A tungsten carbide wire drawing die (German: Ziehstein) is a forming tool with a conical bore that reduces wire or other strand-like material to a precise, smaller diameter. Fritz Leng has made carbide drawing dies in Herborn, Germany since 1948: each die is produced to order, its geometry matched to your material and reduction, hand-polished, with bore sizes from 0.2 to 150 mm and delivery within 24 hours when needed.
What are carbide wire drawing dies used for?
Carbide wire drawing dies are used to draw strand-like material, above all wire for the cable, tube and bar industries. In each draft the wire is pulled through the polished bore of the die; it becomes longer and thinner and takes on the exact shape of the opening. Under the German standard DIN 8584, wire drawing is classified as combined tension-compression forming: the pulling force acts on the exit side, while the actual forming is done by the pressure of the die wall.
For bars and tubes in larger dimensions we manufacture carbide drawing dies with casing diameters up to 450 mm.
What makes a carbide die run trouble-free?
Two things must be right from the start: high-quality carbide in the correct grade, and high-quality steel for the case. Both have to be matched in their composition to the individual application. The function and the service life of the die are then determined by the correct geometry of the drawing angle and bearing length, and by a mirror polish of the working surface.
Calculation and 3D CAD software help us determine the ideal parameters for your wire and reduction. We machine only carbide from leading global suppliers, and on request we deliver a measurement report with every die (see Quality).
Entry radius and entrance angle
The bore profile of a drawing die consists of zones that merge into one another: entry radius and entrance cone, drawing angle, and bearing length. The entry radius, also called the entrance angle, guides the incoming wire and centers it in the die, even when the wire enters in spirals. The entrance cone also feeds lubricant into the die: without a sufficient film, the wire reaches the forming zone dry and its surface suffers. Entry radius and entrance cone may remain unpolished.
Drawing angle: where the entire reduction happens
The drawing angle, often called the approach angle, is the most important section of a wire drawing die. The entire reduction in area and the compacting of lubricant onto the incoming wire surface occur here. The efficiency of any die is determined by the design and accuracy of this approach zone, which must be ground to an accurate conical angle with a smooth surface finish. It must be straight-sided along its entire length, without a distinct radius or blended contour.
The approach angle does all the work in the die and is the first place to look when designing a die or troubleshooting a drawing problem. It has three major functions.
Lubrication zone
The approach angle's first job is to lubricate the surface of the wire prior to reduction by producing pressure that promotes lubricant flow. Without proper lubricant pressure, the die consumes the precoat and any lubricant film applied by previous dies, which increases the risk of scratching in further drafts.
Reduction zone
The reduction zone is where the die reduces the diameter of the incoming wire. This reduction changes the physical properties of the material: it imparts a denser structure, a harder surface and an improved finish. Using the wrong angle or the wrong reduction is the main cause of drawing failures and rejected wire.
Sizing zone
Finally, the approach angle sizes the material at the point where it meets the bearing. The bearing only controls the size; it does not generate the wire's diameter. That is part of the approach angle's job.
Bearing length: 25 to 66 % of the die diameter
The bearing length, also called the sizing zone or cylinder, controls the diameter of the drawn wire, guarantees its roundness and straightness, and produces an even, smooth surface. To produce quality wire, the bearing must therefore be round, parallel and held to a minimal size tolerance.
To avoid premature fatigue of the tool, the bearing length should be between 25 and 66 % of the die diameter. A worked example: a die with a diameter of 2.54 mm and a bearing proportion of 35 % has a bearing length of 0.889 mm.
The choice of bearing length depends on the hardness of the wire to be drawn and on the desired lubricating film:
| Material being drawn | Bearing length (share of die diameter) | Reason |
|---|---|---|
| Harder materials | approx. 25–35 % | less heat development, lower risk of lubrication faults |
| Softer materials | approx. 50 % | longer usable life of the die |
As long as the die still holds size and enough bearing remains, wear rings can be removed by repolishing. We offer this as a service: reconditioning of carbide drawing dies.
Ceramic dies and coatings
Tungsten carbide is the most widely used die material. A variety of carbide grades, hard-material surface coatings and ceramic dies belong to our product range. Which combination is right depends on your material, drawing speed and required service life. Send us your drawing data and we will advise you.
For a detailed comparison of carbide, PCD and ceramic dies, see our article on wire drawing die geometry and material selection.
How your die is made at Leng
You send us your requirement or drawing; we design the die. Drawing angle, bearing length and carbide grade are calculated with our own software for your material and reduction. Bores from 0.2 to 150 mm are ground on internal grinding machines and calibrated on an automatic polishing and calibrating machine, before our staff produce the surface finish by hand with diamond pastes. Every die is inspected with modern measuring equipment and permanently marked by dot-peen or laser; a measurement report is available on request. We are certified to ISO 9001:2015, valid until 16 December 2028. Our stock of carbide blanks keeps delivery times short, within 24 hours when needed.
