Polycrystalline Cubic Boron Nitride Inserts Research Articles

Investigation on preparation of composite vitrified bonding ultrafine diamond grinding wheel and machining of PcBN inserts

The grinding of polycrystalline cubic boron nitride (PcBN) is hard owing to its high hardness and superior wear-resistance capacity. Machining of PcBN tools via vitrified diamond grinding wheels with a size above 10 μm may lead to brittle fracture instead of a ductile machining because of the poor toughness of cubic boron nitride. A uniformly dispersed M0.5/1.5 diamond grinding wheel with a composite vitrified bonding was fabricated to improve the surface roughness of PcBN inserts. It is demonstrated that the preparation of composite vitrified bonding with various additions of vitrified bonding produced by the melting-quenching technique (VB-MQ) has little effect on the performance of vitrified bonding, such as bending strength, CTE and phase and achieves the uniform dispersion of M0.5/1.5 diamond as the addition of VB-MQ is no greater than 50%. Both the grinding ratios and the surface roughness of PcBN inserts are enhanced.

Innovative comparison on performance of PCBN tool and uncoated tool in CNC green turning of LDX2101 duplex stainless steel to minimize surface roughness

The goal of this research is to minimize the surface roughness (SR) by comparing Polycrystalline Cubic Boron Nitride (PCBN) tool and uncoated (cemented carbide) tool during CNC turning of LDX 2101 duplex stainless steel. PCBN inserts were used as the experimental group, whereas uncoated inserts were used as the control group in this research. The selected machining factors were speed of cutting, rate of feed and cut depth. The total number of groups were two and the sample size was 27 samples for each group were used for conducting experiments. The obtained mean SR value for PCBN insert is 3.826559 µm and for uncoated insert is 4.066111 µm. The significant difference between the two inserts is 0.01 (p < 0.05). Within the confines of this research, when LDX2101 duplex stainless steel is machined with PCBN insert it gives lower SR and when the same specimen is machined with uncoated insert it gives higher SR.

Influence of cutting tool material on machinability of Inconel 718 superalloy

Appropriate selection of tool material is very important for effective machining of ‘difficult-to-cut’ aerospace superalloy Inconel 718, especially, under dry condition. Present work aims at investigating performance of physical vapor deposition (PVD) multi-layer (TiN/TiCN/TiN) coated cermet, and PVD TiAlN coated PCBN (Polycrystalline Cubic Boron Nitride) brazed tipped carbide inserts on machinability of Inconel 718. Machinability is assessed based on cutting force magnitude, maximum tool-tip temperature attained, tool wear morphology, chip macro/micro morphology, and end part surface integrity. Later includes detailed analysis on morphology of the machined surface, roughness, and depth of hardened layer. Results obtained thereof, are compared to that of conventional uncoated WC-Co tool. It is evidenced that coated cermet outperformed other two inserts in purview of lower cutting force, better surface finish, and tiny white layer. WC-Co causes extreme cutting temperature than other counterparts. Up to 86 m/min cutting velocity, PCBN tool exhibits minimal flank wear; afterwards, tool is severely affected by huge notch wear. On the contrary, cermet tool suffers from lower flank wear than WC-Co for all cutting speeds tested. Both cermet and PCBN inserts are found remarkably affected by notching, and coating dissipation. Attrition wear is evidenced only in case of WC-Co insert. Coated cermet, thus, appears as a better choice for dry turning of Inconel 718.

Minimum Quantity Lubrication through the micro-hole textured PCD and PCBN inserts in the machining of the Ti–6Al–4V alloy

A novel cutting tool development with the micro-hole textures on the flank and rake face of the cutting inserts helps in the reduction of tribological properties. The machining of Ti–6Al–4V alloy leads to some challenges during machining namely higher cutting temperature, and rapid tool wear. In this research, a comparison study has been performed with the new cutting tool inserts with surface modification such as Polycrystalline Cubic Boron Nitride (PCBN) and Polycrystalline Diamond (PCD) inserts for high-speed machining of Ti–6Al–4V alloy. The influence of the micro-hole textured insert on the machining of the Ti–6Al–4V alloy was investigated with the Minimum Quantity Lubrication (MQL) method. Compared to modified PCBN inserts, modified PCD inserts showed better results in all the performance characteristics.

