Marcio Bacci da Silva

Some observations on wear and damages in cemented carbide tools

Cutting tools are subjected to extremely unfavorable conditions during machining operations. High cutting temperatures, compressive and shearing stresses, chemical attacks, variable cyclic thermal and mechanical loads are some adverse conditions that wear and damage these tools. Therefore, it is crucial to understand the process of tool wear and damage and how the cutting parameters affect it in order to underpin decisions regarding the most favorable conditions to address the problem. This article treats on some forms and mechanism of wear and damage that cemented carbides can undergo during machining. Special attention was given to damages caused during interrupted cutting (e.g., milling), such as fracture, chipping and thermal fatigue. Experimental details and results of the latter phenomenon, which was studied under different cutting conditions, are discussed and confronted with literature. Keywords : Cemented carbide tools, milling, tool damage, thermal fatigue

Lubrication and application method in machining

Suggests that a very low volume of lubricant is enough to improve the cutting operation because the area that requires lubrication is small. An estimate of the volume of lubricant necessary has been carried out (7.2ml h‐1) and some comments are presented about results of previous experiments using extremely low volumes of lubricant (108ml h‐1). The low volume of lubricant is applied in the same way as the conventional system. In these previous experiments the effect of lubrication is measured by surface finish, cutting force and workpiece temperature. The improvement in surface finish when low volume of lubricant is applied is similar to the results obtained with tests carried out using the conventional cutting fluid system. This improvement is not due to lubrication on the rake face to avoid built‐up edge, but action on the machined surface after it has been formed.

Burr produced on the drilling process as a function of tool wear and lubricant-coolant conditions

This work shows the resulting height and shape of the burrs produced by drilling holes with ratio L/D = 3. The tool used in the tests was the solid twist HSS drill coated with TiAlN, with diameter of 10 mm, to drill the microalloyed steel DIN 38MnS6. The height of the burr was studied under different lubricant/coolant systems, namely: dry machining, use of Minimum Quantity Lubrication (MQL) at the flow rate of 30 ml/h, and fluid applied in the conventional way (flooding). The following cutting fluids were used: vegetable oil (MQL), mineral oil (MQL and flooding) and semi-synthetic oil (flooding). The trials were carried out at two cutting speeds (45 and 60 m/min) and the criterion adopted for the end of the test was the catastrophic failure of the drill. The results showed that the height of the burr increases primarily with the wear of the tool and that this increase is almost exponential after 64% and 84% of drills life, for the speeds of 45 and 60 m/min, respectively. Furthermore, the results generally showed that the smallest burr height was obtained for the dry machining and the largest for the MQL systems.

Analyses of Effects of Cutting Parameters on Cutting Edge Temperature Using Inverse Heat Conduction Technique

During machining energy is transformed into heat due to plastic deformation of the workpiece surface and friction between tool and workpiece. High temperatures are generated in the region of the cutting edge, which have a very important influence on wear rate of the cutting tool and on tool life. This work proposes the estimation of heat flux at the chip-tool interface using inverse techniques. Factors which influence the temperature distribution at the AISI M32C high speed steel tool rake face during machining of a ABNT 12L14 steel workpiece were also investigated. The temperature distribution was predicted using finite volume elements. A transient 3D numerical code using irregular and nonstaggered mesh was developed to solve the nonlinear heat diffusion equation. To validate the software, experimental tests were made. The inverse problem was solved using the function specification method. Heat fluxes at the tool-workpiece interface were estimated using inverse problems techniques and experimental temperatures. Tests were performed to study the effect of cutting parameters on cutting edge temperature. The results were compared with those of the tool-work thermocouple technique and a fair agreement was obtained.

Performance of high-speed steel taps at high cutting speed

The main goal of this paper is the evaluation of the performance of high-speed steel taps when machining grey cast iron at high cutting speeds. It is used for two types of high-speed steel, one with addition of vanadium (HSS-E) obtained by conventional method, classified as AISI M3 and other obtained by powder metallurgy (HSS-PM), classified as AISI M7. These two tool materials are used in two coated situation: with TiN and multilayer TiN-TiNAl. The tests were carried out at two different cutting speeds, 37.5 and 75 m/min. The tool life criteria were based on dimensional tolerances of the threads, on tool wear and also on catastrophic failure of the tool. Analysis in the Scanning Electron Microscope (SEM) and optical microscope were done to determine the type and mechanisms of wear. The results showed that the effect of the cutting speed depends on the coating. The best performance was achieved with the multilayer coating TiN-TiNAl.

