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Technical Q&A

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Question:

Can Lube Evaluation for the wire drawing process be conducted by instrumenting the production equipment itself?

Answer:

Instrumenting drawing equipment on the production line is a possibility. Another possibility is to dedicate a specially designed, highly instrumented, laboratory unit for Lube Evaluation. There are pros and cons for each approach that must be evaluated.

One reason for the commitment of a lab unit for the task of lube evaluation is to avoid disruption of the production line for testing, because the operators might become irritated and you lose their cooperation. Another reason is that you do not want to flush all the lubricant out of a big machine in order to run a test. It becomes too expensive.

More information is provided in the publication ref188.

A segment of our seminar on Wire Drawing (May 1998) will cover the subject of Lube Evaluation.


Question:

What keeps a floating plug in position, and where can I learn about the mechanics of tube drawing with floating plugs?

Answer:

The plug maintains its equilibrium position because the resultant axial force acting on the plug is zero. This axial force is composed of:

  • friction drag in the direction of the flow of the tube,
  • the axial component of the pressure force acting between the plug and the tube,
  • the lubricant pressure acting on the plug, and
  • the liquid drag transferred from the tube to the plug through the shear in the lubricant between them. (See Figure 1.)

If the plug temporarily wavers out of position, the balance of these forces is disturbed and a non-zero resultant axial force develops to push the plug back to its equilibrium position of zero axial force.

Here we will describe the "built-in" mechanism that is incorporated into the design of the system to automatically establish and maintain the position of the plug. The mechanism senses the position of the plug and corrects it instantaneously, without external sensors and controls, as follows:

Since the angle of the cone of the plug is smaller than that of the die, the plug is forced to contact the inside of the tube midway between the large and small diameter on the inside of the converging tube. If the plug is pushed too far into the exit, the point of contact approaches the entrance, increasing the area of contact between the plug and the tube, and the subsequent increased force exerted by the tube on the plug will drive the plug back to the entry. The opposite will occur if the plug is pushed too far away from the exit, i.e., the contact point will move towards the exit, the force exerted by the tube on the plug will drop and the plug will restore its equilibrium in the middle. The change in the position of the plug is sensed by changed forces which instantaneously and directly drive the plug in the right direction to restore the plug into its equilibrium position.

 

FIGURE <1> [ 48k]

 

The point of equilibrium is established through the proper choice of the parameters, such as:

  • the lubricant, which might be a fluid squirted into the back of the plug, or solid lubricant coating on the inside of the tube, contributing to the friction value,
  • the plug and die angles, and
  • the diameter and length of the Nib.

The relations between the position of the plug and the independent process parameters are discussed in Chapter 9 of the "Handbook of Metalforming Processes".


Question:

What is the formula for the determination of the diameter of the Nib and that of the body of a floating plug in tube drawing?

Answer:

The design rules for the drawing of tubes over a mandrel or a plug are strongly dictated by the factors controlling the behavior of the tube during the process of tube sinking without a plug under otherwise identical conditions. This behavior during tube sinking can be studied experimentally, or modelled analytically. Such an analytical model, and the software available for it, are described in our numerous papers and textbooks, as listed in the reference list, and in our seminar on tube making.

The diameter of the Nib is determined by the expected inner diameter of the tube when the tube is produced by the process of tube sinking without a mandrel or plug. In order for the Nib to control the inner surface its diameter should be slightly larger than the expected diameter from tube sinking under otherwise identical conditions. The diameter of the Nib should not exceed that size by too much, or the tube will tear by thinning. The role of the plug is to control the precision of the size, the surface finish of the inside of the tube and to prevent the "orange pill" and flaking phenomena. The wall thickness during tube sinking even without a plug can be controlled by the other parameters, such as die angle.

The length of the Nib can be determined by the need to establish a zero axial force on the plug. The angle of the conical surface of the plug is slightly smaller than that of the die.

