Основы технологии процессов обработки металлов давлением (Fundamentals of the technology of metal forming) : учебно-методическое пособие

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Министерство науки и высшего образования Российской Федерации Сибирский федеральный университет

ОСНОВЫ ТЕХНОЛОГИИ ПРОЦЕССОВ ОБРАБОТКИ МЕТАЛЛОВ ДАВЛЕНИЕМ (FUNDAMENTALS OF THE TECHNOLOGY OF METAL FORMING) Учебно-методическое пособие

Электронное издание

Красноярск СФУ 2019

УДК 621.7(07) ББК 34.5я73 О753 Составители: Рудницкий Эдвард Анатольевич Сидельников Сергей Борисович Шубкина Ольга Юрьевна О753 Основы технологии процессов обработки металлов давлением (Fundamentals of the technology of metal forming) : учеб.-метод. пособие / сост. : Э. А. Рудницкий, С. Б. Сидельников, О. Ю. Шубкина. – Электрон. дан. (1,5 Мб). – Красноярск : Сиб. федер. ун-т, 2019. – Систем. требования: PC не ниже класса Pentium I ; 128 Mb RAM ; Windows 98/XP/7 ; Adobe Reader V8.0 и выше. – Загл. с экрана.

This guide provides materials for laboratory work necessary for students to consolidate the basic principles of technological processes of metal forming. Recommended for the students of the program track 22.03.02 “Metallurgy”.

УДК 621.7(07) ББК 34.5я73 © Сибирский федеральный университет, 2019

Электронное учебное издание Подготовлено к публикации издательством Библиотечно-издательского комплекса Подписано в свет 20.08.2019. Заказ №9083 Тиражируется на машиночитаемых носителях Библиотечно-издательский комплекс Сибирского федерального университета 660041, г. Красноярск, пр. Свободный, 82а Тел. (391)206-26-16; http://rio.sfu-kras.ru E-mail: [email protected]

CONTENT INTRODUCTION ............................................................................................. 4 GENERAL METHODOLOGY INSTRUCTIONS ............................................ 5 GENERAL LABORATORY WORK PROCEDURE ........................................ 5 GENERAL SAFETY RULES FOR LABORATORY WORKS ......................... 5 LABORATORY WORK №1. Study of the influence of the sample material and the degree of deformation on the longitudinal rolling force (longitudinal rolling) ............................................................................................................... 6 LABORATORY WORK №2.Study of the effect of the length of the workpiece and the presence of lubricant on the extrusion force (extrusion) ....................... 14 LABORATORY WORK №3.Study of the effect of the degree of deformation on the draw force and the mechanical properties of metal (drawing) ................ 19 LABORATORY WORK №4.Study of the influence of friction coefficient on the upsetting force (upsetting) .......................................................................... 24 LABORATORY WORK №5.Determination of stamping force in open and closed stamps (die forging) .............................................................................. 28 LABORATORY WORK №6.Study of the influence of technological parameters on the force of sheet stamping operations (sheet-metal forming) ...................... 36 GLOSSARY OF TERMS ................................................................................ 40 ABBREVIATIONS.......................................................................................... 50 REFERENCES ................................................................................................ 51

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INTRODUCTION The guideis designed to perform laboratory work on the discipline “Fundamentals of the technology of metal forming” and compiled in accordance with the requirements of the Federal State Educational Standard of Higher Education 3 to train bachelors of the program track 22.03.02 “Metallurgy”. The guidelines contain the description and procedure of six laboratory works, which cover the main issues of determining the force parameters of rolling, extrusion, drawing, upsetting, die forging and sheet stamping. Laboratory works provide revision and training of the material considered during lectures and tutorials.

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GENERAL METHODOLOGY INSTRUCTIONS Methodology instructions provide performance of laboratory works under the guidance of the teacher with the help of the laboratory assistant. During the work the student records the results of it, after which they are processed. For each laboratory work a report is compiled in accordance with the requirements of the Company Standard 4.2-07-2014: Name and number of work. The task and aim of the work. Theory in brief. Initial data and work procedure (the sequence of work stages is described). Analysis of the results of the experiment (tables, graphs, figures, drawings are attached; the used formulas should have explanations in the text and a link to information sources). GENERAL LABORATORY WORK PROCEDURE The study of the content and methodology of the work are carried out according to “manuals” and instructions. The study of the safety rules and safety instructions working with the equipment, devices and instruments which are used in the laboratory work. Preparation of samples and tools for the work (sizing, lubrication, etc.). Verifying the correct operation of equipment and instruments. Carrying out an experiment. Calculations and making a report. Defending a laboratory work. GENERAL SAFETY RULES FOR LABORATORY WORKS Before starting work, a student must be instructed at a workplace with a journal entry on safety arrangements. When performing a laboratory work, a student mustdo only those actions that are assigned by the teacher. The work must be done carefully without any distraction. Any moving and rotating parts and assemblies of the machines mustn’t be touched, for which a student must stand at a certain distance (behind the yellow safety line) from the equipment. In the process of work constantmonitoring of the correct operation of devices and instruments must be done. Any noticed faults must be reported to the teacher or the laboratory assistantimmediately.

