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The wood processing industry seeks to reduce maintenance and production costs while increasing productivity and revenues accordingly. Improving the surface quality of wood in the first phase of transformation helps to maximize the use of wood fibers. Variable engineered micro-geometry was applied to teeth of guided circular saws used in a bull-edger system, and its effect on the surface quality of SPF (spruce-jack pine-balsam fir) boards was assessed. Trials were carried out on a test bench with two types of saw blades: saws with up-sharp tips without edge modification, and saws with modified cutting edges based on a waterfall profile. Cants were fed at the rate of 145 m/min for a cutting speed of 2600 rpm resulting in a nominal feed per tooth of 1.33 mm. Saws with three levels of wear (after 0, 255, and 900 min of working at a sawmill) processed the cants under frozen and unfrozen wood conditions. A total of 336 board samples were produced. Surface quality of boards was assessed using standard parameters of roughness and waviness. The results revealed that the saw with modified waterfall edge profile showed better performance in terms of wood surface finish and wear rate due to the variable engineered micro-geometry. Frozen cants had a better surface finish. Roughness and waviness parameters were sensitive to changes in wear of tips. [ABSTRACT FROM AUTHOR]

The development of uniform tensile properties in cold-rolled BCC metals is generally achieved by annealing. The final microstructure of these components is typically characterized as having a rather coarse microstructure and therefore lower tensile properties. Cross-rolling offers a great potential of homogenizing the microstructure without losing the benefits of the rolled microstructure and crystallographic texture. The research summarized below examines the effect of cross-rolling and an austempering heat treatment on the mechanical properties of the AISI 8670 steel sheets. Comparison with the conventional production methods was performed to quantify the efficiency of the new deformation and heat treatment approach. The results clearly indicate that the combination of cross-rolling and low temperature austempering generates favorable isotropic mechanical properties by creating uniform strength of α and ε fiber textures and homogeneous lower bainitic microstructure. Increases in UTS and toughness of 40% and 57% respectively were systematically obtained with the new combination of deformation path and heat treatment. [ABSTRACT FROM AUTHOR]

Ultrasonic welding additive manufacturing (UWAM) enables the production of metallic components by forming metallurgical bonds between superimposed thin foils using continuous ultrasonic welding. The aluminum alloys that were considered in this study were AA5005 (0.8%-wt. Mg), AA5052 (2.4%-wt. Mg), and AA5056 (4.9%-wt. Mg). The influence of Mg content on UAM was investigated with respect to the following criteria: microstructural changes in welded foils, ultrasonic welding energy, geometry of the joints, and tensile properties along different building directions. Joint resistance was found to be correlated to the ultrasonic welding energy input, where the dominant parameters are temperature, welding speed, and the amplitude of vibration. Energy can be raised by decreasing the welding speed or by increasing the amplitude of vibration leading to better joint properties but reducing tensile properties in the two other orthotropic directions of the build. The aluminum components built by AM were characterized with having anisotropic tensile properties due to the process itself and the strain hardening of the foils during fabrication. When comparing tensile results with those of the base material, optimum tensile properties in the longitudinal direction (X) are 5% higher, identical in the transverse direction (Y), and 55% lower for specimens sampled along the direction of deposition (Z). Depending on the orientation of the tensile specimens with regard to the deposition direction (Z), strain at rupture was 25% in the X-direction and 7% along the Y-direction. No specimens could be adequately built using AA5056-H38 foils. Characterization of the few joints that could be produced showed that this behavior was due to the presence of a significant amount of Mg oxide at the interface of neighboring foils paired with a drastic increase of hardness compared to what was measured for the other alloys. [ABSTRACT FROM AUTHOR]

