Press Brakes Research Articles

Strategies of Heating and Hardening External Corners on the Example of Bending Tools for Press Brakes

Strategies of Heating and Hardening External Corners on the Example of Bending Tools for Press Brakes

A framework for planning a reconfigurable assembly system for press brake production

This article presents the design of a framework for the development of a reconfigurable assembly system (RAS) to facilitate the assembly of press brakes varieties. A consideration of press brake varieties is achieved by examining the parts taxonomy of press brakes from which a framework for assembly process plan is developed that considers all the types of press brakes identified from the classification. Also, a layout for the RAS is developed by considering a prototype of the major enabling equipment of the system which is a reconfigurable assembly fixture (RAF). The development of the assembly process plan and layout of the RAS enabled the design of a reconfiguration model for operation in the RAS. The designed assembly framework will provide: rapid and physical reconfiguration of the RAF in the RAS; generation of assembly sequence for press brake varieties; and allocation of assembly operations to assembly work cells in the system. [Submitted 27 May 2020; Accepted 3 December 2020]

Prediction and optimization of multipoint dimple sheet forming of structural steel using Taguchi method

In this paper, multipoint dimple sheet forming process parameters is investigated in terms of optimization using finite element technique and Taguchi method. Dimples are produced using punch and die press braking operation. Dimple sheet formed using roller is very complex due to nonlinear structure, costly and widely used in construction, in many industrial applications. In this work, Ansys simulation software is used for accurate and critical understanding effect of sheet thickness, diameter of dimple, depth of dimple and distance between dimples in dimple forming process. The major objective is to determine the effect of the process parameters to obtain the optimal multipoint forming design of the dimple sheet. The hemispheric punch chosen for dimple is based on commonly used for various dimple sheet applications. Process parameters are sheet thickness, diameter of dimple, depth of dimple and distance between dimples has been analyzed using Taguchi method. The material selected for this work is structural steel. The results obtained indicate that the parameter sheet thickness is the most effective one on forming force. Tensile test of optimal parameter, result predicts that the dimple sheet strength is greater than that of the plain sheet.

Numerical Prediction of Residual Stresses Distribution in Thin-Walled Press-Braked Stainless Steel Sections.

Stainless steels are increasingly used in construction today, especially in harsh environments, in which steel corrosion commonly occurs. Cold-formed stainless steel structures are currently increasing in popularity because of its efficiency in load-bearing capacity and its appealing architectural appearance. Cold-rolling and press-braking are the cold-working processes used in the forming of stainless steel sections. Press braking can produce large cross-sections from thin to thick-walled sections compared to cold-rolling. Cold-forming in press-braked sections significantly affect member behaviour and joints; therefore, they have attained great attention from many researchers to initiate investigations on those effects. This paper examines the behaviour of residual stress distribution of stainless steel press-braked sections by implementing three-dimensional finite element (3D-FE) technique. The study proposed a full finite element procedure to predict the residual stresses starting from coiling-uncoiling to press-braking. This work considered material anisotropy to examine its effect on the residual stress distribution. The technique adopted was compared with different finite element techniques in the literature. This study also provided a parametric study for three corner radius-to-thickness ratios looking at the through-thickness residual stress distribution of four stainless steels (i.e., ferritic, austenitic, duplex, lean duplex) in which have their own chemical composition. In conclusion, the comparison showed that the adopted technique provides a detailed prediction of residual stress distribution. The influence of geometrical aspects is more pronounced than the material properties. Neglecting the material anisotropy shows higher shifting in the neutral axis. The parametric study showed that all stainless steel types have the same stress through-thickness distribution. Moreover, R/t ratios’ effect is insignificant in all transverse residual stress distributions, but a slight change to R/t ratios can affect the longitudinal residual stress distribution.