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LABORATORY WORK №1: Study of the influence of the sample material and the degree of deformation on the longitudinal rolling force (longitudinal rolling) The aim is to calculate the coefficient of deformation and rolling force, by quantifying the magnitude of the relative deformation. Laboratory equipment: rolling mill machine DUO180; a caliper gauge; material – aluminum, lead. Theory in brief Rolling is the process of metal deformation by cobbing the incoming billet between rotating rolls in order to reduce the cross-section of the billet and give it the specified form. (Fig. 1.1, а).

a

b

Figure1.1 – Longitudinal rolling: а – process flow diagram, b – geometry deformation containment volume

Rolling – is one of the most common types of metal treatment under pressure, which is subjected to about 80 % of the smelted metal in our country. The wide application of rolling is explained by a number of advantages over other types of metal treatment under pressure (pressing, drawing), as well as the high performance of this process and the lower cost of the final products. In the process of longitudinal rolling, which is most common, the deformation of the incoming billet 2 is carried out between rotating in different directions by the rolls 1, the hollow space between which is smaller than the original thickness of the incoming billet. 6

The rolling process is considered simple, or symmetrical if it is carried out in smooth uncalibrated rolls with parallel axes located in one plane. Both rolls are driven, have equal diameters and rotate in different directions with the same circumferential speed. The surface condition of both rolls is the same, i.e. coefficients and friction forces on them are the same. Finally, it is suggested that a strip of rectangular cross-section with the same physicomechanical properties is subjected to rolling over the whole volume, and affected by the rolling force only. In the process of longitudinal rolling plastic, flow is not subjected to the entire volume of the processed metal, but only a small part located near the rolls. Therefore, the volume of the rolled metal enclosed between the plane of the metal inlet АА1 in the rolls and the exit plane of the BB1 metal from the rolls is called the geometric deformation zone (Fig. 1.1, b). The arc AB, along which the wrought metal contacts the rolls, is called a contact arc, and the central angle corresponding to the contact, is called the gripping angle. The projection of the deformation zone on the horizontal axis is the length of the deformation zone l. In the process of rolling, the initial strip with the thickness H0is compressed by rolls to the thickness H1 by the amount of absolute reduction of thickness:

Н = Н0 – Н1

(1.1)

Since the incompressibility condition of a metal, an increase in the length and width of the strip occurs. Thus, the shape of the geometric deformation zone in the process of rolling is characterized by the gripping angle α, the height of the section H0 and H1, the length of the deformation zone ld, and the initial and final width of the strip B0 and B1. To find α and ld use the formula: cos   1 

Н D

(1.2)

D – the diameter of the roll. To estimate the amount of deformation in the process of rolling such dimensionless values as the ratio of reduction , coefficient of spreading , the ratio of drawing , are used which are determined by the following formulas: 1





B1 L1 H0 ,  ,  , B0 L0 H1

(1.3)

L0 и L1 – the length of the billet before and after rolling respectively. According to the constancy of volume law:

    7

V1 1 V0

(1.4)

V0 и V1 – the volume of metal, before and after rolling respectively. To characterize the deformation in the process of rolling the ratio of drawing  is used which shows how many times the length of the incoming billet after rolling has increased, and the relative degree of reduction :



H 0  H1 100% H0

(1.5)

If rolling is carried out in several passes, the total coefficient of drawing sum is determined as the multiplication ratio of drawing after each pass:

sum = 123 n-1n

(1.6)

n – number of passes during rolling. Metal capture with the help of the rotating rolls, conducted with the changes in the size of the rolled strip, is provided by friction between the strip and the working surface of the rolls. Metal capture conditions are usually considered for two periods of rolling: unsteady and steady states. The first period includes the capture of the strip by rolls (or forced feed it into the gap between the rolls) and filling the deformation area until a certain length of the front end of the strip outside the deformation area. As the gap between the rolls is filled, the deformation conditions of the metal are continuously being changed, which allows calling this period of rolling as unsteady. Let us consider this period in more detail (Fig. 1.2(a)).

а

b

Figure 1.2 – Rolling schemes: a – unsteady period, b – steady period

The second rolling period begins when the front end of the strip is released through the exit section and ends when the rear end of the exit section is reached. Throughout the time of the second period, the parameters of the deformation zone remain unchanged, so the second period of the rolling process is called steady. If we assume that in the steady- rolling period, the normal contact voltage is distributed evenly along the length of the deformation

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area, the resulting force of the rolls on the metal will pass through the middle of the arc of contact (Fig. 1.2, b). The following factors can improve the metal capture with the help of the rolls: increasing the ratio of friction, for example, by making ragging on the rolls; reducing the value of compression; increasing the diameter of the rolls at compression; using of push force directed at the incoming billet along the axis; narrow wedge (mill operation the front end of the incoming billet at an angle), etc. It should be noted that although the use of greasing makes it difficult to capture the metal, cold rolling of the sheets is usually carried out with a greasing in order to obtain a high-quality surface. The gripping angles at cold rolling with greasing are 3-4, without greasing – 5-8. In the process of hot rolling at breakdown mill (blooming and slabber)  = 18-34. The forces that occur in the process of rolling are perceived by the cast roll and through the bearings, the pressure device, is transmitted to the shoe. When calculating the rolling schedule or when designing a new mill, you need to know: what forces will act from the metal on the rolls and other parts of the mill in order to fully utilize the power parameters without the risk of accidents and breakdowns. The force in the process of rolling can be determined by the formula: Pn  p  F

(1.7)

р–

average rolling pressure;F – contact area. To determine the average rolling pressure there are a large number of formulas. Statistical analysis of calculations performed using many formulas showed that the main influence on the rolling pressure is two factors: the ratio of friction , moreover, either Ziebel’s law (hot rolling) or Amonton-Coulomb’s law (cold rolling) is taken as friction condition; geometric factor of the shape of the deformation zone

l z  h

(1.8)

h  h1 h 0 2 l – deformation zone length, h – average rolled strip thickness

Hot rolling: l 

Rh

Cold rolling: 9

(1.9)

l  

Rh  m 2 p 2 R 2  mpR

(1.10)

