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Investigation of FM heavy forging process by the Moiré method Part III: A direct forging process standard
ELSEVIER
Journal of Materials Processing Technology, 47 (1995) 311 322
Journal of Materials Processing Technology
Investigation of FM heavy forging process by the Moir6 method Part III: A direct forging process standard S h u n L o n g W a n g a,,, Qi Xiang C a o b FaculO" of Mechanical Engineer&g, Unicersity 0[ Technology, Eindhoven, Netherlands b Department (if' Mechanical Enghwering, Ts&ghua Unirersity. Beifing, People's Republic of China (Received July 25, 1993)
Industrial Summary
For producing large high quality forgings, a detailed procedure for planning the process based on systematic research is needed. Little work can be found on the process standard of the Free from Mannesmann (FM) method. In Part I El] and lI [2], the single and consecutive reduction results of the FM forging process were reported. The optimal Anvil Width Ratio (AWR) was found to be W/H o = 0.6. The rational turnover and anvil staggering procedure were obtained. In this paper, first the difference of the forging effect between an initially round and a square cross section testpiece is discussed. Secondly, for planning the rational anvil distribution in the real production process, the elongation rate and spread rate during the forging process are obtained. Finally, based on systematic investigation on the FM forging process, a standard for the direct FM reduction process which can ensure the internal quality of large forgings, is proposed and discussed.
I. Introduction Large forgings are often key components in assembled items of equipment and there is an increasing need to guarantee the quality of such forgings. As the size of large forgings increases, the traditional upsetting process is limited by the load capacity of the press and the internal metallurgical quality of the heavy steel ingots is also made worse. To poduce large but sound forgings with available equipment, several direct reduction processes have been put forward and used, such as the JTS, WHF, FM and V shaped anvil processes, the FM process being investigated in the present research.
* Corresponding author. 0924-0136/95/$09.50 f ) 1995 Elsevier Science S.A. All rights reserved. SSDI 0 9 2 4 - 0 1 3 6 ( 9 5 1 0 1 3 3 2 - U
312
S.L. Wang, Q.X. Cao/Journal q[ Mater&ls Processing Technology 47 (1995) 311 322
The FM method uses an unsymmetrical anvil arrangement and is an effective forging method used in industrial production. Much of the published research on the FM forging process is focused on the cavity closing and the internal stress/strain distribution under the single reduction process, little work being found on the detailed standard for the pass design. The standard of the current FM process is based mainly on accumulated experience, the lack of an accurate procedure based on the results of systematic experiments being an important reason for the unreliability of the quality of large forgings. Thus a systematic investigation is needed to determine the optimal technological parameters and to put forward a new standard for the direct-reduction process which can ensure the elimination of internal metallurgical defects. In parts I [1] and part II [2] of this work, the optimal AWR and rational turnover and anvil-staggering procedure were reported. In this paper, continuing the work of parts I and II, first the difference of the forging effect between an initially round and a square cross-section testpiece is discussed; then the elongation rate and spread rate during the F M forging process are obtained for planning the rational anvil reduction position; finally, based on systematic investigation of the FM forging process, a standard for the direct FM reduction process is proposed and discussed.
2. Forging effects of round and square cross-section testpieces In the heavy forging process, in order to reduce the number of forging passes and keep the ingot at high temperature, sometimes the main reduction process starts from the round cross-section ingots. It is very important to have a clear understanding of the difference of the forging effect between an initially round cross-section and a square cross section ingot. Figs. 1 and 2 show the Moir6 patterns for round cross-section testpieces when W/Ho = 0.4, 0.6. It can be seen that for initially round testpieces, when AH/Ho = 5% and 10%, and W/Ho = 0.4 or W/Ho = 0.6, the zone of large deformation is not at the centre of the testpiece. This is because the contact area between the upper anvil and the testpiece is small, the material flowing mainly laterally in the upper part. When AH/Ho is increased to 15%, the deformation at the ingot centre increases quickly. Thus, when the main reduction process starts from an initially round cross-section testpiece, an increase of reduction rate after AH/Ho > 10% is important for the increase of the deformation at the ingot centre, a small reduction rate of AH/Ho < 10% causing mainly surface and sub-surface material flow and having little effect on this closing of the internal cavities. Shown in Fig. 3 are the Moir6 patterns when W/Ho = 0.6 for a square crosssection testpiece, for which testpiece, no matter whether AH/Ho = 5%, 10% or 15%, the zone of large deformation is always at the centre. Thus an important conclusion can be drawn: the deformation-zone geometry of a square cross-section testpiece is determined mainly by the AWR, W/Ho, and has less dependence on the reduction rate, ~H/Ho. Using the optimal AWR of W/Ho = 0.6 can ensure that the zone of large deformation is at the centre of the ingot.
S.L. Wang, Q.X. Cao / Journal (?/Materials ProcesshTg Technology 47 f1995) 311 322
313
(a)
(b)
(c) Fig. 1. Moir~ patterns for W/H0 = 0.4, showing, on left, the U field and, on right, the V field, for a round cross-section where AH/Ho is: (a) 5%; tb) 10%; (c) 15%.
