Keith E. Rouch

A study of cutting process stability of a boring bar with active dynamic absorber

Abstract In this paper, the use of an active dynamic absorber to suppress machine tool chatter in a boring bar is studied. The vibrations of the system are reduced by moving an absorber mass using an active device such as an piezoelectric actuator, to generate an inertial force that counteracts the disturbance acting on the main system. An equivalent lumped mass model of a boring bar with active dynamic absorber is considered. A cutting process model that considers the dynamic variation of shear and friction angle, that causes self-excited chatter during the cutting process, is applied to the lumped mass model. The theory of regenerative chatter is also applied to the model. Stability boundaries have been calculated for maximum permissible width of cut as a function of cutting speed. A comparison of the boundaries for chatter-free cutting operation of a plain boring bar, a boring bar with passive tuned dynamic absorber and a boring bar with active dynamic absorber is provided in this paper. The comparison shows that a substantial increase in the maximum permissible width of cut for stable cutting operation, over a range of cutting speeds, is obtained for a boring bar equipped with an active dynamic absorber.

Product Sustainability Index (ProdSI)

As a result of the rapidly depleting global resources, continuing climate change and increasing environmental pollution, and the associated growth in customer awareness, improving product sustainability has become a global trend. Comprehensive sustainability assessment techniques are needed to assess a products sustainability performance throughout its entire life cycle. This article presents the Product Sustainability Index (ProdSI) methodology and its application. This methodology is metrics based and provides a comprehensive assessment of the overall product sustainability throughout its total life cycle, covering the four life cycle stages: pre‐manufacturing; manufacturing; use; and postuse. In this article, first the fundamentals of sustainable manufacturing and product sustainability assessment (PSA) are presented, followed by a review of existing PSA methodologies. Major product sustainability elements that are used to define product sustainability clusters and individual sustainability metrics are then presented. Finally, the ProdSI methodology for PSA, which follows a hierarchical approach for sustainability metrics identification and overall PSA, is introduced. The application of the methodology is demonstrated in a numerical example of ProdSI evaluation for two generations of a consumer electronics component.

Towards integration of hybrid models for optimized machining performance in intelligent manufacturing systems

Abstract This paper discusses integration issues involved in comprehensive evaluation of optimized machining performance for intelligent manufacturing systems . Machining performance is evaluated by major measures such as cutting forces/power/torque, tool-wear/tool-life, chip-form/chip breakability, surface roughness/surface integrity and part accuracy. The machining performance is discussed from a systems framework comprising three primary elements that constitute a machining system; the machine tool , cutting tool and work material . Hybrid methodologies, comprising suitable blends of different modeling techniques are emphasized in this paper. These models can be supplemented by sensory data which defines the unique characteristics of a specific machining system. The modeling of machining performance using traditional techniques, hybrid methodologies and sensor-based information is followed by optimization methods to obtain the optimized machining performance for the specific machining system. The presented methodology provides an effective means for developing intelligent , integrated models and optimization modules within modern machine tools to enable instantaneous assessment of machining performance with suitable on-line process and control strategies.

Use of finite element structural models in analyzing machine tool chatter

It is widely accepted and well-documented that regenerative machine tool chatter is due to system instability. It is also well-known that machining system stability depends on both structural parameters and cutting process parameters. This paper focuses on the use of structural finite element (FE) models in the stability analysis of turning operations. The method presented allows for inclusion of both cutting tool and workpiece flexibility in the analysis. A structural model representing the machine tool system is created using the commercial FE code, ANSYS. This structural model can include practically any degree of detail desired. The structural model is then imported into a stand-alone FORTRAN program, which incorporates a cutting process model, and calculates the lobed borderline of stability. Numerical examples are provided.

A Metrics-Based Methodology for Establishing Product Sustainability Index (ProdSI) for Manufactured Products

The paper presents a new methodology for generating the five-level Product Sustainability Index (ProdSI) based on a set of product sustainability metrics. The evaluation method includes processes of data normalization, weighting and aggregation. Data normalization is applied to convert measured physical data into dimensionless scores that each metric specifies. Weighting factors are assigned and the priority evaluation methodologies are discussed. The normalized data is aggregated to generate a ProdSI score to represent the actual sustainability content in the product. Finally, a demonstration of the methodology is presented with a numerical example.

