advances in mechanical engineering 2014 shih 2014_216246

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Research ArticleEffects of Forging Stream Line on Tensile StrengthUsing FEM Simulation

Ching-Wei Shih, 1 Gow-Yi Tzou, 2 and Kao-Hua Chang 1

Department of Mold and Die Engineering, National Kaohsiung University of Applied Sciences, Chien Kung Road,Kaohsiung , TaiwanDepartment of Mechanical and Automation Engineering, Kao-Yuan University, Jhongshan Road, Lujhu District,Kaohsiung , Taiwan

Correspondence should be addressed to Gow-Yi zou; [email protected]

Received November ; Accepted February ; Published March

Academic Editor: Wen-Hsiang Hsieh

Copyright © Ching-Wei Shih et al. Tis is an openaccess article distributed under the CreativeCommons AttributionLicense,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Because bolt usages always have the requirement o tensile strength, with a view to reach the requirement o tensile strength, thematerial property or orming method and dies design can be used to obtain it. Te study aims at the orming method and diesdesign to per orm the multistage analysis o bolt to realize the effect o orging stream line continuity on tensile strength. Te study uses Simu act-FEM sofware to do the multistage orming simulation to modi y the dies design and orming method. Te amounto broken orging stream line can be used to identi y whether the bolt is good or not. From the comparison o realistic orgingproduct, the results can veri y the acceptance o FEM simulation.

1. Introduction

Kim and Im [ ] think that differentmultistage orming meth-ods have been proposed by ocusing on different productrequirements; thusdifferentmultistage orming methods willhave different mechanical conditions or end products. Inaddition,during orging itwillalso affect theli espano moldsand the quality o products and urther affect the productionprogress. Te orging processes are nothing more than the

ollowing methods, including upsetting, orward extrusion,backward extrusion, combined extrusion, and punching ortrimming. Different multistage orming methods indicatethose orming ideas and concepts or making products andarrange them in different orders; thus different ormingmethods will decide the sizes and dimensions o materials,the selection o machines, and the design methods o dies.Generally speaking, when selecting appropriate ormingmethods, one needs to consider whether these methodscon orm to the production conditions, such as the numbero stages, the orging orce or the individual stage and whole

orging process, thediameter o wires, thedies, andthe lengtho ront/rear punch. Additionally, the simulation o orming

method needs to understand the distribution o effectivestrain and stress or nal products, and the orging orce oreach stage also needs to be controlled within a proper range.Li et al. [ , ] think that the design direction o multistage

orming method generally depended on subjective workingexperience and technologies o designers, but there still areinsufficient experiences or undistributed considerations. Forthe manu acturing o product, the most important issue isthat how to use the lowest costs, including money and time,to produce better products. Tere ore, in order to shortenthe lead time o designing the orming methods, reduce thecost o dies and use proper orming methods or machines;thus it is necessary to look or effective methods. In recentyears, due to the accelerating computation and lowering costo computers, it makes a signi cant advancement o designand development or metal orming by using Finite ElementMethod (FEM), especially it produces a more precise, rapid,and stable simulation tool.

When carrying out the sofware simulation analysis,Nagaile et al. [ – ] conduct actual cylinder compression testand ring compression test in order to obtain actual orming

ow stress ormula and rictional actor; among which, use

Hindawi Publishing CorporationAdvances in Mechanical EngineeringVolume 2014, Article ID 216246, 9 pageshttp://dx.doi.org/10.1155/2014/216246

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Advances in Mechanical Engineering

billet to conduct the cylinder compression test, and lowerrictional actor as possible to be zero ( = 0) , so as to

obtain the relation equation between actual strain and stressor materials; in addition, it can be used as the relation basis

that yielded rom materials’ strain and stress when they arereceiving orces during the sofware simulation. Moreover,

the ring compression test needs to use the specimens withcertain size and select the lubricating conditions as closeas actual orging process to carry out the compression testthen the measurement and the simulation o estimation, inorder to obtain the m value o constant shear rictional actoras the parameter basis or the sofware simulation analysis.Canta et al. [ ] carry out the nite element simulation andanalysis on the spark plug and use Super orm sofware toconduct thesimulation or theprocess o plastic de ormation,and the results are consistent with the actual products. Buijk et al. [ , ] use Simu act- orming sofware simulation toadjust the -stage cold orging orming method. First they explore the orming orce oreachstage to select thebene cialpre orming shape in order to make the orce be an equalizedstatus in each stage. It mainly intends to increase the orcewithin the range o bearing capacity or dies in the stage withlower orce to share thepartial orming orce orthe next stageand reduce and lower the orce or the stage with higher loadoriginally. Tere ore, die’s li espan can then be extended sincethe orceo each stagebecome more balanced andreached theproper orming method o production.