C o m p a r i n g the results between the r o u n d and the square cross-section testpieces, the initially square cross-section testpiece with W / H o = 0.6 can ensure that the zone of greatest d e f o r m a t i o n at the ingot centre for a n y reduction rate. Thus an ingot cross-section W / H o = 0.6 is suggested for the main reduction process.
3. The spread rate and the elongation rate In process p r o c e d u r e planning, the s p r e a d a n d the e l o n g a t i o n rate are very i m p o r tant for calculating the rational anvil l o c a t i o n s and the ingot cross-section conversion.
314
S.L. Wang, Q.X. Cao / Journal 0[ Materials Processing; Technology 47 (1995) 311 322
(a)
(b)
(c) Fig. 2. As for Fig. l, but for W/Ho = 0.6.
After one pass-reduction, only when the geometry of the testpiece is calculated, can the optimal forging sequence proposed in part II [2] be used. Different forging methods, different values of AWR, and different reduction rates all have influences on the spread rate and the elongation rate. The unsymmetrical deformation of the FM process makes its elongation and spread-characteristics quiet different from those of the conventional forging process. In this section, 4 0 m m dia. by 60 mm length round cross-section testpieces and 40 mm by 60 mm length square cross-section testpieces were used to measure the elongation rate and the spread rate for W/Ho = 0.4, 0.5, 0.6, the 180 ° turnover and rational staggering procedure being used. The forging procedure is shown in Fig. 4.
S.L. Wang, Q.X. Cao / Journal qf Materials Processing Technology 47 (1995) 311 322
315
(a)
(b) f
(c) Fig. 3. As for Fig. 2, but for a square cross-section.
The spread rate AB/Bo, and the elongation rate, A L / L o are influenced mainly by AWR, W/Ho, and reduction rate, A H / H o . The following assumptions are made: AB/Bo = .~*AH/H o,
A L / L o = f l * A H / H o,
where ~ and fl are called the spread rate and the elongation rate, respectively. W h e n W/Ho < 0.6, the greatest deformation is not in the centre, so that in addition whilst fl is defined as the elongation rate of the centre line, /~' is defined as the elongation rate of the lower surface (contact with the lower platform).
316
S.L. Wang, Q.X. Cao / Journal o/' Materials Processing Technology 47 (1995) 311 322
IM*H4 D
C I
131
~21
1
I
. . . .
A(1)
B(2)
!2t .
.
.
~113i
14 I .
.
D(4)
c(3)
Fig. 4. The forging procedure (A, B half-anvil staggering; C, D half-anvil staggering).
3.1. The round cross-section experimental results In the real production process, the steel ingot or the ingot after the upsetting process can be treated as a round cross-section ingot. After the first and third reductions, due to the non-uniform deformation, the cross-section of the testpiece is very irregular, the ~,/3 values being difficult to measure. The/3' value is very important for the rational anvil distribution of the second and fourth passes, so only the/3' values are given after first and third passes. After the second and fourth passes, the crosssections are regular, in which case the c~and [:t values being given. The ~ and//values of the fourth pass are calculated using the length and width after the second pass as the reference. The following definitions are made:
: AH/Ho, the single-side reduction rate Lo, Bo : the initial testpiece length and diameter L2, L4 : the average testpiece length after the second and fourth passes
r
B2,B4
: the average testpiece width after second and fourth passes
L 2 = (1 +/3*2*r)*Lo,
B2 = (1 + ~*2*r)*Bo,
L4 = (1 + fl*2*r)*L2,
B 4 = (1 -t-~2*r)*B2.
The experimental results are processed by the least-squares method, the results showing that the average elongation rate/3 and spread rate ~ are independent of the AWR when W/Ho = 0.4 ~ 0.6. When r < = 10%, c~ and/3 also have no dependence
S.L. Wang, Q.X. Cao / Journal Of Materials ProcessbTg Technology 47 (1995; 311 322
317
on the reduction rate r, but when r > 10% the values 7 and fl are related to the reduction rate r. Table 1 presents the results. From Table 1, it is seen that increase of AWR, the value of fl' increase, whilst when r > 10%, with increase of AWR, both ~ and fl increase. The values of a, fl and fl' can be used to calculate the testpiece dimensions for planning the right position for reduction and controlling the testpiece geometry.
