Experimental Study on Hard Turning Hardened GCr15 Steel with PCBN Tool

This paper discusses experimental results of turnin g experiments on GCr15 bearing steel hardened to 60～64 HRC. The objective was to d etermine the effect of the cutting parameters on cutting force, chip morphology and resultant workpiece surface quality, more specifically surface texture, micr ostructure alterations, changes in microhardness and residual stresses distribut ion. The changing rules of the main cutting force was shown in this paper which feature a increasing tendency with the improvement of the workpiece hardness wit hin the cutting parameter scope. The rule of cutting force changing with the wor kpiece hardness is accord to the traditional metal cutting theory. Stress value decrease with increasing cutting speed and workpiece hardness. The comparison of the machined surface roughness and harden layer depth of machined surface for d ifferent hardness is shown in Fig.1. The machined surface roughness is the worst when the workpiece hardness is around 50HRC. When the workpiece hardness is ove r 50HRC, the surface roughness value shows a descending tendency with the additi on hardness. The machined superficial harden layer depth shows an increasing ten dency with the improvement of the workpiece hardness. When the workpiece hardnes s is 50HRC the machined superficial harden layer depth is tiptop. When the workp iece hardness is over 50HRC the depth changes little with the addition of workpi ece hardness. The remnant stress status of the machined surface is shown in Fig. 2, which is press stress status both in surface and in base for less cutting par ameters under two kinds of cutting condition. But experiment results show that t ensile stress can be produced under uncomfortable cutting conditions. The deform ation created by the chip formation is reduced whereduce with [TPP126A,+35mm77mm,Z,PY#]Depth from surface (μm) ■ v=200m/min,f=0.24mm/r,ap=0.8mm,60HRC ● v=200m/min,f=0.15mm/r,ap=0.5mm,60HRC Fig.1 The subsurface residual stress between the two experimentsHardness (HRC) Fig.2 The surface finish vs. workpiece hardness the workpiece hardness is improved.

Influences of Tool Wear on Residual Stress and Fatigue Life of Workpiece in Hard Cutting Process

Tool wear has an important influence on the residual stress distribution on the machined surface.Also,it will influence the fatigue life of finished workpiece. In this research,the hard turning process of hardened die steel Cr12 MoV was studied by using PCBN tool with considering tool wear. Based on the numerical treatment of residual stress,the dispersion and distribution curves of different tool wear were fitted,and the influence mechanism of tool wear on the residual stress distribution of machined surface was analyzed.Based on the theory of fatigue mechanics and mathematical statistics,the mathematical model for difference of stress dispersion and fatigue life was established. The rotating and bending tests were carried out on the standard parts after cutting process for the workpiece. The influence of tool wear on fatigue life was revealed by fracture surface morphology and fatigue life study. The results provide theoretical support for control of residual stress and the fatigue property of the machined surface under the actual working conditions.

Cutting Temperature and Tool Wear of Hard Turning Hardened Bearing Steel

A study was undertaken to investigate the performan ce of PCBN tool in the finish turning GCr15 bearing steel with different hardness between 30～64 HRC. The natural thermocouple was used to measure the cutting tem p erature, tool life and cutting temperature were investigated and compared. The m aterial can be heated by this instrument which using low voltage and high elec trical current, while PCBN can’t be heated by electrifying directly, so the ke ntanium layer coating over the PCBN is heated, so the PCBN is heated and its th ermoelectric property is got by this method. [TPP129,+60mm88mm,Y,PZ#] Fig.1 Effect of cutting depth and workpiec hardness on. the cutting temperatureThe objective was to determine the influence of the workpiece hardness on change s in cutting temperature and tool wear characterize. It can be found from Fig.1 that the cutting temperature show an increasing tendency with the improvement of workpiece hardness within the cutting speed scope when the workpiece hardness i s under HRC50. And on the other hand, it is found that the cutting temperature s how the downtrend with the improvement of workpiece hardness when the workpiece hardness is over HRC50. According to experimental results, the critical hard ness when turning hardened GCr15 bearing steel with PCBN tool is about HRC50. Th e wear causes of PCBN tool have been found out through taking photos on the micr o-shape of PCBN poly-laminate initial surface as well as face and flank of wea r tool and analysis on chemical elements. It is discovered that the PCBN tools a re not suitable for cutting the workpiece at nearly critical hardness, because n ear the critical hardness, PCBN wear at the highest speed. For researching the w ear rule of PCBN tool, the tool wear experiments have been carried on by using b earing steel GCr15 at hardness HRC40 and HRC60 with changing cutting speed. The indexes of tool life equations is gained under two kinds of conditions w hich are bigger than 0.6, so the effects of cutting speed on the PCBN tool are m uch less than that of carbide tool and ceramic tool.