The chatter phenomena and the bamboo marks are directly related to the oscillations of the plug. The expected wall thickness of the tube varies with speed, and the dragging force on the plug changes accordingly. The plug jumps in and out at a periodic rhythm leaving rings called "bamboo marks".

The parameters that control the process of tube drawing with floating plugs are:

  • the diameter and lenght of the body of the plug,
  • the viscosity of the lubricant,
  • the geometry of the enclosed entrapped lube between the plug and the tube,and
  • the drawing speed.

You can learn of these factors in the seminar on tube sinking.


The phenomena of skidding, (bamboo marks or stick-slip) and its relation to the above parameters is also treated in the seminar on tube making. During this seminar we also present the software for the treatment of the process of tube sinking, and the guidelines (experimental and numerical) of the plug design.


Question:

What is hydrodynamic lubrication? Can hydrodynamic lubrication occur between the tube and the plug during tube drawing?

Answer:

When a very thin film of fluid separates the workpiece from the tool and there is practically no metal to metal contact between them, then hydrodynamic lubrication prevails. Such a phenomena can be established when the pressure at the entry zone between the plug and the tube is high. (see eddy flow in the entrapped lubricant). Eddy flow occurs because any liquid that contacts the surface of a solid (metal) will adhere to that surface at the first molecular depth, as elaborated in the next paragraph.

When a liquid is in contact with a solid (metal) the liquid adheres to the surface of the solid and the first layer of liquid clings to the surface and moves with it. Thus, in our description the liquid that touches the tube moves with the tube at the speed of the drawn tube. Because the plug is stationary, the liquid that touches it becomes stationary itself. The profile of the speed of the liquid in the gap between the tube and the plug is undergoing a reversal as the point of contact between the plug and the tube is reached. A pressure is generated by the reversal of the direction of the flow of the lubricant. When the pressure is high enough the point of contact gets closer to the exit of the tube and the lubricant will create a gap between the plug and the tube and escape through this gap.

The factors that promote higher pressure and therefore hydrodynamic lubrication are:

  • high drawing speed and therefore high lubricant velocity,
  • high lubricant viscosity,
  • smaller die and plug angles,
  • smaller gap between the larger plug body diameter the tube,
  • longer plug body, and
  • the diameter and length of the Nib.

The effect of the reservoir of lubricant piling at the entry side of the plug is somewhat complex. On the one hand this reservoir supplies the liquid that enters the gap and produces the eddy flow and pressure of the entrapped lubricant in the wedge, which affect the hydrodynamic phenomena. On the other hand this liquid mass at the back of the plug produces a seal between the plug and the tube on their contact conical surface. Too much liquid may not only prevent liquid from escaping but under critical conditions (of small diameter plug body) may push the plug to escape. (A phenomena called "swallowing".)

The relations between the position of the plug and the independent process parameters are discussed in Chapter 9 of the "Handbook of Metalforming Processes".

The nature of the contribution of the diameter and length of the body of the plug, in combination with the viscosity of the lubricant, and the geometry of the enclosed entrapped lube between the plug and the tube will be introduced in the upcoming seminar on tube making. The phenomena of skidding, (bamboo marks or stick-slip) and its relations to the parameters above and to speed, is also treated in the seminar on tube making.


Question:

How useful is it to assist the tube drawing process with the application of ultrasonic vibrations?

Answer:

The application of ultrasonic vibration was attempted 30 to 40 years ago with great enthusiasm. It was applied as a panacea, without discrimination, to any situation. In most of the cases it was found ineffective and a nuisance. These failures caused to the disapproval of the process, even when it could have been helpful.

To understand the possibilities one should be aware of a few facts.

