Sheet Metal Industry Research Articles

Optimal design of flat patterns for 3D folded structures by unfolding with topological validation

There are applications in the sheet metal, paperboard, packaging and various other industries for the computer-aided design of flat patterns for folding into some desired 3D folded structure made of piecewise flat faces. This paper describes a methodology for the automatic development of flat patterns for any given folded structure based on enumerating all possible spanning trees of the face adjacency graph (the graph that represents the connectivity among the faces of the structure) since any spanning tree represents a potential topological unfolding of that structure. Complications found in non-manifold structures, such as where more than two faces are joined at one common edge, are also addressed in this work by way of recognizing topologically invalid spanning trees. Furthermore, a strategy is also developed to detect overlapping of faces within the pattern purely by checking its topology defined in the spanning tree, without first having to geometrically construct the pattern layout. Finally, three measures of compactness are adopted as the optimality criteria for the methodology to output flat pattern results ranked according to their compactness. The procedure is implemented as a computer program and applied to six example structures in this paper to illustrate the capabilities of the methodology.

Multi-point sandwich forming of a spherical sector with tool-shape compensation

The need for a cost-effective means of rapid, small-batch quality parts manufacture is greater than ever in the sheet metal industry. A new reconfigurable multi-point forming process, multi-point sandwich forming (MPSF), has been conceived and investigated as a possibly useful method to fulfill this need. This process is different from to conventional multi-point forming, in that a re-usable die sheet is used, a large distance between pins exists in the reconfigurable die and the upper die is made of polyurethane. In the work described in this paper, the performance of a multi-pin die with pins in circular array and an adjustable blank holder is investigated. This die is suitable to form work-pieces with rotational symmetry. Also, a die shape optimization design method using inverse displacement compensation is presented. Experimental and simulation results from forming a spherical shell sector, with a diameter of 380 mm show this method is feasible and effective. The results also show the blank holder can reduce/eliminate dimples that sometimes arise in the work-piece and the deformation of the interpolator during the forming process can induce a shape error in the formed work-piece.

Change in Prevalence of Asbestos-Related Disease Among Sheet Metal Workers 1986 to 2004

In 1985, the Sheet Metal Workers International Association and the Sheet Metal and Air Conditioning National Association formed The Sheet Metal Occupational Health Institute Trust to examine the health hazards of the sheet metal industry in the United States and Canada. Between 1986 and 2004, 18,211 individuals were examined. The mean age of this cohort was 57.9 years, and the participants had worked for a mean (± SD) duration of 32.9 ± 6 years in the sheet metal trade. Twenty-three percent of participants were current smokers, 49% were former smokers, and 28% were never-smokers. A total of 9.6% of participants (1,745 participants) had findings that were consistent with parenchymal disease (International Labor Organization [ILO] score, ≥ 1/0); 60% of those with an ILO score ≥ 1/0 were classified as 1/0, 34% as 1/1 to 1/2, and 6% as ≥ 2/1. A total of 21% of participants (3,827 participants) had pleural scarring. There was a lower prevalence of nonmalignant asbestos-related disease among those who began to work after 1970, when compared to workers who began to work before 1949; those who began to work between 1950 and 1969 had a prevalence between the other two groups. The strongest predictor of both parenchymal and pleural disease on a chest radiograph was the calendar year in which the worker began sheet metal work; work in a shipyard was also an important risk. The results of this study suggest that the efforts to reduce asbestos exposure in the 1980s through strengthened Occupational Safety and Health Administration regulation have had a positive public health impact.

Cold roll forming of a U-channel made of high strength steel

Cold roll forming is a bending process where the bending occurs gradually in several forming steps from an undeformed strip to a finished profile. The process is very interesting for the sheet metal industry due to the high speed in which the profile can be produced. High strength steel has, in recent years, become more common in cold roll forming. These materials have advantages but also disadvantages that affect the design of the process. Simple models in literature [K.F. Chiang, Cold roll forming, ME Thesis, University of Auckland, August 1984] predict that the longitudinal peak membrane strain in the flange of a profile is independent of the material properties. However, Ingvarsson [L. Ingvarsson, Förenklad teori för rullforming av elementär v-profil, jämförelse mellan normalt och höghållfast stål, VAMP 15- rullforming 23 april 2001] compared mild and ultra high strength in a roll forming experiment and the conclusion was that the material properties will affect the finished profile. This paper is a fundamental study performed in order to understand the observation by Ingvarsson [L. Ingvarsson, Förenklad teori för rullforming av elementär v-profil, jämförelse mellan normalt och höghållfast stål, VAMP 15- rullforming 23 april 2001]. The objectives of this study are to investigate the change in the longitudinal peak membrane strain at the flange edge and the deformation length when the yield strength increases. These are important since they can be used to determine the number of forming steps and the distance between them when designing the cold roll forming machine. The result from the simulations show that the longitudinal peak membrane strain decreases and the deformation length increases when the yield strength is increased.

