Effects Of Undeformed Chip Thickness Research Articles

An investigation on material removal mechanism in ultra-high-speed grinding of nickel-based superalloy: three-dimensional simulation and experimental verification

Ultra-high-speed grinding is a significant method for the advanced manufacturing of the difficult-to-machine material components, e.g., nickel-based superalloy. However, unclear mechanism of material removal behavior is still the main problem. The present work intends to establish the three-dimensional (3D) finite element simulation model of ultra-high-speed grinding with single abrasive grain. The effects of undeformed chip thickness and grinding speed on the morphology of grinding traces and chips are investigated. The parameters, such as pile-up ratio and shear slip frequency, are characterized experimentally, and the mechanism of material removal behavior in the process of ultra-high-speed grinding has been accordingly researched deeply. The results indicate that the pile-up ratio decreases firstly and then increases with an increase of undeformed chip thickness; the lowest pile-up ratio would be obtained when the undeformed chip thickness is 0.8~1 μm. When the grinding speed is below 240 m/s, with the increase of grinding speed, the distance between the sawtooth of the grinding chips is reduced, while the sawtooth degree is increased. When the grinding speed exceeds 400 m/s, the chip shape changes from serrated fracture to banded continuity, and the frequency of adiabatic shear slip goes up with the increase of grinding speed, which helps to reduce the grinding force, making the grinding process more stable and decreasing the difficult machinability of Inconel 718 nickel-based superalloy.

Investigation of Tool Wear and Chip Morphology in Dry Trochoidal Milling of Titanium Alloy Ti-6Al-4V.

Titanium alloys are widely used in the manufacture of aircraft and aeroengine components. However, tool wear is a serious concern in milling titanium alloys, which are known as hard-to-cut materials. Trochoidal milling is a promising technology for the high-efficiency machining of hard-to-cut materials. Aiming to realize green machining titanium alloy, this paper investigates the effects of undeformed chip thickness on tool wear and chip morphology in the dry trochoidal milling of titanium alloy Ti–6Al–4V. A tool wear model related to the radial depth of cut based on the volume of material removed (VMR) is established for trochoidal milling, and optimized cutting parameters in terms of cutting speed and axial depth of cut are selected to improve machining efficiency through reduced tool wear. The investigation enables the environmentally clean rough machining of Ti–6Al–4V.

Mechanism of brittle fracture in diamond turning of microlens array on polymethyl methacrylate

Diamond cutting is a popular method to fabricate microlens array (MLA) on polymethyl methacrylate (PMMA); however, it is limited by brittle fracture, which is formed easily on the surface of MLA during the cutting process. In this paper, the formation mechanism of the brittle fracture is studied via a series of experiments including the slow tool servo (STS) cutting experiment of MLA, surface scratching experiment and sudden-stop cutting experiment. The effects of undeformed chip thickness, feed rate, and machining track on brittle fracture formation are investigated in detail. In addition, based on the fracture formation mechanism, a bi-directional cutting approach is proposed to eliminate the regional brittle fracture of the microlens during diamond cutting. An experiment was then conducted to verify the method; the results demonstrated that bi-directional cutting could eliminate brittle fracture entirely. Finally, a spherical MLA with the form error (vPV) of 60 nm and the surface roughness (Ra) of 8 nm was successfully fabricated.

Analytical modeling of temperature distribution in lead-screw whirling milling considering the transient un-deformed chip geometry

High temperature often occurs at the local cutting area during lead-screw whirling milling, which significantly affects workpiece surface integrity as well as tool life. The cutting process of lead-screw whirling milling comprises several recurrent characteristics, such as the un-deformed chip thickness and un-deformed chip width. The combined effects of un-deformed chip thickness and width cause time-varying variation in the size of the heat source, thus further affect the temperature distribution in the cutting area. This paper proposes a transient thermal analytical model to analyze the temperature distribution in the cutting area for lead-screw whirling milling. According to the complex trajectory of the tool relative to the rotation workpiece, the un-deformed chip geometry has been studied in detail at the two cutting stages. The time-varying tool-chip contact area and boundary equations of frictional heat source are firstly formulated to describe the size of the time-varying heat source. Secondly, the transient thermal analytical model is constructed taking into account the heat liberation intensity of the time-varying heat source. A series of experiments of whirling milling for lead-screw shaft are carried out, and the theoretical results evaluated by the proposed analytical model agree well with the experimental results. Furthermore, the effects of cutting conditions and un-deformed chip geometry on the temperature distribution have been analyzed, which can be used for process designers to make decisions in choosing the cutting parameters with optimized surface integrity and tool life.

Investigation on size effect of grain wear behavior during grinding nickel-based superalloy Inconel 718

In order to explore the effect of undeformed chip thickness (UCT) on the grain wear behavior, the single grain grinding experiment was carried out on the typical difficult-to-cut material, such as nickel-based superalloy Inconel 718. The grinding forces of single grain were measured, and the grain wear morphology was also characterized under different UCT values. The variations of grain wear behavior, grinding forces, and radial wear of single grain were investigated under the conditions of UCT range from 0.2 to 1 μm. The results show that size effect could change the grain wear behavior in grinding. In the beginning of wear, the crescent depression is observed on the rake face at each value of UCT. As the grain wears more seriously, the crescent depression would change into a new rake face or new cutting edge. Besides, with the increase of specific material removal volume (SMRV), the grinding forces tend to increase firstly and then remain stable under different UCT values. Furthermore, the size effect of grain wear behavior also takes effects on the grinding force ratios. The quantitative analysis of radial wear further proves that size effect leads to the change of grain wear amount in grinding.

