Week 14 challenge
objective: The objective of this project is to model a butterfly valve and to apply GD&T to the various parts of the butterfly valve and the assembly.
Introduction
Siemens NX 12: NX, formerly known as "Unigraphics", is a sophisticated high-end CAD/CAM/CAE, which has been owned since 2007 by Siemens PLM Software in 2000.
It is used, among other duties, for:
Design (parametric and direct solid/surface modeling)
Engineering analysis (static; dynamic; electro-magnetic; thermal, using the FEA technique; and fluid, using the finite volume method).
Manufacturing completed design by using included machining modules.
Butterfly Valve: A butterfly valve is a valve that isolates or regulates the passage of a fluid. The closure mechanism is a disk that rotates. A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is completely open or closed when the disc is rotated a quarter turn. The "butterfly" is a metal disc affixed on a rod. When the valve is closed, the disc is turned so that it completely seals off the passageway. When the valve is entirely 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 restrict flow.
GD & T: Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It employs 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 required on each controlled feature of the part. GD&T is used to define the nominal (theoretically perfect) geometry of components 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 characterise the symbols and define the rules used in GD&T. One such standard is the American Society of Mechanical Engineers (ASME) Y14.5
Parts of Butterfly Valves
Butterfly valve body Shaft Disc Plate Lever Retainer Nut Bolt Commands Used
Line: This feature enables us to create a straight line. The line can be a continuous line or a construction line.
Circle: This feature allows us to create circles.
Rectangle: This feature enables us to create squares or rectangles.
Arc: This enables us to create an arc.
Trim: This is used to trim designs.
Extrude Bose: This feature enables 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 incisions, or revolved surfaces. Axis of revolution can be 3d illustration.
Circulr pattern: This allows us to create a pattern in a circle
Fillet: This is used to create circular boundaries.
Hole: A Hole feature is used to produce 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 primary part of the butterfly valve. The body connects to two pipelines on its two sides and it regulates to flow. For the creation of this part, straightforward features like to revolve, extrude, and move objects are used in the modeling application of NX.
Features used to construct the Butterfly Valve :
Sketch Extrude datum plane and coordinate counterhole Bore unite Methodology:
Initially, Select the XY coordinate and click on the line tool from the Sketch menu.
After that sketch is Extruded, the ears of the butterfly valve are drawn and are copied on both sides of the cylindrical component, 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 construct a counterbore on that cylindrical surface.
Finally, three holes are created for mounting of the body and then, the part is preserved.
2. Shaft
It is another essential component of the butterfly valve. It inserts into the body of the valve and rests perpendicular to the direction of flow. It retains the disc inside the body and is clamped with the lever outside the body. It is constructed 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 implemented 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 rests, and position tolerance for the cylindrical body of the shaft concerning the defined datums. Composite position tolerance is implemented in the case of disc positioning holes as it repeats creating a pattern.
Features used to create Shaft :
Sketch Revolve Datum plane Extrude chamfer Methodology:
Initially, Select the XY to coordinate and click on the line tool from the Sketch menu.
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 in diameter are constructed in the rear recess portion of the shaft.
Drafting Methodology
A1 size of the sheet is used to produce a drawing of the shaft.
Here, only two datums are used as one degree of freedom is required for the efficient functioning of the shaft.
Datum A1 and A2 are given to the component 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 essential for the functioning of the shaft.
3. Disc Plate
This disc plate is the primary component of the butterfly valve which regulates the flow in the valve. The orientation of this disc determines the discharge rate of the fluid. It is not precisely circular, rather it is elliptical in profile. The holes in it serve to position it properly on the shaft created earlier. A simple feature like extrude can produce this part in NX. To implement 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 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 employed to reduce the manufacturing cost.
Features used to create Shaft :
Sketch Extrude Methodology:
The 3D model of the Retainer is created with the aid of the 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 aid 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, and C are applied.
Datum target areas A1, A2, A3(Primary datum-A) are applied to one side of the Retainer which comes in contact with the upper component of the body.
Datum-B is applied to one of the openings of the retainer where the bolt is inserted.
Datum-C is applied to the other opening of the retainer.
Finally, the other tolerances like Perpendicularity, position, the profile of a surface are applied to the other openings and the surface of the retainer, the drawing is saved in the required folder.
