Week 14 challenge

AIM:

To Assemble and apply GD&T to the butterfly valve assembly drawing using SIEMENS NX CAD.

OBJECTIVE:

• The objective is to design & assemble the components of the butterfly valve using various modeling & assembly features in SIEMENS NX CAD.
• Developing drawing sheets of butterfly valve assembly using various drafting tools.
• Understanding various GD&T symbols and applying the same to the butterfly valve assembly.

INTRODUCTION:

A butterfly valve belongs to a family of QUARTER-TURN valves. A butterfly valve is a flow control device that incorporates a rotational disk to control the flowing media in a process. The disk is always in the passageway, but being relatively thin, it offers little resistance to flow.

In operation, the valve is fully opened or closed when the disc is rotated a quarter turn. When the valve is closed, the disc is turned so that it completely blocks the passageway. And, when the valve is open the disc is rotated a quarter turn/90 deg so that it allows the unrestricted flow of the fluid. The valve may also be opened incrementally to throttle flow. Many different types of valves are used in flow control. They are used for a variety of reasons, such as phase (liquid or gases), pressure, piping restrictions, and solids content. Other valves are chosen for their capability to open and close in a quarter turn.

Early use of butterfly valves focused on water applications, but new designs and component materials have allowed them to be utilized in growing industrial fluid applications. Presently, butterfly valves can be found in almost every chemical plant handling a variety of diverse fluids.

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. This article is based on that standard, but other standards, such as those from the International Organization for Standardization (ISO), may vary slightly. The Y14.5 standard has the advantage of providing a fairly complete set of standards for GD&T in one document. The ISO standards, in comparison, typically only address a single topic at a time.

Parts of Butterfly Valves:

• Butterfly valve body
• Shaft
• Disc Plate
• Lever
• Retainer
• Nut
• Screw

BODY OF BUTTERFLY VALVE

• Butterfly valves generally have bodies that fit between two pipe flanges. This butterfly valve has a lug body design consisting of protruding lugs that provide bolt holes matching those in the pipe flange.
• Create two circles of required diameter and use Extrude command to form a cylindrical body/housing.
• On that cylindrical body create three lugs with holes in them. This will help us connect the butterfly valve to the pipe flanges. We have created the lugs on the mid-plane and then Extruded them with reference to the mid-plane (i.e. symmetrical value).
• Using the Move object command, we created similar lugs on the outer surfaces of the body with the help of lugs created earlier.

• 
• Create a new datum plane and draw a circular sketch of the required diameter. Extrude this sketch up to the cylindrical body using extrude command.
• Then create counterbored holes in the body using the Hole command so that we can insert shaft/stem in it. Specify all the required values of diameter and hole depth accordingly.

• Create another datum plane on the other side of this newly created feature. Develop a circular sketch on this new plane and then extrude it up to the cylindrical body.

• Combine all the features to form a single object using Unite command.

DRAWING SHEET WITH GD&T:

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 modelling 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
• Chamfer

PROCEDURE:

• Initially, Select the XY coordinate and click on the line tool from the Sketch tab.
• 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:

• A2 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.

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 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 disc plate:

• Sketch
• Extrude

PROCEDURE:

• 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) are 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.

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

PROCEDURE:

• 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.

Lever

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 lever:

• Sketch
• Extrude

PROCEDURE:

• 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.

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 surface which comes in contact with the lever. Perpendicular tolerance is applied to the hole or the thread and is defined as datum B. Size tolerance is also applied to the thickness of the nut.

Features used to create Nut:

• Sketch
• Extrude
• Revolve

PROCEDURE:

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

BUTTERFLY VALVE ASSEMBLY:

• After designing every component. we have created the final assembly model using SIEMENS NX CAD.

Features used to assemble:

• Move component
• Assembly constrains
• Touch
• Infer center/axis

MODEL VIEWS:

DRAWING SHEET WITH GD&T:

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.