Heterogeneity of Adhesive Joint Properties.

This paper presents the results of a study of adhesive joints, focused on the heterogeneity of the properties of the adhesive material in the adhesive joint. The main objective of the study was to determine potential differences in the material properties of adhesive joints made with selected structural adhesives. Due to the impact of the joined material on the adhesive during the curing of the joint as well as the impact of phenomena occurring during the curing of the adhesive, the properties of the adhesive joint may vary along the thickness of the joint. Determining the differences in material properties over the thickness of the adhesive bond is important for more accurate prediction of adhesive bond strength in FEM simulations. In order to observe changes in the material properties of bonds, nanoindentation tests have been carried out on eight adhesive joint bonds made with common structural adhesives used to join sheets of aluminium alloy or corrosion-resistant steel. Basing on the achieved test results, load/unload curves were developed for imprints at characteristic spots of the joints. Distinct differences in the achieved average force value were observed for imprints located in the wall-adjacent zone and in the centre of the adhesive joint; this can be interpreted as areas of the joint with different material structures of higher or lower density of imperfections or porosities. Differences in the load/unload curves for 'rigid' and 'flexible' adhesives were analysed. The summary includes a conclusion that an adhesive joint is characterised by heterogeneous properties along its thickness.

Capability Analysis of AZ91D Magnesium Alloy Precision Milling Process with Coated Tools.

Process capability analysis is the main tool of statistical process control. It is used for the ongoing monitoring of product compliance with imposed requirements. The main objective and novelty of the study were to determine the capability indices for a precision milling process of AZ91D magnesium alloy. Machining was performed in terms of variable technological parameters and using end mills with protective TiAlN and TiB2 coatings intended for the machining of light metal alloys. The Pp and Ppk process capability indices were determined based on the measurements of the dimensional accuracy of the shaped components that were taken on a machining centre with a workpiece touch probe. Obtained results demonstrated that the type of tool coating and variable machining conditions had a significant impact on the machining effect. The selection of appropriate machining conditions enabled a terrific level of capability to be achieved at a tolerance of 12 µm, several times lower than under unfavourable conditions where the tolerance was up to 120 µm. Improvements in process capability are mainly achieved by adjusting the cutting speed and feed per tooth. It was also shown that process estimation based on improperly selected capability indices might lead to an overestimation of the actual process capability.

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.

Apparent Young's Modulus of Epoxy Adhesives.

This article presents the results of a study of the properties of epoxy adhesives in an adhesive joint. The study analysed changes in Young's modulus values as a function of the rigidity of the adhesive and the type of joined material. The values of Young's modulus values were determined on the thickness of the adhesive joint using the nanoindentation method and in a tensile test of dumbbell shape sample for the adhesive material. The obtained results were analysed in terms of changes to the values of Young's modulus of the adhesive as a function of the distance from the joined material-adhesive phase boundary and compared to the adhesive material. Zones were distinguished in the layer of the adhesive joint-adjacent to the wall and the core, with different values of Young's modulus. Conclusions were drawn, indicating the relationship between the adhesive joint thickness and the increase in the value of Young's modulus. Significant differences were found in the values of Young's modulus of the adhesive joint compared to Young's modulus of the adhesive in the form of plastic.

Dimensional Accuracy and Surface Quality of AZ91D Magnesium Alloy Components after Precision Milling.

This study investigates a precision milling process conducted with the use of conventional end mills and a standard CNC (Computer Numerical Control) machine tool. Milling tests were performed on samples of AZ91D magnesium alloy using TiB2- and TiAlN-coated three-edge end mills measuring 16 mm in diameter. The following technological parameters were made variable: cutting speed, feed per tooth and axial depth of cut. The effects of precision milling were evaluated by analysing the scatter of dimension values obtained in successive tool passes. In addition to that, deviations from the assumed nominal depth as well as obtained ranges of dimension varation were analysed. The study also examined surface quality obtained in the precision milling process, based on the basic surface roughness parameters: Ra, Rz and RSm. Results have confirmed that the use of conventional cutting tools and a standard CNC machine tool makes it possible to manufacture components characterized by relatively small scatter of dimension values and high accuracy classes. Additionally, the results have shown that the type of tool coating and variations of individual technological parameters exert impact on the dimensional accuracy and surface quality obtained.

Surface Roughness after Milling of the Al/CFRP Stacks with a Diamond Tool.