A model for achieving reconfiguration in a smart assembly work-cell

The reconfigurable assembly system is a type of a smart assembly system that can survive the challenges of personalised customisation of product design in the manufacturing sector. Reconfigurable assembly fixtures (RAFs) have been identified as enabling equipment in assembly work cells of reconfigurable assembly systems. RAFs can rapidly adapt to different dimensions of product sizes in the same part family. In this article, a reconfiguration model (RM) for achieving rapid positioning and immobilisation of press brake models is developed for a reconfigurable assembly fixture used for assembling press brakes. The model sets the reconfiguration limits of the RAF based on fixture workspace synthesis and physical dimensions of the press bake. It converts the physical dimensions of the press brake into travel length of locators and computes the operating parameters of the RAF. It also attempts to integrate the operation of the RAF with the assembly procedure in the system. The reconfiguration model is validated using different dimensions of press brake models. The reconfiguration model yielded results for operating parameters of the RAF, which are presented graphically and discussed extensively in order to compare the response of the model to the expected behaviour of the RAF. Comparing the responses of the RM to different press brake models shows different values for the operating parameters of the RAF which is valid. Also, the article established and supports the fact that the operations of a RAF are incomplete without a RM. The originality of the article lies in the development of customised mathematical models for the RM that is meant for the RAF and its validation using different press brake models as the product to be assembled.

Dimpling of CR4 Sheet and Its Parametric Optimization using Taguchi method

Dimple sheet is formed using cold rolling or press braking process. Wider use of dimple sheet in various fields may create interest in the study of dimple sheet. This paper describes a numerical modeling approach and results into the mechanical property. A mechanical tensile test on plain sheet and dimpled sheet CR4 steel material were conducted for evaluation of numerical results. A finite element explicit dynamic analysis approach is used to simulate the tensile test. Tensile tests are carried out as per orthogonal array of Taguchi method. True stress–strain data obtained from tests were used to optimize the process parameters, this could correlate to the increase in the strength of the dimpled sheet as observed in experimental tests and simulations.. The process parameters of dimple forming such as dimple depth, dimple diameter and distance between dimples are analyze for strength of sheet on CR4 steel material. Design of experiments is implemented for to optimize process parameters by using a Taguchi method design. The effect of the process parameters on response have studied by means of main effect plots which are developed by SN ratio and optimum parameter is selected on the basis of signal to noise ratio.

A cost-effective device for online measurement of sheet metal bending angle on CNC press brakes based on capacitive sensors

Sheet metal bending on press brakes is one of the most widespread manufacturing processes. A common issue in press brake bending is the deviation of the actual bending angle from the theoretical one due to elastic spring-back of the sheet metal. This is typically rectified by a systematic trial-and-error process, which has to be based on a suitable measuring device that is flexible enough to adapt to a wide range of computer numerically controlled machines, accurate enough with respect to modern manufacturing needs and cost effective enough to be used on low cost press brakes. This work presents the development of such a device resembling a miniature robotic arm and employing capacitive sensors. Two stepping motors adapt the arm to any bending angle sheet configuration. The measuring process is commanded by a microcontroller. Statistical evidence on accuracy and repeatability of the system is provided, being better than 0.1° and 0.3° whilst cost is kept reasonable.

A cost-effective device for online measurement of sheet metal bending angle on CNC press brakes based on capacitive sensors

A cost-effective device for online measurement of sheet metal bending angle on CNC press brakes based on capacitive sensors

Industrial validation of strain in cold roll forming of UHSS

Cold roll forming is a highly productive sheet metal forming process capable of producing an exceptional range of profile geometries. Over the last few years customers have increased the demand for high value components, through the specification of complex profiles, tighter tolerances and/or use of high strength materials. In particular, there has been a high interest by the automotive industry in utilising ultra-high strength steels (UHSSs) within the roll forming process. These steels are ideal for the forming of lightweight products, which possess increased material performance when compared to traditional low strength steels. The industry’s attraction towards the roll forming process may be due to the increased deformation capabilities it can provide and due to the formability limitations of UHSS when using traditional stamping or press braking processes. This investigation aimed to determine an appropriate approach to simulating the cold roll forming process using UHSSs for future industrial applications. Currently a large volume of research can be found on the material characterisation and formability of UHSS using traditional processes. While the interest in roll forming is rapidly increasing over time, there remains a large research gap in this field. Hence, a dual phase steel (DP1000) and complex phase steel (CP1000) provided by TATA Steel were analysed using a five pass roll forming assembly to form the following two profiles: (a) V-section; and (b) flat strip with rib feature. The principal strains along the outer radius of each specimen were analysed using a GOM Argus photogrammetry system. A circle grid analysis was the method used to complete these measurements. The strain analyses were compared with corresponding strains along the surface of the finite element (FE) analysis model results. The non-linear FE simulations were carried out using COPRA® FEA RF 2017. Correlations in the results were achieved, setting a foundation for further investigations on the formability of UHSSs.

