Working with Neutral Format Surface and Solid … with Neutral Format Surface and Solid Models in...

Working with Neutral Format Surface and Solid

Models in Autodesk Inventor® JD Mather – Pennsylvania College of Technology

Session ID ML205-1P In this class we will learn how to utilize neutral format data such as IGES, STEP

and ACIS files in Autodesk Inventor. Particular attention will be focused on techniques for repair of flawed data in the Inventor Construction Environment. The Feature Recognition functionality for imported neutral and proprietary format files will also be covered.

About the Speaker: Dr. JD Mather is an Assistant Professor of CAD & Product Design at Pennsylvania College of Technology, Penn State. He previously worked in industry for 15 years, including positions as journeyman machinist, research and development technician, and industrial engineering technician. Dr. Mather has been an Autodesk Inventor® Certified Expert since release 7. He is also a Certified SolidWorks® Professional. Dr. Mather placed second for Autodesk Inventor® in the AU 2006 Avatech Altogether Smarter Challenge, and he placed first in the same category at AU 2007. [email protected]

Working with Neutral Format Surface and Solid Models in Autodesk Inventor®

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Session Objectives

After attending this session, you will be able to:

Use ACIS files beyond version 7 in your Inventor models.

Use IGES and STEP files in your Inventor models.

Use composite surfaces in your assembly drawings.

Use imported IGES and STEP geometry for creating tooling.

Use the Inventor Construction Environment to repair some types of imported geometry problems.

Target Audience

This is a power-track session intended for users with advanced experience with Autodesk

Inventor. Manufacturing/mechanical engineers, designers and those involved in Inventor

training should attend.

Introduction

Working with neutral format files can be challenging. There is often no “easy button”

solution. You must be willing to experiment and try many different techniques when your initial

efforts are unsuccessful. In a 90-minute class I am very limited in what we can cover. The

problems chosen for this class were picked for brevity in solution while still covering most of the

available tools. In some cases the problems might appear rather trivial – but that is because I

have spent countless hours in preparing the presentation of their solutions. I have limited the

problems to those that can be solved within Inventor without 3rd party software (except for a

single brief case with ACIS format files that I’ll describe shortly).

There is ample information available on the Internet on the history of the various file types

including ACIS, IGES and STEP. This will not be a history class.


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We are going to look specifically at some techniques for working with less-than-ideal geometry

in neutral format files. Of course you should not have to learn or be concerned with these

techniques if the geometry were ideal. But we don’t always work in an ideal world.

Step number one in addressing any geometry conversion problem is to communicate with the

source vendor/customer. If you can work together towards a solution it should be easier to get

a good neutral file from native geometry in the originating software than to repair geometry in

different software.

Open the file ML205-1P-1.dwg in AutoCAD and execute the List command on some of the

geometry. The list command returns information that the file contains “BODY”s and it shades

like surfaces or solids. You might want to add a bolt circle hole-pattern to the flanges, but

editing operations cannot be performed on the geometry.

Many AutoCAD 3rd party add-ons create geometry based on the ACIS kernel. The geometry

might not be editable without the 3rd party add-on.


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Side Note

Before we continue, a tip about ACIS (*.sat) files. Autodesk products will read up to ACIS v7

files. An ACIS file beyond that version will need to be converted to v7. Refer to Spatial

Technology Corporation for further information on Hoops ACIS Viewer and other ACIS

information.

Search Google for the Hoops ACIS Viewer.

In Hoops, from the pull-down menu Tools>Options change the Export Version Number to v7.0

and save the file. Notice that the highest version listed is v15.0. ACIS is now beyond that

version, so you might get a file that you cannot convert to v7.0. In that case your best recourse

is to contact Spatial or contact the source of the ACIS file. They can set the ACIS version

Option when saving the file in the software they are using to create the geometry.


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Open the ML205-1P-1.dwg file in Inventor. Be sure to click Options and set the File Open

Options to Import. Click Finish in the DWG/DXF Import Wizard.

