Effect of focal laser photocoagulation in eyes with mild to moderate non-proliferative diabetic retinopathy

AIM：To report the effect of focal laser photocoagulation on both the severity of hard exudates（HEs） and the rate of disease progression in eyes with mild to moderate non-proliferative diabetic retinopathy（NPDR）.METHODS： We retrospectively reviewed the medical records of 33 patients（60 eyes） who had been diagnosed with mild to moderate NPDR between January 2006 and December 2012.The patients were divided into 2 groups：Group A（38 eyes in 20 patients treated using focal laser photocoagulation） and Group B（treated without laser photocoagulation）.We also reviewed the best corrected visual acuity measurements,and the fundus photographs taken at both baseline and follow-up visits. RESULTS： In Group A,HE severity grade had decreased significantly from baseline to the final visit（P 〈0.05）,but this was not the case in Group B（P =0.662）.The cumulative probabilities of retinopathy progression at 5y were 26% in Group A and 30% in Group B.KaplanMeier survival curves showed no significant difference between the groups with regard to retinopathy progression（P =0.805）.CONCLUSION： Focal laser photocoagulation reduced the levels of HEs in eyes with mild to moderate NPDR.However,the treatment was not able to decelerate the progression of DR.

Importance of 3-D image reconstruction of spectraldomain OCT on outcome of grid laser photocoagulation for diffuse diabetic macular edema

AIM:To present the outcome of modified grid laser photocoagulation(GLP)in diffuse diabetic macular edema(DDME)in eyes without extrafoveal and/or vitreofoveal traction.METHODS:Inclusion criteria for the retrospective study were DDME eyes of patients with typeⅡdiabetes mellitus that had≥4 months of follow-up following GLP.Only one eye per patient was analyzed.Using 3-D spectral-domain optical coherence tomography(3-D SDOCT),eyes that had either extrafoveal or vitreofoveal traction,or had been previously treated by an intravitreal medication(s)were excluded.Treated DDME eyes were divided into 4 groups:A)"Classic"DDME that involved the central macula;B)edema did not involve the macular center;C)eyes associated with central epiretinal membrane(ERM);D)DDME that was associated with macular capillary dropout≥2 disc-diameter(DD).RESULTS:GLP outcome in 35 DDME eyes after 4-24(mean,13.1±6.9)months was as follows:Group A)18eyes with"classic"DDME.Following one or 2(mean,1.2)GLP treatments,best-corrected visual acuity(BCVA)improved by 1-2 Snellen lines in 44.4%(8/18)of eyes,and worsened by 1 line in 11.1%(2/18).Central macular thickness(CMT)improved by 7%-49%(mean,26.6%)in77.8%(14/18)of eyes.Causes of CMT worsening(n=4)were commonly explainable,predominantly(n=3)associated with emergence of extrafoveal traction,5-9months post-GLP.Group B)GLP(s)in DDME that did not involve the macular center(n=6)resulted in improved BCVA by 1-2 lines in 2 eyes.However,the central macula became involved in the edema process after the GLP in 3(50%)eyes,associated with an emergence of extrafoveal traction in one of these eyes 4months following the GLP.Group C)GLP failed in all 5eyes associated with central ERM.Group D)GLP was of partial benefit in 2 of 6 treated eyes with macular capillary dropout≥2DD.CONCLUSION:Eyes with DDME that involved the macular center were found to achieve favourable outcomes after GLP(s)during mid-term follow-up,unless complicated pre-GLP or post-GLP by vltreoretinal interface abnormalities,often extrafoveal traction or ERM,or by capillary dropout≥2DD.Prospective studies with larger cohorts are required.

Focal epithelial hyperplasia in a human immuno-deficiency virus patient treated with laser surgery