This study presents the results of research on the surface quality of hybrid sandwich structures after milling with a diamond blade tool. It identifies the effects of feed and machining strategy on the roughness and topography of the surface. It provides an analysis of Ra and Rz surface roughness parameters as well as Sp, Sz, and Sv surface topography parameters. The processed object was a two-layer sandwich structure consisting of aluminium alloy 2024 and CFRP (carbon fibre-reinforced polymer) composite. The minimum values of the Ra and Rz surface roughness parameters were obtained on the aluminium alloy surface, whereas the maximum values were obtained on the CFRP surface. The same was true for the 3D surface roughness parameters-the lowest values of Sp, Sz, and Sv parameters were obtained on the surface of the metal layer, while the highest values were obtained on the surface of the composite layer (the maximum value of the Sp parameter was an exception). A surface topography analysis has revealed a targeted and periodic pattern of micro-irregularities for the vast majority of the samples considered. The statistical analysis shows that the surface roughness of the aluminium alloy was only affected by the feed rate. For the CFRP, the feed rate and the interaction of milling strategy and feed rate (S × fz) had a statistically significant effect. The obtained results provide a basis for designing such sandwich element processing technology, for which differences in roughness and topography parameters for the component materials are lowest.

Apparent Young's Modulus of the Adhesive in Numerical Modeling of Adhesive Joints.

This article is an evaluation of the phenomena occurring in adhesive joints during curing and their consequences. Considering changes in the values of Young's modulus distributed along the joint thickness, and potential changes in adhesive strength in the cured state, the use of a numerical model may make it possible to improve finite element simulation effects and bring their results closer to experimental data. The results of a tensile test of a double overlap adhesive joint sample, performed using an extensometer, are presented. This test allowed for the precise determination of the shear modulus G of the cured adhesive under experimental conditions. Then, on the basis of the research carried out so far, a numerical model was built, taking the differences observed in the properties of the joint material into account. The stress distribution in a three-zone adhesive joint was analyzed in comparison to the standard numerical model in which the adhesive in the joint was treated as isotropic. It is proposed that a joint model with three-zones, differing in the Young's modulus values, is more accurate for mapping the experimental results.

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.

Adhesive Joint Stiffness in the Aspect of FEM Modelling.

The paper presents the results of nanoindentation testing, carried out along the thickness of the adhesive joint joining sheets of aluminum alloy. The purpose of the tests was to determine changes in the Young's modulus in the joint resulting from the active impact of the joined aluminum alloy sheets on the adhesive during curing of the adhesive bond. Structural changes that take place during curing of the joint, especially in the boundary zone, can have a significant impact on the adhesive properties and consequently, on the adhesive joint strength. The Young's modulus of the adhesive (Ek) in the joint assumes variable values as the distance from the connections changes. This phenomenon is called the apparent Young's modulus. The problem is to define the size of the boundary zone in which the value of Ek significantly differs from the value in the so-called core. Based on the obtained results of experimental tests, a numerical model was built taking into account the observed differences in the properties of the joint material. The stress distribution in the adhesive joint, single-lap connection with the three-zone adhesive joint, was analyzed in comparison to the classical numerical model in which adhesive in the adhesive joint is treated as isotropic in terms of rigidity.

Modification of Ti6Al4V Titanium Alloy Surface Layer in the Ozone Atmosphere.

The paper reports the results of a study on the Ti6Al4V titanium alloy involving the XPS (X-ray photoelectron spectroscopy) photoelectron spectroscopy method. The position of bands in the viewing spectrum serves as a basis for the qualitative identification of atoms forming the surface layer, while their intensity is used to calculate the aggregate concentration of these atoms in the analyzed layer. High-resolution spectra are used to determine the type of chemical bonds based on characteristic numerical values of the chemical shift. The paper also presents the 3D results of surface roughness measurements obtained from optical profiling, as well as the results of energy state measurements of the Ti6Al4V titanium alloy surface layer after ozone treatment. It was shown that the ozone treatment of the Ti6Al4V titanium alloy removes carbon and increases concentrations of Ti and V ions at higher oxidation states at the expense of metal atoms and lower valence ions. The modification of the surface layer in ozone atmosphere caused a 30% increase in the Ti element concentration in the surface layer compared to the samples prior to ozone treatment. The carbon removal rate from the Ti6Al4V titanium alloy samples amounted to 35%, and a 13% increase was noted in oxides. The tests proved that the value of the surface free energy of the Ti6Al4V titanium alloy increased as a result of ozone treatment. The highest increase in the surface free energy was observed for Variant 4 samples, and amounted to 17% compared to the untreated samples, while the lowest increase was equal to 14%. For the analyzed data, the maximum value of standard deviation was 0.99 [mJ/m2].

Investigation of briquetting of metal waste from the bearing industry.

An economical method to process the metal waste that comes from the ball-bearing industry is presented. The purpose of the study was to determine the physical-chemical properties of the material, to present the most suitable binders and identify the factors that can affect briquette strength. The mechanical strength and resistance to gravitational drop were defined for both fresh briquettes and those that had been seasoned. The briquette structure was also tested. On the basis of the results of experimental studies and laboratory trials two techniques for processing the waste from the ballbearing industry on an industrial technological scale were developed. The economic and ecological impacts of these industrial applications were examined. The results of the investigations suggest that the briquettes might be recycled in steel-making furnaces. The reported solution to the problem of management of this type of waste appears to be universal and could also be applied by other waste-related enterprises.