Machine Hammer Peening Research Articles

Simulation and experimental study on surface modification of 6061‐T651 aluminum alloy by machine hammer peening

AbstractMachine hammer peening is a surface treatment technique employed to enhance the surface properties of the treated samples. In this present work, the theoretical analysis, finite element simulation and experiment of single peening are carried out to investigate the relationship between the machine hammer peening force and geometric dimensions of the single peening indentation deformation, including diameter and depth. The single peening experimental results are in accordance with theoretical and simulation analysis. The machine hammer peening experiment with grate tool path are done and the results including surface topography, surface roughness, surface hardness, x‐ray diffraction analysis and wear resistance are discussed. This work seeks to explore the effects of process parameters like machine hammer peening force, indentation and pitch spacing on surface roughness and hardness. The results reveal that the surface hardness and roughness are positively associated with machine hammer peening force and small indentation and pitch spacing lead to high hardness. The x‐ray diffraction analysis validate machine hammer peening is a mechanical treatment without new compound generated. The friction test results in an enhancement in wear resistance of treated samples.

β-Grain refinement in WAAM Ti-6Al-4 V processed with inter-pass ultrasonic impact peening

As-deposited Wire-Arc Additive Manufactured (WAAM) Ti-6Al-4V parts typically contain large columnar β-grains on a centimetre scale, with a strong 〈001〉 fibre texture, leading to anisotropic mechanical properties and unacceptable scatter in damage tolerance. Inter-pass deformation, introduced by the application of Ultrasonic Impact Peening (UIP) across each added layer, has been shown to be effective in refining the β-grain structure and achieving a weaker texture. The depth of deformation and the grain refinement mechanism induced by UIP have been investigated by combining advanced electron backscatter diffraction (EBSD) characterization with a ‘stop action’ observation technique. UIP facilitates a similar refinement mechanism and nearly the same depth of deformation as conventional machine hammer peening, with the advantages of a much higher strain rate, lower peak force, and two orders of magnitude lower impact energy, making it a faster and more economical process. β recrystallization is seen within the deformation zone during re-heating through the α → β transition. Although new recrystallized β-grains formed in the UIP surface-deformed layer to a shallower depth than that of remelting, recrystallization initiated ahead of the melt pool and the recrystallized grains grew downwards to a greater depth before remelting. These refined grains were thus able to survive and act as nucleation sites at the fusion boundary for epitaxial regrowth during solidification, greatly refining the grain structure.

The microhardness, morphology and tribological property of TC4 subjected to machine hammer peening

Ti alloy has become an indispensable material in harsh working environments due to its excellent wear resistance, corrosion resistance and impact resistance. These environments place stringent requirements on the fatigue life, friction and wear, and surface strength of materials. Therefore, this study aims to deeply explore the surface mechanical properties of Ti-6Al-4V (TC4) alloy after machine hammer peening (MHP) treatment. By conducting experiments on TC4 alloys treated with different hammering energies, the changes in surface hardness, morphology, roughness, tensile properties, and friction properties were analyzed, and the strengthening mechanism of MHP was discussed. Experimental results show that MHP treatment can effectively improve the surface properties of TC4. With the increase of hammer energy, due to the double-sided hammering of the plate, the microhardness first increases, then decreases, and then rises again. The tensile strength and yield strength of the sample increase slightly, but the elongation at break decreases. The surface roughness of the sample increases first and then decreases. Similarly, after MHP treatment, the wear resistance of the samples increased, the friction coefficient decreased, and the wear amount and surface height difference showed a trend of first increasing and then decreasing. The wear mechanism mainly included adhesive wear, abrasive wear and fatigue wear.