Focal epithelial hyperplasia(FEH), or Heck's disease, is a rare disease of the oral mucosa; it is mostly found in children or young adults who are immunosuppressed and who live in regions with low socioeconomic status. It is characterized by asymptomatic papules on the oral mucosa, gingiva, tongue, and lips. Healing can be spontaneous, and treatment is indicated if there are aesthetic or functional complications. Human papillomavirus, especially genotypes 13 and 32, has been associated with FEH and is detected in the majority of lesions. Histopathologically, FEH is characterized by parakeratosis, epithelial hyperplasia, focal acanthosis, and fusion and horizontal outgrowth of epithelial ridges. A 37-year-old male patient was referred to the Department of Oral and Maxillofacial Sciences at the Sapienza University of Rome, complaining of numerous exophytic lesions in his mouth. He stated that the lesions were not painful but he had experienced occasional bleeding after incidental masticatory trauma. He had received no previous treatment for the oral lesions. His medical history revealed that he was human immuno-deficiencyvirus positive and was a smoker with numerous, asymptomatic oral papules clinically and histologically corresponding to FEH. The labial and buccal mucosa were especially affected by lesions. Surgical treatment was performed using a 532-nm potassium titanyl phosphate laser(SmartLite, Deka, Florence, Italy) in continuous mode with a 300 μm fiber and power of 1.4 W(power density 1980.22 W/cm2). After anesthesia without vasoconstrictors, the lesions were tractioned with sutures or an Allis clamp and then completely excised. The lesions were preserved in 10% formalin for histological examination, which confirmed the clinical diagnosis of FEH. In this case, the laser allowed excellent control of bleeding, without postoperative sutures, and optimal wound healing.

Long-term outcomes of focal laser photocoagulation for the treatment of polypoidal choroidal vasculopathy

AIM:To evaluate the long-term effect and safety of focal laser photocoagulation treatment in eyes with polypoidal choroidal vasculopathy(PCV).METHODS:Medical records of 13 eyes of 13 patients with PCV were followed-up for more than 2 y after focal laser photocoagulation treatment.The patients were diagnosed with PCV using indocyanine green angiography,and eyes with other comorbid ocular diseases were excluded.The measurement outcomes of the study were the post-treatment regression and recurrence of polyps,complications,and changes in visual acuities.Paired t-test was performed to compare visual outcome before and after the treatment.RESULTS:The mean age of the 13 patients was 70.2±5.5 y,and the follow-up period was 72.3±31.0(range,25-118)mo.Three eyes had juxtafoveal polyps and 10 eyes had extrafoveal polyps.Of the 13 eyes,9 eyes(69.2%)had regression of polyps 1.7±1.2(range,0.9-4)mo after focal laser photocoagulation.Five eyes(55.6%)showed recurrence of polyps during the follow-up periods,and the recurrence period was 12.8±18.9(range,1.9-48)mo.Mild subretinal hemorrhage occurred in two eyes(15.4%)27 and 72 d after laser treatment,respectively.There were no statistically significant differences in visual acuities at baseline;1,2,3 y post-treatment(all P>0.05);and last follow-up(0.63±0.5,0.73±0.70,0.67±0.57,0.75±0.7,and 0.95±0.8 log MAR,respectively).CONCLUSION:Focal laser photocoagulation is beneficial for early regression of polyps in eyes with PCV and does not result in significant submacular hemorrhage during the long-term follow-up.Furthermore,it can be primarily considered in eyes with PCV with extrafoveal or juxtafoveal polyps to regress risky polyps as well as to maintain visual acuity without serious hemorrhagic complications.

Focal ablation therapy presents promising results for selectively localized prostate cancer patients

Due to its lower risk of consequences when compared to a radical approach, focal treatment is a viable and minimally invasive option for treating specific localized prostate cancer. Although several recent good nonrandomized trials have suggested that focused therapy may be an alternative choice for some patients, additional high-quality evidence is needed before it can be made widely available as a conventional treatment. As a result, we have summarized the most recent findings from the 38th Annual European Association of Urology Congress, one of the most renowned annual conferences in the area of urology, regarding focal ablation therapy for patients with localized prostate cancer. Additionally, we also provided clinical trials in progress for researchers to better understand the current research status of this field.

The Characteristics of Glued Tensile Shear Strength Constituted of Wood Cut by CO_(2) Laser