Influence of the undeformed chip cross section in finishing turning of Inconel 718 with PCBN tools

Inconel 718 is a difficult-to-cut material due to its poor thermal conductivity, severe work hardening and high strength at high temperature. Machining of Inconel 718 with Polycrystalline Cubic Boron Nitride (PCBN) tools at high speed in finishing operations may lead to brittle fracture in the cutting tool because of the low toughness of PCBN inserts in comparison to other cutting materials. PCBN inserts shaped with large tip radius are commonly used to remove small values of depth of cut in order to counteract these aspects. When applying multipass turning strategies with this configuration, a significant peak may occur in the response of the machining forces at the end of the pass in the second and successive passes. This fact may also be present when turning inner profiles or into a shoulder. The increase of the undeformed chip cross section and the high specific cutting forces of Inconel 718 give rise to this peak of the machining forces. In this work, different tests involving multipass finishing turning in Inconel 718 have been carried out in order to study the magnitude of the peak forces for different cutting conditions. A PCBN tool at high cutting speed with coolant has been employed at different feed rates and depths of cut. On the other hand, an analytical study of the undeformed chip section at the end of each turning pass has been performed in order to determine its relation to the machining peak forces. The results have shown that these peaks in the machining forces are strongly related to the tool tip radius and the cutting parameters. The machining force at the end of a turning pass can increase significantly their values during a short interval. Consequently, this effect may influence tool wear progression leading to a premature breakage of the tool.

Assessment on abrasiveness of high chromium cast iron material on the wear performance of PCBN cutting tools in dry machining

Polycrystalline Cubic Boron Nitride (PCBN) has been considered as the main cutting tool material for hard turning, which has the comparable surface finish quality as grinding, and high efficiency, economical technology in production. It is well known that the abrasiveness of the workpiece have the very important role of the machinability of the materials. Therefore, the tool wear of the PCBN insert correlates with abrasiveness of the materials very much. In the presented paper, the influence of the micro hardness distribution is used to explain the wear mechanism in machining of the high abrasive materials and proposed a model to predict the abrasiveness. The work material is high chromium cast iron and cutting tool material is PCBN. Abrasiveness are evaluated from the micro hardness distribution by nanoindentation for the distinguish microstructure with hardness. The mapping image of the micro hardness showed the matched features with microstructure images from the scanning electron microscope (SEM). The different chemical composition groups are presented as three heat treatment conditions in experiments, which are as-cast, annealed and hardened. Based on the hardness distribution, this paper presented a model to evaluate the abrasiveness index of the material. The high performance machining is done on six material. The wear mechanism is abrasion in tool wear dominantly and flank wear showed the linear relationship with abrasiveness index. The abrasive wear on the cutting edge suggests that sliding and chipping are the main wear modes which is caused by the combination effect of carbides and matrix. The four mechanisms of diffusion, chemical, abrasive and micro chipping are happening in the tool wear of hard turning. In the dry machining by PCBN insert, abrasiveness is correlated with abrasive and chipping very much and accelerated the crater wear in machining. Abrasiveness index of the material has ability to predict wear performance in dry machining of HCWCI materials by PCBN inserts. The application of the abrasiveness is a potential parameter of machinability to improve the machining efficiency and reduce the cost of machining.

Experimental study of the wear behavior of PCBN inserts during cutting of GH4169 superalloys under high-pressure cooling

Serious tool wear and poor chip breaking are the major issues in cutting process of superalloys under normal-pressure cooling. Towards those issues, this paper proposed an experimental evaluation on cutting tool wear of polycrystalline cubic boron nitride (PCBN) in machining of GH4169, a nickel-based superalloys, under high-pressure cooling. The several level pressures of coolant are tested, and then the rake face and flank wear of cutting tool are studied, as well as the cutting forces and the chips. These research result shows that the high-pressure coolant can reduce the wear value VB of inserts flank and the cutting force and is advantageous to chip breaking. Therefore, the machinability of nickel-based superalloys GH4169 can be improved by the high-pressure cooling.

A Tool Holder for Clamping Cutting Inserts Used for Turning in a Metal Cutting Operation

Metalworking industry is looking for increase in productivity and maintaining costs per part. One of the most effective methods is the drastic increase of cutting speed by use of Polycrystalline Cubic Boron Nitride (PCBN). The challenge in cast iron machining with ISO/ANSI inserts are high tooling costs and insufficient stability of the insert due to form locked clamping mechanism. The paper presents Beyond shield: an innovative clamping mechanism which provides better rigidity and less movement of the insert, combining with a new designed PCBN inserts shape which results in lower grinding, lower manufacturing time and eventually lower cost. Video abstract [Display omitted]

Measurement of Transient Tool-Internal Temperature Fields During Hard Turning by Insert-Embedded Thin Film Sensors