Investigation on microstructure and wear resistance of WC coated aluminum alloy using machine hammer peening

Due to the characteristic of low density and high strength, Aluminum alloy have been applied in various industries. However, poor surface properties, such as wear resistance, are the main reason for limiting its application. In this study, machine hammer peening (MHP) was used for embedding tungsten carbide (WC) particles in near-surface zone of aluminum alloy and the microstructure and wear resistance were investigated. The results show that WC particles can be embedded into aluminum alloy using MHP and WC coatings were generated with large and medium WC particles. The values of surface roughness were increased with increasing of WC particles sizes and XRD analysis indicated that no new compound was found during coating process. The significant increasing of wear resistance of WC coating has been obtained. MHP is a novel technique for obtaining WC coating and improving the tribological performance of aluminum alloy. Furthermore, it offers new possibilities to embedding hard particles in substrates of various materials.

Numerical analysis of the dependence of damage on friction during deep drawing of asymmetric geometries

The manufacturing of three-dimensional sheet metal components, such as car body parts, heavily relies on deep drawing. With the increasing demand for lightweight measures in the automotive industry due to CO2 limitation requirements, various methods are currently employed to reduce the weight of deep drawn components. However, these methods often overlook the potential for influencing the stress-strain dependent damage state within the component, even though it can greatly affect its performance in subsequent applications, and thus offers lightweight potentials. Friction between the deep drawing tools and the sheet metal is a key factor influencing the stress-strain state, and hence, represents a lever that can be utilized to manipulate the damage state in the component. This paper focuses on the numerical analysis of the dependence of damage on friction during deep drawing. Therefore, a rectangular geometry with an asymmetrical material flow is numerically investigated. A friction ratio is introduced with different constant friction coefficients for the corner of the tools and the straight sides. The established load paths at a chosen reference point are then considered in the form of selected stress and strain characteristics and the numerically predicted damage state is compared. The results are used to derive a recommended friction ratio that leads to less damage in the corner of the geometry. Afterwards strip drawing tool surfaces are modified to manipulate their friction properties using machine hammer peening. Subsequently, the influence of the structures of the strip drawing tool surfaces is quantified using strip drawing tests. The identified contact normal stress dependent friction coefficients are then implemented in the numerical simulation and the established numerical predicted damage state is examined to gain a more comprehensive understanding of how the friction ratio and the structure of the tool surfaces influence the damage state.

Reluctance Based Actuator for Discrete Machine Hammer Peening

In machine hammer peening, an actuator system moves a ram in oscillating motion, which is oriented in angular position, preferably perpendicular, to a workpiece surface. On the tip of the ram, a hammer head with application specific shapes can be mounted. The hammer head is moved across the targeted workpiece surface area by means of a machine tool or an industrial robot. The impacts in defined patterns enable modifications of the surface integrity like smoothing the surface roughness or increasing fatigue strength by induced compressive residual stresses. This paper presents a novel DC-driven actuator system using a highly dynamic short-stroke linear reluctance motor to provide a time or trigger controlled hammer head movement including a system for process monitoring. In contrast to conventional systems, Deterministic Impact Peening (DIP) can be realized by position or speed related triggering of the impacts. The reluctance-based actuator with its geometrically optimized mechatronic system design provides performance characteristics favorable to known machine hammer peening systems. The position-controlled triggering of the hammer head is able to achieve uniform or defined local elastoplastic deformations on the workpiece surface, thus resulting in deterministic residual stress distributions.

Surface Integrity of Additively Manufactured Workpieces after Machine Hammer Peening

Additively manufactured workpieces often exhibit issues such as porosity, roughness, and induced tensile residual stresses. The surface characteristics of such workpieces can be modified by post-processing techniques like Machine Hammer Peening (MHP). However, the influence of MHP on surface characteristics of additively manufactured workpieces has not been comprehensively studied. Thus, this study investigates the influence of MHP on surface integrity of workpieces created using wire-based Laser Metal Deposition (LMD-w) with Inconel 718 wire. The effect of secondary temperature on surface integrity is first evaluated. Following this, the impact of MHP process parameters on surface integrity is systematically investigated. The quantification of surface integrity is achieved by measuring its key aspects such as topography and surface layer characteristics, including surface roughness, waviness, hardness, recrystallization, and residual stresses. Microstructural analysis of the selected samples is conducted employing Scanning Electron Microscope (SEM) and optical microscopy. The obtained results provide valuable insights into the effectiveness of MHP on the surface integrity of LMD-w workpieces, along with practical guidelines for its optimization. Extending its impact, the study enhances the broader understanding of surface treatment in additive manufacturing.

