An experimental investigation on drilling of aluminum alloy (Al 7075) using high speed steel cutting tools

Aluminum alloys 7075 have been increasingly chosen as a main part in aerospace industry due to its property which is low in weight but having high strength. This paper focuses on the effect of cutting parameters and cutting condition when drilling Aluminum alloy 7075 in terms of tool wear, surface roughness and hole circularity. The drilling was conducted using high speed steel (HSS) having point angle of 118 ° and 6 mm tool diameter. The drilling test was conducted with a constant feed rate of 0.15 mm/min, cutting speeds of 22,44 and 66 m/min, and different cutting conditions (dry and cutting fluid). Drilling Aluminum Alloy 7075 with presence of cutting fluid and low cutting speed (22 m/min) resulted in reduced tool wear by 20 to 30 % and improved surface roughness by 30 % as compared to drilling in dry condition with same cutting parameter.

Drilling of 7075 Aluminum Alloys

Aluminum alloy (Al 7075) has been increasingly used as structural components in automotive and aerospace industry due to their low density, high strength and good corrosion resistance compared with other metals. To manufacture and assemble the components, drilling operations are often conducted. However, Al 7075 is ductile and soft, which causes difficulty in drilling, resulting in material adhesion, high tool wear, short tool life and poor hole quality. As a result of the poor hole quality, there is a high percentage of part rejection, which can increase the manufacturing time and cost. This chapter discusses challenges and techniques to drill Al 7075 in terms of the cutting parameters and drilling conditions to prolong the tool life and achieve good hole quality. Drilling experiments on Al 7075-T6 (heat-treated) were conducted using carbide cutting tools at various cutting parameters. Reducing cutting speed and increasing feed rate resulted in reducing tool wear, whereas a reduction in surface roughness, hence improved machined surface finish, was found when both cutting speed and feed rate were reduced in drilling Al 7075-T6. Producing good hole quality is vital during the drilling process to ensure a good assembly and product service performance

Drilling of 7075 Aluminum Alloys

Aluminum alloy (Al 7075) has been increasingly used as structural components in automotive and aerospace industry due to their low density, high strength and good corrosion resistance compared with other metals. To manufacture and assemble the components, drilling operations are often conducted. However, Al 7075 is ductile and soft, which causes difficulty in drilling, resulting in material adhesion, high tool wear, short tool life and poor hole quality. As a result of the poor hole quality, there is a high percentage of part rejection, which can increase the manufacturing time and cost. This chapter discusses challenges and techniques to drill Al 7075 in terms of the cutting parameters and drilling conditions to prolong the tool life and achieve good hole quality. Drilling experiments on Al 7075-T6 (heat-treated) were conducted using carbide cutting tools at various cutting parameters. Reducing cutting speed and increasing feed rate resulted in reducing tool wear, whereas a reduction in surface roughness, hence improved machined surface finish, was found when both cutting speed and feed rate were reduced in drilling Al 7075-T6. Producing good hole quality is vital during the drilling process to ensure a good assembly and product service performance

A study of fatigue and fracture in 7075-T6 aluminum alloy in vacuum and air environments

Axial load fatigue life, fatigue-crack propagation, and fracture toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at pressures ranging from atmospheric to 5 x 10 to the minus 8th torr. Analysis of the results from the fatigue life experiments indicated that for a given stress level, lower air pressures produced longer fatigue lives. At a pressure of 5 x 10 to the minus 8th torr fatigue lives were 15 or more times as long as at atmospheric pressure. Analysis of the results from the fatigue crack propagation experiments indicated that for small stress intensity factor ranges the fatigue crack propagation rates were up to twice as high at atmospheric pressure as in vacuum. The fracture toughness of 7075-T6 was unaffected by the vacuum environment. Fractographic examination showed that specimens tested in both vacuum and air developed fatigue striations. Considerably more striations developed on specimens tested at atmospheric pressure, however

Optimization of surface roughness and circularity deviation and selection of different alluminium alloys during drilling for automotive and aerospace industry

This paper presents the influence of cutting parameters like cutting speed, feed rate, drill diameter, point angle and clearance angle on the surface roughness and circularity deviation of Alluminium alloys during drilling on CNC vertical machining center. A plan of experiments based on Taguchi method has been used to acquire the data. An orthogonal array, signal to noise (S/N) ratio and analysis of variance (ANOVA) are employed to investigate machining characteristics of Alluminium alloys using HSS twist drill bits of variable tool geometry and maintain constant helix angle of 45 degrees. Confirmation tests have been carried out to predict the optimal setting of process parameters to validate the proposed approach and obtained the values of 3.7451µm, 0.1076mm for surface roughness and circularity deviation respectively. Finally, the output results of taguchi method fed as input to the AHP and TOPSIS. the results generated in both AHP and TOPSIS suggests the suitable alternative of  aluminium alloy, which results in better surface roughness and less error in circularity

