Surface grinding of carbon fiber reinforced plastic (CFRP) with an internal coolant supplied through grinding wheel

Carbon fiber reinforced plastic (CFRP) is widely used in the aerospace industry due to its high specific strength and elastic modulus. When cutting CFRP with tools such as an endmill, problems such as severe tool wear, delamination, and burrs in the CFRP can arise. Grinding, on the other hand, is supposed to improve the quality of the machined surface and tool life, according to its machining property. However, the amount of heat generated during grinding is still a considerable problem in that it is significantly higher than the temperature with conventional cutting. In order to achieve the high performance machining of CFRP, this study aims to show the effect of supplying an internal coolant through the grinding wheel on the surface of the CFRP. Face grinding of CFRP using a cup-type grinding wheel was conducted. Vitrified aluminum oxide grinding wheel was used. Three different coolant supply systems were tested: dry grinding, coolant supply using an external nozzle, and coolant supplied internally through the grinding wheel. The results showed that matrix resin loading on grinding wheel was significantly reduced by the internal coolant supply. Hence, the grains of the grinding wheel were able to cut the fibers sharply, without delamination or burr formation on the ground surface, and surface roughness was reduced compared to the machined surface with endmill. The internal coolant supplied through the grinding wheel showed greater cooling ability, and markedly reduced grinding temperature, keeping it lower than the glass-transition temperature of the matrix epoxy resin of CFRP. Because the coolant was supplied to the grinding point directly through pores in the grinding wheel, chips were eliminated from the pores, and coolant supply was sufficient to cool the ground surface.     

Thermal influence on surface layer of carbon fiber reinforced plastic (CFRP) in grinding

In this study, we investigated thermal influence on surface layer of CFRP in grinding with heat conduction analysis using grinding temperature at wheel contact area on dry and wet condition. Moreover, the thermal affected layer was analyzed through an experiment to examine the temperature of glass transition and thermal decomposition of the matrix resin that composes the CFRP used in this study. The influence of thermal effect on grinding of CFRP was verified based on observation of ground surface finish after grinding using SEM and the measurement of surface roughness. From the measurement result of DSC (Differential Scanning Calorimetry),TG-DTA (Thermogravimetry-Differential Thermal Analysis), It was found that the thermal affected layer of CFRP includes a layer in which the matrix resin is changed in quality by exceeding the glass transition temperature and a layer in which the matrix resin is thermally decomposed by exceeding the thermal decomposition temperature. In addition, it was found that the surface roughness was significantly reduced if the thermal affected layer with thermal decomposition was generated. In each grinding atmosphere, it tended to increase of grinding temperature at wheel contact area with increasing in the setting depth of cut. In the case of dry grinding, grinding temperature at wheel contact area increased up to t thermal decomposition temperature of the matrix resin. However, in the case of the wet grinding, grinding temperature at wheel contact area did not increase until thermally decomposition temperature. From the result of simulation about thermal affected layer, influence of grinding heat increased with increasing in the setting depth of cut. Ultimately, the thermal affected layer with thermal decomposition was generated in dry grinding. Moreover, from the results of SEM observation, it was confirmed that the surface finish properties deteriorated significantly due to thermal decomposition of the matrix resin in the case of Δ = 400 μm in the setting depth of cut at fiber angle θ = 0°. On the other hand, it was confirmed that the micro damage of carbon fiber was occurred in wet grinding at each setting depth of cut.     

磨削过程中磨削液的有效利用及其实现技术

在磨削加工过程中,一般都是利用向磨削区供给充分冷却液的方法来抑制零件表面温度升高和解决热损伤。但是由于砂轮的高速旋转,会在砂轮的表面形成一个高压空气边界层,阻止磨削液有效的进入磨削区,使加工条件恶化,磨削区温度升高,影响了工件的表面质量和完整性。通过合理的选择供液压力、流量和供液方式及喷嘴形式来提高进入磨削区有效磨削液的比例,进而更好的发挥磨削液的冷却作用,降低磨削区温度,保证工件表面质量和表面完整性,同时也有利于实现绿色磨削加工。     

加压内冷却砂轮的研制及磨削性能研究

针对高温合金材料在磨削加工过程中存在磨削烧伤问题,为避免气障效应并强化冷却液在磨削弧区的换热效果,提出采用加压式内冷却断续磨削方法。利用数值模拟方法和3D打印技术对砂轮基体、加压内冷却系统和密封结构等进行设计和验证,制备了用于平面磨削的加压内冷却开槽CBN砂轮。在相同的磨削加工参数条件下,使用加压内冷却方法与外部喷射冷却方法进行镍基高温合金磨削对比试验,分析了砂轮速度、磨削深度和工件进给速度等加工参数对磨削温度、加工表面粗糙度和表面形貌的影响规律,验证了加压内冷却断续磨削方法对磨削弧区的强化换热效果。结果表明：在相同试验参数条件下磨削镍基高温合金,加压内冷却法比外部喷射冷却法的换热效率更高,得到的磨削温度更低,表面粗糙度更小,加工表面更为光滑细腻。     