The performance of engineered wood products is highly associated with proper bonding and an efficient cutting method.This paper investigates the influence of CO_(2) laser cutting on the wetting properties,the modified che-mical component of the laser-cut surface,and the strength and adhesive penetration near the bondline.Beech-wood is cut by the laser with varying processing parameters,cutting speeds,gas pressures,and focal point positions.The laser-cut samples were divided into two groups,sanded and non-sanded samples.Polyvinyl acetate adhesive(PVAc)was used to bond the groups of laser-cut samples.After assembly with cold pressing,the tensile shear test was carried out.Numerical modelling was carried out to determine the partial elongation and shear strain of the glue line.Based on this,the shear modulus and linear elasticity of the glue line were estimated.Scan-ning electron microscopy was used to assess the adhesive penetration into the porosity structure of the laser-cut samples,and the depth of the heat-affected zone.The laser-cut surface was analysed by Fourier transform infrared spectroscopy.The wetting properties of the laser-cut surface were investigated by using a contact angle goni-ometer.The numerical model of the strain-stress curve confirmed the experimental model.The highest modulus of the linear elasticity of the glue in the numerical calculation belongs to the joint containing laser-cut samples at a gas pressure of 21(bar).The penetration depth of PVAc adhesive into the porosity structure of the laser-cut sam-ples was similar to that of sawn samples.The deepest heat-affected zone in the laser-cut samples was 150µm.A PVAc drop disappeared immediately on the laser-cut surface without sanding,but gradually on the sanded surface.In contrast,the drop on the sawn surface remained with an angle of 32°–48°.The degradation of hemi-cellulose and lignin was proven by the lower intensity of the C=O and C-O Bonds,compared to the sawn surface.

一种基于激光点云数据的微距栅格体积算法

针对规则格网算法难以满足激光点云模型高精度体积计算的问题,提出了一种基于激光雷达点云数据的微距栅格体积算法。该方法首先运用葛立恒凸包算法提取凸包点集,然后运用微距格网划分、高程插值和网格体积累加的方法计算体积。与规则格网法不同,这种算法充分利用激光雷达数据高密度点云特征,采用格网微分和增大插值半径的方法改善模型表面的连续性,进而提高计算精度。实验结果表明,微距栅格体积算法具有较好的时间复杂度和较高的计算精度,适宜于激光点云模型高精度体积计算。

电化学脱合金Ti6Al4V基台对人牙龈成纤维细胞的影响

目的探讨电化学脱合金Ti6Al4V基台对人牙龈成纤维细胞(human gingival fibroblasts,HGFs)的影响,为种植基台表面改性设计提供实验依据。方法根据试样不同表面进行分组:NC组(阴性对照,光滑表面无其他处理)、NM-1组(纳米网-1,1 mol/L NaOH电化学脱合金处理1 h,电压2 V)、NM-2组(纳米网-2,5 mol/L NaOH电化学脱合金处理1 h,电压2 V)。扫描电镜(scanning electron microscopy,SEM)观察不同试样表面形貌及HGFs在其表面的黏附状态,接触角测量仪测定试样表面亲水性。CCK-8评估HGFs在不同试样表面的增殖情况;qRT-PCR检测HGFs在不同试样表面Ⅰ型胶原(collagenⅠ,COL1A1)、Ⅲ型胶原(collagenⅢ,COL3A1)、纤连蛋白1(fibronectin 1,FN1)、黏着斑激酶(focal adhesion kinase,FAK)、黏着斑蛋白(vinculin,VCL)、整合素α2(integrinα2,ITGA2)、整合素β1(integrinβ1,ITGB1)等黏附相关基因表达水平;免疫荧光染色,激光共聚焦显微镜(confocal laser scanning microscope,CLSM)观察HGFs在不同试样表面vinculin蛋白表达情况;天狼猩红染色评价HGFs在不同试样表面胶原纤维分泌合成情况。结果SEM观察到NM-1组和NM-2组表面形成有序均一的三维网状结构,网格直径NM-1组约为30 nm,NM-2组约为150 nm;NM-1组和NM-2组对比NC组,水接触角显著下降(P<0.0001);NM-1组细胞增殖能力较NC组显著提高(P<0.01),NM-1组和NM-2组的水接触角及细胞增殖能力差异无统计学意义(P>0.05)。SEM镜下可见HGFs黏附24 h后在各组试样表面均黏附良好,NM-1组和NM-2组细胞与NC组对比伸展面积更大,形态纤长,细胞伪足更发达。qRTPCR结果显示NM-1组中COL1A1、COL3A1、FN1、FAK、VCL等黏附相关基因表达水平显著高于NC组和NM-2组(P<0.01)。vinculin蛋白免疫荧光结果表明,NM-1组vinculin蛋白表达水平最高,单个细胞黏着斑数量最多(P<0.01)。天狼猩红染色结果显示NM-1组胶原纤维分泌合成量最高(P<0.0001)。结论Ti6Al4V经电化学脱合金改性后所构建的三维纳米网状结构有促进HGFs黏附增殖和胶原分泌合成的作用,其中网格直径约为30 nm的NM-1组对HGFs的促进作用明显。

