ma115-5.pdf

Autodesk Inventor Part Modeling:

The First Step, Part II

Autodesk Inventor Part Modeling: The First Step, Part II Anthony Dudek BP North America, Inc. Thomas Short - Munro & Assoc., Inc

MA115-5 Lofts, tangents, and bores -- no need to fear Autodesk Inventor Part modeling. Well show you everything you need to know to be the hero back in the office. This class will demonstrate most of the sketch tools and part features in Autodesk Inventor and illustrate logical techniques and guiding principles to help you create accurate and healthy parametric parts that will behave in your assemblies. Proper sketch and part modeling is the foundation for Inventor assemblies and capturing the proper design intent.

About the Speakers: Anthony is a project manager and knowledge manager at British Petroleum. He is a former design engineer, CAD manager, software developer, ATC instructor, and CAE industry analyst. He is considered to be an agent of change and a proponent of technology, though not enamored of it (still no Blackberry). An instructor at AU for the past 14 years, Anthony will be teaching his classes with his colleague, Tom Short. Anthonys classes are designed to show users how to maximize their efficiency, and he strives to make his classes fun as well as informative. [email protected]

Tom Short is a mechanical engineer registered as a professional in Michigan. He has taught and consulted on AutoCAD, Autodesk Inventor, and Autodesk Mechanical Desktop for many years in the U.S. and other countries. At Munro & Associates, Inc., Tom is a consultant on Lean Design, and has worked with a variety of companies helping them improve their designs for simplicity and ease of assembly. He is also an author with books on Inventor and Mechanical Desktop. Tom has presented at every Autodesk University since its inception. [email protected]



Objectives

Take a good look at the powerful tools available to assist you in designing incredible parts in Autodesk Inventor.

Gain more Inventor power from these techniques to make you famous! Acquire a better understanding of parametric design methodology inside the latest

release of Autodesk Inventor.

Outline

3:30 3:45 15 min. Introductions Class Objectives

3:45 4:15 30 min. More Advanced Part Modeling Techniques

4:15 4:50 35 min. Parametric Control Techniques

4:50 5:00 10 min. Summary - Question & Answer

Sweeps and Lofts

The Process for Creating a Sweep or Loft

The process is essentially the same for either creating a Sweep or a Loft Feature. That is why they are both covered in this Section.

Create paths or rails that are necessary to control the sketchs direction or flow.

Create the work feature(s) that will hold the Sketch(es)

Create the Sketch(es) for the various cross sections

Use the Inventor tool Sweep or Loft - to create the feature

Sweeps require two Sketches, usually at right angles to one another, but not necessarily. Lofts generally require more than two Sketches in order to achieve a smooth transition between Sections.

Creating 2D Sweep Features

Sweep Features are typically created for piping or tubing, but are not limited to these uses. You may be able to quickly create a feature with a Sweep that would take much longer with Extrude Cut & Join Features. For example, a picture frame with mitered corners is best modeled with a Sweep Feature. Youll do that soon in Example-10-02. This Inventor tool has a variety of other applications in piping, tubing and other such types of geometry.



1.) Create a Sweep Path

The first step is to create a Path for the Sweep Feature. This is simply a Sketch on a Work Plane, dimensioned and constrained as any other. The path may be open or closed depending on the shape of the final solid Feature. Well be doing just that in Example-10-03. For now, Open Example-10-01 and examine the two sketches setup there. If its piping, as in the Example, then the path will be open. If its the picture frame in Example-10-02 then the path is closed. Notice the path lies entirely on a plane and is therefore considered a 2D path. Later in this Chapter well work with 3D paths and the ways of creating them. The default XZ Plane in Inventor was used for the paths work plane, as was the XY Plane for the Sweeps cross section. In our Example of the piping it is best to plan the path so that it originates at a known point, such as the origin 0,0. Youll see why in a minute.

2.) Create a Cross Section

As stated above every Sweep Feature requires a Sketch that will serve as the cross-sectional profile of the Sweep feature. This sketch will, of course, either be on a part face or a Work Plane. In most cases, a Work Plane will be necessary. In Example-10-01 we have used the parts XY Plane and the path starts at 0,0. With the cross sections sketch on the parts XY Plane then we are assured that the cross section is at the start of the path and that it intersects it. That is one of the stipulations in Inventor that the cross section intersect the path in some way. Although it is not required that the cross-section begin at the paths beginning it may intersect the path somewhere along the paths length. Go ahead and use the Inventor Sweep tool to sweep the cross section along the path in our Example. The Sweep tool is located on the Part Features Palette and is shown in Figure. The Profile and Path buttons are obvious, but the Output type bears some examination. Mainly, you will want to leave the setting where it is to produce a solid, but take note that the other produces a surface. The More tab contains nothing more than an entry box for a Taper Angle value. Try it for the effect, but be careful as the taper angle runs out very quickly over the length of the sweep and soon results in an error. When finished take a moment to examine the results. Is it necessary that the cross section be perpendicular to the path? No, in fact, the cross section if angled to the path will result in a foreshortened cross sectional area, as in an ellipse from a circular sketch.

