Cutter Geometry Research Articles

Fabrication of a polymer-based biodegradable stent using a CO2 laser

This paper deals with CO2 laser machining of biodegradable polymers. We investigate the influence of laser parameters on the quality and geometry of cuts made in poly(l-lactide) and poly(l-lactide-co-glycolide). Because of the thermal character of material removal, liquid phase occurs and heat propagates into the material, changing its properties near the cutting zone. For this reason, the mechanical properties of laser cut samples were examined. Oar-shaped samples cut with a CO2 laser were compared with injection moulded samples and also with those manufactured using a KrF excimer laser. Samples with dimensions comparable to those of stent struts were examined in a uniaxial quasi-static tensile test. The influence of laser power and scanning speed on the geometry of cuts was investigated. Narrow cuts (120µm) were made in 250µm-thick polymer sheets. A tubular stent based on poly(l-lactide) was designed and then fabricated using a CO2 laser. We noted that this method allows achieving stent struts that are 300µm wide; however, for such narrow elements the influence of the heat-affected zone can be critical. We believe that this technique has a potential to become an alternative, cost-efficient method of manufacturing biodegradable stents.

Effect of cutter geometric configuration on aerodynamic noise generation in face milling cutters

Aerodynamic noise spectrum of rotary face milling cutters consists of a broad range of high frequencies and discrete tones. This paper aims to develop a method to calculate the aerodynamic noise generation and propagation by rotary face milling cutters. The effects of milling cutter geometry on the generation of aerodynamic noise are analyzed. Based on the computational fluid dynamics (CFD) method, the Ffowcs Williams–Hawkings (FW–H) equation is used to predict the sound pressure level (SPL) of aerodynamic noise in face milling cutters. The accurate calculation of time-varying flow variables along with the rotation of cutter is very important for the prediction of aerodynamic noise. In this case, the Navier–Stokes (N–S) equation is employed to evaluate the pressure and velocity fields around the milling cutters, first in a steady mode with the Multiple Reference Frames (MRF) model, and then in an unsteady mode with sliding mesh technique (SMT) by introducing the steady flow variables as its initial fields. It is found that both the overall aerodynamic noise due to the entire cutter and the aerodynamic noise only due to the cutter gullet regions are significantly affected by the number of cutter teeth/gullet regions. Moreover, six representative milling cutters with different tooth numbers and geometries of gullet regions are chosen to study the effects of gullet configuration on aerodynamic noise generation, and the characteristics of noise spectra generated by the cutters are analyzed. The aerodynamic noise generated only by the cutter gullet regions is found to be strongly dependent on the gullet design-volume and shape. The results also reveal that the gullet design advantage of Cutter C in reducing noise generation among the eight-tooth designs, and the gullet design advantage of Cutter A in reducing noise generation among the five and seven-tooth designs in this investigation.

Influence of Three-Dimensional Stability Lobes on the Cutter Design

According to the model of three-dimensional stability and the relationship between the parameters of oblique cutting and milling coefficients, this paper analyzes the influence of the cutter geometry parameters (helix angle, normal rake angle) on the three-dimensional stability of the spindle speed, axial and radial depths. On the same cutting condition, it should choose the cutter of having the bigger helix angle and normal rake angle to cut the thin-walled plate, which can increase the stability of cutting process and improving efficiency and quality.

A finishing cutter selection algorithm for additive/subtractive rapid pattern manufacturing

The additive/subtractive rapid pattern manufacturing (RPM) process sequentially deposits thick material slabs and then machines them into desired geometries in a layer-by-layer manner. Although most rapid manufacturing systems mainly intend to increase flexibility in manufacturing rather than to reduce processing speed, it is still practical to choose the optimized sets of cutters and machining parameters specifically for each layer to improve both the machining quality and efficiency. This paper presents an algorithm to automatically select finishing cutter geometry, diameter, and calculate machining parameters for the RPM process. Inputs to this algorithm are StereoLithography file from a computer-aided design model and a cutter library. Finishing cutter selection is based on geometry accessibility and machining process efficiency analysis. The algorithm has been implemented in RPM automatic process planning software and the experimental result on a sample part is presented to show the efficacy of this algorithm.