Special Tip for AU attendees: TBA

The geometry imports as a Composite surface.

Right click on the Composite node in the

browser and select Copy to Construction. Then

right click on the Composite node and select

Delete.


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You will now see a folder called

“Construction” at the top of the

browser. Right click on the folder

and select Edit Construction. This

will take you into the Construction

Environment (CE). Notice that the

Panel Bar changes to reveal a

new set of tools for this

environment.

Expand the Construction folder and

the “0” group. Right click on the

Surfaces and select Quality Check

and then click Examine and Done. No

problems were found with the

geometry.


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Right click on the surfaces again and

this time select Stitch, then Apply

and Done.

Notice that the geometry is now listed as

Solids (1) in the browser. Right click on

the Solid and select Copy Object.


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Click OK with the options set as shown. Then click

Return to exit the CE and return to the Modeling

Environment.

That completes this problem, save the file.

Special Tip for AU attendees:

Explain this stuff, including

confusing error prompt in earlier

releases.

Open with ML205-1P-2.stp with

Composite Group Mapping.

Click Options when opening the

file.


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Inventor generates a translation report that you can use to get more information about the file.

If the translation report does not open automatically you can access it by expanding the 3rd

Party node in the browser and double click on Translation Report.

Close the file.

We will re-open it with different Options.


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Again, open the file ML205-1P-

2.stp this time with the options

shown.

We want to set our Group

Mapping to Construction Group.

Notice that the geometry imports as 2 solids in

the CE.

Enter the CE by right clicking or double

clicking on the Construction folder.


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Key tip: Change the selection filter from Select Faces and

Edges to Feature Priority.

Right click directly on one of the solids

in the graphics window and select

Copy Object.

Click OK with the default options.


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Return from CE and Save As with

the filename Bracket and delete the

Construction folder. Save again.

Special Tip for AU attendees: TBA

Go back to the original file

and Save As with the

filename Sensor. Delete

the Construction folder and

save again. You can now

assemble the two parts in

an iam file using Mate-

Flush constraints between

the respective parts XY, XZ

and YZ planes.

Now it’s your turn, see if you can duplicate the steps from Problem 2 with Problem 3, ML205-

1P-3.igs. Note that you can assemble the parts in an iam using Mate-Flush with the respective

part xy, xz, yz origin workplanes. Problem 2 was a STEP file while this one is an IGES file.


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Open Problem 4, ML205-1P-

4.igs and right click on the

Surface1 in the browser. Select

Copy to Construction and then

delete the surface feature from

the modeling environment.

Switch to the Construction

Environment.

Right click on the surface and

Unstitch.

As usual run a quality check.


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Stitch the surfaces back

together.

We find a missing surface in

the part. It appears that the

part is symmetrical so maybe

we can use a mirrored

surface to repair the solid.

First we try a simple

Boundary Patch, but that

doesn’t work, so let’s see

how to mirror the missing

surface.

First we need to isolate the surface that we intend

to mirror. We can do this by right clicking on the

surface and select Move to Group. In this case we

have an empty group. If necessary we could have

selected Create New Group.


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Stitch the remaining surfaces and RMB Copy Object. Set the Output to Create New Surface

and Delete Original. Repeat this process for the isolated surface.

Uncheck Translucent for the two copied surfaces.

Create a new Workplane through the center of the part by

clicking on the two planar faces on either side after starting the

command. Use the workplane to Mirror the surface feature to

the other side. Use the Stitch command to create the solid.


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Tip: Perhaps you need the newly stitched solid in dwg format for

a customer or vendor. Select the Applications>AEC Exchange

pull down menu.

Open ML205-1P-5.stp with the

Options as shown.

Our part translates as a solid but

doesn’t appear to be correct.

Close the file.


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Open ML205-1P-5.stp again, this

time with the Options as shown.