  • Ultrasonic equipment is limited in the energy it can deliver. It might only reach up to 10% of the power that the motor of the bull block delivers at a steady state drawing speed.
  • Although at steady state speeds the power supplied by the ultrasonic equipment may be negligible, at start up lower speed this power may accede the power supplied by the bull block.
  • At start-up the friction is higher than at steady state speeds.
  • If the tube breaks at start-up, or stick-slip occurs at start-up, and no other solution is found, it makes sense to explore the use of ultrasonic vibrations. The introduction of ultrasonic vibrations will reduce the friction at start-up, and therefore will reduce the drawing force, the vibrations, and tearing at start-up.

Question:

When is it useful to replace a single die with a double or triple die pass for tube sinking (or wire drawing) in a single draw?

Answer:

The assumption is made in this evaluation that the drawing is performed by a single set of tongs. In the first alternative the entire reduction is performed through a single die. The second alternative is that the same total reduction is performed through two or three dies arranged in tandem (one after the other). Each die causes a smaller reduction, while the pulling is applied at the exit from the die box. Note that as an alternative to the employment of multi-dies, one can always consider replacing a single die with more stations with several dies and a pull at the exit from each die, at higher production costs.

SUMMARY

We will use analytical simulation models to determine the optimal die angle and the drawing stress for wire and for tube drawing through a single die and through tandem dies. By comparing the drawing stress we will determine whether or not the use of multiple dies in tandem actually reduces the load. For tube sinking we will also observe the effect of these choices on the final wall thickness. We will provide the procedures for the determination, but first we will present the summary and conclusions.

   Wire Drawing

The relative drawing stress (sxf/so) and the values of the optimal semi-cone angle of the die (aopt), as functions of the independent input parameters as they are determined by Eq. (3.1) of the "Handbook of Metalforming Processes" are presented in Table 1. Friction factor (m), percent reduction in area (r%), and size ratio (Ro/Rf) are the input parameters and they are also displayed in Table 1.

In general the drawing stress increases when multiple dies replace a single die. See details by clicking here to Appendix. 1.

FIGURE<2> [ 108k]

   TubeSinking

The relative drawing stress (sxf/so) and the wall thickening ratio of the emerging tube (tf/to) as functions of the input parameters of the process (as determined by Eq. (9.3) of the "Handbook of Metalforming Processes") are presented in Table 2.

In general, during tube sinking, as in wire drawing, the drawing stress increases when multiple dies replace a single die.

However, the range of control over the emerging wall thickness can be expanded by selecting a multi-die arrangement. During tube sinking the wall thickness of the emerging tube is a function of: Reduction Ratio (Ro/Rof), Die Angle (a), Initial Wall Thickness (to/Ro) and Friction (m). The emerging wall thickness as a function of reduction is described next. Starting with Ro/Rof=1 and increasing this ratio, tf/to will initially increase monotonously, reach a peak and then commence to decrease with further increases in Ro/Rof . See section (9.4.3.3) of the "Handbook of Metalforming Processes".

The emerging wall thickness may decrease or increase slightly depending on the choice of the parameters listed above. Common knowledge suggests that, in the range of reasonably high reductions, if a reduction through a single die is too high, the emerging wall thickness gets thinner. By replacing the single large reduction with a pair of dies with a smaller reduction in each die, a final thicker wall can be produced. Such a measure penalizes the economy and introduces an extra processing step. With the introduction of multi-dies in a single die box, this extra step is circumvented.

If the required wall thickness is higher than that which can be made in a pass through a single die, then a slightly heavier wall thickness can result in the use of multi-dies, but the wall will never be as thick as the one you can get by sinking through two stations. See details by clicking here to Appendix. 2.

