Zhi Qiang Yu

The adaptive slicing algorithm and its impact on the mechanical property and surface roughness of freeform extrusion parts

ABSTRACT In the process of fused deposition modelling, the layer thickness plays a vital role in determining the surface quality and forming time. If a larger layer thickness is adopted, the molding time will be shorter, as a result, the surface accuracy of the product will be worse at the same time. If a smaller thickness is used, the surface quality of the product can be guaranteed, but the molding time will be very long accordingly. Therefore, there exists conflict between guaranteeing the surface quality and shortening the forming time of the part. This paper adopts adaptive slicing algorithm to solve this conflict. According to the curvature of the model, an appropriate thickness value is adopted automatically where the model curvature is large, a smaller thickness value is necessary, on the contrary, a larger thickness value is used. The tensile strength experiment was made through the specimens of ASTM D638 to study the influence of layer thickness. The temperature of the first six layers in the processing of building was collected. The ultra-depth picture of the cross-sectional area showed that the temperature would affect the neck length between adjacent filaments. Moreover, the surface roughness of the cylinder with different layer thicknesses was measured and the Ra curve figures showed the surface roughness was also influenced by layer thickness. The experiment results suggested the layer thickness was a critical factor in determining mechanical property and surface roughness by changing the layer counts and the neck length between adjacent filaments. It can be noted from the experiments that the adaptive slicing algorithm was not only good at enhancing the surface accuracy and tensile strength, it could also improve the building efficiency.

Chatter Prediction for Variable Pitch and Variable Helix Milling

Regenerative chatter is a self-excited vibration that can occur during milling, which shortens the lifetime of the tool and results in unacceptable surface quality. In this paper, an improved semidiscretization method for modeling and simulation with variable pitch and variable helix milling is proposed. Because the delay between each flute varies along the axial depth of the tool in milling, the cutting tool is discrete into some axial layers to simplify calculation. A comparison of the predicted and observed performance of variable pitch and variable helix against uniform pitch and uniform helix milling is presented. It is shown that variable pitch and variable helix milling can obtain larger stable cutting area than uniform pitch and uniform helix milling. Thus, it is concluded that variable pitch and variable helix milling are an effective way for suppressing chatter.

The effect of process parameters in fused deposition modelling on bonding degree and mechanical properties

The purpose of this paper is to study the effects of these major parameters, including layer thickness, deposition velocity and infill rate, on product’s mechanical properties and explore the quantitative relationship between these key parameters and tensile strength of the part.,A VHX-1000 super-high magnification lens zoom three-dimensional (3D) microscope is utilized to observe the bonding degree between filaments. A temperature sensor is embedded into the platform to collect the temperature of the specimen under different parameters and the bilinear elastic-softening cohesive zone model is used to analyze the maximum stress that the part can withstand under different interface bonding states.,The tensile strength is closely related to interface bonding state, which is determined by heat transition. The experimental results indicate that layer thickness plays the predominant role in affecting bonding strength, followed by deposition velocity and the effect of infill rate is the weakest. The numerical analysis results of the tensile strength predict models show a good coincidence with experimental data under the elastic and elastic-softened interface states, which demonstrates that the tensile strength model can predict the tensile strength exactly and also reveals the work mechanism of these parameters on tensile strength quantitatively.,The paper establishes the quantitative relationship between main parameters including layer thickness, infill rate and deposition velocity and tensile strength for the first time. The numerically analyzed results of the tensile strength predict model show a good agreement with the experimental result, which demonstrates the effectiveness of this predict model. It also reveals the work mechanism of the parameters on tensile strength quantitatively for the first time.

The Quantitative Research of Interaction between Key Parameters and the Effects on Mechanical Property in FDM

The central composite design (CCD) experiment is conducted to evaluate the interaction between parameters and the effect on mechanical property. The layer thickness, deposition velocity, and air gap are considered as the key factors. Three disparate levels of the parameters are utilized in the experiment. The experimental results suggest that all these parameters can affect the bonding degree of the filaments, which affects the final tensile strength of the specimen. A new numerical model is built to describe the cooling process of the fused filament, which shows a perfect coherence with the practical temperature file of filament. It reveals what the forming mechanism of the bonding between filaments is and how these parameters act on final tensile strength of the specimen of this way from temperature. It is concluded that the parameters are not working alone; in fact they all contribute to determining the mechanical property, while the air gap plays the predominant role in determining the final tensile strength, followed by layer thickness as the next predominant factor, and the effect of deposition velocity is the weakest factor.

Instantaneous Uncut Chip Thickness Model in End Milling Based on an Improved Method

The instantaneous uncut chip thickness is an important parameter in the study of milling force model. By analyzing the real tooth trajectory in milling process, accurate instantaneous uncut chip thickness can be obtained to solve the complex transcendental equation. Traditional chip thickness models always simplify the tooth trajectory to get approximate solution. A new instantaneous uncut chip thickness model is proposed in this paper. Based on real tooth trajectory of general end milling cutter, a Taylors series is used to approximate the involved infinitesimal variable in the transcendental equation, which results in an explicit expression for practical application of the uncut chip thickness with higher accuracy compared to the traditional model.

