THE SURFACE INTEGRITY IN MACHINING HARDENED STEEL SKD11 FOR DIE AND MOLD

Milling cutters were evaluated by tool wear, cutting force and vibration. Surface integrity of grinding and milling were investigated by comparing residual stress distributions, metallurgical structure, hardened layer depth and surface roughness. And influence of cutting tool wear on surface integrity was investigated. Experimentations revealed that the preferable surface integrity would be obtained if the proper milling cutter as well as a small wear criterion were adopted to avoid the advent of tempered martensite. The research results pointed out the feasibility of taking milling as the finish machining process instead of grinding in machining hardened steel with high efficiency.     

An Investigation of the Wear Mechanisms of Polycrystalline Cubic Boron Nitride (PCBN) Tools when End Milling Hardened Steels at Low/Medium Cutting Speeds

The commercial availability of PCBN tools has created the possibility for great improvements in the area of machining hardened steels. Roughing and finishing cuts can be carried out to achieve a surface finish as good as that obtained by grinding. Through this procedure, fabrication time can be greatly reduced and quality increased. This work presents a study of the wear of PCBN and cemented carbide tools when end milling hardened steels at low/medium cutting speeds. The experiments were carried out using a 12.0 mm diameter end milling tool with an indexable insert tipped with PCBN. Removal rate was 384 mm 3 min −1 . Carbide inserts were also tested under the same cutting conditions. The tests were carried out in the dry condition. Three different hardened steels were cut and the wear mechanism was investigated using a scanning electronic microscope (SEM). The minimal wear mechanism found was a combination of adhesion and abrasion. The wear occurred predominantly on the flank face, although some indications of crater wear were also detected. The amount of wear was significantly smaller for PCBN tools than for cemented carbide tools.     

Tribological compatibility and improvement of machining productivity and surface integrity

Machining process productivity and machined part quality improvement is a considerable challenge for modern manufacturing. One way to accomplish this is through the application of PVD coatings on cutting tools. In this study the wear rate and wear behavior of end milling cutters with mono-layered TiAlCrN and nano-multilayered self-adaptive TiAlCrN/WN PVD coatings have been studied under high performance dry ball-nose end-milling conditions. The material being machined in this case is hardened H13 tool steel. The morphology of the worn surface of the cutting tool has been studied using SEM/EDX. The microstructure of the cross-section of the chips formed during cutting was analyzed as well. The surface integrity of the workpiece material was also evaluated. Surface roughness and microhardness distribution near the surface of the workpiece material was also investigated. The data presented shows that achieving a high degree of tribological compatibility within the cutting tool/workpiece system can have a big impact on tool life and surface integrity improvement during end milling of hardened tool steel.     

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.     

高速铣削淬硬钢时切削载荷平稳化研究

和传统的铣削加工相比,高速铣削淬硬钢更需要稳定的切削载荷,以尽可能减少刀具碎裂和过度磨损。本研究借助三向压电石英测力仪,使用TiAlN涂层球形端铣刀,在13500 r/min的转速下,对淬火45#钢(47HRC~48HRC)进行了高速铣削试验,建立了高速铣削下的多项式切削力试验模型,模拟了以恒定切削力为目标、优化进给率的加工实例。结果显示,稳定的切削载荷能有效地提高加工效率,避免刀具剧烈磨损。     

Design and fabrication of a new micro ball-end mill with conical flank face

Micro ball-end milling is an efficient method for the fabrication of micro lens array molds. However, it is difficult to meet the machining quality of micro dimple molds due to the wear and breakage of the milling cutter, which presents large challenges for designing geometric structure and edge strength of micro ball-end mills. In this study, a new configuration of a micro ball-end mill for micro dimple milling is designed and named the micro conical surface ball-end mill. The cutting edge is formed by intersecting the conical surface and the inclined plane. A practical grinding method is proposed based on the kinematic principle of the six-axis computer numerical control (CNC) grinding machine for micro conical surface ball-end mills and is validated by grinding simulations and experiments. Micro dimple milling experiments are conducted on the hardened die steel H13 to investigate the cutting performance of the mill. The milling force, the micro dimple roundness error, and the tool wear morphology are observed and analyzed. The results show that the radial milling force is more stable and the wear resistance is improved for the micro conical surface ball-end mill compared to the traditional micro spiral blade ball-end mill. Therefore, a more stable roundness at the entrance hole of the micro dimple can be obtained by using this design after a number of micro dimples have been milled.     