R – roller radius; h – reduction in thickness; m – the parameter considering the elastic flattening of the rollers, with a sufficient degree of accuracy can be taken equal to m=1/9500; p – average rolling pressure excluding elastic roller flattening. To determine the pressure in the process of cold rolling, the most widely used formulas are Tselikova’s formula (1.11) and Stone’s formula (1.15):  hy 2h i рК   h   1  h1 К–

  h y     h   1

     1    

(1.11)

average strain resistance equal to К  1,15  s s 

(1.12)

 s0   s1 2

(1.13)

s0, s1 – yield point of the metal before and after rolling, which is determined by Fig.14;  – friction parameter 

2l h

(1.14)

 – the ratio of friction: when rolling aluminum on dry rollers  = 0,2-0,25; on greasing with lube  = 0,08-0,09; l – the length of the deformation zone with regard to the elastic flattening of the rollers is calculated by the formula. This formula is nomographed (Fig.1.3, a). Stone’s formula: рК

е – the base of natural logarithm;

K

е х 1 х

(1.15)

– average strain resistance. x

2l h0  h1

(1.16)

Stone’s formula is also nomographed and tabulated. Thus, the pressure in the process of cold rolling is determined by the method of successive 10

approximations, i.e. at first the pressure without considering of elastic flattening of the rolls is found using the formula (1.9), and then, substituting this value into the formula (1.10), the length of the deformation zone is calculated considering elastic flattening, which substitute the formulas  and x, considering friction. Then, using the formulas (1.11) or (1.15), find the rolling pressure with regard to the elastic deformation of the rolls.

a b Figure1.3 – Dependencies of technological parameters and mechanical properties: a – the dependence of the average rolling pressure on the magnitude of the deformation, the ratio of friction and the size of the deformation zone; b – the dependence of the yield point of aluminum on the magnitude of the relative deformation

In addition, the pressure of rolling is influenced by the initial thickness of the billet. As the strip thickness decreases, the ratio of the contact surface to the deformable volume increases and the rolling pressure changes according to a hyperbolic law. Procedure Calculation of the coefficient of deformation. Measure the thickness, width, and length of the sample of aluminum sized H0B0L0. Roll the sample in five passes with cobbing of about one millimeter per pass. Measure thickness after each pass Hi, width Bi and length Li at the same points. Carry on calculations and fill in table 1.1. According to the table 1, build graphics λi, ηi, βi=f(n) and λsum, sum=f(n) Table 1.1 Deformation coefficients in the process of rolling Passage number, n

Hi

Bi,

∆Hi

Li

Fi

λi

ηi

βi

Influence of reduction and ratio of friction on rolling pressure. 11

Λsum

sum

Aluminum and lead sample are rolled in one pass. One sample size is rolled throughoil greased rolls, the other (without changing the solution) through dry rolls, rubbed with chalk. Find the contact area of the metal with the rolls according to the formula F  b  l

(1.17)

b – strip width, mm; l – the length of the deformation zone, determined by the formula (1.10). Knowing the total force Pn and the contact area F, calculate the average experimental rolling pressure using the formula pоп 

Pn F

(1.18)

The calculated rolling pressure is determined using the nomogram (Fig. 1.3, a) and formulas (1.15), (1.18). The deformation resistance for aluminum is set according to the schedule (Fig. 1.3, b). All data are entered in table 1.2. Make conclusions. Make a report. Table 1.2 Experimental and calculated data of the rolling process р

Н0 Н1 Н B0

B1



s0

Рcalc according according according according _ F s1 to the to the to the to the K formula formula formula formula (1.11) (1.15) (1.11) (1.15) With greasing (lead) calc

Without greasing (lead) Aluminium

Questions: The geometry of the deformation zone in the process of rolling. Parameters of deformation in the process of rolling. The condition of the metal capture rolls. Types of longitudinal rolling and the resulting products. Method of the tube rolling. The classification of rolling mill machine. General characteristics of the equipment of the reduction mill line. Forming rolls. 12

The essence of the method of successive approximations in the process of cold rolling. Parameters that affect the pressure and rolling force.

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LABORATORY WORK №2: Study of the effect of the length of the workpiece and the presence of lubricant on the extrusion force (extrusion) The aim is to determine the pressing force, learn the method for determining the deformation to resistance and the ratio of friction experimentally and by calculation. Laboratory equipment: hydraulic press «Krause» with a force of 0.4 MN; a portable container and a matrix; a caliper gauge; processed material – lead. Theory in brief Extrusion is the process of giving a shape to the metal being processed by squeezing it out of a closed volume through a channel formed by a pressing tool – a die. The essence of the extruding process is demonstrated by the example of direct pressing (Fig. 2.1). The workpiece (1), heated to the temperature of extrusion, is placed in a container (2). On the output side of the container, the die (5) is placed in the die holder (3), which forms the contour of the moulding (4). The pressure is given through the press extrusion ram (7) and the pressure pad (6) from the main cylinder of the press. Under high pressure, metal flows into a die opening, forming a defined product.