An FPGA-based low-cost VLIW floating-point processor for CNC applications

Abstract In the high-speed free-form surface machining, the real-time motion planning and interpolation is a challenging task. This paper presents the design and implementation of a dedicated processor for the interpolation task in computerized numerical control (CNC) machine tools. The jerk-limited look-ahead motion planning and interpolation algorithm has been integrated in the interpolation processor to achieve smooth motion in the high-speed machining. The processor features a compactly designed floating-point parallel computing architecture, which employs a 3-stage pipelined reduced instruction set computer (RISC) core and a very long instruction word (VLIW) floating-point arithmetic unit. A new asynchronous execution mechanism has been employed in the processor to allow multi-cycle instructions to be performed in parallel. The proposed processor has been verified on a low-cost field programmable gate array (FPGA) chip in a prototype controller. Experimental result has demonstrated the significant improvement of the computing performance with the interpolation processor in the free-form surface machining.

The Digital Manufacturing Equipment and Development of High Speed and High Precision with Monitoring and Intelligent Maintenance

With the development of science technology in aerospace, automobile and ship, energy and military, the product parts space type face increasingly complex and surface quality requirements more stringent. So there are higher requirements to the digital manufacturing equipment to realize high speed and high precision machining. This paper summary the related research in condition monitoring, remote control, fault diagnosis and intelligent maintenance, and based on the lack of monitoring and diagnosis technology of whole life cycle, unperfected quality control technique, the lower intelligent level in the current equipment, it establish full range monitoring and the whole life cycle of the intelligent maintenance system and present fault diagnosis, control and maintenance solutions for the whole life cycle, and point out the new development direction of the integrated monitoring and intelligent maintenance in CNC equipment.

A Transient Faults Diagnosis Method Based on EEMD, Spectral Kurtosis Theory and Energy Operator Demodulating

When an early fault turns up in rotating machinery, the normal vibration signal will be modulated with periodic transient shock pulses. It’s significant to diagnose these periodic shock pulses for early fault prognostic and diagnostic tests. Usually demodulating is one of the most effective and common used method. Because of the strong background noise, it’s very difficult to select the parameters of band-pass filter. In this paper, we propose to use Ensemble Empirical Mode Decomposition (EEMD) coordinating with spectrum kurtosis theory to choose the Intrinsic Mode Functions (IMFs) to reduce the background noise and select the parameters of band-pass filter adaptively by fast-kurtogram. Energy operator demodulating method is used to demodulate the rebuilt signal to identify the faults frequencies. Energy operator demodulating displays better accuracy and little edge error. The achieved accuracy in the simulation indicates that this proposed transient faults diagnosis method is highly reliable and applicable in early transient faults diagnosis of industrial rotating machinery.

The Research of Straight Bevel Gear Face-Hobbing Method on General Five-Axis Machine Tool

To avoid the influence of column vibration on machining precision, it is necessary to simulate the stiffness characteristics of the columns for CNC grinding machine, and to optimize the structure of the column by using sensitivity method. Based on structural characteristics of the grinding machine and structural characteristics of the columns, a finite element model is established to simulate and calculate the first-four models of the columns. In order to optimize the structure of the column, a sensitivity analysis is made to calculate the sensitivity of natural frequencies and mass of the column to each panel and ribbed plate. Considering a weighting factor and taking integrated natural frequency of the column as an optimization objective, the mass of the column as a constraint, an optimization equation is established. By a quadratic programming method, the parameter optimization of the column is got as follows: the mass decreased by 4%, integrated natural frequency increased by 2%. Dynamic stiffness of the column has been optimized by harmonic response analysis, the results showed that the largest column in the Z resonance peak reduced by 8.44%.

Dynamics Simulation Analysis of Column for NC Bevel Gear Grinder

To avoid the influence of column vibration on machining precision, it is necessary to simulate the stiffness characteristics of the columns for CNC grinding machine, and to optimize the structure of the column by using sensitivity method. Based on structural characteristics of the grinding machine and structural characteristics of the columns, a finite element model is established to simulate and calculate the first-four models of the columns. In order to optimize the structure of the column, a sensitivity analysis is made to calculate the sensitivity of natural frequencies and mass of the column to each panel and ribbed plate. Considering a weighting factor and taking integrated natural frequency of the column as an optimization objective, the mass of the column as a constraint, an optimization equation is established. By a quadratic programming method, the parameter optimization of the column is got as follows: the mass decreased by 4%, integrated natural frequency increased by 2%. Dynamic stiffness of the column has been optimized by harmonic response analysis, the results showed that the largest column in the Z resonance peak reduced by 8.44%.