高速铣削淬硬模具钢的工艺性与经济性研究

高速加工机床及其刀具技术的最新发展使得在模具和零件制造领域实现“以切代磨”成为可能 ,用超硬刀具高速切削淬硬模具钢等难加工材料已得到越来越广泛的应用。由于模具或零件的高速切削加工可免除磨削或抛光等后续工序 ,因此精加工时如何保证工件最终表面质量同时将加工成本控制在可接受范围之内是研究人员关注的重要问题。本文在调查的基础上分析了用于高速铣削淬硬模具钢的整体硬质合金涂层立铣刀的切削性能和经济性 ,并给出了部分应用实例     

PCBN刀具的硬态切削加工机理

从PCBN刀具的物理特性、靡损特性、锯齿形切屑的形成机理、切削力和金属软化效应、已加工表面质量等方面综述了PCBN刀具切削淬硬钢的适应性,着重从刀具磨损,已加工表面白层和残余应力的形成论证了PCBN刀具在淬硬钢切削加工中的可行性。     

旋转超声磨削加工中刀具结合剂类型与加工性能的关系

实验分析了硬脆材料旋转超声磨削过程中刀具结合剂类型对加工性能的影响以便提高加工精度和加工表面的完整性.首先,采用能谱分析研究了铁基、陶瓷基和青铜基3种超声振动刀具中结合剂与金刚石颗粒的把持形式,并根据相同加工工艺条件下刀具磨损形式确定了把持力大小.然后,结合超声振动刀具特性,通过旋转超声磨削加工实验研究刀具结合剂类型与切削力、刀具磨损量、加工表面完整性的关系,并对实验结果进行了分析.实验结果表明:相对于陶瓷基和青铜基结合剂超声振动刀具,铁基结合剂超声振动刀具把持力最大,Z轴切削力平均值最小(为46.8 N);加工18 000 mm3材料后,刀具轴向磨损量最小(为0.1 mm);而陶瓷基结合剂超声振动刀具加工表面质量最好,表面粗糙度最大值为21.79 μm.结果证实铁基超声振动刀具适用于粗加工,陶瓷基超声振动刀具则适用于精加工.     

CHIP MORPHOLOGY CHARACTERIZATION AND MODELING IN MACHINING HARDENED 52100 STEELS

Hard machining is attracting more and more attention as an alternative to grinding in finish machining some hardened steels. The saw-toothed chips formed in hard machining have their own unique characteristics. The saw-toothed chip morphology is of great interest since the understanding of the saw-toothed chip morphology and its evolution in machining helps unveil hard machining chip formation mechanisms as well as facilitate hard machining implementation into industry. In this study, the effect of tool wear and cutting conditions on the saw-toothed chip morphology was examined in machining 52100 hardened 52100 bearing steel. It was found that the chip dimensional values and segmentation frequency were affected by tool wear and cutting conditions while the chip segmentation angles were approximately constant under different tool wear and cutting conditions. The shear band spacing has also been predicted at the same order of magnitude as the measurement, and improved spacing modeling accuracy is expected if the cutting process information can be better predicted first.     

CHIP MORPHOLOGY CHARACTERIZATION AND MODELING IN MACHINING HARDENED 52100 STEELS

Hard machining is attracting more and more attention as an alternative to grinding in finish machining some hardened steels. The saw-toothed chips formed in hard machining have their own unique characteristics. The saw-toothed chip morphology is of great interest since the understanding of the saw-toothed chip morphology and its evolution in machining helps unveil hard machining chip formation mechanisms as well as facilitate hard machining implementation into industry. In this study, the effect of tool wear and cutting conditions on the saw-toothed chip morphology was examined in machining 52100 hardened 52100 bearing steel. It was found that the chip dimensional values and segmentation frequency were affected by tool wear and cutting conditions while the chip segmentation angles were approximately constant under different tool wear and cutting conditions. The shear band spacing has also been predicted at the same order of magnitude as the measurement, and improved spacing modeling accuracy is expected if the cutting process information can be better predicted first.     

