Laser Surface Modification of H13 Die Steel using Different Laser Spot Sizes

This paper presents a laser surface modification process of AISI H13 tool steel using three sizes of laser spot with an aim to achieve reduced grain size and surface roughness. A Rofin DC'015 diffusion'cooled CO2 slab laser was used to process AISI H13 tool steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, overlap percentage and pulse repetition frequency (PRF). Metallographic study and image analysis were done to measure the grain size and the modified surface roughness was measured using two'dimensional surface profilometer. From metallographic study, the smallest grain sizes measured by laser modified surface were between 0.51 3m and 2.54 3m. The minimum surface roughness, Ra, recorded was 3.0 3m. This surface roughness of the modified die steel is similar to the surface quality of cast products. The grain size correlation with hardness followed the findings correlate with Hall'Petch relationship. The potential found for increase in surface hardness represents an important method to sustain tooling life

Optimization of Pulsed Nd:YAG Laser Melting of Gray Cast Iron At Different Spot Sizes for Enhanced Surface Properties

This paper presents a laser surface modification process of gray cast iron using different laser spot size with an aims to eliminate graphite phase and achieve minimum surface roughness and maximum depth of molten zone and microhardness properties. The laser processing was conducted using JK300HPS Nd:YAG twin lamp laser source pulse TEM 00 mode, 50 W average power, 1064 nm wavelength and different laser spot sizes of 1.0 mm, 1.2 mm, 1.4 mm and 1.7 mm. Three controlled parameter were peak power (Pp), pulse repetition frequency (PRF) and traverse speed (v). Increasing spot size the parameter setting where peak power is increased and pulse repetition frequency and traverse speed is decreased. The modified surface of laser surface melting was characterized for metallographic study, surface roughness and hardness. Metallographic study and surface morphology were conducted using optical microscope while hardness properties were measured using Vickers scale. Surface roughness was measured using a 2D stylus profilometer. From metallographic study, the graphite phase was totally eliminated from the molten zone and formed white zone. This phenomenon affected hardness properties of the modified surface where maximum hardness of 955.8 HV0.1 achieved. Optimization of laser surface modification was conducted for minimum surface roughness and maximum depth of modified layer and hardness properties. From the optimization, the higher desirability is 0.902. The highest depth of molten zone obtain from spot size 1.4 mm at 132 µm and the highest hardness is 989 HV0.1 at laser’s spot size 1.0 mm. The surface roughness increased when the spot size increased from 3.10 µm to 7.31 µm. These finding indicate potential application of enhanced gray cast iron in high wear resistance automotive components such as cylinder liner and break disc

Thermal fatigue properties of laser treated steels

This paper presents the thermal fatigue resistance of laser treated steels. The C40 and AISI H13 steels were machined into a geometry which allowed thermal gradients on the inner and outer surface during testing. A CO2 laser system was used with a focused spot size of 0.09 mm on the sample surface. The laser peak power and pulse repetition frequency (PRF) range were set to 760 and 1515 W, and 2900 to 3500 Hz respectively. The thermal fatigue machine used consists of Nabertherm model cylindrical high temperature furnace with digital control panel, controlled temperature quenching system, and pneumatics control sample movement mechanism. The thermal fatigue test involved immersion of samples into molten aluminium, and quenched in ionised water emulsion at 17°C temperature. The quenching system equipped with thermocouple to control the water temperature. Testing was done at a total of 1,750 number of cycles. Internal surface cooling was controlled by water inlet and outlet tubes. Samples were cleaned using NaOH solution after thermal fatigue testing to remove oxides on the surface. The solution temperature and magnetic stirrer speed were set to 100°C and 4.5 rpm respectively. Samples were characterised using scanning electron microscope (SEM), energy discharge x-ray spectroscopy (EDXS) and 2D stylus profilometer. Presence of different phases on the sample surface were analysed from back-scattered detector micrographs. Heat checks were observed on laser glazed surface at several regions. Carbides and oxides elements were detected on the sample surface after the thermal fatigue test. The relationship between surface roughness of laser treated surface and thermal fatigue behaviour was investigated