As a result, Crowgey [ ] uses the simulation analysissofware, except or greatly increasing the efficiency o mak-ing dies, shortening the production cycle o new products,and increasing the li espan o dies; it also can provide new-coming designers with the prompt understanding o ormingmethod, the analysis o de ect, and the improvement o simulation. Tere ore, it can save great time o preprocessplanning to urther upgrade the design level o dies.

2. Finite Element Simulation

. . Research Purpose. In addition to the size o bolt thatneeds to con orm to certain speci cations, the tensilestrength in mechanical conditions also has to con orm tothe level standards. In the orming process, it not only requires the dimensions o dies but also needs the level o integrity orthe orging streamline which is the jointbetweenbolt head and grip, and it can be considered as anotherkey indicator or reacting tensile action. And the level o integrity or orging stream line will be signi cantly varieddue to different orming methods. Tere ore, we use theSimu act simulation sofware to conduct the simulation orthe orming method and the modi cation o dies dimensionsand set the orging streamline on materials, in order to attachit to the node o grids. Along with the material de ormationoccurred by load and the node move, the nal number o breakage or the orging stream line caused by the plasticde ormation in the joint between the head and grip can beused as the basis o determining whether the tensile strengthcapability o nished bolt product reaches the requirementor not.

R0.4/0.8

1608

Ø24 Ø11.22

F : Dimensions o bolt.

Cut-off 2nd stage1st stage 3rd stage

F : Original orming method o bolt.

. . Bolt Speci cation and Testing Result. Te speci cation o bolt is BSW / - p-L , which stands or that BSW / - p is

or its thread, and the length is mm. Te diameter o gripshould be . mm, and head diameter should be mm.Te total length should be mm including the head, andthe tolerant -angle or the joint between head and grip canbe . mm to . mm; the details are shown in Figure . Itsmaterial is AISI carbon steel and requires strength orbolt; that is, the tensile strength o nished products shouldbe more than kg /mm2 ( MPa).

Design o the original orming method is shown inFigure , which uses a -stage horizontal screw orgingmachine to produce the bolt product. It selects eeding mate-rials with the diameter o . mm, the length o . mm,and the volume o . mm3 , and the cavity diameters o dies are . mm, . mm, and . mm, respectively, orthe st, nd, and rd stages. All stages are carried out by using the open die upsetting method; it is a pre ormationat the st stage, the pre ormation is carried out to roughly distribute the volume o the head and grip. At the nd stage,the shape o the head is almostpre ormed. Te rd stage is theprocedure o upsetting orming or the head, and the -angleis . mm or the joint between the head and grip.

Figure shows a orming nished product manu acturedby the original orming method, which carries out thetensile strength test by using the universal testing machinetill the product breakage, and its tensile strength is only

. kg /mm2 ( . MPa), which is lower than the required


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F : ensile test result o nished product by using universaltesting machine.

Te breakageof stream lines

∼2.7 mm

F : De ect o bolt orming ( = 0.4 mm).

strength, kg /mm2 ( . MPa); thus it is apparently notcon ormed to the required speci cation.

Generally speaking, manu acturers will think that theinsufficient tensile strength is caused by the decarburizationo wires or the improper selection o materials; however, thisis not really the act. Tus, with the view to explore thecauseso insufficient strength, the researcher corrodes the cross-section o nished product and uses the optical microscopeto observe thedistribution o its orging streamline, as shownin Figure , where the diameter with continuous stream isaround . mm with = 0.4 mm. In general, the mostoptimal distributiono orging streamline shall be a completeconnection rom the head to grip without any breakage;even i there is a -degree bend between the head andgrip o nished products, the orging stream line must besuccessive to be able to take the maximum required tensilestrength. However, Figure shows that there are certainbreakages o orging stream line under the head; the integralsuccessive orging stream line rom the grip to the head isonly / o the grip diameter. Te rest has no successivebreakage; that is, when conducting the tensile test, almost

all the loads bore by the / o the grip diameter, which isonly accounted or % in cross-section area, and this ispossibly one o the key causes o insufficient tensile strength

or bolt. As a result, it uses the nite element simulation sof-ware (Simu act- orming) to conduct the orging stream linesimulation.

. . FEM Forging Stream Line Analysis. It uses the Simu actsimulation sofware to simulate the orming method shownin Figure , and the joint between the headand grip in the rdstage is the same as the original orming method with setting

-angle as . mm. Inaddition, set the vertical stream line onthe initialmaterials (cut-off) to make such streamline changealong with the material ow during the plastic de ormation.Te stream lines o original orming method or each stageare shown in Figure . At the rd stage, it is noted that somestream lines in the joint are broken.

