Submitted master’s thesis deals with rotary draw bending of tubes as a subprocess of automobile’s stabilizer bar production. The main goal of the thesis is to clarify the influence of the process parameters of the bend on the resulting shape and properties of the product. Submitted thesis includes theoretical description of the chosen tube bending technology, description of defects and possibilities of their removal. The description of the bending machine used for stabilizer bars production is done afterwards. Practical part of the thesis includes experiments clarifying influence of parameters on the resulting shape of the stabilizer bar.

The objective of this research is to simulate a pushorming operation for the manufacturing of copper tube elbows using the finite element method. This model may be useful in the design of tooling. The influences of lubricant type, the tube blank material, and a minute surface defect are considered in the model. Tensile tests of annealed copper specimens are conducted to derive stress-strain data, defining the material behavior of the copper tube blank. In addition, friction tests are performed to obtain static and dynamic friction coefficients for a wet and dry lubricant types, which are used in the forming process. The finite element study of the forming operation has proven to require a considerable amount of time for modeling and processing. The verification examples and the pushorming models demonstrate the ability of the finite element program to include: contact with friction, the actuating of hydraulically controlled components, buckling, and nonlinearity.

Plastic  deformation of tubes can be achieved in numerous ways. One of the most useful type is CNC tube bending machines which is used in many industries such as aerospace, automotive, HVAC systems and so on. It is important that all components of system should mate properly after producing and because of this bend shaping requires sensitive operation on each components to ensure regularity of production processes with high quality end-product. Thus, the CNC tube bending industry to become widespread. However it brings some troubleshooting like wrinkling, springback, breakage and ovalisation. This failures depends on geometry of the material such as bending radius, tube thickness and also friction factor between dies and the tube. Effects of all parameters should be examined before generating the theory for a best solution. Therefore, prediction of the required moment for the proper bending process with low cost and shortened production time is needed. All of these requirements can be achieved through a C++ form application program.

Master thesis analyzes rotary draw bending of the tubes without using a mandrel. Bending process is accompanied by many defects due to large displacement of formed material. One of the major defects is flattering of the cross section also called ovality. In order to decrease ovality comes up a proposal of the changes to the tool design. Modifications of tool’s geometry are numerically analyzed by finite element method in software ANSYS. According to the results of the simulations an optimized pressure die is manufactured. Several experimental tests are accomplished to verify the effect of the optimized tool design. Approximately 100 bends confirm a decrease of ovality using modified pressure die.

Bending of thin-walled tubing to a prescribed bend radius is typically performed by bending it around a mandrel of the desired bend radius, corrected for spring back. By eliminating the mandrel, costly setup time would be reduced, permitting multiple change of radius during a production run, and even intermixing different products on the same line. The principal challenge is to avoid buckling, as the mandrel and shoe are generally shaped to enclose the tube while bending. Without the shaped mandrel, buckling will likely occur sooner, that is, at larger bend radii. A test apparatus has been built for arborless bending. It has been used to determine the limits of bend radius, wall thickness, material properties, etc. on buckling. Key to the process is a set of moveable clamps, which grip the tube and rotate to produce the bend. A complex control system moves the clamps radially to maintain pure bending, without superimposing tension or compression. A series of tests were performed to document the safe region of operation to avoid buckling. Charts have been created to assist the operator, as well as the design engineer, in determining the minimum bend radius. Similar tests will be required for each additional tube size, thickness, material, etc.

Rotary draw bending, which has very good flexibility and easy tooling, is one of the most preferred bending types for tubular profiles. Cross-section distortion and the spring-back phenomena are commonly faced problems in bending processes. Spring-back is the inevitable problem that is to be solved by manufacturer, generally by overbending. For hollow tubes cross-section distortion is another difficulty since using hollow tubes results in higher strain rates and distortions. During the process the thickness of the hollow tube at the inner surface, which is contacting with the die, increases and the thickness of the tube at the outer surface decreases. Wrinkling is another important defect that occurs at the inner surface of the tube in large diameter thin walled tube bendings. This research compares the experimental results with the finite element analysis of the rotary draw bending process. The aim is to obtain bending characteristics of the two material types, SS304 and St37 and so, to reduce the number of the bending in manufacturing. The main parameters in rotary draw bending process are the bending angle, bend radius, material properties and the geometry of the tube that is to be bent. In this study, to deal with the process, two different materials, three different bending angles and three different tube geometries are used in experiments as well as in finite element analysis. In finite element analysis explicit method is used. It is seen that the experimental results are in good agreement with the numerical results.