3.2. The square cross-section experimental results The round cross-section testpiece becomes a square cross-section after 4 passes of FM reduction or 2 passes of conventional reduction. The experimental results are processed also by the least-squares method, the results showing that the elongation rate has no relationship with the reduction rate whilst it is a linear function of the AWR. Table 2 gives the ~ and fi values of the square cross-section testpieces. The spread rate is obtained by the constancy of volume condition and verified by the results of experiment. For square cross-section testpieces, the elongation rate and the spread rate of the second and fourth passes are almost the same, so that Table 2 only gives the ~ and fl values for the first two passes. Figs. 5 and 6 show the elongation rate and the spread rate when r = 15%, from which it is noted that when W/Ho = 0.4 - 0.6, with increase of the AWR, the elongation rate, [~, increases whilst the spread rate, ~, decreases, which is in contrary to the case with conventional forging processes. The main reason for this phenomenon is the non-uniform deformation caused by the unsymmetrical anvil arrangement of the FM process. Fig. 7 is a schematic diagram of the FM process when W/Ho < 0.6. When W/Ho < 0.6, the greatest deformation is not in the centre, so that the greatest elongation and spread are also not in the centre. As shown in Fig. 7, where H1 is the Table I T h e ~ a n d fl v a l u e s o f r o u n d c r o s s - s e c t i o n t e s t p i e c e s
Passes
r < -
10%
r > 10%
fi'
1 2 3 4
0.15 0.30
r > 10%
0.35
0.35 + 1.61r - 0.1)
0.36
0.36 + 1.6(r - 0.1)
W,'Ho
0.30 + 4 5 . 5 ( r - 0.1) z 0.06 + 0.3
0.34
r < = 10%
W/Ho
0.34 + 4 5 . 5 ( r - 0.1) z
Table 2 The ~ and [/values of square cross-section testpieces Passes
1~'
1
2
[/'
:~
- 0 . 1 3 + 0.7 W,'Ho
0.50 + 0.3 W / H o
1
[/2 + 2rf12(I - 2r)(1 + 2rf12 )
318
S.L. Wang, Q.X. Cao/Journal of Materials Processing Technology 47 (1995) 311 322
distance from the upper anvil to the region of greatest deformation a n d H~ = 2H1, the e l o n g a t i o n a n d spread characteristics of the F M m e t h o d with the A W R given by W/Ho are similar to those of the c o n v e n t i o n a l reduction m e t h o d with the A W R given by W/H'o. Table 3 presents the values of W/H'o for different values of W/Ho.
~.70 68 66 64 62 60
0.4
W/no 0.6
0.5
Fig. 5. The elongation rate (r = 15%).
68 "~66 64 62 60 58
0.4
W/Ho 0.6
0.5
Fig. 6. The spread rate (r = 15%). i/J ///////////
(
'A
Fig. 7. The Schematic diagram of the deformation zone ( W/Ho < 0.6). Table 3 Comparison of values of W/Ho
W/Ho
H'o
W/H'o
Htimax/H
0.4 0.5 0.6
0.4Ho 0,66Ho Ho
1.0 0.76 0.6
0.80 0.67 0.50
S.L. Wang, Q.X. Cao / Journal (?[Materials Processing Technology 47 (1995) 311 322
319
For the conventional reduction method, with the increase of W/Ho, the spread rate increase and the elongation rate /~ decrease. For the FM method, when W/Ho < = 0.6, the greatest deformation is not at the centre of the testpiece, the value of W/H'o decreasing with increase in the value of W/Ho. This explains the difference of the elongation characteristics between the FM and the conventional method. The results of repeated experiments verified the validity of Figs. 5 and 6. In this section, the elongation rate and the spread rate of the FM reduction method were obtained by experiment. These values are very useful in predicting the testpiece geometry, in planning the right place for reduction anvil, and in planning the distribution of the material. The above results were obtained by an R - T experiment with lead: they should be evaluated and improved by results from real production process. The valid range of the above results is W/Ho = 0.4 ~ 0.6.
4. The standard of the direct FM forging process Currently, process planning is based mainly on accumulated experience, which absence of a scientific basis is a major reason for the unreliability of the quality of heavy forgings. A detailed standard of the FM forging process which can ensure the quality of large forgings, should be stated. Formulated, this to include several important aspects: initial ingot cross-section before the main reduction, initial AWR range, rational turnover procedure, rational anvil-staggering method, single-side reduction rate, the minimum main-reduction forging ratio, etc. Based on the systematic investigation on the FM process, the following aspects can be drawn as the standard of the direct FM forging process.
4.1. Initial ingot cross-section For the main reduction processes, when only 4 passes are used, an ingot of initially square-cross section is recommended.
4.2. Initial A WR range From part I [1], the initial AWR range of the main FM reduction process of a square cross-section ingot can be chosen as W/Ho = 0.5 0.6, considering the strainand stress-distribution of the single-reduction results.
4.3. Rational turnover procedure In Fig. 8, A, B, C, D represent the directions of reduction. From part II [2], in the main FM reduction process, the rational turnover procedure is to turn the ingot in the clockwise direction by the sequence: A B - C - D B A - D - C .
320
S.L. Wang, Q.X. Cao / Journal ~?f Materials Processing Technology 47 (1995) 311 322
A
c
D
B
Fig. 8. The directions of reduction.
4.4. Rational anvil-staggering method A rational turnover and staggering procedure can ensure the closing of all of the internal cavities and the obtaining of a uniform refined microstructure at the ingot centre. From part II [2], half-anvil staggering when the turnover 180 + is suggested. The elongation rate can be used for planning a rational anvil staggering procedure, Fig. 4 showing such an example.