PREDICTION OF CUTTING FORCES IN BROACHING OPERATION

Prediction of cutting forces is one of the fundamental stages in the modeling of machining processes. The costly machining tests can be replaced by virtual simulations where cutting parameters and material properties can be altered repeatedly with no cost. Broaching is one of the machining operations which is extensively used in the industry. The geometry of broaching tool varies according to the desired profile of the workpiece which can be a simple line or complicated curves. This broad range of geometries imposes complexity on the distribution of the chip load along the cutting edge. Therefore, introducing a practical force model for broaching operation can be challenging. An attempt is made in this paper to present a force model for broaching. The newly proposed force model expresses the cutting edge as a B-spline parametric curve and uses its flexibility to calculate the chip load as well as cutting forces for orthogonal and oblique broaching. Verified by previously published experimental results, the presented model has a great capability to simulate broaching cutter geometry along with cutting forces.

High speed CNC machining of AISI 304 stainless steel; Optimization of process parameters by MOGA

This work is to establish the relationship with the basic parameters to the responses namely Surface roughness (Ra) and Material Removal Rate (MRR). The Taguchi based Box-Behnken RSM (Response Surface Methodology) method is used to develop prediction formula and Multi Objective Genetic Algorithm (MOGA) is used for High speed CNC milling process optimization with higher Spindle speed, Feed rate and Depth of cut for better surface finish and material removal rate. The Ra and MRR is resultant of various controllable process parameters are Spindle speed, Feed rate and Depth of Cut, Hardness of the material, wet or dry machining, type of insert, and Dynamic forces on the job, tool wear rate with Cutter geometry. The need for scientific selection of machining parameters, conditions and the most suitable type of cutting tool has been felt over the years to eliminate the human intervention to reduce the errors and to improve productivity of the system. High speed CNC milling process is scientifically optimized using this method formulating a mathematical model that relates the surface roughness and MRR with cutting parameters in end milling, precisely to the Spindle speed, Feed rate, Depth of cut and insert type, which reduces human intervention on the process. Keywords: CNC milling, optimization, surface finish, DOE, ANOVA, material removal rate, Box-Benkhen method, genetic algorithm, stainless steel

A genuine face milling cutter geometric model for spiral bevel and hypoid gears

Accurate tooth surface and good surface quality are critical to achieve the low-noise bevel gear drives. Face milling, traditionally works as tooth roughing process, can now possibly be used for finishing process because its high speed can produce good tooth surface quality. But with the previous simplified cutter geometric model in tooth modeling, the high accurate tooth surface cannot be obtained. In this paper, a genuine face milling cutter geometric model for spiral bevel and hypoid gears is proposed. This model exactly matches with the cutter geometry in the industrial application when not considering the fabrication tolerances and tool wear . In the modeling, the blades of the genuine cutter are parameterized with blade angle, rake angles, and relief angles. The side and circular cutting edges of blades are represented on the blade rake plane, rather than the normal plane as the simplified cutter geometry. The mathematic model of the genuine tool profiles on the normal plane is derived. It can be conveniently used by the existing tooth modeling program and easily customized by specifying the geometric parameters. In comparison with the genuine tool profile with the simplified tool profile, the big geometric errors of the simplified blade profile are founded, which proves that the genuine cutter geometric model is correct and essential.

A Novel Design Method of Variable Helix Cutters to Attain robust Regeneration Suppression

Regeneration is major mechanism to generate self-excited chatter vibration in cutting. Variable helix cutters are useful to suppress regeneration. Although optimization of pitch/helix angles is significantly important at the same time, there is no practical design method to optimize the variable helix cutter geometry so far. In order to attain robust regeneration suppression, a new design method of variable helix cutters is proposed in the present study. The pitch angles vary along axial position due to disagreement of the helix angles. Because of this nature, regeneration can be suppressed in a robust manner with respect to changes of chatter frequency and/or spindle speed. Optimal pitch/helix angles are formulated on the basis of distinctive relationship between the cutter geometry and “Regeneration Factor (RF)”, which is an index to quantify influence of regeneration in the process.Through analytical investigations, it is confirmed that regeneration can be suppressed effectively in low immersion milling with variable helix cutters by the proposed method, resulting in significant chatter stability increase.