4. Lever
A lever is a handle that is used to rotate to modulate the flow. It is attached to the shaft with the aid of a key to fix 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 conduit. It is created using simple features like extrude in NX after the appropriate base sketch is created. For the application of GD&T on the lever, a section view is also created to demonstrate how different datums are defined and tolerances are provided. Position tolerance is applied to the appropriate holes after the perpendicular tolerance is applied to the first hole. To control the key slot, minor tolerance is applied to its width of it. Profile tolerances are provided to the surfaces which come to contact with other components as per the requirement.
Features used to create Shaft :
Sketch Extrude Methodology:
With the help of a 2D drawing of the lever, the 3D model of the lever is designed with the help of various operations.
2. The diverse operations used are Trim, Extrude, circle, Tangency, etc.
3. Finally, the part is saved in the required subdirectory.
Drafting Methodology
After the design of the lever, the drafting of the lever is done for employing the GD&T.
Three datums A, B, and 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 affixed to the hole where the bolt comes in contact.
C datum- It is applied to the other hole to completely constrain the portion.
Finally, all the other tolerances like position, Flatness, and Profile of a surface are applied to the part.
5. Retainer
This part serves 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 correct functioning of the disc inside the body. The construction of the retainer plate involves only a simple feature like extruding in NX. For the GD&T application in the retainer plate, analogous steps are followed as in the case of the disc. Primary, secondary, and tertiary datums are defined appropriately as per the design intent, and datum targets are applied to the holes. Perpendicular and position tolerances are employed 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 aid of the 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 aid 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, and C are applied.
Datum target areas A1,A2,A3
Primary datum-A is affixed to one side of the Retainer that contacts the upper body region.
The Datum-B marking is affixed to one of the retainer's holes where the bolt is inserted.
Datum-C is applied to the other retainer opening.
The remaining tolerances, such as Perpendicularity, position, and surface profile, are then applied to the other openings and the retainer's surface, and the drawing is saved in the required folder.
6. Nut
It is the final component that serves to secure the lever to the stem. It allows for positional maintenance or disassembly as needed. It is constructed using NX's straightforward extrude and revolve functions. To implement GD&T to this nut, the contact surface with the lever is defined as the primary datum. Datum B defines the perpendicular tolerance applied to the opening or thread. Also subject to size tolerance is the thickness of the fastener.
The following elements were used to produce the Shaft:
Methodology: Sketch Extrude Rotate
Using the specified dimensions, the Nut is modeled in three dimensions.
Initially, the hexagonal nut is extruded with a 25mm depth and a 37mm diameter opening.
Lastly, a fillet with a radius of 10 mm is produced using the revolve option.
Drafting Methodology
Datum A is assigned to the Nut surface that will come into contact with the Lever surface.
The Hole is given Datum B.
Finally, additional surface and feature tolerances are specified for Nut.
Assembly
Following the design, all models should be assembled with the proper constraints. The assembly is constructed by first positioning the body and then mating other parts to it using the various joints provided by NX. First, the shaft and disc are joined together with the screws in place to produce a sub-assembly which is then joined to the body in position. After mating the retainer plate with the body, fasteners are used to secure them together. After that, the lever is mated to the shaft in a position that is then fixed after the fastener is mated with the shaft.
Features used to Assembly
Infer Axis/center Touch Align Concentric Move Component Methodology
The Assembly file is loaded in NX CAD.
The preceding components are appended to the assembly file.
Now, one by one component is assembled using the Move part command and assembly constraint command.
Different constraints are used to assemble the butterfly valve, such constraints are Infer Axis, Touch, and Align.
Finally, the assembly of the butterfly valve is saved in the folder where all the other components are saved.
Drafting Methodology
The earbuds of the butterfly valve receive the datum target areas A1, A2, and A3.
Datum target area A2 and A3 are given with perpendicular tolerance and Position tolerance respectively.
Sub datum D is given to the third ear.
Finally, other tolerances are given to the surfaces and features of the Butterfly Valve.
Conclusion
In this exercise, 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 communication with the manufacturers effective and efficient. Hence, a design process in a true industrial manner is followed in this design of the butterfly valve understanding the design process more with the application of GD&T with industrial standards.