Excessive Heat Accumulation Research Articles

Covalent Organic Frameworks with Regulated Water Adsorption Sites for Efficient Cooling of Electronics.

The excessive heat accumulation has been the greatest danger for chips to maintain the computing power. In this paper, a passive thermal management strategy for electronics cooling was developed based on the water vapor desorption process of the covalent organic frameworks (COFs). The precise regulation for the number of carbonyl group and the ratio of hydrophilicity and hydrophobicity within pore channels was achieved by water adsorption sites engineering. In particular, COF-THTA with abundant water adsorption sites exhibited highest water uptake and desorption energy, which facilitate efficient cooling of electronics. In proof-of-concept testing, COF-THTA coating (40 × 40 mm) provided a temperature drop of 7.5 °C in 25 minutes at a heating power of 937.5 W/m2, and remained stable after 10 intermittent heat cycles. Furthermore, the equivalent enthalpy of COF-THTA coating can reach up to 1136 J/gcoating. In real application scenarios, COF-THTA coating improved the performance of two real computing devices by 26.73% and 22.61%, respectively. This strategy based on COFs provides a new thinking for passive thermal management, exhibiting great potential in efficient cooling of electronics.

Improvement of curing efficiency and heat resistance of CFRP by the growth of SiCNWs on CF

Carbon fiber-reinforced polymer composites are widely used in modern industry. However, poor heat transfer between layers of carbon fiber cloth during the curing process leading to poor curing of the substrate, long curing cycles, and excessive heat accumulation has become an urgent problem to be solved. A common approach is dispersing highly thermally conductive fillers in the polymer matrix to improve the curing efficiency of the composites. Different from adding fillers, we report a novel method of in situ growth of SiC nanowires (SiCNWs) on the surface of carbon fiber (CF) by the chemical vapor deposition (CVD) method and study the effects of CVD deposition time on curing efficiency and thermal stability of the composites. The results indicate that the nano bridge effect of SiCNWs significantly improves the curing efficiency of the composites. Compared with pure CF/epoxy composites, the curing efficiency can be increased by 38.72%. The cross-linking point between SiCNWs and the resin matrix enhances the thermal stability of the composites and increases the heat resistance index ( T HRI) by 8.4°C.

Comprehensive analysis of thermal performance and low-grade energy charging efficiency of pipe-embedded building envelopes enhanced with single-level tree-shaped fin structures

Pipe-embedded walls (CnPWs) are structural and energy composite building components that can resist external disturbances by forming stealth thermal shielding layers. To tackle the mismatch between the heat charging rate and heat diffusion rate during energy charging processes, as well as the unsatisfactory robustness of stealth thermal shielding layers, the single-level tree-shaped metal finnd pipe-embedded walls (TfPWs) are proposed. To verify the effectiveness of TfPWs and obtain dynamic performances, a simulation study is conducted on 8 risk variables in 4 pairs through the validated numerical model. Results showed that the improved design was effective in obtaining more robust thermal shielding layers in auxiliary energy supply mode, the effect gained prominence as both the injection temperature and pipe spacing were augmented. In room heat load reduction mode, favorable benefits arise when pipe spacing exceeds 400 mm. The maximum increase rate of total injected energy under different reduction ratios of external insulation layer was 11.83%–31.91 %, while the maximum extra total heat loss was 5.33 %. Secondly, the trunk fins and branch fins played different roles in minimizing the excessive heat accumulation surrounding pipes, and the vertical and horizontal sizes of heat accumulation region mainly increased with the increase in trunk fin size and branch fin size respectively. Meanwhile, the utilization efficiency of fin material was higher when trunk fin size was smaller, and parameter combinations with trunk fin size of 0.2b and branch fin size of 0.4a/0.6a could achieve a better balance between material input and performance increase. Thirdly, the improvement effect of single left branch fin schemes was close to that of double branch fin schemes and significantly better than that of single right branch fin schemes. It was recommended to use single left branch fin schemes with an inclination angle of 60°. Finally, even if the reduction ratio of external insulation layer in different cities increased to 80 %, the inside surface temperature of TfPWs was still greater than room air. Taking CnPWs with standard external insulation layer as references, the TfPWs applied in Harbin, Beijing, and Shanghai could achieve similar or better results even when the reduction ratio of external insulation layer increased to 60 %, while TfPWs applied in Guangzhou could exhibit better performance even when the reduction ratio of external insulation layer increases to 80 %.