Figure 2.1 – A profile direct pressing scheme

It is necessary to know the extruding force for the rational choice of extruding equipment that ensures the implementation of the extruding process, to determine the force conditions of operation of the extruder, power production costs and other indicators. Measuring the forces and tension in the process of extrusion can be reached by experimental work, by modeling or analytically. The most accurate results are observed experimentally. To get the results, the change in pressure of liquid p in the main cylinder which is shown, in the manometer, is fixed in the 14

current hydraulic press, and, knowing the cross-sectional dimensions FPL of the main press plunger, the change in extruding force is determined Р pr  рFpl . The results of many experimental studies of the force conditions of various types of the extruding process made it possible to state a number of relationships that determine the nature of the influence of the following main factors and conditions on the pressing pressure. In general, the main forces that are balanced by the total pressing pressure during the working process are: the frictional forces occurring of the container side surface and the arbor if it exists (TKR); frictional forces occurring on the cobbling part of the plastic zone(TM); forces occurring from internal friction, which counteract the implementation of the main deformation, i.e., compression of the workpiece to the specified dimensions in the conditions of pressing without contact friction (RM); frictional forces occurring on the lateral side surface of the calibrating belt (or belts) of the matrix (TP). The total force P (kN) of the press required to effect the deformation is: Р  RМ  Т KR  Т М  Т P

(2.1)

The components of the pressing force in the process of extrusion of a round rod from a round ingot are determined by the formulas: RМ 

DK2 ln    S 4 cos 2 ( / 2)

(2.2)

Тkr  DK ( LZP  huz)   КР S

 (

(2.3)

DK2  ln    М  S ТМ  4 sin

(2.4)

Тp  D pr  lp   p S  

(2.5)

DK 2 ) is the ratio of drawing; DKis the diameter of the container; DPR – the Dpr

pressed rod diameter, mm;  is the angle of inclination of the forming die opening to the extrusion axis (for a flat die, the angle is assumed to be 60 o); σS – average over the length of the plastic zone, the amount of resistance to L3 P  L30 (

D3 2 ) DK – the

deformation of the metal, MPa (for lead, σS = 15 MPa); length of the extruded ingot, mm; L30, D3– the length and diameter of the 15

original piece; huz 

( DK  D pr )  (0,58  ctg ) 2

– the height of the elastic zone, mm;

LP, DPR – the length and diameter of the calibrating belt, mm; μКR, μМ, μP – the ratio of friction, on the surface of the container, a cobbling part and calibrating beltof the matrix (can be taken in the process of pressing with lubricant: μКR = μМ = μP = 0,1 – 0,2; without lubricant: μКR = μМ = 0,5, μP = 0,2 respectively. The main factors that influence the extruding force are: Strength properties of a metal. The lower the deformation resistance of a metal, the less is the tension and the extruding force. The degree of deformation. The greater the deformation, the more energy is used, the greater force is required, all other conditions being equal, for extruding. Ingot length. An increase in the length of the ingot means an increase in the surface on which the friction tension acts, and, consequently, an increase of extruding force. The condition of the tool surface and lubrication. Tool wear or coarse surface finish of the tool increases the ratio of friction, as a result of which the extruding force increases. Lubrication of the container and the die, on the contrary, reduces the extruding force. In the general case, the pressing force almost linearly depends on the resistance to deformation σS – the intensity of the tension required for the plastic deformation of the material in the process of specified thermomechanical conditions of deformation. The resistance to deformation depends considerably on the chemical composition of the material being processed, its structure, temperature, degree, and rate of deformation. Therefore, it is sometimes called the dynamic yield point. Knowing the change in deformation resistance depending on the described above factors makes it possible to get a solution to a number of practical tasks for calculating the power and temperature-speed parameters of the extruding process, finding the best options to achieve maximum efficiency of the extruding process in terms of production and quality of press products. Resistance to deformation can be defined in various ways: graphically, according to nomograms for a number of specific metal processing temperatures, depending on the degree and rate of deformation. For given conditions, specifying refining σS, interpolation is performed in the range in the process of study; according to the tables for specific values of temperature, degree, and rate of deformation; by approximation of experimental data by analytical dependencies; by carrying out the experiments on plastometers. The resistance to deformation and the ratio of friction can be determined through experimentally found working pressures with their subsequent substitution into the theoretically grounded formula of I.L. Perlina. This allows determining the parameters for a particular case of extrusion accurately with less 16

loss of time and cost. For this purpose, an indicator diagram of the change in the extruding force is built in the course of the extrusion ram, and at the beginning of the steady-state stage a change in the extruding force ∆Рpr is found depending on the displacement of the extrusion ram ∆L. Then the current resistance to deformation for the pressed metal is the following: S 

Ppr    Кr DK L

(2.6)

The resistance to deformation and the ratio of friction can be determined during extruding of the workpiece of different lengths, determining the maximum extruding forces. In this case, the resistance to deformation is the following: S 

Ppr1  Ppr 2

   Кr DK ( L1  L2 )

(2.7)

PPR1 and PPR2 the maximum extruding forces of workpieces of length L1 and L2, respectively, with L1 > L2; DK – the diameter of the container; π = 3,14; μKR is the ratio of friction of the metal being extruded against the container walls. The ratio of friction of the lubricant:  SМ  0,5 

Рmax BSМ  Рmax SМ    S  DK ( L3 R  huz )

(2.8)

This method allows finding σSin the process of extrusion in the manufacturing environment, to adjust the extruding process for achieving optimal manufacturing conditions using automated control systems.