Effects of undeformed chip thickness on grinding temperature and burn-out in high-efficiency deep grinding of Inconel718 superalloys

High-efficiency deep grinding experiments of nickel-based superalloy Inconel718 were conducted with a vitrified cubic boron nitride wheel. An investigation was made to detect the relationship between the undeformed chip thickness and grinding temperature and burn-out behavior of the workpiece material. The results display that the grinding forces and grinding power increase with the increase of the undeformed chip thickness. When the coolant is in the nucleate boiling state, the grinding temperature keeps stably at below 140 °C; however, the grinding temperature increases rapidly to the materials burn-out point once the coolant enters the film boiling state. The critical range, 0.65 ∼ 0.75 μm, is determined for the undeformed chip thickness under the defined experimental condition, which could take a great effect on controlling the grinding burn-out and increasing the grinding efficiency.

Experimental Investigation on Cutting Characteristics in Nanometric Plunge-Cutting of BK7 and Fused Silica Glasses.

Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation.

Micromachining of coarse-grained multi-phase material

The high demand of miniaturized components, coupled with geometric and material range limitations of traditional lithographic techniques has generated a strong interest in micromechanical machining. In micromachining the so-called size effect is a dominant factor. This is attributed to the fact that the unit or physical size of the material to be removed can be of the same order of magnitude as the tool edge radius or grain size. This paper explores the micro-machinability of multi-phase ferrite—pearlite steel that has a relatively large average grain size (10 μm). The investigation and cutting tests examined the effect of undeformed chip thickness, tool edge radius, and workpiece grain size on the specific cutting force, burr size, surface finish, and tool wear. The work clearly shows that micro tool edge radius and workpiece material grain size are valuable inputs in determining micromilling conditions that ensure the best surface finish and reduced burr size. Cutting conditions recommendations are also put forwards for roughing and finishing passes in micromilling of AISI 1045 tool steel.

Improved dynamic cutting force model in ball-end milling. Part I: theoretical modelling and experimental calibration

An accurate cutting force model of ball-end milling is essential for precision prediction and compensation of tool deflection that dominantly determines the dimensional accuracy of the machined surface. This paper presents an improved theoretical dynamic cutting force model for ball-end milling. The three-dimensional instantaneous cutting forces acting on a single flute of a helical ball-end mill are integrated from the differential cutting force components on sliced elements of the flute along the cutter-axis direction. The size effect of undeformed chip thickness and the influence of the effective rake angle are considered in the formulation of the differential cutting forces based on the theory of oblique cutting. A set of half immersion slot milling tests is performed with a one-tooth solid carbide helical ball-end mill for the calibration of the cutting force coefficients. The recorded dynamic cutting forces are averaged to fit the theoretical model and yield the cutting force coefficients. The measured and simulated dynamic cutting forces are compared using the experimental calibrated cutting force coefficients, and there is a reasonable agreement. A further experimental verification of the dynamic cutting force model will be presented in a follow-up paper.

Improved Dynamic Cutting Force Model in Peripheral Milling. Part I: Theoretical Model and Simulation

The accurate prediction of cutting forces is important in controlling the tool deflection and the machining accuracy. In this paper, the authors present an improved theoretical dynamic cutting-force model for peripheral milling with helical end-mills. The theoretical model is based on the oblique cutting principle and includes the size effect of undeformed chip thickness and the influence of the effective rake angle. A set of closed-form analytical expressions is presented. Using the cutting forces measured by Yucesan [1] in tests on a titanium alloy, the cutting-force coefficients are estimated and the cutting-force model verified by simulation. The simulation results indicate that the improved dynamic cutting-force model does predict the cutting forces in peripheral milling accurately. Simulation results for a number of particular examples are presented.

Prediction of cutting force distribution and its influence on dimensional accuracy in peripheral milling

Cutting force has a significant influence on the dimensional accuracy due to tool and workpiece deflection in peripheral milling. In this paper, the authors present an improved theoretical dynamic cutting force model for peripheral milling, which includes the size effect of undeformed chip thickness, the influence of the effective rake angle and the chip flow angle. The cutting force coefficients in the model were calibrated with the cutting forces measured by Yucesan [18] in tests on a titanium alloy, and the model was proved to be more accurate than the previous models. Based on the model, a few case studies are presented to investigate the cutting force distribution in cutting tests of the titanium alloy. The simulation results indicate that the cutting force distribution in the cut-in process has a significant influence on the dimensional accuracy of the finished part. Suggestions about how to select the cutter and the cutting parameters were given to get an ideal cutting force distribution, so as to reduce the machining error, meanwhile keeping a high productivity.