Deposition Residual Stress Research Articles

Machining characteristics of 316L stainless steel in hybrid manufacturing via a three-dimensional thermal-mechanical coupled model

The residual stress distribution obtained by coupling the laser metal deposition residual stress and the milling residual stress is one of the crucial factors affecting the quality and performance of hybrid manufacturing parts. However, it is challenging to explore directly through experiments. A three-dimensional thermal-mechanical fully coupled model for hybrid manufacturing of 316L stainless steel was established, taking into account the multi-physics during laser metal deposition and milling. The accuracy of the hybrid manufacturing model is validated from multiple dimensions using temperature, deformation, and milling force. A height deviation normalization method is proposed to eliminate the influence of printing height deviation caused by randomly fluctuated process parameters on the measuring deformation of the part. The minimum root-mean-square relative error of model temperature is 4 %, the minimum error of printing height deviation is 8 %, and the minimum relative error of milling force in the feed direction is 26 %. The simulated milling force of hybrid manufacturing shows that the factors affecting the milling force rank as the axial depth of cut, the radial depth of cut, milling speed, and spindle speed. The simulated residual stress distribution zone along the depth direction of hybrid manufacturing divides into the work hardening layer, the elastic recovery zone, and the elastic stability zone. The hybrid manufacturing residual stress equals the milling residual stress in the work hardening layer, superimposes linearly with the product of the milling residual stress and depth in the elastic recovery zone, and equals the residual stress of laser metal deposition in the elastic stability zone.

Implementing a Cohesive Zone Interface in a Diamond-Coated Tool for 2D Cutting Simulations

The interface properties and deposition residual stresses may have significant effects on the diamond-coated tool performance. However, it is still not fully understood how the interface mechanical behavior and deposition residual stress together influence the thermo-mechanical behavior of a diamond-coated tool during machining. In this study, a two-dimensional (2D) cutting simulation incorporating both deposition residual stresses and an interface cohesive zone model has been developed to demonstrate the feasibility of evaluating coating delamination of a diamond-coated tool during cutting. It has been shown that even the residual deposition stresses alone may result in failure initiations in the cohesive zone (i.e., the interface). In addition, the study further demonstrates the implementation of a cohesive zone interface in a diamond-coated tool in 2D cutting simulation. An example of cohesive failures occurred during the cutting simulation is presented. The result further shows that a larger uncut chip thickness will result in cohesive delamination of the coating-substrate interface during cutting.

A numerical study of cutting edge radius effects on stress evolutions of diamond coated tools

The stress state of a diamond coated tool is interrelatedly influenced by coating and subsequent machining. Moreover, the cutting edge geometry strongly impacts the stress fields around the tool tip in both processes. In this study, finite element modelling and cutting simulations were applied to investigate stress evolutions in a coated tool from deposition to machining, with the edge radius effect emphasised. For the deposition residual stress, edge sharpness results in significant stress concentrations at the edge rounding area. In machining, the thermal load is more dominant to the stress evolutions than the mechanical load. Increasing the edge radius generally results in increased stress reversal. Moreover, the edge hone effects on stress reversal are more prominent at a small uncut chip thickness. Since the edge radius has conflicting effects on the deposition stresses and machining loads, there may exist an optimal edge radius for the tool stress conditions.

Coating thickness effects on diamond coated cutting tools

Chemical vapor deposition (CVD)-grown diamond films have found applications as a hard coating for cutting tools. Even though the use of conventional diamond coatings seems to be accepted in the cutting tool industry, selections of proper coating thickness for different machining operations have not been often studied. Coating thickness affects the characteristics of diamond coated cutting tools in different perspectives that may mutually impact the tool performance in machining in a complex way. In this study, coating thickness effects on the deposition residual stresses, particularly around a cutting edge, and on coating failure modes were numerically investigated. On the other hand, coating thickness effects on tool surface smoothness and cutting edge radii were experimentally investigated. In addition, machining Al matrix composites using diamond coated tools with varied coating thicknesses was conducted to evaluate the effects on cutting forces, part surface finish and tool wear. The results are summarized as follows. (1) Increasing coating thickness will increase the residual stresses at the coating–substrate interface. (2) On the other hand, increasing coating thickness will generally increase the resistance of coating cracking and delamination. (3) Thicker coatings will result in larger edge radii; however, the extent of the effect on cutting forces also depends upon the machining condition. (4) For the thickness range tested, the life of diamond coated tools increases with the coating thickness because of delay of delaminations.

Numerical simulations of 3D tool geometry effects on deposition residual stresses in diamond coated cutting tools

Deposition residual stresses in diamond-coated cutting tools significantly impact the coating adhesion and machining performance. In this study, Computer-Aided Design (CAD) software was used to create the solid model of coated tools, and further exported to Finite Element Analysis (FEA) software for 3D simulations of residual stresses generated. Design of experiments approach was employed to systematically investigate the tool geometry effects. Major results are summarised as follows. • the cutting edge radius is the most significant factor • for a 5 µm edge radius, the radial and circumferential normal stresses (�1 r and �1 �� ) are about 1.5 GPa in tension and 3.7 GPa in compression, respectively.

Integrated Design and Analysis of Diamond-coated Drills

The objective of this paper is to investigate the drill geometry effects on the deposition residual stresses in diamond coated carbide drills, especially the interface stresses. The approaches include (1) solid modeling of diamond-coated two-flute twist drills using commercial computer-aided design (CAD) software, and (2) finite element analysis (FEA) to simulate residual stresses in a diamond-coated drill, which are generated during the deposition process due to the mismatched thermal expansion coefficients. It is noted that the residual stresses generated by deposition in diamondcoated drills can be significant, on the order of GPa. The modeling methodology is employed to design drills of different geometries. Further, to compare interface stresses around the cutting edge, 2D FEA is applied to simulate residual stresses of the drill cross-sections and the interface stress data at the drill cutting edge is transformed to quantitatively evaluate the drill geometry effects. The major results are summarized as follows. (1) The micro-level geometry such as the edge radius has the most dominant effects on the interface stresses by the deposition. (2) In particular, the radial normal stresses can become largely tensile, over 1.0 GPa, which may affect the coating adhesion integrity. (3) Changing the macro-level geometry such as the helix angle, point angle, and web-thickness will affect the wedge angle, 10 o to 20 o