Process Planning Support for Intermediate Steps Design of Axisymmetric Hot Close-Die Forging Parts
Department of Material Science and Technology, University of Rousse, 8 Studentska Street, Rousse 7017, Bulgaria
Abstract Hot close-die forging processes are broadly used in manufacturing at the present time. The researchers still not strictly answered on the significant questions about necessity and shape of intermediate steps. General algorithm for process planning support for intermediate steps designs of axisymmetric hot close-die forging parts are presented in this study. Example of using this algorithm also is included in the paper. Keywords: Hot close-die forging, Intermediate steps, Process design
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1. Introduction Hot close-die forging processes continue to be one of widely used in manufacturing at the present time. Theoretical backgrounds of these manufacturing processes have been developed at the beginning of XX century. Important meaning for this was the development of the theory of plasticity. Unfortunately, the researchers still not strictly answered on the one of the significant question in the area of forging - about necessity of appliance of intermediate steps while hot close-die forging is performed. There are different approaches used in engineering practice. Most of them are based on the experience or trial-error method. As a result of generalization of above methods expert systems have been created and are into use. Recently, criterions for necessity of intermediate steps have been proposed in several studies [1,2,3, 4]. The necessity of intermediate steps is in strong connection with shape of these steps. The shape design is important task for engineers too. Design methods are proposed in the works of many investigators, for instance [5,6,7,8].
Despite of too many proposed methods and approaches for the different subtasks of a real planning process of hot close-die forging, process design is embarrassed because of very hard to formalizing of the process planning rules. In the present work, general algorithm for process planning support for intermediate steps designs of axisymmetric hot close-die forging parts are presented. 2. General algorithm for process planning support for intermediate steps designs of axisymmetric hot close-die forging parts The presented on the figure 1 algorithm consider only a part from the whole forging process – design of intermediate steps of forging. Especially, the method discusses the necessity of intermediate steps and their geometrical shape. The input data include forging part drawing and initial billet dimensions. Like interstitial result, the processed data consists a set of alternative forging sequences. These alternatives can be different as regards of the numbers of intermediate steps and their shape. Later, from the different cases the designers can choose appropriate variant for specific
Input data: Forging part drawing and billet dimensions 1 Choice of criterion for the necessity of intermediate step Criteria for necessity of intermediate step Necessity of intermediate step procedure Is the intermediate step necessary? NO Forging without intermediate step
Designing of the intermediate step’s shape by different alternative methods
Instructions and recommendations for designing
The number of intermediate steps is more 3 NO Shape 1 1 Shape 2 1
Shape N 1
Design of intermediate shapes procedure
Fig. 1. Algorithm for process planning support for intermediate steps designs of axisymmetric hot close-die forging.
Forging sequence procedure
Compose of forging sequence 1
Compose of forging sequence 2
Compose of forging sequence N
Simulation of forging process (FEM, model material)
Choice of forging sequence from the different alternatives
Rules for choice
Send data for design of forging dies
Fig. 1. Algorithm for process planning support for intermediate steps designs of axisymmetric hot close-die forging (continuation).
forging part according to the technological requirement. Like an integral part of the process planning of forging sequence, verification by simulation of hot close-die deformation process is included. Shown algorithm allows the intervention from process designer. This is possible in three cases: • Determining criteria for necessity of intermediate step; • Choosing instructions and recommendations for designing of intermediate steps’ shapes; • Choosing the rules of forging sequence from the different alternatives. Thus, the engineers have opportunity to influence upon
the final results according the specific conditions of the forging process. These three points are the same, which there are not strong generally accepted rules and recommendations. This peculiarity ensures flexibility of the proposed algorithm. 3. Example process design and discussion In this paper as an example, illustrating proposed method for process planning support, forging part with shape shown on figure 2 is used. As a criterion for necessity of intermediate step proposed in  shape complexity factor is used. Applying the algorithm shown above necessity of only one intermediate step
between the initial billet with dimensions ∅45X84 and final shape of forging part is needed. Different intermediate shapes are designed according with the research works [2, 5, 7, 8, 9, 10].
also in fewer grades for preform 2. This is a symptom for necessity of billet with larger volume than used.
Fig. 2. Investigated axisymmetric forging part with "H" type cross section
They are shown on figure 3. Die filling together with the total values of the works done for different intermediate dies are used for the choosing of the most suitable decision of the process planning task. Software package for finite element analysis of metal forming processes was used to verification derived decisions after applying proposed method (fig 1). The simulation was carried with the low-carbon steel, forged on hydraulic press. The initial forging temperature was ТF =1200°С. The temperature of the die was ТT=300°С. The lubricant used for simulation was emulsion of graphite and water. In order to investigate the effect of the preform shape on the forces and works done of the final impression data for their values have been received. Results are shown in Table 1. Comparing total works done for different preform dies, it is clearly, preform 1 ensure the smaller work done. Values of total works done for cases 2, 5 and 6 are higher, but still close to preform 1. Moreover, distribution of works done among preform and final impressions for preforms 1 and 6 are about equal. This corresponds to already well-known forging practice. Filling of final dies was studied in this work too. Defect free forging in finishing impression was obtained for preforms 1, 5 and 6. Unfilling of die was the result of computer simulation for preforms 3 and 4,
Fig. 3. Different intermediate shapes designed according [9, 5, 7, 8, 10, 2].
Obviously, this will bring bigger flash amount, which will provoke more intensive die wear and major consumption. Especially, this will be stronger asserted for cases 3 and 4. For example, the difference of total works done for forging with used in this study billet for preform 1 and preforms 3 and 4 come at 30÷35 %. This difference will increase if billet volume enlarges. The values of effective strains for preforms providing filling of final dies are analyzed also in this study. Most equable is distribution of effective strains in final impression for forging with preform 1.
Table 1 Values of the forces and the works done for different cases of die forging Preform Forging in preform die Forging in final die F [MN] W [kJ] F [MN] W [kJ] 1 0,0888 3,7323 3,5282 4,8716 2 0,2688 3,3155 1,5676 5,5880 3 1,8139 9,0691 1,1523 2,5262 4 1,3818 8,3503 1,2689 2,6723 5 0,1081 1,9023 1,8151 7,1363 6 0,1421 4,2915 3,4948 4,8147
Total values F [MN] W [kJ] 3,6170 8,6039 1,8364 8,9035 2,9662 11,5953 2,6507 11,0226 1,9232 9,0386 3,6369 9,1062
A part of the above pointed out algorithm is also used for the determination of necessity of preform shapes for the eleven different forgings shown on figure 4 .
The results obtained applying the proposed algorithm for process planning support for intermediate steps designs of axisymmetric hot close-die forging allow to conclude: • It is suitable method, which enables to get several alternatives for shape and number of intermediate stages and to select the most appropriate case for specific part. • The algorithm is flexible and addition can be done, especially in connection with the criterions for necessity of intermediate steps, the instructions and recommendations for preform design and the rules for choice of eligible variant for close-die forging. • Investigations are needed to confirm the opportunity to using this algorithm for forgings with more complex shapes.
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Fig. 4. Different investigated forgings for determination for necessity of preform shapes .
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