Designing orthopaedic seat cushion made of rattan using quality function deployment approach

Using ergonomic orthopaedic chairs can address spinal issues, particularly HNP, due to their flexible and elastic properties. By achieving optimal ergonomic design, various positive aspects can be achieved, such as increasing work quality productivity and reducing the cost of injuries or accidents. This research demonstrates diverse product design approaches to enhance posture health ergonomics, address specific musculoskeletal disorder issues, and consider local needs and available materials. Rattan is a tropical vine widely used in the furniture industry and predominantly found in wooded areas such as Indonesia. This research combines market research, morphology, ergonomic study, concept selection, QFD, HoQ, stiffness test, and prototype review. The QFD method was chosen in this study due to its excellence in connecting consumer desires with the product development process. Data of respondents consist of 51 % of respondents were male, 49 % were female, 88 % were aged between 18 and 34 years old, and 10 % were aged between 35 and 54 years old. The approach of 6 stages of product design as the primary framework for developing our product such as: planning, concept development (concept screening, product morphology, concept selection), system-level design, detailed design, testing, refinement and launching. Based on the calculations using the HOQ, it is identified that the primary focus in designing the rattan-based orthopaedic seating, lies in the orthopaedic design that provides maximum comfort for the spine. The comparison results indicate that the stiffness level of rattan weaving is nearly like latex, with a similarity percentage of 89 %. Data analysis using the QFD method indicates that the primary priority aspect is the orthopaedic design, followed by the selection of quality materials, cost-effectiveness, versatility, and appealing design aspects. Rattan's superior air circulation provides comfort by preventing excessive heat accumulation, excellence in strength and durability, ensuring ease of lightweight modelling, and providing more sustainable material.

Bio-curvilinear shading device for cooling load reduction in office buildings assessed by a novel energy simulation framework

Excessive heat accumulation is one of the main challenges in office buildings with curtain wall systems. This challenge requires a staggering amount of cooling energy, especially in desert and temperate climate zones. Hence, an effective and practical shading device is necessary to address this issue using a bio-inspired strategy to reduce cooling energy consumption and enhance sustainability. This study uses a Bio-Curvilinear Shading Device (Bio-CSD) to improve cooling energy efficiency, cost-effectiveness and CO2 reduction in the desert and temperate climate zones in Iraq. To alleviate overheating issues, we designed a Bio-CSD and a modified Bio-Curvilinear Shading Device (mBio-CSD) from a cactus, namely the Ogonchu plant (Pilosocereus chrysostele). Fifty-one scenarios were investigated to examine the prevalence of three distinct office building typologies: linear [T1], concentric [T2], and courtyard [T3]. The Bio-CSD and the mBio-CSD were simulated using a novel energy simulation framework for curvilinear shading devices using IDA Indoor Climate and Energy (ICE) software v4.8. Our findings revealed that the Bio-CSD outperforms a Rectilinear Shading Device (RSD) under identical conditions with the same surface area. The Bio-CSD allows maximum cooling energy savings of 31 %, 24 %, and 22 % and 23 %, 19 %, and 16 % for the three office building typologies (T1, T2 and T3) in temperate and desert climate zones, respectively. Our Bio-CSD can be a cost-effective and eco-friendly solution to mitigate overheating issues while ensuring more natural light penetration during winter, with reduced material use and lower costs.

3D hierarchical graphene-based composite for ultra-high heat-conducting film

In order to pursue lightness and portability, modern electronic devices usually use a compact layout to place various components, but this highly integrated design increases the heat density of the device and causes heat accumulation. Excessive heat accumulation will reduce the reliability of the device and even cause thermal failure. The advantages of light weight, easy processing and low cost of polymer-based thermally conductive composites have become main concerns of modern thermal management materials, but the low thermal conductivity (TC) has seriously limited their application. Here, 3D hierarchical anisotropic oriented graphene-based composites with high TC are fabricated by layer-by-layer self-assembling of one-dimensional carboxylated cellulose nanofibers (CNF–C) and poly dopamine modified nickel particle-coated two-dimensional graphene nanosheets (PDA-Ni@GNS). Owing to the well-defined flaky packing layers and the hydrogen bonding, the composite exhibits not only sufficiently high in-plane TC of 28.8 W m−1 K−1 and tensile strength of 124 MPa, but also exhibits hydrophobic property. A generalized four-parameter model (FPM) is found to reasonably predict the entire CPU temperature evolution versus time. This work presents a facile strategy for constructing 3D hierarchical interfacial structure to obtain excellent versatility of anisotropic thermal management composites.

