Shanghai Jiao Tong University 1 UG: Free Form Feature ME 250: Design & Manufacturing I School of Mechanical Engineering

Shanghai Jiao Tong University 1

UG: Free Form Feature

ME 250: Design & Manufacturing I

School of Mechanical Engineering


Outline

Introduction Create and Edit Splines Create Surfaces Summary


Introduction

Create the curves used to construct sheet bodies.

Create the sheet bodies that will define

the surfaces that make up the solid.


Examples


Examples


Examples


Objectives

Create simple well-defined geometry that captures the design intent.

Analyze the sheet bodies/curves for continuity and flow as well as their relationship to surrounding geometry.

Edit the sheet bodies/curves in the

areas that need modifications.


Free Form Modeling ProcessPoint _ based

Curve _based

Sheet _ based

Free Form Feature

Create/Analysis/Edit

Form Feature & Operation Feature

Sew/Thicken/Trim BodySolid Sheet

Extract

Sew/ThickenNote:

Point _based sheet is non parametric

Curve _based sheet is parametric (Smart Sheet) 100%

Sheet _based sheet is most parametric


Free Form Modeling ProcessGeneral Process：

Create & Analysis Spline (Optional) ：

Build “Primary Sheet”：

Build “Transition Sheet”：

Analysis Face ： Analysis → Face

Edit Free Form Feature

Note: Using Edit→ Features → Parameters… or Using MB3 pop menu on node within PNT 。

Build Solid Body：


Curves

Most Free Form Modeling applications will require the use of a previously created edge or generating curve.

It is important to control the complexity of these curves, as the complexity will be passed on to its associated body.


Curves


Curves Points, Lines Conics

Arc, Ellipse, Parabola, Hyperbola, A General Conic

Splines Law curves


A General Conic When 0.001<rho<0.500, ellipse When rho=0.500, parabola When 0.500<rho<0.999, hyperbola


Rho


Law Curve

Law Curve uses a combination of X, Y, and Z components to define a law spline. You can define both two and three-dimensional law splines.


Helix


Splines Splines created in Unigraphics are

NURBS (Non-Uniform Rational B-Splines).

They are created using defining data(points, slope and curvatures), poles or as the result of another operation.


Spline Segments Single segment curve Multiple segment curve

Single segment splines are an excellent first choice to simple model.

Multiple segment splines are used to generate more complex sheet/solid bodies.


Spline Degree The degree of a spline refers to degree

of the polynomial expression that defines it mathematically.

Y=ax3+bx2+cx+d This equation has a degree of 3.


Spline Degree Single segment spline degree = number

of points or poles – 1 Multiple segment spline degree =

number of points or poles – number of segments

Splines can have a minimum degree of 1 and a maximum degree of 24.


Spline Degree A 3 degree multiple segment spline and

a 4 or 5 degree single segment spline are recommend.


Continuity The term continuity refers to the change

in flow of curve. A curve can have C0, C1, C2 continuity.

The continuity types reflect the geometry combinations used in the creation of a curve.


Continuity

C0 continuity is continuous with respect to position and contains a corner.

C1 continuity is continuous with respect to tangency and contains a tangent point.

C2 continuity is continuous with respect to position, slope, and curvature.


Spline By Poles Through Points Fit


By Poles When a spline is defined

"By Poles", it gravitates toward the points you select (referred to as poles), but does not pass through them (except at the endpoints). Curve Type Curve Degree


Through Points

A "Through Points" spline passes through all the points you select (these are the defining points). Curve Type Curve Degree Slopes Curvatures


Slopes

Automatic Slope Vector Component Direction to Point Vector to Point Slope of Curve Angle


Curvatures

Curvature of Curve Enter Radius


Fit

Fit Method Curve Degree


Points


Analysis spline


Edit Splines


Specify constraint


Edit Splines


Example


Example


Free from feature Insert-Surface


Free from feature


Through the Points

Through Point From Poles

From Poles gives you better control of the overall shape and character of the body than does the Through Points. The use of poles also minimizes unwanted undulations in the face of the free form feature.

From Point Cloud This is a simple way to create a sheet body that

approximates a large "cloud" of data points, typically produced by scanning or digitizing.


A Ruled Body

Section strings are on opposing ends of the sheet body.


A Ruled Body Pick Section String 1 and

continue to click OK until the cue line prompts you for Section String 2.

Pick Section String 2 Select an Alignment

string. Type in the appropriate

values for the Tolerance, Temp u Count and Temp u Count


Through Curve Bodies Through Curve option specify rows

defined by section strings. The amount of section strings can vary

between 2 and 150.


Through Curve Bodies

Pick the strings. Set the Patch type. Set the Alignment. Verify the V degree Type a value in the

Tolerance text box. Select the appropriate

constraint for the first and last section strings.


Through Curve Mesh

Through Curve Mesh creates a sheet body by defining primary and cross strings.


Through Curve Mesh Pick the first primary curve. This

can be made up of a series of continuous curves.

Pick the next primary curve. Pick the first cross curve. Repeat

this step until you pick all cross curves.

Pick a Spine String if needed. Select the appropriate constraint

for the first and last section strings.


Swept Features

Swept Features create sheet or solid bodies using a profile swept along one, two, or three guide strings.

You can specify one section string, with a maximum of 400.

If the spine is used, the body limits are controlled by the length of the spine curve.


Section Body

You can use the Section option to construct bodies through cross sections that you define using conic, cubic, and quintic construction techniques.

To comply with industry standards, and to make data transfer easy, the Section option produces a body with B-surfaces as output.

A typical application for sections would be in the design of an aircraft fuselage, or auto body panel.


Section Body

A typical application for sections would be in the design of an aircraft fuselage, or auto body panel.

To comply with industry standards, and to make data transfer easy, the Section option produces a body with B-surfaces as output.


Use the Section Option

You can use the Section option to construct bodies through cross sections that you define using conic, cubic, and quintic construction techniques.


End points-Apex-Shoulder


Slope


Analysis and edit


Analysis


Analysis


Analysis


Extension Sheet Body

The length of extension can be either a specified distance or a percentage of the existing sheet body.


Surface Fillet

This creates an unparameterized sheet tangent to two sheets or faces that is either circular or conical in a cross-sectional shape.


Offset

This creates an offset sheet body from a face of a solid of from another sheet body.


Quilt

You can combine a group of sheet bodies in to one sheet body with one face to simplify operations requiring these faces.


Bridge

Create a sheet that spans a gap between two existing sheets. The resultant sheet matches either curvature or tangency of the two existing sheets.


Thicken Sheet

Create a solid body from a sheet body by giving volume and mass to the sheet.


Mouse Model


Exercise

A beautiful or cool cap

Documents

Shanghai Jiao Tong University 1 UG: Free Form Feature ME 250: Design & Manufacturing I School of Mechanical Engineering