(Tip: These are the initial options I

use when opening any IGES or

STEP file that I’m not sure of the

content. The reason I do this is

because opening a file with Auto

Stitch and Promote turned on can

take anywhere from minutes to

hours. There is no point in using

the Post translation options if a

quick visual inspection indicates

that the geometry is hopelessly

flawed.)

The geometry imports as surfaces in the CE.

Run the Quality Check.


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Delete the loop features as shown. (Recall

how to set the Feature Priority selection

filter?)

Stitch the surfaces.

Copy the 2 stitched surfaces to the ME using

the following options.

Select the Output as Create New

Surfaces and Delete Original.


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Create Boundary

patches to close up

the open rings on

both ends.

Stitch the

surfaces into a

disjointed solid.

Alternatively you could

use Sculpt.


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Start a new sketch on the YZ Plane and Project

Geometry the axis in each hole.

Hit F7 for Slice Graphics and sketch the line and

arc shown. Add tangent constraints between the

lines and the arc as needed. Change the lines to

Construction linetype.

Start a sketch on one of the ring faces and Project

Geometry the two circular edges.

Sweep the sketch as shown. We had to

create 2 sketches to fix this part. Now

let’s look and another method that does

not require the creation of any sketches.

Next we look at an alternative technique

to fix this part.


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Open the file ML205-1P-5.stp as done previously and delete the two outer torus features.

Stitch the surfaces and promote (Copy Object) the surface to the modeling environment.

Measure the distance from the inside cylindrical

surface to the outside cylindrical surface.

Thicken/Offset the arced surface.


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Sculpt the surface.

Open ML205-1P-6.igs with the options shown.

If we expand the Construction folder notice that

there are 2 Solids, 1 Surface and 2 Wires.

Close the file.


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Now open the file ML205-1P-6.igs with the

indicated settings (see Group Mapping).

Notice this time we have 3 Solids and the

1 Surface.

The solids are easy to

promote as we have

done previously so we

will isolate the surface

and concentrate on

that repair.


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First I Unstitch the

surface and then

run a Quality

Check. The

Diagnostics

indicates 4

problems.

RMB to find the problem.

I will click on each BODY and select Refit face.

Repeat the Quality Check and Stitch to a solid and

promote.


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Open ML205-1P-7.igs with the Create

Groups From: Levels (Layers) option.

We already know how to separate out the

two solids into different ipt files so I’ll

leave that to you. RMB on the Group and

Group 3 and uncheck visibility. Group 3

contains wires that you might need for

some reason. We will not use them.

Also turn off the visibility of the 3D

sketches.

Enter the CE and RMB on the Construction folder

and Define New Group.

With the selection filter set to Feature Priority

select the smaller part, RMB and Move to Group

the newly created empty group. Turn off the

visibility of Group 2, the green part, leaving only

the smaller blue part visible.


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Unstitch the surface and then run a Quality Check on the resulting 309 surfaces.

If you Stitch the surfaces you will get a solid but it has some

sliver faces that I don’t think were part of the original design

intent.

(Actually, this appears to be a bit random at least one time I

got a solid as shown, but usually I get a surface body.)

You will have to use the Select

Other tool to select and then

delete these sliver faces. You

might have great difficulty in

locating them.

There are a total of eight sliver faces located in

two different areas of the model. You can locate

them by rotating the model around and look for

darker areas where there are multiple surfaces

over top of each other.

Stitch the part up again and the gaps will be

closed. Promote the solid and save the file.


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Make the other surface in

the CE visible again and

Unstitch, run the Quality

Check and then try to Stitch

back up to a solid. Two free

edges will be found. RMB

on one of them in the Stitch

dialog box and select Find In

Window. (Note: Undo the

Stitch if it is back to 1

surface, you should have

136 surfaces.)

Click the Extract Loop

tool and checkmark

Delete Wires in the

dialog box. Select the

surface shown and

click Apply and Done.

Move the resulting

untrimmed surface into

a new group and

Stitch the remaining

135 surfaces together.

