Short-notice changes in diameter tolerance can be dealt with very quickly. With a new drawing die, production simply continues.

Photos: Jankowski

Compact wire drawing machine, here as double drawing type for phosphated wire rod, reduced to 3,45 mm.

This diagram shows relation between tensile strength and change in diameter.

Wire-drawing Economizes Purchase to Size

PDF

Zurück

Over the last four years, at Jankowski GmbH+Co.KG alone, the number of clients also taking up wire drawing, has increased to 50%. It becomes ever more apparent, that the drawing of wire offers much more potential for savings than purchasing does. The mere purchase price of carbon steel wire rod up to a diameter of 5,5 mm is 25 % lower than cold-drawn annealed cold-drawn ( +U+C+AC+LC respectively “KGK”) wire. In case of stainless steel, this difference even amounts to 40%. Not only your purchasing department will be happy about this, because by investing into a wire-drawing machine, also the drive mechanism of the wire plate is included into the system.
Additionally, strength and formability of the wire can be influenced by wire drawing, thus allowing diversity of material grades to be reduced effectively. Moreover, the number of different dimensions to be stocked will be less. The complete diameter range from 0,5 to 1,0 mm – in particular cases even up to 1,5mm – can be covered by one single wire rod. Presently, by double-drawing, wire rods with 5,5 mm diameter can be reduced down to 3,5mm, while reductions up to 43% can be achieved in one single draw. Drawing has already proved its value for comparably simple cold-form parts. An additional advantage is that stock-keeping of wire rods is not complicated at all. Costs for accommodation are cut in half. Wire rods can be stocked on top of each other while finished drawn wire needs to be stocked with much more care. For wire rods, a simple roofing construction is sufficient, as a little flash rust does not have any negative influence on the production process. Any remnants of wire, which are a significant part of the total costs, can be used for future orders. Even short-notice changes of diameter tolerances can be adhered to using the same initial wire rod. With the procurement of a new drawing die within a few days, production simply continues. With the increase of tonnage used – for example from 1 ton to 2 tons of wire - change over time at the press can be cut in half. In this context, it is often argued, that the tooling time of the wire drawing machine has also to be taken into consideration when calculating cost effectiveness. This certainly is correct. Tooling time for changing of rings is between 5 to 15 minutes per each change. But considering that there always is a buffer of 5 to 10 wire windings on the drawing disk, a new coil of wire can easily be put onto the wire plate, while these buffers are being used up. In doing so, tooling times are cut in two. The pointing of wire also can take place apart from the production line.

Logistic expense is reduced approximately fivefold. The success of wire drawing becomes evident in the thoroughness of its proceedings. The statement of a Jankowski customer shows this clearly: He states that by this process, production costs have become less and the thus achieved saving of cost was passed on to his clients. In doing so, the working load increased, enabling him to produce at even more competitive prices.
Next to profitability, quality plays a vital role. Roundness of wire can be specified up to 0,005 mm. This pays off especially in the case of thin wires and machines with high speed and output. Cold forming machines by Wafios Umformtechnik are a good example: They have a rotation matrix block, type HC-4-35 with an output of 800 parts/min and a speed of 40 m/min. or type HE4-40 with 700 parts/min. Equally important is the constancy of diameter which improves productivity by approximately 10%. Here, service life of machines is increased by constancy of volume and nearly proportional wear of both toolings. It is, however, not correct in this context to claim that service time of machines would suffer due an increase of the material’s tensile strength. The hardness value of tooling – supported by surface coating - is 64 HRC.

Here, a difference of 100 N in the wire is insignificant. This applies to non-alloy steel grades as well as to alloy steel grades. In contrast, a dimensional tolerance of 0,02 for a wire of 15 mm diameter and a length of 100 mm with a 0,3% variation in volume is significantly more disadvantageous for the service life of tooling. Also, surfaces are no longer damaged by transport or storage. This not only results in increased quality, but also in increased productivity. Two-sided, square, hexagon or polygon profiles can easily be formed by pre-drawing round wire. A reduction of costs starting from 20% upwards is possible by this forming process alone. Also, the application of lubricants is an interesting aspect of wire drawing. Wire rods are inserted individually. This creates an even coating which has positive effects on the forming process. Jankowski have gathered positive experience in the entrainment of lubricants using the low-viscosity drawing medium Multi Draw Adhesive Viscose (max. 2000 PAS). Compatibility with press oil is ideal; tunnel formation is avoided by flex levelling of low-viscosity grease.
Wire shaping under temperature is also very successful. Especially where stainless steels are concerned, the degree of deformation is influenced considerably. Using a drawing temperature of 200°C on an austenitic wire 1.4301 for example, leads to a reserve in deformation degree of 60 % (5 N per 1,5N/degree of deformation). At a 20° reduction this means a 70 N lower resistance during the subsequent forming process. Upon entering into the cold forming machine, the wire is cold. Therefore, the operating temperature of the press is by 200°C lower as with the use of pre-heating devices, which stand in front of the press. Thus service life of tooling is increased notably: for example for a screw head in 1.4301, service life increases from 2 h to 5 h. A wire in 1.4401 has a 30% better formability from 11,4 to 8 N. Even in a ferrite-austenitic material – duplex steel 1.4362 – the strength decreases by 20% from 20 to 15 N when heated to 200°C. Speaking in terms of formability, this corresponds to a benefit which increases from 20 to 27%).
This also is an advantage when material grades are to be chosen: You can centre your focus on product properties mainly and only secondly you need to look at formability. And so, in combination with an intelligent choice of material, the price difference to low-price countries can be compensated largely.