TK50/AP复合物三维纳米网格结构的构筑及其性能研究

为了改善1,1’-二羟基-5,5’-联四唑二羟胺盐(TK50)的释能特性,采用冰模板法构筑了TK50/高氯酸铵(AP)(TK50/AP)复合物三维纳米网格结构。通过场发射扫描电子显微镜、X射线粉末衍射、差示扫描量热仪、比表面积和孔径分析仪、热-红联用仪及激光点火装置对其形貌、微结构、热分解和燃烧性能进行了研究。结果表明,TK50/AP复合物的三维纳米网格结构包含大量的中孔(2~6 nm),比表面积和孔体积分别为7.059m^(2)·g^(-1)和0.09 cm^(3)·g^(-1)。XRD衍射峰强度大大降低,由Scherrer公式计算的平均晶粒度为83.80 nm。DSC曲线有2个放热峰,位于228.1℃处尖锐的强放热峰,其峰温较原料TK50提前12℃,活化能增加144.86 kJ·mol^(-1);位于325.6℃处弱的宽峰,其峰温较原料AP提前105.6℃,活化能增加24.21 kJ·mol^(-1)。热-红联用测试结果表明复合物的热分解速率更快、能量释放更完全。TK50/AP复合物表现出高效稳定的激光点火燃烧(LIC)性能,点火延迟时间从原料TK50的50 ms、混合物的60 ms降低到20 ms,激光点火阈值从原料TK50的25.12 mJ、混合物的12.56 mJ降低到6.28 mJ。复合物的纳米尺寸效应和多孔网格结构优异的传热传质特性是其热分解和LIC性能显著改善的主要原因。

轮廓几何特征融合下的电网设备激光除锈控制参数自适应确定方法

基于激光除锈轮廓特征,在进行电网设备除锈控制参数确定时,主要依托于单一的轮廓几何特征,导致除锈后表面粗糙度偏差较大。设计一种以轮廓几何特征融合为核心的参数自适应确定方法,根据激光除锈工作原理,建立激光除锈有限元模型。采用边界矩分析算法,提取电网设备除锈的多个轮廓几何特征;融合多个轮廓几何特征,设计基于融合特征的参数确定方法,有效选择各项控制参数;通过响应面分析,自适应确定电网设备激光除锈控制参数。实验结果表明:该方法可使除锈后表面粗糙度与目标表面粗糙度值之间偏差减小2.7μm,与其他激光除锈控制参数设置结果相比,除锈后表面粗糙度偏差降低了54.24%、63.51%。

动力电池焊接熔深在线监测与闭环控制

采用光学相干层析(OCT)对焊接熔深进行在线监测,研究了OCT监测技术的稳定性及焦距自适应性。结果表明:OCT监测的熔深结果与金相结果吻合度高,其误差不超过3.65%。OCT技术对焊接工况的变化不敏感,随着焊接功率、焊接速度及保护气流量的变化,OCT监测的熔深结果误差稳定在0.24%~3.65%之间。在±2.5mm的波动范围内,不同高度焊件OCT监测的熔深标准差仅0.072mm,其过程能力指数CMK达3.51。由此证明,OCT熔深监测技术具有优异的抗干扰能力及焦距自适应性,可以实现对焊接熔深的闭环控制。

Comparison of anti-vascular endothelial growth factors, laser treatments and a combination of the both for treatment of central retinal vein occlusion

