Experimental studies of step drills and establishment of empirical equations for the drilling process

Various sizes of step drills were manufactured by a CNC grinder machine and used in the drilling process with different speeds and feed rates to produce single step holes in S1214 free machining steel. The performance of step drills was compared with that of conventional twist drills in the drilling of the free machining steel for the same task. The influences of drill size, feed rate and cutting speed on the performance of step drills were studied. Experimental results show that for better cutting performance, the small diameter should not be less than 60% of the large diameter. Also, most of the changes in the characteristics of the thrust force were influenced by the smaller drill of the step drill. On the other hand, the small diameter part of the step drill only contributed about 30% of the torque. From the experimental results, empirical equations for drilling thrust force and torque have been established for step drills.     

蓝宝石套料用金刚石钻头关键制备技术研究

蓝宝石套料用金刚石钻头不同于常规的工程钻头,要求钻头锋利度好、寿命长、径跳小,还要求蓝宝石晶棒表面加工质量好,因此对金刚石钻头的制备、检验等方面提出了很高的要求。对金刚石钻头的刀头、钻管、配方设计,以及成品钻头需重点检验的指标等进行了分析,并就刀头制备、钻头焊接和后续处理等关键技术进行了阐述。研制了4英寸（内径?103 mm）金刚石钻头用于钻进蓝宝石晶体,效率比相同规格台湾某公司钻头提高12%,寿命大约是台湾某公司钻头的95%,蓝宝石晶棒次品率低于0.5%,可满足客户的使用要求。      

Φ127mm×9.19mm IEU S-135钻杆腐蚀失效分析

对发生管体刺穿、外壁腐蚀的Φ127mm×9.19mm IEU S-135钻杆进行了失效分析。结果表明,钻杆的化学成分、金相组织、机械性能均符合API标准及订货技术条件。钻杆管体刺穿是由于内壁发生严重H_2S腐蚀+氧腐蚀造成的。钻杆管体外壁腐蚀是由氧腐蚀引起的。     

和田青玉超声波深孔高速钢麻花钻钻削试验研究

基于和田玉特殊的物理性能,采用直径为2、1.5、1 mm的高速钢麻花钻,在其主轴转速为700、1500、1800r/min;进给量为3μm/r和5μm/r的情况下;分别进行附加超声波振动和不附加超声波振动加工试验;在钻削加工过程刀具磨损,扩孔量、孔内表面粗糙度三个方面进行对比分析,超声振动波钻削能获得更好的加工质量和效率,并能减少钻头的磨损和破坏,为和田玉精密加工提供了一种新的深孔加工工艺方法。     

煤矿井下随钻测量定向钻进用PDC钻头的研制

煤矿井下随钻测量定向钻进需要设计高品质的PDC钻头。本论文从PDC钻头的结构参数到PDC切削齿的选型均进行了较深入的分析研究;同时研制了96 mm胎体式定向钻进用PDC钻头,并进行了现场试验,共钻进1个主孔和4个分支孔,平均钻进时效为4.12 m/h,累计进尺达1 001.6 m。试验结果表明,该钻头造斜效果好,使用寿命长,完全能满足使用要求。     

Automation of centered micro hole drilling using a magnetically levitated table

This paper presents the automation of centered micro hole drilling, using a magnetically levitated table. Centered micro hole drilling, an example of which is nozzle outlet hole drilling, has previously been performed manually by skilled craftsmen. If a micro hole is drilled when the center line of the drill and the center line of the guide hole are not aligned, the misalignment may cause drill breakage. By using a magnetically levitated table, a workpiece can be aligned frictionlessly. When the horizontal support stiffness of the table is set small, by lowering the drill slowly, centering can be performed due to the contact force between the drill tip and the conical surface of the nozzle. Spinning nozzles were used as experimental workpieces, and 0.1–0.5 mm diameter drills were used.     

关于0.38mm气动加速叶轮五轴联动加工技术的讨论

主要讨论了0.38mm气动加速叶轮的五轴联动加工技术。由于该叶轮叶片厚度仅为0.38mm，因此在加工工艺上，打破传统模式，采用高速铣，小直径刀具等方式。建立起一套较特殊的加工工艺。     

Generalized groove-type chip breaker effects on drilling for different drill diameters and flute shapes

This paper proposes a generalized formulation to place chip-breaker grooves on drills of varying diameters. To verify the effectiveness of this generalization the groove is placed on the drill rake face of 6.35 and 3.18 mm diameter drills of standard and parabolic flute shapes using a fabrication process utilizing electro-discharge machining (EDM). The results indicate that chip size is reduced. The robustness of the placement of the groove is assessed with experiments validating effective distance from the cutting lip and groove depth thereby facilitating drill regrinding. Experiments are also conducted to study chip clogging when the chip-breaker groove is employed on small drill diameters.     