03.16: Multiplanar K‐joints on cold‐formed open sections: An experimental study with high strength steels

ABSTRACTThe design, laboratory investigation and main results of an experimental programme on the joints of an innovative 3D truss made of high strength steel (HSS) is presented. An entire truss of triangular cross‐section was fabricated (two compression chords and a single tension chord) to provide realistic loading conditions. Both compression and tension chords were fabricated by cold forming hot‐rolled HSS plates by means of press braking. The chords were as follows: — an open angle‐type profile with 45° contained angle as tension chord (U‐chord), — a semi‐closed octagonal profile made of 3 sectors bolted along their length every 1.2 diameters as compression chords (P‐chord). The focus of this study is on the tension chords joints where a pair of tension and a pair of compression diagonals converge. Joints were tested to ultimate load by introducing shear to one bay of the truss at a time. Two design approaches for the joints were tested resulting in four individual tests.Ultimate load levels, stiffness and failure modes varied between the considered joint configurations. Stiffening increased the ultimate load by as much as 170% of that of the unstiffened version achieving higher utilisation of the tension chord, thus making more efficient use of HSS. The stiffness loss at loads close to failure varied between 60% – 80%. Two distinctive failure modes were observed, one caused by cracking of the welds connecting the diagonal's gusset plates to the tension chord while the second by cross‐section tensile fracture of the circular hollow section (CHS) diagonal.

Cost Effectiveness of CFRP Repair Technique for Cold Formed Steel Beams

Objectives: Structural steel can be broadly classified into hot rolled steel and cold formed steel (CFS). CFS manufactured from roll forming or press braking operation. The main advantage of CFS sections are thin wall and light weight. These thin wall leads to buckling of structural member. This paper aims to study the capacity of Carbon Fibre Reinforced Polymer (CFRP) strengthened CFS channel beams, buckling behaviour, deflection and cost studies on CFRP strengthening. Methods/Statistical analysis: In this study three different length of CFS channel sections are selected for testing in which beams are tested for bending. All the beams were tested in plain section and CFRP strengthened series in universal testing machine. Findings: Experimental results shows the enhancement in capacity of beam due to CFRP strengthening. The local and distortional buckling modes were observed as failure modes. Experimental results were compared with maximum load resistance calculated by AISI specification which are in good agreement. Cost studies were compared on replacing a new member with CFRP strengthened channel member. Improvements/Applications: CFRP strengthening is suitable for enhancement of capacity of beams and repair. This CFRP strengthening technique can applied to reinforced concrete members, hot rolled steel, in filled steel tubes and bridges etc.

Development of a STEP-compliant design and manufacturing framework for discrete sheet metal bend parts

Metal sheets have the ability to be formed into nonstandard sizes and sections. Displacement-controlled computer numerical control press brakes are used for three-dimensional sheet metal forming. Although the subject of vendor neutral computer-aided technologies (computer-aided design, computer-aided process planning and computer-aided manufacturing) is widely researched for machined parts, research in the field of sheet metal parts is very sparse. Blank development from three-dimensional computer-aided design model depends on the bending tools geometry and metal sheet properties. Furthermore, generation and propagation of bending errors depend on individual bend sequences. Bend sequence planning is carried out to minimize bending errors, keeping in view the available tooling geometry and the sheet material properties’ variation. Research reported in this article attempts to develop a STEP-compliant, vendor neutral design and manufacturing framework for discrete sheet metal bend parts to provide a capability of bidirectional communication between design and manufacturing cycles. Proposed framework will facilitate the use of design information downstream at the manufacturing stage in the form of bending workplan, bending workingsteps and a feedback mechanism to the upstage product designer. In order to realize this vendor neutral framework, STEP (ISO 10303), AP203, AP207, and AP219 along with STEP-NC (ISO14649) have been used to provide a basis of vendor neutral data modeling.