Influence of the strain rate on the Surface Integrity on 42CrMo4 generated by machine hammer peening

Machine hammer peening is as well as deep rolling known to smoothen the surface, strain hardening and for inducing high compressive residual stresses in high depths in the surface and subsurface layer of steel. Although the beneficial effects of this manufacturing technology are well described, the influence of the strain rate on the surface and subsurface properties of machine hammer peened steel has yet to be examined. In this study three different kinetic impact energy levels and three different hammer diameters – resulting in nine different strain rates - are applied. For specimens made of hardened 42CrMo4 (AISI 4140), the analysis of the surface and subsurface properties by means of metallographic cross-sections and XRD measurements indicate that a variation of the strain rate mainly affects the depth effect at high levels of compressive residual stresses.

From Wire to Component: Aluminium Lithium Alloy Development for Wire and Arc Additive Manufacturing

The Innovative Aluminium filler Wires for Aircraft Structures (IAWAS) project aimed to demonstrate the potential of Wire Arc Additive Manufacture (WAAM) for the production of aluminium lithium components. Preliminary testing demonstrated the possibility of depositing an 2395 aluminium lithium filler wire using a plasma arc heat source and a local shielding device. The deposit had a low porosity level but also low ductility caused by long, vertical, segregated grain boundaries. Both chemical composition and deposition conditions are known to impact the deposit microstructure. In-situ alloying, an efficient technique to develop new material, was implemented using plasma arc as a heat source on aluminium lithium alloys. The results aligned with the literature review on the impact of copper on crack sensitivity and led to the design of a new alloy. Unfortunately, the composition selected yielded challenges during the drawing process, and the filler material quality was poor, leading to a low WAAM deposit quality. Machine hammer peening was implemented on the AA2395 alloy, resulting in a drastic increase in ductility and yield strength of 480 MPa after solution treatment and ageing. This alloy was used to manufacture an aluminium lithium demonstrator to showcase the potential of WAAM to produce real-life components.

Influences of Machine Hammer Peening on Inconel 718 Workpieces Manufactured by Wire-based Laser Metal Deposition

Additive manufacturing techniques, such as laser metal deposition (LMD), have been used to produce complex-shaped workpieces with high accuracy and material utilization. However, the as-built workpieces often suffer from typical defects such as porosity, surface roughness, and tensile residual stresses that may limit their mechanical properties and service life. To overcome these limitations, post-processing steps such as mechanical forming are recommended to improve the material properties. Surface treatment, such as machine hammer peening (MHP), can significantly improve wear resistance and fatigue strength of the additively manufactured workpiece. MHP is a deterministic, high-frequency forming process that can produce smooth surfaces with high compressive residual stresses. It also offers advantages in producing defined surface structures that exhibit friction-reducing properties. However, the influence of MHP process parameters, such as hammer frequency, step over distance, and stroke distance, on the surface integrity of additively manufactured workpieces is still unknown. In the present work, the influence of MHP on Inconel 718 workpieces manufactured by wire-based laser metal deposition (LMD-w) is analyzed. A Design of Experiments (DoE) of LMD-w parameters was employed to manufacture the workpieces. The workpieces with the least typical defects such as cracks and pores were then selected. In the next step, the selected workpieces were post-processed based on a DoE of MHP parameters. To investigate the influences of MHP on the microstructure of the workpieces, the resulting mechanical properties were measured. It was found that for Inconel 718 workpieces manufactured by LMD-w, MHP can significantly improve surface properties by reducing roughness and increasing hardness. Therefore, this study shows that MHP is a promising post-processing technique to enhance the surface integrity and mechanical properties of LMD-w manufactured workpieces.

