Force Model & Solid Model Report MIE 313 Design of Mechanical Components. Amado, Juliana A. Nestor, Charlene Walsh, Peter J.
Table of Contents Force Model & Solid Model Report... i Abstract:... iv Introduction:... 1 Objectives:... 2 Procedure:... 2 Work Analysis of Applied Force:... 3 Free Body Diagrams:... 4 Lifter:... 4 Dog:... 4 Clamp-Block:... 5 Force Models:... 6 Lifter... 6 Dog... 6 Clamp Block... 7 Future Task Plans:... 8 Conclusion:... 9 Appendix:.....I Solid models I Clamp Block.I Lifter II Dog.III Project Proposal.IV ii
Table of Figures Figure 1. Table Saw Fence... 1 Figure 2. Clamp Block, Lifter, & Dog Assembly... 1 Figure 3. Section of Fence Assembly... 3 Figure 4. FBD Lifter... 4 Figure 5. FBD Dog... 4 Figure 7. Lifter Force Model... 6 Figure 8. Dog Force Model... 6 Figure 9. Clamp Block Force Model... 7 Figure 10. Clamp Block Solid Model... I Figure 11. Lifter Solid Model...II Figure 12. Dog Solid Model... III iii
Abstract: The part being analyzed is the clamp block component of the clamping mechanism of a table saw fence assembly. The clamping system acts as a spring and applies normal force to the fence rails. This normal force results in friction forces that prevent the fence from sliding sideways along the fence rails. The clamp block has failed by fracture near a point where its section changes abruptly. The overall objective of this project is to analyze the mode of failure of the clamp block and redesign it accordingly. At this stage solid models of the clamp block and two other adjoining components in the fence assembly have been created. The input forces applied to the system by the user have been established. Free body diagrams of the three components have been drawn and, using the system input forces, reaction forces have been calculated for each component. Using the information from the free body diagrams shear force and bending moment diagrams for each component have been calculated and drawn. The location of the clamp block s maximum bending moment coincides closely with the actual point of failure of the clamp block. In addition there is an abrupt change of section in the failure area, so stress concentration is also a factor. iv
Introduction: The focus of this analysis is the clamp block component of the clamping mechanism of a table saw fence assembly. In operation the fence is used to set the cutting width of the saw. It moves on two pipe rails that are perpendicular to the fence and saw blade. The user sets the cutting width, then clamps the fence to the rails by applying force to the hand lever. Once the user has rotated the hand lever to the locked position the system acts as a spring, storing the applied energy. This spring energy is what maintains the normal force on the rails that is necessary to keep the fence from sliding sideways. Figure 1. Table Saw Fence The component in this system that has failed is the clamp block. It has fractured as shown below in Figure 2. Figure 2. Clamp Block, Lifter, & Dog Assembly 1
Objectives: The overall objective of this project is to analyze the mode of failure of the clamp block and redesign it accordingly. At this stage the short-term objective is to create solid models of the critical components in the fence assembly and establish the forces applied to the system and its components during the worst case of normal operation. The solid models and input forces can then be used as input to the Pro-Mechanica FEA software package and as parameters for simplified hand calculations. Procedure: There are eight components in the fence assembly, but the scope of analysis will be restricted to the clamp block, lifter, and dog. This document will present: I. Work analysis of the force applied to the hand lever. II. Free Body Diagrams for: 1. Lifter 2. Dog 3. Clamp Block III. Force Model including shear and moment diagrams of: 1. Lifter 2. Dog 3. Clamp Block IV. Future Task Plans V. Perspective views of solid models 1. Lifter 2. Dog 3. Clamp Block 2
Work Analysis of Applied Force: The force being applied to the hand lever results in forces acting on the Clamp Block, Lifter, and Dog. In order to find these forces and develop FBD s for the Clamp Block, Lifter, and Dog, the tension in linking rod must be established. Figure 3. Section of Fence Assembly At the beginning of the hand lever rotation the entire system is at rest- there is no elastic energy stored in the system and so the initial applied force is zero. As the hand lever is rotated the components of the system are stretched and the required input force increases until it reaches a maximum at the locked position. Using Data from Human Factors Design Handbook, an applied force of F=160 N has been established as the upper range of force that an average person can easily apply when pushing down on a lever from a standing position. Assuming the force varies linearly from 0 N to 160 N over the displacement then F av =80 N. Using the principle of conservation of energy, the work applied at the hand lever equals the work done on the linking rod. W lever = W rod Sf θf π/3 F ds = T ds = F av cos θ r dθ T rod (.003m) = (-80 N) (0.100m) cos θ dθ Si θi 0 8 sin (π/3) = T rod (0.003m) T rod = 2300 N 3
Free Body Diagrams: Using the rod tension T from the previous section and the geometry of the components the free body diagrams of the Lifter, Dog, and Clamp Block can be drawn and the reactions calculated. Lifter: [ Ma = 0] T d 1 RD d 2 = 0 (2300 N)(0.03 m) Rd (0.023 m) = 0 0.023 Rd = 69 N Rd = (69) 0.023 Rd = 3000 N Figure 4. FBD Lifter [ F x = 0] [ F y = 0] T Rx = 0 Ry Rd = 0 2300 N Rx = 0 Rx = 2300 N Ry = 3000 N Dog: From previous calculation of forces acting on the lifter; Rd was equal to 3000 N. Then: [ F y = 0] Rd Rr = 0 Rr = 3000N Figure 5. FBD Dog [ F x =0] [ M A =0] R 1 R 2 = 0 0.022 Rr 0.035 R 1 = 0 R 2 =1900 N R 1 = 1885 1900 N 4