How to Constrain the Cross Section of a Sweep

The following Practice will show you how to create the Work Plane for the Cross Section of a Sweep and also how to constrain the Cross Section Sketch to the Path Sketch. Open Practice-10-01.ipt and examine the Path Sketch that is there already. The Path is all done. Your task is to create the Cross Section Sketch. The first step in that task is to put a Work Plane on the outer endpoint of the Path. Pick the Work Plane tool and pick the endpoint of the Path the endpoint, not the line. Once thats done then pick the line.

This is an effective method of placing a Work Plane perpendicular to a line in a Sketch. With the Work Plane in place its a simple matter of creating a Sketch on it do so.



The default coordinate system of the Sketch will have the Z axis pointing into the Sketch towards the upper left hand corner of the screen. We dont want that Return back to the Part environment, right click on the Work Plane in the Browser, choose Flip Normal, and double-click on the new Sketch and you should find the Z axis pointing out as shown in Figure XX. Our Cross Section Sketch will be a circle, of course. In order for the Sketch to be constrained to the Path we must Project the endpoint of the Path onto our Cross Section Sketch. Do so now. You should notice a slightly darker dot at the end of the Path. Turn off the coordinate system indicator, if necessary. Now, pick the Circle tool and hover over the Projected endpoint. There should appear a green dot. If not, then you hadnt Projected the endpoint successfully. If there is a green dot pick the endpoint of the Path and drag the circles radius out a small way. Dimension the circles diameter (.05) and it should be fully constrained. It is very important to Project the Paths endpoint first, then draw the Cross Sections geometry. If you dont then youll find it very difficult to constrain the new geometry to that Projected endpoints dot. Return to the Part environment and pick the Sweep tool from the Tool Panel and complete the Part.

Creating 3D Sweeps

Although 2D Sweeps are great Inventor is a 3D modeling software application and the need for 3D Sweeps is everywhere in engineering today. The applications include wiring, piping, tubing, etc. 3D Sweeps can be created in Part files (ipt) or Assembly files (iam). 3D Sweeps are based on a 3D Sketch which is basically the Path for the 3D Sweep. 3D Sketches are created with lines and work features, such as Work Points and Work Planes. Creating a 3D Sketch is the hard part. Once thats done the Sweep tool takes care of the rest. The basic principle to creating a 3D Sketch is define Work Points and then connect the dots with a line.

In the next two Examples we are going to create the same 3D Sweep for a pipe run, but were going to use two different methods. The first Example-10-04 is easier than the second Example-10-05. Both are very good examplesof 3D Sweeps in Inventor. Open Example-10-04 and examine what is setup for you. Notice the Work Planes in the Browser they are named according to the offse

t values used to create them. The finished version of the

creating our 3D Sweep.

Example is shown in Figure.

As you can see the Work Planes that are setup in Example-10-04 will be instrumental in Right-click on the model background and choose New 3D Sketch.

Notice that a 3D Sketch icon appears in the Browser. You will be creating seven (7) Work Points in the following steps. When finished you will then connect the Work



Points with a Line using the Auto-Bend feature to include fillet radii at the corners. Letbegin:

s

e a ork Point (in any order): The XZ

rk Plane 6in. Another Work Point should appear.

t?

in. It is buried in the Document Settings dialog box under the Tools ull-down menu. Look on the Sketch tab and change the value to 6.00. As

youll otice that Inventor is applying 6in fillets automatically. If you right-click

d ch

of the e and Project the two circles representing the

3D line path that you created for the Path. Choose

TIP: Keep in mind that if you cant pick a particular Work Plane in the model screen then you can easily select it in the Browser.

Select the Work Point tool from the 3D Sketch Palette. It takes three (3) planes to definpoint right? So pick three Work Planes to define the first WPlane, the YZ Plane and then the Work Plane Start. A Work Point should appear on the model screen at the intersection of the three Work Planes.

The Work Point tool is repeating so no need to select it from the Palette. Pick the XZ Plane,the YZ Plane and the Wo

Continue on for the third point. Pick the YZ Plane, the Work Plane 6in and the Work Plane 42in. Getting the idea?

