Finite Element Analysis of a CNC Milling Machine

Finite Element Analysis of a CNC Milling Machine Vice and Potential Modifications. Phil Miller Finite Element Analysis in Design – DP 238

Introduction What is FEA? What is the problem? Finite Element Analysis consists of using a computer model of a material or design that is stressed analyzed for specific results. It is used in the development of new product design to check potential flaws and in existing product refinement. The system can place multiple loads of a model to simulate real life situations that the product could experience. I hoped to investigate a problem which related to my degree so began looking at problems within engineering workshops. Due to the nature of engineering workshops there are many large and heavy pieces of machinery. A major component regulary used are machine vices, so I began to look at potentials improvements and investigate flaws within the general design.

Milling Machine Vice

Background Research Topics • • • Types of machine vice Materials (Grade of Casting) Geometry Relevant British Standards Determine resonable objectives Machine Vice Specification Tilt Lock Machine Vice CRITERIA A B C D E F Width of jaws (mm) Depth of jaws (mm) Width fixed base (mm) Height of fixed base (mm) Overall length (mm) Tenon slot (mm) 100 28 180 57 290 5 This vice was selected due to the fact it is regulary used within machine shops on milling machines. The university has a model very similar for me to use in my project.

Selected Model

Objectives • • • To gather relevant and useful information about a machine vices standard design features (Material, Dimensions. . . Etc. ) To have an understanding of the British standards relating to the vice and how these effect its operation (Grade of casting, Geometry…Etc. ) To have a greater understanding of the potential tests to be carried out of the vice (Normal static study, Buckling, Fatigue, Failure analysis…Etc. ) To carry out research for potential improvement to the machine vice (Material suitability, Design, Geometry, Removal of material…Etc. ) If possible, decrease the mass of the vice by 1 Kg while not reducing the rigidity by more than one percent.

Meshing & Simulation FEA is a tool for performing engineering analysis. It includes the use of mesh generation techniques for dividing a complex problem into small elements. The software uses parameters to place multiple loads such as force and pressure onto the model, simulating a real life situations these are then calculated and estimates are made regarding the models reaction.

Method Analysis Potential Forces Free Body Diagram – This is a breakdown of all forces acting on the model and the reaction forces expected to be produced. These figures were based on manufacturing specification and manual calculation. Produce Meshed Model The model as a whole had to be adjusted for a mesh to be completed. All parts of the assembly which were not appropriate were removed to make meshing possible.

Method Forces and Fixings The forces acting on the jaws were taking for the manufactures specification for maximum load. The fixings represent the pressure acting on the vice being held to the machine bed. Run Simulation The simulation is run with all fixings and forces which are to be tested. Results can begin to be collected and the model analysis can begin.

Collecting Results Mesh Local Size (mm) Max Stress - Von Mises (Mpa) 10 30 8 35 6 38 4 39 There is a collection of different stresses over different mesh sizes. The stresses recorded is higher the smaller size of the mesh in the model. Mesh Local Size (mm) Vs Max Stress - Von Mises (Mpa) Max Stress - Von Mises (MPa) All required simulations are run on the model. The values can be collected and plotted. Analysis on the mesh can be carried out and plotted also. 45 40 35 30 25 20 15 10 5 0 0 2 4 6 8 Mesh Local Size (mm) 10 12

The testing begins with trying to investigate the rigidity of the model before and improvements can be made. Total Force (k. N) Displacement (mm) 5 10 15 20 0. 0018 0. 0036 0. 0055 0. 0073 The force is gradually increased over both jaws and the displacement is recorded and plotted. Although the displacement seems insignificant when related to potential engineering tolerances it could have a large effect. Displacement (mm) Results 0. 008 0. 007 0. 006 0. 005 0. 004 0. 003 0. 002 0. 001 0 Applied Forces (k. N) Vs Displacement (mm) 0 5 10 15 Total Applied Force (k. N) 20 25

Potential Improvement The research carried out on potential improvements showed that there are different techniques to improve the distribution on load. Improvements could have been made to the design through the following methods: • Coring • Fillets on Mating Faces and Corners • Reallocation of Load.

References WEBSITES: • http: //its. foxvalleytech. com/machshop 3/basicmill/Work. Hold. htm • http: //www. cnccookbook. com/CCMill. Tips. Techniques. htm (01/01/11 09: 48) • http: //www. google. co. uk/patents? hl=en&lr=&vid=USPAT 3650522&id=UUA 0 AAAAEBAJ&oi=fnd&d q=machine+vice+&printsec=abstract#v=onepage&q=machine%20 vice&f=false (Mechanical Clamping Device : Patent Number – 3650522) • http: //www. google. co. uk/patents? hl=en&lr=&vid=USPAT 2667799&id=y. WFn. AAAAEBAJ&oi=fnd&d q=milling+machine+vice+british&printsec=abstract#v=onepage&q&f=false (Milling Vice Patent : Patent Number – 2667799) • http: //www. dapra. com/workholding/hydravise/specs. htm • http: //www. slideshare. net/roehmgmbh/rhm-vices • http: //grabcad. com/library/machine-vice--22 § http: //www. sv. vt. edu/classes/MSE 2094_Note. Book/97 Class. Proj/num/widas/history. html BOOKS: • Haan, E. R. "Selecting and using a bench vise" • Winston A. Knight, Boothroyd Geoffrey. “Fundamentals of Metal Machining and Machine Tools, Third Edition” • “Zeus Precision Data Charts and References Tables for Drawing Office, Toolroom & Workshop”