Chip Thickness Values Research Articles

Improved analytical chip thickness model for milling

In this paper an analytic expression for chip thickness in milling was formulated while considering the cycloidal motion of the teeth, runout, and uneven teeth spacing. In order to generalize the equation, the cutting parameters associated with milling (linear feed, tool rotational speed, and radius) were combined into a single, non-dimensional parameter. The new parameter allowed abstraction of the milling process and enabled selection of the maximum possible chip thickness in milling. Equations for entry and exit angles of a cut were also developed. The chip thickness values given by the new model were compared to prior models and showed lower error levels.

Evidence of Ductile Tearing Ahead of the Cutting Tool and Modeling the Energy Consumed in Material Separation in Micro-Cutting

Orthogonal cutting experiments using a quick-stop device are performed on Al2024-T3 and OFHC copper to study the chip–workpiece interface in a scanning electron microscope. Evidence of ductile tearing ahead of the tool at cutting speeds of 150m∕min has been found. A numerical finite element model is then developed to study the energy consumed in material separation in micro-cutting. The ductile fracture of Al2024-T3 in a complex stress state ahead of the tool is captured using a damage model. Chip formation is simulated via the use of a sacrificial layer and sequential elemental deletion in this layer. Element deletion is enforced when the accumulated damage exceeds a predetermined value. A Johnson–Cook damage model that is load history dependent and with strain-to-fracture dependent on stress, strain rate, and temperature is used to model the damage. The finite element model is validated using the cutting forces obtained from orthogonal micro-cutting experiments. Simulations are performed over a range of uncut chip thickness values. It is found that at lower uncut chip thickness values, the percentage of energy expended in material separation is higher than at higher uncut chip thicknesses. This work highlights the importance of the energy associated with material separation in the nonlinear scaling effect of specific cutting energy in micro-cutting.

A study of the effect of tool cutting edge radius on ductile cutting of silicon wafers

Ductile mode cutting of silicon wafers can be achieved under certain cutting conditions and tool geometry. An experimental investigation of the critical undeformed chip thickness in relation to the tool cutting edge radius for the brittle-ductile transition of chip formation in cutting of silicon wafers is presented in this paper. Experimental tests for cutting of silicon wafers using diamond tools of different cutting edge radii for a range of undeformed chip thickness are conducted on an ultra-precision lathe. Both ductile and brittle mode of chip formation processes are observed in the cutting tests. The results indicate that ductile cutting of silicon can be achieved at certain values of the undeformed chip thickness, which depends on the tool cutting edge radius. It is found that in cutting of silicon wafers with a certain tool cutting edge radius there is a critical value of undeformed chip thickness beyond which the chip formation changes from ductile mode to brittle mode. The ductile-brittle transition of chip formation varies with the tool cutting edge radius. Within the range of cutting conditions in the present study, it has also been found that the larger the cutting edge radius, the larger the critical undeformed chip thickness for the ductile-brittle transition in the chip formation.

An Analytical Model for the Prediction of Minimum Chip Thickness in Micromachining

In micromachining, the uncut chip thickness is comparable or even less than the tool edge radius and as a result a chip will not be generated if the uncut chip thickness is less than a critical value, viz., the minimum chip thickness. The minimum chip thickness effect significantly affects machining process performance in terms of cutting forces, tool wear, surface integrity, process stability, etc. In this paper, an analytical model has been developed to predict the minimum chip thickness values, which are critical for the process model development and process planning and optimization. The model accounts for the effects of thermal softening and strain hardening on the minimum chip thickness. The influence of cutting velocity and tool edge radius on the minimum chip thickness has been taken into account. The model has been experimentally validated with 1040 steel and Al6082-T6 over a range of cutting velocities and tool edge radii. The developed model has then been applied to investigate the effects of cutting velocity and edge radius on the normalized minimum chip thickness for various carbon steels with different carbon contents and Al6082-T6.

