Week 14 challenge

ASSEMBLY OF THE BUTTERFLY VALVE

Objective:     

• To design of Butterfly Valve in appropriate dimension with the application of GD&T - ASME Y14.5 2009.
• To assemble all the individual parts of the butterfly valve by assigning suitable assembly constraints.
• To understand the concept of geometric tolerance and dimensioning. 

Softwares Used

• Siemens NX 12

Introduction

     Butterfly Valve: 

• A butterfly valve is a valve that isolates or regulates the flow of a fluid. The closing mechanism is a disk that rotates.
• A butterfly valve is from a family of valves called quarter-turn valves.
• In operation, the valve is fully open or closed when the disc is rotated a quarter turn. The "butterfly" is a metal disc mounted on a rod.
• When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid.
• The valve may also be opened incrementally to throttle flow.

     GD & T:

• Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances.
• It uses symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describe nominal geometry and its allowable variation.
• It tells the manufacturing staff and machines what degree of accuracy and precision is needed on each controlled feature of the part.
• GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features. 
• There are several standards available worldwide that describe the symbols and define the rules used in GD&T. One such standard is the American Society of Mechanical Engineers (ASME) Y14.5 

Design methodology Flowchart:

Parts of Butterfly Valves

• Butterfly valve body 
• Shaft / Stem
• Disc Plate 
• Lever / Handle
• Retainer 
• Nut
• Bolt

Commands Used

• Line: This feature allows us to create a straight line. The line can be a solid line or a construction line.
• Circle: This feature allows us to create circles.
• Rectangle: This feature allows us to create squares or rectangles.
• Arc: This allows us to create an arc.
• Trim: This is used to trim sketches.
• Extrude Bose: This feature allows us to create solid bodies.
• Revolve: Revolves add or remove material by revolving one or more profiles around a centreline. You can create revolved boss/bases, revolved cuts, or revolved surfaces. Axis of revolution can be 3d sketch.
• Circular Pattern: This allows us to create a pattern in a circle
• Fillet: This is used to create circular edges.
• Hole: A Hole feature is used to create holes on the model.
• Unite: Unite is used to convert two or more solid bodies into one solid body

Design and Methodology

1)Butterfly valve body

• The body is the housing for the internal components and it is the main part of the butterfly valve.
• The body connects to two pipes on its two sides and it regulates to flow.
• For the creation of this part, simple features like to revolve, extrude, and move objects are used in the modeling application of NX.

Features used to create the Butterfly Valve :

• Sketch
• Extrude 
• datum plane and coordinate 
• counterhole Bore  
• unite 

Methodology:

Initially, Select the XY coordinate and sketch tab create the inner and the outer circle of the body and finish sketch.

Now extrude the sketch to the required lenght to create a solid component. 

After that sketch is extruded, the ears of the butterfly valve are drawn and are copied on both sides of the cylindrical portion, then it is extruded.

Now a new plane is created on the surface of a cylinder using the datum plane option and a cylinder is created on that plane.

Then, the Hole command is used to create a counterbore on that cylindrical surface. Apply unite to unite all the extruded components.

Finally, three holes are created for mounting of the body and then, the part is saved.

2) Shaft 

It is another important component of the butterfly valve. It inserts into the body of the valve and sits perpendicular to the direction of flow.

It holds the disc inside the body and is clamped with the lever outside the body.

It is created using simple features like revolve and extrudes features in the NX modeling environment.

After the part creation is completed, the drawing is created in the drafting application of NX, and GD&T is applied using the features of NX.

For this shaft, position tolerance should be given to the holes which hold the disc, a profile of the surface should be applied to the surface where the disc sits, and position tolerance for the cylindrical body of the shaft concerning the defined datums.

Composite position tolerance is applied in the case of disc positioning holes as it repeats creating a pattern.

Features used to create Shaft :

• Sketch 
• Revolve
• Datum plane 
• Extrude - subtract
• Chamfer

Methodology:

Initially, select the sketch tab create the base drawing of shaft without considering the recess areas.

Revolve command is used to get the desired shape of the shaft.

Then Extrude command is used to create a recess portion in the front and rear portion of the shaft.

Finally, two holes of 12.5mm diameter are created in the rear recess portion of the shaft.

Drafting Methodology 

• A1 size of the sheet is used to create a drawing of the shaft.
• Here, only two datums are used as one degree of freedom is required for efficient working of the shaft.
• Datum A1 and A2 are given to the part which comes in contact with the body of the butterfly valve.
• Datum B is given to the base of the shaft.
• Different tolerances are given to some features which are important for the functioning of the shaft.

3) Retainer

This part helps to retain or to fix the shaft with the body of the butterfly valve.

It prevents the shaft from coming out of the body and keeps it in position for the proper functioning of the disc inside the body.

The creation of the retainer plate involves only a simple feature like extrude in NX.

For the GD&T application in the retainer plate, similar steps are followed as in the case of the disc.

Primary, secondary and tertiary datums are defined properly as per the design intent, and datum targets are applied to the holes.

Perpendicular and position tolerances are applied to lock the DOF of the retainer in position. A profile tolerance is also applied to control the upper surface of the retainer.

Features used to create Shaft :

• Sketch  
• Extrude 

Methodology: 

The 3D model of the Retainer is created with the help of given dimensions.

Initially, the concentric holes of 200mm and 56mm diameter are drawn and the other 3 circles of 20.3 mm diameter are drawn with the help of 150mmBCD by using the Pattern option.

Finally, the 2D sketch is extruded and the part is saved in the required folder.

