Poor Stiffness Research Articles

Study on Deformation of Thin-Walled Workpieces Milling Machining Based on Finite Element Method

In the mechanical products, there are always some poor stiffness and high precision thin-walled workpieces which will produce deformation in the machining process easily, so it is difficult to control the machining accuracy and to meet the requirement of higher machining accuracy. Based the finite element numerical simulation key technology, this paper analyzes the machining deformation, including geometric model simplification, mode selection, dynamic loading, a 3D simulation model of thin plate features establishment. Through the finite element numerical simulation analysis of the thin plate, we analyze the influence on processing deformation from different processing parameters and different constraints.

Kinematics Analysis of Double-Cutter & Double-Surface Symmetrical Machining Tool for Large-Scale Marine Propeller

The traditional large-scale marine propeller processing equipments have such disadvantages as single-surface machining, propeller blade vibration, poor stiffness, repeated clamping and long processing time. The method of double-cutter & double-surface symmetrical machining is proposed for large-scale marine propeller based on the parallel-serial mechanism. The processing method can overcome proposed disadvantages, and improve machining efficiency and accuracy. The structural design of the processing equipment is introduced and the coupling kinematics parameters of the parallel spindle platform are analyzed. The inverse kinematics solution and improved forward kinematics solution are discussed in detail. And the forward kinematics solution can solve a troublesome problem about the selection of good initial parameters. A simplified prototype is built to verify the solution method which could be used in the future actual application as a foundation.

Synchronous Optimization of Clamping Force and Cutting Parameters for Thin-Walled Parts

Machining accuracy of thin-walled parts is easily affected by clamping and cutting deformation due to its poor stiffness. In this paper, synchronous optimization method of clamping force and cutting parameters is presented based on GA and FEM. The optimization objective is to minimize the maximum deformation and to improve the machining efficiency. GA is used to optimize cutting parameters and clamping force, and FEM is used to predict the machining deformation of the thin-walled workpiece. Finally, taking a titanium alloy thin-walled part with irregular shape as an example, the optimal clamping force and cutting parameters at every cutting position are obtained to demonstrate the feasibility of the method.

The Simulation and Analysis of the New Type Large Vacuum Container Flange Welding Process

Flange is the key part of the large vacuum container and its stiffness property affects the sealing effect and the stability of the container. Large flange welding process will have a greater impact on its structural strength. In view of the traditional way of forming large vacuum container flange has problems that processing and manufacturing are difficult, more material consumption, and poor stiffness, a new type of flange structure was support. The new design has hollow structure and the welding process of cover flange was simulated through the finite element method. After that, the stress and the deformation were analyzed and then the proper welding scheme was optimized.

Virtual Prototyping Simulation of Flexible Multi-Point Auxiliary Support Fixture for Blade Machining

Spatial curved blades have been widely used in major aerospace manufacturers due to their light weight, high structural efficiency, high reliability, etc. However, their processing deformation, processing difficulty, and so on limit their use. In order to deal with the situation, flexible multi-point auxiliary supporting fixture for the processing of spatial curved thin-walled parts has become a major topic of current researches. The layout of positioning and clamping points of the flexible multi-point fixture direct affects the stiffness of clamping positions on the thin-walled parts to be processed. When cutting force is definite at a certain point in machining, the greater the stiffness at the processing positions on the part, the smaller the processing deformation due to the cutting force. Therefore, in order to reduce the machining deformation due to the poor stiffness, a suitable positioning and clamping layout is needed to improve the surface stiffness at the machining positions. Thus, the machining quality of thin-walled parts can be improved.

Optimum Design of Multi-Links Finger Grippers

The grippers for industrial robots with two or more DOF and a single driving motor are used to grasp the work pieces with poor stiffness in terms of low positioning accuracy. These grippers have a simple structure and are proper and suitable to blanks or semi-finished work pieces, with major dimensional deviations, which are handled between various tasks from manufacturing process. The geometrical symmetry of the system made by fingers and work piece is got by a suitable distribution of the force. This distribution is realized by an adequate design of the gripper fingers. In present paper some considerations concerning the optimum synthesis of the gripper mechanism with two multi-links fingers are shown.