Laser surface hardening of AISI H13 tool steel

An attempt was made to improve the surface hardness and wear properties of AISI H13 tool steel through solid solution hardening and refinement of microstructures using a 200 W fiber laser as a heat generating source.The hardness of laser melted zone was investigated.In order to identify the effect of heat input on the laser melting zone,scanning conditions were controlled.The results show that,the hardness of as-received AISI H13 tool steel is approximately Hv 240,and the hardness after laser surface heat treatment is around Hv 480-510.The hardening depth and width are increased with the increase in the heat input applied.Application of experimental results will be considered in tooling industry.

Design and Manufacturing of Ultra-Hard Micro-Milling Tool

Based on the study of existing typical micro-milling tools and the actual demand for micro-milling tools, the P3 design principle and design flow for ultra-hard micro-milling tool were introduced to give basic guidance for the optimization of micro-milling tools. Then, according to the P3 design flow, the manufacturing process of polycrystalline diamond(PCD) micro-milling tool was proposed, and the PCD micro-milling tool with diameter of 0.5 mm was developed. Finally, the micro-milling test on the slot was carried out to study the milling performance of PCD micromilling tool.

FLOW STRESS MODEL FOR HARD MACHINING OF AISI H13 WORK TOOL STEEL

An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.

非刀具破岩理论与技术研究进展与趋势

随着我国深地战略的逐步实施,深部资源开采和地下空间建设迎来新的机遇,但也面临诸多挑战,高地应力、高地温和坚硬岩体等极端地质条件层出不穷。岩石破碎技术是所有资源开采和地下空间建设的主要工程活动,是决定施工工艺和工程效率的主要因素。在极端地质条件下,以刀具为基础的岩石破碎技术由于刀具磨损快、岩石破碎效率低,已成为遏制深地战略顺利实施的关键技术瓶颈,为解决深地岩石高效破碎难题,保障深地战略的顺利实施,迫切需求革命性的岩石破碎技术。无刀具破岩技术作为刀具破岩技术的重要补充,是突破刀具破岩技术瓶颈的可行性思路。为此,将无刀具破岩技术归纳为冲击破岩、热应力破岩和冲蚀磨损破岩3类技术体系,系统分析了水射流、激光和磨料空气射流等16种岩石破碎技术,总结了每种技术的发展历史和技术原理,分析了其破岩优势和技术瓶颈。得出,目前非刀具破岩技术没有在资源开采和地下空间建设中广泛应用的主要原因为破岩能耗高、适用较差和技术装备复杂等。相比刀具破岩,非刀具破岩技术破岩能量利用率较低,水射流破岩比能耗为刀具的40~70倍。微波、激光和等离子体等技术对施工环境要求较高,无法适用于钻井、隧道掘进等受限和恶劣环境。为解决极端地质条件岩石破碎难题,提出多种非刀具破岩技术协同破岩的思路,充分发挥每一种非刀具破岩的技术优势,构建了以射流切缝卸除高地应力、粒子冲击体积破碎坚硬岩体的破岩理念,最大限度降低岩石破碎能耗,简化系统装备,为岩石破碎技术向非刀具化发展提供理论支撑。

不同阴极运动状态下镍-金刚石刀具性能研究

利用复合电沉积技术制备了超薄镍-金刚石刀具。利用扫描电子显微镜(SEM)、能谱分析(EDS)对刀具的成分及微观组织结构进行了表征。探究了不同阴极运动状态对刀具微观结构、硬度、耐磨性及金刚石微粒均匀性的影响。首次采用阴极自旋转方式制备镍-金刚石刀具。结果表明:阴极旋转所制备的刀具要优于阴极不旋转所制备的刀具。