Рmax is the maximum pressing force; Pmin is the minimum pressing force; Px is the current pressing force; Lxis the current length of the ingot; L is the length of the pressed ingot Figure 2.2 – The scheme of the indicator diagram

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Procedure Two lead samples of the same diameter and different lengths should be extruded without lubrication (at the same time, the container, the sample, and the die should be wiped with acetone) by direct pressing through a single die into a round rod. In the process of extrusion in both cases, measure the maximum extruding force. A lead sample of a given diameter and length should be extruded with lubrication with machine oil by the method of direct pressing through a single die into a round bar used in claim 1. Measure the maximum extruding force in the process of extrusion. Find the resistance to deformation of lead in the described case of extrusion taking the value μКР = 0,5 and using the formula (2.7). Find the ratio of friction from the lubricant according to the formula (2.8). Calculate the extruding forces using the formula (2.1) in all cases and compare them with the experimentally obtained values. Fill in the table 1 with the data obtained. Make conclusions. Make a report. Table 1 Results of calculations and measurements №

Diameter of container

Length of workpiece

Rod diame ter

 s ср

Lubricate d or not

Rм

TKR

Tм

Тp

Pcalc

Pexp

Questions: How is the extruding force determined? List the known methods for determining the extruding force, their advantages and disadvantage? What extrusion parameters does the extruding force depend on? What is resistance to deformation? How is the resistance to deformation determined by extrusion? What determines the resistance to deformation in the process of extrusion? How is friction measured when metal is extruded and where does it work? How is the extruding force changed in the process of direct and reverse extrusion? Why is the extruding force increased at the final stage of the process? How is the power and operation of equipment determined in the process of extrusion? 18

LABORATORY WORK № 3: Study of the effect of the degree of deformation on the draw force and the mechanical properties of metal (drawing) The aim is to determine draw force and strength plastic properties by making the experiment. Laboratory equipment: R5 testing tensile machine (prototype of a drawing machine); draw dies of various diameters; a caliper gauge, a marker. Theory in brief Drawing is one of the most common methods of metal pressure treatment. By drawing wire, rods, pipes are obtained. The process of drawing (Fig. 3.1) consists of pulling the bar through a smoothly tapering die hole. In this case, the transverse dimensions of the bar decrease, and its length increases. The bar for drawing is produced by rolling or pressing. The force, under the action of which the metal is pulled, is called the draw force 𝑃𝑑 . In the process of drawing, the normal force N and the friction force T directed in the opposite direction from the force of drawing is applied on the bar from the side of the drawing.

Figure 3.1 – The scheme of the process and the forces applied on the metal in drawing

Under the action of the draw force, the bar is deformed and takes the shape and dimensions of the smallest section of the die drawing hole. As a result, the cross-sectional area of the workpiece decreases and its length increases. The shape and dimensions of the section of the product when drawing rods, wires, profiles of continuous sections and pipes without wall thinning are determined only by the configuration and dimensions of the gauging zone of the die draw hole. A variety of materials are processed by drawing: steel, aluminum, copper, nickel, titanium and alloys based on them; refractory metals and their alloys, as well as precious metals and alloys. 19

The semi-finished products obtained by drawing are circular wire with a diameter of 0.008–17 mm; square, rectangular, hexagonal and other wire; round, square, hexagonal, trapezoidal, and other bars; round tubes with a diameter of 0.3 – 500 mm with a wall thickness of 0.05-25 mm, oval, rectangular and others. In addition, by using this method of pressure treatment shaped profiles with different cross-sectional shapes and different sizes can be produced In the process of drawing the following deformation parameters are used: drawing ratio, relative drafting, elongation to failure, integral (logarithmic) deformation. The drawing ratio shows how many times the length or the cross-sectional area the product has increased during the cycle: 𝜆=

𝐿1 𝐿2

=

𝐹0 𝐹1

(3.1)

𝐿0 and 𝐹0 are, the length and cross-sectional area of the workpiece respectively,before drawing, and L1 and F1 are after drawing. Relative drafting is the ratio of the cobbing of the cross-sectional area of the product for the cycle of the drawing to its initial value: ɛ=

𝐹0 −𝐹1 𝐹0

100%

(3.2)

Elongation to failure – the ratio of increasing of the length of the product for the cycle to its initial value: d 

L1  L0 100% L0

(3.3)

Integral (logarithmic) deformation – the natural logarithm of the ratio of the cross-sectional area of the product before and after the cycle of drawing: F  i  ln 0   F1 

(3.4)

or i  ln   ln

(3.5)

1   1  

The draw force is the longitudinal force applied to the metal being drawn at its exit from the drawing die. This is one of the main parameters characterizing the perfection of the technological process. The less the drawing force, the lower the drawing cycle and, consequently, the less the danger of breaks, the lower the energy consumption for metal deformation, the less the pr, less die wear. The intensity of drawing can be determined either experimentally or analytically. For the experimental determination of the draw force by 20

anaessure of the metal being drawn onto the walls of the working area the die, and, consequentlylytical calculations, there are many different formulas. The simplest and quite suitable formula for determining the force when drawing rods and wire is the Petrov’s formula: 𝑃𝑑 = 𝜎𝑟 (𝐹0 − 𝐹1 )(1 + ʄ ∙ 𝛼 )

(3.6)

𝜎 +𝜎

𝑃𝑑 is the draw force, N;𝜎𝑟 = 𝑟0 𝑟1– temporary resistance to rupture of 2 metal, MPa σd0 , σ𝑑1 – ultimate tensile strength of metal before and after drawing, respectively, MPa; 𝐹0 , 𝐹1 – cross-sectional area the wire before and after drawing, 𝑚𝑚2; λ = 𝐷02 /𝐷12 – drawing ratio; 𝐷02 , 𝐷12 – wire diameter before and after deformation, mm; ʄs the friction ratio (when lubricated with engine oil ʄ = 0,10-0,12); α is the angle of the die in degrees. If the draw force is divided by the cross-sectional area of the product at the exit of the die 𝐹1, then we get the draw tension p. The drawing cyclemust be less than the deformation resistance of the metal in its state after drawing 𝜎𝑑1, otherwise plastic deformation may occur even after the metal leaves the draw die. This will lead to a skew of the crosssectional shape of the product after drawing and, as a result, it may break. Therefore, in the process of drawing, the following condition must be observed p

Pd   d1 F1

(3.7)

The draw condition without breaks is written as follows: 𝐴𝑓 =

𝜎𝑟1 𝑝

>1

(3.8)

𝐴𝑓 – assurance factor. In practice, the assurance factor usually varies from 1,35 to 2,00 (sometimes up to 2.50). In this case, the thinner the product and the higher the requirements for the quality of its surface and dimensional accuracy, the greater the assurance factor. Therefore, the maximum value 𝐴𝑓 reaches in the last calibration cycle, where the product is given the final shape and size. The drawing strength and tension is influenced by many factors: the degree of deformation per the cycle; strength properties of the metal being pulled; the geometry of the longitudinal profile of the die hole; friction on the contact surfaces of the deformed metal and tool; the shape of the final and initial cross-sections of the product; anti-tension; tool vibration.

