错齿BTA深孔振动钻削刀具系统径向减振特性研究

BTA深孔钻削刀具系统刚性差,加工过程极易发生多个方向的颤振,而刀具颤振对孔的加工精度和刀具的使用寿命具有重要影响。根据错齿BTA内排屑深孔钻刀具系统的特点,构建了深孔钻削过程刀具系统径向动力学模型,通过其特征方程研究了径向动力学特性。为了获得普通钻削与振动钻削条件下刀具系统径向振动的行为特征,将切削加工过程离散为满足状态方程连续条件的多个微小切削单元,并采用差分方程求解方法给出了普通钻削与振动钻削过程刀具径向振动位移的数值解。仿真和实验结果表明,所建立径向动力学模型的求解结果与实验结果相吻合,振动钻削对刀具系统径向振动具有较强的抑制效果,与普通钻削相比,孔加工圆度和表面粗糙度都有了明显改善。     

碳纤维增强树脂基复合材料制孔技术研究现状与展望

碳纤维增强树脂基复合材料(CFRP)具有优越的物理和力学性能,已在航空制造工业中得到大量应用。在主承力结构中,CFRP与金属材料的连接通常为机械连接。然而,CFRP的各向异性严重影响了其制孔质量。由于CFRP和金属具有截然不同的材料属性,CFRP/金属叠层结构制孔技术成为飞机装配过程中的一大难题。本文首先阐述了CFRP及其叠层结构在切削过程中的切屑形成机制、钻削力和钻削热的研究现状;其次,剖析了钻削过程中典型加工损伤,如毛刺与撕裂、分层缺陷及孔壁表面损伤的产生原因和影响因素;然后,介绍了CFRP制孔刀具材料和几何结构的优化设计研究进展,并综述了螺旋铣孔、变工艺参数钻削、"以磨代钻"和振动辅助制孔等多种CFRP及其叠层结构加工新技术及钻削过程的仿真研究。最后,借鉴钎焊工具和超声振动技术的独特优势,提出了磨粒有序排布钎焊金刚石工具的超声振动加工构想,以达到CFRP及其叠层结构的精密高效制孔加工这一目的。     

双顶角钻头钻削CFRP复合材料的刀具磨损机制

为了研究碳纤维增强树脂基(CFRP)复合材料切削中刀具在不同部位的磨损机制和规律,以典型的硬质合金双顶角钻头作为研究对象,主要研究对出口分层影响较大的横刃和对最终制孔成型影响较大的第二主切削刃的磨损机制及规律。通过减小磨损测量间隔,并引入切削刃钝圆半径以及后刀面磨损带宽度,表征了横刃和第二主切削刃在加工中的衰变过程。基于显微刃口观测和钝圆半径变化,揭示横刃易崩刃和第二主切削刃磨损后又受到重新刃磨的磨损机制,获得了此类型钻头不同部位的磨损规律。同时,基于上述的磨损表征,研究不同切削部位磨损量对钻削轴向力和力矩的影响,横刃轴向力与横刃钝圆半径变化相关性较小,而钻削最大力矩与第二主切削刃后刀面磨损变化规律相一致。     

碳纤维增强复合材料螺旋铣孔切削力及加工质量研究

针对传统钻孔方法加工复合材料时易导致分层、撕裂等缺陷的问题,采用螺旋铣作为新的制孔技术,根据飞机装配现场的实际加工条件,构建以机器人为移动载体、螺旋铣孔终端执行器为加工单元、螺旋铣孔专用刀具为切削工具的加工系统,采用该加工系统对碳纤维增强复合材料(CFRP)螺旋铣孔关键工艺参数进行正交试验,并讨论了刀具主轴转速、每齿进给量和轴向切削深度等工艺参数对切削力的影响规律;通过对加工缺陷的监测,探讨了切削力与CFRP分层、撕裂等缺陷之间的关系;最后对工艺参数进行优化,经试验验证,优化后轴向切削力较优化前降低26%以上,孔入口及出口处均无撕裂、毛刺,加工质量最优。     

