Toroidal grinding method for curved cutting edge twist drills

In this paper, a new grinding procedure for the curved cutting edge twist drills is presented, i.e., the toroidal grinding procedure. Within this procedure, the clearance surface of the twist drill is a cylindrical helicoid surface with a constant pitch. Based on the principle of distance minimization and envelope theory, a numerical method of calculating the grinding wheel profile is developed. This grinding method allows the profile of the main cutting edge to be continuous and obtained directly during the grinding procedure. The feasibility of the toroidal grinding method is verified by drill grinding experiment and drilling measurements.     

Drilling thick fabric woven CFRP laminates with double point angle drills

Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates.     

New type drill with three major cutting edges

Drilling performance of a new type twist is described. The new type drill has three major cutting edges, three chisel edges and three flutes. This drill is an efficient means of making a hole with high accuracy and no reaming. Recently, some research on drill materials including surface coating, drill point geometry, cutting forces and tool life have been carried out in order to increase the cutting performance of drills. All the drills used in these experiments were ordinary drills with two major cutting edges. The authors calculated the point geometry of the new type drill, and also examined the cutting characteristics of the drill with respect to cutting forces, hole accuracy and tool vibration. The experimental results showed that the whirling vibration which frequently occurs in an ordinary drill with two major cutting edges disappears when the new type drill is used, and thereby rifling marks do not results on the hole surface. Consequently, a hole with high roundness and straightness is obtained.     

An investigation of the cutting fluid flow in self-piloting drills

The conditions of the coolant flow through the inlet annular channels, machining zone and outlet channels of self-piloting drills were investigated. Experiments were performed on B.T.A. and Ejector drills to determine the influence of the drill design parameters on the flow parameters. The influence of the inlet channel's clearance and eccentricity on the pressure distribution and energy loss was analytically examined. Experimental investigations of the static and dynamic pressure distribution of the cutting fluid in the machining zone were performed with different drill heads. Conditions for reliable chip removal from the machining zone and the boring bar were defined. The results obtained constitute a reference for designers of self-piloting drills and drilling processes.     

多切削刃金刚石颗粒烧结试验研究

为提高金刚石工具的锋利度和加工效率,延长其使用寿命,采用低温烧结的方法对金刚石颗粒表面进行多刃化处理。使用扫描电镜照片和质量损失率对不同烧结工艺的金刚石颗粒多刃化效果进行表征,并进行了碳化硅晶片研磨试验。结果表明:金刚石颗粒多刃化处理的最佳烧结工艺为:烧结温度750 ℃,烧结时间480 min,期间通10 kPa氧气2次,每次通气2 min,通气间隔2 h。在此条件下可获得大小适中,凹坑分布均匀的多刃化金刚石颗粒表面。碳化硅晶片研磨试验证明:多刃化金刚石颗粒与常规金刚石颗粒相比,材料去除率可提高1.1倍,研磨后晶片表面粗糙度R_a约为常规金刚石颗粒的24%,多刃化处理可显著提高金刚石颗粒研磨碳化硅晶片的抛光效率和精度。      

Influence of pretreatment and deposition parameters on the properties and cutting performance of NCD coated PCB micro drills

Nowadays, a broad growing market of printed circuit board (PCB) micro drills has been developed. In this study, nano- crystalline diamond (NCD) coated printed circuit broad (PCB) micro drills are fabricated by the hot filament chemical vapor deposition (HFCVD) technique. The main factors affecting their cutting performance are generally their breaking strength, film-substrate adhesion, continuity and smoothness of coatings, and coating thickness. Consequently, the corresponding pretreatment and deposition parameters including pretreatment zone, pretreatment time in Murakami's reagent, substrate temperature during the deposition process, as well as the deposition time are optimized. A novel pretreatment zone, only involving cutting zone of micro drill, is proposed by cantilever flexural tests. Then, the substrate temperature is optimized to be about 850 °C by temperature simulation and its verification tests. Furthermore, the pretreatment time in Murakami's reagent and the deposition time are determined to be 10 min and 2 h by high speed dry drilling of copper clad laminates (CCLs).     