4.5. Single-side reduction rate and the minimum main-reduction .forging ratio From part II [2], the critical single-side reduction rate for the closing of all of the internal cavities in 4 passes of reduction is AH/Ho = 11.25%, in a room temperature (R T)experiment. From part I [1], it is shown that the R - T e x p e r i m e n t a l results can be used with safety for the real production process. The single-side reduction must not be too large, otherwise the height to width ratio after 90 + turnover is too high, which causes a double-bulging problem in the subsequent forging passes. Thus, the singleside reduction rate is recommended as AH/Ho = 12%, which can ensure the closing of all of the internal defects and for obtaining a fine internal microstructure. Considering the case where W/Ho = 0.6 is used, the elongation rate is/72 = 0.5 + 0.3 × 0.6 = 0.68 and after 4 passes of reduction the total forging ratio is Yt = (1 + flz2r) 2 = 1.35. Thus the minimum main direct FM reduction forging ratio is Yl = 1.35. Forging-pass designs for two 50 kg steel ingots and two 1000 kg steel ingots were made using this new proposed standard, the experimental results showing that both the internal quality of the testpiece and its mechanical properties were very good, which verified the validity of the new standard. Continuing work on product verifications will be undertaken. The above five aspects can be used as the principle in the planning of the main FM reduction process. Using these principles and the elongation-rate and spread-rate values, detailed pass designs can be made: computer-aided planning software will be developed to assist in this objective.
S.L. Wang, Q.X. Cao / Journal ol Materials Proces'sing Technology 47 (1995) 311 322
321
5. Discussion
In this investigation on FM reduction process (Parts I, II, Ill), physical modelling is used mainly, experiments with lead at R T being carried out and verified by experiments with steel at H T. The R - T Moir6 method and the newly developed H - T Moir6 modelling technique were used to obtain the material flow patterns and the strain/stress distribution. Compared with numerical simulation (such as the FiniteElement Method), this physical modelling method can simulate the real production process accurately and the results are credible. Thus the development of physical simulation is still very important, especially for complex forming processes. The combination of numerical simulation with physical simulation is important to meet the trend in bulk forming processes to net or near-net shape forming and the prediction of the final quality control (microstructure, properties, etc.) From the present research, using the optimised forging parameters, the minimum FM reduction forging ratio is Yl = 1.35, thus a great number of large shaft-shaped forgings can be produced from the ingot by the direct reduction process. Using the newly proposed standard for the direct FM reduction process, the internal quality of such large forgings can be ensured and the conventional upsetting process can be eliminated. Thus with available press capacity, larger forgings can be made, of high quality and at low production cost, using the new standard. Some further work should be done, this work including: the verification of the new process standard with real products and subsequent improvement of the process standard; examination of the mechanical properties and microstructure of products made using the proposed standard; researching of the closing mechanism of internal cavities and the construction of closing criteria; and the programming of user-friendly computer-aided software for the FM method using the proposed standard, etc.
6. Conclusions
1. In the main FM reduction process, an initially square cross-section ingot with the optimum AWR is recommended, to ensure that the maximum deformation is focused at the ingot centre at any reduction rate. 2. The elongation rate and the spread rate that were obtained by experiment which can be used for calculating the conversion of the cross-section of the ingot and the rational position of anvil reduction to ensure the best forging effect. 3. The direct FM reduction process standard that has been proposed and discussed has many advantages, such as the ensuring of the internal quality of heavy forgings, the elimination of the upsetting procedure, and the reduction of production cost.
References
[1] S.L.Wang and Q.X. Cao, Investigationof the FM heavyforging processby the Moiremethod. Part I: Single reduction results, J. Mats. Proc. Tech.
322
S.L. Wang, Q.X. Cao / Journal ~['Materials Processing Technology 47 (1995) 311 322
[2] S.L. Wang and Q.X. Cao, Investigation of the FM heavy forging processes by the Moir6 method. Part II: Consecutive reduction results. J. Mats. Proc. Tech. [3] S.L. Wang, Modelling FM (free from Mannesmann effect) heavy forging process by Moir6 method, Ph.D. Thesis, Tsinghua University, 1991 (in Chinese). [4] K. Nakajima, K. Watanabe, S. Watanabe and 1. Tamura, Study on the closing and consolidation of internal cavities in heavy ingots by hot free forging. Proc. 4th ICPE, Tokyo, 1980, p. 166 [5] 1. Tamura, S. Watanabe, K. Watanabe and K. Nakajima, Development of new processes for control of internal deformation and internal stress in hot free forging of heavy ingots, Trans. ISIJ Jpn., 24 (1984) 101. [6] K.D. Haverkamp and H.P. Heil, Deformation conditions for close forging of the core zone by drawing down, Stahl Eisen, 105 (22)(1985), 1214. [7] S.P. Dudra and Y-T. Ira, Investigation of metal flow in open-die forging with different die and billet geometries, J. Mat. Process. Tech., 21 (1990) 143-153. [8] E. Erman, N.M. Medei, A.R. Roesch and D.C. Shah, Physical modelling of the blocking process in open-die press forging, J. Mech. Work. Tech., 19 (1989), 165-194. [9] Q.X. Cao, S.Y. Ye, B. Xie and Y.X. Zhong, Modelling of free large forging processes by photoelectric scanning Mori+ method, Proc. 2nd ICTP, Stuttgart, 1987. [10] S.L. Wang, An introduction to Moir6 method, TUE Internal Report, WPA 1278, 1992. [11] Q.X. Cao, S.Y. Ye, B. Xie and X.T. Ma, The principle and Application o[' Moirb Method, Tsinghua University Press, May 1983 (in Chinese). [12] Q.X. Cao, B. Xie and Y.X. Zhong, The engineering application and automatic fringes processing of Moir6 method, China Railway Press, Apr. 1990 (in Chinese).