Effect of Machine Hammer Peening Conditions on β Grain Refinement of Additively Manufactured Ti-6Al-4V

Ti-6Al-4V components built with wire plus arc additive manufacturing (WAAM) generally have long columnar β grains that cause anisotropic behavior when the material undergoes static and cyclic failure. Recently, machine hammer peening (MHP) has been proved to induce prior-β grain refinement in WAAM resulting in isotropic properties and increased strength. In this study, MHP was investigated for WAAM walls to establish the dependency of the β grain refinement on peening parameters, such as energy, tool radius, and distance between impact steps. All combinations of parameters investigated resulted in grain-refined microstructures. The plastic strain theory failed to explain these results, as the microstructure refinement achieved did not match the strain distribution obtained. Thus, a new theory of accumulated energy was proposed in which the dynamic deformation of the MHP process should also be taken into consideration. The mechanical properties for the MHP conditions showed higher strength and decreased anisotropy as the energy per length increased. This was attributed to the reduction in texture in the WAAM walls. Thus, when applying MHP, the energy per unit length is controlling the grain size obtained and improved mechanical properties can be achieved.

Correcting distortions of thin-walled machined parts by machine hammer peening

Thin-walled aerostructural components frequently get distorted after the machining process. Reworking to correct distortions or eventually rejecting parts significantly increases the cost. This paper proposes a new approach to correct distortions in thin-walled components by strategically applying hammer peening on target surfaces of a machined component. Aluminium alloy 7475-T7351 was chosen for this research. The study was divided in two stages. First, the residual stresses (RS) induced by four different pneumatic hammer peening conditions (modifying the stepover distance and initial offset) were characterised in a test coupon, and one of the conditions was selected for the next stage. In the second stage, a FEM model was used to predict distortions caused by machining in a representative workpiece. Then, the RS induced by hammer peening were included in an FEM model to define two hammer peening strategies (varying the coverage area) to analyse the capability to reduce distortions. Two workpieces were machined and then treated with the simulated hammer peening strategies for experimental validation. Results in the test coupon showed that pneumatic hammer peening can generate high compressive RS (-50 to −350 MPa) up to 800 μm depth, with their magnitude increasing with a reduced stepover distance. Application of hammer peening over 4 % of the surface of the representative workpiece reduced the machining-induced distortions by 37 %, and a coverage area of 100 % led to and overcorrection by a factor of five. This confirms that hammer peening can be strategically applied (in target areas and changing the percentage of coverage) to correct low or severe distortions.

Multi-objective optimization of the subsurface residual stress field of TC4 alloy in machine hammer peening

Machine hammer peening (MHP) is a surface strengthening process by introducing residual compressive stress at the part's surface. Many indicators of residual stress, such as the surface residual compressive stress and depth of residual compressive stress, significantly impact the fatigue performance of parts and thus need to be optimized. The present study focuses on two main problems in multi-objective optimization of the subsurface residual stress field induced by MHP: the relationship between a specific residual stress field and a combination of impact velocity and indentation distribution and how to implement the MHP process that could produce such a combination. The latter problem was first addressed by a kinematic model of the MHP device, which can optimize the MHP device input parameters to achieve the target axial impact velocity. For the former problem, a finite element model was first established to simulate the residual stress field induced by MHP. Then, the response surface method was used to optimize the simulated residual stress field with multiple objectives. Based on the above two models, we can obtain the appropriate MHP parameters to induce a target subsurface residual stress field. A verification experiment was carried out, and the residual stress field obtained was relatively close to the theoretical one, with a deviation of 1.7 % for the depth of residual compressive stress and 13.8 % for the surface residual compressive stress.

