A New Method for Identification and Modeling of Process Damping in Machining

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
E. Budak ◽  
L. T. Tunc
Keyword(s):  
Stability Limit ◽  
Damping Coefficient ◽  
Test Results ◽  
Limited Data ◽  
Damping Force ◽  
Process Damping ◽  
Analytical Stability ◽  
Practical Model ◽  
The Stability ◽  
Stability Limits

Although process damping has a strong effect on cutting dynamics and stability, it has been mostly ignored in chatter analysis as there is no practical model for estimation of the damping coefficient and very limited data are available. This is mainly because of the fact that complicated test setups were used in order to measure the damping force in the past. In this study, a practical identification and modeling method for the process damping is presented. In this approach, the process damping is identified directly from the chatter tests using experimental and analytical stability limits. Once the process damping coefficient is identified, it is related to the instantaneous indentation volume by a coefficient which can be used for different cutting conditions and tool geometries. In determining the indentation coefficient, chatter test results, energy, and tool indentation geometry analyses are used. The determined coefficients are then used for the stability limit and process damping prediction in different cases, and verified using time-domain simulations and experimental results. The presented method can be used to determine chatter-free cutting depths under the influence of process damping for increased productivity.

An Analytical Design Method for Milling Cutters With Non-Constant Pitch to Increase Stability

2000 ◽  
Author(s):  
Erhan Budak
Keyword(s):  
Surface Finish ◽  
Design Method ◽  
Stability Limit ◽  
Analytical Stability ◽  
Chatter Vibrations ◽  
Constant Pitch ◽  
Improved Stability ◽  
Limited Frequency ◽  
The Stability ◽  
Explicit Relation

Abstract Chatter vibrations result in reduced productivity, poor surface finish and decreased cutting tool life. Milling cutters with non-constant pitch angles can be very effective in improving the stability of the process against chatter. In this paper, an analytical stability model and a design method are presented for non-constant pitch cutters. An explicit relation is obtained between the stability limit and the pitch variation which leads to a simple equation for optimal pitch angles. A certain pitch variation is effective for limited frequency and speed ranges which are also predicted by the model. The improved stability, productivity and surface finish are demonstrated by several examples.

An improved semi-analytical approach for modeling of process damping in orthogonal cutting considering cutting edge radius

2019 ◽  
Vol 234 (3) ◽  
pp. 641-653 ◽  
Author(s):  
Chang Cao ◽  
Xiao-Ming Zhang ◽  
Tao Huang ◽  
Han Ding
Keyword(s):  
Computational Efficiency ◽  
Orthogonal Cutting ◽  
Finite Amplitude ◽  
Cutting Edge ◽  
Workpiece Surface ◽  
Process Damping ◽  
Flank Face ◽  
The Stability ◽  
The Time Domain ◽  
Stability Limits

Process damping generated between the tool flank face and the wavy finish workpiece surface has a non-negligible effect on cutting dynamics and chatter stability, especially at low cutting speeds, resulting in higher stability limits. In modeling of process damping, the calculation of extruded volume is one of the most critical challenges, especially in machining with honed tools due to the complex and time-variable contact condition between the arc cutting edge and the finite amplitude wave surface. In this study, a semi-analytical method with high computational efficiency is proposed to calculate the extruded volume in cutting with honed tools. Based on this method, we construct the stability lobes under the condition of finite vibration amplitude accurately and efficiently, which overcomes the limitation of analytical methods based on the assumption of small amplitude vibrations and the low computational efficiency of numerical method. The predicted cutting stability is verified against both the experimental results and the time-domain simulation results.

