Flange Components Research Articles

Numerical modelling of large deformation in metal powder forming

In this paper, the transient dynamic analysis of metal powder during the cold compaction process is simulated by the finite element method based on a ‘Total’ and ‘Updated’ Lagrangian formulation. Since the compaction process involves a very large reduction in volume, the behaviour of the powders is assumed to be that of a rate-independent elasto-plastic material. The process is therefore described by a large displacement finite element formulation for the spatial discretization. A generalized Newmark scheme is used for the time domain discretization and then the final nonlinear equations are solved by a Newton-Raphson procedure. A combination of a Mohr-Coulomb and elliptical cap yield model is utilised as a constitutive model to describe the nonlinear behaviour of powder materials. An incremental elasto-plastic material model is used to simulate the compaction process and a plasticity theory for friction is employed in the treatment of the powder-tooling interface. The interfacial behaviour between the die and powder is modelled by using an ‘interface’ element mesh. Finally, the powder behaviour during the compaction of a plane bush, a cutting tool and a rotational flanged component is analysed numerically. The predictive compaction forces at different displacements, the variation with time of the displacement, relative density and stress contours are obtained. It is shown that the proposed large displacement elasto-plastic finite element approach is capable of simulating the metal powder during compaction.

Finite Element Simulation and Experimental Validation for Multilevel Powder Compact

The simulation of a complete cold compaction cycle for a green powder component and an experimental comparison are presented. In the modelling development, the powder was assumed to be a rate independent elastoplastic material. The process was described by a small displacement based finite element formulation and an elliptical cap yield surface was used to represent the powder densification. A friction model based on a plasticity analogy was found to be necessary in the analysis of the part ejection process. Laboratory and factory based experiments were carried out to provide detailed information about the material parameters, tooling motion, and validation of the numerical simulation work. Two examples were studied, a plain bush component and an axisymmetric flanged component. The numerical simulation results were validated against the experimental data and the comparison showed good agreement. The versatility of the simulation allows the complete representation of the green compact generation cycle. PM/0776

An investigation into the preforming of tubes

A major disadvantage of traditional cold forging is represented by the inability to forge slender geometries such as tubes, because these tend to collapse under axial forces. Recent research has revealed that, for the forming of hollow flanged components from tubes, a controlled material flow can be achieved by injection forging. However if the height of the flange is high compared to the wall thickness of the tube, instability problems arise causing the tube to buckle. According to previous work by the authors this may be prevented by increasing the wall thickness of the tube locally through the preforming of a simple inner flange on the tube. These preliminary investigations have been restricted to a reduced number of component geometries in terms of the major process parameters; being the inner- to outer-tube diameter proportion and the flange-towall-thickness ratio. In continuation of this work the present paper focuses on a systematic mapping of the optimal preform design in order to allow an establishment of actual preform design rules for the injection forging of tubular components for a whole range of parameter combinations. The analysis builds on a comprehensive finite element analysis in conjunction with experimental tests in aluminium performed for strategically important parameter combinations in order to support the theoretically established formability limit diagrams.

Towards nett-shape manufacturing of tubular components

This paper summarizes the results of work-in-progress research with a self developed two-step radial extrusion technique in which a simple preforming operation has been added to the conventional radial extrusion process. The proposed technique requires only simple modifications of the tool. Finite element models conditioned from previous experiments in aluminum served as a design tool for elaborating the process sequence and tool geometry which prevents the development of certain flow failures occurring in the traditional radial extrusion. Metal experiments were performed to test the tool design. As a result, it was possible to verify that the range of shapes that can be produced starting from a tube has been extended. Comparisons between theoretical predictions and experimental measurements obtained for a typical flanged component are provided for material flow, geometrical profile, effective strain distribution and required forming load. Finally the potential of the two-step radial extrusion technique is illustrated for the radial extrusion of a closed die shaped component.

Application of the finite element method to powdered metal compaction processes of multi-level flanged parts

A plasticity theory applicable to powdered metal compaction is summarized and its discretization for the finite element analysis is briefly described. The compaction processes of axisymmetric flanged components are simulated. For the analysis of compaction of two-level components, the investigations were performed for different compact geometries and various compacting methods. Highlights of the results for a given part geometry with two compaction methods are reported in terms of relative density distributions within the compact and pressure distributions along the dies and punches. The compaction process of three-level flanged components was also analyzed for two compacting methods. General conclusions from these simulation results are: (1) the compaction process is more effective with increased relative motions within the compact; and (2) the effect of various compaction schemes of combination of punch motions is not significant for the pressure distribution on punches and energy consumption in compaction processes. However, the variation of the punch forces in three-level component compaction, due to punch operating schemes, may be an important consideration in the critical design of compaction tooling system.

Pressurization of bone cement under standard, flanged and custom acetabular components for total hip replacement.