Dynamic temperature distribution characteristics of a large glasshouse with cooling system during the start-stop stage

Excessive heat accumulation leads to high temperature in the glasshouse, the high temperature directly affects the normal growth of crops. This research based on the cooling system as the cooling method of glasshouse, experimental and computational fluid dynamics technique were used to investigate the cooling effect in the start-stop stage. CFD was used to simulate and optimize the temperature dynamics during the start-stop phase of the glasshouse cooling system in the most common summer climates (rainy and sunny). A glasshouse test platform was built in Wuhan in order to conduct temperature experiments to verify the effectiveness of the simulation. The results show that starting the cooling system in summer can effectively reduce the temperature inside the glasshouse in a short time (when it is rainy, the temperature is reduced by 8.1 °C; when it is sunny, the temperature is reduced by 5 °C). During the start-stop stage, the temperature trend of the horizontal and vertical planes is the same. Until the system is running stably, the indoor temperature is maintained uniform and stable, with little fluctuation. In order to create the best growing environment for crops, the air velocity of the air supply outlet is increased to 6.0 m/s on sunny days, which is helpful to increase crop yield and reduce greenhouse gas emissions.

Ocean fronts as decadal thermostats modulating continental warming hiatus

Over the past decade, an unexpected cooling trend has been observed in East Asia and North America during winter. Climate model simulations suggest that this pattern of stalled warming, besides accelerated warming, will repeat throughout the course of global warming, influenced by the natural decade-long variations in the climate system. However, understanding the exact factors affecting the pace of warming remains a challenge. Here we show that a pause in warming over continental areas—namely, local warming hiatus—can be accompanied by excessive heat accumulation north of the ocean fronts. This oceanic condition, often manifesting in the form of marine heatwaves, constrains the subseasonal growth of atmospheric planetary waves, significantly increasing the likelihood of cold extremes in downstream continents. Our results underscore the importance of closely monitoring changing ocean fronts in response to human-induced warming, which can potentially reshape the inherent decade-long fluctuations within regional climates over the long term.

Improving thermal conductivity of graphene films with assistance of melamine

Due to the high degree of integration and high-power-density, excessive heat accumulation significantly endangers the performance of electronics. Therefore, developing high-performance thermal interface materials has become particularly vital for ensuring the regular operation of the electronics. Graphene-based materials attract great attention due to graphene’s intrinsic excellent thermal conductivity. However, the internal defects in graphene and the lack of interlayer heat conduction pathways between graphene microsheets dramatically reduce the thermal conductivity of graphene-based materials. Herein, melamine is used to improve the thermal properties of graphene films prepared by thermal reduction of graphene oxide (GO) microsheets. With an addition of 3 wt% of melamine, the in-plane and through-plane thermal conductivities of the graphene films with a thickness of 35 μm reach 1.32 × 103 and 5.09 W m−1 K−1, respectively. This is likely due to the covalent connection of graphene microsheets through amide structure formed by the chemical reaction between melamine and GOs, and the remedy of defects in graphene by nitrogen doping with the assistance of high-temperature annealing. The operation temperature of LED is greatly reduced, when the prepared graphene films is used as thermal interface material, compared to other commercial products. The results provide a promising way to improve the thermal properties of graphene films, which is of great significance for various applications, such as thermal management for high-power-density electronics.

Tailoring the microstructure and mechanical properties for Hastelloy X alloy by laser powder bed fusion via scanning strategy

Irregular large pores induced by laser powder bed fusion (LPBF) are inherent defects, which greatly domain the mechanical properties of as-built components. Laser remelting is an effective method to diminish the porosity and increase the energy input, while excessive heat accumulation is generally at the expense of powder spatter. In the study, LPBF-fabricated Hastelloy X alloy was built by combining laser remelting and five scanning strategies (three meander and two chessboard strategies) to investigate the scanning strategy effects on the related microstructure and mechanical properties via experiment and simulation. In comparison, results showed that the average temperature of the powder model rises from 622.02 K to 880.88 K, and the cooling rate approximately increases from 106 K/s up to 107 K/s for the chessboard strategy. The chessboard strategy with a large scanning island yields the highest density (99.34%). More homogeneous grain also nucleates due to the evident 〈111〉 micro-texture distribution. The refined microstructure achieved by the chessboard strategy with laser remelting leads to a superior combination of tensile strength (∼820 MPa) and elongation (∼30%). Grain boundary strengthening and dislocations hardening are the dominant mechanisms of as-built Hastelloy X alloy.