Identification of the specific cutting force for geometrically defined cutting edges and varying cutting conditions

Cutting force modeling is a major discipline in the research of cutting processes. The exact prediction of cutting forces is crucial for process characterization and optimization. Semi-empirical and mechanistic force models have been established, but the identification of the specific cutting force for a pair of tool and workpiece material is still challenging. Existing approaches are depending on geometrical idealizations and on an extensive calibration process, which make practical and industrial application difficult. For nonstandard tools and five axis kinematics there does not exist a reasonable solution for the identification problem.In this paper a co-operative force model for the identification of the specific cutting forces and prediction of integral forces is presented. The model is coupled bidirectionally with a multi-dexel based material removal model that provides geometrical contact zone information. The nonlinear specific forces are modeled as polynomials of uncut chip thickness. The presented force model is not subjected to principal restrictions on tool shape or kinematics, the specific force and phase shift are identified with help of least square minimization. The benefit of this technique is that no special calibration experiments are needed anymore, which qualifies the method to determine the specific forces simultaneously during the machining process. In this paper, experiments with different cutting conditions are analyzed and systematically rated. Finally, the method is validated by experiments using different cutting conditions.     

Turning of stainless steel with worn tools having chamfered main cutting edges

A force model is proposed in this study for a single-point tool with a chamfered main cutting edge incorporating a wear factor. The variations of shear plane areas occurring in the tool-worn situation are also used. Cutting experiments are conducted on stainless steel bars and the experimental data correlated closely with the theoretical values. A preliminary discussion is also made of the design of special tool holders and their geometrical configurations. The tool holders were milled using medium carbon-steel bars and these holders with the mounting tips were ground to fit various specifications.     

The preparation of cutting edges using a marking laser

During the machining process, high mechanical and thermal loads occur at the cutting edge. Such loads can cause tool failure. Specifically non-uniform and sharp cutting edges that have a low cutting edge stability lead to such failures. In order to enhance the tool performance, the cutting edges are prepared by manufacturing both a pre-defined cutting edge geometry, and an appropriate cutting edge roughness. This paper describes the use of a low-cost marking laser for the preparation of cutting edges as an alternative to conventional preparation techniques, such as brushing or blasting. Cutting edge radii of 9?C47 ??m can be prepared with a machining accuracy of 1.5 ??m. The maximum preparation time for an individual cutting edge is approximately 10 s. Uncoated indexable inserts manufactured in this way were tested in a face milling operation. The results of these investigations (using prepared cutting edges) show both an increase in tool life and an improved surface roughness of the machined workpieces compared to those using non-prepared cutting edges.     

Electro-spark coatings for enhanced performance of twist drills

Surface engineering approaches are being increasingly employed for enhancing the effective life of twist drills with a view to reduce machining costs. The electro-spark coating (ESC) technique provides a promising means of depositing wear resistant coatings that can potentially enhance the performance of these tools. However, it is often necessary to also optimize the machining conditions for coated tools to achieve an enhanced tool life. In the present investigation, varying spindle speeds were employed at a fixed vertical feed to evaluate the performance of WC-8Co ESC coated HSS drills in comparison to bare HSS drills. The number of holes drilled before reaching a preset average flank wear (0.5 mm), or catastrophic failure of the drill, was taken as the measure of tool life. The drill flank wear, monitored at regular intervals, as well as the cutting torque and thrust measured for all holes, were considered to be the key criteria for optimizing the cutting conditions. Results indicate that the WC-8Co coated drill tool life can be increased by a factor of more than 5, depending on the machining conditions selected. Furthermore, flank wear of the drill was found to increase rapidly at the end of drill life. Cutting torque data was also found to provide a useful indicator for predicting the end of tool life.     