Tool life and machinability models for drilling steels

Four models for drilling steels are developed from an extensive machinability experiment. General purpose HSS drills were used for drilling 0.12% carbon steel. Predictive models were developed for tool life, thrust and torque on the drill, and surface roughness of the holes drilled. The research consisted of a laboratory experiment involving four independent variables; cutting speed ranging from 162 to 330 mm/s (32 to 65 sfpm), feed ranging from 0.0635 to 0.381 mm/rev (0.0025 to 0.015 ipr), drill diameter ranging from 7.54 to 14.68 mm (0.2969 to 0.5781 in.), and steel hardness ranging from 146 to 330 BHN. The experiment was designed as a central composite design with 30 treatment combinations. Tool life varied from 3.98 to 265.5 min. Full second-order models, containing 15 terms, were simplified to reduced models. Model fits ranged from an R-square of about 0.68 to about 0.92.     

Significantly enhanced drilling ability of the orthopedic drill made of Zr-based bulk metallic glass composite

Zr-based bulk metallic glass composite (BMGC) presents superior unique properties, including high hardness, high fracture strength, high toughness, large elastic limit, excellent corrosion resistance, and was believed as a promising material for medical-tool applications. In this study, the 4 mm diameter rods of ZrCuAlAgSi-based (Zr-based) BMGC containing ex-situ Ta particles were successfully fabricated by two-step arc melting and suction casting method. These Zr-based BMGC rods was ascertained their amorphous nature by X-ray diffraction and differential scanning calorimetry analyses, and then machined into the orthopedic drill bits with 2 mm in diameter. The drilling tests of the commercial and Zr-based BMGC orthopedic drill bits were conducted by a specially designed indentation-drilling rig. The data of thrust force as a function of drilling distance between drill and porcine bone was recorded and analyzed to evaluate the drilling ability of the Zr-based BMGC made and commercial orthopedic drills, respectively. As a result, the Zr-based BMGC made drill presents 73% reduced thrust force than the commercial one, this indicates that the Zr-based BMGC made drill has less friction force and performs much better drilling ability.     

Accuracy estimation of drilled holes with small diameter and influence of drill parameter on the machining accuracy when drilling in mild steel sheet

The miniaturization of component parts has advanced in the modern industrial product sector. Corresponding with this new wave, there is a strong demand for the establishment of minute-scale techniques to manufacture products with high quality involving the drilling of small holes. Non-traditional machining techniques such as electro discharge machining can be applied to make small holes. However, there is much practical value if small holes can be made by the traditional drilling process. In this paper, a method for estimating the drilled hole accuracy using a Fourier series analysis is proposed and this method is applied to small holes 1 mm in diameter drilled in mild steel for machine structure use. As a result, it is clarified that the bending rigidity of drill and the thinning of the drill point exert a large influence on the drilled hole accuracy.     

Small-hole drilling in engineering plastics sheet and its accuracy estimation

In recent manufacturing processes, the small diameter hole drilling process is frequently used owing to its good characteristics. The drilling process can easily be adapted to wide variations in lot size, processing accuracy, processing spot patterns where holes are made, and so on. Many machine elements, which have small diameter holes, are manufactured using engineering plastics of superior material and machining properties. However, it is not easy to drill holes with a diameter smaller than 1 mm, in recent machining technology as well. In this report, 1-mm diameter holes are drilled on two engineering plastics sheets and their drilling accuracy is discussed.     

Performance evaluation of endrills

This paper evaluates the performance of a relatively new type of drill called an endrill which is a cross between a drill and an endmill. Investigations into the effects of its cutting conditions on the drilling forces, surface finish, drill wear and hole oversize were carried out. It was found that endrills produced better quality holes than conventional twist drills, better surface finish and less oversize of the holes. Hence, with proper feed, speed and flow rate of the pressurized flushing coolant, a good finish of about R_a = 1 μm can be attained without reaming. Thus, the productivity of finished holes can be remarkably improved. Compared to twist drills, lower torque and thrust were observed which yielded improved tool life and reduced power consumption. No “walking phenomenon” was observed when this kind of drill was used and the amount of hole oversize was found to average about 0.7% of the drill diameter as compared to 1.6% when twist drills were used. Finally, general equations for the drill torque and thrust were derived from the experimental results.     

Analysis of stresses in micro-drills using the finite element method

The trend towards higher density printed circuit boards requires smaller holes down to 0.1 mm diameter to be drilled through the board layers. Drills of this size are inherently more susceptible to drill breakage and must be used with restricted operating parameters. In order to analyse the stresses occurring in microdrills, finite element methods are used. Three-dimensional models of drills are defined by setting node points of the drill geometry. Measured forces from experimental tests are used to determine drill loading. Principal stress isograms on drill cross-sections are presented for different drill geometries and correlation with actual drill life is made.     