Pick the Work Plane 6in, the Work Plane 36in and the Work Plane 42in. Got a Work PoinDont get cocky now.

Pick the Work Plane 36in, the Work Plane 42in and the Work Plane 54in. Almost there.

Pick the XZ Plane, the Work Plane 35in and the Work Plane 54in. One more to go.

Pick the XZ Plane, the Work Plane 30in and the Work Plane 54in. All done! Very good!

Now, we need to draw a 3D line connecting the dots as it were. First, we need to set the Auto-Bend radius to 6p you may know the in is understood.

Select the Line tool from the 3D Sketch Palette and pick the Work Points you created in order one through seven. As you connect the dots nyoull notice that Auto-Bend is turned on in the Context Menu.

When through with all the points, right-click ansimple matter of Returning back to the Part environment and creating the cross section sketch. With your cursor pick the Work Plane Start. Press S on the keyboard and you should have a sketch started and be in the Sketch environment. No need to draw anything, just zoom in on the 4 Stub pipe sticking out

oose Exit. Now its a

TeID and OD of the pipe. Refer to Figure.

No need to constrain anything either. Finish the sketch and select the Sweep tool from the Palette. Pick the sketch for the Profile and the



OK and step back and admire your work. Pay close attention to the anatomy of the 3D Sweep in the Browser.

.

ffset values. Keep in mind that these offset values could be equations or User Parameters.

ed

s

und

on,

ing

d.

k

l fer to Figure for an explanation of the dialog

are listed on the left as you pick them. Any rails that you

the bottom edge of the Hilt feature. You want the hook to start from the handle right?

Editing the 3D Sweep

How do you edit the 3D Sweep? Mainly, this involves editing the 3D Sketch that controls the3D Sweep. And editing that will depend on how it was made. In Example-10-04 you would change the offset values on the Work Planes that control the Work Points of the 3D SketchIn Example-10-05 you would do the same except the Work Planes are buried in the 3D Sketch and you would have to uncover them to change the o

Creating Loft Features

When we discuss lofts, or lofting as the process is called, we are referring to the process of fitting a solid (or surface) through a series of crosssections to affect an organic shape. These cross sections nenot be parallel to one another. The cross sections dictate how the Lofts shape will appear. The user defines the cross sections with Sketches and Inventor throws in a little higher math to create some truly interesting shapes. Lofts are typically used to create topology such as a cars body, a shiphull, the Microsoft Mouse or even the human hand. Other applications would include modeling transitions between two known geometric shapes such as foin HVAC systems. Just think of any non-uniformshape that couldnt be modeled by ExtrusiRevolution or Sweep as shown in Figure.

In our first Example well be creating a hook commonly found at any construction site for pickup loads with a crane. It serves as an excellent example of what exactly a Loft is and when it is useOpen Example-10-06 and examine what has beensetup already. Youll notice many sketches, 16 in fact, and if you look in the Browser the 16 WorPlanes that those sketches are based on. The Example is all ready to be lofted. Select the Loft tooand rebox.

The Curves Tab typically the only one youll ever need. The cross section Sketchesmay pick are listed on the right.

In the Curves Tab youll notice the left-hand pane is labeled Sections. This is where your cross sections will be listed as you pick them on the screen. You neednt select the promptClick to Add although you could simply start picking the cross sections on the screen. Not so fast! The first one to be picked is not one of the sketches - its



Then pick the sketches in order. All 16 of them. Refer to Figure. The final selection is the bottom edge of the Tip feature.

When youve got them all hit OK to exit the dialog box. Sit back and admire your work. Finish the part off by applying a -10 UNC Thread feature to the Haft feature. In the Figure at the beginning of this Section is the finished Hook Example. We added a polished metal Color to the part for effect. If you want to save your work its a good idea to save it to a different file name.

Are lofts this easy? Typically not. What youre missing is the several hours of trial and error that it might take to make all those sketches. If you examine our Example further youll notice that there is a Shared Sketch that controls the Work Planes that control the Sketches for the Loft. This is a clever way of controlling the sketches that make up a Loft as typically there is no other effective method for constraining the Loft sketches to the Part. The Shared Sketch is based on the Parts XZ Plane. A 2D outline of the side view of the hook was drafted. At key points on the 2D outline Construction lines were drawn across the outline. They were then trimmed to the outline. The Construction lines were used as the basis for Work Planes that were perpendicular to the Parts XZ Plane. On each Work Plane, in turn, a Sketch was created and the Construction line that controlled that particular Work Plane was then Projected onto the Sketch. An ellipse was then drawn with its center at the midpoint of the Projected Construction line reference line and its major axis endpoint at the endpoint of the same reference line. Its minor axis endpoint was merely dragged out. An elliptical dimension was applied with a value of .40 in. This was done for each and every Work Plane. The value of .40 was used for the majority of the ellipses except those near the Tip as the Hooks thickness narrows as it reaches the Tip.