Figure shows that this orming method resulted in

breakage on partial orging stream line at the nd stage andyielded even more breaking orging stream lines at the rdstage. Te magni ed simulation result at the rd stage isshown in Figure .

Simulation (Figure (b)) is the simulation setting the-angle o die as . mm, and Simulation (Figure (a))

is the simulation result using the original orming methodwith setting the -angle o die as . mm, and this con-dition is identical to the actual orging die. Te range is

rom the center to . mm or measuring intact orgingstream line in this gure, and the radius o grip is . mm.Tere ore, the ratio o intact orging stream line is only accounted or . % o the cross-section area or the grip,

which is very similar to the result o actual orging nishedproduct.Te resultobtained in “Simulation ” is the range o intact

orging stream line, rom the center to . mm. Te ratio o intact orging stream line is accounted or . % o the cross-section area or the grip. Obviously, it is able to reduce thenumber o breakage or the orging stream line and increasethe area o bearing the tensile when increasing the -angle o die rom . mm to . mm.

Comparing Figure with Figure , the error betweensimulation ( . mm in Figure ) and experiment ( . mmin Figure ) is . %. It is noted that the simulation result isin good agreement with the experiment. Its tensile strength

with = 0.4 mm is only . kg /mm2

( . MPa), whichis lower than the required strength, kg /mm 2 ( . MPa);thus it is apparently not con ormed to the required speci ca-tion.

Figure is realistic bolt orming with = 0.8 mm; romthis gure the diameter with continuous stream is around

. mm with = 0.8 mm, and the error between simulation( . mm in Figure ) and experiment ( . mm in Figure )is . %. Te tensile strength with = 0.8 mm is measuredas kg /mm2 ( . MPa); it is quite satis actory or therequired strength, . MPa. It indicates that increasing the

let can increase the amount o stream lines to increase thetensile strength.




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1st stageComponents

1p1DCut-off 1A

Z

XY

(a)

2nd stageComponents

2p2DCut-off 2A

Z

XY

(b)

3rd stageComponents

3p3DCut-off 3A

Z

XY

(c)

F : Forming simulation result o original orming method or each stage.

Simulation 1

R0.4

2.79 mm

(a)

Simulation 2

R0.8

3.44 mm

(b)

F : Forging stream line simulation status o different -angles.

3. Analysis of Defect Causes and Improvementin Forming Method

Te results mentioned above o orming simulation show that the insufficient tensile strength is caused by too many breakages o orging stream line. Tus, the exploration o the causes o breaking the orging stream line becomes akey direction or improving the de ect. In the multistage

orming process, in order to move billet to enter the diescavity smoothly at thenext stage, the internaldiameter o diescavity at the next stage will be generally bigger than the oneat the previous stage, and it will cause a problem then.

For theoriginal orming methodshown in Figure ,attherd stage it conducts the head rom the open die upsettingor the outer dies; at the beginning, the internal diameter o

dies cavity or billet is the dimension at the nd stage, whichmust be smaller than theoneat the rd stage;in addition,evenconsidering the springback o material afer billet departing

rom the dies cavity, the diameter o its grip is still smallerthan the internal diameter o dies cavity at the next stage;otherwise it cannot enter the dies cavity at the next stage.When the head upsetting is slowly ormed, the grip diameterhas still not yet completely lled the gap between billet anddies cavity, and the punch continuously moves orward, the




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29.5

1

1 % (forming)

(a)

2

68.85 % (forming)

(b)

3

88.52 % (forming)

(c)

4

95.08 % (forming)

(d)

F : Simulation changes in orging stream line at the rd stage simulation process ( = 0.4 mm).

at the st stage, and the result does not have any breakingorging stream line, until the rd stage when it starts to make

the breaking orging stream line. Te magni ed simulation

result at the rd stage is shown in Figure .Simulation (Figure (a)) is the simulation result using

the original orming method with setting the -angle o diesas . mm. Te range is rom the center to . mm ormeasuring intact orging stream line in this gure, and theradius o grip is . mm.Tere ore, the ratio o intact orgingstreamline is accounted or . %o thecross-section area orthe grip,which is the same as the result in Simulation , and italso shows that, even i the orming method changed and the

-angle o mold was set as . mm, the result is still identicalto the one o the original orming method with setting its -angle as . mm; thus it indicates a great improvement in the

orging stream line afer modi ying the orming method.

Simulation (Figure (b)) is the simulation by settingthe -angle o dies as . mm. Te result obtained rom therange o intact orging streamline rom thecenter to . mm

and the ratio o the intact orging stream line are accountedor . % o the cross-section area or the grip. Obviously,

it changed the orming method and increased the -angleo mold rom . mm to . mm and obtained signi cantimprovement in the result.