Hybrid deflection prediction on machining thin-wall monolithic aerospace components

Thin-wall machining of monolithic parts allows better quality parts to be manufactured in less time. This brings advantages, particularly in inventory management and manufacturing efficiency. However, due to poor stiffness of thin-wall parts, deformation is more likely to occur in the machining process, which results in dimensional form errors. This paper describes a new methodology for prediction of wall deflection during machining thin-wall features with reduced analysis time from weeks to hours. The prediction methodology is based on a combination of the finite-element method and statistical analysis. It consists of a feature-based approach to parts creation, finite-element analysis of material removal, and statistical regression analysis of deflection associated with cutting parameters and component attributes. The prediction values have been validated by machining tests on titanium parts and show good agreement between simulation model and experimental data.

Research on Dynamic Instability of Irregularly-Shaped Arch Bridge Based on Catastrophe Theory

According to the characteristic of poor stiffness of V-shaped beams, transverse dynamic instability model of V-shaped is presented by Catastrophe Theory. Mechanism of stability of V-shaped is analyzed. Coordinates of two cusps and instable bifurcation set is derived. Effect of nonlinear coefficient and frequency ratio on amplitude of V-shaped beams are analyzed. When nonlinear coefficient is , continuous change of can arise abrupt change of amplitude. Then the jumping phenomenon can leads destruction of V-shaped beams.

Fatigue Reliability and Optimal Design Research of TBM Cutter

Tools of tunnel boring machine CAD models have been built by CAD software, it is analyzed static characteristics and fatigue characteristics by finite element analysis and obtaining the displacement in the poor stiffness conditions. Improving its structure to strengthen stiffness and fatigue life by the calculate result. The final result shows that the structure can satisfy its rigid command and can fit the soil conditions above 5%-10%. Damage frequency of tools is greatly deduced. It provides a theoretical basis for the actual design and product manufacturing.

Bearing Capacity of Frame’s Column Strengthened with Addition Flange Wall

A large number of frames damaged due to the poor lateral stiffness in “5.12” earthquake. Additonal flange wall could effectively improve the lateral stiffness. This paper analyzed the behavior capability of special-shaped column of the practical engineering structures, meanwhile, obtained N-M curve, Mx-My curve and M-φ of biaxial eccentricity compression based on numerical integration method.The results show that,the failure mode of special section column after reinforcing and rectangular column under the biaxial eccentricity compression are conform,including fail in tension or compression and the limit failure. When the axial compression ratio is quite slightly,and section eccentric tension destruction, the thrust increases, the anti-bending ability increases.When section bearing destruction, along with axle strength enlargement, the anti-bending ability reduces.And the results reveal the axial compression ratio could influence the bearing capacity and ductility of frame’s column obviously.

Effect of Suture Material and Bone Quality on the Mechanical Properties of Zone I Flexor Tendon–Bone Reattachment With Bone Anchors

To compare the initial biomechanical properties of zone I flexor tendon to bone repairs performed using pull-out and anchor techniques and to investigate the effect of bone quality and suture materials on the strength of anchor repairs. Using computed tomography, we measured bone mineral density and cortical thickness of the distal phalanx of 60 cadaver fingers (mean age, 77 years). Flexor digitorum profundus tendons were then transected at their insertion sites and repaired using a 4-strand grasping suture and either pull-out or anchor fixation. For pull-out repair (n = 20), the suture strands (Supramid 3-0; S. Jackson, Inc., Alexandria, VA) were passed through the distal phalanx and tied over a dorsal button. For anchor repair, 2 bone anchors were inserted into the distal phalanx, and tendons were grasped using either Supramid (n = 21), Ethibond (Ethicon, Inc., Somerville, NJ; n = 10), or FiberWire suture (Arthrex Inc., Naples, FL; n = 9) (all 3-0). Mechanical properties of the repaired tendon-bone constructs were determined in linear, load-to-failure loading and correlated with bone characteristics. The FiberWire-anchor repair group had the best combination of mechanical properties, with ultimate force to failure no different from the pull-out repairs but with greater stiffness and reduced displacement. Pull-out suture repairs had significantly higher ultimate force-to-failure values than did Ethibond-anchor and Supramid-anchor repairs (p < .01). However, pull-out repairs had significantly reduced stiffness and greater displacement at 20 N force than did anchor repairs from all groups (p < .05). Both bone mineral density and cortical thickness correlated significantly with ultimate force (p < .01). Almost all anchors pulled out for bone mineral density below 420 mg/cm(3) or cortical thickness less than 0.31 mm, which occurred only for specimens aged greater than 75 years. The mechanical properties of the double Mitek bone anchors were sensitive to both suture material and bone quality. FiberWire-anchor repairs provided the best combination of mechanical properties. Pull-out suture repairs had good strength but poor stiffness. Anchor fixation may be contraindicated in patients greater than 75 years because of poor bone quality.