This paper presents a novel approach for obtaining thermal data from the close vicinity (70–700 μm) of the tool-workpiece interface while machining hardened steel. Arrays of microthin film C-type thermocouples with a junction size of 5 μm × 5 μm were fabricated by standard microfabrication methods and have been successfully embedded into polycrystalline cubic boron nitride (PCBN) using a diffusion bonding technique. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were performed to examine material interactions at the bonding interface in order to determine optimal bonding parameters. Static and dynamic sensor performances have been characterized. The sensors exhibit excellent linearity up to 1300 °C, fast rise time of 150 ns, and sensitivity of ∼19 μV/ °C. The PCBN inserts instrumented with embedded thin film C-type thermocouples were successfully applied to measure internal tool temperatures as close as 70 μm to the cutting edge while machining hardened steel workpieces at industrially relevant cutting conditions. Correlations between temperature and cutting parameters have been established. The embedded microthin film sensor array provided unprecedented temporal and spatial resolution as well as high accuracy for microscale transient tool-internal temperature field measurements. Tool-internal temperature maps were generated from acquired data. In the frequency domain, obtained thermal data indicated the onset of regenerative machining chatter earlier and more effective than conventional force measurement by dynamometer.

Tool Embedded Thin Film Microsensors for Monitoring Thermal Phenomena at Tool-Workpiece Interface During Machining

Existing thermal sensors for machining processes are having difficulties to reliably provide high spatial and temporal resolutions for monitoring and control of the dynamic thermal phenomena at the tool-workpiece interface during machining. This paper presents a novel approach to obtain transient tool internal temperature data reliably from a very close distance to the tool-workpiece interface. An array of nine microthin film thermocouples, fabricated using standard microfabrication methods, has been embedded into polycrystalline cubic boron nitride (PCBN) cutting inserts by means of diffusion bonding. Scanning electron microscopy was performed to examine thin film sensor and host material interactions at the bonding interface and to determine optimal bonding parameters. The thin film microthermal sensors were statically and dynamically characterized by heating in a tube furnace and application of pulsed laser radiation. The embedded thin film thermal sensors exhibit good linearity, sensitivity, and extremely fast response time. The instrumented PCBN inserts were applied in machining of aluminum alloy 6061 disks at various cutting speeds and feed rates. Embedded into the PCBN inserts at numerous distances of 75–450 μm from tool rake face and 100–500 μm from tool flank face, these microsensors enabled the sensing of transient cutting temperature fields with high spatial and temporal resolutions. The temperature data obtained during cutting demonstrate the functionality of the tool embedded microthermal sensors and their value for fast, accurate, and reliable monitoring, which will be of significance for both fundamental study and in-process control of machining operations.

Experimental investigations while hard machining of DIEVAR tool steel (50 HRC)

This paper describes hard machining which offers many potential benefits over traditional manufacturing techniques. In this work, investigations were carried out on end milling of hardened tool steel DIEVAR (hardness 50 HRC), a newly developed tool steel material used by tool- and die-making industries. The objective of the present investigation was to study the performance characteristics of machining parameters such as cutting speed, feed, depth of cut and width of cut with due consideration to multiple responses, i.e. volume of material removed, tool wear, tool life and surface finish. Performance evaluation of physical vapour deposition-coated carbide inserts, ball end mill cutter and polycrystalline cubic boron nitride inserts (PCBN) was done for rough and finish machining on the basis of flank wear, tool life, volume of material removed, surface roughness and chip formation. It has been observed from investigations that chipping, diffusion and adhesion were active tool wear mechanisms and saw-toothed chips were formed whilst machining DIEVAR hard steel. PCBN inserts give an excellent performance in terms of tool life and surface finish in comparison with carbide-coated inserts. End milling technique using PCBN inserts could be a viable alternative to grinding in comparison to ball end mill cutter in terms of surface finish and tool life.

Online PCBN tool failure monitoring system based on acoustic emission signatures

The paper describes an online tool failure monitoring system based on acoustic emission (AE) signatures. The system was developed primarily to detect failure of polycrystalline cubic boron nitride (PCBN) inserts in milling high-chromium materials. In face milling of high-chromium materials, almost without exception, PCBN inserts fail due to fracture on the nose or rake face. The change in the root mean square of AE signals (AE /spl Delta/RMS) was found to be the best indicator of the tool failure process for the subject tool-work combination. From the experiments, the critical values of AE /spl Delta/RMS where the tool fractures, called AE /spl Delta/RMS/sub c/, were obtained. Regression analysis was performed to fit a model of.