Active optimal vibration control using dynamic absorber

A typical spring-lumped mass system undergoing forced vibrations is discussed. A secondary absorber mass connected to the main system through an active force generating element (such as a piezoelectric pusher) is considered as a viable means of suppressing vibrations of the system. State variable techniques are used to formulate the complete system, and optimal state feedback control is studied for such a system. Two approaches for optimal control are taken. First, an optimal control law for a system with known disturbance is considered, while in the second approach optimal control for a linear quadratic regulator problem is studied. The response of the system obtained with optimal control is compared with the response under no control. The results obtained from the two approaches of optimal control are then compared. The results are also compared with those obtained from a previous study of an active dynamic absorber.<<ETX>>

A finite element analysis of the effects of the abdomen on regional lung expansion

A finite element model of the dog lung, heart and abdomen, consisting of three solid linearly elastic bodies, was developed to study the effects of gravity on the vertical stress distribution and lung volume in different body positions at functional residual capacity (FRC). The geometry of the lung was obtained from an isolated dried dog lung after inflation to total lung capacity (TLC). The compliance of the rib cage, diaphragm and the abdomen was simulated by spring elements located on their surfaces. In the prone position, gravitational forces acting only on the lung contributed to the vertical gradient (0.19 cmH2O/cm) in transpulmonary pressure (Ptp). This result was independent of chest wall compliance. In the supine position, the addition of the heart and abdomen with a compliant diaphragm and abdominal walls increased the vertical Ptp gradient to 0.53 cmH2O/cm. In the head-up (upright) position, both heart and abdominal weight contributed to the vertical gradient (0.47 cmH2O/cm). Diaphragmatic compliance was of less importance to the vertical gradient in the head-up and head-down positions in the absence of the abdomen. The smallest vertical gradient (0.11 cmH2O/cm) was obtained in the head-down position with abdominal weight reducing the gradient caused by lung weight. Lung volume at FRC was virtually unaffected by gravity in the prone body position, was reduced by gravity in the supine and head-down positions but increased in the head-up position. The effects of a compliant diaphragm and abdominal weight are important contributors to the distribution of stress and volume in the intact lung.

Experimental Evaluation of Squeeze Film Damper Coefficients with Frequency Domain Techniques

This paper describes the procedures and results of an experimental approach for obtaining dynamic properties of a squeeze film damper design. A hydraulic actuator was used to apply a sinusoidal force to the damper mounted in the bearing housing over a frequency range. A load cell and a displacement probe provided the data for response and stimulus, which were then processed into amplitude and phase components for the transfer function between input and output. This transfer function was then further sampled and processed to provide directly the stiffness and damping coefficients. The paper provides a discussion of the experimental unit, the techniques used for testing and analysis of data, and presents typical results for comparison with theory over a range of excitation frequencies and viscosities. The effect of fluid inertia is confirmed at high frequencies and low viscosities.

Active vibration control via electromagnetic dynamic absorbers

An actively controlled electromagnetic absorber is considered for reducing the chatter in a boring bar. The absorber is suspended inside the free end of the boring bar and consists of a mass with four poles, each pole having a coil attached to it. In the present study, the magnetic force, which is inherently a nonlinear function of current and air gap, is approximated using linearized model. The dynamic characteristic of the boring bar is modeled using Timoshenko beam finite elements, while a lump parameter model is used for the absorber. Two approaches are used in the controller design. The first approach uses full state feedback with quadratic performance index. The second approach uses direct output feedback based on the results of the first approach. The effects of residual modes and spillover on the performance of the overall system are discussed for the two approaches. Simulation results show that a significant increase on the boring bar damping ratio can be achieved by using the proposed electromagnetic absorber.

Modeling of complex rotor systems by combining rotor and substructure models

Abstract Rotor systems have several unique characteristics in comparison to other dynamic systems, especially gyroscopic effects in rotating portions, non-symmetric matrix terms, and properties which are functions of speed or frequency. This paper describes an approach which combines the capabilities of a general-purpose program with a program specifically addressing design of rotor systems. The approach involves modeling the non-rotating portions in terms of a superelement/substructure. This linear symmetric representation in the form of the reduced matrices is introduced into the rotor system program, and combined with conventional (but possibly non-symmetric) finite element matrices of the rotating components, bearings, and destabilizing effects.