Machine Hammer Peening and Its Effect on the Surface Integrity of Arc-Sprayed WC-W2C-FeCMnSi Coatings

With respect to post-processing techniques in the field of surface engineering, it was recently found that machine hammer peening (MHP) represents a promising approach to functionalizing thermally sprayed coatings as the MHP contributes to a compression of the coating, enabling the potential to reduce the coating porosity as well as the protruding peaks of the rough as-sprayed coating surface. The MHP also has the potential to induce compressive residual stresses in the coating surface, which can positively affect the mechanical and tribological properties. Arc-sprayed tungsten carbide-reinforced Fe-based coatings pose an appropriate candidate to counteract the wear of tribologically stressed surfaces. Due to the inherent process characteristics, however, these coatings are mostly characterized by a heterogeneous lamellar microstructure with residual porosity and interstratified with a certain amount of oxides, as well as the presence of tensile residual stresses. To adjust their microstructural and mechanical coating properties, the applicability of a subsequent MHP was evaluated in this study. Therefore, arc-sprayed WC-W2C reinforced FeCMnSi coatings are deposited using either argon or compressed air as atomization and shroud gas, providing different lamellar structures and oxide content. The effect of MHP on the surface integrity of the WC-W2C-FeCMnSi coating is investigated with respect to its porosity, lamellar structure, hardness, and residual stresses, which are known as relevant influencing factors on the performance of tribologically stressed components. It was found that the MHP leads to reduced porosity and lamella thickness as well as increased hardness due to strain hardening effects. Furthermore, it was demonstrated that the MHP leads to the introduction of compressive residual stresses, which contribute to a decline in tensile residual stresses in the near-surface area.

Precisely tuning the residual stress anisotropy in machine hammer peening

Precisely tuning the residual stress anisotropy in machine hammer peening

Non-destructive characterization of strain induced surface hardness increase by measuring magnetic properties of AISI 304

The goal of this work is to establish a correlation between the surface integrity and magnetic properties of stainless steels like AISI 304 (X5CrNi18-10). In metastable austenitic stainless steels, a phase transformation from the austenitic to the martensitic phase can occur even at room temperature. In this work, machine hammer peening (MHP) is used to selectively introduce the activation energy required for martensite formation on discrete areas of the surface. The phase transformation is confirmed by electron back scatter diffraction (EBSD) and micrographs. A correlation between the energy input by MHP, magnetic properties, and surface hardness is established. Using this approach, characterization of the surface integrity by measuring magnetic properties can be achieved. In addition, a novel solution to code and encode information with high information density onto metastable austenitic materials is proposed.

Wälzfestigkeit maschinell gehämmerter Oberflächenstrukturen im Zahnflankenanalogieversuch

Rolling-sliding contacts, such as the tooth flank contact, are tribological systems whose properties are determined by the interactions between the contacting bodies, the lubricant and the ambient medium. Innovative manufacturing processes are being used to reduce friction and increase the load-carrying capacity of highly loaded rolling-sliding contacts. For mixed friction conditions, bowl-shaped structures in particular, generated for example by laser machining, have led to improved running behavior. Similar to laser machining, machine hammer peening (MHP) also produces a deterministic surface structure that can exhibit improved tribological properties. In recent years, MHP has been used specifically to optimize the service life of highly stressed tools, e.g. in deep-drawing processes, and has been developed further in a targeted manner. In this report, the rolling strength of machine-hammered surfaces is evaluated using fatigue tests on a disk-on-disk test rig gear-typical contact conditions. The MHP can be used to increase the contact strength in a targeted manner, whereby the selection of the process parameters during surface hammering represent an important influencing factor. In particular, the surface can be pre-damaged by excessive impact energy as a result of the ram stroke.

