A statistical data-based approach to instability detection and wear prediction in radial turning processes

Radial turning forces for tool-life improvements are studied, with the emphasis on predictive rather than preventive maintenance. A tool for wear prediction in various experimental settings of instability is proposed through the application of two statistical approaches to process data on tool-wear during turning processes: three sigma edit rule analysis and Principal Component Analysis (PCA). A Linear Mixed Model (LMM) is applied for wear prediction. These statistical approaches to instability detection generate results of acceptable accuracy for delivering expert opinion. They may be used for on-line monitoring to improve the processing of different materials. The LMM predicted significant differences for tool wear when turning different alloys and with different lubrication systems. It also predicted the degree to which the turning process could be extended while conserving stability. Finally, it should be mentioned that tool force in contact with the material was not considered to be an important input variable for the model.The work was performed as a part of the HIMMOVAL (Grant Agreement Number: 620134) project within the CLEAN-SKY program, linked to the SAGE2 project for geared open-rotor development and the delivery of the demonstrator part. Funding through grant IT900-16 is also acknowledged from the Basque Government Department of Education, Universities and Research

Research on emulsion mist generation in the conditions of minimum quantity cooling lubrication (MQCL)

U radu se opisuje učinak parametara stvaranja emulzijske izmaglice i udaljenosti mlaznice od kontaktne površine reznog klina s obratkom na promjer i broj kapljica dospjelih u zonu rezanja. Dati su uvjeti stvaranja emulzijske izmaglice u kojoj su sve kapljice, dovedene u zonu rezanja u datom vremenu, u to vrijeme isparile. Opisana je analiza protoka topline u MQCL metodi i dokazano je da protok zraka i udaljenost mlaznice od zone rezanja imaju najvažniji učinak na promjer kapljica.The paper presents the effect of emulsion mist generation parameters and the distance of the nozzle from the contact zone of the cutting wedge with the workpiece on the diameter and number of droplets supplied into the cutting zone. The conditions of emulsion mist generation, in which all the droplets supplied to the cutting zone in a given time, are evaporated in this time. An analysis of heat flow in the MQCL method was presented and it was proved that the air flow and the distance of the nozzle from the cutting zone have the most significant effect on the diameter of droplets

Effect of anti-wear additive on cutting tool and surface layer of workpiece state under MQCL conditions

Rad prikazuje rezultate istraživanja utjecaja dodatka emulziji radi manjeg trošenja reznog alata oznake Crodafos EHA-LQ-(MH) na stanje obrađene površine korozijski postojanog čelika 1.4310 nakon tokarenja. Istraživanje sadrži usporedbu sljedećih uvjeta obrade: suha obrada, hlađenje MQCL metodom i hlađenje MQCL metodom s aditivom Crodafos EHA-LQ-(MH). U radu se prikazuje utjecaj AW dodatka emulziji na hrapavost obrađene površine mjeren parametrom Ra pri različitim brzinama rezanja vc i masenim protocima emulzije E. Ustanovljeno je da se MQCL+AW metodom smanjuju vrijednosti Ra parametra za 14 % do 35 % u usporedbi sa suhom obradom i za 17 % u usporedbi s MQCL metodom. Obrađena površina obratka i stražnja površina alata snimana je mikro X-zračenjem i provedena je spektroanaliza. Provedena je i kemijska analiza rezne oštrice i površinskih slojeva obrađene površine. Rezultati pokazuju da su vodene kapljice u MQCL metodi vrlo dobro transportno sredstvo aktivnih sastojaka AW aditiva koje stvaraju suhi sloj maziva na obrađenoj površini.The work presents the results of investigation of the influence of anti-wear additive Crodafos EHA-LQ-(MH) added to the emulsion mist on the condition of machined surface of 1.4310 stainless steel after turning. The investigation included the comparison of the following cutting conditions: dry machining, cooling by the MQCL method and cooling by the MQCL method with Crodafos EHA-LQ-(MH). In the paper, the influence of the Anti-Wear (AW) additive on the roughness parameter Ra of the machined surface for various cutting speeds, vc, and mass flow of the emulsion E has been shown. It was found that the MQCL+AW method decreases the Ra parameter values by 14 % to 35 % in comparison with dry cutting and by 17 % in comparison with MQCL method.The machined material and the rake face of the cutting wedge have been subjected to micro X-ray spectroanalysis. Chemical analysis of the cutting wedge and the surface layer of the machined material has been performed. The results show that water dropletts in MQCL method are very good transport facility for active compounds of AW additive that consequently form the dry-film lubricant on the machined surface

Optimisation of machining parameters during ball end milling of hardened steel with various surface inclinations

This paper proposes a method for the reduction of forces and the improvement of efficiency during finish ball end milling of hardened 55NiCrMoV6 steel. The primary objective of this work concentrates on the optimal selection of milling parameters (cutting speed – vc, surface inclination angle α), which enables the simultaneous minimisation of cutting force values and increased process efficiency. The research includes the measurement of cutting forces (Fx, Fy, Fz) during milling tests with variable input parameters and calculation of process efficiency accounting for cutting parameters and surface inclination. The paper then focuses on the multi-criteria optimisation of the ball end milling process in terms of cutting forces and efficiency. This procedure is carried out with the application of the response surface method, based on the minimisation of a total utility function. The work shows that surface inclination angle has a significant influence on the cutting force values. Minimal cutting forces and relative high efficiency can be achieved with cutting speed vc = 375 m/min and surface inclination angle α = 15°