On the Modeling and Analysis of Machining Performance in Micro-Endmilling, Part I: Surface Generation

This paper examines the surface generation process in the micro-endmilling of both single-phase and multiphase workpiece materials. We used 508 μm dia endmills with edge radii of 2 and 5 μm to machine slots in ferrite, pearlite, and two ductile iron materials at feed rates ranging from 0.25 to 3.0 μm/flute. A surface generation model to predict the surface roughness for the slot floor centerline is then developed based on the minimum chip thickness concept. The minimum chip thickness values were found through finite element simulations for the ferrite and pearlite materials. The model is shown to accurately predict the surface roughness for single-phase materials, viz., ferrite and pearlite. Two phenomena were found to combine to generate an optimal feed rate for the surface generation of single-phase materials: (i) the geometric effect of the tool and process geometry and (ii) the minimum chip thickness effect. The surface roughness measurements for the ductile iron workpieces indicate that the micromilling surface generation process for multiphase workpiece materials is also affected by the interrupted chip-formation process as the cutting edge moves between phases resulting in burrs at the phase boundaries and the associated increases in surface roughness.

Influence of woodworking machine cutting parameters on the surrounding air dustiness

From epidemiological studies experts conclude that wood workers are subjected to an increased health risk of nose and nasal cavity cancer under the influence of oak- and beech-wood dust. That is why, pursuant to Croatian regulations, the limit mass concentration for oak- and beech-wood respirable dust is 1 mg/m3 and for total dust 3 mg/m3. In this study the dustiness of the air surrounding woodworking machines has been researched in two woodworking companies, furniture factory and carpentry. Sampling of respirable and total wood dust from the surrounding air was carried out during workday by the method of personal samplers fixed on workers suit and then the daily dose of workers exposure was determined. Measured mass concentrations exceeded the Croatian limit values: in the furniture factory 16% of samples for respirable dust and 18% for total dust and in the carpentry 38% for respirable dust and 65% of all samples for total dust. In the furniture factory, mass concentration of respirable particles was higher near the belt sander than near the circular saws. At the workplaces of these woodworking machines higher mass concentration of respirable and total wood dust was measured than in the air around other machines, such as spindle moulder, band saw and jointer. In the carpentry mass concentration of respirable particles near the circular saws was significantly higher than near the jointer or lamello router. The highest share of respirable particles in total wood dust are recorded at the workplaces with low concentration of total wood dust and around machines with cutting parameters achieve the lowest value of chip thickness.

Towards high cutting speed in wood milling

High cutting speed machining processes have been used for about 10 years for metals. This technology presents many advantages re- lated to output and surface quality. For timber machining, commonly used velocities are already high. However, literature about cutting velocity function during a machining process is rare. Nevertheless, some published results have shown the effect of speed on chip formation. In order to perform experiments at high cutting speeds, we used a prototype model of a CN routing machine, which allowed us to conduct machining from 3m s -1 to 62 m s -1 . Surface analysis was carried out by an optical roughness measurement device. The wood species studied is beech. Tests have been performed with constant chip thickness value. wood / milling / cutting speed / surface quality

Towards a model predicting cutting forces and surface quality in routing layered boards