FIGURE<3 >[ 126k]

APPENDIX 1 WIRE DRAWING

TABLE 1. SINGLE DIE VS. MULTI DIES WIRE DRAWING
(Total Percent Reduction in Area, r% = 35%)
  A B C D E F G
1 Dies Friction
factor
m
r% per
Die
Ro/Rf Die Semi
Cone
Angle in
degrees
Partial
Drawing
Stress
Total
Drawing
Stress
2 1 Die 0.05 35.000 1.240 7.277 0.626 0.626
3              
4 1st of 2 0.05 19.354 1.114 5.146 0.353 0.353
5 2nd of 2 0.05 19.354 1.114 5.146 0.353 0.706
6 2nd of 2 0.03 19.354 1.114 3.986 0.322 0.675
7              
8 1st of 3 0.05 13.360 1.074 4.200 0.256 0.256
9 2nd of 3 0.05 13.360 1.074 4.200 0.256 0.512
10 3rd of 3 0.05 13.360 1.074 4.200 0.256 0.768
11              
12 1 Die 0.20 35.000 1.240 14.550 0.820 0.820
13              
14 1st of 2 0.20 19.354 1.114 10.310 0.491 0.491
15 2nd of 2 0.03 19.354 1.114 3.990 0.322 0.813
16              
17              
18 1st of 3 0.20 13.360 1.074 8.385 0.256 0.369
19 2nd of 3 0.03 13.360 1.074 3.247 0.231 0.487
20 3rd of 3 0.03 13.360 1.074 3.247 0.231 0.718
21              

The columns in Table 1 represent the parameters as follows:

Column A
Displays the number of dies in the die box, i.e., 1, 2 or 3.
 
Column B
Displays the value of the friction factor (m).
 
Column C
Displays the percent reduction in area affected (r%).
 
Column D
Displays the ratio between the incoming and exiting (Ro/Rf) wire size for each die. Note that for multiple die use we intentionally distributed the load between the dies evenly.
 
Column E
Displays the choice of the die angle for each die. To make a fair comparison between single and multiple die draws we will choose the optimal die angle for each die. The optimal die angle is that angle which minimizes the drawing force for each die (as treated in Section 3.6.2 of Ref. 3 of Books in the reference list).
 
Column F
The partial stress, displays the component of the relative drawing stress required to overcome the resistance occurring through the respective die. The relative drawing stress is the ratio of the drawing stress to the strength of the wire (sxf/so).
 
Column G
The total relative drawing stress, displays the relative drawing stress at the exit from the last die. The drawing stress experienced at the exit from a previous die becomes an Intermediate tension existing between two subsequent dies. Thus the stress load to pull the wire through the subsequent die is the sum of the partial stress load to draw through the die plus the back tensile stress imposed by the pull through the previous die. See the "Handbook of Metalforming Processes".

The calculations are presented in the next section. As clearly demonstrated, the optimal die angle monotonously decreases with decrease in reduction and in friction.

In lines 2-10 of Table 1 we compare statistics of drawing with a total reduction of 35% and friction value of m = 0.05, for a single die (line 2) against multiple dies (lines 4, 5, and 8-10). In this output, for a constant low friction value, we observe that a single die requires lower drawing stress. Even if the friction for the second die (line 6) is lower (m= 0.03), a single die is favored. However, lines 12 to 20, demonstrate that if drawing through a single die results in excessively high friction, and if intermediate lubrication dramatically improves the lubricity, then multiple dies show significant improvement over a single die draw.

Part of the original question was:
When is it useful to replace a single die with a double or triple die pass for wire drawing?

If there are no serious lubrication problems that can't be handled otherwise, and if the lubricant is not wiped off the surface of the wire before the wire reaches the exit from the die, then the drawing force with a single die is lower than for a multi-die arrangement. However, one justification for the use of multi-dies, may be the more effective application of the lubricant through the portal between subsequent dies. At that intermediate point the tension in the wire (causing lower pressure between the wire and the die), and the higher speed of the wire, both promote better lubrication. If we assume in the two die arrangement that the friction through the single die and through the first die of a double die arrangement is m= 0.2, and through the second die of a double die arrangement is m= 0.03, then the use of double die makes more sense. The calculations for triple die will lead to the same observation.

