In-Process Height Displacement Measurement Using Crossed Line Beams for Process Control of Laser Wire Deposition

We propose the use of the line section method with crossed line beams for the process control of laser wire deposition. This method could be used to measure the height displacement in front of a laser spot when the processing direction changes. In laser processing, especially laser deposition of metal additive manufacturing, the laser process control technique that controls the processing parameters based on the measured height displacement in front of a laser processing spot is indispensable for high-accuracy processing. However, it was impossible to measure the height displacement in front of a processing laser spot in a processing route in which the processing direction changes as the measurement direction of the conventional light-section method comprising the use of a straight-line beam is restricted although the configuration is simple. In this paper, we present an in-process height displacement measurement system of the light-section method using two crossed line beams. This method could be used to measure the height displacement in a ±90° direction by projecting two crossed line beams from the side of a laser processing head with a simple configuration comprising the addition of one line laser to the conventional light-section method. The height displacement can be calculated from the projected position shift of the line beams irrespective of the measurement direction by changing the longitudinal position on the crossed line beams according to the measurement direction. In addition, the configuration of our proposed system is compact because the imaging system is integrated into the processing head. We could measure the height displacement at 2.8–4 mm in front of a laser processing spot according to the measurement direction by reducing the influence of intense thermal radiation. Moreover, we experimentally evaluated the height displacement measurement accuracy for various measurement directions. Finally, we evaluated continuous deposition in an “L” shape wherein the deposition direction was changed while using a laser wire direct energy deposition machine for the laser process control based on the in-process height displacement measurement result. We achieved highly accurate continuous deposition at the position wherein the processing direction changes despite the acceleration and deceleration of the stage by laser process control.

INVESTIGATION OF THE EFFECT OF AREAL ROUGHNESS MEASUREMENT LENGTH ON FACE MILLED SURFACE TOPOGRAPHIES

Surface roughness is of great importance in the manufacturing industry, as it affects surfaces’ tribological properties (wear, friction, lubrication, etc.), corrosion resistance, fatigue strength and appearance. Areal roughness measurement, which provides a more comprehensive characterization of surfaces, is becoming increasingly popular, but systematic studies are still lacking, so measurements are often analyzed differently. In this paper, the effect of the measurement length is analyzed in the main measurement direction on areal roughness of face milled surface topographies, which were measured with a confocal chromatic sensor.

Understanding of surface roughness of wood based on analysis its structure and density

Understanding of surface roughness of wood based on analysis its structure and density. The main aim of presented paper was to investigate the influence the wood density and anatomical details on surface roughness. The scope of study included samples from ten different species of wood (mainly tropical) because of wide range of density and anatomical difference. The results allow to conclude that the roughness of tested wood species demonstrated variation, depending on the wood section and the measurement direction. In general, radial sections showed higher roughness than tangential sections due to interlocked fibres in tested wood species (fibres cut in various ways on the radial section of the wood). Roughness measured perpendicular to the wood fibres were twice as high as those measured parallel to the grain. Wood density was not an important indicator determining surface roughness for tested wood species. The determining element for the roughness measured across the fibres was the diameter of the vessels. Further research is advisable due to the enormous variability of the structure and properties of wood.

The Effect of Insertion Angles and Depths of Dental Implant on the Initial Stability

The objective of this study was to evaluate the effect of the measurement directions of the Periotest value (PTV) and implant stability quotient (ISQ) of dental implant fixtures inserted at various angles and depths. Five groups were organized: vertically inserted implants in an evencrestal position; implants inserted at a 17° tilt in a distal subcrestal position; implants inserted at a 17° tilt in a mesial supracrestal position; implants inserted at a 30° tilt in a distal subcrestal position; and implants inserted at a 30° tilt in a mesial supracrestal position. The PTV and ISQ were measured along four directions (buccal, lingual, mesial, and distal directions) in all specimens. The PTV and ISQ exhibited a highly negative correlation when the fixture was vertically inserted. Compared to the implants inserted vertically and at the distal subcrestal position, the fixture with a greater tilt and inserted at the mesial supracrestal position had a lower stability. The PTV and ISQ of the tilted implants were affected by the measurement direction, inserted angulation and depth.

Electrical conductivity of anisotropic PMMA composite filaments with aligned carbon fibers – predicting the influence of measurement direction

Revealed logarithm longitude electrical conductivity σ∥ and transverse electrical conductivity σ⊥ of PMMA/CF composite filaments.

4D seismic feasibility study: The importance of anisotropy and hysteresis

Core velocity measurements are an essential part of any 4D seismic feasibility study. During recently conducted core velocity measurements, we found some interesting results regarding velocity anisotropy and hysteresis. These findings include: (1) the stress sensitivity of velocity varies depending on the propagation direction, (2) velocities measured during loading have a significantly larger stress sensitivity than those measured during unloading, and (3) horizontal effective stress has a noticeable impact on velocity anisotropy. We conducted rock physics analysis and 1D seismic forward modeling, incorporating velocity anisotropy, and found that the estimated 4D seismic signal is largely affected by velocity anisotropy and hysteresis. These findings suggest the importance of considering the velocity measurement direction and the nature of the stress change to obtain a realistic 4D seismic signal. Neglecting these considerations may lead to a significantly underestimated or overestimated modeled seismic response.

Measuring the roundness deviation in the Vblock measurement method

In this paper the measurement capabilities of form deviation of cylindrical surfaces using V-Block method are studied. The paper presents the influence of the V - Block angle to the ratio coefficient of dimension, and the ratio coefficient of form deviation on the k-harmonic. The equations for the dimension ratio coefficient and the form ratio coefficient of kharmonic are obtained. These equations give the opportunity to choose the most appropriate combination for the V-block angle and the measurement direction, angle β. Studies have been made using V-Blocks with the most common angles by symmetrical and non-symmetrical measurement schemes. Using V-Blocks for measurement is rational and appropriate in cases where for all measured details the number of harmonics are known in advance.

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

Hysteresis Characteristic in Hump Region of a Pump-Turbine Model

The hump characteristic is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations could be observed, which are harmful to the safe and stable operations and even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), the hysteresis characteristic was found during the hump region. The analysis of performance characteristics reveals that the hump instability is resultant of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of fast Fourier transform confirms that the hump characteristic is related to the low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cease of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis characteristic. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.