Effect of parameters on grinding forces and energy while grinding Al (A356)/SiC composites

Abstract

Grinding processes require a high energy input per unit volume of material removed, which is converted to heat at the grinding zone, resulting in increased force and wear. In the present study, the influence of grinding parameters like work speed and depth of cut on grinding forces and energy was studied. An attempt has been made to study the forces and energy involved while grinding aluminium alloy (A356)/silicon carbide (SiC) composite material with different grinding wheels. Experiments were carried out on a surface grinding machine. Three different types of wheels like SiC, cubic boron nitride (CBN) and diamond wheels were used. The grinding forces increased with increase in depth of cut and work speed. SiC exhibited high grinding force compared to the CBN wheel. In the case of the diamond wheel, it was even less. The specific grinding energy was highest for the diamond wheel followed by CBN and SiC wheels. The specific grinding energy decreased with increase in depth of cut and work speed.     

内冷却砂轮工装研制

由于磨削加工中过高的磨削温度,可采用内冷却砂轮磨削,将切削液直接浇注到磨削区内部,破坏了磨削区的封闭性,从根本上解决磨削温度高引起的工程实际问题.在普通磨床上采用内冷却砂轮磨削就必须提供内冷却砂轮工装,通过对砂轮内冷却总体方案、内冷却砂轮工装设计进行了研究,研制出了结构简单,性能可靠高的内冷却砂轮工装,将该工装用于M7130C平面磨床进行磨削加工,大大降低了磨削区温度,有效避免磨削烧伤,提高了磨削加工质量,效果良好.实验表明内冷却砂轮可加工某些难加工材料,扩大了磨床加工范围.     

球面磨削温度场数值仿真的研究

根据杯形砂轮磨削球面的特点,采用绕球面旋转加载的半圆弧热源模型对磨削过程进行有限元仿真,研究球面磨削时工件表面的温度场分布.将仿真结果与实验结果进行比较,发现有限元仿真值与实验测得量相当接近.     

一种新的磨削加工砂轮锋利度在线建模与监测方法的研究

本文通过考察外圆磨削循环中工件每转实际磨削深度变化规律与砂轮锋利度的密切关系，提出用神经网络ＡＲＴ２模型对磨削过程中工件每转实际磨削深度变化规律进行数据处理，可以实现在线识别磨削过程砂轮的锋利度。针对磨削加工的特点，提出新的ＡＲＴ２模型匹配度判据。设计制作了相应的数据采集处理系统，对实际磨削过程不同工艺参数的情况下砂轮锋利度进行识别，证实了这种新的识别砂轮锋利度模型及监测系统是十分有效的。     

砂轮磨钝的在线辨识研究

介绍了以磨屑热辐射流温度作为辨识砂轮磨钝特征信号和理论依据，并用神经网络方法建立了智能辨识系统，实验结果表明，磨屑热辐射流温度信号是较好的辨识砂轮磨钝的信号源。     

超高速磨削温度的实验研究

用人工热电偶方法对40Cr和45#钢的超高速磨削温度做了深入的实验研究.发现提高砂轮线速度,工件的磨削温度随之升高;但从某一速度开始继续提高砂轮线速度,磨削温度却呈明显下降的趋势.这就预示超高速磨削温度较低,适合磨削.同时对超高速磨削的比磨削能进行了研究,表明大切深超高速磨削是可行的,发现40Cr钢的超高速磨削性能优于45#钢.     

磨削弧区温度在线监测技术研究

设计了一种可以在生产现场的强背景干扰下在线监测磨削弧区温度的新方法。并通过实际磨削测温实验及烧伤跟踪实验对该方法的可行性进行了分析。结果表明,该方法简单、实用,可实现磨削温度的在线监测,特别适用于断续式ＣＢＮ砂轮磨削过程的温度监测。     

柱塞斜槽磨削裂纹的成因及对策

通过对开裂柱塞的裂纹形貌、化学成分、硬度和金相的分析,指出了过高的磨削热是产生磨削裂纹的主要原因,而调整磨削参数和合理选择砂轮及冷却液则可以有效地防止。     

碳纤维增强复合材料低温冷风磨削试验研究

采用SD80N100B金刚石砂轮开展了单向碳纤维复合材料的低温冷风磨削与常温干式磨削的对比试验研究,探讨了低温冷风与磨削参数对碳纤维复合材料磨削性能的影响。采用扫描电镜与超景深电子显微镜观察了磨削后的表面形貌和亚表面损伤情况,并分析了表面粗糙度的影响规律。试验结果表明：与常温干式磨削相比,低温冷风磨削的磨削力增大,表面粗糙度减小;在低温冷风和常温干式两种磨削方式下,纵向90°磨削较其他磨削方向的磨削力更大,表面粗糙度更小。     

