Continuous process chains for profile wires

November 2018 — Dies for drawing and rolling are designed and optimised today using CAE software. However, for many firms this is a strenuous effort. Often, they rely on employee experience or procedures based on the "trial and error" principle. Both are neither sustainable nor cheap.

That’s why sometimes producers rather reject customer inquiries for difficult profile shapes. However numeric methods for the simulation of wire rolling by means of non-linear, elasto-plastic finite element analysis (FEA) improve the speed and quality of tool design. They also lead to a better understanding of the shaping process. Appropriate software like “Copra Wire Rolling” can continuously depict the complete workflow. In order to identify design errors early, it is best practice to employ a continuous process chain from design to the virtual implementing of a tool set. Thus, material compression or the desired surface area can be specified, considerably alleviating the work load of the designer. Moreover, the software makes suggestions for the shaping process. The following approach illustrates the benefits of a continuous process chain for rolled wire profiles. 

In the first step, the designer draws the final cross section of the wire with a CAD function. The required closed polyline is subsequently analysed and transferred to the interface of “Copra RF”. Afterwards the software provides all relevant profile information like geometry and surface area in a spread sheet for further processing. As soon as the final cross section of the wire profile is available, Copra RF calculates the required diameter of the incoming wire. For very flat end profiles like in the case example, the software calculates a flat oval. The required diameter of the round wire can be obtained by definition of the assumed compression. 

Afterwards, the shaping steps are calculated from the final to the initial cross section, meaning that the designer merely has to set the number of steps as well as the deformation rate of each step in percent. Individual stations can subsequently be modified manually. For the manual creation based on experience values, Copra RF provides a function for balancing of surface areas within the desired ratios. From the calculated or designed stations, Copra RF generates the contours of the top and bottom rolls. 

However, the most important aspect is the simulation and verification of the employed forming strategy. For the designer, the finite element analysis is a powerful tool for testing the shaping process – without the need to make real tests on the machine. 

The new Release of Copra Wire Rolling introduces various new functions like “Apply Tension in Wire” or “Define Annealing Stations”. The latter gives designers the possibility of defining stations after which the material is subsequently annealed. In addition, it is now possible to implement a predefined tension force in rolling direction. Copra Wire Rolling 2019 furthermore allows adjustment of the remesh properties at each individual station. The respective properties for material, mesh as well as process parameters can be accessed at any time, e. g. to easily compare the behaviour of different materials. Finally, the stresses and strains will be displayed in rolling direction.

The case of an arrow profile shows the optimisation by means of simulation. As the image illustrates, too much material is flowing to the left side in the first design, leading to burrs in those areas. However, there is material missing on the right side. The material behaviour is analysed within the individual station in order to draw conclusions about the necessary optimisation. Through adjustments of the existing cross sections or by redesigning, the new variant will be created in short order, having the same initial diameter for round wire as well as flat oval. The geometry of the intermediate stations is created out of the existing stations with common CAD-functions like “copy”, “scale” or “modify”.

There is now too much material in the arrow hat, in addition to deviations at the end of the profile. However, the strategy seems to work better overall. The profile cross section is filled after employing the new strategy. But it is obvious that there is still too much material. Based on the results, the diameter of the incoming round wire is reduced and the roll geometry in the last station adjusted accordingly. This optimising step is productive, reaching the desired profile geometry. It showed that by means of simulation, the reshaping of the arrow profile can be optimised in only three steps. The cost for a comparable effort on the machine would be a multiple of that. There is an array of analysing possibilities available for the designer: Among others the calculation of the actual material reduction within each station as well as the occurring forming forces. 

As indicated, the FE simulation allows statements about the feasibility of a wire project without any risk. Furthermore, it reduces the time between design of the forming stations and verification of the shaping strategy significantly – a lengthy trial and error process is unnecessary. 

Data M Sheet Metal Solutions GmbH
Am Marschallfeld 17
83626 Valley/Germany
Contact persons are Albert Sedlmaier and Stefan Freitag
Tel.: +49 8024 640-0

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