Journal of Materials Processing Technology, 47 (1995) 311 322
Journal of Materials Processing Technology
Investigation of FM heavy forging process by the Moir6 method Part III: A direct forging process standard S h u n L o n g W a n g a,,, Qi Xiang C a o b FaculO" of Mechanical Engineer&g, Unicersity 0[ Technology, Eindhoven, Netherlands b Department (if' Mechanical Enghwering, Ts&ghua Unirersity. Beifing, People's Republic of China (Received July 25, 1993)
Industrial Summary
For producing large high quality forgings, a detailed procedure for planning the process based on systematic research is needed. Little work can be found on the process standard of the Free from Mannesmann (FM) method. In Part I El] and lI [2], the single and consecutive reduction results of the FM forging process were reported. The optimal Anvil Width Ratio (AWR) was found to be W/H o = 0.6. The rational turnover and anvil staggering procedure were obtained. In this paper, first the difference of the forging effect between an initially round and a square cross section testpiece is discussed. Secondly, for planning the rational anvil distribution in the real production process, the elongation rate and spread rate during the forging process are obtained. Finally, based on systematic investigation on the FM forging process, a standard for the direct FM reduction process which can ensure the internal quality of large forgings, is proposed and discussed.
I. Introduction Large forgings are often key components in assembled items of equipment and there is an increasing need to guarantee the quality of such forgings. As the size of large forgings increases, the traditional upsetting process is limited by the load capacity of the press and the internal metallurgical quality of the heavy steel ingots is also made worse. To poduce large but sound forgings with available equipment, several direct reduction processes have been put forward and used, such as the JTS, WHF, FM and V shaped anvil processes, the FM process being investigated in the present research.
* Corresponding author. 0924-0136/95/$09.50 f ) 1995 Elsevier Science S.A. All rights reserved. SSDI 0 9 2 4 - 0 1 3 6 ( 9 5 1 0 1 3 3 2 - U
312
S.L. Wang, Q.X. Cao/Journal q[ Mater&ls Processing Technology 47 (1995) 311 322
The FM method uses an unsymmetrical anvil arrangement and is an effective forging method used in industrial production. Much of the published research on the FM forging process is focused on the cavity closing and the internal stress/strain distribution under the single reduction process, little work being found on the detailed standard for the pass design. The standard of the current FM process is based mainly on accumulated experience, the lack of an accurate procedure based on the results of systematic experiments being an important reason for the unreliability of the quality of large forgings. Thus a systematic investigation is needed to determine the optimal technological parameters and to put forward a new standard for the direct-reduction process which can ensure the elimination of internal metallurgical defects. In parts I [1] and part II [2] of this work, the optimal AWR and rational turnover and anvil-staggering procedure were reported. In this paper, continuing the work of parts I and II, first the difference of the forging effect between an initially round and a square cross-section testpiece is discussed; then the elongation rate and spread rate during the F M forging process are obtained for planning the rational anvil reduction position; finally, based on systematic investigation of the FM forging process, a standard for the direct FM reduction process is proposed and discussed.
2. Forging effects of round and square cross-section testpieces In the heavy forging process, in order to reduce the number of forging passes and keep the ingot at high temperature, sometimes the main reduction process starts from the round cross-section ingots. It is very important to have a clear understanding of the difference of the forging effect between an initially round cross-section and a square cross section ingot. Figs. 1 and 2 show the Moir6 patterns for round cross-section testpieces when W/Ho = 0.4, 0.6. It can be seen that for initially round testpieces, when AH/Ho = 5% and 10%, and W/Ho = 0.4 or W/Ho = 0.6, the zone of large deformation is not at the centre of the testpiece. This is because the contact area between the upper anvil and the testpiece is small, the material flowing mainly laterally in the upper part. When AH/Ho is increased to 15%, the deformation at the ingot centre increases quickly. Thus, when the main reduction process starts from an initially round cross-section testpiece, an increase of reduction rate after AH/Ho > 10% is important for the increase of the deformation at the ingot centre, a small reduction rate of AH/Ho < 10% causing mainly surface and sub-surface material flow and having little effect on this closing of the internal cavities. Shown in Fig. 3 are the Moir6 patterns when W/Ho = 0.6 for a square crosssection testpiece, for which testpiece, no matter whether AH/Ho = 5%, 10% or 15%, the zone of large deformation is always at the centre. Thus an important conclusion can be drawn: the deformation-zone geometry of a square cross-section testpiece is determined mainly by the AWR, W/Ho, and has less dependence on the reduction rate, ~H/Ho. Using the optimal AWR of W/Ho = 0.6 can ensure that the zone of large deformation is at the centre of the ingot.