Copy object the two

surfaces (one is the

135 stitched, the other

is the untrimmed) as

surfaces to the ME.

You could use the Trim Surface tool to trim

back the surface to the correct boundaries,

but this step isn’t really necessary.

The Sculpt tool will find the enclosed

volume.


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Open file ML205-1P-8.igs with the

options shown.

Our assembly

browser fills up

with parts but

the graphics

window is

empty.

If we double

click on the

parts in the

browser we

see that the

parts are

surfaces in

the CE.


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Open the file again with Auto Stitch and Promote

turned on. Save the file. All of the parts except one

are base solids.

Start a new idw and create an isometric

view of the assembly. Notice that part

number U-6, the surface part, is missing

from the view.

Expand the part and RMB

on the surface feature and

select Include. The surface

will now appear in the

drawing. (Note: Earlier if we

had tried to create a view of

the assembly when all parts

were surfaces we would

have gotten an error – we

must have at least one solid

in the assembly.)


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However, we can create

an idw of a single part that

is only surfaces.

We open the U-6 surface file and

go through our usual steps of

unstitching and running Quality

Check in the CE. There are no

errors returned but a visual

inspection reveals suspect

geometry.

We can Extract Loop (un-trim) the

questionable surfaces but the

result is spheres that for this

design would be difficult to re-trim.

Isolate the questionable surfaces into a group by themselves.

Special Tip for AU

attendees: TBA

Stitch the remaining

surfaces and then copy to

the ME as surface.


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Start a new sketch on the xy-plane.

Project Geometry the larger sphere edge

as construction linetype and sketch the

constrained arc as shown.

Start a new sketch on the yz-plane

and Project Geometry the smaller

sphere as construction linetype and

sketch the constrained arc as shown.

Revolve the

two arcs and

then attempt

to Sculpt the

two revolved

arc surfaces

and the

original

stitched

surface. The

operation has

no effect on

the part.

Extend the 4 edges as shown.


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Try the Sculpt again

and now we get a solid.

The obvious question is, “How did you know to extend those 4 surface edges?” For those of

you in attendance at AU I will show you the trick to identifying a case like this.

Open file ML205-1P-9.

You might have a zero

thickness part for which

you need to make

tooling.

I start by removing some of the

holes in the CE with the Extract

Loop command.


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Some of the other holes are closed with the Boundary

Patch command in the ME after creating sketch

geometry.

Once a sketch boundary is established we can Extrude – To Next.

Open file ML205-1P-10.igs.

For this problem we need the 3D path centerline of the tube. The tube is a series of cylinders

with torus segments connecting the cylinders.


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Open the file ML205-1P-10.ipt that I have

already started for you.

Change the lines to construction and

place a sketch point near the apparent

intersection of each set of lines. Add

coincident constraints to find the true

intersection.

Go to Tools>Document

Settings and set the 3D Sketch

Auto-Bend Radius to 100mm.

(I’ll explain later how I arrived at

this radius.)


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Start the line command and RMB make sure the Auto-Bend is turned

on.

Click on the line endpoint

away from the arc and

then the sketch point,

continue on selecting the

only the sketch points until

reaching the other end of

the tube.

Once you have the 3D centerline you can use the Measure>Loop Length to find the length.

Start a new metric file and Derive Component the solid body and the 3D sketch. With a bit of

work a toolbody for creating a mold for the tube can be generated. It takes some time to set this

up so I will simply show the steps on an existing file.


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Once the toolbody is created it is used to create both sides of a mold with a complex split line.

Sometimes it can be a bit more difficult as the 3D sketch will not find the center of the circles on

the end of the cylinders. Recall that an arc is a planar entity. Also recall that a plane can be

defined by two intersecting lines. We can use the axis of each cylinder to define the plane of

the connecting torus segments. 2D sketches with Project Cut Edges can be used to establish

the centerlines.

Working with Neutral Format Surface and Solid … with Neutral Format Surface and Solid Models in...

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