machining of steels hardened up to 45 HRC (Rockwell C). The current paper is therefore concerned with continuous turning of AISI 4340 steel hardened from 250 to 525 HV using coated carbide tools in order to investigate whether this cutting tool grade is capable of providing a satisfactory performance when machining a steel with increasing levels of hardness. Machining forces, tool life, and wear mechanisms were assessed and the results indicated that the relationship between the hardness of the work material and the machining force is not straightforward. In general, the machining force components increased with the work material hardness, however, the cutting force decreased slightly as the work hardness increased from 250 to 345 HV. Tool wear was lower when machining the 345 HV workpiece compared with cutting the 250 HV steel. Finally, abrasion was the principal wear mechanism observed and catastrophic failure took place when attempting to machine the 525 HV steel.

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.

An optimisation procedure to determine the coefficients of the extended Taylor's equation in machining

Abstract An optimum experimental design to determine the coefficients of the Extended Taylors Equation in machining is proposed. The technique is based on the minimisation of the ratio between maximum and minimum singular values of the matrix of sensitivity of the tool life related to the machining parameter variations. This procedure generates the best set of cutting conditions to be used in tool life tests which results in a fast convergence of the coefficients and their confidence intervals. This technique was compared to the commonly used fractional factorial design when face milling AISI 1045 steel with cemented carbide cutting tools. The results showed a considerable reduction in the number of tests required to obtain a reliable equation when the optimum experimental procedure was used when compared to the factorial design.

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.