21

Procedure Take four samples of annealed copper wire and measure its diameter. Sharpen the ends of three samples to cycle the dies through the die hole and connect to the grip of the testing machine. Lubricate the surface of the wire with lubricant and start drawing on the tensile testing machine through drawing dies with a diameter of 2,9; 2,6 and 2,4 mm. When the drawing process is defined, measure the draw force on the gauge dial. Make a tensile test of the original and three drawn samples, measure the strength of rupture, calculate ultimate tensile strength using the formula. 𝜎𝑟 =

𝑃𝑟

(3.9)

𝐹1

𝑃𝑝 is the strength of rupture, H; 𝐹1– is the cross-sectional area of the sample after drawing, mm2 . Calculate the draw force using a formula the formula (3.6) for each drawing and compare it with the experimental one. Calculate the draw tension and the safety factor using the formulas based on the experimental data (3.7, 3.8). 𝜎𝑟 = 𝑓 (ɛ) 𝑎𝑛𝑑 𝛿 = 𝑓(ɛ) Construct adependence diagram. Fill in the table 3.1 with the data. Make conclusions. Make a report. Table 3.1 Measured and calculated data of the drawing process № sample

Diameter of wire

ɛ

𝑃𝑟

𝜎𝑟

δ

𝑃𝑑

p

𝐴𝑓

Questions: Define the process of drawing. Name the types of products obtained by drawing. Name the parameters of the deformation in the process of drawing. What is the effect of various parameters on the strength and tension of drawing? What is the effect of drawing modes on metal properties? Specify the equipment for drawing. What are the tools for a drawing process? What preparatory operations are carried out for a process of drawing? 22

What are the features of a drawing technology on a chain mill? What specific tool is used in the process of pipedrawing?

23

LABORATORY WORK № 4: Study of the influence of friction coefficient on the upsetting force (upsetting) The aim is to determine the upsetting force at different modes of deformation experimentally and analytically. Laboratory equipment: Hydraulic press «Krayze» with force of 0,4 MN; backup for upsetting with varying working surface cleanliness; a caliper gauge. Theory in brief Upsetting is a technological operation in which an increase in the crosssection of the workpiece, perpendicular to the current force, occurs due size reduction in height (Fig. 4.1).

Figure 4.1 – The scheme of the upsetting. Н0

Figure 4.1 shows Н0,D0 – initial height and diameter of the billet; Нк – the height of the billet after upsetting; D – the diameter of contact of sample and backup; D – maximum diameter of the sample after upsetting; DПР – the diameter DПР  1,13

V HK

of the sample after upsetting: . To avoid the loss of stability and the buckling occuring, the billet with the following height is subjected to upsetting Н0  (2,5  3)D0

(4.1)

D0 – the diameter of the incoming billet.

In the process of upsetting, as a result of the interaction of the tool surface and the deformable metal, contact friction forces arise that prevent radial movement of the contact metal layers. These forces are maximal near the contact surface and decrease towards the middle of the height of the billet (Fig. 4.2). As a result of the contact friction forces in the near-contact zones 1, called zones of difficult deformation, distinct tense state of all-round compression 24

occurs (Fig. 4.2). These zones, as it were, expand zone 2 which is between them, a zone of localized deformation, where, under the action of vertical compressive stresses and minor radial stresses, maximum tangential stresses arise at an angle of 450 to the sample axis (Fig. 4.2). The inner zone 2 at its deformation in the radial direction influences zone 3 and causes tensile stresses in it, which can reach a significant value and cause longitudinal cracks on the side surface of the upsetted billet.

Figure 4.2 – The scheme of the stress state along the longitudinal section of the billet in the process of upsetting

Such a scheme of stresses arising in the process of upsetting causes uneven (roll crowning) deformation of the sample. In the case of a cylindrical billet, cross-sectional sections, when there is no friction anisotropy, retain their circular shape, and the meridional cross sections remain barrel-shaped. The degree and nature of barrel depends on the magnitude of the friction ratio. In the general case, when the billet is extremely high, there are three stages of deformation. At the first stage, when D0 / H0< 0,5 upsetting occurs with double barrel formation, the greater the magnitude of the friction ratio forces, the sharper the barrel formation and the earlier the two barrel formations merge into one. This is explained by the fact that with a significant amount of friction forces of the zone of obstructed deformation, they have large dome volumes and height. The second stage of upsetting occurs with a continuous approach of zones of difficult deformation until the moment of their interaction with D0 / H0 = 2  4. At the third stage, the height of zones of difficult deformation due to their interaction decreases, which is accompanied by a sharp increase in the force, and the effort is greater, the greater the friction force. Upsetting force is determined by the formula Р   S (1 

 DK 3 HK

25

)0.785DK2

(4.2)