Why are so many sketches necessary? Seems like a lot of work. If you want the final loft shape to be smooth and conform to specifications youll create as many sketches as it takes. As an experiment, open Example-10-06 again and this time select only a few of the sketches skipping over intermediate ones and see what the final Loft shape is. Chances are youll get an error because Inventor doesnt have enough information to make a smooth transition from one sketch to another the changes in direction are too abrupt.



Closed Loop Loft

The next Example is a good example of a Closed Loop type Loft. These are typically seen in sheet metal body applications such as this one for an airplane engine cowling as shown in the Figure.

Open Example-10-07 and examine what is setup there already. Take note that there are 16 sketches based on 16 Work Planes. All the sketches are the same, just their orientation in 3D space is different. As in the last Example, the Work Planes and the sketches are controlled by the Shared Sketch. This is also an example of a Loft that is based on sketches alone there are no existing part edges.

Select the Loft tool and select Sketch1. Continue selecting sketches in order. If you have trouble picking one on the screen use the Browser to pick it from there. As you know, Inventor supports this in the Browser. When you reach the last sketch there is one more thing to do check the Closed Loop check box. This will connect the first and the last sketch profiles so as to form a Closed Loop Loft. Good job!

Editing the Loft Feature

How do you edit the Loft feature? Basically, the same as for a Sweep. Editing the feature itself will provide access to the Loft Feature creation dialog box allowing you to change such things as the Boolean operation or whether the output should be a surface or a solid or furthermore, editing the Point Set used to control the final Lofted shape. Alternatively, editing the Work Planes that form the basis for the Cross Section Sketches will also change the Lofts shape. Of course, editing the various Sketches that form the basis for the Loft will have the most effect on its final shape and appearance.



On Parametric Design

In Inventor there are several methods available to affect parametric control. They are discussed below in order of parametric control they provide to the designer:

1st - Numeric Values

From the very basic in which you dimension a sketch with numeric values specifically telling Inventor what a given distance will be always. Example 5.00. You have seen these in use everyday. Why are they so limiting?

2nd - Equations

Next in line would be wherein you specify relationships between those dimension values. Example: D1=D0/2. In this method the dimension D1 has no explicit numeric value, instead it is driven in relation to the value of D0. You have seen this method employed here today. It has its advantages.

3rd - Model Parameters

Moving along we have the concept of Model Parameters. Inventor provides a special dialog box for our use as we can rename the D0, D1 dimension labels and give them sensible English names that help to identify their use. Mathematical equations may be set up as in the previous method.

4th - Microsoft Excel Spreadsheet

Further along we learn that we can take those Named Parameters and list them in a spreadsheet and further manipulate them therein using the inherent power of Excels logic functions to arrive at values for our designs.



5th - iParts

Finally, we can create what is known as an iPart Factory to automagically produce variants of our Parts based on a spreadsheet that we can set up as shown in the Figure below.

Model Parameters and Parametric Control

Were going to go back to our earlier Exercise Part and see if we can leverage our existing design and add some parametric control. We dont want to rename the D0, D1 Model Parameters for this method.

Using the Parameters tool, we Link to an already prepared MS Excel spreadsheet. In this case, DemoPart.xls as seen in the Figure. This will bring in the Named Parameters that are defined in this spreadsheet. Once its Linked we an then go into each of our Dn Model Parameters and refer to the Named Parameters from the spreadsheet. This is done by left-



clicking in the Equation field and picking the right-pointing arrow and choosing List Parameters from the context menu as shown in the Figure below:

The Parameter names are left alone while in the Equation area the Linked Parameters are used to control those Features in the Part. From then on the Part is manipulated via the spreadsheet. Furthermore, there is an entry in the Browser for the 3rd Party linked spreadsheet.

In Closing

I hope that everyone can now see that effective Part Modeling is something that can be learned and applied to make your part designs smarter and more efficient. It has been shown that Autodesk Inventor is packed with the tools and features that are required to produce todays complex parts in todays complex world. I hope that you now have the knowledge you need to go back to the office and design it better, faster and cheaper.

We sincerely thank you for your time and attention,

Anthony Dudek

[email protected]

Thomas Short, P.E.

[email protected]

Portions reprinted from Learning Inventor 12 published by Goodheart-Willcox publishers.

ma115-5.pdf

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