Modelling and prevention of meshing interference in gear skiving of internal gears

Gear skiving is a highly productive process for machining of internal gears which are required in large quantity for electric mobility transmissions. Due to the complex kinematics of gear skiving, collisions of the tool and workpiece can occur during the process. Models exist to check for collisions of the tool shank or collisions in the tool run-out. While these models are sufficient for the process design of external gear skiving, at internal gears meshing interferences between tool and workpiece can appear outside the contact plane on the clearance face of the tool. To test for meshing interference requires comprehensive assessment of workpiece, tool and process kinematics. Currently, this is often done by time consuming CAD-simulation. In contrast, this paper presents an automated geometrical model for the analysis of meshing interference. The test for collisions is thereby performed along the whole height of the tool and especially includes constructive clearance angles and eccentric tool positions. The model is developed for user-friendly implementation and practical applications. The model for avoiding meshing interference in gear skiving is validated on two different process applications. In doing so, influences of the tool and process design on the interference situation are investigated, compared and discussed. Furthermore this new approach enables the prevention of meshing interference or tooth tip collisions in the early tool design by adjusting the process kinematics or the tool design itself. The maximal viable tool height can be quantified and recommendations for improving the clearance face situation are suggested.

Influence of the microstructure of tool coatings based on Ti and Al on the blunting process during chipboard processing

Influence of the microstructure of tool coatings based on Ti and Al on the blunting process during chipboard processing.This work concerns three different tool coatings containing Ti and Al. i.e. TiN, AlTiN, TiAlSiN applied to cutting tools used in the machining of wood materials. In the case of the AlTiN coating, a multilayer structure with alternately arranged AlTiN and TiN nano-layers was used. The above coatings were applied to standard replaceable knives used for CNC milling heads made of WC-Co cemented carbide. The deposition process was carried out using the RF Magnetron Sputtering method. During the measurement on a workshop microscope, the VBmax index measured on the clearance face was adopted as the wear criterion. The research proved a very good behaviour of the TiN/AlTiN multilayer coating, for which the longest average service life which was recorded exceeded the results obtained for the reference tool by about 30%. The addition of silicon, which was supposed to increase the abrasion resistance, only did not improve the durability of the blade, it actually worsened it by 6%. In addition, the coating, which has been widely used in the machine industry for a very long time, i.e. TiN, did not extend the tool life significantly (+ 7%).

Characteristic of the wear of a tool coating based on amorphous carbon during chipboard milling

Characteristic of the wear of a tool coating based on amorphous carbon during chipboard milling. The study verified the durability and the course of wear during the durability tests of the TiAlN / a-C:N double tool coating. The aforementioned coating consisted of a bottom layer of TiAlN and a top layer based on nitrogenenriched amorphous carbon. Standard replaceable cutters for milling heads made of WC-Co sintered carbide were subjected to the modification process. The coating was applied using plasma by RF Magnetron Sputtering. During the tests, the blade wear was measured using a workshop microscope. The VB max indicator measured on the clearance face was adopted as the blunting criterion and its maximum value was set on 0,2 mm. The results show that the additional coating of amorphous carbon contributed to the increase of the tool durability determined with cutting distance. The use of only a single layer based on TiAlN shortened the durability by about 3%. On the other hand, applying both the bottom and top layers TiAlN /a-C:N) extended the cutting distance by about 24%. The research showed a clear advantage in terms of the durability of the blades modified with a multi-layer coating in relation to a single-layer. Moreover, the positive effect of the top layer containing amorphous carbon on tool durability has been demonstrated.

On the Formation Mechanisms of Adhering Layer during Machining Metal Material

Built-up Layer (BUL)/Built-up Edge (BUE) formed on the tool surface can be treated as a protective, thermal barrier or lubricant films especially in the extreme severe conditions when machining the metal materials, which can sustain the tool effective and wear resistance. In order to have a thorough understanding of the adhesion effect during machining, experiments have been carried out to investigate the performance and the formation mechanisms of adhering layer on the carbide tool in machining of aluminium alloys A6063, carbon steel S45C and difficult-to-cut hardened steel S45C (H-S45C). The morphology of tool adhered surface was examined by employing Scanning Electron Microscopy (SEM), the dimensions of adhering layer were measured by Laser Scanning Microscopy (LSM) and the elements on the tool were analyzed by Electron Probe Micro Analyser (EPMA), respectively. The atomic-scale cluster adhesive friction model is proposed to explain the tool-chip contact conditions, which considers the nature of the shear strain, shear strain rate and temperature distribution in the secondary deformation zone. The model is a dynamic model and the rate equation approach can be applied to estimate the formation process of adhering layer during machining. Results have shown that the adhering layer will give rise to BUL on the tool rake face and the BUE on the cutting edge and clearance face.