A study on the springback in the sheet metal flange drawing

Abstract The flange drawing process is used to make flanges from the sheet metal blank using the die, punch and blank holder optionally with the supporter. This process is being applied in many sheet metal industries. One of concerns of this process is that the flanged section formed is mostly not parallel with the original blank due to the springback occurrence, which could affect the quality of the formed part. This study has focused on the evaluation of springback occurring in the sheet metal flange drawing process by controlling some process factors like the punch corner radius (PR) and die corner radius (DR), the blank-holding-force (BHF), the supporting-force (SF), the lubrication and so on. The springback phenomenon in the flange drawing process has been studied first using the finite element method (FEM) in order to understand what the main causes of springback are. The distribution pattern of local x -component of stress along the longitudinal direction of the blank has been revealed to be very important in predicting the final shape of the flange. This fact has been backed up by the experimental results carried out with the developed test dies. The Taguchi table L 18 has been used to determine which of the process factors of the flange drawing is the most influencing to make the flanged section parallel with the original blank in spite of springback occurrence. The results show that the punch corner radius (PR) is the most important factor of the process.

Automatic production planning of press brakes for sheet metal bending

This paper discusses the planning module of system that has been developed in a research project investigating the possibilities for automatic planning of press brakes. Only limited attention has been given to production-planning problems for bending processes in the sheet-metal industry. A well-considered production-planning module provides an important opportunity for cost saving and flow-time reduction. The module will support and may replace an experienced planner. Under certain assumptions, the planning problem can be modelled both ways as a Travelling Purchaser Problem (TPP) and as a Generalized Travelling Salesperson Problem (GTSP). A hierarchical decomposition approach is presented to solve the TPP, while the GTSP is solved using guided local search (GLS). These methods are compared based on a set of problems from a real production environment and perform well.

Analysis of pin characteristics for a variable geometry mold

The sheet metal industry has considered the use of a variable geometry mold for years. Its application to the vacuum forming of plastic sheets, however, is rather new. One significant problem is the dimpling effect resulting from the discrete nature of the mold surface. The purpose of this research is to determine the most appropriate pin type and configuration for a viable variable geometry mold, considering the dimpling effect and other quality issues. Through analyzing the consequences of several pin types and configurations, we conclude that a flat top, square pin in a closed-pack configuration is the most appropriate option.

Optimization of Sheet Metal Process Parameters of a Shield Case Piece Using Computer Simulation

Numerical simulations based on Finite Element Analysis (FEA) are widely used to predict and evaluate the forming parameters before performing the physical processes. In the sheet metal industry, there are basically two types of FE programs: the inverse (one-step) programs and the incremental programs. In the present paper, the forming process of the shield case piece (LTA260W1-L05) was optimized by performing simulations with both types of software. The main analyzed parameter was the blankholding force while the rest of the parameters were kept constant. The criteria used to determine the optimum value was based on the Forming Limit Diagram (FLD), fracture and wrinkling of the material, thickness distribution, and the principal strains obtained. It was found that the holding force during the forming process deeply affects the results, and a range of values was established in which the process is assumed to give a good quality piece.

CCKBS: A component check knowledge-based system for assessing manufacturability of sheet metal parts

This paper describes a knowledge-based system developed for assisting product designers, process planners and die designers working in small and medium sheet metal industries for assessing manufacturability of sheet metal parts. Knowledge obtained from die designers, product design handbooks, catalogues and broachers has been analyzed, tabulated and incorporated into a set of production rules of the IF–THEN variety. The knowledge-based system is coded in the AutoLISP language and loaded into the prompt area of AutoCAD. During consultation, the proposed system generates friendly prompt eliciting from the user for job related. The system output includes recommendations on the suitability of geometrical features of the part for required manufacturing operations. This arrangement facilitates interfacing of design with drafting and can be operated on a PC/AT. Illustrative examples have been included for demonstrating the usefulness of the proposed system. The knowledge base of the proposed system can be modified depending upon the capabilities of a specific shop floor. The low-cost of the system makes it affordable for planners working in small and medium-sized enterprises.