S.L. Wang, Q.X. Cao / Journal (?/Materials ProcesshTg Technology 47 f1995) 311 322
313
(a)
(b)
(c) Fig. 1. Moir~ patterns for W/H0 = 0.4, showing, on left, the U field and, on right, the V field, for a round cross-section where AH/Ho is: (a) 5%; tb) 10%; (c) 15%.
C o m p a r i n g the results between the r o u n d and the square cross-section testpieces, the initially square cross-section testpiece with W / H o = 0.6 can ensure that the zone of greatest d e f o r m a t i o n at the ingot centre for a n y reduction rate. Thus an ingot cross-section W / H o = 0.6 is suggested for the main reduction process.
3. The spread rate and the elongation rate In process p r o c e d u r e planning, the s p r e a d a n d the e l o n g a t i o n rate are very i m p o r tant for calculating the rational anvil l o c a t i o n s and the ingot cross-section conversion.
314
S.L. Wang, Q.X. Cao / Journal 0[ Materials Processing; Technology 47 (1995) 311 322
(a)
(b)
(c) Fig. 2. As for Fig. l, but for W/Ho = 0.6.
After one pass-reduction, only when the geometry of the testpiece is calculated, can the optimal forging sequence proposed in part II [2] be used. Different forging methods, different values of AWR, and different reduction rates all have influences on the spread rate and the elongation rate. The unsymmetrical deformation of the FM process makes its elongation and spread-characteristics quiet different from those of the conventional forging process. In this section, 4 0 m m dia. by 60 mm length round cross-section testpieces and 40 mm by 60 mm length square cross-section testpieces were used to measure the elongation rate and the spread rate for W/Ho = 0.4, 0.5, 0.6, the 180 ° turnover and rational staggering procedure being used. The forging procedure is shown in Fig. 4.
S.L. Wang, Q.X. Cao / Journal qf Materials Processing Technology 47 (1995) 311 322
315
(a)
(b) f
(c) Fig. 3. As for Fig. 2, but for a square cross-section.
The spread rate AB/Bo, and the elongation rate, A L / L o are influenced mainly by AWR, W/Ho, and reduction rate, A H / H o . The following assumptions are made: AB/Bo = .~*AH/H o,
A L / L o = f l * A H / H o,
where ~ and fl are called the spread rate and the elongation rate, respectively. W h e n W/Ho < 0.6, the greatest deformation is not in the centre, so that in addition whilst fl is defined as the elongation rate of the centre line, /~' is defined as the elongation rate of the lower surface (contact with the lower platform).
316
S.L. Wang, Q.X. Cao / Journal o/' Materials Processing Technology 47 (1995) 311 322
IM*H4 D
C I
131
~21
1
I
. . . .
A(1)
B(2)
!2t .
.
.
~113i
14 I .
.
D(4)
c(3)
Fig. 4. The forging procedure (A, B half-anvil staggering; C, D half-anvil staggering).
3.1. The round cross-section experimental results In the real production process, the steel ingot or the ingot after the upsetting process can be treated as a round cross-section ingot. After the first and third reductions, due to the non-uniform deformation, the cross-section of the testpiece is very irregular, the ~,/3 values being difficult to measure. The/3' value is very important for the rational anvil distribution of the second and fourth passes, so only the/3' values are given after first and third passes. After the second and fourth passes, the crosssections are regular, in which case the c~and [:t values being given. The ~ and//values of the fourth pass are calculated using the length and width after the second pass as the reference. The following definitions are made:
: AH/Ho, the single-side reduction rate Lo, Bo : the initial testpiece length and diameter L2, L4 : the average testpiece length after the second and fourth passes
r
B2,B4
: the average testpiece width after second and fourth passes
L 2 = (1 +/3*2*r)*Lo,
B2 = (1 + ~*2*r)*Bo,
L4 = (1 + fl*2*r)*L2,
B 4 = (1 -t-~2*r)*B2.
The experimental results are processed by the least-squares method, the results showing that the average elongation rate/3 and spread rate ~ are independent of the AWR when W/Ho = 0.4 ~ 0.6. When r < = 10%, c~ and/3 also have no dependence
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on the reduction rate r, but when r > 10% the values 7 and fl are related to the reduction rate r. Table 1 presents the results. From Table 1, it is seen that increase of AWR, the value of fl' increase, whilst when r > 10%, with increase of AWR, both ~ and fl increase. The values of a, fl and fl' can be used to calculate the testpiece dimensions for planning the right position for reduction and controlling the testpiece geometry.