Laser Micro-Processing Of Amorphous And Partially Crystalline cu45Zr48Al7 Alloy

This paper presents a microstructural study of laser micro-processed high-purity Cu45Zr48Al7 alloys prepared by arc melting and Cu-mould casting. Microprocessing of the Cu45Zr48Al7 alloy was performed using a Rofin DC-015 diffusion-cooled CO2 slab laser system with 10.6-µm wavelength. The laser was defocused to a spot size of 0.2 mm on the sample surface. The laser parameters were set to give 300- and 350-Wpeak power, 30% duty cycle and a 3000-Hz laser pulse repetition frequency (PRF). About 100-micrometer-wide channels were scribed on the surfaces of disk-shaped amorphous and partially crystalline samples at traverse speeds of 500 and 5000 mm/min. These channels were analysed using scanning electron microscopy (SEM) and 2D stylus profilometry. The metallographic study and profile of these processed regions are discussed in terms of the applied laser processing parameters. The SEM micrographs showed that striation marks developed at the edge and inside these regions as a result of the laser processing. The results from this work showed that microscale features can be produced on the surface of amorphous Cu–Zr–Al alloys by CO2 laser processing

Laser cladding process to enhanced surface properties of hot press forming die: A review

Laser cladding is one of the advance processes in laser surface treatments. The process involved a laser beam to combines another material that has different metallurgical properties on a substrate, whereby a very thin layer of the substrate has to be melted for it to achieve metallurgical bonding with minimal dilution of added material and substrate. The resulted properties were characterized by surface topography, subsurface microstructure, hardness, and residual stresses. The objective of this paper is to review the factors that affected of cladding process to get the best cladding, suitable to enhance hot press forming die surface and subsurface. The parameter control, metallurgical bonding between coating and substrate, and effect of powder size were discussed

Mechanical characterisation of water-jet shot peened H13 tool steel surface

A wear-resistant surface is achievable via the surface treatment of various sources such as laser, water-jet, ion beam, and plasma. This paper investigates the parameters of water-jet shot-peened H13 tool steel for minimum surface roughness and maximum hardness properties. Water jet processing parameters are significant in determining the surface roughness as well as hardness properties. Water-jet shot-peened (WJSP) was used in this experiment to improve the surface properties of H13 tool steel. The parameters are pressure and feed rate of 172 MPa to 310 MPa and 2600 mm/min to 10000 mm/min. The shot-peened samples were characterised for surface topography, surface roughness, and hardness properties. A laser confocal microscope was used to determine the dimension of the modified surface from shot peening and average surface roughness. Hardness properties were measured using the Vickers scale. From topography analysis, the surface roughness reading on the shot-peened surface was measured as much as 6.88 µm to 14.06 µm. Minimum surface roughness measured was 6.88 µm on sample processed at pressure and feed rate 172 MPa and 2600 mm/min. The hardness properties of the shot-peened subsurface were between 196 HV and 227 HV. The resulted hardness properties were due to plastic deformation from abrasive particle bombardment during shot peening. The findings are important to designing enhanced surface properties for mould and die applications

Optimization of laser melting parameter to enhanced surface properties in hot press forming die

This paper presents laser melting process with various parameter to enhanced surface properties of AISI H13 tool steel. The design of experiment (DOE) optimisation was conducted to obtain significant model using regression analysis. DOE were analysed using response surface method (RSM) with Box-Behnken design approach. Design Expert 7 software was used to design parameter of laser melting process. The laser melting processes was conducted using Nd:YAG laser system with pulsed mode at a constant average power of 100 W, overlapping rate of 30 to 50%, peak power of 1700 to 2500 W and pulse repetition frequency (PRF) of 50 to 70 Hz respectively. The responses were characterised for sub-surface hardness, melt depth and surface roughness. The results show that optimum parameter of 2500 W peak power, 60 Hz PRF and 30% overlapping rate produced highest surface hardness of 793.7 HV0.1 with 0.21 mm melted depth and 3.89 µm surface roughness from experimental data. This finding was important to enhance properties of AISI H13 tool steel for hot press forming die using laser process