铝合金硬质阳极氧化关键工艺中的有限元分析

[目的]结构复杂的2A11铝合金零件在整体硬质阳极氧化时易出现烧损、膜层均匀性较差等问题。[方法]基于AnodizingManager阳极氧化仿真技术,采用有限元分析方法对典型工艺方案进行仿真计算,并基于仿真结果开展优化试验方案设计。[结果]经试验验证,通过构建新型遮蔽物与导电点,可以改善硬质阳极氧化零件表面氧化膜厚度的均匀性,提高产品合格率。[结论]对于复杂结构的铝合金硬质阳极氧化,数值模拟技术是完全可行的,其应用彻底改变了传统工艺优化的“经验设计——现场试制——纠错”研发模式,可节省大量的时间与成本。

全断面硬岩地层盾构刀具使用寿命延长研究

针对长距离全断面硬岩地层掘进工况下,盾构刀具易发生磨损失效,缩短刀具工作寿命的问题,结合穗莞深城际铁路机场站-固戍工作区间,分析9 m级泥水盾构机掘进过程中,刀具磨损的基本规律以及磨损失效的原因。为延长盾构刀具的使用寿命,基于硬岩地层下刀具磨损的基本规律,从刀具更换标准、刀具防松装置、刀具零部件替换以及刀具耐磨工艺等多方面加以改进,提出一系列减少刀具磨损的有效措施。

高速钢大圆刀的热处理

高速钢大圆刀外径为200~420 mm、内径为145~254 mm、厚度为5~10 mm,不仅精度要求高,硬度要求高达62.5~64 HRC,大多采用盐浴炉淬火、回火。安徽嘉龙锋钢公司对外径为310 mm、内径为190 mm、厚5 mm的W6Mo5Cr4V2钢刀具在锻后退火和去应力退火后,在保护气氛炉中加热至1175~1185℃奥氏体化和氮气冷却,随后在台车式炉中540~550℃×3 h回火3次。结果表明:大圆刀的精度和硬度均符合要求。

硬岩地层盾构掘进滚刀磨损机制与预测方法研究

硬岩地层采用盾构法全断面掘进时,常出现刀具严重磨损、偏磨、刀箱破裂、崩刃等工程问题,导致工期延长、增加维护成本。因此,探索刀具磨损机制和科学控制,对于保证连续长距离的安全施工具有重要意义。通过分析刀具在岩层中掘进的磨损情况,基于磨损摩擦学的原理,提出刀具磨损包括疲劳磨损、磨粒磨损及粘着磨损三机制共同作用的原理。以徐州市某地铁线路盾构区间段工程数据为样本,对比分析了采用本方法得到的刀具磨损值、长短时记忆算法(LSTM)的机器学习预测值,以及实际磨损值的对应关系,提出了减小刀具磨损和延长刀箱寿命的施工控制措施。结果表明,本方法与传统方法相比,极大地提升了刀具磨损预测的精度,减小开仓时间,提升了掘进效率。

2023年探矿工程十大新闻

1我国第一口万米深地科探井开钻2023年5月30日,我国第一口万米科探井——深地塔科1井在新疆塔里木盆地开钻。这标志着我国向地球深部探测技术系列取得新的重大突破,钻探能力开启“万米时代”,将为我国未来的科学研究和油气资源开发提供重要的基础和支持。

大扭矩螺杆钻具定子用橡胶材料的研究

从生胶、硫化体系、补强体系和特种功能助剂等着手,通过拉伸性能表征和耐磨性能、弹性模量及门尼粘度等实验比对,制备了大扭矩螺杆钻具用橡胶材料。结果表明,所获橡胶材料Shore A硬度为88,弹性模量在19 MPa以上,比常规产品提高1倍,而且加工性能优良,综合性能佳;通过对成品样机进行台架试验,表明采用该橡胶的螺杆钻具整机效率可提高20%,满足大扭矩螺杆钻具目标要求。

硬料螺纹孔铣削加工技术研究

Cr12MoV材料经热处理后硬度达到56~62 HRC,切削性能差,切削难度大,以热处理后Cr12MoV材料的模具零件螺纹孔为例,传统的加工方式一般采用电火花机床进行螺纹孔加工,加工效率低,为提高加工效率采用铣刀铣削加工。经加工测试,得出铣削加工硬料螺纹孔提升了加工效率,降低了加工成本,在加工过程中更加安全环保。

