Development of an automated wood welding process

Friction welding of wood is an active field of research and would seem to be a potential joining technology in wood industries in the near future. Despite numerous scientific publications in this field, automated industrial applications of this technique are not common up to now. In this paper, we developed an automated welding process that can be easily implemented in industry. The use of beech wood samples is motivated because (i) this species is abundant in the forest resource, (ii) the anatomical structure is homogeneous and therefore highly suitable for the welding process and (iii) the average wood density is high. For the welding process, a sequential control was developed and four different welding modes were applied. We tested four welding modes with a constant rotation speed of the drilling machine (1800?t.mn). During the dowel insertion, the linear displacement was tested for two different constant speeds and for two varying speeds. The results of the pull-out strength test show that the forces during the welding process as well as the strength of the joints produced differ depending on the welding mode. Based on the results it can be recommended that a two-step welding process is applied for wood welding. With the two steps, the forces at the welding machine are kept low and the quality of the joint is high. The sequential control developed can be applied and adapted for different industrial applications. These findings should convince industrial decision-makers of the applicability of this process for daily production.     

Aktivlöten von keramischen Segmenten für den Einsatz in verschleißkritischen Bereichen von Schmiedegesenken

Active brazing of ceramic inlays for the application in wear critical areas of forging dies The use of reinforcing ceramic segments in forging tools is investigated and has been successfully tested with model of dies recently. With reinforcing ceramic segments, however, the thermal widening of the steel tool is a major problem for forging dies. Further, only rotationally symmetrical ceramic inserts can be used as reinforcements which restricts the shape capabilities in tool design significantly. A considerably greater design flexibility is possible if the ceramic segments are brazed into the die body material. To this end, reactively brazed ceramic‐metal composites are to be developed and tested for feasibility in the forging process.     

Reprocessing of aluminum chips by hot backward extrusion

In this work the recycling of cold pressed aluminum chips by a hot backward extrusion process is investigated. By using a non-melting approach common casting losses are avoided. After cold compaction, the hot backward extrusion process is carried out with a high speed hydraulic forming press under variation of forming speed, temperature and force. Subsequently, forged parts were analysed by mechanical tests and metallographic examinations. The investigations have shown that aluminum chips can be consolidated into a semi-finished part with local relative densities up to 100 %. In comparison to common continuous non-melting chip recycling techniques the investigated process chain has the potential to reduce the effort of post-treatment noticeable by producing semi-finished components from aluminum waste.     

The Effect of Texture Shape on the Load-Carrying Capacity of Gas-Lubricated Parallel Slider Bearings

Surface texturing is used to increase hydrodynamic pressure and reduce friction and wear between gas-lubricated parallel sliding surfaces. The shape, geometry, and density of the patterned microtexture features (??dimples??) play a key role in the tribological performance of the textured slider bearings. The objective of this paper is to compare the load-carrying capacity of commonly used dimple shapes for gas-lubricated textured parallel slider bearings. Six different texture shapes are considered, including spherical, ellipsoidal, circular, elliptical, triangular, and chevron-shaped dimples. The pressure distribution and load-carrying capacity generated by different texture shapes are simulated using the compressible Reynolds equation over a domain containing a column of ten dimples. The texture geometry and density are optimized in terms of maximum load-carrying capacity for each individual dimple shape, as a function of operating parameters such as relative velocity and spacing between the two sliding surfaces. The maximum load-carrying capacity of each individual texture shape??with optimized geometry and density??is then compared relative to each other. It is concluded that the ellipsoidal shape results in the highest load-carrying capacity, and the optimal geometry and density are found to be almost independent of the operating conditions.     

Basic study on the process combination of deposition welding and subsequent hot bulk forming

Today most technical parts and components are made of monolithic materials. Nevertheless, the previously used monolithic materials reach their technological and constructive limits, so that an improvement of the component properties can be realized by hybrid parts. Forging of previously joined semi-finished products to net shape hybrid components is a promising method to produce functional adapted parts in a few process steps. This new process chain offers a number of advantages compared to other manufacturing technologies. Examples are the production of specific load-adapted forging parts with a high level of material utilization, an improvement of the joining zone caused by the followed forming process and an easy to implement joining process because of the simple geometries of the semi-finished products. This paper describes the production process of hybrid steel parts, which are produced by a combination of a deposition welding process with a subsequent hot forging (upsetting) or cross-wedge-rolling. It could be shown that the innovative process chain enables the production of hybrid parts whereby the forging processes lead to an improvement of the mechanical properties of the laser deposited material.     

Investigation on a new process chain of deposition or friction welding and subsequent hot forging

According to the state of the art most current forging parts and technical components are made of mono‐materials. Nevertheless, parts consisting of only one material increasingly reach their specific material and constructive limits in the established production processes. Through use of previously joined raw parts consisting of different materials, it is possible to produce application‐optimized hybrid parts. This paper describes the production chain of hybrid parts produced by combining two different joining processes with subsequent hot compression tests. The joining of various materials is realized by a deposition welding with a laser‐stabilized gas‐metal‐arc deposition welding (LGD) process and a conventional friction welding process. Subsequently, the hybrid samples are compressed under varying forming parameters such as temperature and deformation degrees. In order to characterize the joining zone, metallurgical investigations are carried out.     

Discharge capacity of broad-crested intakes

Conclusions  

Influence of wire mesh characteristics on reinforced soil model wall failure mechanisms-physical and numerical modelling

This paper presents the details of experimental and numerical analysis performed on three 0.8?m-high reinforced earth model walls with strip footing surcharge near the wall facing. The study investigates how wire mesh strength and geometry affect the failure mechanism. All three walls were nominally identical, except for reinforcement strength and geometry. The displacement field of the entire cross section was captured by high-resolution digital camera through transparent sidewall. The resulting images were analyzed using digital image correlation software. The results indicate that both reinforcement strength and aperture size influence the type of failure mechanism. Numerical modelling was also applied to assess the influence of sidewall friction (3D model) and reinforcement stiffness and strength (2D model) on the failure mechanism of the walls. The parameters for the numerical models were derived from independent tests and results, which were compared with the experimental observations. A good level of agreement with measurements was confirmed, even for the 2D model that excluded sidewall friction.     

Influence of the pressure holding time on strain generation in fuel injection lines

An influence of the pressure holding time on residual strain generation during the autofrettage process was studied experimentally for the first time in the present work. It is the state of the art that fuel injection lines are held at the autofrettage pressure for only a few seconds in an industrial production. In doing so, it is assumed that a desirable residual stress–strain pattern is generated. However, the results of the experimental investigations outlined in this work indicated that completion of the plastic deformation caused by the autofrettage process and generation of the desirable stress–strain pattern require a much longer period. As shown, a third-order polynomial equation best described the interdependence between the time required for the completion of the process, the corresponding autofrettage pressure and the generated strain state. The method presented can be used as a tool for the determination of the optimal autofrettage process parameters in industrial production of fuel injection lines.     

Influence of heat pipe cooling on the wear of hot forging dies

The temperature of hot forging dies has a high influence on the wear of tool surfaces. In order to reduce the thermal impact on tool life, passively acting heat pipes are tested and the results are presented within this paper. For this purpose, the upper die of a commonly used hot forging tool was equipped with heat pipes and serial forging trials have been performed. The influence of the heat pipes on the die temperature as well as the effects on wear behavior are presented. The heat pipe cooling leads to a lower die temperature and thus to a reduction of adhesive wear. The wear is examined by optical and tactile measurements as well as by micrograph analyses. Conclusively, hardness tests of the tool edge layer are carried out.