Effect of the Technological Parameters of Milling on Residual Stress in the Surface Layer of Thin-Walled Plates.

The production of thin-walled elements, especially those with large overall dimensions, poses numerous technological and operational problems. One of these problems relates to the machining-induced strain of such elements resulting from residual stress generated during the machining process. This study investigates the effect of the technological parameters of milling on residual stress in the surface layer of thin-walled plates made of aluminum alloy EN AW-2024 T351 for aerospace applications. The results have shown that residual stress increases with the cutting speed only to a certain point, reaching the maximum value at vc = 750 m/min. At a cutting speed vc = 900 m/min, residual stress significantly decreases, which probably results from the fact that the milling process has entered the High-Speed Cutting range, and this inference agrees with the results obtained for the cutting force component. Residual stress increases with the feed per tooth, while the relationship between residual stress and milling width is the same as that established for residual stress and variable cutting speed. Positive tensile stress is obtained in every tested case of the milling process. The results have also shown that the induced residual stress affects the strain of machined thin-walled parts, as proved by the strain results obtained for milled thin walls.

Effect of the Geometry of Thin-Walled Aluminium Alloy Elements on Their Deformations after Milling.

The aim of this paper is to analyse the effect of the selected geometric properties of thin-walled structures on post-machining deformations. In the study, EN AW-7075 T651 and EN AW-6082 T651 aluminium alloys were used to prepare specially designed thin-walled sample elements, i.e., elements with walls arranged in a semi-open and closed structure and with a dimension of 165 × 262 × 50.8 mm consisting of bottom and vertical stiffening walls and so-called ribs with a thickness of 1 mm. The measurements of the absolute deformations of the thin-walled bottom were performed with the use of a Vista coordinate-measuring machine by Zeiss with a PH10 head by Renishaw. Based on the obtained results, it was found that absolute deformation values were higher for walls arranged in a semi-open structure. It is related to a lower rigidity of the tested structure resulting from the lack of a stiffening wall, which is the so-called "rib". Notwithstanding the geometry of the elements, greater absolute deformation values were recorded following conventional cutting methods. The use of high-speed cutting (HSC) provided positive outcomes in terms of minimising the deformation of thin-walled elements. Additionally, it was found that higher absolute deformations were obtained for EN AW-7075 T651 alloy.

Post-Machining Deformations of Thin-Walled Elements Made of EN AW-2024 T351 Aluminum Alloy as Regards the Mechanical Properties of the Applied, Rolled Semi-Finished Products.

The paper presents an evaluation of post-machining deformations of thin-walled elements as regards the mechanical properties of the applied, rolled semi-finished products. Nowadays, wrought aluminum alloys, supplied primarily in the form of rolled plates, are widely applied in the production of thin-walled integral parts. Considering the high requirements for materials, especially in the aviation sector, it is important to be aware of their mechanical properties and for semi-finished products delivered after plastic working to take into account the so-called "technological history" concerning, inter alia, the direction of rolling. The study focused on determining the influence of the ratio of the tension direction to the rolling direction on the selected mechanical properties of the EN AW-2024 T351 aluminum alloy depending on the sample thickness and its relation to the deformation of thin-walled parts. Based on the obtained results, it was found that the sample thickness and the ratio of the tension direction to the rolling direction affected the mechanical properties of the selected aluminum alloy, which in turn translated into post-machining deformations. Summarizing, the textured surface layer had a significant impact on the mentioned deformation. Greater deformations were noted for samples made of a semi-finished product with a thickness of 5 mm in comparison to 12 mm. It was the result of the influence of the surface layer, which at lower thickness had a higher percentage of contents than in thicker samples.

A Comparison of the Geometrical Accuracy of Thin-Walled Elements Made of Different Aluminum Alloys.

In modern constructions, especially aircraft, the aim is to minimize the weight of the components used. This necessitates the use of innovative construction materials, or the production of these parts with ever-decreasing wall thicknesses. To simplify assembly and improve strength properties, so-called structural elements are being used in the form of monolithic elements, which are replacing the assemblies of parts joined by, for example, riveting. These structures often have a complex, thin-walled geometry with deep pockets. This paper attempts to assess the accuracy of manufacturing thin-walled elements, in the shape of walls with different geometries, made of various aluminum alloys. Machining tests were conducted at different cutting speeds, which allowed comparisons of the geometric accuracy of parts manufactured under conventional and high-speed cutting conditions. Based on the result obtained, it was found that the elements made of EN AW-7075 T651 alloy underwent the greatest deformations during machining in comparison to other two materials (EN AW-6082 T651 and EN AC-43000). An increase in the geometrical accuracy of the manufactured elements was also observed with the increase in the cutting speed for the HSC range. Hence, to minimize the postmachining deformation of thin-walled elements, the use of high-speed cutting is justified.

Cutting Force during Surface Layer Milling of Selected Aluminium Alloys.

This paper presents the analysis of cutting force during surface layer milling of selected aluminium alloys, which are widely used in the aviation industry. The cutting force is one of the most important parameters determining the machinability of the material and also provides important information about the course of the cutting. The study analysed the influence of the technological parameters, i.e., cutting speed vc and depth of cut ap as well as the relation between cutting tool feed direction and rolling direction on the value of cutting force during milling of selected aluminium alloys, i.e., EN AW-2017A T451 and EN AW-2024 T351. The material anisotropy is a very important issue, since the engineering industry faces enormous problems related to the cutting of the tested materials that are usually supplied in the form of rolled plates. The surface layer was cut due to the fact that it accumulates the greatest residual stresses. The measurement process of cutting force was performed by using 9257B Kistler piezoelectric dynamometer. As part of the analysis of the results, the measurement uncertainty was also estimated, which was determined on the basis of two components obtained by using the A and B methods, respectively.