4. General Discussion

Since the tensile strength was only MPa o nished prod-ucts that were obtained rom the original orming method( = 0.4 mm), it did not reach the required standards andcould not carry out the production. Tus, working personnelwere directly based on their experience and changed the




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11.04 mm

29 mm

(a)

21 mm

13.2 mm

(b)

F : Changes in dimensions be ore and afer the st stage simulation orming o original orming method.

Cut-off 2nd stage1st stage 3rd stage

F : Modi ed orming method.

1st stageComponents

1P21D2Cut-off 1A

Z

XY

(a)

2nd stageComponents

1p2DCut-off 2A

Z

XY

(b)

3rd stageComponents

3p3DCut-off 3A

Z

XY

(c)

F : Simulation result o modi ed orming method.




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Simulation 3

3.44 mm

R0.4

(a)

Simulation 4

4.66 mm

R0.8

(b)

F : Forging stream line simulation distribution o modi ed orming method.

-angle into . mm to conduct the trial and tensile test atthat time, and the result shows that the bolt did not break under the standard stress MPa and reached a quali edstatus. Tere ore, the change in -angles is obviously help ulto the tensile strength; that is, better tensile strengths can beobtained with larger -angles, and such tendency is identicalto the result o simulation. Similarly, this study uses the

number o breakages or the orging stream line in plasticde ormation to show the capability o billet or bearing thetensile strength in the end result; in addition, there is acorrelation between them and the tendency is identical tothe actual tensile test. Another aspect is the gap between thebillet diameter and the internal diameter o dies cavity atthe next stage, when the orming method has been changed,the material de ormation makes the internal diameter o bolt increased, then the gap in the entire mold cavity canbe reduced at the next stage. Te simulation o modi ed

orming method shows that such method can also reduce thenumber o breakages or the orging stream line in plasticde ormation; thus it can improve the tensile strength or

nished products.Tere ore, no matter which orming method or partial

modi cation o dies dimension is, afer using the simulationsofware to yield results, then one observes the number o breakages or the orging stream line in plastic de ormationwhich can be used as the basis o effective comparison withthe good or poor bearing tensile strengths or those nishedproducts that were produced rom various conditions.

5. Conclusions

Based on the results o a oresaid simulation analysis andactual tensile test, one has the ollowing conclusions.

( ) Te dies with bigger R-angles can reduce the num-ber o breakage or the orging stream line in theplastic de ormation and also can obtain better tensilestrength.

( ) I the gap between the diameter o billet obtainedat the previous stage and the inner diameter o diescavity at the next stage is smaller, then the number

o breakages or the orging stream line in the plasticde ormation will be lesser; thus it can upgrade thetensile strength or nished products.

Conflict of Interests

Te authors declare that there is no con ict o interestsregarding the publication o this paper.

References

[ ] H. S. Kim and Y. . Im, “Expert system or cold orging processdesign based on a depth- rst search,” Journal of Materials

Processing Technology , vol. , no. – , pp. – , .[ ] G. Li, J. . Jinn, W. . Wu, and S. I. Oh, “Recent developmentand applications o three-dimensional nite element modelingin bulk orming processes,” Journal of Materials Processing Technology , vol. , no. – , pp. – , .

[ ] S. I. Oh, W. . Wu, and K. Arimoto, “Recent developmentsin process simulation or bulk orming processes,” Journal of Materials Processing Technology , vol. , no. – , pp. – , .

[ ] G. Nagaile and . Altan, “Computer aided engineering inorging,” in Proceeding of the rd JSTP International Seminar on

Precision Forging , Nagoya, Japan, March .[ ] M. Shirgaokar, H. Cho, and . Altan, “New Development

in FEM Based Process Simulation to Predict and EliminateMaterial Failure in Cold Extrusion,” in International Conference




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on Developments in Bulk Forming , Stuttgart, Germany, May .

[ ] . Altan and D. Hannan, “Prediction and elimination o de ectsin cold orgingusing processsimulation,” VDIBerichte, no. ,pp. – , .

[ ] . Altan, G. Nagaile, and G. Shen, Cold and Hot Forging:

Fundamentals and Applications , ASM International, .[ ] . Canta, D.Noveanu, andD.Frunza, “Modeling andsimulationo combined extresion or spark plug body parts, materialsprocessing anddesign: modeling,” Simulation andApplications,NUMIFORM, CP , pp. – , .

[ ] A. J. Buijk and C. Schultz, “Simulation based optimizationo a cold heading process to extend die li e, using simu act.Forming,” SENAFOR Con erence SFA- , .

[ ] A. J. Buijk and H. Sehgal, “Simulation based optimization o ahot orging process to avoid a lap, using simu act. Forming,”SENAFOR Con erence SFA- , .

[ ] N. Crowgey, “Cold Forged Fastener Development utilizingSimu act. orming Sofware,” Simu act th Roundtable, .

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