The performance Of DLC-coated and uncoated ultra-fine carbide tools in micromilling of Inconel 718

Coating is an important factor that affects cutting-tool performance. In particular, it directly affects surface quality and burr formation in the micro milling process. After the micromechanical machining process, surface quality is very hard to increase by a second process (grinding, etc.). In addition, in micromechanical machining, the cutting tool needs to have a good resistance to wear, owing to the fact that the cutting process is carried out at high speed. In this study, the machinability of Inconel 718 superalloy was investigated, using a Diamond Like Carbon (DLC) coated tool. The experimental tests were carried out in dry cutting conditions for different feed rates and depth of cuts. It was found that the dominant wear mechanism for all cutting parameters was identified to be abrasive and diffusive wear. Besides, a significantly Built Up Edge (BUE) formation was observed in uncoated tool. The results clearly show that DLC coating significantly decreased BUE. In addition, a smaller cutting force and better surface roughness were obtained with a DLC-coated tool. In conclusion, DLC coating can be used in micro milling of Inconel 718. It reduces the BUE and burr formation, improves surface roughness.     

A productive and cost-effective CBN hard milling-based fabrication method of hardened sliding guideways made of refined cast iron

Sliding guideways have received renewed interest in recent years as machine tool linear motion guides, due to a demand for machine tools to have good dynamic performance, which is of vital importance when machining difficult-to-cut materials. While the traditional fabrication approach of the sliding surface is grinding, this paper investigated the possibility of an alternative cubic boron nitride (CBN) milling-based manufacturing approach while utilizing Al and Mg additives in the cast iron material for better machinability and productivity. Machining results have shown a dramatic improvement in machinability especially in terms of tool wear at certain cutting conditions with the refined hardened cast iron and a CBN tool. It was found by the post experimental analysis that oxide films of the Al and Mg additives were generated at the cutting edge of the CBN tool to protect the tool from wear. Because of suppression of tool wear, a very constant surface roughness can also be achieved. A case study has also demonstrated the effectiveness of the CBN milling-based manufacturing approach with the refined cast iron and the found high-speed cutting conditions.     

A study on cubic boron nitride (CBN) milling of hardened cast iron for productive and quality manufacturing of machine tool structural components

To improve efficiency and cost performance of cast iron machine tool component fabrication, an alternative process must be developed in order to replace the grinding process, which often causes a bottleneck in production. As an alternative manufacturing approach, this research applies cubic boron nitride (CBN) hard milling operations to eliminate the grinding process in order to improve the overall manufacturing process. A variety of hardened cast iron materials with Al and Mg additives and CBN tool types were prepared and tested based on a design of experimentation (DOE) to observe their effect on surface quality and tool life. Al and Mg were added to raw cast iron to achieve generation of oxide layers at the cutting edge during milling to protect the tool from wear. By executing the DOE, the optimal cutting conditions for achieving the best surface quality were introduced. Also, additional machinability tests were conducted with the optimal conditions in order to evaluate tool wear characteristics and surface quality of the machined workpieces. Based on the observation of the used tool by electron probe micro-analyzer (EPMA), a protective oxide layer of additives was observed at the cutting edge. Hardened cast iron with Al and Mg additives is found to show preferable wear and surface quality characteristics.     

Surface grinding of carbon fiber reinforced plastic (CFRP) with an internal coolant supplied through grinding wheel

Carbon fiber reinforced plastic (CFRP) is widely used in the aerospace industry due to its high specific strength and elastic modulus. When cutting CFRP with tools such as an endmill, problems such as severe tool wear, delamination, and burrs in the CFRP can arise. Grinding, on the other hand, is supposed to improve the quality of the machined surface and tool life, according to its machining property. However, the amount of heat generated during grinding is still a considerable problem in that it is significantly higher than the temperature with conventional cutting. In order to achieve the high performance machining of CFRP, this study aims to show the effect of supplying an internal coolant through the grinding wheel on the surface of the CFRP. Face grinding of CFRP using a cup-type grinding wheel was conducted. Vitrified aluminum oxide grinding wheel was used. Three different coolant supply systems were tested: dry grinding, coolant supply using an external nozzle, and coolant supplied internally through the grinding wheel. The results showed that matrix resin loading on grinding wheel was significantly reduced by the internal coolant supply. Hence, the grains of the grinding wheel were able to cut the fibers sharply, without delamination or burr formation on the ground surface, and surface roughness was reduced compared to the machined surface with endmill. The internal coolant supplied through the grinding wheel showed greater cooling ability, and markedly reduced grinding temperature, keeping it lower than the glass-transition temperature of the matrix epoxy resin of CFRP. Because the coolant was supplied to the grinding point directly through pores in the grinding wheel, chips were eliminated from the pores, and coolant supply was sufficient to cool the ground surface.     

