articleapplications of drop simulation in 3g phone development_W

1、HomeApplications of Drop Simulation in 3G phone DevelopmentChen HongjunMotorola BJDC Advanced ME Lab e-mail: Abstract:This paper presents some applications of ABAQUS/Explict in phone drop test simulation in the process of Motorola mobile phone development. Computer Simulation has

2、been used to help mechanical design in the concept design stage as well as in the detail design stages.IntroductionMotorola has successfully used ABAQUS/Explict in designing new phone models in Beijing Design Center (BJDC), one of them is A388 PDA phone which has made fully success in high- end mobi

3、le market. In order to further satisfy customers requirements, a new 3G multimedia phone which includes many new functions and design concepts that are quite different from previous products. At the beginning, there were several ID concepts of mechanical designs to choose, the most favorable two are

4、 a flip-type phone and a bar-type phone Fig.1. Both of the two ID concepts adopted a series of new part designs and design concepts. The main new parts included in the 3G phone are digital camera, loudspeaker, more thinner colour LCD module, central band and large U-flip open window. With the initia

5、l ID, battery is directly attached to PCB without any baffle. These new design concepts were very concerned by mechanical design engineer, and must be tested and simulated to be mechanically strong enough in the final assembly. According to Motorola new product design process, several cycles of Acce

6、lerated Life Test (ALT) must be done to ensure the product quality. One of the series of ALT is phone drop test. Drop simulation by ABAQUS/Explicit was involved in helping to decide the internal mechanical structure of the phone in the feasibility study stage, and helped to predict and analyze the s

7、tructural risks in the detail design stage.Fig.1a U-flip type IDFig.1b Bar-type IDFeasibility Study AnalysisIn the feasibility study stage, finite element analysis was used to predict the possibility of the ID concepts. There were several uncertainties about the two new IDs, the concentration was on

8、 the following concerns. The first concern of designer was the direct contact of LCD module andOctober 2002Page 7battery block to PCB, which may result in a big impact to PCB when the phone drops to ground, and thus led to some components failure on PCB. The second concern was the flip large U-shape

9、 opening that may make the flip structure very weak in the twisting deformation mode, and thus put the hinge and lens in danger. There was also worry about the hinge assembly that may possibly separate from the flip, the stiffness of the new central band was a big concern as well.To study the two ID

10、 concepts, two phone CAD models were built up by design engineers using Pro/Engineer, these CAD models were then imported into MSC.Patran for setting up FEA model. Several drop test simulations were used to predict the IDs structural strengths, the simulations were phone drops to a rigid ground in d

11、ifferent drop directions.Considering the complexities of different parts, different meshing strategies were adopted for different parts respectively Fig.2. For the housing, flip and central band parts, because their geometries and topologies are very complicated, 10-node high order modified tetrahed

12、ral elements were used, and skinned membrane elements were used to recover their surface stresses and strains. For LCD module, 4-node large strain quad elements were used for its front and real steel bezels, and 6-node reduced hexahedral elements were used for glasses, touch panel (TP) and electroni

13、c light panel (EL) separately. To simulate the LCD glass strain more accurately, 2 glass layers were modeled separately by mismatching meshes in the boundary with each layer has 3 elements along thickness in order that it can capture the bending mode of the LCD glass, the 2 glass layers were connect

14、ed around their periphery using multi-point constraints. For PCB, 4-node large strain quad elements were used, and for PCB components, 6-node reduced hexahedral elements were used. The material properties used in the phone simulation referred to a Motorola phone material library4.Fig.2a Meshes of Ho

15、using, flip and lensFig.2b Meshes of LCD module, PCB and BandThe drop simulation was performed on an Ultra60 Sun workstation with 2 CPUs parallel computing. Each job took 2 working days to finish. Simulation results showed that battery directly contacting to PCB without baffle could make the PCB und

16、ertake large impact and led to very large bending Fig.4, this must be avoided in detail mechanical design. The results also showed the U-shape flip has some twisting deformation between the two fork legs Fig.6, but the connections among hinge, flip and front housing retained good Fig.3, 5, there wer

17、e no separation of hinge from flip, and flip from front housing, the insertion quantities of hinge follower to flip, and flip to front housing are large enough to satisfy the design need Fig.7-8.Lens will sustain some of the twisting force from flip, so more attentions should be paid to lens- flip c

