The changeless speed articulation outer race is one of the chief burden back uping parts in autos. Its geometry is really complicated and its needed preciseness is high. Mohammadi and Sadeghi [ 1 ] , mentioned that the hammering procedure to organize an outer race is a combined hot and cold forming which consists of tow executing sequence at elevated temperature, chilling and concluding ironing at room temperature. The procedure was simulated with numerical simulation tool and so physical patterning with commercial lead was performed in order to verify the dependability of numerical simulation consequences. Experiments with theoretical account stuff showed the happening of malleable break and surface defects in concluding ironing sequence. In order to modify tooling design, an effort has been made to imitate failure happening during concluding ironing sequence for theoretical account stuff utilizing malleable break failure standards. These standards are of import tools to be used in concurrence with practical experiments and several ductile break standards have been proposed and used in foretelling defect happening in metal forming processes yet. The public presentation of the theoretical failure standards depends on geometric parametric quantities and distortion mechanics. For illustration Clift et al [ 2 ] investigated several malleable break standards to pattern harm happening in simple upsetting, bulge and strip compaction and tenseness. Decisions looking to bespeak that merely Freudenthal ‘s generalised plastic work per unit of volume are capable of gauging break induction sites for all of the procedures. Venugopal et al [ 3 ] evaluated assorted theoretical failure standards refering to workability in cold forging reported in the published literature for their dependability and sensitiveness in foretelling the happening of malleable break in metalworking. It was claimed that no theoretical failure standard can be described as genuinely geometry-independent for metalworking operations. Gouveia et al [ 4 ] described the use of malleable break standards in concurrence with the finite component method for foretelling surface and internal failures in cold metalworking procedures. Four antecedently published malleable break standards were selected by the writer, and their comparative truth for foretelling and quantifying break induction sites is investigated. The writer claimed that free surface snap and internal snap under a tri-axial tenseness or tension-compression province of emphasis can be estimated in turn utilizing both the Cockcroft-Latham and the Oyane ductile break standards. However, these standards are unable to roll up the harm associated with the happening of a material defect restricting a stationary dead metal zone.
A reappraisal of the published literature referred above reveals that the public presentation of the theoretical failure standards depends on geometric parametric quantities and distortion mechanics. Therefore in order to foretell harm happening on the parts with complicated geometry and critical application like the outer race, it is indispensable to measure harm standards based on the happenstance between harm patterning consequences and practical experiments.
Sing the consequences of the research has been done by Venugopal et al [ 3 ] and Gouveia et al [ 4 ] , and the standards which were accessible by Deform3D package, four normally used theoretical failure standards were selected and integrated into the FE Software and their comparative truth for right anticipation of the location of defects on the lead specimen ( from physical mold ) were investigated.
2. Procedure simulation and physical mold
Figure 1: schematically shows suggested hammering sequences for a CV joint outer race.
Figure 1: Forging sequences of CV joint outer race
The forging procedure to organize an outer race is a combined hot/cold forming which consists of tow executing sequence at elevated temperature, chilling and concluding ironing at room temperature. This procedure is investigated by Kim et all [ 5 ] and mohammadi and sadeghi [ 1 ] . The first preforming sequence is a forward bulge to do a caput with an extruded rod portion while the concluding preforming sequence is a hot closed-die forging to determine a complicated cup with a sized rod. An ironing operation is carried out as the last operation after chilling. Ironing procedure has the possible to enable close net form constituent to be made. In this sequence that is shown in figure 1, a combination of bending and majority distortion is carried out. Bending is done with downward motion of the clout taking to radial force per unit area of lower dice to outer border of the preform.
Due to symmetry of the outer race merely one sixth of the note is needed to be analyzed by numerical simulation. The procedure was simulated under the conditions shown in Table 1.
Table 1: procedure status
Close dice forging
Speed of clout
To be brief, merely the simulation consequences for pressing sequence are presented. Figure 2 shows effectual stress distribution at one sixth of the specimen after distortion in concluding ironing sequence.
Figure 2: effectual emphasis distribution at one sixth of the specimen at the terminal of distortion ( frontward and rearward position )
To verify simulation consequences, physical mold with commercial lead was preformed. The true stressaa‚¬ ” strain curves of the work metal can be obtained from compaction trials. The stress-strain equation applied in simulation for lead note is:
A??’ = 38.964 [ MPa ] .