高速铣合金铸铁实验结果的稳健设计优化分析

针对高速切削新型合金铸铁类难加工材料时,因刀具磨损严重而导致刀具成本高的问题,采用成本较低的硬质合金刀具对Cr15Mo工件进行了铣削实验,研究了切削参数对切削力和表面粗糙度的影响,获得了可达到磨削加工效果（Ra=0.4 μm）的最佳参数组合,即切削速度vc=800 m/min,轴向切削深度ap=0.4 mm和进给量f=0.6 mm/r。基于稳健设计优化原理对实验结果进行了理论分析,研究结果表明：理论分析结果与实验结果具有很好的一致性,为同时实现高速、高质量和低成本加工的多目标参数优化方法提供了一种有效的途径。     

曲面铣削过程加工路径对切削力和磨损的影响研究

针对不同走刀路径下的复杂曲面加工过程进行球头铣刀铣削Cr12MoV加工复杂曲面研究,分析不同走刀路径下铣削力和刀具磨损的变化趋势。试验结果表明:通过对比分析直线铣削和曲面铣削过程中的最大未变形切屑厚度,可以得出单周期内曲面铣削的力大于直线铣削过程的力,铣削相同铣削层时环形走刀测得的切削力普遍大于往复走刀测得的切削力;以最小刀具磨损为优化目标,运用方差分析法分析得出不同走刀路径的影响刀具磨损的主次因素,同时利用残差分析方法建立球头铣刀加工复杂曲面刀具磨损预测模型,并通过试验进行验证。     

Implications of the reduction of cutting fluid in drilling AISI P20 steel with carbide tools

The machining of hardened steel is becoming increasingly important in manufacturing processes. Machined parts made with hardened steel are often subjected to high service demands, which require great resistance and quality. The machining of this material submits the tools to high mechanical and thermal loads, which increases the tool wear and affects the surface integrity of the part. In that context, this work presents a study of drilling of AISI P20 steel with carbide tools, analyzing the effects on the process caused by the reduction of cutting fluid supply and its relation with the tool wear and the surface integrity of the piece. The major problem observed in the tests was a difficulty for chips to flow through the drill flute, compromising their expulsion from the hole. After a careful analysis, a different machining strategy was adopted to solve the problem.     

Prediction of cutting force, tool wear and surface roughness of Al6061/SiC composite for end milling operations using RSM

The results of mathematical modeling and the experimental investigation on the machinability of aluminium (Al6061) silicon carbide particulate (SiCp) metal matrix composite (MMC) during end milling process is analyzed. The machining was difficult to cut the material because of its hardness and wear resistance due to its abrasive nature of reinforcement element. The influence of machining parameters such as spindle speed, feed rate, depth of cut and nose radius on the cutting force has been investigated. The influence of the length of machining on the tool wear and the machining parameters on the surface finish criteria have been determined through the response surface methodology (RSM) prediction model. The prediction model is also used to determine the combined effect of machining parameters on the cutting force, tool wear and surface roughness. The results of the model were compared with the experimental results and found to be good agreement with them. The results of prediction model help in the selection of process parameters to reduce the cutting force, tool wear and surface roughness, which ensures quality of milling processes.     

Some studies on hard turning of AISI 4340 steel using multilayer coated carbide tool

Hard turning with multilayer coated carbide tool has several benefits over grinding process such as, reduction of processing costs, increased productivities and improved material properties. The objective was to establish a correlation between cutting parameters such as cutting speed, feed rate and depth of cut with machining force, power, specific cutting force, tool wear and surface roughness on work piece. In the present study, performance of multilayer hard coatings (TiC/TiCN/Al₂O₃) on cemented carbide substrate using chemical vapor deposition (CVD) for machining of hardened AISI 4340 steel was evaluated. An attempt has been made to analyze the effects of process parameters on machinability aspects using Taguchi technique. Response surface plots are generated for the study of interaction effects of cutting conditions on machinability factors. The correlations were established by multiple linear regression models. The linear regression models were validated using confirmation tests. The analysis of the result revealed that, the optimal combination of low feed rate and low depth of cut with high cutting speed is beneficial for reducing machining force. Higher values of feed rates are necessary to minimize the specific cutting force. The machining power and cutting tool wear increases almost linearly with increase in cutting speed and feed rate. The combination of low feed rate and high cutting speed is necessary for minimizing the surface roughness. Abrasion was the principle wear mechanism observed at all the cutting conditions.