小冲孔能量法评价Q345R的屈服强度

小冲孔试验技术(SPT)是测量在役构件材料力学性能的新方法。文章介绍了基于弹性能量理论预测材料屈服强度的小冲孔能量法,并对试验原理及步骤进行了详细阐述。在验证试验重复性的基础上,对Q345R进行小冲孔能量法试验,并与常规拉伸试验、小冲孔偏移法和双斜率法的结果进行对比。结果表明,能量法测试Q345R屈服强度的误差为5.52%,远小于双斜率法和偏移法试验结果的误差。在此基础上,根据有限元模拟,结合载荷-位移(L-D)曲线与能量-位移(E-D)曲线,分析了试样厚度、压球直径、下模孔径、冲压速度以及试样边缘减薄等因素对小冲孔能量法结果的影响。得出试样厚度0.5mm、压球直径2.4mm、下模孔径4mm为最佳几何尺寸搭配。     

厚0.15mm宽幅取向硅钢的轧制

为在设计最小可轧厚度为0．20mm的森吉米尔轧机上生产厚0．15mm宽幅冷轧硅钢薄板，分析了影响最小可轧厚度的因素后，通过减小工作辊辊径、降低乳化液浓度、控制张力设定等措施，取得了成功。     

Nanocrystalline CVD diamond coatings for drilling of WC-Co parts

Drilling of pre-sintered cemented carbide parts is a challenging task due to the high hardness and abrasive nature of the WC grains. This operation is commonly done using uncoated cemented carbide drill bits but the tool life is very limited requiring tool re-sharpening after a few holes. A solution for the improvement of the tool performance is here exploited by the use of nanocrystalline diamond (NCD) films as high abrasion resistant coatings. These coatings were grown in a hot filament chemical vapor deposition (HFCVD) reactor. Filament temperatures in the range of 1940-1980 °C were crucial to obtain highly adherent and very uniform coatings at the cutting edge and on the surfaces of the flutes. The performance of the coated tools was evaluated in through-hole drilling of a pre-sintered cemented carbide showing outstanding cutting efficiency when compared to that of an uncoated tool: maximal 940 mm/min infeed rates (app. 1 s to drill 17 mm) instead of 20 mm/min for the latter; absence of tool wear in contrast to a flank wear of about 50 μm in the uncoated tool after only 4 holes; hole edge integrity even at the highest infeed rates while grain decohesion at the hole edge takes place when using bare drill bits.     

Taguchi analysis of delamination associated with various drill bits in drilling of composite material

This paper presents a prediction and evaluation of delamination factor in use of twist drill, candle stick drill and saw drill. The approach is based on Taguchi’s method and the analysis of variance (ANOVA). An ultrasonic C-Scan to examine the delamination of carbon fiber-reinforced plastic (CFRP) laminate is used in this paper. The experiments were conducted to study the delamination factor under various cutting conditions. The experimental results indicate that the feed rate and the drill diameter are recognized to make the most significant contribution to the overall performance. The objective was to establish a correlation between feed rate, spindle speed and drill diameter with the induced delamination in a CFRP laminate. The correlation was obtained by multi-variable linear regression and compared with the experimental results.     

1 580 mm半连续热轧带钢生产线轧制节奏分析

半连续式热轧带钢生产线轧制节奏影响因素众多,不同厚度规格产品节奏瓶颈区域有所不同。结合某1 580mm半连续式热轧带钢产线,分别对薄、厚规格产品轧制节奏的影响因素进行了分析,并采取梯次配置出钢信号触发点、优化设计定宽节奏和卷取减速距离等措施,使该生产线轧制节奏由月均26.0卷/h提升至月均29.8卷/h,产能得到大幅提升。     

Wear characteristics of the cemented carbide blades in drilling limestone with water jet

Drilling hard rock with water jet is considered to be an efficient way to improve the work life of the cemented carbide blade. In this paper, cemented carbide material YG-6 is used on the drill bit in limestone drilling with water jet. Wear characteristics of the cemented carbide blades in drilling limestone with water jet is studied. Experiment results showed that the water jet pressure and nozzle diameter played an important influence on the wear rates of the cemented carbide blades in the drill bits. The wear rates of YG-6 blades decreased when the jet pressure increased. But the decline speed of wear rates was not even, it declined more and more slowly when the jet pressure upon 10 MPa. It was also showed that wear rates decrease with the increase of the nozzle diameter in the drill bit, for the bigger nozzle diameter could provide more impact force which could reduce the mechanical force on the YG-6 blades. SEM photographs were taken to characterize the wear mechanism of the cemented carbide blades in limestone drilling with water jet. Surface analysis demonstrated that cemented carbide blades in limestone drilling with water jet showed circular action of brittle fracture, grain pullout and polishing, which induced material removal process.