考虑刀具磨损影响的CFRP复合材料钻削轴向力预测

在碳纤维增强树脂(CFRP)复合材料钻削过程中,随着刀具磨损量的累积,轴向力会逐渐增加,轴向力过大会导致CFRP复合材料一系列的加工缺陷。为实现在CFRP复合材料钻削过程中随刀具磨损量的累积轴向力变化的有限元分析及预测,建立了CFRP复合材料钻削仿真模型,通过对ABAQUS仿真软件二次开发,利用Python语言开发子程序,将考虑磨损量累积的轴向力预测模型导入仿真软件,运用ABAQUS软件对CFRP复合材料钻削中轴向力进行研究,实现了随着刀具磨损量累积轴向力变化的预测功能。随后通过CFRP复合材料钻削试验,分析了轴向力随钻削孔数的变化规律,以验证轴向力的预测结果。结果表明:3D钻削有限元模型能够良好地预测实际加工过程中刀具未磨损时轴向力的大小,其误差为9.10%;在考虑磨损量累积后,轴向力预测模型能够较准确地预测实际加工过程轴向力的大小,其最大误差不超过10%。      

深孔钻加工工艺浅析

在切削加工中,孔加工约占加工总量的1/3,而深孔加工又占孔加工的40%,目前钻削加工单从精度、工艺及经济上都占有优势,在将来一段时间仍将继续使用,深孔加工目前面临的难题-刀具折断,刀具折断包括工件也会报废,成本浪费极大,针对上述加工情况对深孔加工关于刀具工艺从切削参数、刀具顶角角度设计、切削工艺等方面阐述为断刀问题解决提供参考。     

玻璃纤维增强聚丙烯复合材料制孔损伤

为抑制玻璃纤维增强聚丙烯复合材料（GF/PP）制孔损伤并提高其制孔效率,本文通过钻削实验获得多种进给速度下的GF/PP复合材料钻削轴向力和出口温度,使用高速摄影设备对刀具钻出过程进行在线观测,研究出口材料去除过程及其损伤成因,分析进给速度对GF/PP复合材料制孔损伤的影响规律。结果表明：GF/PP复合材料的钻削出口温度在低速进给时显著升高,在高速进给时基本趋于稳定;出口撕裂是重要的出口损伤形式,成因是大片毛刺受副切削刃的撞击和撕挤,进给速度过高或过低均会加剧损伤; 0°毛刺在低速进给时较严重,入口撕裂在高速进给时较严重。     

CFRP管面钻削缺陷形成机制

碳纤维增强复合材料(CFRP)传动轴因性能优越广泛应用于汽车、航空航天、船舶、冷却塔风机等轻量化领域,但其钻削过程中容易出现毛刺、分层等缺陷。为了揭示CFRP管面钻削缺陷形成机制,选择双锋角钻头和三尖二刃钻对CFRP管面钻孔,利用分步钻削盲孔和通孔的方法,分析了损伤部位的受力情况,揭示了入口撕裂、出口毛刺和分层产生原因。根据实验结果,发现双锋角钻头钻孔时入口撕裂损伤较大,损伤位置在钻头与管面接触最低点,且主要是那部分水平缠绕CFRP管的纤维,原因是水平缠绕的纤维屈曲变形最大,对切削力更加敏感。双锋角钻头和三尖二刃钻的横刃对孔最终出口分层没有影响,主切削刃的切削行为决定孔最终出口分层。相同钻头钻孔时,轴向力不是唯一影响分层因子的因素,还需考虑切削热。相比双锋角钻头,三尖二刃钻因锋利的外缘尖角能有效划断纤维,使出口分层较小。     