Milled Surface Generation Model for Chip Thickness Detection in Peripheral Milling

Prediction of forces between tool and workpiece is essential in order to optimize machining and preserve process stability. In the last decades different predictive approaches have been developed: mainly mechanistic and numerical models. Mechanistic models could be applied to a wide range of cutter geometry and workpiece combination, even if a specific tuning, depending on material and application, is always needed. Numerical models could take in account many operative conditions than analytical ones, and allow predicting other parameters like stress, strain rate, temperature distribution, etc., but the computational time required is often unacceptable. The paper presents an innovative hybrid numerical-analytical approach for uncut chip cross-sectional area calculation in 2.5 axis end milling operations. The proposed model uses a mechanistic cutting force model to couple tool and workpiece finite element (FE) models: FE time domain simulations provide to predict effective paths of tool teeth relative to the workpiece, taking into account the dynamics of the entire system; while an appropriate algorithm, developed in Matlab®, allows to achieve a more realistic uncut chip area, from which it is possible to calculate the cutting forces. This approach provides an accurate representation of the machined surface. Simulation is compared with experimental results.

A Gear Cutting Predictive Model Using the Finite Element Method

Current processes for producing transmission gears involve hobbing, milling or shaping of a forged stock to obtain the gear shape. Gears are typically formed by hobbing tools made from solid tooling material, such as tungsten carbide, and have dozens of teeth. The gear hobbing process entails several teeth in cut simultaneously. Generation of in-volute tooth profiles results in varying chip loads from pass to pass. In this paper, details are provided for a finite element-based model of gear hobbing and milling processes. The model explicitly meshes gear cutter geometries with dozens of teeth. These cutters are used to simulate the complicated kinematic motion between tool and workpiece. Thermo-mechanical coupled calculations within an explicit dynamic formulation are per-formed on the tool and workpiece during chip removal. The complex geometry of involute tooth profiles results in complicated contact scenarios on the evolving workpiece geometry during tooth profile generation. Tooth-workpiece-chip contact is enforced rigorously and is particularly complicated with the confined space of gear hobbing. Advanced adaptive meshing strategies are developed and employed to maintain the resolution of the tool-workpiece interaction while multiple teeth are in contact. Cutting forces, temperatures and stresses in the tool and workpiece are predicted for steel workpiece materials. Models are validated through a set of initially simplified experiments where incremental complexity is added, allowing for direct comparison between predicted and measured forces and chip shapes.

A Study of Reduced Beam Section Profiles using Finite Element Analysis

Reduced beam section (RBS) is one of the several connection types, which is economical and popular for use in new steel moment frame structures in seismic zone. To form RBS connection, some portion of the beam flanges at a short distance from column face is purposefully trimmed so that the yielding and plastic hinge occurs within this area of flanges. Use of RBS connection is found advantageous due to: a) the shear force in the panel zone is reduced; b) the force demand in column continuity plates i.e. stiffeners are reduced; and c) strong-column - weak-beam requirement is satisfied. Although, radius cut RBS is qualified by ANSI/AISC, FEMA codes, various flange cut shapes like constant, tapered, radius cut, drilled holes are possible to reduce the cross sectional area of beam flanges. The purpose of this study is to understand behavior of RBS beam-to-column moment connections for various flange cut geometries. This document represents nonlinear finite element analysis of the connection models performed using the computer program, ANSYS/Multiphysics Keywords - Steel structures, steel connections, reduced beam section, RBS profiles

Specific energy distributions for sinusoidal multi-cutters in groove-sawing process