In this paper, rolled sheets of aluminum alloy 5052-H18 were joined by friction stir welding. Several samples were welded by varying the principal parameters including tool rotational speed, linear speed, tool shoulder diameter, and pin diameter. Response surface methodology (RSM) was used as the statistical design of experiment technique for parameter optimization. A predictive model was developed to determine optimum parameters that maximize tensile strength. Results showed that the tool rotational speed was the most important parameters affecting the tensile strength of aluminum alloy 5052 joints. Maximum tensile strength was achieved using the rotational speed of 1233 rpm, the linear speed of 107 mm/min, the shoulder diameter of 12.8 mm, and the pin diameter of 1.8 mm. The difference in tensile strength between the predicted value and the measured value was 2.1%. The effect of tool rotational speed and linear speed on the size of the heat-affected zone was investigated. Consequently, a three-dimensional model was developed to predict the size of heat-affected zone and the temperature history of the material during the FSW process and the results were compared with experimental data. [ABSTRACT FROM AUTHOR]

One of the most exciting possibilities brought forward by some additive manufacturing (AM) processes is their ability to deposit materials on existing parts. Mainly achievable with directed energy deposition systems, it is thus possible to repair worn or broken components. Two applications were studied in this research: (1) complete construction and (2) repair of tensile specimens made of 316L-Si stainless steel. The latter series was produced by adding material on existing half specimens made of wrought 316L stainless steel. All specimens were built along the Z-axis. Tensile specimens machined from wrought were also tested for comparison purposes. Three conditions were tested for each series of AM specimens: as-built, stress relieved and HIPed. The results show that yield strength, ultimate tensile strength (UTS) and elongation are higher than the typical tensile properties reported for annealed 316L. Repairs show excellent bond resistance with the wrought material and good mechanical properties with a mean UTS of 647 MPa in the as-built condition. [ABSTRACT FROM AUTHOR]

The effects of temperature (T) and moisture content (MC) on bark/wood shear strength (BWSS) were studied. Fifteen stems of black spruce (Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) Mill.) logs were selected and cross-cut into three 1.25 m log sections, corresponding to bottom (1.3 m), middle (3.8 m), and top (6.3 m) positions. BWSS was measured at five temperatures, ranging from 10 to − 30 °C, and at five levels of sapwood moisture contents (SMC), obtained by air-drying, from green state to near to the fiber saturation point (FSP). Bark and sapwood properties, MC and basic density (BD) were also determined. Temperature had a significant effect on BWSS for both species. This property was similar between 10 and 0 °C, and significantly increased as temperature decreased below 0 °C. However, the influence of temperature on BWSS depended on SMC and it varied between the two species. For black spruce, for each temperature between 0 and − 20 °C, BWSS showed similar values for SMC between 157 and 62%. At − 30 °C, BWSS showed a tendency to increase with SMC. For balsam fir, the BWSS increase due to the decrease in temperature was more important as the SMC increased. BWSS increased as SMC approached the FSP of wood for both species. Among the studied covariates, inner bark MC and inner and outer bark BDs significantly affected BWSS. Inner bark MC and SMC affected BWSS similarly. Multiple regressions were developed for prediction purposes, which explained 68 and 69% of BWSS variability for black spruce and balsam fir, respectively. [ABSTRACT FROM AUTHOR]

Effects of cutterhead diameter and log infeed position on the mechanism of chip formation and size distribution of black spruce chips produced by a chipper canter were evaluated. Two cutterhead diameters (448.7 and 661.5 mm) combined with three infeed positions or vertical distance from the cutterhead axis to the bedplate on which the log was supported, were tested. The mean angle between the chipping rake face with respect to the grain (mean attack angle) was calculated for each infeed position. The nominal linear cutting speed was fixed at 23.5 m/s. Rotation speed and feed speed were adjusted to obtain a nominal chip length of 25.4 mm. Ninety-six logs were transformed under frozen and unfrozen wood temperatures. The high-speed images showed that the attack angle and temperature of logs (frozen and unfrozen wood) played an important role in the mechanism of chip formation. Within a knife cut, the images also showed that chip thickness was mainly defined by radial-longitudinal and in a lesser degree by tangential-longitudinal splitting ruptures. Furthermore, chip size distribution was also affected by the cutterhead diameter, attack angle, and temperature condition. Mean chip thickness decreased as attack angle increased for both cutterhead diameters, regardless of wood temperature condition. Further, frozen logs produced thinner chips than unfrozen logs (regardless of the cutterhead diameter and/or attack angle). The maximum amount of pulpable chips was produced during the fragmentation of unfrozen logs at the greater attack angle for both cutterhead diameters. These results give useful information to estimate changes in chip size distribution that could occur within the studied range of infeed positions (or attack angles) and cutterhead diameters. [ABSTRACT FROM AUTHOR]