 – is the friction coefficient between the sample and the backup;  S – stress of

material flow (for lead  S = 15 MPa); DK , H K – the diameter and height of the sample after upsetting. Upsetting with the formation of a “barrel” leads either to a decrease in the productivity of the equipment if a run-in of the billet on the side surface is applied after the precipitate, or to an increased consumption of metal, if not to apply the burnishing, since the formation of a “barrel” will be required extra volume of metal V . Under production conditions in the upsetting of steel billets in a hot state, the friction coefficient  will be maximum, therefore, barrel formation will also be maximum. Reducing barrel formation is an important task of developing upsetting technology. This leads to a reduction n in the uneven of deformation, a decrease in the volume of the billet and a reduction in the risk of cracking on the lateral surface of the upset billet, and this is especially important when the draft is prepared from low-plastic materials. To reduce barrel formation, technological lubricants are used, billets are deposited between bearing disk of a more ductile metal, or a paired upsetting is produced. Procedure Take lead samples from a laboratory assistant. Upset samples during several stages (Hk) on mirror backup lubricated with engine oil (  = 0,10); on the backup with a polished working surface without lubrication  ( = 0,28); on the backup with a rough machined surface without lubrication  ( = 0,50). Record the force Рexp.(kN) and measure Hkafter each stage of upsetting. Calculate the diameter of the upsetted sample using the formula DK  D0

H0 HK

. Determine the force P (kN) at the final moment of deformation at each stage of the upsettingusing the formula (4.2). Fill in the table 4.1 with data. Construct a graph of the dependence of the upsetting force on the conditional strain indicator of the upsetting P exp, Р  f  D  for different types K

H   K

samples. Make conclusions. Make a report.

26

Table 4.1 Measured and calculated data of the drawing process Experiment №

Friction coefficient

Experimental data Рexp.

Hk

Dk

Dk/Hk

Calculated data Fk

P

Рexp./Р

Questions: What is upsetting? Why is deformation uneven during upsetting? What influences barrel formation during upsetting? What stresses are in the zone of difficult deformation? What are the reasons for the possible formation of cracks on the lateral surface of the upsetted billet? How do the relative sizes of the sample and the magnitude of the forces of contact friction affect the required upsetting force under the experimental conditions? How can the degree of deformation during upsetting be calculated? Why is the diameter of the upsetted billet calculated, and not determined by measurement? How does barrel formation affect the process of producing forgings by upsetting? What are the ways to reduce barrel formation?

27

LABORATORY WORK № 5: Determination of stamping force in open and closed stamps (die forging) The aim is todetermine the force of open and closed stamping experimentally and by calculation. Laboratory equipment: a hydraulic press with a force of 0.6 MN or 1 MN; stamp for stamping in open and closed streams; a calipergauge, a hacksaw, a scale ruler. Theory in brief. The task of die forging is to obtain a forging that is close in shape and size to the finished part. A stamp is used for this process. It has two or more parts, with the conjugation of which a volume cavity forms in the form of a stamped forging. The process of stamping consists in the forced redistribution of the metal of the workpiece, corresponding to the shape of the die cavity. The cavity of the stamp is called a stream. The stamp can be single-impression or multipleimpression. For embedding the workpiece in the stream and removing from it forgings stamps are equipped with one or two connectors. To facilitate removal of the forging from the stamp, the side walls of the cavity are made with a slope. Production of forgings is carried out in stamps on stamping steam-air hammers, crank, friction and hydraulic presses. Hammers, friction and hydraulic presses have a free motion of moving parts, and crank presses have a regulated stroke. Therefore, on free-running machines, stamping is carried out in several strokes (strokes), and on crank machines –in one stroke. Forging stamping can be carried out in open and closed stamps. Stamping in an open stamp is characterized by the formation of a burr (flash) that performs some technological functions. The deformation of the workpiece in the cavity of the open stream of the stamp can be divided into four stages. At the first (Fig. 5.1 a, b), a free draft of the workpiece occurs until the lateral surface of the workpiece touches the walls of the stream cavity. At the second stage (Fig. 5.1 c), the metal begins to fill the cavity of the stream, the stage ends at the moment when the metal starts to flow into the gap between the halves of the stump, i.e., the beginning of the formation of burr. At the third stage (Fig. 5.1, d) the metal flows, filling the cavity of the stream and the partly hollow groove. At this stage, the round closes the cavity of the stream along the surface of the connector and creates a support that prevents the metal from flowing out of the cavity of the stream. As the thickness of the flash in the area of the bridge decreases resistance to leakage of the metal increases due to the higher cooling rate of the thin flash as compared with the entire volume of the workpiece. In addition, with a low height of the precipitated burr, the upper and lower contact zones of obstructed deformation are practically connected, which also increases the resistance to flow of the metal in the burr in the bridge zone. 28

These factors contribute to the qualitative filling of the stream of the stamp at the end of the third stage. At the fourth stage, the forgings are stamped to the required height by displacing the excess metal into the hollow groove storage (Fig. 5.1, e).

Figure 5.1 – Stamping Stages a-e – in the open and f-i – in closed stamping streams

The nominal volume of the metal workpiece, guaranteeing the filling of the stream (excluding carbon loss) is calculated by the formula: Vworkpiece = Vforging+Vburr

(5.1)

Vforging,Vburr –is the volume of forging and burr, respectively. The volume of forging is calculated from the nominal dimensions with the addition of half a positive deviation to the vertical dimensions. The volume of the burr for hammering is determined on the basis of the size and type of the hollow groove (Fig. 5.2), selected according to table 5.1.