Design and Test of a Semi-Passive Flow Control Device for Inlet Distortion Suppression

2000 ◽  
Author(s):  
Link C. Jaw ◽  
William T. Cousins ◽  
Dong N. Wu ◽  
David J. Bryg
Keyword(s):  
Stability Limit ◽  
Stability Margin ◽  
Aircraft Engine ◽  
Major Effect ◽  
Prototype System ◽  
Test Results ◽  
Inlet Distortion ◽  
Temperature And Pressure ◽  
The Stability ◽  
Suppression System

Advanced turbine engines often operate with reduced stability margin to increase performance. Aircraft engine temperature and pressure inlet distortion has a major effect upon the stability of the compression system. Suppression of inlet distortion can provide greater stability margin for the engine, thereby reducing operability restrictions on the engine by allowing closer operation to the stability limit. SMI has designed and tested a semi-passive distortion suppression system. The system uses flow injection to modify temperature and pressure inlet distortion. The prototype system was tested on a Honeywell T55 compressor rig. This paper presents both the design of the system and the test results. The test results show that this semi-passive distortion suppression system was able to reduce the surge margin degradation caused by the presence of pressure or temperature distortion. Special design considerations for this type of system are discussed, based upon the results of the prototype test. It is shown that distortion control can be a viable addition to the design of an aircraft engine.

Design and Test of a Semi-Passive Flow Control Device for Inlet Distortion Suppression

2000 ◽  
Vol 123 (1) ◽  
pp. 9-13 ◽  
Author(s):  
Link C. Jaw ◽  
William T. Cousins ◽  
Dong N. Wu ◽  
David J. Bryg
Keyword(s):  
Stability Limit ◽  
Stability Margin ◽  
Aircraft Engine ◽  
Major Effect ◽  
Prototype System ◽  
Test Results ◽  
Inlet Distortion ◽  
Temperature And Pressure ◽  
The Stability ◽  
Suppression System

Advanced turbine engines often operate with reduced stability margin to increase performance. Aircraft engine temperature and pressure inlet distortion have a major effect upon the stability of the compression system. Suppression of inlet distortion can provide a greater stability margin for the engine, thereby reducing operability restrictions on the engine by allowing closer operation to the stability limit. SMI has designed and tested a semi-passive distortion suppression system. The system uses flow injection to modify temperature and pressure inlet distortion. The prototype system was tested on a Honeywell T55 compressor rig. This paper presents both the design of the system and the test results. The test results show that this semi-passive distortion suppression system was able to reduce the surge margin degradation caused by the presence of pressure or temperature distortion. Special design considerations for this type of system are discussed, based upon the results of the prototype test. It is shown that distortion control can be a viable addition to the design of an aircraft engine.

Identification and Modeling of Process Damping in Milling

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
L. T. Tunc ◽  
E. Budak
Keyword(s):  
Energy Balance ◽  
Time Domain ◽  
Stability Limit ◽  
Process Damping ◽  
Damping Coefficients ◽  
Tool Geometries ◽  
Different Types ◽  
Stability Limits ◽  
Milling Tools ◽  
Cutting Speeds

In this study, a practical identification method for process damping is presented for milling, and the information obtained from identification is used for modeling purposes. In the proposed approach, the process-damping coefficients in x and y directions are identified directly from the experimental stability limits. Then, they are used in identification of the indentation constant through energy balance formulation. The identified indentation constant is further used in modeling of process damping and estimation of stability limit for different cutting conditions and tool geometries. Milling tools with two different types of flank geometries, namely, planar and cylindrical, are considered in this study. The predictions are verified by time-domain simulations and experimental results. It is shown that the presented method can be used for identification and modeling of process damping in milling to determine chatter-free cutting depths at relatively low cutting speeds.

An Analytical Design Method for Milling Cutters With Nonconstant Pitch to Increase Stability, Part I: Theory

2003 ◽  
Vol 125 (1) ◽  
pp. 29-34 ◽  
Author(s):  
E. Budak
Keyword(s):  
Surface Finish ◽  
Design Method ◽  
Stability Limit ◽  
Analytical Stability ◽  
Chatter Vibrations ◽  
Improved Stability ◽  
Limited Frequency ◽  
The Stability ◽  
Explicit Relation

Chatter vibrations result in reduced productivity, poor surface finish and decreased cutting tool life. Milling cutters with nonconstant pitch angles can be very effective in improving stability against chatter. In this paper, an analytical stability model and a design method are presented for nonconstant pitch cutters. An explicit relation is obtained between the stability limit and the pitch variation which leads to a simple equation for determination of optimal pitch angles. A certain pitch variation is effective for limited frequency and speed ranges which are also predicted by the model. The improved stability, productivity and surface finish are demonstrated by several examples in the second part of the paper.

