Dieless Wire Drawing

DIELESS WIRE DRAWING

Submitted to:

Prof. D. Ravi Kumar (MEL335)

Submitted by:

Rohit Gothwal2010ME20796

Department of Mechanical EngineeringIndian Institute of Technology Delhi

New Delhi-110016

Introduction

In conventional wire drawing operations, the wire is pulled through a conical aperture called

a die to reduce its diameter. Considerable cost is associated with pre-cleaning of the wire

prior to entry to the die, tooling, and lubrication materials. Die wear, which occurs at the

approach and bearing surfaces due to frictional and heating effects, can rapidly diminish tool

life. Economic viability dictates that the tooling costs associated with any metal forming

process are kept to a minimum [2]. Hence, elimination of the die would greatly enhance the

economics of the wire drawing process.

Previous researchers have noted that a hydrodynamic force generated by a polymer melt in

the wire drawing die during conventional drawing caused a reduction in the wire diameter.

The researchers concluded that successful dieless drawing was achievable if the drawing

velocities and temperature profiles permitted the occurrence of transformation plasticity. In

this class of plasticity, deformation occurs during a phase change and a threshold stress is

necessary to initiate gross deformation [3].

Fig. 1. Conventional wire drawing.

The dieless drawing process consists of mechanically loading a rod or wire that is locally

heated to lower its yield strength below the level of stress applied by the wire takeup and

feeding systems. The wire is stretched under the applied tension in the heated zone. Before

the wire or rod is stretched beyond the breaking point, it leaves the heated zone, at which

point its strength [1].

Basic Elements

All dieless wire drawing systems must contain the same basic elements namely [2].

A heating device

o Many differing and varied heating methods exist. These include resistance

heating as used by Tiernan [2] where current was used as a heating method

utilising the Joule effect.

o A more recent utilised a laser to heat the wire to its critical temperature.

Unfortunately, this method is in the infancy stages of its development and lasers

with enough power are not yet commercially viable.

o The most efficient and cost effective solution is induction heating. This method uses

the magnetic induction principals of eddy current generation to heat a sample to its

critical temperature.

Induction heating coils and cooling device elements.

A cooling device

The optimum-cooling medium is a mix of purified water and an inert gas. Air has

been used as a cooling medium on many experimental systems but this has led to the

formation of a layer of oxide on the drawn wire surface. Yonggang et al. [2] used

argon gas as an oxidation inhibitor to successfully control the materials surface

chemistry.

A method of applying a tensile force and a data acquisition control system

Many methods of applying a tensile load have been utilised.

o One such method involves the use of rollers and take-up/pay-off wheels as

illustrated in Fig. 1.

o Another method involves the use of bearings and linear slides in a vertical

fashion as depicted in Fig. 2.

Fig. 2. Experimental plant

Machine design and operation

The machine is designed to produce infinitely variable reductions in mild steel wire of

maximum diameter, 5.0mm at temperatures between 400 and 900◦C at drawing speeds of up

to 1.5m/s [2].

The wire is passed around both roller electrodes as shown in the schematic diagram in Fig. 4,

their individual angular velocities were controlled to produce a tensile load in the wire

parallel to its longitudinal axis.

Fig. 4. Schematic diagram of the roller electrodes and associated drawing kinematics.

The current to heat the wire was obtained from a 1600A power converter. The machine, which was controlled by an IBM PC, is shown in Fig. 5.

Data acquisition and machine control system

The instability of the dieless drawing process coupled with the complex nature of the

machine operation necessitated the use of an automated data acquisition and machine control

system. Data was acquired for two purposes [3].

1. Primarily, to record the test parameters of the wire as it was formed

2. Secondly, to record data from the machine transducers to al- low machine control and

monitoring to be achieved.

The system is designed to sufficiently control the roller angular velocities and wire

temperature to achieve a desired reduction in the wire diameter. An easy-to-use

interface enabling the operator to input desired drawing parameters, e.g., drawing

velocity and wire temperature is developed.

A PC based system was used to achieve the aforementioned requirement due to its

cost-effectiveness and flexibility. Two data acquisition boards were required; a

multifunction (MIO) board to process analog and timing signals, and a digital

input/output (DIO) board to process the remaining digital signal.

The hardware was controlled by LabVIEW software.

The user interface consisted of numerous controls and indicators. The controls

allowed the user to input values and choices, which control the machine and data

acquisition process. The remaining instruments on the front panel displayed the cur-

rent status of the machine, e.g., the actual temperature of the wire and actual current

flowing through the wire.

Simplified flow chart of machine control and data acquisition program [1].

Experiments

A complete program of dieless drawing was undertaken on low-carbon steel wire of nominal

diameter, 2.65 mm. The drawing limit of the dieless drawing method is dependent on the

mechanical and metallurgical properties of the wire material, the temperature profile along

the wire, and the drawing velocity. The wire temperature is dependent on the amount of

current passed through the wire and the drawing speed.

Results

A maximum drawing velocity of 1.4 m/s was attained without wire fracture during

the drawing process.

The maximum reduction achieved in cross sectional area during a single pass was

72%. This reduction was obtained at a test temperature of 780 ◦C.

Variation in wire diameter with percentage reduction.

The variation in wire diameter for various reductions in the cross-sectional area of

mild steel wire of nominal diameter 2.65 mm is shown in Fig. 8. Drawing was

conducted at a temperature of 650 ◦C and a velocity of 1.1 m/s.

Fig. 8. Wire diameter variation vs. reduction of area in dieless drawing of mild steel wire.

Drawing load vs. displacement

The theoretical drawing load to achieve a reduction of 58 % in the cross-sectional area of the mild steel wire of nominal diameter 2.65 mm at 650 ◦C by dieless drawing was calculated. In this particular draw, a necked region formed in the wire that subsequently resulted in wire fracture. The theoretical drawing loads and those predicted by finite element code are presented in

Fig. 9. Theoretical and FE predicted load for 58% reduction in mild steel wire.

Benefits

Pre-cleaning and lubrication requirements can be eliminated from the process.

Ability to draw difficult to form materials such as shape memory alloys which are

susceptible to strain hardening [2]and the ability to produce variable cross-section

products

References

[1]. P. Tiernan, M.T. Hillery, An analysis of wire manufacture using the dieless drawing method 2007.

[2]. M.D. Naughton, P. Tiernan, Requirements of a dieless wire drawing system, 2007.

[3]. P. Tiernan, M.T. Hillery, Dieless wire drawing—an experimental and numerical analysis 2004