AIM：To compare changes in visual acuity and macular edema in patients with central retinal vein occlusion（CRVO）treated with intravitreal injections of bevacizumab,macular grid photocoagulation combined with pan retinal photocoagulation（PRP）,or both（bevacizumab＋grid＋PRP）.· METHODS：Our study is a retrospective cohort clinical study that examined patients that suffered from ischemic CRVO with macular edema.Study inclusion criteria were ischemic CRVO with macula edema and the availability of complete medical records for at least 12 mo after treatment.Excluded were patients with diabetes or any other retinal disease.We reviewed the medical records of patients treated in one ophthalmology departmentcomparing changes in visual acuity and macular edema in patients treated with intravitreal injections of bevacizumab vs those that were treated with macular grid photocoagulation and PRP or both.The main outcome measures were the differences in best corrected visual acuity（BCVA） and in macular thickness,as assessed by optical coherence tomography,between the enrollment and the final follow up visits.· RESULTS：Sixty-five patients met inclusion criteria.There were no statistically significant differences among the three groups in the mean changes in macular thickness as measured by ocular coherence tomography（131.5±41.2,108.6±29.2,and 121.1±121.1,P=0.110）,or in visual acuity（0.128±0.077,0.088±0.057,and 0.095±0.065）,for intravitreal injections,macular grid photocoagulation＋PRP and a combination of the treatments,respectively,P =0.111.The proportions of patients with macular edema after treatment were：26.1%,28.6%,and 14.3%,respectively,P=0.499.· CONCLUSION：Similar benefit was observed for intravitreal injections,laser photocoagulation,or a combined regimen in the treatment of CRVO.A nonstatistically significant trend for reduction in macular edema was observed following combined treatment.

Is laser photocoagulation still effective in diabetic macular edema? Assessment with optical coherence tomography in Nepal

AIM: To find out the outcome of laser photocoagulation in clinically significant macular edema (CSME) by optical coherence tomography (OCT). · METHODS: It was a prospective, non-controlled, case series study enrolling 81 eyes of 64 patients with CSME between August 2008 and January 2010. All patients received modified grid photocoagulation with frequency doubled Nd: YAG laser. Each patient was evaluated in terms of best-corrected visual acuity (BCVA) and regression or progression of maculopathy after laser therapy at 1, 3 and 6 months. Spearman’s correlation test was used to show the correlation between BCVA and total macular volume (TMV). Analysis of variance (ANOVA) was used to compare among groups and independent t-test was used to compare in each group. · RESULTS: There is high correlation between BCVA and TMV (P ≤0.001). BCVA improved in 50.6%, remained static in 39.5 % and deteriorated in 9.9% patients after 6 month of treatment. The Baseline TMV (mean and SD) were 9.26±1.83, 10.4±2.38, 11.5±3.05, 8.89±0.75 and 9.47±1.98 mm3 for different OCT patterns, ST (sponge like thickening), CMO (cystoid macular edema), SFD (subfoveal detachment), VMIA (Vitreo macular interface abnormality) and average TMV respectively (P =0.04). After 6 months of laser treatment, the mean TMV decreased from 9.47±1.98mm3 to 8.77±1.31mm3(P =0.01). In ST there was significant decrease in TMV, P =0.01, Further within these groups at 6 months, they were significantly different, P =0.01. · CONCLUSION: OCT showed the different morphological variant of CSME while the response of treatment is different. TMV decreased the most and hence showed the improvement in vision after 6 months of laser treatment. In the era of Anti vascular endothelial growth factors (VEGFs), efficacy of laser seems to be in shadow but it is still first line of treatment in developing nation like Nepal where antiVEGFs may not be easily available and affordable.

Theoretical analysis and experimental research on thermal focal length of a YVO_4/Nd:YVO_4 composite crystal

This paper investigates the temperature field distribution and thermal focal length within a laser diode array （LDA） end-pumped YVO4/Nd：YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd：YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd：YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd：YVO4 rectangular crystal for the YVO4/Nd：YVO4 composite crystal and the Nd：YVO4 single crystal are researched respectively. Calculating the thermal focal length within the Nd：YVO4 rectangular crystal was done by an analysis of the additional optical path differences （OPD） caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd：YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd：YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd：YVO4 crystal and the Nd：YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd：YVO4 laser is more advantageous than the laser with Nd：YVO4 single crystal.

Present Tectonic Stress Field in the Capital Region of China Inverted from Focal Mechanisms of Small and Strong Earthquakes

A dense seismic network was installed in the capital region of China in recent years,which makes it possible to resolve the focal mechanisms of small earthquakes. We gathered large earthquake focal mechanisms from the last fifty years and moderate or small earthquake focal mechanisms from between 2002 and 2004,and calculated the present tectonic stress field of the capital region by the grid search method, which weighs different sized earthquakes and can improve the accuracy of the stress field inversion. The analysis of inversion results of different sub-regions shows that the azinuth of the maximum principal compressive stress axis is NE43°- 86° in the Beijing-Zhangjiakou-Datong area,NE38°-86° in the Tangshan area,and NE79°- 81° in the Xingtai area. Inversion results of this paper are similar to previous results,which proves the correctness of the approach. As revealed by the results,the stress field of the capital region is characterized by overall consistency and sub-regional differences. This study provides reference for earthquake mechanism explanation and geodynamics research.