29

Figure 5.2 – Hammer die groove

To use this table, at first, it is necessary to calculate the height of the bridge (thickness of the flash) h0 and the criterion of forging complexity Ks. ℎ0 = 0,015√𝐹𝑓

(5.2)

Ff – is the area of the forging section in the plane of the die stamp. For a round forging ℎ0 = 0,015𝐷𝑓

(5.3)

Df – is the diameter of the forging in the plane of the connector. The nearest calculated standard value h0 is selected from table 5.1. The choice of the number of grooved grooves is estimated by the value of the complexity criterion 𝐶𝑐 =

𝐻𝑓 ×𝑃𝑓2 ×𝑅𝑐𝑓 (𝐻𝑓 +𝐷𝑓 )2 ×𝑆𝑓

(5.4)

Sf – is the area of the axial section of the forging; Pf – the perimeter of the axial section of the forging; Rcf– is the distance from the axis to the center of gravity of a half axial section of the forging; Hf– is the height of the forging. Number of hollow groove determined under the conditions: if Cc≤ 2, then the groove № 1 is selected; if Cc ≤ 4, then the groove № 2 is selected; if Cc> 4, then the groove № 3 is selected. The volume of the burr Vburr is calculated taking into account the fact that the hollow groove is not completely filled with metal 𝑉𝑏𝑢𝑟𝑟 = 𝑆 × 𝐵𝑓 × 𝜉

(5.5)

S – is the cross-sectional area of the hollow groove in cm2 is selected from table 5.1; Bf – the perimeter of the forging in the plane of the die stamp; 𝜉– the fill factor of the hollow grooves, which is selected from the table 5.1.

30

Table 5.1 Dimensions of hollow grooves, mm Number grooves depending on the Сс 1 2 3 S, S, b1 b b1 b b1 cm2 cm2 18 0,52 6 20 0,61 8 2 20 0,69 7 22 0,77 9 25 22 0,80 8 25 0,91 10 28 22 1,02 9 25 1,13 11 30 25 1,36 10 28 1,53 12 32 28 2,01 12 32 2,33 14 38 30 2,68 14 38 3,44 16 42 32 3,43 15 40 4,34 18 46 35 4,35 16 42 5,30 20 50 38 6,01 18 46 7,45 22 55

R at the depth of the stream hw 0,6 0,8 1,0 1,6 2,0 3,0 4,0 5,0 6,0 8,0

Hw 3,0 3,0 3,0 3,5 4,0 5,0 6,0 7,0 8,0 10

40

1,0 1,0 1,0 1,0 1,5 1,5 2,0 2,0 2,5 3,0

1,0 1,5 1,5 1,5 2,0 2,0 2,5 2,5 3,0 3,0

1,5 1,5 2,0 2,0 2,5 2,5 3,0 3,0 3,5 4,0

b 6 6 7 8 9 10 11 12 13 14

S, cm2 0,74 0,88 1,04 1,55 1,77 2,78 3,85 5,06 6,42 9,03

Table 5.2 Values of the fill factor of the hollow grooves Forging weight, kg 5

Groove number 2 0,5 0,6 0,7

1 0,4 0,5 0,6

3 0,6 0,7 0,8

In the stamps of the hot forging crank driven press, the hollow groove has an open storage (Fig. 5.3), and its dimensions are determined from Table5.3. The volume of the burr when stamping on the hot forging crank driven press, due to the absence of normalized width in the storage of the stamp is determined differently than when stamping on hammers using the formula 𝑉𝑏𝑢𝑟𝑟 = 𝑝(𝑏ℎ3 + ℎ2 𝐵)

(5.6)

P – is the perimeter of the forging, mm; b – bridge width, mm; h3– bridge thickness, mm; В– the width of the burr in the storage. For forgings weighing up to 0,5 kg, B = 10 mm is accepted, weight up to 2 kg – B = 15 mm, with a mass of more than 2 kg –B = 20 mm, h2– the average thickness of the burr over the storage, h2 = 2h3.

31

Figure 5.3 – The shape of the hot forging crank driven groove press

According to the standard pattern the volume of the workpiece the calculated diameter of the original rod is determined using the formula 3

𝐷𝑤 = 1,08 √

𝑉𝑤 𝑚

(5.7)

m = H3/D3, 1,25≤m≤3,5; H3– workpiece height. According to the tables state standards of goods GOST on the rolled product range a bar is chosen, the diameter of which is closest to the calculated. Knowing the diameter and volume of the workpiece, its height is calculated. The forging, stamped in an open stream, is obtained with a burr, which is sheared on a shearing press in an edging stamp. When cutting burr cutting of fibers occurs, which somewhat reduces the quality of the metal forgings. Stamping in a closed die of a stamp occurs without the formation of a flash or with the formation of a slight end burr formed by wicking an insignificant amount of metal into the gap between the upper and lower parts of the stamp. The deformation of the workpiece in the cavity of a closed stream of the stamp can be conventionally divided into three stages. At the first (Fig.5.1, g) there is a free workpiece upsetting until it touches the walls of the stream. The second stage is the filling of the cavity of the stream, except for rounding in the corners of the stamp (Fig.5.1, h). The third stage is the complete design of the forging with a slight leakage of metal into the gap between the upper and lower die, if the volume of the workpiece was slightly greater than the volume of the forging. The size of the gap is usually not more than one millimeter.

32

Table 5.3 Dimensions of a groove for a burr of the hot forging crank driven stamp Press force, MN 6,3 10 16 20 25 31,5 40 63 80 100

Groove dimensions, mm h

b

h1

R

1-1,5 1-2 2-2,5 2,5-3 2,5-3 3,5-4 3,5-4 4-5 5-6 6-7

5-6 6-7 6-7 6-8 6-8 8-10 8-10 9-11 11-12 12-14

5-6 6-7 6-7 6-8 6-8 8 8 10 12 15

15 15 20 20 20 25 25 25 30 30

The smallest depth of the stream H, mm