It is very rare that a multi-die arrangement is required to improve the lubrication. Better lubricants and lubrication systems can provide lower friction with a single die. (Please see the question on Hydrodynamic lubrication)

The calculations for the relative drawing stress can be performed when the friction values (m) are determined experimentally. The procedure for the measurement of friction is described in Chapter 3 of the "Handbook of Metalforming Processes", and in the following pages of this web site.

During our numerous visits to wire making facilities we did not find many applications of multi-die arrangements. When we found it, it was not always clear to the present staff why the multi-dies where originally installed. Even when benefits were demonstrated, it was not always explained convincingly. I am sure that a few readers of this present appraisal can shed much more light on the concept. If you are willing, I ask that you forward to me at <avitzur@metalforming-inc.com> any information on the subject. I cannot open a conversation box, but if you will indicate your preference I will consider providing your comments with acknowledgement.

Treatment of the Analytical Simulation for Wire Drawing

SINGLE DIE

As a typical example we will consider a 35% total reduction in area,

(r% = 35%),

with assumed friction value of

m = 0.05

The ratio of the initial (Ro) to final (Rf) size of the rod, (Ro/Rf) is:

Ro/Rf = 1/SQRT[1-(r%/100)]

For 35% reduction in area Ro/Rf = 1.24

We will select the die angle by calculating the appropriate optimal die angle, which minimizes the drawing force for the prevailing reduction and friction values.

    Optimal Die Angle (aopt)

(see Section 3.6.2 of Ref. 3 of Books in the reference list)

The optimal die angle in degrees can be approximated directly by the equation:

aopt = (180/3.1416)*SQRT[(3/2)*m*ln(Ro/Rf)]

For 35% reduction in area and friction value of: m = 0.05

aopt = 7.277 degrees

    Relative Drawing Stress (sxf/so)

(The ratio of the drawing stress (sxf) to the flow strength (so) of the rod)

The relative drawing stress for flow through conical converging dies is calculated by Eq. (3.1) of the "Handbook of Metalforming Processes".

The Relative Drawing Stress becomes

sxf/so = 0.626

The procedures and equations to determine the die angle and the drawing stress as functions of reduction, friction, flow strength of the wire, etc. are provided in Chapter 3 of the "Handbook of Metalforming Processes", in many of the papers listed in the reference list, and presented in Seminars, and a user-friendly software package called " Flowthru".

MULTI DIES IN TANDEM

For the same total reduction as above (r% = 35%), 2 or 3 dies in tandem are placed to affect this total reduction in smaller reductions per die. If identical reductions are made in each of the individual dies, and the exit sizes from the first and second die are R1 and R2 respectively, then:

For two dies: Ro/R1 = R1/Rf = (Ro/Rf)1/2 = 1.11355

Percent Reduction in Area is r% = 100[1-(Rf/Ro)2] = 19.3544

The optimal die angle for both dies is:

aopt = (180/3.1416)*SQRT[(3/2)*m*ln(Ro/R1)] = 5.146 degrees

The relative drawing stress for drawing through the first die, as calculated by Eq.(3.1) of the Handbook is: sxf/so = 0.353
The relative drawing stress for drawing through the second die, as calculated by Eq.(3.1) of the Handbook is: sxf/so = 0.706

Please note that the drawing stress from the second die is due to the back tension exerted by the need to draw through the first die plus the resistance to the draw through the second die.

For Three dies: Ro/R1 = R1/R2 = R2/Rf = (Ro/Rf)(1/3) = 1.074333

Percent Reduction in Area is: r% = 100[1- (Rf/Ro)2] = 13.36

The optimal die angle for all three dies is:

aopt = (180/3.1416)*SQRT[(3/2)*m*ln(Ro/R1)] = 4.2 degrees

The relative drawing stress for drawing through the first die, as calculated by Eq.(3.1) of the Handbook is: sxf/so = 0.256

The relative drawing stress for drawing through the second die, as calculated by Eq.(3.1) of the Handbook is: sxf/sxf = 0.512, and through the third die is: sxf/so = 0.768.