Effect of initial blank temperature in hot press forming towards 22MnB5 springback failure

The springback failure of ultra-high strength boron steel (22MnB5) in hot press forming (HPF) process was characterized under bending and membrane conditions. Hot press forming for U–shaped parts with ultra-high strength boron steel were experimented and simulated to study the effect of initial blank temperatures on springback failure in the automotive industry. The results specify the various preheated temperature of 22MnB5 blank effect toward springback occurrences with reference to hot press forming dies design. ANSYS Workbench was used to verify finite element (FE) simulations of the processes in order to consolidate the knowledge of springback. The validated numerical simulation model were used in analyzing the stress and strain distributions along the formed part in the FE models, it was found that the springback angle was related in averaging value throughout quenching, regardless of the forming conditions. Springback failure mainly caused dimension deviation in hot press form parts due to the impact of thermal restoring moments and quenching rate of hot press forming process

Superhydrophobic zinc oxide/epoxy coating prepared by a one-step approach for corrosion protection of carbon steel

Corrosion in carbon steel (CS) has been an existing issue and it calls attention to the need for improved corrosion protection. At present, superhydrophobic (SHB) coating technology has piqued the interest of researchers as alternative means of mitigating metal corrosion. Herein, a one-step solution deposition process was used to prepare an SHB coating based on nano-zinc oxide/epoxy (ZnO/EP) on CS and its corrosion resistance performance was analyzed by the means of electrochemical analysis and compared with that of the blank CS metal and the regular coatings (plain EP and regular ZnO/EP). Results implied the as-prepared SHB coating shows remarkable improvement in corrosion protection for the substrate. Notably, it exhibited higher in both impedance modulus (|Z|) and coating resistance (Rc) results approaching 1010 Ωcm2, than those of regular coatings by 3 orders of magnitude to that of plain EP (∼107 Ω cm2), and 1 order of magnitude to regular coating (∼109 Ω cm2), indicating its superior corrosion resistance performance. Besides that, the superior inhibitive effect of the SHB ZnO/EP (ZES) is also proven by the potentiodynamic polarization (PDP) results, in which the Icorr value is suppressed down to 2.08 × 10−11 A/cm2, thereby achieving an excellent corrosion rate result of 3.38 × 10−11 mm/year. The exceptional barrier protection is ascribed to the presence of a stabilized air interlayer captured within the coating/electrolyte interface thus effectively blocking the penetration of electrolyte into the coating. This facile yet effective one-step processed SHB coating offers an effective route to improve the corrosion resistance performance of the CS metal and thereafter expand its potential applications

Thermomechanical modelling of laser surface glazing for H13 tool steel

A two-dimensional thermomechanical finite element (FE) model of laser surface glazing (LSG) has been developed for H13 tool steel. The direct coupling technique of ANSYS 17.2 (APDL) has been utilised to solve the transient thermomechanical process. A H13 tool steel cylindrical cross-section has been modelled for laser power 200 W and 300 W at constant 0.2 mm beam width and 0.15 ms residence time. The model can predict temperature distribution, stress–strain increments in elastic and plastic region with time and space. The crack formation tendency also can be assumed by analysing the von Mises stress in the heat-concentrated zone. Isotropic and kinematic hardening models have been applied separately to predict the after-yield phenomena. At 200 W laser power, the peak surface temperature achieved is 1520 K which is below the melting point (1727 K) of H13 tool steel. For laser power 300 W, the peak surface temperature is 2523 K. Tensile residual stresses on surface have been found after cooling, which are in agreement with literature. Isotropic model shows higher residual stress that increases with laser power. Conversely, kinematic model gives lower residual stress which decreases with laser power. Therefore, both plasticity models could work in LSG for H13 tool steel