齿轮磨削中磨削力数学模型的研究

基于锥面砂轮磨齿展成运动的几何模型,计算出砂轮在任意冲程中所磨除金属材料的几何形状尺寸,在平面磨削磨削力计算公式的基础上对该被磨除金属材料沿磨削宽度方向进行积分,得到了齿轮磨削加工过程中磨削力的计算公式,应用该公式进行了仿真计算,得到了两种提高齿轮磨削加工质量的方法。     

断续磨削时工件表层温度场解析

建立了周期变化的移动热源模型,并引进卷积概念,推导了计算断续磨削时工件表层非稳态脉动温度场的理论公式。该公式可以包容连续磨削的情况,且可计算任意时刻的瞬态温度分布。利用推得的公式对断续磨削时的温度场及其降温机理作了深入的研究,并对关于理论公式进行了实验校核。     

磨削加工过程建模的研究进展

综述了磨削加工过程的几何建模过程中砂轮几何模型的建立方法、磨粒去除工件材料机制的研究进展,指出了其中存在的一些问题;阐述了磨削加工过程的物理建模过程中磨削力机理解析建模、经验公式建模的研究动态,分析了这些建模方法的局限性,简要介绍了磨削温度场建模中能量分配和热源形状的研究进展;讨论了对磨削加工过程进行数值模拟所存在的一些难点。     

Coolant flow in surface grinding with non-porous wheels

A parameter that is often used in the assessment of cooling efficiency in grinding is the amount of fluid that flows through the grinding zone. This paper shows that when grinding with wheels possessing no bulk porosity, only a portion of the flow through the grinding zone is effective. Even at the highest wheel speeds employed, it is observed that ample fluid travels on the wheel surface and is re-directed into the grinding zone — a phenomenon that may adversely affect cooling and wheel cleaning. Therefore fluid rejection off the wheel is important. A theoretical model for fluid rejection is proposed, that describes the drop formation process, presents the operating instabilities, identifies characteristic time and length scales, and predicts the amount of rejected fluid. Although the surface roughness of the wheel is important in quantifying coolant flow rates, a smooth wheel is employed in this work to study first order effects. Preliminary experimental results obtained for a rough grinding wheel are in conformance with those for a smooth wheel.     

Evaluation of wheel life by grinding ratio and static force

A degree of sharpness in wheel grains affects the surface roughness and dimensional accuracy in the grinding process. If a wheel with dull grains is used, the grinding force is increased and the surface roughness is deteriorated. In ovder to produce a precision component economically, the magnitude of the wear amount in the grinding wheel has to be limited. In this study, experimental evaluation of a wheel life varying with the grinding ratio and static grinding force was conducted. The grinding ratio and grinding force were measured to seek the grinding performance of the WA wheel. The relationship between the grinding ratio and static grinding force was presented.     

Modeling and numerical simulation for the machining of helical surface profiles on cutting tools

The classical conjugation and envelope method is very accurate and effective for forward and inverse calculations of grinding helical surfaces. However, this method involves complicated mathematics and requires that the profiles be continuous. It can also result in undercutting or interference to the desired surface profiles. In this paper, a new approach is proposed to simulate the grinding process of helical surfaces on cutting tools. The paper begins with the reconstruction of cutter helicoids from sampled points. Using the recovered helical parameters from the sample points, the cross-sectional profile of the cutter surface is derived using a polynomial curve. A numerical method for calculating the profile of the grinding wheel required for the cutter surface profile is then provided. Finally, an optimization method is presented for solving the problem of inverse calculation to determine the helical surface profile for a given grinding wheel profile and setting parameters. The feasibility of the approach is tested by simulation results, which shows that the proposed approach can eliminate undesired tool-work interferences and undercutting.     

Dry grinding by special conditioning

Dry grinding is one of the most favourable processes from an economical as well as an ecological point of view. However, it is rather difficult to achieve this goal due to the nature of the grinding process. A common method for reducing and eliminating the use of metalworking fluid is to reduce any harmful heat generation observed in the process. Any change in the grinding parameters such as depth of cut, feed rate, or grinding speed, or the characteristics of the grinding wheel such as grit size, bonding, and porosity, can have a great influence on heat generation. This paper presents some of the very good results of the systematic research works that were done to reduce heat generation by special conditioning using a single-point diamond dressing tool based on the new innovative concept.