The dice was made from MO40 steel and no lubricator was utilized in the metal experiments and distortion was carried out with clash coefficient of 0.08. A 30 ton cosmopolitan hydraulic imperativeness was used to execute experiments at room temperature. Due to utilize of commercial lead in physical mold as the theoretical account stuff, distortion procedure was simulated for commercial lead to verify dependability of numerical simulation consequences in existent procedure. Figure 3 shows lead portion after distortion in pressing sequence from top position. Dimensional comparing between the lead note after physical mold and simulation consequences showed close conformity of simulation consequences and physical mold.
Figure 3: lead specimen after distortion in pressing sequence of physical mold
There are non any malleable break and surface harm and other defects in internal parts of lead specimen. As shown in figure 3 there are some furrow on the border of the specimen. Figure 4 shows another position of the specimen. As seen in figure 4, there are some surface defects like lapping near the flash of the specimen ( part A ) .
Figure 4: surface defects on the external country of the lead specimen specified by ( A )
3. Evaluation of failure standards
To get down with, four normally used failure standards named Cockcroft-Latham ( COCK ) , Frudenthal ( FRUD ) , Brozzo ( BROZ ) and Oyane ( OYAN ) were chosen from the published literature.
Typical standards for room temperature malleable break are normally based on combinations of emphasis with strain or strive rate instead than on either of these measures individually. It was shown by Atkins and Mai [ 6 ] that about all the integrated stress-strain standards are versions of Freudenthal ‘s critical plastic work per unit of volume.
Where is the output strength of the stuff ; A??’ is the effectual emphasis, is the incremental effectual strain ; C the threshold value of the standard at the blink of an eye of break induction.
In position of the importance of the largest tensile emphasis, Cockcroft and Latham [ 7 ] have suggested an alternate break standard based on a critical value of the tensile energy per unit of volume. Cockcroft and Latham ‘s standard states that break will happen when the cumulative energy due to the maximal tensile emphasis exceeds a certain value. This standard has provided good understanding at foretelling the location of a tensile failure based on a maximal harm value. The theoretical account is based on the equation:
Explicit dependance of the degree of both the largest chief emphasis, and the hydrostatic emphasis, , was proposed by Brozzo et al [ 8 ] by agencies of an empirical alteration of the above mentioned standard.
Experimental consequences reported by Dodd and Bai [ 9 ] show once and for all that malleable break in metalworking procedures follows a null growing theoretical account. Harmonizing to this theoretical account, nothingnesss initiate at inclusions or difficult second-phase atoms in parts of the micro-structure that are extremely deformed, turn under fictile distortion caused by normal or shear emphasis systems and eventually linkup between each other to organize macroscopic clefts. Based on this hypothesis, Oyane standard, derived under the cardinal Torahs of the theory of malleability for porous stuffs being expressed as
Where A is a material invariable to be determined by experimentation.
Upsetting of cylinder is the simplest and the most widely used tool for workability trial and specifying threshold values ( ) for failure standards. In this survey, threshold value of standards is archived from published information of upsetting of lead metal. Table2 shows critical values per standards.
Table 2: Threshold value of the standard
Cockroft & A ; latham
Brozzo et Al
Oyane et Al
3.1 Damage mold
The four theoretical failure standards with their threshold values were incorporated into DEFORM 3D. Due to symmetry of the outer race merely one sixth of the note is needed for harm mold. Simulation conditions were the same as mentioned for pressing sequence in table 1. The theoretical distribution of harm in work piece is achieved by DEFORM 3D for four standards. Figure 5 shows harm patterning consequences for COCK. To accomplish more lucidity, merely the upper portion of the specimens on which defects will look is shown in crystalline position. The chance of defect happening at a part can be calculated by spliting the sum of harm value on the part by the maximal value calculated by the package. The predicted location of defect has shown by pointers.
Figure 5: harm patterning consequences by COCK standard
As shown in figure 5, the harm value in the part M that is marked by pointer is 0.119 and chance of harm happening is 55 % that can be calculated by spliting 0.119 by the maximal value of 0.214. In part N the chance of harm happening is 44 % .
Figure 6 shows harm patterning consequences for FRUD standard. As shown in figure 6, two parts are marked as the likely location of defects. The chance of defect happening in part D ( on the flash ) is 66 % and in part C is 77 % .
