TCC EGR 110 - EGR 110 Inventor Lecture

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EGR 110 Engineering Graphics File: N110IL8 Inventor Lecture #8 Mass Properties of Solids A powerful analysis feature available in Inventor is the ability to determine the mass properties of complex objects. Many engineering students will later calculate many of these properties in courses like Statics and Mechanics of Materials. The calculations can become quite involved, even for fairly simple objects, so the ability of Inventor to find mass properties for complex object made of various types of materials is quite impressive. In particular, Inventor can be used to specify the material type for each part, including the density, and then it can calculate: - Volume - Mass - Surface Area - Center of Gravity - Mass Moments of Inertia - Principle Moments of Inertia Center of Gravity It is often important to know the center of gravity of a part in order to use it properly. The center of gravity of the boom of a crane is important in determining the max load that the crane can lift and weights are added to wheels on automobiles in order to “balance” the wheels such that their center of gravity will be in line with the axle of the wheel. Example: Students taking EGR 140 - Statics will learn to calculate the center of gravity for various types of objects. Shown below is a problem from a Statics text used recently in EGR 140. The solution is also shown. You do not need to understand the solution at this point, but it will be nice to see that we can build the part in Inventor and achieve the same result. Problem 5-113 (Statics, 7th Edition, by Beer & Johnston) A bronze bushing is mounted inside a steel sleeve. Knowing that the density of bronze is 8800 kg/m3 and steel is 7860 kg/m3, determine the center of gravity of the assembly.Page 2 Solution: The centroid or center of gravity of the referred to as  z ,y ,x Note that symmetry implies that 0 z x  so we only need to find .y Divide the object into three parts as shown: A – Bronze bushing B – Upper part of steel sleeve C - Lower part of steel sleeve Note that the volume of a cylinder is:     HD - D4 V:iscylinder hollow a of volume theandHD4 H2D HR V2inner2outer222                36-22C36-22B36-22Am 10 x 2.7489 028.00.010 - 0.0154 Vm 10 x 4179.4 020.00.015 - 0.02254 Vm 10 x 6.7293 008.00.015 - 0.0364 Vmeters)in values(using so m/s 9.81 g andgravity) todueeleration (mass)(acc ht or Weig mg W andolume)density)(v (mass massor V m: thatnote Also2 Part Material Volume (m3) Mass Density (kg/m3) Mass (kg) Weight (N) (mm) y A Bronze 2.749E-06 8874 0.0244 0.2393 14 B Steel 4.418E-06 7860 0.0347 0.3406 18 C Steel 6.729E-06 7860 0.0529 0.5189 4 B and C Steel 1.115E-05 - - - 0.0876 0.8595 9.55 A, B, and C - - - 1.390E-05 - - - 0.1120 0.8595 10.52 The centroid is calculated using a weighted average of the centroids of each part, so x z y A B C portion) steel (entire mm 9.55 0.85954(0.5189)18(0.3406) W W Wy Wy WWy yassembly) (entire mm 10.52 1.09884(0.5189)18(0.3406)14(0.2393) W W W Wy Wy Wy WWy y CBCCBBBCCBACCBBAAABCPage 3 Example: Build of model of Problem 5-113 above and use the mass properties of Inventor to find the center of gravity. 1. Create a metric part for the steel sleeve - Since the solution above has the axis of the assembly along the y-axis, begin the part by: o Selecting on the xz plane o Making the xz plane visible o Adding a Sketch Plane to the xz plane - It is important that the position of the object is known precisely with respect to the origin, so select Project Geometry from the 2D Sketch Panel and then pick Center Point under the browser. The Center Point should be clearly seen as a dot on the sketch plane. - Note that two extrusions are required for the part. Only the sketch plane for the first extrusion is shown below. 2. Find the center of gravity (CG) for the steel sleeve just created. To do this: - Select View – Center of Gravity from the main menu. The center of gravity axes icon should appear. Note that the origin of this icon is located at the CG. - Pause the mouse over the center of gravity symbol until the select tool appears. Click on one of the arrows until the coordinates for the CG appear. Note that the axes are color coded as follows: x-axis: Red y-axis: Green z-axis: BluePage 4 3. Create a metric part for the bronze bushing in a similar manner (again be sure that it is centered at the origin). Only one extrusion is required for this part. 4. Create a metric assembly drawing. - Use the steel sleeve as the base part. Note that the origin for the assembly will be the same as the origin of the base part. - Next add the bronze bushing to the assembly - Use an Insert Constraint to complete the assembly.Page 5 5. Change the properties of each part and copy the mass properties to a Word document. - Right-click on the steel sleeve in the Parts Browser and select Edit. - Right-click on the steel sleeve in the Parts Browser again and select iProperties. - Select the Physical tab and change the Material to Steel, Mild (see below) - Click the Clipboard button on the Properties window above and the information in the window will be copied to the clipboard. - Open a new Microsoft Word document and select Paste. The mass properties information should be pasted into the document as shown below. Physical Properties for Steel Sleeve General Properties: Material: {Steel, Mild} Density: 7.860E-006 ( kg/( mm^3 ) ) Volume: 1.115E+004 mm^3 Mass: 0.088 kg Area: 5.320E+003 mm^2 Center of Gravity: X: 2.999E-016 mm Y: 9.549 mm Z: -8.618E-016 mm Mass Moments of Inertia Ixx 12.163 kg mm^2 Iyx Iyy -2.771E-016 kg mm^2 13.230 kg mm^2 Izx Izy Izz 2.921E-016 kg mm^2 2.671E-016 kg mm^2 12.163 kg mm^2 Principal Moments of Inertia I1: 12.163 kg mm^2 I2: 13.230 kg mm^2 I3: 12.163 kg mm^2 Rotation from XYZ to Principal Rx: 0.00E+000 deg Ry: 0.00E+000 deg Rz: 0.00E+000 degPage 6 - The mass properties for the bronze bushing are shown below. Physical Properties for Bronze Bushing General Properties: Material: {Bronze, Soft Tin} Density: 8.874E-006 (


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