Mostafa Shazly

A dynamic programming approach for minimizing the number of drawing stages and heat treatments in cylindrical shell multistage deep drawing

Deep drawing is an important sheet metal forming process that appears in many industrial fields. It involves pressing a blank sheet against a hollow cavity that takes the form of the desired product. Due to limitations related to the properties of the blank sheet material, several drawing stages may be needed before the required shape and dimensions of the final product can be obtained. Heat treatment may also be needed during the process in order to restore the formability of the material so that failure is avoided. In this paper, the problem of minimizing the number of drawing stages and heat treatments needed for the multistage deep drawing of cylindrical shells is addressed. This problem is directly related to minimizing manufacturing costs and lead time. It is required to determine the post-drawing shell diameters along with whether heat treatment is to be conducted after each drawing stage such that the aforementioned objectives are achieved and failure is avoided. Conventional computer-aided process planning (CAPP) rules are used to define the search space for a dynamic programming (DP) approach in which both the post-drawing shell diameter and material condition are used to define the states in the problem. By discretizing the range of feasible shell diameters starting from the initial blank diameter down to the final shell diameter, the feasible transitions from state to another is represented by a directed graph, based upon which the DP functional equation is easily defined. The DP generates a set of feasible optimized process plans that are then verified by carrying out finite element analysis in which the deformation severity and the resulting strains and thickness variations are investigated. Two case studies are presented to demonstrate the effectiveness of the developed approach. The results suggest that the proposed approach is a valuable, reliable and quick computer aided process planning approach to this complicated problem.

A Rule-Based Process Design and Finite Element Analysis of Multistage Deep Drawing of Box Shapes

In this paper a computer-aided rule-based process design of multi-staged deep drawing of box shaped shells is developed. A decomposition method is adopted in the algorithm for geometry description of the part under consideration. The shell geometry, tooling dimensions and load required are determined for each stage. A finite element analysis is carried out to verify and adjust the output of this process design algorithm. The deformation severity and the resulting strains and thickness variations are investigated. The forming limit diagram (FLD) is adopted as a basic reference to monitor possible part failure in the process.Copyright

Characterization of sandwich panels for indentation and impact

The integrity of sandwich structures which are susceptible to impact may deteriorate significantly due to collapse of the core material and delamination of the face sheets. The integration of a thin polyurethane interlayer between the composite face sheet and foam core is known to protect the core material and substantially improve the resistance to impact. The objective of the present work is to characterize the response of sandwich panels, as well as that of the constituents to impact. In particular, the response of polyurethane and foam samples under a range of quasi-static and dynamic loading rates is determined experimentally. Furthermore, the response of sandwich panels to quasi-static indentation and low velocity impact is examined to quantify the extent of damage and how it is affected by the integration of polyurethane interlayers in their construction. This information is useful in the modelling of high velocity impact of sandwich panels; an effort which is currently underway. The results illustrate the benefit of using polyurethane interlayers within the construction of sandwich panels in enhancing their performance under quasi-static indentation and impact loads.

Effect of Variable Blank Holder Force on the Springback and Weld-Line Movement During Draw-Bending of Tailor Welded Blanks

Tailor welded blanks (TWBs) manufactured by drawing processes suffer from two major defects; weld-line movement (WLM) and springback. These defects can be reduced by using a counterpunch or controlling the value of the blank holder force and its scheme. This work presents a finite element analysis of the effect of variable blank holder force (VBHF) on springback and WLM of bench mark problem of draw-bending process of a TWB. The proposed VBHF scheme is developed based on the reaction forces predicted in a finite element model for artificially clamped weld-line case. The results obtained by applying VBHF are compared with those obtained using a counterpunch. The use of counterpunch is found to eliminate Vertical WLM in all the considered cases. Whereas side WLM using VBHF is found to be less than that obtained using counterpunch. When compared to the counterpunch technique, the springback values are found to be improved by applying the VBHF schemes.Copyright

Finite Element simulation of In-Service Sleeve Repair Welding of Gas Pipelines

The purpose of this study is to investigate the influence of welding sequence on the risk of burn-through, cold cracking and residual stresses during in-service sleeve repair welding of gas pipelines. Based on ABAQUS software, axisymmetric finite e1ement models were conducted to calculate transient temperature distributions and resulting residual stress field after multi-pass sleeve fillet welding of in-service API 5L-X65 36” Schedule pipes. Influence of welding sequence was investigated by comparing residual stresses and transient deformations for sequential welding; in which welding of the two circumferential pipe/sleeve fillet welds was made in sequence, to the case of performing the two welds at the same time. Sequential welding was found to reduce weld zone distortion and residual stresses due to the sleeve freedom to expand axially while conducting the first fillet weld. The upper limit of heat input was found to generate higher pipe wall peak temperature, but not to the extent of initiating pipe wall melt through.

An Integrated Approach for Optimized Process Planning of Multistage Deep Drawing

This work is concerned with the process design of multistage deep drawing, where an integrated artificial intelligence (AI) approach is presented with a special focus on box-shaped parts. This approach combines three AI tools, namely part shape recognition, expert system for process design governing rules, and search and optimization via dynamic programming. Validation and final selection of optimized process plans are done using finite element analysis with full account of the formability limits of the material used. The main advantage of the proposed integrated approach is its capability of generating valid, optimized process plans in a relatively short time compared to traditional approaches. Two case studies are presented for demonstrating its effectiveness.

Impact resistance of sandwich plates

Abstract Assessment of the resistance of sandwich plates to impact and penetration is of principal importance in determining the ability of structures to maintain their integrity in service. In this chapter, the focus is on efforts to modify the standard sandwich construction to mitigate damage under impact and improve the overall performance of sandwich structure. First, quasi-static indentation is considered in an experimental effort to identify the damage mechanisms caused by pointed objects. Results from finite-element modeling of the indentation, including damage, are also presented. Next, the response of sandwich plates and their constituent materials to high strain rates caused by impact is discussed. In all cases, standard and modified sandwich plate designs are considered and their performance is compared.