Application of Multivariate Adaptive Regression Splines to Sheet Metal Bending Process for Springback Compensation

An intelligent regression technique is applied for sheet metal bending processes to improve bending performance. This study is a part of another extensive study, automated sheet bending assistance for press brakes. Data related to material properties of sheet metal is collected in an online manner and fed to an intelligent system for determining the most accurate punch displacement without any offline iteration or calibration. The overall system aims to reduce the production time while increasing the performance of press brakes.

Design, simulation and experimental investigation of a novel reconfigurable assembly fixture for press brakes

A reconfigurable assembly fixture is a major and important component of a reconfigurable assembly system. It is required for the assembly of a variety of press brake models in order to reduce the assembly time and overall production time. The stages and requirements for the design of an assembly fixture and understanding of the assembly process for press brake models were used to design a reconfigurable assembly fixture. A detailed design analysis of parts of the fixture and the hydraulic system is considered and presented in this article. The stress and displacement analysis of the parts is executed using Solidworks express simulation. The parameters of the hydraulic components were determined from force requirements, and the hydraulic system was modelled physically using Matlab Simscape hydraulics. The response of the hydraulic system was obtained for each actuator in the system in order to depict the output of the actuators from the spool displacement of the valves. Stress analysis conducted on parts of the fixture showed that it can withstand maximum stresses that are lesser than the yield strength of the material used for the part. It was also established that synchronization of hydraulic actuators can best be achieved by the use of a sine input to the electrohydraulic valve. An experimental investigation was done using FESTO hydraulic test bench in order to observe the synchronized extension and retraction of the hydraulic actuators. The simulation of the hydraulic system, electric system and the programmable logic controller was prepared using automation studio. The design is envisaged to provide the industries with relevant information on accurate location and gripping of press brake frames rather than turning and repositioning of the frame in order to fit other parts during assembly. The article provides relevant information on the design analysis of a reconfigurable assembly fixture for press brakes which is novel because articles on reconfigurable assembly fixtures have not considered its application to press brake assembly.

Theoretic Analysis on the Influence of the Press-Brake Manufacturing Precision on the Bending Precision of Sheet-Metal

The bending sheet metal inevitably exist bending errors including angle error, linearity error and length error of sideline for reasons that the structure of press brake, the manufacturing precision of press brake and mould and the inhomogeneous characteristics of processed sheet metal. The processing errors of sheet metal can affect the assemblage, increasing subsequent repair to the mold and forming calibration, extending the product development cycle, restricting the further promotion and application of bending forming, especially on the forming high strength and high spring-back sheet metal. The PBH110-3100 CNC press brake in Jiangsu Yawei Co.Ltd. is studied to increase the bending precision of press brake in this study. The bending errors in press break are analyzed in depth according to the elastic mechanics theory, and the rule that the manufacturing precision of press brake affect the press precision is educed. The analysis results have real significance on improving the press precision and reliability of press brakes.

Sheet metal productivity improvement through a new press brake design

A new press brake design proposed as a reconfigurable bending press machine (RBPM) is reported. The design is a means of increasing sheet metal bending productivity. Conventional press brakes are dedicated machines with fixed capacity, but the RBPM has characteristics of a reconfigurable machine tool, which enables the new press brake to be scalable, customisable and flexible. The RBPM design has two major objectives, namely geometric transformation and productivity adjustment. Geometric transformation is achieved through vertical and horizontal reconfigurability, while productivity adjustment is enabled by plug and produce devices. Geometric transformation allows sheet metal benders to adjust the press brake's height and length, thus improving the capability of the RBPM. This allows small-scale manufacturers of sheet metal products such as door frames to be able to adjust their machines to produce various sizes of products at low cost. A scaled-down prototype was made to specifications of 1.2 m total length and total capacity 30 kN (3 tons) for bending aluminium sheets of up to 0.51 mm thickness.