3.2. The square cross-section experimental results The round cross-section testpiece becomes a square cross-section after 4 passes of FM reduction or 2 passes of conventional reduction. The experimental results are processed also by the least-squares method, the results showing that the elongation rate has no relationship with the reduction rate whilst it is a linear function of the AWR. Table 2 gives the ~ and fi values of the square cross-section testpieces. The spread rate is obtained by the constancy of volume condition and verified by the results of experiment. For square cross-section testpieces, the elongation rate and the spread rate of the second and fourth passes are almost the same, so that Table 2 only gives the ~ and fl values for the first two passes. Figs. 5 and 6 show the elongation rate and the spread rate when r = 15%, from which it is noted that when W/Ho = 0.4 - 0.6, with increase of the AWR, the elongation rate, [~, increases whilst the spread rate, ~, decreases, which is in contrary to the case with conventional forging processes. The main reason for this phenomenon is the non-uniform deformation caused by the unsymmetrical anvil arrangement of the FM process. Fig. 7 is a schematic diagram of the FM process when W/Ho < 0.6. When W/Ho < 0.6, the greatest deformation is not in the centre, so that the greatest elongation and spread are also not in the centre. As shown in Fig. 7, where H1 is the Table I T h e ~ a n d fl v a l u e s o f r o u n d c r o s s - s e c t i o n t e s t p i e c e s
Passes
r < -
10%
r > 10%
fi'
1 2 3 4
0.15 0.30
r > 10%
0.35
0.35 + 1.61r - 0.1)
0.36
0.36 + 1.6(r - 0.1)
W,'Ho
0.30 + 4 5 . 5 ( r - 0.1) z 0.06 + 0.3
0.34
r < = 10%
W/Ho
0.34 + 4 5 . 5 ( r - 0.1) z
Table 2 The ~ and [/values of square cross-section testpieces Passes
1~'
1
2
[/'
:~
- 0 . 1 3 + 0.7 W,'Ho
0.50 + 0.3 W / H o
1
[/2 + 2rf12(I - 2r)(1 + 2rf12 )
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distance from the upper anvil to the region of greatest deformation a n d H~ = 2H1, the e l o n g a t i o n a n d spread characteristics of the F M m e t h o d with the A W R given by W/Ho are similar to those of the c o n v e n t i o n a l reduction m e t h o d with the A W R given by W/H'o. Table 3 presents the values of W/H'o for different values of W/Ho.
~.70 68 66 64 62 60
0.4
W/no 0.6
0.5
Fig. 5. The elongation rate (r = 15%).
68 "~66 64 62 60 58
0.4
W/Ho 0.6
0.5
Fig. 6. The spread rate (r = 15%). i/J ///////////
(
'A
Fig. 7. The Schematic diagram of the deformation zone ( W/Ho < 0.6). Table 3 Comparison of values of W/Ho
W/Ho
H'o
W/H'o
Htimax/H
0.4 0.5 0.6
0.4Ho 0,66Ho Ho
1.0 0.76 0.6
0.80 0.67 0.50
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For the conventional reduction method, with the increase of W/Ho, the spread rate increase and the elongation rate /~ decrease. For the FM method, when W/Ho < = 0.6, the greatest deformation is not at the centre of the testpiece, the value of W/H'o decreasing with increase in the value of W/Ho. This explains the difference of the elongation characteristics between the FM and the conventional method. The results of repeated experiments verified the validity of Figs. 5 and 6. In this section, the elongation rate and the spread rate of the FM reduction method were obtained by experiment. These values are very useful in predicting the testpiece geometry, in planning the right place for reduction anvil, and in planning the distribution of the material. The above results were obtained by an R - T experiment with lead: they should be evaluated and improved by results from real production process. The valid range of the above results is W/Ho = 0.4 ~ 0.6.
4. The standard of the direct FM forging process Currently, process planning is based mainly on accumulated experience, which absence of a scientific basis is a major reason for the unreliability of the quality of heavy forgings. A detailed standard of the FM forging process which can ensure the quality of large forgings, should be stated. Formulated, this to include several important aspects: initial ingot cross-section before the main reduction, initial AWR range, rational turnover procedure, rational anvil-staggering method, single-side reduction rate, the minimum main-reduction forging ratio, etc. Based on the systematic investigation on the FM process, the following aspects can be drawn as the standard of the direct FM forging process.
4.1. Initial ingot cross-section For the main reduction processes, when only 4 passes are used, an ingot of initially square-cross section is recommended.
4.2. Initial A WR range From part I [1], the initial AWR range of the main FM reduction process of a square cross-section ingot can be chosen as W/Ho = 0.5 0.6, considering the strainand stress-distribution of the single-reduction results.
4.3. Rational turnover procedure In Fig. 8, A, B, C, D represent the directions of reduction. From part II [2], in the main FM reduction process, the rational turnover procedure is to turn the ingot in the clockwise direction by the sequence: A B - C - D B A - D - C .
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A
c
D
B
Fig. 8. The directions of reduction.
4.4. Rational anvil-staggering method A rational turnover and staggering procedure can ensure the closing of all of the internal cavities and the obtaining of a uniform refined microstructure at the ingot centre. From part II [2], half-anvil staggering when the turnover 180 + is suggested. The elongation rate can be used for planning a rational anvil staggering procedure, Fig. 4 showing such an example.