Effects of Cutting Parameters on Tool Insert Wear in End Milling of Titanium Alloy Ti6A14V

Titanium alloy is a kind of typical hard-to-cut material due to its low thermal conductivity and high strength at elevated temperatures, this contributes to the fast tool wear in the milling of titanium alloys. The influence of cutting conditions on tool wear has been focused on the turning process, and their influence on tool wear in milling process as well as the influence of tool wear on cutting force coefficients has not been investigated comprehensively. To fully understand the tool wear behavior in milling process with inserts, the influence of cutting parameters on tool wear in the milling of titanium alloys Ti6A14V by using indexable cutters is investigated. The tool wear rate and trends under different feed per tooth, cutting speed, axial depth of cut and radial depth of cut are analyzed. The results show that the feed rate per tooth and the radial depth of cut have a large influence on tool wear in milling Ti6A14V with coated insert. To reduce tool wear, cutting parameters for coated inserts under experimental cutting conditions are set as： feed rate per tooth less than 0.07 mm, radial depth of cut less than 1.0 mm, and cutting speed sets between 60 and 150 m/min. Investigation on the relationship between tool wear and cutting force coefficients shows that tangential edge constant increases with tool wear and cutter edge chipping can lead to a great variety of tangential cutting force coefficient. The proposed research provides the basic data for evaluating the machinability of milling Ti6A14V alloy with coated inserts, and the recommend cutting parameters can be immediately applied in practical production.

全断面硬岩地层土压/TBM双模盾构滚刀性能评价

为了提高土压(EPB)/隧道掘进机(tunnel boring machine,TBM)双模盾构掘进效率,减少滚刀磨损,以深大城际铁路机场东站—黄麻布站区间为依托,以该隧道左线里程ZDK8+583.0~ZDK8+359.8全断面硬岩掘进段为研究对象,对区间所采用的EPB/TBM双模盾构滚刀性能展开研究。首先,根据滚刀功能和类型的不同,对该区段的滚刀更换情况以及磨损状况进行统计分析,并获得最优性能的滚刀;然后,为更好地指导开仓换刀,以最优性能滚刀为例对滚刀使用寿命进行评估;最后,根据现场实际情况建立刀具信息管理系统。研究结果表明:中铁装备宽刀更适合该类地层的掘进,所搭建的刀具管理系统能很好地实现刀具信息化管理,确保现场施工更经济、高效。

Experimental Study on Wear Characteristics of PCBN Tool with Variable Chamfered Edge

Owing to heavy dynamic and thermal loads, PCBN tools are seriously worn during hard cutting, which largely constrains the improvement of their machining performance. Therein, the chamfered structure of a cutting edge has a notable influence on the tool wear. Thus, a comparative study was carried out on the wear morphology and wear mechanism of PCBN tools with either a variable chamfered edge or an invariable chamfered edge. The results indicate that, for a PCBN tool with a variable chamfered edge, the rake wear area is far from the cutting edge and slowly extends toward it. A shallow large-area crater wear occurs on the rake face, and the flank wear area has a long triangular shape with a smaller wear area and width, and the cutting edge remains in a good state during the cutting process. In contrast, for a PCBN tool with an invariable chamfered edge, a deep small-area crater appears on the rake face, and the wear area is close to the cutting edge and quickly extends toward it. Thus, it is easy for chips to accumulate in the crater, resulting in large-area and high-speed wear on the flank face. In addition, the tool shows a weak wear resistance. In the initial wear stage, the rake wear mechanism of the two cutting tools is a mixture of abrasive, oxidation, and other types of wear, whereas their flank wear mechanism is dominated by abrasive wear. With an aggravation of the tool wear, the oxidation and diffusion wear mechanism are both increasingly strengthened. The rake wear of the cutter with a variable chamfered edge showed an obvious increase in the oxidation and diffusion wear, as did the flank wear of the cutter with an invariable chamfered edge. This study revealed the wear mechanism of the PCBN tool with a variable chamfered edge and provided theoretical and technological support for its popularization and application in the machining of high-hardness materials.