Figure 6: harm mold consequences for FRUD standard
Figure 7, 8 show harm patterning consequences for BRUZ and OYAN standards. Predicted locations of harm happening are near the flash border for both standards but BRUZ shows more understanding to physical mold consequences. Besides the chance of harm happening for both of the standards is 33 % that shows similar application of these standards for this specimen.
Figure 7: harm mold consequences for BRUZ
Figure 8: harm mold consequences for OYAN
3.2 EVALUATION of standards
As shown in figure 5, COCK standard has introduced two parts M, N as the possible location of defects. Region M wholly matches the physical mold consequences ( part A in figure 4 ) . But part N is non on the flash border of the specimen and is located near the border on the flash organic structure.
The application of FRUD standard is about similar to COCK. As shown in figure 6 two parts ( C, D ) have been introduced as the possible location of defects. The Region C is located above the part A of physical patterning specimen. But the part D is on the border of the flash and wholly matches the physical mold consequences.
Neither of BRUZ and OYAN standards has predicted any break happening in the part A ( figure 4 ) . But both the standards particularly the former have about genuinely predicted defect happening on the border of flash.
As can be seen the COCK and FRUD standards particularly the former were in close conformity with experimental consequences in anticipation of break happening in the part A. In fact, With respect to the distortion phases in concluding ironing sequence that is shown in figure 9, and the geometry of the preform at the part ( A ) , it is noticeable that this defect can be due to emphasize concentration at mentioned part. Thus the standards which are stress based like COCK which is based on chief emphasis, have better application and public presentation than the other.
Figure 9: distortion phases in concluding ironing sequence
Wrinkle happening on the border of the flash that can be seen in figure 3 is due to break up fictile distortion and high values of strain at the zone. All standards showed this defect near the flash but standards of BRUZ and FRUD were in better understanding with experimental consequences severally.
Wholly COCK and FRUD standards showed higher public presentation in anticipation of free surface defects on the organic structure of the specimen and on the flash border in turn but none of the standards could foretell the location of both defects wholly.
Because of the importance of the defect occurred in part A ( figure 4 ) , and with stipulating the ground of this phenomena, an effort has been made to modify the geometry of perform of concluding ironing sequence. In order to cut down stress concentration as the chief prima cause of break happening in part A, the filet radius on the preform was modified and physical mold experiments was retried for modified geometry. Figure 10 shows lead specimen after alteration of preform. As can be seen in figure 10, no malleable break and surface defects occurred on the specimen. It should be added that the flash will be trimmed so the defect on the border of the flash will do no job in industrial merchandise.
Figure 10: lead specimen without defects after alteration of perform
The public presentation of the theoretical failure standards depends on distortion mechanics. Hence the first measure towards harm mold is to measure harm standards for the instance. In the present survey physical mold experiments was preformed with commercial lead and four normally used failure standards were chosen and integrated into the FE Software Deform3D to pattern harm happening on the lead portion. Following decisions were obtained from comparing of experimental and deliberate location of harm:
Both the physical mold experiment and harm mold consequences showed the possibility of happening of tow type of surface defects that the former is on the flash and is non of importance and the later is on the external surface of the specimen below the flash. It is due to emphasize concentration and is of great significance.
COCK standard showed close conformity with experimental consequences in foretelling the happening of rupture on the organic structure of the specimen ( part A ) besides BRUZ and FRUD standards were in better understanding with experimental consequences in foretelling furrow on the border of flash but by and large none of the standards could foretell the location of both defects wholly and precisely.
Due to the importance of the defect occurred in part A, the consequences showed that the theoretical failure standard based on the maximal chief tensile emphasis was more dependable and sensitive in foretelling the break in the instance.
In metal forming processes which there are the possibility of stress concentration on the distortion zone, emphasis based standards like COCK will be helpful and good and can be considered as the premier campaigner to pattern harm.
With stipulating the cause of defect happening in part A, the geometry of the preform was successfully modified. Consequently by alteration of the perform geometry in simulation and physical mold phases, a major measure was taken towards cut downing die try-out and lead times for existent procedure.
Sing the consequences of the present research and other researches done by Venugopal et Al ( 2002 ) and Gouveia et Al ( 2000 ) , it is obvious that due to assorted provinces of emphasis in forging of complicated parts like the outer race, a individual failure standard is non able to foretell all types of defects and amendss. Therefore developing subprograms which can use assorted harm standards in analogue with each other can assist maker to accomplish high quality merchandise without existent trial.