One of the principal energy absorbing structural components that influences the crashworthiness of a vehicle is the side-rail, which is also commonly referred to as an s-rail due to its shape that is reminiscent of an “s”. To improve the crashworthiness of a vehicle, in the wake of significant environmental pressures requiring vehicle light-weighting, the parameters that govern the crash response of the s-rail and the implications of light-weight material substitution need to be better understood. In this work, the main parameters that govern the crash response of an s-rail and the variables that influence them were identified and assessed through a combined experimental and numerical modelling programme. In particular, the as-formed properties of aluminium alloy s-rails, due to the tube bending and hydroforming fabrication route were examined. Tube bending, hydroforming and crash experiments were conducted to examine and assess the effects of initial tube thickness, strength, geometry, bend severity, work hardening, thickness changes and residual stresses on the crash response of the s-rail. The forming process variables, springback, thickness, strains, and force and energy response measured in the experiments were used to validate the finite element models developed herein. The validated numerical models of tube bending, hydroforming and crash provided additional insight and also allowed further investigation of the parameters governing the crash response of s-rails. The relevant parameters governing the crash response of s-rails were isolated and the basis for a set of design guidelines, in terms of maximizing energy absorption or minimizing mass, was established. The overall size is the most influential design parameter affecting the energy absorption capability of the s-rail, followed by the initial thickness, material strength, cross-sectional geometry, bend severity and hydroforming process employed, and finally boost in bending. The most significant conclusion made based on this research is that the effects of forming history must be considered to accurately predict the crash response of the s-rail. There are additional conclusions with respect to the tube bending and hydroforming processes, as well as s-rail crash response, that will contribute to improving the design of s-rails for better crashworthiness of vehicles.

One of the principal energy absorbing structural components that influences the crashworthiness of a vehicle is the side-rail, which is also commonly referred to as an s-rail due to its shape that is reminiscent of an “s”. To improve the crashworthiness of a vehicle, in the wake of significant environmental pressures requiring vehicle light-weighting, the parameters that govern the crash response of the s-rail and the implications of light-weight material substitution need to be better understood. In this work, the main parameters that govern the crash response of an s-rail and the variables that influence them were identified and assessed through a combined experimental and numerical modelling programme. In particular, the as-formed properties of aluminium alloy s-rails, due to the tube bending and hydroforming fabrication route were examined. Tube bending, hydroforming and crash experiments were conducted to examine and assess the effects of initial tube thickness, strength, geometry, bend severity, work hardening, thickness changes and residual stresses on the crash response of the s-rail. The forming process variables, springback, thickness, strains, and force and energy response measured in the experiments were used to validate the finite element models developed herein. The validated numerical models of tube bending, hydroforming and crash provided additional insight and also allowed further investigation of the parameters governing the crash response of s-rails. The relevant parameters governing the crash response of s-rails were isolated and the basis for a set of design guidelines, in terms of maximizing energy absorption or minimizing mass, was established. The overall size is the most influential design parameter affecting the energy absorption capability of the s-rail, followed by the initial thickness, material strength, cross-sectional geometry, bend severity and hydroforming process employed, and finally boost in bending. The most significant conclusion made based on this research is that the effects of forming history must be considered to accurately predict the crash response of the s-rail. There are additional conclusions with respect to the tube bending and hydroforming processes, as well as s-rail crash response, that will contribute to improving the design of s-rails for better crashworthiness of vehicles.

The work deals with the analysis of the influence of process parameters, material factor and tools power effect to compliance with the limit shape tolerances of specified parts of bending tubes by method of wrapping. Their evaluation using statistics and the resulting recommendations for process optimization.

This diploma thesis has been elaborated within the Master's study of department 2307 that submits a production hooped component. The material of the component is steel ČSN 15 130. Single – part as far as small–lot production. On the basis of the literary study problems bend tubing was sugested the method: rotary draw bending. For this method was sugested mechanical bending machine with mandrel support arm, for bending with mandrel and exact bends in three – dimensional.