It is well known that a large proportion of ferrous PM components require secondary machining operations for dimensional conformance or for producing geometrical features that cannot be generated during die compaction. Nevertheless, the machining behavior of PM parts is generally characterized as being 'difficult' due to the presence of residual porosity that lowers thermal conductivity and induces interrupted cutting. Several admixed additives such as MnS and BN-h can be used to improve the machining behavior of PM steels. Nevertheless, their negative effect on mechanical properties, especially fatigue resistance, makes their utilization uninteresting for the fabrication of high-performance PM steel components. This article summarizes the work carried out to develop a novel PM steel that was especially engineered to form machinability enhancing precipitates. This new material is pre-alloyed with tin (Sn) in order to form Cu-Sn (Cu(α)) precipitates during transient liquid phase sintering. The newly developed material presents machinability improvement of 165% compared to reference material used in the PM industry as well as increases in toughness and fatigue resistance of 100% and 13%, respectively. [ABSTRACT FROM AUTHOR]

Sinter-hardenable steel powders eliminate the extra steps normally required for heat treating since they allow for direct quenching of components at the end of the sintering cycle with a forced convection cooling unit. The current article presents the results of the effect of the alloying method on the optimization of compressibility and sinter-hardenability of sinter-hardenable PM steels. Water-atomized steel powders were produced. Two successive designs of experiments were used to optimize the chemical composition with prealloyed (nickel, chromium, molybdenum, and manganese) and admixed elements (nickel, chromium, manganese, and copper). Static mechanical properties were also characterized. Results show that among all of the combinations of chemical elements and within the range of concentrations studied, the optimum sinter-hardenable powder had the following prealloyed chemistry: 1.5 wt pct Ni, 1 to 1.25 wt pct Mo, and 0.40 to 0.55 wt pct Cr. [ABSTRACT FROM AUTHOR]

Admixing pure elements to powder mixes can cause the formation of heterogeneous microstructures in sintered parts. For instance, nickel is renowned for forming nickel-rich areas (NRA) in powder metallurgy (PM) nickel steels due to its poor diffusivity in iron matrix (or lattice). The present work is aimed at characterizing the principal diffusion mechanisms of nickel and their influence on microstructures and properties of PM nickel steels. A new wavelength dispersive X-ray spectrometry (WDS) approach linking line scans and X-ray maps to concentration maps is proposed. Grain boundary and volume diffusion coefficients of admixed nickel have been determined in PM nickel steels using Suzuoka's equation. Results also show that nickel distributes itself in the iron matrix mainly by surface and grain boundary diffusion. [ABSTRACT FROM AUTHOR]

The green machining process is virtually a must if the powder metallurgy (PM) industries are to solve the lower machining performances associated with PM components. This process is known for lowering the rate of tool wear. Recent improvements in binder/lubricant technologies have led to high-green-strength systems that enable green machining. Combined with the optimized cutting parameters determined in Part I of the study, the green machining of PM components seems to be a viable process for fabricating high performance parts on large scale and complete other shaping processes. This second part of our study presents a comparison between the machining behaviors and the sintered properties of components machined prior to or after sintering. The results show that the radial crush strength measured on rings machined in their green state is equal to that of parts machined after sintering. [ABSTRACT FROM AUTHOR]

The green machining process is an interesting approach for solving the mediocre machining behavior of high-performance powder metallurgy (PM) steels. This process appears as a promising method for extending tool life and reducing machining costs. Recent improvements in binder/lubricant technologies have led to high green strength systems that enable green machining. So far, tool wear has been considered negligible when characterizing the machinability of green PM specimens. This inaccurate assumption may lead to the selection of sub-optimum cutting conditions. The first part of this study involves the optimization of the machining parameters to minimize the effects of tool wear on the machinability in turning of green PM components. The second part of our work compares the sintered mechanical properties of components machined in green state with other machined after sintering. [ABSTRACT FROM AUTHOR]