A study of factors affecting the performance of micro square endmills in milling of hardened tool steels (original) (raw)

Design of micro square endmills for hard milling applications

The International Journal of Advanced Manufacturing Technology, 2011

In experiments of machining hardened tool steels (such as AISI H11, H13, and D2, up to 56 HRC) by commercial Ø 0.5 mm square endmills, it is observed that the tested micro endmills showed severe wear at an early stage of the process due to chipping off around cutting edge corners, resulting in unsatisfactory tool life and product appearance (burr formation). Detailed examination of current tool geometry shows that it is mainly inherited from that of macro endmills, making the cutting edge corners the weakest part on the tool. As the micromilling process is characterized by small values of machining parameters, the cutting edge corners of the micro endmill are the most loaded part of the cutting edges. New design rules are studied for improving the stiffness and strength of micro endmills used in micro hard milling applications. Analytical modelling and finite element method analysis are used to aid the design of tool geometry. By using a larger neck angle, optimizing tool core geometry, and choosing a negative rake angle, tool stiffness and cutting edge strength are improved. The new endmill designs, both two-flute and four-flute, are tested in experiments on hardened tool steels and showed considerable lower tool wear and increased tool life. Furthermore, the geometrical accuracy and appearance of the workpiece (burr formation) has been improved drastically.

Tool Wear in Micro-Endmilling: Material Microstructure Effects, Modeling and Experimental Validation

This paper reports an investigation of material microstructure effects on tool wear in micro-scale machining of multi-phase materials. A new generic approach is proposed to estimate the tool wear that utilises empirical data about the effects of micro milling process on cutting edge radius. Experiments were conducted to study independently the influence of two main phases in steel, pearlite and ferrite, on tool wear under different cutting conditions. Based on this empirical data two regression models were created to estimate the increase of cutting edge radius when machining single and multi-phase steels. To validate the models they were applied to predict the tool wear when machining two different multi-phase steel samples. The results showed a good agreement between the estimated and the actual tool wear.

Influence of Workpiece Hardness on Tool Wear in Profile Micro-milling of Hardened Tool Steel

Tribology in Industry

Machining of engineering metallic materials on micro-level is very complicated. Micro-milling with solid tools, as one of microengineering technologies, is an acceptable process to machining of complex metallic micro-parts. The main problem in micro-milling is sensitivity of cutting tool, due its suppleness and short tool life, and its influences to workpiece accuracy and quality. In this paper is experimentally investigated tool wear of micro-milling tool. During machining tests, influence of workpiece hardness and process parameters is evaluated. Workpiece was cold work alloyed tool steel X155CrVMo12, hardened to different hardness 45, 54 and 63 HRc. Cutting tool was carbide ball-end micro-mill with TiAlN coating, and diameter of 0.6 mm. For different combination of input parameters, tool wear curves is presented, and signification of input parameters on tool wear is evaluated and discussed.

Experimental investigation of tool wear in micro milling

2015

The objective of this paper is to experimentally investigate the micro-machinability of stainless steel 316 under both dry and minimum quantity lubrication conditions. The machinability was assessed in terms of tool wear, tool life, cutting forces and surface finish. The tool life was characterised as the amount of material removed, instead of the conventional cutting times. The machining performance under MQL is superior to the dry machining for both process conditions in terms of the tool life. The magnitude of the machining forces showed cyclic pattern for both MQL and dry machining. The SEM images and the cutting force signals suggested that the dominant mode of the tool wear in micro-milling is edge chipping and abrasive wear at the tool tip. The surface roughness at the bottom of the slots improved significantly with the application of MQL for all levels of the tool wear.

Tool wear modelling using micro tool diameter reduction for micro-end-milling of tool steel H13

The International Journal of Advanced Manufacturing Technology, 2019

Micro components have been demanded increasingly due to the global trend of miniaturization of products and devices. Micro milling is one of the most promising processes for micro-scale production and differs from conventional milling due to the size effect introducing phenomena like the minimum chip thickness, making the prediction of micro milling process hard. Among challenges in micro milling, tool life and tool wear can be highlighted. Understanding tool wear and modelling in micro milling is challenging and essential to maintaining the quality and geometric tolerances of workpieces. This work investigates how to model the diameter reduction of a tool caused by tool wear for micro milling of H13 tool steel. Machining experiments were carried out in order to obtain cutting parameters affecting tool wear by considering the diameter reduction. Dry full slot milling with TiAlN (titanium aluminium nitride)-coated micro tools of diameter d = 400 μm was performed. Three levels of feed per tooth (f z = 2 μm, 4 μm and 5 μm) and two spindle speed levels (n = 30,000 rpm and 46,000 rpm) were used and evaluated over a cutting length of l c = 1182 mm. The results show that lower levels of feed per tooth and spindle speed lead to higher tool wear with a total diameter reduction over 22%. The magnitude of the cutting parameters affecting tool wear was determined by ANOVA (analysis of variance), and the model validation meets the statistical requirements with a coefficient of determination R 2 = 83.5% showing the feasibility of the approach to predict tool wear using diameter reduction modelling in micro milling.