Custom acetabular components are proposed to achieve uniform cement mantles, even in irregular acetabula presented at revision, in order to enhance fixation. One aim of developing custom components was to permit pressurization of bone cement by the components at insertion and maintain the pressure during polymerization. A model acetabulum was set up for the insertion of standard, flanged and custom components under constant force. Cement pressure was measured at the floor of the acetabulum by means of a piezoelectric diaphragm transducer. Polythene tubes were inserted in the model acetabular walls to estimate penetration of cement into cancellous bone. Insertion of the standard and flanged components caused cement pressures up to 106 kPa which decayed to less than 21 kPa as cement escaped at the rim and the components came into contact with the acetabulum. The custom component maintained a pressure of over 60 kPa during polymerization from an initial pressure of 105 kPa and examination of cement mantles on removal showed no evidence of contact. The custom component also showed enhanced penetration of cement, especially around the rim of the acetabulum. It is concluded that the custom component design achieves higher cement pressures and that better fixation will result.

THARIES Resurfacing Arthroplasty

The unsatisfactory results of total hip arthroplasty in the young patient led to the development of the concept of hip resurfacing. Total hip articular replacement by internal eccentric shells (THARIES) resurfacing was introduced in 1975, with the primary goal of bone stock preservation and the hope of increased durability in the young patient. Major changes in design and technique include thicker and more uniform acrylic layers, metal-backed flanged acetabular component, and reduction in femoral size for preservation of acetabular bone stock. Of the 584 hips (average patient age, 48 years) with one- to ten-year follow-up study, there have been 72 failures (revision rate, 12.3%) with 66 cases of loosening (nearly all beginning in or limited to the acetabular side), two neck fractures, and four sepses. Survivorship analysis revealed that the single most important factor related to prosthesis failure is age followed by diagnosis and experience of the surgeon. Osteoarthritis and rheumatoid arthritis were favorable categories with congenital dysplastic hip (CDH), osteonecrosis, and previous failed resurfacing being unfavorable categories. Experience has taught the importance in preserving acetabular bone stock, providing bone graft for socket coverage in severe dysplasia, and removing dead bone in osteonecrosis. While resurfacing did not solve the problems of the young patient, even those patients who failed often gained time for application of the newer techniques and materials. The femoral component infrequently failed. The head remained vascular. This leads the authors to conclude that the surface arthroplasty concept is a viable alternative to total hip arthroplasty and seems to be ideal for the application of porous technology.

An experimental study of the ratchetting and creep of thick flanged tubes subjected to steady axial mechanical loading and transient thermal loading

The aims of the investigation were to obtain experimental data against which finite element predictions can be assessed and to see whether the lead alloy used was suitable as a “ratchetting” model material. Thermal ratchetting tests were performed on lead alloy flanged tube components. In some of the tests, dwell periods were allowed between successive thermal shocks. Electrical resistance strain gauges were used to measure the ratchet and creep strains in plain tube and stress concentration regions. It was found that both the plain tube and peak fillet ratchet strains increased with increasing mechanical and thermal load for short dwell periods. However, the ratio of the peak fillet to plain tube ratchet strains reduced with increasing mechanical and thermal load. Also, the ratio of the peak fillet to plain tube ratchet strains increased with increasing dwell period. The data obtained from the lead alloy model component tests were found to correlate with data from a number of different components made from various materials, indicating that the material may be useful as a “ratchetting” model material.

An All Metal UHV Flange Seal for Dissimilar Materials

An inexpensive all metal flange seal has been developed for the all aluminum Aladdin RF accelerating cavity that couples up to stainless steel beam transport lines without using aluminum-stainless steel bonded materials. The seal is capable of at least 10-9 Torr without detectable leakage and can be baked out at temperatures of at least 300°C. It utilizes commercially available sealing rings and slightly modfied Varian CFF flange components.

Prosthetic Replacement of the Patellofemoral Joint

We are just beginning to fully appreciate the significant role of the patellofemoral joint in total knee replacement surgery. Most of the new generation prostheses have a flanged femoral component. The tendency is to make the flange more anatomic in shape as more attention is paid to patellar tracking. Most systems have an optional polyethylene button to resurface the patellar side of the patellofemoral joint, and indications for its use are increasing. Although pain relief with patellar buttons seems uniform, the potential complications of stress fracture, loosening, and wear must temper our enthusiasm for their use until there is longer follow-up. Vitallium hemiarthroplasty of the patella is available in prostheses with and without the requirement for cement fixation. Most investigators have good results in chondromalacia (as a secondary procedure), but the experience in the literature is small. Results have been poor when the femoral side of the joint has been involved. Metal to plastic isolated patellofemoral prostheses have been designed to treat disease on both sides of the patellofemoral joint or to salvage unflanged total knee replacements with residual patellofemoral symptoms. Short term experience has been promising.

Thrust Balancing Exhaust Fitting for Safety and Relief Valves

A description is given of the stress distribution in an elastically strained standard safety valve installation, followed by a discussion of the problem introduced by settlement and vertical expansion in finding a means of support for rapid and extensive changes of load. Given is a method for absorbing today’s greater design thrusts safely and economically, while meeting the need to accommodate varying positions in space. Basically, a greater thrust has meant reinforcement of the valve, piping and supports. However, the use of readily available standard valve, flange and other high pressure components to the fullest extent possible consistent with safety is much preferred. After considerable experience with the application of these principles, they are now presented for general consideration along with illustrations of practical designs that have evolved in their use.