The general aim of work reported here was to assist designers and operators of routers and similar tools for cutting wood-composite boards, by providing a model predicting cutting force components from readily available material properties. This initial study explored, for edge cutting, the variation within a single medium density fibre board across the thickness and in various cutting directions in the plane of the board. Material properties of interest were specific gravity and friction coefficient. In slow linear cutting on a modified milling machine, carbide router inserts cut the edges of layers cut from a medium density fibre board. Specific gravity and coefficient of sliding friction were measured for each layer. Cuts were also made on full-thickness edges in various directions in the plane of the board. Chip thickness was varied from 0.025 to 0.8 mm. Parallel and normal force data and digital video images of chip formation were stored for analysis. Specific gravity increased as the fourth power of the distance from the central plane to the surface. Friction coefficient values, estimated both from cutting forces and from rubbing forces during return, varied about a value of 0.23, with no significant difference between layers. The values for cutting force per mm width of cut increased progressively from the central plane to the surface, in a logarithmic relation with specific gravity. The cutting forces did not vary with cutting direction in the plane of the board. For a sharp edge with 32° rake angle cutting at chip thickness values above 0.1 mm, the normal force component was negative, indicating reduced feed force and improved surface quality. With dulling, the threshold value of chip thickness for this increased. It is concluded that elaboration of this approach would generate relationships suitable for incorporating in a useful general model. However, it may be found that weight per unit area of board will suffice as a proxy for cutting resistance in modelling the cutting of full-thickness edges.

CHATTER ONSET IN NON-REGENERATIVE CUTTING: A NUMERICAL STUDY

A non-linear model of non-regenerative cutting is analyzed. When damped, the model has a stable fixed point for small values of chip thickness. As chip thickness is increased, the fixed point becomes unstable via a sub-critical Hopf bifurcation. This transition corresponds to the onset of chatter. When dynamic noise is added to the system, chatter onset can occur in the sub-critical parameter region, although chatter-free cutting is predicted by the stability analysis of the fixed point. A noisy bifurcation diagram is compared qualitatively to a diagram obtained experimentally in regenerative cutting. Similar features regarding the onset of chatter are observed in both diagrams.

超精密ダイヤモンド切削における切りくず観察と鏡面生成機構に関する考察

The purpose of this research is to clarify the behavior of ultra-precision diamond machining with an infeed range of approximately 1 to 10nm. The machining behavior and the sharpness of the diamond tool edge were monitored by a cutting noise equipment, the chips checked by observing with a scanning electron microscope (SEM) and the machined surface was observed with an interference microscope. As a result, it was concluded that a mirror-like machine surface is generated at the depth of the machined section which is smaller than the cutting edge radius of a tool. Hence, it is very important to pay close attention to the chip producing behavior. The shear angle was not maintained throughout the chip, as two different shear angles, such as 14 and 17 degrees, were observed. These values were changed by the value of undeformed chip thickness compared with the cutting edge radius. Even during micro infeed ultra-precision diamond machining, the surface temperature of chips during machining is assumed to be rather high, exceeding the melting temperature (approximately 660 deg.) of aluminum alloys.

Computer Models for the Mechanics of Three-Dimensional Cutting Processes—Part II: Results for Oblique End Turning and Drilling

Using the method described in Part I, numerical models for predicting chip form and the principal components of power consumption are developed for oblique end turning and drilling. Applying the method involves mainly specifying appropriate sets of independent variables for minimization calculations. Results predicted using the rigid-viscoplastic material model are compared with measurements from unlubricated tests on steel and aluminum alloy samples. The agreement between predicted and measured results for turning is generally good, particularly for chip thickness values, chip-tool contact lengths, and the qualitative effect of varying the depth of cut. The agreement is not as good for drilling; in drilling the main cutting edge torque contribution and qualitative effects of varying the spindle speed and feed rate are accurately predicted, but the average chip thickness is consistently underestimated while chip radii of curl are overestimated. The lack of agreement for the last two outputs appears to be due to constraint from the hole drill flute surf aces which would limit maximum radii of curl.

A numerical method for calculating temperature distributions in machining, from force and shear angle measurements

The finite element method is applied to calculate the temperatures in orthogonal machining with account being taken of the finite plastic zones, (a) in which the chip is formed and (b) in which further plastic flow occurs at the tool-chip interface, and also of the shape and thermal properties of the cutting tool. Mathematical models of both primary and secondary deformation are described. These allow complete temperature distributions to be obtained, given only the experimental values of tool force and chip thickness, and the thermal properties of the work and tool. The method has potential use in a predictive theory where only the fundamental properties of the work and tool materials are known.