This paper proposes a new method for establishing the relations of specific energy of a material for sinusoidal multi-cutters in groove-sawing process. Effects of specific energy on sinusoidal multi-cutters with different cutter geometries, cutter locations, cutters arrangements, and cutter-by-cutter overlap ratios are studied. Experimental results prove that the specific energy is function of undeformed cutting areas in groove-sawing process. The groove sawing force in 3-axis is decomposed by cutting force in x-direction, side force in y-direction and vertical force in z-direction. The average specific energy of sinusoidal multi-cutters for workpiece Al 6061 in different wavelength (n=1–7) is 1580MPa, the average specific coefficient in y-direction is 0.44 and the average specific coefficient in z-direction is 0.20. The chip loading on each cutter is related to the average cutting depth, cutting width and cutter angle. The maximum chip loading of cutter order occurs in cutting overlap-area ratio between 0.22 and 0.23. The specific energy with multi undeformed cutting areas demonstrated the trend as the exponent decay. The specific energy varied with cutter location on sinusoidal wave, and the maximum variation of error occurred on cutter number n=3 per unit wave. The groove-sawing force model for sinusoidal-wave cutters can be established for the function of multi undeformed cutting areas by known specific energy, and it agreed well with the experimental results. Variations of error for sinusoidal multi-cutters are investigated for different cutter topologies. Through the geometry parameters design for multi-cutters to reduce specific energy on machining, the maximum material removal rate and longer tool life can be achieved.

Analysis of drift in iso-scallop planning—machining by regions

Computer-aided manufacturing (CAM) occupies an increasingly significant role in engineering with all it has to offer in terms of new possibilities and improving designer/manufacturer productivity. Our present work is devoted to the integration of a module for automatic generation of cutter paths into a CAM program to machine freeform surfaces by end milling. The study addresses the more global issue relating to the adoption of tool path planning with constant scallop height. For present purposes, the cutter geometry is taken as given and does not enter into the study’s parameter choices. The main problem posed by planning for iso-scallop tool paths lies in the management of drift in trajectories, which leads to the path looping due to the fact that global programming over the surface remains unattainable. The proposed solution is to define surface subdivision criteria (machining by regions) enabling iso-scallop planning to be implemented in each region. We conducted our study on a three-axis numerical control machine tool.

Paper 110: Patellar Cut Obliquity in the Sagittal Plane May Be Predictive of Peri-prosthetic Patella Fracture in Cemented Total Knee Arthroplasty

Patellar cut geometry has been proposed to influence patellar fracture after total knee arthroplasty (TKA). To our knowledge, there are no large studies in current literature directly examining the association of patella fractures to the integrity of the patellar cut. This paper examines the thickness and obliquity of the bony patellar resection in 74 patella fractures occurring in cemented all-polyethylene patellar components. We retrospectively reviewed 5,073 TKAs performed between 10/4/88 to 8/31/2004 by a single surgeon. Within this period, 74 peri-prosthetic patella fractures in 68 patients were identified and compared to a matched control group. Post-operative radiographic assessments of all patellae included merchant and lateral views of the patellae. Thickness of the remaining patellar bone was measured using both merchant and lateral radiographs. Patellar cut tilt was evaluated on lateral and merchant views using 10mm thickness measurements from the midpoint on each view. Geometric and statistical analysis was conducted. With greater sagittal obliquity angles, patellae were 1.196 times more likely to experience a fracture than our controls. Patella fracture after TKA may be due to trauma or a stress fracture around the construct. Bone removal for the fixation lugs can weaken the patella, causing fracture through the stress risers. This effect may be magnified with a more generous or oblique cut. Improvement in surgical technique to retain a more level cut could theoretically help prevent the problem.

Correlation between machining direction, cutter geometry and step-over distance in 3-axis milling: Application to milling by zones

Computer-Aided Manufacturing (CAM) occupies an increasingly important role in engineering with all it has to offer in terms of new possibilities and improving designer/manufacturer productivity. The present study addresses machining of free-form surfaces on a 3-axis NC machine tool. There have recently been a large number of studies devoted to planning tool paths on free-form surfaces with various strategies being adopted. These strategies are intended to increase efficiency by reducing the overall length of machining. Often, the choice of the cutter is arbitrary and the work focuses on planning. In order to boost productivity, the present work offers assistance in choosing the cutting tool, the machining direction and cutting by surface zones, adopting a milling strategy by parallel planes. To do so, a comparison is made between milling using a spherical end milling cutter and a torus end milling cutter with the same outer radius. This comparison relates to the radius of curvature of the trace left by the cutter at the point of contact between the tool and the workpiece in relation to the direction of feed motion.