Drafting Methodology

• After the modeling, the part is taken to the drafting portion where the three datums A, B, C are applied.
• Datum target areas A1,A2,A3
• Primary datum-A is applied to one side of the Retainer which comes in contact with the upper portion of the body.
• Datum-B is applied to one of the holes of the retainer where the bolt is inserted.
• Datum-C is applied to the other hole of the retainer.
• Finally, the other tolerances like perpendicularity, position, the profile of a surface are applied to the other holes and the surface of the retainer, the drawing is saved in the required folder.

4) Disc Plate

This disc plate is the main component of the butterfly valve which regulates the flow in the valve.

The orientation of this disc determines the flow rate of the fluid. It is not perfectly circular, rather it is elliptical in profile.

The holes in it help to position it properly on the shaft created earlier.

A simple feature like extrude can create this part in NX.

To apply GD&T for this part, the primary datum is defined on the surface where it comes in contact with the surface of the shaft, and perpendicular tolerances are applied as per the requirement.

As the cost increases, while machining the entire contact surface, small circular datum targets are created and GD&T is applied to reduce the manufacturing cost.

Features used to create Shaft :

• Sketch 
• Extrude 

Methodology:

The 3D model of the disc is created with the help of given dimensions.

Initially, a ellipse of major and minor diameter 102.5mm and 96.9mm respectively is created, two screw holes of dia 12.5mm seperated by a distrance of 100mm is created.

Finally, the 2D sketch is extruded to 6mm and the part is saved in the required folder.

Drafting Methodology

• After the modeling, the part is taken to the drafting portion where the three datums A, B, C are applied.
• Datum target areas A1, A2(Primary datum-A) are applied to one side of the disc which comes in contact with the shaft.
• Datum-B is applied to one of the holes of the disc where the bolt is inserted.
• Datum-C is applied to the other hole of the disc.
• Finally, the other tolerances like the profile of a surface is applied to the surface of the disc, the drawing is saved in the required folder.

5) Lever / Handle

A lever is a handle that is used to rotate to regulate the flow. It is attached to the shaft with the help of a key to fixing it in position concerning it.

So when it is rotated, the shaft rotates which in turn rotates the disc and regulates the flow inside the pipe.

It is created using simple features like extrude in NX after the proper base sketch is created.

For the application of GD&T on the lever, a section view is also created to show how different datums are defined and tolerances are provided.

Position tolerance is applied to the proper holes after the perpendicular tolerance is applied to the first hole.

To control the key slot, small tolerance is applied to the width of it.

Profile tolerances are provided to the surfaces which come to contact with other parts as per the requirement.

Features used to create Shaft :

• Sketch  
• Extrude 

Methodology: 

With the help of 2D drawing of the lever, the 3D model of the lever is designed with the help of different operations.

The different operations used are Trim, Extrude, circle, Tangency, etc.

Finally, the part is saved in the required folder.

Drafting Methodology

• After the design of the lever, the drafting of the lever is done for applying the GD&T.
• Three datums A, B, C are applied to the part.
• A datum- To the bottom surface of the lever that comes in contact with the other surface.
• B datum- It is applied to the hole where the bolt comes in contact.
• C datum- It is applied to the other hole to completely constraint the part.
• Finally, all the other tolerances like position, Flatness, Profile of a surface are applied to the part.

6) Nut 

It is the last part that helps to fix the lever in position with the stem.

It allows to keep it in position or to disassemble whenever required.

It is created using simple extrude and revolve features in NX.

To apply GD&T for this nut, the primary datum is defined on the hole.

Perpendicular tolerance is applied to the surface which comesin contact with the lever and act as datum B.

Size tolerance is also applied to the thickness of the nut.

Features used to create Shaft :

• Sketch  
• Extrude
• Revolve  

Methodology: 

The 3D modeling of the Nut is created with the given dimensions.

Initially, the hexagonal shaped nut is extruded with a depth of 25mm and a hole of 37mm diameter.

Finally, the fillet of radius 10mm is provided by using the revolve option.

Drafting Methodology

• Datum A is given to the Hole.
• Datum B is given to the bottom surface of Nut which is going to come in contact with the Lever surface.
• Finally, other tolerances are given to the surfaces and features of Nut.

Assembly

After the design, all the models should assemble with appropriate constraints.

The assembly is created by first placing the body in position and mating other parts to it with the application of different joints provided in NX.

First, the shaft and disc are joined together with the screws in place to create a sub-assembly which is then joined to the body in position.

The retainer plate is then mated with the body and screws are used to fix them. After that, the lever is mated to the shaft in a position that is then fixed after the nut is mated with the shaft.

Features used to Assembly 

• Infer Axis/center
• Touch Align
• Concentric 
• Move Component 

Methodology

The Assembly file is opened in NX CAD.

The above parts are added to the assembly file.

Now, one by one part is assembled using the Move part command and assembly constraint command.

Different constraints are used to assemble butterfly valve, such constraints are Infer Axis, Touch, Align.

Finally, the assembly of the butterfly valve is saved in the folder where all the other parts are saved.

Drafting Methodology

Datum target area A1,A2 and A3 is given to the ears of the butterfly valve.

Datum B, C and D are applied to the holes of the ears, datum B withperpendicular tolerance and C & D with Position tolerance.

As the valve connects the two pipes, the ear holes in the other end is also position toleranced with respect to datum B, C & D individually.

Finally, other tolerances are given to the surfaces and features of the Butterfly Valve.

Conclusion

In this project, a butterfly valve is designed and assembled in parametric CAD software, Siemens NX. GD&T according to ASME Y14.5 is applied at every stage of the part design process in order to make the communication with the manufacturers effective and efficient. Hence, a design process in a real industrial manner is followed in this design of butterfly valve understanding the design process more with the application of GD&T with industrial standards.