Analytical Model Approach for Tool Temperature Prediction in Broaching Nickel-Based Alloys

The following article suggest an analytical model approach for tool temperature prediction in broaching nickel-based alloys. The presented approach is based on an existing model proposed by Komanduri and Hou in 2001, however, includes several modifications in order to better describe the phenomena observed in thermo-graphic measurements acquired during broaching experiments. The novel model approach includes different assumptions regarding the location of heat sources in the cutting zone as well as adiabatic boundary conditions. Moreover, an advancement of the model was made to regard variable contact conditions between tool clearance face and work piece caused by tool wear.

Machinability of ZTC4 Titanium Alloy Analysis Using Finite Element Simulation and Milling Experiment

In this paper Finite element methods (FEM) and cutting experiment were used to investigate the machinability of titanium alloy ZTC4 (cast Ti6Al4V). Machinability was evaluated as cutting force, temperature, and surface roughness. Two-dimension (2D) and three-dimension (3D) machining process FEM models were established. Material constitutive applied Johnson-Cook model synthesizing elastic and plastic deformation. Chip separated criteria adopted arbitrary Lagrangian Euler (ALE) algorithm. Heat generation source included the rake face chip flow under conditions of seizure and chip/tool friction, clearance face tool/workpiece friction. 3D discrete milling tool was modeled and the milling process was simulated. The ZTC4 milling experiments were designed and carried out with same cutting conditions of the 3D FEM simulation. The results of FEM simulation and the experiment were compared and analysed. The influences of the machining variables to the machinability of ZTC4 were discussed.

Cutting Forces Modeling in Finish Turning of Inconel 718 Alloy with Round Inserts

In turning, the applied forces have to be known as accurately as possible, especially in the case of difficult-to-cut materials for aircraft workpieces finishing operations. Traditionally, edge discretisation methodology based on local cutting laws is used to determine the cutting forces and results are usually considered suitable. Nevertheless, only the rake face is considered in most of studies and the cutting relations are determined by direct identification with a straight edge. This study deals with finishing operations of Inconel 718 alloy with one type of round insert. The main objective is to formulate a novel cutting forces model, taking into account the clearance face. First, a generic model based on a geometrical description using homogeneous matrix transformation is presented. Then, cutting coefficients are identified by inverse identification from experimental measurements distributed with an orthogonal design experiment including tool wear. Finally, modeling and experimental values of the cutting forces are compared and the identified model is analysed.

Finite Element Simulation of Ultrasonic Vibration Orthogonal Cutting of Ti6Al4V

In this paper Finite Element Methods (FEM) were used to simulate the ultrasonic vibration Orthogonal cutting of titanium alloy Ti6Al4V. Machining conditions were similar to those used for manufacture. Material constitutive applied Johnson-Cook model combining elastic and plastic deformation, the material hardening for extreme shear strain and strain rate, material softening for adiabatic shear of chip flow-zone. Chip separated criteria adopted arbitrary Lagrangian Euler algorithm (ALE). Heat sources included the rake face chip flow under conditions of seizure and chip/tool friction, clearance face tool/workpiece friction. Thus, the orthogonal ultrasonic vibration machining of Ti6Al4V FEM models were established. The simulation results included the chip formation, the cutting force/stress and temperature distributions through the primary shear zone and the chip/tool contact region. The cutting force, cutting temperature of the ultrasonically and conventionally machining were compared. The reasons of the decrease of chip deformation coefficients, cutting force and temperature and the increase of shear angle in ultrasonic machining were discussed.

Failure Mechanism of Twist Drill in Vibration Drilling of Duralumin

Based on experiments of common drilling and vibration drilling on duralumin (2A12), the failure mode and failure reason of twist drill are studied theoretically and experimentally. The result shows that, compared with common drilling, the wear of clearance face and rake face decreases evidently during vibration drilling, and the wear of chisel edge and marginal point of twist drill hardly happens. Moreover the probability of drill breakage is very low during vibration drilling. However, if amplitude is bigger, the tipping of chisel edge often appears.

A comparison of temperature reduction in high-pressure jet-assisted turning using high pressure versus high flowrate

Cooling with high pressures in turning operations is an effective method for providing higher productivity. Reduced temperature and improved chip control are dependent on the pressure and flowrate of the fluid jet. The aim of the tests was to investigate how the relationship between pressure and flowrate affects the heat dissipation from the cutting zone. Tests were performed on two steel grades and one titanium alloy, allowing the same jet momentum for all materials to enable comparison between pressure and flow. Conventional cooling was used as a reference. Measurements were conducted with thermocouples attached to the clearance face of the tool. The temperature was generally reduced by approximately 50 per cent when high-pressure cooling was applied compared with conventional cooling. The results show that different pressure and flow relationships have a small but significant influence on heat dissipation from the cutting zone for the steel materials. Results show that it is important to have the right combination of pressure and flow in order to achieve optimum temperature reduction. Materials with a higher ductility benefit more from a higher flowrate while materials with a lower ductility require higher pressure. The same jet momentum was used in both cases.