Rapid Toolpath Correction for Five-Axis High Efficiency Machining Based on Image Analysis

Five-axis high speed machining can improve the efficiency and accuracy obviously, but the machining errors and tool interference are likely to happen due to the complexity of tool motion. So the collision detection and verification of tool path are very important and necessary before machining the part. Using a combination of process simulation and collision detection based on image analysis, a rapid detection approach is developed in this research. The geometric model provides the cut geometry for the collision detection and records a dynamic geometric information for in-process workpiece. For the precise collision detection, a strategy of image analysis method is developed in order to make the approach efficient and maintian a high detection precision. An example of five-axis machining propeller is studied to demonstrate the proposed approach.

Reduction of geometry-based errors in five-axis machining through enhanced 5D interpolation

Geometry-based errors constitute a special category of CAM-originated machining inaccuracies that significantly influence the precision of five-axis surface machining operations. Geometry-based errors reflect the inability of the cutter to accurately trace a prescribed 3D tool path in five-axis machining. Their magnitude constitutes an overlapped effect of the adopted interpolation scheme, cutter, and surface geometries, as well as kinematics of the five-axis machine tool, assumed free of errors by the CAM software. Although the presence of these errors is inherent in the current configuration of five-axis computer numerically controlled machining systems, little efforts were made so far towards their reduction. In this regard, the present study has investigated the magnitude of geometry-based errors as generated by various 5D interpolation schemes. These enhanced interpolation functions were determined by enforcing better approximations of the ideal machine control coordinate (MCC) trajectory as calculated in five-axis machine tool’s joint space. By comparing the geometry-based errors generated by the enhanced 5D interpolation schemes with linear interpolation baseline, it was found that significant error reductions will be obtained when synchronized 5D quadratic functions are used to approximate the ideal MCC curve in joint space. Moreover, the parametric synchronization between rotational and translational machine tool motions represents an essential requirement for limitation of the amount of geometry-based errors.

The Mechanism of Surface Trajectories and Milling Forces in Micro-Milling Processing

In practical industrial processing, in order to make the tiny functional devices assembly accuracy as high as possible, which raises an very high requirement for surface quality of micro workpiece. Some of the important factors in controlling the surface quality with the level of the trajectories and forces of the blade across on the workpiece have a great relationship. This paper presents generalized mathematical models of the trochoid and forces combined with the helix cutter geometry used in the industry. And then from both of these aspects analytical laws in-depth of the trochoidal curves and micro-cutting forces variation. It will be of great reference value for the study of micro-milling mechanism.

An investigation of hybrid laser–waterjet ablation of silicon substrates

A novel hybrid laser–waterjet ablation technology is developed to minimize the thermal damages, which occur during material melting and vaporization associated with the traditional laser machining processes. With this technology, the target material is heated and softened by a laser and the softened material is expelled by a waterjet. The waterjet also takes a cooling action. Using a single-crystalline silicon as the specimen material, the process parameters relevant to the hybrid process were investigated along with the interactions between the laser and waterjet. Further, the cut geometries and the surface characteristics after machining have been experimentally studied. It has been found that almost no heat-affected zone (HAZ) with a higher material removal rate can be achieved when using this hybrid laser–waterjet technology, as compared to the conventional laser dry micromachining process.

High Performance Titanium Milling at Low Cutting Speed

When machining titanium alloys the process stability limits increase very rapidly with reduced cutting speed. The stability rise is stronger than the drop of the cutting speed and it results in growth of removal rate. The increase in removal rate results in savings of machining costs. There is definite advantage in cutter geometry with irregular pitch for increasing the limit of stability. Use of PM HSS tools at low speeds for milling titanium alloys can be the most economical option. The paper introduces the concept of load intensity for assessing tool wear in milling.