Experimental Study on the Minimum Undeformed Chip Thickness Based on Effective Rake Angle in Micro Milling

Micro milling is widely used to manufacture micro parts due to its obvious advantages. The minimum undeformed chip thickness, the effective rake angle, and size effect are the typical characteristics and closely related to each other in micro milling. In this paper, the averaging method is proposed to quantitatively estimate the effective rake angle in the cutting process. The minimum undeformed chip thickness is explained based on the effective rake angle and determined to be 0.17 rn (tool cutting edge radius). Then, micro milling experiment was conducted to study the effect of the minimum undeformed chip thickness. It is found that the minimum undeformed chip thickness results in the unstable cutting process, the uneven peaks on cutting force signal, and the dense characteristic frequency distribution on frequency domain signal. The dominant ploughing effect induces the great specific cutting energy and the deteriorated surface roughness due to the minimum undeformed chip thickness.

Mathematical Modeling of Cutting Forces in Microdrilling

In drilling, the primary and secondary cutting lips of the drill shear the material while the central portion of the chisel edge indents the workpiece, making the cutting process complex to understand. As we go for microdrilling, it exhibits an added complexity to the cutting mechanism as the edge radius gets comparable to chip thickness at low feeds. The presented work models the forces by the primary cutting lip of a microdrill analytically using slip-line field that includes the changes in the effective rake angle and dead metal cap during cutting for cases of shearing as well as ploughing. To study the variation of forces experimentally, the primary cutting lip and chisel edge forces are separated out by drilling through pilot holes of diameter slightly above the drill-web thickness. Finally, the analytical and experimental results are compared and the model is calibrated.

Impact of Spindle Speed on Micro-Milling Stability

Milling efficiency is hampered by excessive tool vibrations that negatively impact the work-piece quality. This is more of a concern in micro-milling where sudden tool breakage occurs before the operator can adjust cutting parameters. Due to different chip formation mechanisms in micro-milling, an increased tool-radius to feed-rate ratio, and higher spindle speeds, micro-milling is a highly non-linear process which can produce multiple and broadband frequencies which increase the probability of tool failure. Micro-milling is studied through the development and analysis of a 3-D nonlinear micro-milling dynamic model. A lumped mass, spring, damper system is assumed for modeling the dynamic properties of the tool. The force mechanism utilized is a slip-line field model that provides the advantages of being highly dynamic by accounting for the constantly changing effective rake angle and slip-line variables. Accurate prediction of the chip thickness is important in correctly predicting the dynamics of the system since the force mechanism and its variables are a function of the chip thickness. A novel approach for calculating the instantaneous chip thickness which accounts for the tool jumping out of the cut and elastic recovery of the work-piece is presented. The effective rake angle and helical angle is accounted for resulting in a 3-D micro-milling model. The model is shown to resolve the high frequency force components that are seen in experimental data available in literature. Also, exciting the system at various spindle speeds results in dynamic states of motion that negatively impact the process through increased vibration amplitude and a broad frequency bandwidth.

Basic Study on Micro V-Groove Cutting of Tungsten Carbide Using Diamond Tools

Micro V-groove cutting of cobalt-free tungsten carbide using two types of V-shaped diamond tools is performed using mist of zinc dialkyl-dithiophosphate (ZnDDP) as lubricant. The two types of tool tested are 1) mono-crystalline diamond and 2) poly-crystalline diamond made of approximately 30 nm-sized diamond crystals. The geometry of the V-groove-cutting process is theoretically investigated and the relationship between V-groove angle, original rake angle, and effective rake angle is clarified. Through the cutting experiments, the effects of diamond types and rake angle on tool-wear characteristics are explained. When rake angle is set at zero degrees, tool chipping frequently occurs for both types of diamond tools even when ZnDDP is supplied. However, when rake angle is set at -30 degrees for poly-crystalline diamond, tool wear is minimized.

Mathematical Modeling of Cutting Forces in Micro-Drilling

In drilling, the primary cutting lips and the secondary cutting lips of the drill shear the material while the central portion of the chisel edge indents the workpiece, making the cutting process complex to understand. As we go for micro-drilling, it exhibits an added complexity to the cutting mechanism when the edge radius gets comparable to chip thickness at low feeds. The presented work models the forces by the primary cutting lip of a micro-drill analytically using slip-line field that includes the changes in the effective rake angle and dead metal cap during cutting for cases of shearing as well as ploughing. To study the variation of forces experimentally, the primary cutting lip and chisel edge forces are separated out by drilling through pilot holes of diameter slightly above the drill-web thickness. Finally, the analytical and experimental results have been compared and the model has been calibrated.

High Speed Non-Linear Micro-Milling Dynamics

The efficiency of the milling process is limited due to excessive vibrations that negatively impact the tool and work-piece quality. This becomes even more of a concern in micro-milling where sudden tool breakage occurs before the operator can adjust cutting parameters. Due to different chip formation mechanisms in micro-milling, an increased tool-radius to feed-rate ratio, and higher spindle speeds, micro-milling is a highly non-linear process which can produce multiple and broadband frequencies which increase the probability of tool failure. This paper investigates micro-milling through the development and analysis of a 3-D nonlinear micro-milling dynamic model. A lumped mass, spring, damper system is assumed for modeling the dynamic properties of the tool. The force mechanism utilized is a slip-line field model that provides the advantages of being highly dynamic by accounting for the constantly changing effective rake angle and slip-line variables. Accurate prediction of the chip thickness is important in correctly predicting the dynamics of the system since the force mechanism and its variables are a function of the chip thickness. A novel approach for calculating the instantaneous chip thickness which accounts for the tool jumping out of the cut and elastic recovery of the work-piece is presented. The derivation for the effective rake angle is given and the helical angle is accounted for resulting in a 3-D micro-milling model. The results of simulating the model demonstrate its capability of producing the high frequency force components that are seen in experimental data available in literature. The advantages of using this approach over the constant empirical force coefficient approach when studying micro-milling dynamics is discussed and the instability of the system is investigated utilizing instantaneous frequency.

A New Mechanistic Approach for Micro End Milling Force Modeling

This paper investigates the mechanistic modeling of micro end milling forces, with consideration of the effects of plowing, elastic recovery, effective rake angle, and flank face rubbing. Two different mechanistic models are developed for shearing- and plowing-dominant regimes. Micro end milling experiments are conducted to validate the model for Aluminum 6061; and, the model appropriately predicts force profiles for a wide range of feed rates, and prediction of the root mean square (RMS) values of the resultant forces is, on average, within a 12% error. The study of the model shows that plowing and rubbing force contributions are significant, especially at low feed rates. The edge radius is found to have a significant effect on plowing and rubbing force components and the effective rake angle, which indicates that it is important to maintain a low edge radius to reduce micro end milling forces.

Numerical Modeling of Minimum Uncut Chip Thickness for Micromachining With Different Rake Angle

In micromachining, when the undeformed chip thickness becomes comparable to the edge radius of the cutting tool, the effective rake angle becomes to be negative and has significant effect on the determination of the minimum uncut chip thickness. The determination of the minimum uncut chip thickness is essential in micro machining in order to achieve desired surface integrity and accuracy. In this paper, an Arbitrary Lagrangian Eulerian (ALE)-based numerical modeling is proposed to determine the minimum uncut chip thickness for Copper by changing the cutting tool’s nominal rake angle. According to the relationship between the minimum uncut chip thickness and the effective rake angle, a mathematical model that reflects the relationship between the effective rake angle and the nominal rake angle is established.