What is aWire Die?
There are four aspects of the wire drawing process that determine the quality of the wire: quality of the incoming material, the type of lubricant, the set-up of the machine, and the drawing die. Each area can be investigated at length to improve the end product; the focus here is on drawing dies. Wire Drawing dies are made of several materials:tungsten carbided, natural diamond, synthetic diamond, and polycrystalline diamond. Selection of the type of die often depends on the material being drawn and the desired surface finish of the wire. For example, if a high polish is required on the wire, typically a natural diamond is used. For larger wire dies, tungsten carbide is often used because of the increased expense for a large diamond needed to produce the die. Polycrystalline diamond is often used as a cost-effective alternative to natural diamond and as a long-life alternative to tungsten carbide. Wire drawing dies work well when the tapered hole is highly polished, as this reduces the amount of friction it takes to pull the wire through the die.
A wire die's geometry is critical to its performance. There are several critical aspects of the drawing die geometry:
- The entrance cone – The purpose of the entrance is to properly allow lubricant to enter the die along with the wire. More lubricant typically means less friction and wear on the die
- The reduction area – The reduction area is where the work is taking place in the die. Themetal is cold-worked as it is pulled through the tapered hole. The reduction angle is critical to the performance of the die and changes based on material drawn.
- The bearing –The bearing sets the size of the exiting wire. The bearing length (often expressed as a percentage of the diameter) depends on the material drawn. Harder materials typically have longer bearing lengths.
- The back relief – The polished back relief ensures that the wire comes out the die with as little scuffing as possible. A well poslished surface will reduce fines and shaving.
- The exit cone – The function of the exit cone is to support the bearing area and help distribute the stresses that occur during drawing.