一种超声超低温冰层支撑辅助CFRP钻削方法

提出一种超声振动+超低温液氮+由超低温环境形成的冰冻支撑层(Ultrasonic vibration+Cryogenic liquid nitrogen+Frozen support layer,UCF)来辅助碳纤维增强树脂基复合材料(Carbon fiber reinforced polymer, CFRP)钻削制孔，有效降低钻削缺陷的加工方法。该方法的基本原理为：利用超声作用下的钻头高频振动实现轴向钻削力的弱化，利用超低温液氮以及形成的冰冻支撑层来实现钻削出口侧材料的约束和支撑，并有效降低加工过程的钻削热影响。基于UCF的基本原理，开展了相应的UCF辅助加工实验，通过微观检测表征和缺陷因子计算等手段，与传统钻削模式(Traditional drilling, TD)、低温液氮+冰冻支撑模式(Cryogenic liquid nitrogen+Freezing support,CF)下的CFRP制孔质量进行了对比分析。结果表明，采用UCF模式和CF模式均会引起轴向力增加，但UCF模式下的最大轴向力增幅相对较小；与TD模式相比，采用UCF辅助加工方法最大可使CFRP钻削出口的毛刺因子降...     

基于CFRP层合板钻削轴向力时变曲线的钻头几何形状分析

为探索能够实现碳纤维增强复合材料（CFRP）层合板低损制孔的钻头几何形状,采用4种不同几何形状的钻头,对T800级CFRP层合板进行钻孔实验研究,分析了钻头几何形状对钻削轴向力的影响,探讨了钻削轴向力与分层损伤之间的关系。结果表明:轴向力归零速度与出口分层因子有较好的正相关性,可采用钻削轴向力归零速度来表征钻头几何形状对CFRP层合板钻孔的适用性能。同时,实验发现切削区域具有多阶段几何特征的钻头,在钻出工件底部时轴向力是分阶段缓慢归零,出口分层因子较小。      

CFRP复合材料/钛合金叠层螺旋铣孔工艺

利用螺旋铣变偏心距加工的特点,提出了在刀具回程过程中进行二次精加工的工艺策略。通过正交试验研究了回程各工艺参数对CFRP/Ti-6Al-4V叠层孔加工质量和加工精度的影响规律,并依此优化工艺参数。试验结果显示:采用优化参数的回程精加工工艺提高了叠层孔的制孔精度,避免了复合材料孔壁加工损伤,复合材料孔粗糙度均值从Ra3.52降低到Ra1.31,入口撕裂明显改善,钛合金孔出口无毛刺。     

Experimental study on mechanical drilling of carbon/epoxy composite-Ti6Al4V stacks

This paper concerns the experimental studies on the drilling process of multilayer carbon/epoxy composite-Ti6Al4V stacks and their individual material layers using tungsten carbide drills. The significance of the current work aims to reveal the impact of tool wear on the drilling process for CFRP/Ti6Al4V, CFRP and Ti6Al4V. Four groups of machining tests including drilling individual CFRP, individual Ti6Al4V, multilayer CFRP/Ti6Al4V stacks with and without a cooling treatment were conducted. Drilling forces, cutting temperatures and hole quality attributes were experimentally investigated in terms of the drill wear extents. The mechanism controlling the tool wear effect on the drilling machinability of CFRP/Ti6Al4V was revealed, providing several implications for the industrial manufacturers. The results highlight the significant impact of the titanium chip ejection on the composite surface quality and the necessity of a rigorous tool wear control to guarantee the damage-free drilling of CFRP/Ti6Al4V stacks.     