4.5. Single-side reduction rate and the minimum main-reduction .forging ratio From part II [2], the critical single-side reduction rate for the closing of all of the internal cavities in 4 passes of reduction is AH/Ho = 11.25%, in a room temperature (R T)experiment. From part I [1], it is shown that the R - T e x p e r i m e n t a l results can be used with safety for the real production process. The single-side reduction must not be too large, otherwise the height to width ratio after 90 + turnover is too high, which causes a double-bulging problem in the subsequent forging passes. Thus, the singleside reduction rate is recommended as AH/Ho = 12%, which can ensure the closing of all of the internal defects and for obtaining a fine internal microstructure. Considering the case where W/Ho = 0.6 is used, the elongation rate is/72 = 0.5 + 0.3 × 0.6 = 0.68 and after 4 passes of reduction the total forging ratio is Yt = (1 + flz2r) 2 = 1.35. Thus the minimum main direct FM reduction forging ratio is Yl = 1.35. Forging-pass designs for two 50 kg steel ingots and two 1000 kg steel ingots were made using this new proposed standard, the experimental results showing that both the internal quality of the testpiece and its mechanical properties were very good, which verified the validity of the new standard. Continuing work on product verifications will be undertaken. The above five aspects can be used as the principle in the planning of the main FM reduction process. Using these principles and the elongation-rate and spread-rate values, detailed pass designs can be made: computer-aided planning software will be developed to assist in this objective.
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5. Discussion
In this investigation on FM reduction process (Parts I, II, Ill), physical modelling is used mainly, experiments with lead at R T being carried out and verified by experiments with steel at H T. The R - T Moir6 method and the newly developed H - T Moir6 modelling technique were used to obtain the material flow patterns and the strain/stress distribution. Compared with numerical simulation (such as the FiniteElement Method), this physical modelling method can simulate the real production process accurately and the results are credible. Thus the development of physical simulation is still very important, especially for complex forming processes. The combination of numerical simulation with physical simulation is important to meet the trend in bulk forming processes to net or near-net shape forming and the prediction of the final quality control (microstructure, properties, etc.) From the present research, using the optimised forging parameters, the minimum FM reduction forging ratio is Yl = 1.35, thus a great number of large shaft-shaped forgings can be produced from the ingot by the direct reduction process. Using the newly proposed standard for the direct FM reduction process, the internal quality of such large forgings can be ensured and the conventional upsetting process can be eliminated. Thus with available press capacity, larger forgings can be made, of high quality and at low production cost, using the new standard. Some further work should be done, this work including: the verification of the new process standard with real products and subsequent improvement of the process standard; examination of the mechanical properties and microstructure of products made using the proposed standard; researching of the closing mechanism of internal cavities and the construction of closing criteria; and the programming of user-friendly computer-aided software for the FM method using the proposed standard, etc.
6. Conclusions
1. In the main FM reduction process, an initially square cross-section ingot with the optimum AWR is recommended, to ensure that the maximum deformation is focused at the ingot centre at any reduction rate. 2. The elongation rate and the spread rate that were obtained by experiment which can be used for calculating the conversion of the cross-section of the ingot and the rational position of anvil reduction to ensure the best forging effect. 3. The direct FM reduction process standard that has been proposed and discussed has many advantages, such as the ensuring of the internal quality of heavy forgings, the elimination of the upsetting procedure, and the reduction of production cost.
References
[1] S.L.Wang and Q.X. Cao, Investigationof the FM heavyforging processby the Moiremethod. Part I: Single reduction results, J. Mats. Proc. Tech.
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[2] S.L. Wang and Q.X. Cao, Investigation of the FM heavy forging processes by the Moir6 method. Part II: Consecutive reduction results. J. Mats. Proc. Tech. [3] S.L. Wang, Modelling FM (free from Mannesmann effect) heavy forging process by Moir6 method, Ph.D. Thesis, Tsinghua University, 1991 (in Chinese). [4] K. Nakajima, K. Watanabe, S. Watanabe and 1. Tamura, Study on the closing and consolidation of internal cavities in heavy ingots by hot free forging. Proc. 4th ICPE, Tokyo, 1980, p. 166 [5] 1. Tamura, S. Watanabe, K. Watanabe and K. Nakajima, Development of new processes for control of internal deformation and internal stress in hot free forging of heavy ingots, Trans. ISIJ Jpn., 24 (1984) 101. [6] K.D. Haverkamp and H.P. Heil, Deformation conditions for close forging of the core zone by drawing down, Stahl Eisen, 105 (22)(1985), 1214. [7] S.P. Dudra and Y-T. Ira, Investigation of metal flow in open-die forging with different die and billet geometries, J. Mat. Process. Tech., 21 (1990) 143-153. [8] E. Erman, N.M. Medei, A.R. Roesch and D.C. Shah, Physical modelling of the blocking process in open-die press forging, J. Mech. Work. Tech., 19 (1989), 165-194. [9] Q.X. Cao, S.Y. Ye, B. Xie and Y.X. Zhong, Modelling of free large forging processes by photoelectric scanning Mori+ method, Proc. 2nd ICTP, Stuttgart, 1987. [10] S.L. Wang, An introduction to Moir6 method, TUE Internal Report, WPA 1278, 1992. [11] Q.X. Cao, S.Y. Ye, B. Xie and X.T. Ma, The principle and Application o[' Moirb Method, Tsinghua University Press, May 1983 (in Chinese). [12] Q.X. Cao, B. Xie and Y.X. Zhong, The engineering application and automatic fringes processing of Moir6 method, China Railway Press, Apr. 1990 (in Chinese).