Observation of Tool Life of Micro End Mills

Prediction of mechanical machining tool life is an integral part of commercial manufacturing. Failure of micro end mills is still not well understood, and further work needs to be done to accurately predict tool life. The objective of this study is to observe the distribution of tool life for micro end mills under aggressive machining conditions without lubrication for 300-um-diameter micro end mills while machining 6061-T6 aluminum alloy. The average tool life was 3 to 7 times greater for the nanocrystalline diamond (NCD) coated micro end mills as compared with the uncoated (as received) tools. For both NCD coated and uncoated micro end mills the tool life increased as the cutting speed was increased from 32 to 48 m/min, suggesting the presence of a built-up-edge during machining. The variance in the tool life data was approxi-mately an order of magnitude greater than what is expected in macro-scale machining.

Design and Optimization of Micromilling Cutting Tools

MATEC Web of Conferences, 2018

With the trend towards miniaturization, micromachining become more and more important in fabricating micro parts. The micromachining process that involved in this study is micro milling. The focus of the study is on the comparison performance between various numbers of flutes (4-flutes, 6-flutes and 8-flutes) with various helix angle (25º,30º and 35º) in micro end milling tool geometry with the conventional micro end milling, 2-flutes micro end milling. Cemented carbide is the material that been used for this study. The main problem about the two flutes micro end milling is it easily wears in a short time. In this study, finite element analysis of the model using cantilever beam principle theory. The tools will be modelled and simulate using Abaqus/CAE 6.10. The tool performance of the designed tool will be evaluated by using the maximum principal stress, σ_max. According to the analysis, weakest geometry is 2-flutes micro end milling and the strongest is 8-flutes micro end milling. 8-flutes micro end milling can be the option to replace the conventional micro end milling.

Experimental Investigation in Micro Ball-End Milling of Hardened Steel

Journal of Materials Science and Engineering A, 2015

The study focuses on micro-milling of a hardened tool steel with micro ball-end mills. The purpose is to observe the capability of a set of these mills to machine hard steels used for tooling applications. Different cutting configurations are here tested in order to evaluate their performance and finally enhance their design in this context. Experimental data, in terms of cutting forces, surfaces integrity and machining errors, is obtained from machining tests on a 40NiCrMo16 hardened steel with 0.5 mm diameter coated tungsten carbide micro-tools. The results allow highlighting some cutting, wear and dynamical phenomena related to the process. They are mainly associated to the types of mill and cutting conditions, as feed or tool/surface inclination. In this paper, the tool geometry and its dynamical behavior are mainly discussed.

Micromilling of Hardened AISI D2 Tool Steel

The paper presents an experimental investigation into the slotting of hardened AISI D2 (~62HRC) tool steel using 0.5mm diameter coated (TiAlN) tungsten carbide (WC) end mills. SEM analysis of tool morphology and coating integrity was undertaken on all tools prior to testing. Tool wear details are given based on resulting cutter diameter and slot width reduction. In addition, cutting forces are also presented together with details of workpiece burr formation. A full factorial experimental design was used with variation of cutting speed, feed rate and depth of cut, with results evaluated using analysis of variance (ANOVA) techniques. Parameter levels were chosen based on microscale milling best practice and results from preliminary testing. Main effects plots and percentage contribution ratios (PCR) are included for the main factors. Cutting speed was shown to have the greatest effect on tool wear (33% PCR). When operating at 50m/min cutting speed with a feed rate of 8µm/rev and a depth of cut of 55µm, cutter diameter showed a reduction of up to 82µm for a 520mm cut length. SEM micrographs of tool wear highlighted chipping / fracture as the primary wear mode with adhered workpiece material causing further attritious wear when machining was continued up to 2.6m cut length. All tests produced burrs on the top edges of the slots which varied in size / width to a lesser or greater degree. Under the most severe operating conditions, burr width varied from approximately 50µm to more than 220µm over the 520mm cut length. Cutting forces in general were less than 12N up to test cessation.

Prediction and Optimization of Tool Life in Micromilling AISI D2 (∼62 HRC) Hardened Steel

This paper presents a study for the development the first and second order tool life models of micromilling hardened tool steel AISI D2 62 HRC. The models were developed in terms of cutting speed, feed per tooth and depth of cut, using response surface methodology. Central composite design (CCD) was employed in developing the tool life model in relation to independent variables as primary cutting parameters. All of the cutting tests were performed within specified ranges of parameters using 0.5 mm TiAlN microtools under dry condition. Tool life and dual-response contours of metal removal rate have been generated from these model equations. Tool life equation shows that cutting speed is the main influencing factor on the tool life, followed by feed per tooth and depth of cut. The results were presented in terms of mean values and confidence levels. The adequacy of the predictive model was verified using analysis of variance (ANOVA) at 5% significant level and found to be adequate.