Percentiler and Flagger – low-cost, on-line monitoring of laboratory and manufacturer data and significant surplus to current external quality assessment

2018 ◽  
Vol 42 (6) ◽  
pp. 289-296 ◽  
Author(s):  
Linda M. Thienpont ◽  
Dietmar Stöckl
Keyword(s):  
Low Cost ◽  
Biological Variation ◽  
Analytical Performance ◽  
Performance Goals ◽  
Web Based ◽  
Analytical Stability ◽  
Performance Specifications ◽  
On Line ◽  
The Stability ◽  
Stability Limits

AbstractBackground:We developed two web-based applications called the “Percentiler” and “Flagger”. They use electronically sent data from the analysis of patient samples (medians in the Percentiler; % flagging in the Flagger). Through a graphical user interface, the applications allow on-line monitoring of the stability of analytical performance and flagging rate, both assessed against quality specifications. These are guided by biological variation (Percentiler) and effect of analytical instability on surrogate medical decisions (Flagger). Here, we report on the use of the applications.Methods:We constructed examples with combined observations to investigate whether the Flagger adequately translates the effect of analytical instability observed in the Percentiler, and whether the changes in the flagging rate tolerated by the proposed stability limits is realistic in combination with the analytical performance goals.Results:In general, the examples show that the most prominent flagging rates correlate well with the analytical stability and that the limits proposed for the Flagger are realistically linked to those of the Percentiler. They also show that for certain analytes the specifications for stable flagging rates can be restricted to 20% (relatively to the laboratory’s long-term flagging median) despite ambitious analytical performance goals, while for others they need to be expanded up to 70% in concordance with decreasing biological variation.Conclusions:The examples confirm that the changes in flagging rate is well related to the analytical variation, and that the proposed stability limits are fit-for-purpose. The combined observations may help individual laboratories to define realistic but ambitious performance specifications that apply for their local situation.

scholarly journals Laboratory sample stability. Is it possible to define a consensus stability function? An example of five blood magnitudes

2018 ◽  
Vol 56 (11) ◽  
pp. 1806-1818 ◽  
Author(s):  
Rubén Gómez Rioja ◽  
Débora Martínez Espartosa ◽  
Marta Segovia ◽  
Mercedes Ibarz ◽  
María Antonia Llopis ◽  
...  
Keyword(s):  
Specific Antigen ◽  
Stability Limit ◽  
Medical Laboratory ◽  
Stability Function ◽  
Measured Property ◽  
Bibliographic Search ◽  
The Stability ◽  
Conditions Of Stability ◽  
Time Required ◽  
Stability Limits

Abstract Background: The stability limit of an analyte in a biological sample can be defined as the time required until a measured property acquires a bias higher than a defined specification. Many studies assessing stability and presenting recommendations of stability limits are available, but differences among them are frequent. The aim of this study was to classify and to grade a set of bibliographic studies on the stability of five common blood measurands and subsequently generate a consensus stability function. Methods: First, a bibliographic search was made for stability studies for five analytes in blood: alanine aminotransferase (ALT), glucose, phosphorus, potassium and prostate specific antigen (PSA). The quality of every study was evaluated using an in-house grading tool. Second, the different conditions of stability were uniformly defined and the percent deviation (PD%) over time for each analyte and condition were scattered while unifying studies with similar conditions. Results: From the 37 articles considered as valid, up to 130 experiments were evaluated and 629 PD% data were included (106 for ALT, 180 for glucose, 113 for phosphorus, 145 for potassium and 85 for PSA). Consensus stability equations were established for glucose, potassium, phosphorus and PSA, but not for ALT. Conclusions: Time is the main variable affecting stability in medical laboratory samples. Bibliographic studies differ in recommedations of stability limits mainly because of different specifications for maximum allowable error. Definition of a consensus stability function in specific conditions can help laboratories define stability limits using their own quality specifications.