Effect of lens focusing distance on laser-induced silicon plasmas at different sample temperatures

We investigated the dependence of laser-induced breakdown spectral intensity on the focusing position of a lens at different sample temperatures(room temperature to 300 ℃) in atmosphere.A Q-switched Nd:YAG nanosecond pulsed laser with 1064 nm wavelength and 10 ns pulse width was used to ablate silicon to produce plasma. It was confirmed that the increase in the sample's initial temperature could improve spectral line intensity. In addition, when the distance from the target surface to the focal point increased, the intensity firstly rose, and then dropped.The trend of change with distance was more obvious at higher sample temperatures. By observing the distribution of the normalized ratio of Si atomic spectral line intensity and Si ionic spectral line intensity as functions of distance and temperature, the maximum value of normalized ratio appeared at the longer distance as the initial temperature was higher, while the maximum ratio appeared at the shorter distance as the sample temperature was lower.

Intravitreal Bevacizumab with Grid Photocoagulation for Recurrent Macular Edema Secondary to Retinal Vein Occlusion

Purpose: To assess the efficacy of intravitreal bevacizumab (IVB) combined with grid photocoagulation in the management of recurrent macular edema secondary to retinal vein occlusion (RVO). Methods: This is a prospective, non-randomized, interventional study. Thirty five eyes with branch retinal vein occlusion (BRVO) and 15 eyes with central retinal vein occlusion (CRVO) were treated with grid photocoagulation combined with IVB for recurrent macular edema. The visual acuity, central macular thickness and intraocular pressure were outcome measures. The mean duration of follow-up was 18.1 ± 3.6 months. Results: One month after treatment, 45 of the 50 eyes showed complete resolution of the cystoid space. Compared with initial values, final central macular thickness was reduced significantly in both BRVO and CRVO groups (P < 0.001), but improvement in VA was significant only for eyes with BRVO (P = 0.012). The total number of IVB was 1.8 ± 0.3 for eyes with either BRVO or CRVO. Conclusion: IVB combined with grid photocoagulation is an effective treatment for reducing recurrent macular edema associated with RVO.

New Technology for Grids and Scales Manufacturing in Optical Devices

Using the laser controlled thermocracking method, research results for the new technology of optical grids and scales manufacturing are given in this paper. The opportunity of grids and scales manufacturing is shown for a wide range of the sizes, scale’s pitches and its width: from 10 nanometers up to 10 microns with a backlight in various optical ranges.

The Enhanced Measurements of Laser Micro-jet Processing

In the paper, the enhanced measurements of the laser micro-jet processing are discussed. In fact, within pure water breakdown threshold of laser, the less focal which focused with the appropriate focusing lens and the small nozzle of water chamber enhance the laser power density ,at the same time, the laser beam transport in the wave guided water with the proper total reflection angle. The laser power which depended on the properties of the diameter, the coupling water chamber and the coupling efficiency of the micro-jet and laser beam expect of the properties of laser.

The Effect of Microstructural and Geometric Inhomogeneities Induced by Laser for Forming Strain Analysis on Sheet Metal Formability

A commercially available laser marking system based on diode-pumped Nd:YVO4 laser was used for creating grid patterns for forming strain analysis of a dual-phase steel. The aim was to determine and analyze the influence of laser working parameters on the formability of sheet material by means of an in-depth characterization of this induced microstructural and geometric inhomogeneity. The electrochemical etching served as the reference method without the negative effect of generating inhomogeneity. The formability was evaluated using the cupping test according to Erichsen. While the quantification of geometric inhomogeneity was based on the determination of the notch factor, light microscopy and microhardness measurement were used for the evaluation of microstructural inhomogeneity. Furthermore, on the basis of the results an empirical regression model was established which described in terms of quantity the relationship between the examined factors such as laser power, pulse frequency and scanning speed as well as the command variable and the mark depth. The results showed that microstructural inhomogeneity in the used marking parameters due to their locally very limited formation did not have an appreciable influence on the mechanical properties. In contrast to this, the induced geometric inhomogeneity had a marked influence on the material formability.