A new liquid cooling strategy for firefighting based on heat interception

Incorporating cooling capacity into personal protective equipment has been identified as an effective approach to mitigate heat accumulation and prevent thermal injuries among firefighters. Traditional liquid cooling strategies (TLCS) typically focus on cooling the body after excessive heat accumulation has occurred, which may not be optimal for human health. In this paper, we propose a new liquid cooling strategy (NLCS) by embedding liquid cooling technology into firefighters' suits to create a composite protection system that intercepts heat before it enters the microenvironment under the suit. The performance of the NLCS was evaluated through thermal protective performance tests. The experimental results demonstrate that the protection time of the NLCS is up to 120% higher than that of the TLCS. And the best protective performance and energy consumption can be achieved when the embedding position, pipe length, inlet temperature, and water flow are set to P2, 54 cm, 15 °C, and 0.5 L/min, respectively. This work contributes to a better understanding of the performance of liquid cooling in firefighting garments and provides valuable insights for the design of firefighters' protective clothing incorporating liquid cooling technology.

Layer-to-layer closed-loop feedback control application for inter-layer temperature stabilization in laser powder bed fusion

In laser powder bed fusion (LPBF), part quality and process conditions are highly dependent on the interlayer temperature (ILT) of the exposure surface of printed parts. State-of-the-art closed-loop control applications do not stabilize ILT, which has a decisive influence on the resulting part properties. This paper presents a closed-loop control strategy for LPBF that stabilizes the ILT. The thermal balance is defined with respect to exposure area change in overhanging parts and a control strategy is proposed to maintain the thermal balance by actuating energy input. The proposed control strategy uses an off-axis thermal camera for interlayer temperature acquisition to update the laser power layer to layer. An online optimization-based controller that leverages the repetitive nature of the LPBF process is implemented for the task. The developed controller is validated by experiments with different overhanging geometries. Successful ILT stabilization for various overhanging angles shows the robustness of the controller for an extended number of layers. However, modulation of laser power alone is shown to be insufficient to maintain the ILT within the stable processing window due to excessive heat accumulation in the long term. Nevertheless, the results of this study demonstrate the feasibility of ILT stabilization via of closed-loop control in LPBF and the potential for significant improvements in stabilizing the properties of the printed parts.

Preparation of High Damage Threshold Device Based on Bi2Se3 Film and Its Application in Fiber Lasers

As a handicap for passive mode-locked lasers to operate stably for a long time, the undesirable damage threshold of saturable absorption devices means that it is difficult to maintain a normal operation state under the irradiation brought by ultrashort pulses. To reduce the damage probability when the saturable absorption devices interact with an ultrafast laser, some technologies have been developed to resist the high-energy irradiation of an ultrafast laser that will also increase the difficulty of laser construction at the same time. In this paper we put forward a new research idea to improve the low-damage threshold problem: optimizing the optical transmittance, which will avoid dissociation due to excessive heat accumulation. Using the melt and machine exfoliation method, the high optical transmittance (>95%) saturable absorption devices based on Bi2Se3 are prepared, whose damage threshold (2.45 mJ/cm2) is nearly 5 times higher than commercial SESAM. The devices applied to generate femtosecond pulses exhibit exciting nonlinear optical effects, which enable the mode-locked fiber laser to operate with a pulse duration of 195 fs and a signal-to-noise ratio of 81.73 dB. This discovery not only proves that the passive mode-locked laser-based high transmittance Bi2Se3 can obtain reliable pulse output, but also provides a new perspective for the selection of saturable absorption materials in the future.