Application of TRIZ in the Innovation Design of Feeding Safety Apparatus of Hydraulic Press Brake

The goal of the present research is to design a feeding safety apparatus of hydraulic press brake which can solve the problems of injuries of hands of operators while processing. The research method uses the contradiction matrix of TRIZ to find out the parameters which are to be improved and prevented from deteriorating and design a feeding safety apparatus with essential safety. The principle thereof is to use the driving lever and the supporting lever to generate synchronous movements; the operators do not need to extends both hands in the back of the press break mold, but can support the sheet metals in the front or the back of the press break mold; consequently, the injuries of both hands of the operators being pressed and clipped can be prevented.

A Study on the Nose Radius Influence in Press Brake Bending Operations by Finite Element Analysis

The sheet metal bending is one of the metal forming processes with the simplest geometric interpretation and usually a 2D analysis is considered. The bend over a sheet metal blank consists of a V shape forming by using a punch, with a certain nose radius, forcing the plate against an open die, with a V section. The forming result is a part with an angle obtained between the V legs, flanges, which is known as bending angle. The operation to get the required V angle is called air bending, or free bending. The most common used machines for this forming process are press brakes, special long presses, where the tools, punch and die, are attached to. With the spread use of CNC machines, and their computer control capabilities, most of them using graphical user interface (GUI), became important to get the required shape at first trial. Beyond the required bending angle obtained with just one hit, it is also important to position the gauge system in order to get the successive flange lengths to complete the programmed shape. The main variables controlled by the CNC are the punch penetration inside the die and the position of the back gauge, which is determined by the bend allowance. However this penetration is not the only responsible for the resulting bending angle and the gauging position is not the only responsible for the flange length. Additionally, the radius inside the V shape edge, known as bending radius, influences the geometry and correspondingly the bend allowance. Some authors believe that the punch nose radius has direct influence, both in the bending angle and bend allowance. In this paper, results are presented describing the use of finite element analysis as an aid in the prediction of the inside bending radius, that influences both punch penetration for the final bending angle and the bend allowance for the final flange length. From the air bending analysis, a natural inside bending radius is presented as an important variable in these kind of processes, as well as its minor dependence on the punch nose radius.

Adjustable Tooling System for Air Bending

The productivity of bending on press brakes is strongly affected by the changeover time between consecutive tooling setups. The need for flexible tooling systems that can reduce the setup time is therefore obvious. This is a fortiori true for robot supported bending operations, where the tool system should preferably allow fully automated setup of bending stations. In this article an innovative tooling system concept is presented that can adjust to different punch profiles (from straight tools to deep gooseneck profiles), provide horn tool functionality and allow setups with open punches for collision avoidance during bending. The Leuven bend tooling design can accommodate fully automated changeover between bending jobs. A prototype version of the Leuven bending tool system has been manufactured and extensively tested. Validation results with respect to achievable load levels and stiffness are reported in the article.

Robotic testing of radio frequency devices designed for industrial safety

An experimental setup is proposed to test the performance of safety devices based on radio frequency technology. The setup specifically tests devices designed for improving safety in dangerous areas of small size, such as those surrounding power press brakes. Tested here is a radio frequency identification (RFID) prototype, whose main objective is to prevent accidents by sending a stop signal to a machine when a worker’s wrist, bearing an RFID tag, gets too close to the dangerous area. An ABB IRB 2400L robot is used as a reference system; this system is capable of providing millimeter accuracy. A plastic hand and a wristband with at least one passive RFID tag are attached to the end of the robot arm, which emulates the behavior of a human arm. With this robotic approach, it is possible to test trajectories with different velocities and orientations and to simulate several risky situations associated with machine use. Several experiments are presented that were conducted with the RFID prototype, and statistics are reported on the distance detection capability of this safety system with respect to the plane that defines the dangerous area. A matrix approach is proposed for analyzing the robustness of safety devices that are designed to automatically prevent a worker entering in dangerous areas. The results show the benefits that development of a radio frequency device of this class could confer towards increasing worker safety.