Genetic Algorithm Coding Methods for Leather Nesting

The problem of placing a number of specific shapes in order to minimise waste is commonly encountered in the sheet metal, clothing and shoe-making industries. The paper presents genetic algorithm c...

PROPLAN: an expert system for optimal planning of sheet metal operations

This paper describes a low cost expert system specifically developed for assisting process planners working in small and medium sheet metal industries. The system helps select an optimal process plan for sheet metal operations. Knowledge obtained from the process planners, die designers, product design hand books, catalogues and brochures has been analyzed, tabulated and incorporated into a set of production rules of the IF–THEN variety. The knowledge base system comprises of more than 150 production rules and is coded in the AutoLISP language. For consultation, the user loads the expert system PROPLAN into the prompt area of AutoCAD. This arrangement facilitates interfacing of process design with drafting and is operated on a PC/AT. The system generates friendly prompts designed to elicit from the user data pertaining to the job at hand. The system provides intelligent advice on the optimal process plan for sheet metal operations. Illustrative examples have been included for demonstrating the usefulness of the proposed system. The knowledge base of the present system can be modified depending upon the capabilities of a specific shop floor.

Determining springback amount of steel sheet metal has 0.5 mm thickness in bending dies

Importance of bending dies is very wide in sheet metal industry. Knowing that springback amount of bending material in bending dies is as important as the die itself, because the material leaving the die should be within the allowed tolerance limits. Therefore, in this study the subject of bending dies and springback in bending process has been researched. In order to find springback in bending, a “V” shaped die is designed and it has been aimed to find out how much can steel sheet metal materials resile in various angles and to bring forward springback graphics to add literature. There is little satisfying information in the literature regarding this issue. In order to reach a conclusion, 15 different dies have been prepared, more than 150 samples, each of which has been bent at least 10 times, have been bent and the obtained angles have been measured with profile meter. The acquired results have been statistically evaluated in a computer media and converted to graphics.

Unfolding and Flat Layout Design of Non-Manifold 3D Folded Structures

AbstractThere are practical applications in the sheet metal, packaging and various other industries for research into the automatic development of the flat layout or pattern that can be folded into some desired 3D folded structure. The relevant techniques developed in earlier work are based on generating spanning trees of the face adjacency graph (the graph that represents the connectivity among the faces of the folded structure) since any spanning tree is a potential unfolded flat layout of that structure. However, complications in the structure, such as situations where more than two faces are joined at one common edge, pose problems to the spanning tree unfolding methodology that can lead to incorrect results. This work examines these problems through the connectivity and topological representation issues involved when splitting these common edges, and proposes a strategy to handle such complications by developing algorithms to detect topologically invalid spanning trees. These new algorithms are incor...

An intelligent system for optimal selection of dies and tools for sheet metal operations

This paper describes an intelligent system for assisting process planning staff working in small and medium sheet metal industries for optimal selection of type of die, jig, fixture and inspection gauge for a given job. The problem is tackled through the expert system approach. Knowledge in the form of data, facts, rules of thumb and judgements gathered from product designers, process planners, die designers, process planning handbooks, catalogues and brochures has been analysed, tabulated and incorporated into a set of production rules of the IF-THEN variety. The system is coded in the AutoLISP language and loaded into the prompt area of AutoCAD. This arrangement facilitates interfacing of process design with drafting and can be operated on a PC/AT. For consultation, the system generates friendly prompts eliciting from the user data pertaining to the job. The system output includes recommendations on optimal type of die, jig, fixture and inspection gauge suitable for the job at hand. Illustrative examples have been included for demonstrating the usefulness of the proposed system. The knowledge base of the proposed system can be modified depending upon the capabilities of a specific shop-floor. The low cost of the system makes it affordable for planners working in small- and medium-sized enterprises.

Plastic bending of adhesive-bonded sheet metals

Adhesive bonding is becoming one of the popular joining techniques in sheet metal industries, since it has some advantages over other techniques such as welding and diffusion bonding, e.g., any dissimilar metals are easily adhesive-bonded together, and the adhesive layer existing between the two sheet metals can play the role of vibration damping. Usually, press-formed sheet metal elements are jointed together at the final stage of assembly. However, if it could be possible to press-form adhesive-bonded flat sheet metals into the final products, this would be an excellent technique from the viewpoint of high productivity. In the present work, the plastic bending of adhesive-bonded sheet metals was investigated by performing V-bending experiments. A serious problem encountered in the V-bending was bending-induced large transverse shear deformation of the adhesive layer, which leads to geometrical imperfection of the bent sheets (so-called ‘ gull-wing’ bend), and in some extreme cases, it causes the delamination of the sheet. It was found both from experimental observations and from elasto-plastic stress analysis that the large shear deformation progresses rapidly only at the final stage of V-bending. Consequently, the air-bending operation for adhesive-bonded sheet metals is recommended for suppressing the shear deformation of the adhesive layer to within an acceptable limit.

