DRAWING

Today’s bar drawing activity is performed by means of a rather simple tool system. The drawing die usually made of tungsten carbide is prestressed by a simple steel ring. The drawing tool is fixed to the drawing plate that again is mounted into the actual drawing bench.
In order to service the broad variety of bar drawn dimensions combined with a broad variation in material grades for bars, the manufacturer needs a large number of in principle identical tools with just a slight difference of the inner diameter of the die. In practice, the manufacturer can easily carry several tools prepared for a certain bar dimension, for example 40mm diameter. For servicing this bar dimension, the manufacturer needs a drawing tool system that can handle the variations of the incoming material in regard to the delivered bar pre-dimension, material grade, small differences in material quality, etc. Building on the example of the 40mm bar drawing tool, the manufacturer needs upfront a die with an ID of for example 39.94mm diameter for a low alloyed steel grade, and for a higher alloyed steel grade he needs for example a die with ID 39.82mm diameter for obtaining the specified bar dimension. However, due to the variations of the incoming material, the manufacturer needs a number of tools surrounding this principal bar dimension for compensating for these stochastic variations. In fact, the manufacturer may need one tool for every 0.01mm, making it easy to imagine how many tools the manufacturer needs on the shelf just waiting for their next job. It is not only complex to control and maintain, it is also costly in tool inventory.
In close collaboration with a German manufacturer, Strecon has developed a new tool system for bar drawing. The main idea is to significantly reducing the need of spare tools by replacing the current single tools with a new adjustable tool system. The heart of the new tool system is based on the high-strength Stecon stripwound container technology. In addition, the stripwound container ring is built on the basis of an integrated tungsten carbide ring in order to provide maximum stiffness to the bar drawing die itself. In comparison with current bar drawing tools, the tool stiffness is more than double. This feature has three basic merits: One of reduced die deflection (i.e. elastic stress-strain behavior) during the drawing operation. Another is the possible use of more wear resistant drawing die material (i.e. a harder tungsten carbide grade) in benefit of less die wear and improved service life. A third is the fully controlled die adjustment of the inner diameter to match the need of the specific bar material and pre-dimension.
For two years the new adjustable tool system has been tested and optimised at the German production facility for round bars, and good results have been obtained. In addition to optimisation of the tool system itself, another important learning point has been made. The bar drawing process is the key of the complete production line. If this stops, everything else stops. Therefore, Strecon needed to develop a compact tool assembly press for facilitating a fast, easy and safe adjustment of the bar drawing die in close proximity of the production line. This press is described in more details below.

Tool assembly and die adjustment press

The new tool assembly and adjustment press is developed for servicing a variety of needs. One key motivation originates from the new tool system for the bar drawing business mentioned above. Another need is the assembly and disassembly of the tools for the next production order, or for changing the tool for the current press job.
A third and a more general need is the desire from Strecon to offer an alternative solution to the tool assembly presses usually seen in the market. The aim was specifically to develop a small, compact, ergonomic designed and easy to operate press unit that could facilitate both standard tool assembly/disassembly jobs as well as the most demanding die adjustment requirements, e.g. the inner diameter of a gear spline die (i.e. a few microns), or the axial prestressing of dies under a fully controlled load position (i.e. locking the tool during press load).
The new assembly press requires less than 1m² in space, and is currently offered up to 200t (2,000kN). The height is just less than 2m, and with a total weight of some 1,500kg, the press unit fits into every small corner in the tool room or at the production floor. The hydraulic and electrical systems are all integrated into this small unit, making it very easy to install and move if required, especially as the tool press does not require specific foundation.

Dijet tungsten carbide

Strecon is the authorised European distributor of tungsten carbide tools from Dijet Industrial, Japan. The tools are offered both as preforms and as finished tools depending on the requirements of the individual customer. Dijet is a Japanese high-quality developer and manufacturer of tungsten carbide materials, and supplies its materials for well-known end users like Toyota, Honda, Nissan, Denso as well as tool makers like Nichidai.
Recently, Dijet has introduced a new series of carbide grades with enhanced compressive stress and improved wear, galling and corrosion resistant properties. This new material grade is named NC alloys, and has proven effective in prolonging the service life of the die and punch on various applications. The Dijet product programme includes die inserts, punches, knock out pins, pressure plates and pads, sleeves, etc. for cold work. In addition to a very high product quality, Dijet is very strong on short delivery times, usually a few weeks from order.

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