On the effects of cutting-edge angle on high-feed turning of Inconel 718© superalloy

Machining processes on heat-resistant superalloys—i.e., turbine cases, rings, or shafts—are challenging tasks. The high-added value of such parts makes cycle times be longer than expected. Recently, high-feed turning technique has attracted the attention of practitioners due to its high material removal rate capability. PrimeTurning™ tool unifies the concepts of high-feed and multidirectional turning using multiple active cutting edges. It should be capable of reducing machine downtimes in that kind of parts. However, to avoid early tool replacement and rejects on high added value parts, a deeper knowledge on the high-feed turning process is necessary. Here, inserts specifically designed for high-feed turning in heat resistant Inconel 718© alloy were tested using three cutting-edge angles. The results showed that when chip thickness is more relevant, a cutting-edge angle of 30° reduces the likelihood of notches. Even if force components are high, surface roughness is improved and the risk of fractures is minimized, together with a high evacuation volume. On the other hand, increasing the cutting-edge angle (45° and 60°) without compensating the feed rate, tends to produce tool fractures due to chip overload. Besides, experimental tests showed that long tool-to-workpiece contact times, tend to shorten tool life, due to excessive heat accumulation and poor chip control.

An optimized scanning strategy to mitigate excessive heat accumulation caused by short scanning lines in laser powder bed fusion process

During laser powder bed fusion (LPBF) additive manufacturing of components with complex geometries, short scanning lines easily induce localized excessive heat accumulation, resulting in poor manufacturing qualities, e.g., rough surface and low hardness, etc. An optimized scanning strategy was proposed to mitigate this heat accumulation to be consistent with the standard case. In the proposed strategy, a specific length of scanning line without laser energy was added to each short scanning line, making each scanning line of the same length. The temperature simulation results of 1 mm thin-walled specimen indicated that the conventional scanning strategy could easily drive a harsh increase in peak temperature, further leading to a harsh increase in melt pool size. After applying the optimized scanning strategy, the peak temperature and melt pool size of the 1 mm thin-walled specimen were almost similar to those of the standard specimen. Meanwhile, the corresponding experiments indicated that the average surface roughness and hardness of 1 mm thin-walled case processed by conventional scanning was Ra70 and 320 HV10. The deformation and bumpy area could be observed on the surface, the porosity was high, and the grain size tended to be larger. After optimization, the average surface roughness was decreased to Ra37 and the hardness was increased to 370 HV10. In addition, the above metallurgical defects were greatly reduced. The above scanning strategy was integrated into the self-developed LPBF equipment and manufacturing process, and the thin-walled blade model was processed to verify the feasibility of the optimized scanning strategy for complex parts. Since the scanning strategy is independent of material and process parameters, it is beneficial to improve the process and quality stability of LPBF manufacturing complex parts. • An optimized scanning strategy for mitigating the excessive heat accumulation of the short scanning lines during LPBF process. • The temperature distribution for different lengths of scanning lines could be consistent with standard case. • Problems such as defects in short scanning lines were improved, and surface quality and hardness were also increased. • The optimized scanning strategy could be used for most cases without many trial-and-error experiments.

Impact of urban morphology on the microclimatic regulation of water bodies on waterfront in summer: A case study of Wuhan

Urban water bodies reduce urban heat through evaporation and transfer of sensible heat. However, today's highly intense urban construction patterns cause poor urban air mobility and excessive residual heat accumulation, and weaken water bodies' regulating effects. This study examines the relationship between urban morphology and water bodies' microclimatic regulation during summer in the water-network city, Wuhan, using remote sensing data and the weather research and forecasting (WRF). This study found (1) on the waterfront, the key impact indicators for microclimate in the waterfront are building density (BD) and floor area ratio (FAR), both of which can lead to higher temperatures and lower humidity, (2) BD significantly warmed the waterfront on the large lakes, while FAR impacted the urban main windway areas, (3) urban development with high FAR significantly suppressed the water's cooling ability in the downtown and main windway areas, with the cooling intensity decreased by 28.7% and 20.6%, respectively, and the cooling distance decreased by 13.5% and 15%. These findings provide insights for the practice of climate adaptive planning and design on the water network-related urban areas of Wuhan and other places with similar environments.