Please note that the smaller the reduction per die, with the same friction value (m) , the smaller is the optimal die angle. Nevertheless, the larger the number of dies in tandem, the higher is the total drawing stress (and force) applied at the tongs.

APPENDIX 2. TUBE SINKING

TABLE 2. SINGLE DIE VS. MULTIPLE DIES TUBE SINKING
(In Table 2 the Friction Factor is m = 0.05)
  A B C D E F G H I J
1 Dies Rof/Ro Die
Semi
Cone
Angle
to/Ro Ri/Ro tf/Rof Rif/Rof Partial
tf/to
Total
tf/to
Total
Drawing
Stress
2                    
3 1 Die 0.800 8.50 0.100 0.900 0.12407 0.87594 0.99252 0.99252 0.82351
4                    
5 1st of 2 0.894 8.50 0.100 0.900 0.11347 0.88653 1.01490 1.01490 0.46888
6 2nd of 2 0.894 3.50 0.113 0.887 0.12413 0.87587 0.97850 0.99308 1.11315
7                    
8 1 Die 0.800 8.25 0.200 0.800 0.25312 0.74687 1.01250 1.01250 0.61641
9                    
10 1st of 2 0.894 8.00 0.200 0.800 0.22810 0.77190 1.02010 1.02010 0.37546
11 2nd of 2 0.894 3.30 0.228 0.772 0.25403 0.74597 0.99610 1.01612 0.80747
12                    
13 1 Die 0.800 6.00 0.200 0.800 0.25274 0.74726 1.01096 1.01096 0.66252
14   0.800 8.00 0.200 0.800 0.25311 0.74689 1.01245 1.01245 0.61898
15   0.800 10.00 0.200 0.800 0.25288 0.74712 1.01152 1.01152 0.60957
16   0.800 8.25 0.200 0.800 0.25312 0.74687 1.01250 1.01250 0.61641
17                    

In Table 2 the optimal die angle, the relative exit wall thickness and the drawing stress for tube sinking through a single die and through tandem dies are determined for typical examples. By comparing the options we can study the effect of these choices and get better control of the exit wall thickness.

The columns in Table 2 represent the parameters as follows:

Column A
Displays the number of dies in the die box,i.e., 1, 2, or 3.
 
Column B
Displays the ratio of the emerging to incoming outer radius of the tube as a measure of the severity of the reduction.
 
Column C
Displays the semicone angle of the die.
 
Column D
Displays the relative thickness of the incoming(mother tube).
 
Column E
Displays the inner to outer size ratio of the incoming tube.
 
Column F
Displays the relative thickness of the emerging tube.
 
Column G
Displays the inner to outer size ratio of the emerging tube.
 
Column H
Displays the emerging to incoming wall thickness ratio as calculated from Eq. (9.3) for the individual die.
 
Column I
Displays the ratio of the emerging wall thickness for the specific die to the original incoming wall thickness of the mother tube.
 
Column J
Displays the calculated relative drawing stress at the exit from the specific die, i.e.,first, second or subsequent die.
All the data in Table 2 assumes a friction value of m = 0.05.

Line 3 treats data for a typical single die drawing where the output is: (tf/to), and total relative drawing stress (sxf/so). The choice of the 8.5o semicone angle of the die maximizes the emerging wall thickness for this specific pass.

Lines 5 & 6 treat data for a typical two die pass through a single die box. Here we distribute evenly the load between the two dies, so that we obtain the same total reduction as in line 3. Note that for the second die the optimal die angle is much smaller. The emerging wall thickness for two dies (tf/to = 0.99308) is slightly larger than for a single die (tf/to = 0.99252). However, we pay the penalty of higher drawing stress.

In the next three lines(8,10 & 11) we display data for a thicker tube with similar results, i.e., two dies provide thicker relative emerging wall thickness and higher drawing stress.