Influence of tellurium addition on drilling of microalloyed steel (DIN 38MnS6)

Purpose – This paper seeks to evaluate the influence of tellurium content on the machinability of the microalloyed pearlitic steel (DIN 38MnS6). Two grades of steels were used, one with high (27 times greater) tellurium content and one with a low tellurium content. Machinability of the steel was determined by the number of holes drilled by the tool before undergoing severe deformation. The drilling test matrix was prepared using a fractional factorial design with five input variables studied at two levels (25‐1). Other variables investigated include cutting speed (45 and 60 m/min), feed rate (0.15 and 0.25 mm/rev), geometry of the twist drills and use of minimum quantity lubrication (MQL) at the flow rates of 30 and 100 ml/h. Statistical analysis of the results revealed that composition of the work material was most influential on tool performance. Addition of tellurium to the steel significantly improved machinability, increasing the number of drilled holes by over 100 per cent. The MQL flow rate was the...

Tool wear when tapping operation of compacted graphite iron

The automotive industry has made increasing use of compacted graphite iron in the manufacture of several components traditionally made of gray iron. However, in some cases, the poor machinability of compacted graphite iron compared to that of gray iron renders production costs uncompetitive. Several researches have focused on the machinability of compacted graphite iron, particularly in turning, milling and drilling operations. However, tapping, which is a more complex operation, has received little attention. The main objective of this work is to investigate the performance of cemented carbide taps when tapping ASTM A450 compacted graphite iron using TiAlN-coated M13 × 1.5 taps with four straight flutes. Cutting tools with different wear levels were analyzed after their use in machining engine cylinder blocks. Tool wear was measured and analyzed using scanning electron microscopy and optical microscopy. The main wear mechanisms observed were adhesion and abrasion.

INFLUENCE OF TOOL HOLDER MATERIAL ON INTERFACIAL, INSERT AND TOOL HOLDER TEMPERATURES DURING TURNING OPERATION OF GRAY IRON

Usually studies related to machining temperature consider a system comprised of workpiece, chip and cutting tool, the effect of tool holder material is not taken in account. However, due to its physical properties, the tool holder material, usually carbon steel, has effect in the dissipation of the heat generated. This work studies the effect of the tool holder material on the temperature distribution during the turning operation of gray iron using cemented carbide cutting tool and without cutting fluid. Five tool holders were manufactured from materials with different heat conductivity: carbon steel, stainless steel, titanium, copper and bronze. Temperatures in eight different positions in the tool holder and cutting insert were measured. The average temperature at the chip tool interface was also measured using the tool-work thermocouple method. The results showed that the measured chip tool interface temperature was less affected by the tool holder material, although the temperature distribution at the cutting tool is highly affected.Copyright

Effect of Silicon Content of Aluminum Alloy 6351 in Turning Process

The machinability of three commercial samples of the 6351 aluminum alloy with different silicon content was investigated in this work. Several parameters were used to evaluate the machinability in turning process, including the quality of the machined surface and cutting force. A design of experiments with three levels was used focusing on low values of feed rate (0.10, 0.15 and 0.2 mm/rev). The other parameters involved were: depth of cut (1.0, 1.5 and 2.0 mm), the silicon content (1.1, 1.2 and 1.3%) and two sets of cutting speed, one in the build up edge region (80, 100 and 120 m/min) and the other in a built up edge free region (200, 600 and 1000 m/min). The surface roughness parameter evaluated was Rq. A second design of experiment with three levels using higher values of feed rate (0.2, 0.35 and 0.5 mm/rev) and depth of cut of 2.0 mm was used to evaluate the influence of the silicon content in the cutting force. The effect of cutting fluid (dry machining, minimum quantity of fluid and over head cooling) was also analyzed. The results show that the silicon content has influence on the surface roughness. The statistical model in the build up edge region explains 79.95% of the total variation of roughness and 99% for cutting forces, for the other region this value is 81.99% for surface roughness and 98.96% for cutting force. The diameter of the workpiece has an influence on the results because the variation of hardness.Copyright

Avaliação de superfícies usinadas por diferentes fluidos dielétricos no processo de usinagem por eletroerosão

The Electrical Discharge Machining process is very useful while machining very hard materials, which are very difficult to be machined by traditional process, while can make complex geometries and minimum dimensions. One of the materials that are very used in this process is high-speed steel (ABNT M2), which is very hard and has a high mechanical resistance. This work has as main objective the study of performance of different dielectric fluids used in EDM in tree different pre chosen set-ups of work in terms or metal removal rate (MMR) and wear ratio (WR), roughness parameter (Ra), then discuss and analyze the most important factors that can produce different performance when machining with this process. Have been done five tests with different types of dielectric fluids using a cooper tool. Can be noticed that occurred very important different performance between the fluids, which all the other conditions of operation were unchanged. When using such a fluid the workpiece presented less roughness and a higher MMR in some cases. In other cases, a higher MMR produced in the other hand a Recast Layer less uniform. However, the most important conclusion of this work is about kerosene, which costs 3 times less than the specific dielectric fluids for EDM, presented worst finishing surfaces and not too high MMR as expected, despite all the risks for the operator.