多机并联的厚板等离子切割电源系统研究

通过数字化均流技术并联多台等离子切割电源,增大整套系统的切割电流,提高切割能力,进行厚板等离子切割。研究了一种大功率等离子切割电源系统,采用数字化处理芯片STM32F405RGT6为核心搭建等离子切割电源控制系统,实现等离子切割电源的全数字化控制。利用数字化平均电流算法,实现电源并联的均流控制,保证单台电源输出稳定均一电流。对研制的厚板等离子切割系统进行均流测试和厚板等离子切割试验。结果表明,所设计的等离子切割电源并联切割时电源工作稳定,电流均流分布,割缝质量较好。     

Application in milling of coated tools with rounded cutting edges after the film deposition

Sharp cutting edges of coated tools are often rounded to increase their stability. In the described investigations coated cutting edges of cemented carbide inserts were variously rounded by grinding. The coating thickness distributions in the transient region between tool flank and rake were determined by an appropriate evaluation of ball cratering tests using confocal microscopy. The cutting performance of the tools was examined in milling at different cutting speeds and chip lengths, which were adjusted based on FEM calculations. The results demonstrated that even cutting edges with slightly revealed substrate can effectively withstand the cutting loads.     

Model-based path planning for laser cutting of curved trajectories

An analytical model of evaporative laser cutting over a curved beam trajectory is presented. A curved cutting path produces three main changes in the kerf profile compared with straight-line cutting: (1) an increase in the kerf width, (2) a shift of the kerf centerline position towards the center of rotation, and (3) asymmetry between the inner and outer kerf walls. Laser-cutting experiments were performed on polymethyl-methacrylate (PMMA) workpieces with energy density ranging from 100 J/mm² to 500 J/mm² in order to validate the model. Good agreement was obtained between model estimates and experimental results at low energy densities, while model estimates underestimated kerf eccentricity and asymmetry as energy density approached 500 J/mm². Curvature effects become dominant as the curvature ratio (ratio of radius of beam path curvature to beam radius) decreases below 50 for PMMA. This modeling approach can be used to plan dimensional accuracy, wall taper and material removal rate for laser processing in a number of applications, including laser blanking, sharp comer cutting, form cutting over a curved workpiece, and die board/pattern cutting.     

PCBN刀具的切削性能及其应用

文章阐述了PCBN刀具的切削性能和在实际应用中应该注意的问题,为在机械加工行业中推广应用PCBN刀具作初步的探讨.     

Design characteristics of new types of drill and evaluation of their performance drilling cast iron—II. Drills with three major cutting edges

This paper describes the performance characteristics of a new type of carbide head twist drill with four flutes, four major cutting edges, and one chisel edge. This drill shows great potential for significantly improving drilling accuracy and productivity. The drill produces holes that are as good as reamed holes. The body and point geometries and the cutting characteristics of the four-flute drill are described, along with the accuracies of hole location, angularity, size and roundness. Cutting forces, drill wear and chip morphology during cast iron drilling are also discussed. The four-flute drill deflects and vibrates much less than two-flute drills, especially in interrupted cutting cases. A patent is pending for this drill.     

Cutting performance of two-layered cutting tool tips with thin M20 and K10 sintered carbide plates compared to homogeneous tips

Two-layered cutting tool tips with thin sintered carbide plates on the rake faces are introduced as a means to significantly reduce tungsten consumption in cutting tools as a response to the sharp and manifold rise of global tungsten raw material prices. The objective of this study is investigation of factors leading to premature failure of the two-layered cutting tool tips as compared to homogeneous sintered carbide tips. Cutting tests were performed and the effects of coolant, thin sintered carbide plate material type and its thickness on stress state and fracture are discussed. It was established that the absence of coolant, as well as, higher Young's modulus and less thickness of the thin sintered carbide plate results in higher stresses on the tip's rake face, leading to its premature failure.