Comparison of Microstructure Refinement in Wire-Arc Additively Manufactured Ti–6Al–2Sn–4Zr–2Mo–0.1Si and Ti–6Al–4V Built With Inter-Pass Deformation

The titanium alloy Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242) has been deposited for the first time by a directed energy deposition process using a wire and arc system—i.e., wire-arc additive manufacturing (WAAM)—with and without inter-pass machine hammer peening, and its microstructure investigated and compared to the more commonly used alloy Ti–6Al–4V (Ti64). The application of inter-pass machine hammer peening—where each added layer was deformed before deposition—successfully refined the strongly textured, coarse, columnar β-grain structure that is commonly seen in α + β titanium alloys, producing a finer equiaxed grain structure with a near-random α texture. The average grain diameter and texture strength decreased with the peening pitch. When Ti6242 was deposited under identical conditions to Ti64, by switching the alloy feed wire in-situ, the refined β-grain size decreased across the alloy-to-alloy transition reaching on average 25 pct less in Ti6242 than in Ti64. A similar 25 pct scale reduction was also found in the Ti6242 α-lath transformation microstructure. This comparatively greater microstructure refinement in Ti6242 was attributed to the dissimilar alloying elements present in the two materials; specifically, molybdenum, which has a lower diffusivity than vanadium and led to slower β-grain growth during reheating as well as a finer transformation microstructure.

Identification of Influencing Factors in Machine Hammer Peening with Consideration of Lubricant Influences

Lightweight construction and performance requirements in the automotive industry have resulted in increased power density. At the same time, this increases the load on the workpieces. To counteract the resulting wear, either a more wear-resistant material may be applied or the functional surface may be specifically modified against wear. Machine hammer peening (MHP) is a process for such a targeted adjustment of the functional surface and the surface area properties. MHP is a mechanical surface treatment, which increases the wear resistance of the workpieces by introducing residual compressive stresses and work hardening as well as by smoothing or structuring the surface. To ensure an accurate adjustment of the surface properties, the influencing factors (material, process parameters and lubricant) and their interactions must be sufficiently well studied and understood. In particular, the influence of the lubricant on the surface area properties has not yet been adequately investigated. The objective of the work presented in this paper was to provide a deeper insight into the influence of the type of lubricant on the resulting surface properties in terms of roughness, residual stresses and hardness. The lubricant’s influence was investigated using a partial factorial experimental design. Additional factors investigated, besides the choice of lubricant, were stroke, distance of indentation and step over distance. The results show a strong influence of the lubricant selection, especially on the resulting surface roughness. For the same process parameters, a deviation of 540 % in the resulting surface roughness was measured between two surfaces machined with different lubricants.

Corrosion Fatigue Behavior of Twin Wire Arc Sprayed and Machine Hammer Peened ZnAl4 Coatings on S355 J2C + C Substrate

Offshore installations, e.g., offshore wind turbines and pipelines, are exposed to various mechanical loads due to wind or waves and corrosive loads such as seawater or mist. ZnAl-based thermal sprayed coatings, often in conjunction with organic coatings, provide sufficient corrosion protection and are well established for applications in marine environments. In this study, machine hammer peening (MHP) is applied after twin wire arc spraying to improve corrosion fatigue behavior through increased hardness, reduced porosity, and roughness compared to as-sprayed coatings. Mn-alloyed structural steel S355 J2 + C with and without ZnAl4 coating as well as with MHP post-treated ZnAl4 coating were cyclically loaded in 3.5% NaCl solution. MHP leads to a uniform coating thickness with lower porosity and roughness. ZnAl4 coating and MHP post-treatment improved corrosion fatigue behavior in the high cycle fatigue regime with an increase of the stress amplitude, applied to reach a number of cycles 1.2 × 106, up to 115% compared to sandblasted specimens. Corrosive attack of the substrate steel was successfully avoided by using the coating systems. Stress- and microstructure-dependent corrosion fatigue damage mechanisms were evaluated by mechanical and electrochemical measurement techniques.