The last group of lines demonstrate how to determine the optimal die angle. To make a fair comparison between single and multiple-die draws we choose the optimal die angle for each die. The optimal die angle here is that angle which maximizes the thickness of the emerging tube as treated by Eq. 9.3 of Ref. 3 of Books listed in the reference.

The relative drawing stress (column J) is the ratio of the drawing stress to the flow strength of the tube (sxf/so). When back tension prevails at the entrance to the die, then column J, accounts for it. The drawing stress experienced at the exit from a previous die becomes an intermediate tension existing between the previous and the subsequent dies. Thus the stress load to pull the wire through the subsequent die is the sum of the partial stress load to draw through the die plus the back tensile stress imposed by the drag through the previous die.

Part of the original question was:
When is it useful to replace a single die with a double or triple die pass for tube sinking?

A partial answer is that two dies provide an added control of the emerging wall thickness

If there are no serious lubrication problems that cannot be handled otherwise, and if the lubricant is not wiped off the surface of the tube before the tube reaches the exit from the die, then the drawing force with a single die is lower than for the multi-dies arrangement. However, one justification for the use of multi-dies, may be the more effective application of the lubricant through the portal between subsequent dies. At that intermediate point the tension in the tube (causing lower pressure between the tube and the die) and the higher speed of the tube both promote better lubrication.

The calculations for the relative drawing stress can be performed when the friction values (m) are determined experimentally. The procedure for the measurement of friction during wire drawing is described in Chapter 3 of the "Handbook of Metalforming Processes", and in the following pages of this web site. However the values of friction (m) as determined expermentally for wire drawing may be unreliable when applied for tube. Experimental determination of the friction value for tube sinking is much more complex.

During our many visits to tube making facilities we found only sparse applications of multi-dies arrangements. But the practice is more popular than in the wire industry. It was not always clear to the prsent staff why the multi-dies where originally installed. Even when benefits were demonstrated it was not always explained convincingly. I am sure that a few readers of this present appraisal can shed much more light on the concept. If you are willing, I ask that you forward to me at <avitzur@metalforming-inc.com> any information on the subject. I cannot open a conversation box, but if you will indicate your preference I will consider providing your comments with acknowledgement.(Please see FIGURE<3> and Table 2.)

Treatment of the Analytical Simulation for Tube Sinking

We will use the simulation model for tube sinking, as presented by Eq. (9.3) of the "Handbook of Metalforming Processes", in many of the papers listed in the reference list, and presented in Seminars, and a user-friendly software package called "TubeSink" . Equation (9.3) provides the relative drawing stress (sxf/so ) as a function of the following input parameters:

  1. (Ro/Rof) the ratio of incoming to exit tube outer radius (Diameter/2).
  2. (a) the semi-cone angle of the die.
  3. (m) the friction factor.
  4. (sxb/so) the relative back tension.
  5. (to/Ro) the incoming relative wall thickness of the tube.

Thus, symbolically:

sxf/so = f(Ro/Rof, a , m, sxb/so, to/Ro,and tf/to)

The relative wall thickness at the exit (tf/to) is a unique parameter. We treat it temporarily as an input (independent) parameter,and then subject it to the process of optimization, after which it becomes a dependent parameter. Through an optimization procedure this expression is utilized in the determination of the following dependent parameters: sxf/so ,tf/to and aopt , as functions of Ro/Rof, to/Ro, a, m, and sxb/so.

The maximum possible reduction is determined by setting a limit on the permissible drawing stress (sxf/so). The treatment of this complex procedure is available by a software package called "TubeSink ", as presented in our Seminars.



Question:

What is the concept of wet wire drawing?

Answer:

To be completed at a later date.


Question:

How important is the wire (or tube) alignments on either side of the die during wire (or tube) drawing?

Answer:

To be completed at a later date.

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Last Modified:
Monday April 26 2010

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