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Turning hardened steel using coated carbide at high cutting speeds

The present work studies some aspects of the turning process applied on hardened steel using multilayer coated carbide tools at high cutting speeds. The influence of cutting parameters (vc, f, and depth of cut - d.o.c.) on tool temperature, tool wear, cutting forces, and surface roughness were analyzed. The current literature reports many studies using PcBN on hardened steel, but it is also important to know the results when using coated carbide tools, mainly for economical reasons. Temperature was measured by a thermocouple positioned at the lowest insert face, underneath it. Temperature near the rake face was calculated using the measured gradient within the insert thickness. To measure the gradient a special technique was used with one embedded thermocouple near the rake face and one underneath. Tool wear measurements demonstrated the capability of such tools in turning hardened steel with reasonable tool life. Forces measured resulted in relatively low values, being the radial component the largest of all. For the different cutting conditions studied, the doc has the greatest influence on force and temperature. Additionally, the best surface roughness values were smaller than 0,4 µm Ra.

Influence of the tool edge geometry on specific cutting energy at high-speed cutting

This paper presents specific cutting energy measurements as a function of the cutting speed and tool cutting edge geometry. The experimental work was carried out on a vertical CNC machining center with 7,500 rpm spindle rotation and 7.5 kW power. Hardened steels ASTM H13 (50 HRC) were machined at conventional cutting speed and high-speed cutting (HSC). TiN coated carbides with seven different geometries of chip breaker were applied on dry tests. A special milling tool holder with only one cutting edge was developed and the machining forces needed to calculate the specific cutting energy were recorded using a piezoelectric 4-component dynamometer. Workpiece roughness and chip formation process were also evaluated. The results showed that the specific cutting energy decreased 15.5% when cutting speed was increased up to 700%. An increase of 1o in tool chip breaker chamfer angle lead to a reduction in the specific cutting energy about 13.7% and 28.6% when machining at HSC and conventional cutting speed respectively. Furthermore the workpiece roughness values evaluated in all test conditions were very low, closer to those of typical grinding operations (~0.20 mm). Probable adiabatic shear occurred on chip segmentation at HSC.

Experimental investigations of heat transfer coefficients of cutting fluids in metal cutting processes: analysis of workpiece phenomena in a given case study:

This paper reports an experimental method to estimate the convective heat transfer of cutting fluids in a laminar flow regime applied on a thin steel plate. The heat source provided by the metal cutting was simulated by electrical heating of the plate. Three different cooling conditions were evaluated: a dry cooling system, a flooded cooling system and a minimum quantity of lubrication cooling system, as well as two different cutting fluids for the last two systems. The results showed considerable enhancement of convective heat transfer using the flooded system. For the dry and minimum quantity of lubrication systems, the heat conduction inside the body was much faster than the heat convection away from its surface. In addition, using the Biot number, the possible models were analyzed for conduction heat problems for each experimental condition tested.

DEVELOPMENT OF AN OPTICAL SCANNER TO STUDY WEAR ON THE WORKING SURFACE OF GRINDING WHEELS

ABSTRACT The efficiency of the grinding operation is highly dependent on the grinding wheel surface topography. Several methods for the evaluation of the grinding wheel surface have been developed in the last few years. In some of these methods, the grinding wheel has to be removed from the machine for an evaluation using a microscope or a profilometer. Some other methods are able to measure the topography at the grinding machine, but they do not give detailed information about grain distribution and wear. This paper shows a new method to map the grinding wheel surface. The proposed system is based on an optical scanner capable of measuring the light beam reflected from the wear flat areas on the abrasive grains over the whole wheel peripheral surface. The Mapping System for Grinding Wheels (MSGW) is able to acquire data with the wheel running at the work speed (30 m/s)and the measurement carried out on the grinding machine without stopping. The system is applied on a surface grinding operation where an A...