Pre-Machining of Rolled Plates as an Element of Minimising the Post-Machining Deformations.

The paper presents the influence of the milling strategy, the relation between the cutting tool feed direction and the rolling direction, as well as the pre-machining consisting of the removal of the textured surface layer of rolled plates in the rolling process on the thin-walled elements deformations made of the EN AW-2024 T351 wrought aluminium alloy, after milling. The research used strategies such as: high-performance cutting (HPC), high-speed cutting (HSC) and conventional milling (CM), as well as their combinations. Another tested variable was the relation between the tool feed direction and the rolling direction. In addition, the tests were carried out in the following versions: leaving the textured surface layer created after plastic working and with its removal with technological parameters corresponding to HSC and CM. Based on the obtained results, it was found that the post-machining deformation of thin-walled elements can be minimised owing to the use of a selected milling strategy and its combination with pre-machining (or lack thereof). It was also observed that larger deformations were obtained for samples after milling in the direction perpendicular to the rolling direction.

Techniques for Thin-Walled Element Milling with Respect to Minimising Post-Machining Deformations.

The paper examines the impact of selected machining techniques and the semi-finished product technological history on deformations of thin-walled elements made of EN AW-2024 T351 aluminium alloy after milling. The following techniques have been implemented: High Performance Cutting, High Speed Cutting, conventional finishing (CF) and combinations of these techniques. As for the semi-finished product technological history, the rolling direction has been analysed. It has been assumed that it can be relevant in relation to the cutting tool feed direction and, in consequence, exert considerable impact on the stress, as well as deformation following machining. The interest in this issue proceeds from significant challenges faced by the industry, particularly in the aerospace sector. The analysis of results obtained has shown that milling in the direction perpendicular to the rolling direction results in larger deformations than milling in the parallel direction. Additionally, it has been revealed that applying a correctly selected machining technique makes it possible to minimise post-machining deformations of thin-walled elements.

Milling of an Al/CFRP Sandwich Construction with Non-Coated and TiAlN-Coated Tools.

In this study, the effect of cutting parameters on the quality of an Al/CFRP sandwich structure (aluminium alloy-carbon fibre reinforced polymer) after milling with uncoated and TiAlN-coated tools was examined. The results of the cutting force were also investigated. The research was conducted in a VMC 800 HS vertical machining centre with a variable cutting speed and feed. The milling process was carried out using a non-coated, two-blade carbide milling cutter with a 35° helix angle and an analogous tool with a TiAlN coating. The surface quality was characterised in terms of the height deviation, which is one of the shape deviations after machining hybrid materials. The research showed that the maximum (77.60 µm) and minimum (1.78 µm) values of the height deviations were obtained using the tool with a TiAlN coating. It was found that the tested factors had significant effects on the height deviation, where the feed had the greatest influence and the cutting speed had the lowest influence on the surface quality. The tested factors were not statistically significant in terms of the cutting force.

Influence of Cutting Parameters on the Surface Quality of Two-Layer Sandwich Structures.

Hybrid sandwich structures are more and more widely used in many industries. This is mainly due to their good properties. One of the limitations regarding the use of sandwich structures is their difficult processing. Therefore, it seems reasonable to determine the influence of cutting parameters and machining configuration on the characteristic defect (phase) formed at the boundary of the materials forming a hybrid sandwich structure. This study investigates the effects of layer orientations during milling and machining parameters such as the cutting speed Vc, the feed fz and the cutting width ae. The study is conducted on a two-layer sandwich structure composed of two materials: 2024 aluminum alloy and epoxy-carbon composite with 60% of high-strength carbon fibers. A statistical analysis is performed using the Statistica program. The results show that the change in the cutting parameters has a greater impact on the formation of a defect on the surface of samples when the machining process starts on the side of the composite rather than the metal. The highest defect value is obtained for the milling from the composite layer when the process is performed with the following cutting parameters: Vc = 300 m/min, fz = 0.08 mm/tooth, ae = 5 mm.

Tribological Aspects of Cutting Tool Wear during the Turning of Stainless Steels.

The research paper presents the tribological aspects of cutting tool wear during the turning of stainless steels. An experiment was conducted in order to assess the wear of carbide cutting inserts with CVD-applied anti-wear coatings (CNMG 12 04 08 ZSZ and CNMA 12 04 12-KR 3205) and an uncoated ceramic cutting insert (CNGA 12 04 08 T0102 WG 650). The test subject included the following stainless steel grades X20Cr13 (1.4021) and X8CrNiS18-9 (1.4305). The analysis involved the direct wear indicator, VBBmax, and the indirect wear indicator, which was the roughness of machined surfaces and the Ra parameter. Based on the obtained results for both X20Cr13 and X8CrNiS18-9 steels, it was noticed that the best durability was exhibited by the CNMG 12 04 08 ZSZ insert, whereas the worst durability was identified for the CNGA 12 04 08 T0102 WG 650 insert. When analysing the results obtained with the VBBmax direct indicator, it was observed that in the case of each of the insert, most often the course of their wear was of nature similar to linear. Comparing the VBBmax direct indicator with the indirect indicator, namely, the measured Ra parameter, it was concluded that they were convergent. Upon the deterioration of the surface quality, greater values of the selected geometric measure of wear on the flank face were also identified.