复杂曲面内腔铣削粗加工分层方法优选

大推力涡扇发动机、燃气轮机等国家战略装备引擎广泛使用复杂曲面内腔类零件,该类零件具有侧壁扭曲、整体内扣、深窄等结构特点,难以采用传统平面分层铣削方法高效加工制造。为攻克该类零件的高效加工制造难题,根据该类零件的结构特点和分层铣削加工的基本原理提出一种通过等距偏置线划分铣削层的方法,简称等距偏置分层法。首先,以等距偏置分层法和平面铣削层划分方法为基础分别规划复杂曲面内腔粗加工工艺方案;其次,进行数控仿真和加工实验,随之对比分析两种分层方法的优缺点;最后,使用工艺方案评价模型选出更适合复杂曲面内腔粗加工的分层方法。经计算,等距偏置分层法的评价结果(Evaluation Results,ER)为0.99028,高于平面分层法的评价结果0.77291,这表明等距偏置线分层方法更适合复杂曲面内腔的高效粗加工。

基于次摆线轨迹的铣削层厚度模型

铣削层厚度模型很大程度上影响着铣削加工瞬时铣削力计算精度,在每齿进给量较小情况下能较好地反映铣削层厚度的瞬时变化,但在每齿进给量较大情况下铣削层厚度计算精度不足。该文分析铣削刃随刀具旋转和工件进给的运动规律,建立铣削刀具次摆线轨迹模型,给出铣削起始角和终止角,提出一种基于次摆线轨迹的铣削层厚度模型。通过与现有圆弧模型和等效均匀厚度模型对比,结果表明:该模型在不同每齿进给量下均能保证较高准确性。

Analysis and Control of Surface Delamination Defects During Milling of Orthogonal Aramid Fiber‑Reinforced Composites Laminates

The aramid fiber-reinforced composites(AFRC)can increase the durability of corresponding applications such as aerospace,automobile and other large structural parts,due to the improvement in hardness,heat build-up,wear properties and green environmental protection.However,because of its complex multiphase structure and unique heterogeneity and anisotropy,the poor compression fatigue resistance and the incident surface fibrillation are inevitable.To improve the assembly precision of AFRC,mechanical processing is necessary to meet the dimensional accuracy.This paper focuses on the influence of contour milling parameters on delamination defects during milling of AFRC laminates.A series of milling experiments are conducted and two different kinds of delamination defects including tearing delamination and uncut-off delamination are investigated.A computing method and model based on brittle fracture for the two different types of delamination are established.The results can be used for explaining the mechanism and regularity of delamination defects.The control strategy of delamination defects and evaluation method of finished surface integrity are further discussed.The results are meaningful to optimize cutting parameters,and provide a clear understanding of surface defects control.

Experimental and FEM Study of Coated and Uncoated Tools Used for Dry Milling of Compacted Graphite Cast Iron

Compacted graphite cast iron （CG1） has been the material for high-power diesel engines recently, but its increased strength causes poor machinability. In this study, coated and uncoated carbide tools were used in dry milling experiment and FEM simulation to study the machinability of CGI and wear behaviour of tools. The experimental and FEM simulation results show that coated tool has great advantage in dry milling of CGI. SEM and EDS analysis of tool wear indicate the wear morphology and wear mechanism. Adhesive wear is the main mechanism to cause un- coated tool wear, while abrasive wear and delamination wear are the main mechanism to cause coated tool wear. Stress and temperature distribution in FEM simulation help to understand the wear mechanism including the reason for coat- ing peeled off.

Mathematical Model and Simulation of Cutting Layer Geometry in Orthogonal Turn⁃Milling with Zero Eccentricity

Orthogonal turn-milling is a high-efficiency and precision machining method.Its cutting layer directly affects chip formation,cutting forces,and chatter,and further affects tool life,machining quality,etc.We studied The cutting layer geometry(CLG)in orthogonal turn-milling with zero eccentricity(OTMZE)is studied to explore orthogonal turn-milling cutting layer formation process.OTMZE principles of motion and formation processes are analyzed statically without considering kinetic influences.Mathematical models of the entrance and exit angles,cutting thickness,and cutting depth are established.In addition,these models are validated experimentally and some influences of cutting parameters on the tool cutting layer are analyzed.The results show that OTMZE cutting layer formation can be divided into two stages,chip shapes are nearly consistent with the simulated CLGs,and the most influencial parameter in affecting the cutting layer is found to be the tool feed per revolation of workpiece fa,followed by the ratio of the tool and workpiece speedsλand the cutting depth ap.These models and results can provide theoretical guidance to clarify formation processes and quantitatively analyze changes in cutting layer geometry during OTMZE.In addition,they offer theoretical guidelines for cutting forces and chatter.

Milling Machinability of TiC Particle and TiB Whisker Hybrid Reinforced Titanium Matrix Composites

The milling machinabilities of titanium matrix composites were comprehensively evaluated to provide a theoretical basis for cutting parameter determination. Polycrystalline diamond （PCD） tools with different grain sizes and geometries, and carbide tools with and without coatings were used in the experiments. Milling forces, milling temperatures, tool lifetimes, tool wear, and machined surface integrities were investigated. The PCD tool required a primary cutting force 15 % smaller than that of the carbide tool, while the uncoated carbide tool required a primary cutting force 10% higher than that of the TiA1N-eoated tool. A cutting force of 300 N per millimeter of the cutting edge （300 N/mm） was measured. This caused excessive tool chipping. The cutting temperature of the PCD tool was 20%-30% lower than that of the carbide tool, while that of the TiA1N-coated tool was 12% lower than that of the uncoated carbide tool. The cutting temperatures produced when using water-based cooling and minimal quantity lubrication （MQL） were reduced by 100 ~C and 200 ~C, compared with those recorded with dry cutting, respectively. In general, the PCD tool lifetimes were 2--3 times longer than the carbide tool lifetimes. The roughness Ra of the machined surface was less than 0.6μm, and the depth of the machined surface hardened layer was in the range of 0.15-0.25 mm for all of the PCD tools before a flank wear land of 0.2 mm was reached. The PCD tool with a 0.8 mm tool nose radius, 0% rake angle, 10% flank angle, and grain size of （30＋2） μm exhibited the best cutting performance. For this specific tool, a lifetime of 16 rain can be expected.

Methods for Reducing Interface Aperture Inconsistency During NC Orbital Milling of Aircraft Laminates with Coarse Pitch

The methods for reducing interface aperture inconsistency are studied in NC orbital milling(NCOM)of CFRP/Ti6Al4V laminates with coarse pitch.Comparative experiments show burr,aperture inconsistency and error are typical interface defects.Meanwhile,aperture inconsistency and error are more serious than burr in NCOM with coarse pitch.As one of the major causes of interface defects,axial force and radial force are intensively studied.Based upon the machining principle of orbital milling(OM)and the actual hole-making condition in laminated structures,NCOM experiments with coarse pitch are conducted on CFRP/Ti6Al4V laminates under different cutting conditions.Then,the effects of interlayer clamping,minimal quantity lubrication(MQL),twice milling instead of reaming,and interlayer speed change on interface aperture are analyzed.Research shows that interlayer clamping,interlayer speed change and MQL can effectively reduce out-of-tolerance of interface aperture.When making holes of different diameters with one cutter,axial feed has a greater effect on interface aperture precision than tangential feed.When making holes of the same diameter with different cutters,small diameter cutter will reduce interface aperture precision in a single processing.But the method of“twice milling instead of reaming”can improve the aperture precision effectively.