Fretting-Fatigue Analysis of Shot-Peened Al 7075-T651 Test Specimens

Shot peening is a mechanical treatment that induces several changes in the material: surface roughness, increased hardness close to the surface, and, the most important, compressive residual stresses. This paper analyzes the effect of this treatment on alloy Al 7075-T651 in the case of fretting fatigue with cylindrical contact through the results of 114 fretting fatigue tests. There are three independent loads applied in this type of test: a constant normal load N, pressing the contact pad against the specimen; a cyclic bulk stress σ in the specimen; and a cyclic tangential load Q through the contact. Four specimens at each of 23 different combinations of these three parameters were tested—two specimens without any treatment and two treated with shot peening. The fatigue lives, contact surface, fracture surface, and residual stresses and hardness were studied. Improvement in fatigue life ranged from 3 to 22, depending on fatigue life. The relaxation of residual-stress distribution related to the number of applied cycles was also measured. Finally, another group of specimens treated with shot peening was polished and tested, obtaining similar lives as in the tests with specimens that were shot-peened but not polished.Junta de Andalucía P12-TEP-263

Determination and Analysis of Residual Stresses Induced by High Speed Milling Using a Micro-indent Method

The purpose of this work is to determine and analyze residual stress normal components and anisotropy degrees introduced by high-speed milling in specimens of AA 6082-T6 and AA 7075-T6 aluminum alloys. At each machined sample, the climb and conventional cutting zones were evaluated and compared. This paper includes a comprehensive study of thermal and mechanical effects associated with the residual stress introduction. For normal components determination, an optimized micro-indent method was used. Each measurement sequence from this approach was performed using a high accuracy measuring machine and classified according to thermal deviations measured. The residual displacements were determined with an absolute error down to ±300 nm. The normal components analysis allowed to infer the strong influence of the rolling process previous to high-speed milling and besides, the stress levels associated with thermal effects (higher in AA 7075-T6). Finally, the lower residual stress anisotropy degrees in both materials observed in the conventional cutting zone would indicate more homogenous local plastic stretching in this region for all planar directions.Fil: Vottero, S.. Universidad Tecnológica Nacional. Facultad Regional Rafaela; ArgentinaFil: Diaz, Felipe Victor. Universidad Tecnológica Nacional. Facultad Regional Rafaela; ArgentinaFil: Mammana, Claudio Alejandro. Universidad Tecnológica Nacional. Facultad Regional Rafaela; ArgentinaFil: Guidobono, A.. Instituto Nacional de Tecnología Industrial; Argentin

Evaluation of Thermal Mechanisms to Predict the Transient Electroplastic Effect in Aluminum and an Investigation of Electrically Assisted Drilling

The objective of this research is twofold: first, to evaluate if the microscale Joule heating theory can predict the transient electroplastic effect in 7075-T6 aluminum. Second, to determine if electrical application can have a significant impact on drilling of 1500MPa steel, and if the operation is predictable using a modified Merchant’s machining model. Both 7075-T6 and 1500 MPa steel are of interest to the automotive industry due to their high strength-to-weight ratios. These metals are important to aid in lightweighting to meet increasingly strict governmental fuel economy standards. However, the strength of the steel makes it difficult to machine in post-forming operations. The ductility of the aluminum makes it impossible to form using conventional methods, especially for deep parts such as a body side outer. A potential fix to these problems is electrical augmentation to locally or globally soften the metal. It has been shown that electricity can increase ductility/formability in metals while also decreasing the forming loads and stresses required (this group of phenomena is termed the electroplastic effect). While the effects of electricity are well known, the underlying mechanisms are not, resulting in four key theories, two of which have already been disproven. This research examines one of the remaining two theories to predict the transient electroplastic effect. The microscale Joule heating theory suggests that microscale hot spots develop inside of the metal in areas of high electrical resistivity, such as grain boundaries where dislocations pile up during deformation. A coupled mechanical-thermal-electrical model was partitioned with grains, grain boundaries, and precipitates. Temperature and dislocation density-dependent electrical resistivity was used in order to evaluate the microscale Joule heating theory. It was found that this theory cannot fully explain the resultant stress drop caused during the transient phase of electrically-assisted pulsed tension. During model testing it was discovered that electricity changes the strain hardening behavior of aluminum. To further investigate, the effect of electricity on precipitates was explored through measurement of precipitate size and distribution in specimens treated with different electrical treatments. An electrically-assisted drilling experiment was designed, fabricated, and tested to determine the effect of electricity on a drilling process. A design of experiments study was conducted on 1008 steel to determine if electric current had a significant effect on process temperature, axial force, and tool wear compared to inputs of feedrate and spindle RPM. It was found that current was dominant and that tool wear and cutting forces could be decreased with electric current. The first electrically-assisted drilling model was created by modifying Merchant’s machining model. This model was found to have shortcomings due to knowledge limitations on friction and equipment limitations on temperature measurement. The knowledge generated from the 1008 experiments was used to further the constraining limits of the drilling process, leading to 1000% tool life improvement on drilling of 1500 MPa steel while increasing the achievable feedrate for cutting by 200%