Deformations of thin-walled plate due to static end milling force

Many components used in the aerospace industry are usually thin-walled structures. Because of their poor stiffness, thin-walled parts are very easy to deform in the process of cutting. Due to the gradual reduced thickness during cutting, the end milling of thin-walled plate is a very complicated process. This paper proposes a new analytical deformation model suitable for static deformations prediction of thin-walled plate with low rigidity. The part deformations are predicted using a theoretical deformation equations model, which is established on the basis of reciprocal theorem when the linear load acts on thin-walled plates. The part deformations in end milling process are simulated by using FEM software ANSYS10.0. In the process of simulating, the influences of linear loads, location of the cutter (including x and y direction), thickness of the plates on the deformations of the thin-walled plates are analyzed. The results may help to increase the geometric accuracy of milling flexible thin-walled plates by considering the impact of the milling forces, location of cutter and the part thickness on the deformations of thin-walled structures. Furthermore, the results show that the diverse cutting parameters should be selected at each machining layer to satisfy the machining efficiency and precision in the process of milling thin-walled plate.

Control of paraplegic ankle joint stiffness using FES while standing

The goal of this work was to investigate the feasibility of ankle stiffness control using functional electrical stimulation (FES) while standing, as relevant to the development of feedback systems for balance control in paraplegia. The work was carried out using apparatus in which the subject stands with all joints above the ankles braced, and where ankle moment is provided via FES of the ankle flexor and extensor muscles. A feedback control strategy for ankle stiffness control is proposed in which the ankle moment is controlled to a reference value equal to the product of the desired stiffness and the measured ankle angle. Two subjects participated in the study: one neurologically-intact person, and one paraplegic person with a complete thoracic spinal cord lesion. The results show that during forward-leaning postures, when the plantarflexor muscles are stimulated, relatively high ankle moments of up to 60 Nm can be generated and accurate moment tracking is achieved. As a consequence, ankle stiffness is close to the desired value. During backward lean, on the other hand, the dorsiflexor muscles are stimulated. These muscles are relatively weak and only modest ankle moments of up to around 15 Nm can be produced. As a result, dorsiflexor stimulation readily saturates giving poor stiffness control. It was further observed that when the desired stiffness is higher more external force has to be applied to perturb the body away from the neutral (upright) position. We conclude that: (i) accurate ankle stiffness control, up to the fundamental strength limits of the muscles, can be achieved with controlled FES; (ii) ankle stiffness control using FES in paraplegia has the potential to ease the task of stabilising upright posture by application of additional upper-body forces.

Replacement arthroplasty of the valgus knee. A modified lateral capsular approach with repositioning of vastus lateralis.

Total knee arthroplasty (TKR) using a medial capsular approach gives worse results in arthritic knees with valgus deformity than in those in varus, usually because of swelling, poor wound healing and stiffness, instability, recurrent valgus deformity and poor patellar tracking. A technique for replacement TKR of valgus knees using a lateral capsular approach was described several years ago, but was not routinely adopted because of the difficulties with and complexity of the procedure which included deliberate elevation of the tibial tubercle. In order to avoid this we have modified and simplified the procedure. Our preliminary results suggest that this lateral approach is safe and may give a better outcome than that through the medial capsule for the replacement of valgus knees.