Experimental and theoretical study on workpiece temperature when tapping hardened AISI H13 using different cooling systems

Tapping operations on hardened steels have always been a great challenge. Dry machining and two cooling systems were used when tapping hardened AISI H13 (53 HRC). Embedded thermocouples were used for temperature measurement close to the thread diameter in the radial and axial direction. A FEA model was used to evaluate the heat “Q”, and coefficient of convection “h”. The lowest temperature peak occurred with the flooded system, followed by the MQL, and dry condition. The heat and coefficient of convection increased when using the flooded system, followed by the MQL, compared to the dry condition. Those values were also in accordance with early published works, using different techniques.

An Investigation into the Use of Industrial Robots for Machining Soft and Low Density Materials with HSM Technique

The needs to comply with an increasingly competitive international market lead industries to some innovative solutions, such as the use of robotic arms as machine tools. Although these solutions present some well known drawbacks, there are some advantages and niches of application where success is possible. The present work investigates the use of such pieces of equipment to machine aluminum alloys AA2024 applying high speed machining (HSM) technique, assessing surface finishing as a function of different orientation angles between end mill and machined surface. It also tests the best condition to machine foam for prototyping applications. Results indicate that the directions close to the normal are the best compromises because of dynamic stability of the robot arm structure and roughness as low as 4 µm Ra are possible to be achieved in aluminum alloys. A complex shape such as a semi sphere can be easily machined in foam for rapid and accurate prototype machining. Surface finishing can be very smooth and well suitable for industrial applications in such materials.

Grinding Process Dominance by Means of the Dressing Operation

This work shows a way to dominate the grinding process through the dressing operation. The influence of dressing upon the grinding process performance is investigated regarding to the metal removal rate, surface roughness, cutting forces during the grinding wheel life. The work permits important conclusions, such as: the determination of the dressing conditions to obtain maximum metal removal rate, maximum life for roughing and best surface roughness for finishing operations.

Experimental evaluation of cutting force parameters applying mechanistic model in orthogonal milling

There have been considerable efforts in research to understand the basics of chip formation. Models developed for turning and adapted to milling, yield reasonable results, except in some particular applications. This work develops an experimental method capable of providing cutting data in a fast and reliable way to evaluate the specific cutting presure(Ks), the friction coefficient (m) and the ploughing/elastic forces (FE). Different models for the cutting force can be tested, and the coefficient of determination (R2) assesses the adequacy of models. The particular adopted model, used to test the experimetal method hereby proposed, resulted in a good agreement with experimental data, expressed by R2 values very close to the unity

A Contribution to Improve the Accuracy of Chatter Prediction in Machine Tools Using the Stability Lobe Diagram

The chatter phenomenon can severely limit the power available for milling. The stability lobe diagram (SLD) is a very fast and simple method to predict the chatter free zone, allowing the selection of the most adequate spindle speed and depth of cut for higher productivity. However, the data used to calculate the SLD, coming from frequency response functions (FRFs), must be acquired adequately to improve the predictability. FRFs result differently depending on the activation of the spindle electronic control. The present work uses SLDs to investigate these differences and experimental end milling tests to assess the accuracy of SLDs curves. Results indicate that the inclusion of spindle electronic control provides better accuracy in predicting the chatter in milling.

Modelling and characterisation of roughness of moulds produced by high-speed machining with ball-nose end mill:

Cusps and scallops of hardened steel moulds produced by high-speed milling using a ball-nose end mill were mathematically modelled, characterised by microscopy and experimentally validated. The experimental results show that the part material is crushed or ploughed near the cutter centre, where the cutting speed is very low. This kinematic singularity, associated with tool feed, compresses and bends the ball-nose end mill axially. Because of this double effect, the end mill marks on the part at the end of the milling path cause surface damage and dimensional errors to the hardened mould. A mathematical model may predict the formation of the cusps and scallops and be of use in computer numerical control or computer-aided manufacturing programming to obtain the desired part topography.