Isotropic porous graphite foam/epoxy composites with outstanding heat dissipation and excellent electromagnetic interference shielding performances

In the field of radio frequency chips package, design of isotropic material was a significant challenge to efficiently resolve undesirable electromagnetic radiation and excessive heat accumulation in confined tiny spaces. Here, a brand-new material design concept was proposed and successfully verified through controllable graphitization degree of carbon materials and curvature of twisted graphite sheets during heating and foaming process of asphalt. Concretely, aromatic compounds of the asphalt condensed to form sheet-like macromolecules, which were twisted and oriented along the pore walls. Eventually, these macromolecules were highly graphitized, which expectedly realized the consummate integration of local orientation and macroscopic isotropy. Particularly, a special interlocking epoxy was introduced to prepare epoxy/graphite foam composites (EP-GFs). The EP-GFs (average pore size 0.09 mm) demonstrated an isotropic thermal conductivity up to 118.5 ± 5.8 W·m−1·K−1. Astoundingly, EP-GFs (average pore size 0.244 mm) showed an isotropic electromagnetic interference shielding efficiency (EMI SE), reaching up to 113 dB in 8–12 GHz. Therefore, the EP-GFs completely integrated outstanding thermal conductivity, excellent EMI SE and isotropy macroscopically. Interestingly, the EP-GFs can be cured by Joule heat of low-voltage direct current, and the primary heating region was the contact interface between copper sheets instead of the whole bonded product. This work offered a facile feasible strategy for fabricating isotropic materials to address heat dissipation and electromagnetic pollution of advanced electronic devices in an economical and environmentally friendly manner.

Energy input adaptation according to part geometry in selective laser melting through empirical modelling of thermal emission

Common practice in Selective Laser Melting (SLM) is employing a series of fixed process parameters throughout the whole build. However, process thermal conditions strongly depend on the local geometry of the part. Formation of some common defects, including swelling regions and elevated zones, emerges in critical corner areas due to excessive heat accumulation when constant parameters are used. Adaptation of energy input according to the geometry of the processed zone is highly desirable for avoiding defect formation. To assess the processing conditions, observation of the melt pool and its variation as a function of the process parameters with a coaxial camera operating in near infrared (NIR) demonstrated to be a feasible option. This work develops an empirical model that gives the correct amount of energy input to achieve stable melt pool depending on the single vector length, hence the part geometry. The model was validated on a prototype SLM system, and the results showed that controlling the process parameters considerably improves the geometrical accuracy of the parts with sharp edges prone to hot spot formation.

Ultrashort pulsed laser ablation of zirconia-alumina composites for implant applications

• Influence of alumina content on fs-laser machining of zirconia-alumina composites was studied. • Significant influence of material composition on material removal behavior was demonstrated. • Single phase materials have larger laser ablation thresholds and smaller material removal rate than their composites. • A lower scan speed is preferred for single phase materials while a higher scan speed is beneficial for the composites. Laser texturing of zirconia-alumina ceramics is a promising surface modification method for many applications, such as enhancing osseointegration of alumina toughened zirconia (ATZ) dental implants or improving friction behavior of zirconia toughened alumina (ZTA) hip replacement bearing components. The common problems in laser texturing of ATZ/ZTA ceramics are thermal cracking, low material removal rate (MRR), and laser-induced phase transformation (LIPT). Furthermore, the compositional variation of those ceramics will complicate these problems. In order to improve the manufacturing processability, ultrashort pulsed laser ablation behavior of ATZ/ZTA composites was investigated in this research. Single phase zirconia and alumina were found to have smaller MRRs than their composites, and this behavior was negatively correlated to the materials single-pulse laser ablation threshold. However, under multi-pulse laser irradiation, the ablation thresholds of all materials saturated to the same level, indicating that single phase materials were more sensitive to the incubation effect than their composites. This led to the MRRs of the single phase materials being reduced at larger scan speeds, while the MRRs of their composites remained independent of scan speed. It was also shown that single phase materials were less susceptible to thermal cracking than their composites under excessive heat accumulation. These results suggest that a lower scan speed is preferred for single phase materials in order to achieve a larger MRR, while a higher scan speed is beneficial for the composites for suppressing thermal cracking without compromising ablation efficiency. In addition, no LIPT was detected for zirconia dominated materials after laser ablation.

An Optimized Scanning Strategy to Mitigate Excessive Heat-Accumulation Caused by Short Scanning-Lines in Laser Powder Bed Fusion Process

An Optimized Scanning Strategy to Mitigate Excessive Heat-Accumulation Caused by Short Scanning-Lines in Laser Powder Bed Fusion Process