Process planning for small batch manufacturing of sheet metal parts

The paper describes process planning for order-based small batch sheet metal part manufacturing. In this domain, general purpose CNC machinery and standard tools are being used. An example of a process planning system is given and some areas of special interest are discussed in more detail. Process planning for sheet bending and tolerance reasoning are important and intricate tasks within process planning, whereas abstractions in design and nesting are important due to their relations with other manufacturing functions. In general, manufacturing functions tend to become increasingly intertwined and traditional boundaries become blurred. Sheet metal industries, customers and suppliers alike, can benefit from this.

A neural networks approach to investigating the geometrical influence on wrinkling in sheet metal forming

In sheet metal industries, the ability to predict and avoid surface failures, such as wrinkling, is of great importance. Wrinkling behaviour can be affected by various factors. However, little research has focused on generalisation of the role of geometry on the occurrence of wrinkling. In this paper, the geometrical features of various formed parts are generalised and correlated with surface behaviour (wrinkled or wrinkle-free). A model based on an artificial neural network is introduced to reveal the critical geometrical criteria for wrinkling. This model is a feed forward back propagation neural network with a set of geometrical variables as its inputs and the possibility of the occurrence of wrinkling as its output. After using experimental data to train and test it, the model was applied to new data for prediction of the occurrence of wrinkling. The results are promising. The network can correctly forecast a large portion of the occurrence of wrinkling based on the given information on the geometrical features of points. Besides, by examining the contribution factors of the neural network in its prediction performance, we may also obtain certain information regarding the relative importance of each geometrical variable investigated. It is believed that the neural model can be a useful tool for the product design engineer as well as the workshop practitioner.

Graph Partitioning and Set Covering for the Optimal Design of a Production System in the Metal Industry

In this article, we are dealing with a design problem in the sheet metal industry. We are interested in the process of punching holes in various shapes on metal sheets, the blanks. A multi-head technology for the hole-punching phase is analyzed and the solution procedure is related to classical problems of combinatorial optimization. We shall describe the algorithmic implementation and report numerical results for the best multi-head configurations.

Logistics from IMS towards virtual factory

This paper shows some aspects of the design and control in logistic systems of typical processes in traditional integrated systems, IMS and virtual factories in the sheet metal industry. Main components of the virtual factory are logistics and the information technology background. By globalisation of production, factory inside logistics is replaced by a global logistic concept. In this paper those logistic concepts are summarised, which can be used in designing of material flow, optimising the parameters as well as in performance evaluation for closed loop production of sheet metal processing. The information flow, connected with the material flow, is also represented in the survey. Shared data structures and telecommunication are essential parts of the control strategy in logistic systems.

Influence of punch shapes on the collar-drawing process of sheet steel

Abstract An incremental elasto-plastic finite-element method based on the updated Lagrangian formulation was adopted to predict the limiting condition of collar-drawing until unloading for three punch shapes: conical, cylindrical and spherical. The high non-linearity of the process was taken into account in an incremental manner and an rmin technique was used to limit the size of each increment within a linear relation. Based on a series of collar-drawing tests for these three punch shapes, the fracture thickness under the simple tension test was measured and served as a necking criterion on the hole periphery for the limiting condition of collar-drawing. Predictions of the final shapes, the variation of thickness and the relationship of punch load to punch stroke under the limiting conditions were in good agreement with the results of the experiment. A simulation of the influence of process parameters on the collar-drawing for the three punch shapes indicates that the punch load increases sharply with punch angle in the case of the conical punch and increases gradually with friction coefficient for all of the punches, but decreases with strain-hardening exponent. The maximum punch load decreases with the initial diameter of the hole in the cases of spherical and cylindrical punches but not in the case of the conical punch. It is noted that the relation on the diameter of the hole before and after drawing is linear. Consequently, the initial diameter of the hole for an expanded hole with punch diameter can be determined and verified by the three punch shapes. This can be useful for the sheet metal industry.