Experimental investigation of IN725 under different cooling environments using new tool holder

Heat buildup is an important issue on the cutting edge which then promotes high-temperature wear which consequently leads to poor machinability during dry machining. To improve the machinability, new tool holder designs accommodating cooling techniques have paid considerable attention toward the manufacturing domain recently. Whereas, in this paper, a new tool holder is designed and fabricated to serve for multipurpose cooling arrangements (internal cooling, external cooling) to reduce the heat buildup of the cutting edge along with the consolidated air system to clear away the chips. Initially, need of new tool holder is discussed followed by its manufacturability and machinability characteristics to a machine for nickel alloy Inconel 725. Machinability studies then are compared for dry machining, internal and external wet machining, and tool wear results are discussed. Thus, improvement in tool wear of around 70–75% and 65–72% is observed for internal wet, external wet concerning dry machining, respectively. Whereas, 15–18% (flank wear) and 6–9% (nose wear) improvement are seen for internal wet machining when compared with external wet machining. Results are best understood for internal cooling using a new tool holder.     

基于分层损伤分析的碳纤维增强树脂复合材料-金属传动轴扭转性能

为提高油动四旋翼无人机载重能力,对碳纤维增强树脂复合材料(CFRP)-金属传动轴进行研究。CFRP-金属传动轴扭转强度影响因素为CFRP管制孔质量问题和传动过程中销钉对连接孔的挤压作用。研究导致CFRP管孔入出口分层损伤的力学行为,揭示了CFRP管制孔质量的影响机制并优化了制孔工艺。利用扭转试验对销接式CFRP-金属传动轴和附有内外衬套的混合式CFRP-金属传动轴进行对比分析。结果表明:在CFRP管内外附有铝合金衬套可有效减少制孔时的分层损伤,使孔入口质量提高了4.4%,孔出口质量高了8.3%,同时抑制销钉对连接孔的挤压作用。优化后的传动轴承受扭矩从499 N·m提高到952 N·m。      

Investigating the effect of machining processes on the mechanical behavior of composite plates with circular holes

The influence of the machining quality on the mechanical behavior of CFRP composites is yet not fully understood. There are only few works in the literature that have investigated the effect of the machining quality on CFRP. In fact, most of these works focus only on conventional machining such as axial or orbital drilling. The aim of this paper is to examine the influence of two machining processes namely conventional machining (CM) and abrasive water jet machining (AWJM) on the mechanical behavior of composite plates under cyclic loading. For this purpose, an experimental study using several composite plates drilled with a cutting tool and an abrasive water jet machining was carried out. In order to study the impact of the process of machining on the mechanical behavior, thermographic infrared testing and fatigue cyclic tests were performed to assess temperature evolutions, stiffness degradation, and the damage evolution in these plates. Fatigue testing results have shown that the damage accumulation in specimens drilled with CM process was higher than the AWJM specimens. Furthermore, the endurance limit for a composite plate drilled with CM was approximately 10% inferior compared to specimens drilled with AWJM. This difference can be related to the initial surface integrity after machining induced by the difference in the mechanism of material’s removal between the two processes used.     

Effect of Heat Treatment on the Drilling Performance of Aluminium/SiC MMC

The extremely abrasive reinforcing phases present in metal matrix composites (MMCs) are known to dominate their machining behaviour. Consequently, the properties of the matrix material are often ignored. The work reported here investigated the influence of matrix microstructure on the drilling performance of a 2618 aluminium alloy reinforced with 18% silicon carbide particles. The drills used were 8 mm diameter, titanium nitride coated K10 carbide with through-tool cooling. The workpiece material was drilled in four heat treatment conditions: as-extruded, solution treated and solution treated and aged for 12 and 20 hours. Drilling performance was assessed by measuring the wear on the drills, cutting forces, surface finish and the condition of the worn cutting edges. The results indicated that softer as-extruded and solution treated materials produced less wear and lower cutting forces than the harder aged materials. However, the height of the burrs produced during drilling were found to be greater with the softer materials and the quality of the drilled surface was also inferior. Examination of the worn cutting edges indicated that the wear mechanism was primarily one of abrasion although some attrition and edge chipping was also observed. It was concluded that when drilling these materials, the heat treatment condition of the matrix exerts a significant influence on machinability.