scholarly journals Stability Research Considering Non-Linear Change in the Machining of Titanium Thin-Walled Parts

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2083 ◽  
Author(s):  
Haining Gao ◽  
Xianli Liu
Keyword(s):  
Titanium Alloy ◽  
Prediction Model ◽  
Dynamic Characteristics ◽  
Material Removal ◽  
Milling Process ◽  
Damping Coefficient ◽  
Linear Change ◽  
Process Damping ◽  
Thin Walled ◽  
The Stability

Aiming to solve the problem whereby the damping process effect is significant and difficult to measure during low-speed machining of titanium alloy thin-walled parts, the ploughing coefficient of the flank face is obtained based on the frequency-domain decomposition (FDD) of the measured vibration signal and the energy balance principle, and then the process-damping prediction model is obtained. Aiming to solve the problem of non-linear change of dynamic characteristics of a workpiece caused by the material removal effect in the machining of titanium alloy thin-walled parts, a prediction model of dynamic characteristics of a workpiece is established based on the structural dynamic modification method. Meanwhile, the effect of material removal on the process-damping coefficient is studied, and the internal relationship between the process-damping coefficient and the dynamic characteristics of the workpiece is revealed. The stability lobe diagram is obtained by the full discretization in the titanium alloy milling process. The correctness of the model and stability prediction is verified by experiments under different working conditions. It is found that the coupling characteristics of process-damping and workpiece dynamic characteristics control the stability of the milling process. The research results can provide theoretical support for accurate characterization and process optimization of titanium alloy thin-walled workpiece milling.

Stability, Accuracy, and Efficiency of Sequential Methods for Coupled Flow and Geomechanics

SPE Journal ◽  
2011 ◽  
Vol 16 (02) ◽  
pp. 249-262 ◽  
Author(s):  
J.. Kim ◽  
H.A.. A. Tchelepi ◽  
R.. Juanes
Keyword(s):  
Numerical Solutions ◽  
Stability Limit ◽  
Stability And Convergence ◽  
Coupled Flow ◽  
Unconditionally Stable ◽  
Von Neumann ◽  
Solution Strategies ◽  
Solution Methods ◽  
The Stability ◽  
Stability Limits

Summary We perform detailed stability and convergence analyses of sequential-implicit solution methods for coupled fluid flow and reservoir geomechanics. We analyze four different sequential-implicit solution strategies, where each subproblem (flow and mechanics) is solved implicitly: two schemes in which the mechanical problem is solved first—namely, the drained and undrained splits—and two schemes in which the flow problem is solved first—namely, the fixed-strain and fixed-stress splits. The von Neumann method is used to obtain the linear-stability criteria of the four sequential schemes, and numerical simulations are used to test the validity and sharpness of these criteria for representative problems. The analysis indicates that the drained and fixed-strain splits, which are commonly used, are conditionally stable and that the stability limits depend only on the strength of coupling between flow and mechanics and are independent of the timestep size. Therefore, the drained and fixed-strain schemes cannot be used when the coupling between flow and mechanics is strong. Moreover, numerical solutions obtained using the drained and fixed-strain sequential schemes suffer from oscillations, even when the stability limit is honored. For problems where the deformation may be plastic (nonlinear) in nature, the drained and fixed-strain sequential schemes become unstable when the system enters the plastic regime. On the other hand, the undrained and fixed-stress sequential schemes are unconditionally stable regardless of the coupling strength, and they do not suffer from oscillations. While both the undrained and fixed-stress schemes are unconditionally stable, for the cases investigated we found that the fixed-stress split converges more rapidly than the undrained split. On the basis of these findings, we strongly recommend the fixed-stress sequential-implicit method for modeling coupled flow and geomechanics in reservoirs.

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