Clamp-Block: Figure 6. FBD Clamp Block From previous calculations all the forces acting on the clamp block are known except R f : [ F x =0] R f R x R 1 +R 2 =0 R f -2300 N-1900 N+1900 N=0 R f =2300 N Because the clamp block has a fixed end at the top the force couple of R 1 and R 2 is opposed by an equal and opposite moment at the top of the clamp block. 5
Force Models: Lifter Figure 7. Lifter Force Model Dog Figure 8. Dog Force Model 6
Clamp Block Figure 9. Clamp Block Force Model The Clamp Block has been analyzed as a cantilevered beam. The geometry presented some problems in the determination of the bending moment diagram because the neutral axis changes location in two places along the length of the section. The group decided to simplify the bending moment analysis by assuming a constant location of the neutral axis. This appears to be a valid assumption as the location of maximum bending moment is very close to the actual location of failure, though the magnitude of the M max may need to be established more accurately. 7
Future Task Plans: The next stage of this project is to analyze the stresses the critical components are subjected to. The Project Analysis report will include: Introduction: necessary background information on the problem. Objectives: state what the project objectives are. Plan of work: attack plan to achieve objectives. Design analysis: Solid model Representation of Critical Components Finite Element Analysis of Critical Components (FEA): 1. Explain how the loads are calculated and how they are applied to the component. 2. Explain how the component has been kinematically constrained against rigid body motion. 3. Present analysis results. 4. Discuss the significance of the results in terms of your redesign objectives. 5. Validate results of FEA using simplified stress model for hand calculations. Conclusions: Discuss the current status of the project, including pitfalls, and the next steps that will be undertaken. 8
Conclusion: In the Force Model/Solid Model Report the group has looked at what forces are put into the system and how they interact with the critical components. The user s input energy has been resolved into a tension force in the linking rod using an energy balance. This tension force has been applied to the free body diagrams of the Lifter, Dog, and Clamp Block; reactions at each point of contact have been calculated. Using the free body diagrams shear and moment diagrams have been drawn for each component. The Clamp Block is the component of primary interest. It has been analyzed as a cantilevered beam. The geometry presented some problems in the determination of the bending moment diagram because the neutral axis changes location in two places along the length of the section. The group decided to simplify the bending moment analysis by assuming a constant location of the neutral axis. This has appeared to work out well as the location of maximum bending moment is very close to the actual location of failure. In the Project Analysis Report the bending moment model of the clamp block will be refined to reflect the actual geometry and a more accurate magnitude will be determined. In the future the group s plans for the Project Analysis report are: Use the Pro-E solid models to generate a mesh model for input into the Pro- Mechanica FEA software. Apply loading conditions and kinematic constraints from the Solid Model/Force Report to the FEA of the three components. Create and justify a simplified analysis of the stresses by hand calculation to validate the FEA results. 9
Appendix: Solid models: Clamp Block Figure 10. Clamp Block Solid Model I
Solid Models Lifter Figure 11. Lifter Solid Model Dog Figure 12. Dog Solid Model Th Figure 11. Solid Model II
Solid Models Dog Figure 12. Dog Solid Model Figure 12. Dog Solid Model III
Project Proposal MIE 313-Design of Mechanical Components February 9, 2000 Rotating Leadership Force & Solid Model Report Leader: Peter Walsh Project Analysis Report Leader: Charlene Nestor Project Final Report Leader: Juliana Amado Overview of Part The component that we are analyzing for redesign is part of a table-saw fence assembly. It is a cast metal piece that is part of the fence s clamping mechanism. With one end fixed and the other free to rotate, it is subject to bending and compression. The part would be expected to receive abuse during normal working conditions as the outdoor temperature varies through seasons. The objective of this project is to model the forces acting on this component and analyze the stress and strain that have occurred in order to understand how the part could be redesigned so it will fulfill its function without failure. IV
Plan of work: Schedule Date Leader Work 02/10 Group Project Proposal 03/09-03/21 Walsh Project Force & Solid Model Report Create objectives for the project Develop force model Use Pro Engineer to build solid models of critical components 03/21-04/11 Nestor Project Analysis Report Attain working knowledge of Pro Mechanica Provide explanations of the simplifications of the design objectives Use FEA to a) show detailed load conditions b) apply kinematic constraints 04/11-05/02 Amado Project Final Report Put the work from report number 1 and 2 together Redesign (Make necessary changes) 05/04-05/09 Group Oral Presentations: Introduce our project to public. V