Influence of argon pollution on the weld surface morphology

In this paper the surfaces of butt welded joints in steel tubes were analyzed using an optical 3D measurement system to determine the morphology and topographic parameters. It was established that pollution of the argon shield gas with oxygen did not influence the width of the heat-affected zone. However, the composition of the shield gas significantly influenced the surface asymmetry, Ssk, and its inclination Sku. The measurement of these parameters enabled the selection of a higher quality surface, which was visually proven by the reduction in discoloration of the surface of the weld joint. High quality surfaces eliminate a potential habitat for bacteria and a future source of corrosion as well as providing less resistance to fluid flow

ВЛИЯНИЕ СПОСОБА ОХЛАЖДЕНИЯ ЗОНЫ РЕЗАНИЯ НА УСЛОВИЯ СТРУЖКООБРАЗОВАНИЯ

The paper considers an influence of a cutting zone cooling method on the chip shape and thickening ratio while turning R35 steel with the hardness of НВ 1250 МРа. Cutting with various types of cooling - dry, compressed air and emulsion fog has been investigated in the paper. OPORTET RG-2 emulsol with emulsion concentration of 4% has been used as an active substation. Cutting tool is a turning cutter with a changeable square plate SNUN120408 made of Р25 hard alloy with multilayer wear-resistant coating, upper titanium nitride layer. Front plate surface is flat. Range of cutting speeds - 80-450 m/min, motions - 0,1-0,5 mm/rev, emulsion flow - 1,5-3,5 g/min and compressed air - 4,5-7,0 m3/h, cutting depth - 1,0 mm. In order to reduce a number of single investigations it is possible to use plans based on ЛПх-sequences.It has been shown that the method for cutting zone cooling exerts significant influence on conditions for chip formation. Regression equation describing influence of machining conditions on Ка-chip thickening ratio has been obtained in the paper. The range of cutting modes is extended while using emulsion fog for cooling. In the process of these modes chip is formed in the shape of short spiral fragments or elements. Favourable form of chips is ensured while using the following rate of emulsion - not more than 2 g/min. The investigations have made it possible to determine conditions required for cooling emulsion fog. In this case it has been observed minimum values in chip thickening ratio and chip shape that ensures its easy removal from cutting zone. While making dry turning values of Ка is higher not less than 15 % in comparison with other methods for cutting zone cooling.В статье рассмотрено влияние способа охлаждения зоны резания на форму и коэффициент утолщения стружки при точении стали R35 твердостью 1250 МПа. Исследовали резание при охлаждении всухую, сжатым воздухом и эмульсионным туманом. В качестве активной субстанции использовали эмульсол OPORTET RG-2, концентрация эмульсии - 4 %. Режущий инструмент - токарный резец со сменной квадратной пластиной SNUN120408 из твердого сплава Р25 с многослойным износостойким покрытием, верхний слой - нитрид титана, передняя поверхность пластины - плоская. Диапазон скоростей резания - 80-450 м/мин, подач - 0,1 -0,5 мм/об, расходов эмульсии - 1,5-3,5 г/мин и сжатого воздуха - 4,5-7,0 м3/ч. Глубина резания - 1,0 мм. Для сокращения количества единичных исследований можно использовать планы, базирующиеся на ЛПт-последовательностях.Показано, что способ охлаждения зоны резания оказывает существенное влияние на условия стружкообразования. Получено уравнение регрессии, описывающее влияние условий обработки на коэффициент утолщения стружки Ка.При охлаждении эмульсионным туманом расширяется диапазон режимов резания, при которых формируется стружка в виде коротких фрагментов спирали или элементная. Благоприятная форма стружки обеспечивается при расходе эмульсии не более чем 2 г/мин. В результате исследований определены условия охлаждения эмульсионным туманом, при которых наблюдаются наименьшие значения коэффициента утолщения стружки и форма стружки, обеспечивающая ее легкое удаление из зоны резания. При точении всухую значения Ка больше не менее чем на 15 % по сравнению с другими способами охлаждения зоны резания

Precision surface characterization for finish cylindrical milling with dynamic tool displacements model

In this work a new approach to surface roughness parameters estimation during finish cylindrical end milling is presented. The proposed model includes the influence of cutting parameters, the tool’s static run out and dynamic phenomena related to instantaneous tool deflections. The modeling procedure consists of two parts. In the first stage, tool working part instantaneous displacements are estimated using an analytical model which considers tool dynamic deflections and static errors of the machine – tool-holder – tool system. The obtained height of the tool’s displacement envelope is then applied in the second stage to the calculation of surface roughness parameters. These calculations assume that in the cylindrical milling process, two different mechanisms of surface profile formation exist. Which mechanism is present is dependent on the feed per tooth and the maximum height of the tool’s displacement envelope. The developed model is validated during cylindrical milling of hardened hot-work tool steel 55NiCrMoV6 using a stylus profiler and scanning laser vibrometer over a range of cutting parameters. The surface roughness values predicted by the developed model are in good agreement with measured values. It is found that the employment of a model which includes only the effect of static displacements gives an inferior estimation of surface roughness compared to the model incorporating dynamic tool deflection