18、onnection in detailed design. Fig.3 Flip-type ID Drop simulation DeformationFig.4 PCB bended greatly due to direct Battery impact Fig.5 Hinge connects with flip very well under maximum deformationFig.7 Separation history between hinge and flipFig.6 Flip twisting deformation makes lens undertook larg

19、e separation forceFig.8 Separation history between flip and front housingCross beams of central band have big bending under drop impact, its stiffness needs increasing, otherwise, the central band can not be taken as a seat board for LCD and housing Fig.9. LCD module is basically safe. The maximum p

20、rinciple strain of bottom glass is 0.12% Fig.10, the maximum principle strain at edge is only 0.07% Fig.11, referring to LCD testing data2, LCD glass has 99.5% survival rate of safety with this edge strain. There is more space to reduce thethickness of LCD module. The feasibility drop simulation als

21、o noticed some possible housing connection weak location that may have separation there. Fig.9 Central Band drop deformationFig.10 LCD bottom glass maximum principle strainFig.11 LCD Glass maximum edge principle strainDetailed Design Drop Simulation and ALTThe final ID adopts a combination of the in

22、itial IDs, that is a flip-type phone which has a central band, a large closed-window flip which is connected at its top area, and a large lens is welded into the flip window. Battery is blocked out from PCB by rear housing. Front housing and rear housing is connected by four screws3.The FEA model wa

23、s also built up using the previous modeling strategies. The mesh size was controlled to be larger than 0.2mm for all parts so as to get an acceptable time increment. Aspect ratio for all elements was kept within 0.6 on which accurate calculation results can depend. The meshing is very detail to cove

24、r all the important parts of the phone, it includes front and rear housing, central band, front and rear flip, flip lens, hinge sub-assembly, LCD sub-assembly, PCB and PCB components, receiver and magnet, digital camera, loudspeaker, battery and battery cover. Different parts are connected with cons

25、traint equations and contact relations.There are over 70 contact pairs in the full drop simulation model. The final discretion of the detailed CAD assembly produced a full phone drop simulation model of 411498 nodes and 330193 elementsFig.12. Several drop test simulations in different drop direction

26、s were conducted to check the detailed design.Fig.12 FEM for final IDThe drop simulation results showed there have good correlations between calculated results and ALT results. The LCD glass has a maximum principle strain of 0.22% at its center, the maximum edge strain captured is less than 0.13%. F

27、ront flip has 110 MPa maximum principle stress which is much larger than its static strength 80MPa of ML6339R. A magnet holding failure was detected by simulation and modified by designer. Keypad support has a strain less than 0.003, loudspeaker has a maximum stress less than 2.5Mpa. The maximum str

28、ess of camera is larger than 2Mpa, to keep it safe, a cushion is added. Central band has maximum principle stress of 79Mpa, its cross beam is still relatively weak. Main PCB has a maximum principle strain less than 0.02 Fig.13. To totally view the simulation results, except the flip assembly, the fi

29、nal design is feasible.Side drop stressLoudspeaker stressDigital camera stressMagnet movingLCD Module stressLCD max strainBand stressPCB strainFig.14 Some drop simulation resultsIn the first ALT, no LCD crack occurred, but 8 pieces of lens cracked. The cracking mode concentrated on the following fai

30、lure modes fig.14 By comparison between ALT and drop simulation, we can find that the cracking modes are same with the simulation maximum principle strain modes, the stress data scattered from 30MPa to 46MPa for different dropdirection, the latter is from flip-open drop simulation with flip directly

31、 dropping to the rigid ground Fig.15.To analyze the ALT results, the material properties of lens are compared. Lens used OQ1030 of GE plastics, its tensile break stress is 51MPa at 50mm/min deformation rate. The simulation result seems lower than the material strength. Considering the degradation in

32、fluence of double ultrasonic and, in addition, weld line from molding flow, the real break stress of lens should be lower than GE plastics material datasheet. In order to compare the influence of ultrasonic, a flip tensile test was performed Fig.16., the result shows by ultrasonic can degrade the break force 35%, if we assume a linear relationship between force and stress, the crack stress is about 33MPa, this is in accordance with the drop simulation results above. Different material and assembling technique has replaced