Bead pattern optimization

Plane sheet panels exhibit poor stiffness and NVH (noise, vibration, and harshness) performance due to their flexibility. A common and cost-effective approach in the automotive industry to improve the stiffness and NVH peformance of sheet panels is the addition of beads. However, no systematic methodology is available for determining the optimal pattern of beads in sheet metal. This research explores the feasibility of applying topology optimization methods to the bead design of sheet panels. The approach starts with adding beam elements to the shell element model of the sheet panel to simulate the stiffness improvement of the structure and then uses the topology optimization method to obtain the optimal layout of the beam elements. A cantilever plate is used to perform a preliminary study for bead pattern design and a simplified vehicle structure is used to demonstrate the applicability of the proposed method.

紙塗工用ラテックスの新しい品質設計

Two types of the newly improved SB-latex can provide good performance for coated paper. The first one is the latex which provides better balance between blistering resistance and picking strength for web off-set printing coated paper. It is difficult to reconcile blistering resistance with picking strength only by controlling gel content of latex. Reducing gel contents can give good blistering resistance with the porous coated layer. But the porous structure causes poor picking strength, and vice versa. The newly devised latex has greater thermal sensitivity to the melt flow of latex polymer by changing the quality of gel into higher homogeneous molecular distribution and carboxyl group distribution. This sensitivity results in not only a small pore coating structure which gives good picking strength but also large deformation of pores under high temperature in order to attain good blistering resistance. Dynamic viscoelasticity both of latex film and coating layer was measured. Usefulness of the dynamic viscoelastic measurements in characterizing latex polymer and coating layer is demonstrated. Another one is a newly developed cationic modified latex. Controlling surface electric state of latex can provide suitable interaction between latex and pigment in coating. Such interaction gives coating structure adequate porosity for less print mottle of coated paper. Generally, Tg is the key factor to improve print mottle. Lower Tg latex provides less print mottle due to the produced bulky and porous coating structure. However, lower Tg latex tends to provide poor wet picking strength and poor stiffness. The moderate cationic latex performed less print mottle without reducing Tg. The effect of the moderate cationic latex on print mottle was verified by pilot coating and commercial press.

Cerebral palsy in Riyadh, Saudi Arabia: II. Associations between gestational age, birthweight and cerebral palsy

One hundred and ninety infants with cerebral palsy were studied in Riyadh , Saudi Arabia. Bleeding during pregnancy and toxemic complications seemed to be important causative factors, particularly in preterm and small-for-date infants. Infants born after breech presentation, assisted labour and failed obstetric procedures totalled 20.0% of all cases. Poor feeding, stiffness and infection were the main clinical presentations. Spasticity was the predominant neurological abnormality irrespective of birth weight, with spastic diplegia (31.0%) and quadriplegia (26.3%) contributing greatly to the overall pattern. Speech defects and, to a lesser extent, epilepsy were the most frequent associated handicaps. The majority of children with cerebral palsy (65.8%) were severely handicapped. Saudi Arabia is making rapid economic, social and medical progress, but currently facilities to meet the needs of cerebral palsy victims and their families are inadequate. Based on the above study it is recommended that: (1) paramedical services at community level be initiated; (2) more rehabilitative and educational programs be established; (3) better and more modern obstetric care be provided; (4) close co-operation among the medical professionals be facilitated since cerebral palsy cases can be managed best through a team approach.

Beyond the second order system in track following servos

Voice coil linear actuators are typically characterized as a basic second order system. However, component mechanical resonant frequencies often result in design degradations in the basic second order system. These conditions manifest themselves as possible servo loop instabilities in the frequency domain. This leads to poor static positioning, stiffness and dynamic positioning inaccuracies. This paper details the procedure used in the CDC Storage Module Drive family which, by the use of electronic compensation networks, provide track following improvement as well as minimizing the effect of mechanical resonant frequencies.