Challenge

Advanced Sheet Metal Design Using NX Cad Challenge_2_Box Assembly

RRitesh Shrivastava27 Aug 2022

OBJECTIVE:

Learn to design a sheet metal Box Assembly in an industrial manner by using Siemens NX.

INTRODUCTION:

Sheet metal parts are widely used in machinery, enclosure, brackets, and automobile due to their various advantages. The parts are normally manufactured with a brake press. Sheet metal is nothing, but thin sheets made from metal of sizes ranging from 0.6 to 6mm. In this project, I used the NX CAD tool for designing the sheet metal box. NX CAD is used as a design tool in more than 85% of sheet metal industries.

DESIGN METHODOLOGY:

Box assembly is designed by keeping industrial procedure in mind to follow the design intent. The design methodology used for this project is summarized in the below flowchart.

DESCRIPTION:

All the features used during designing the box assembly are described below.

Sketch:

For creating any sheet metal surface, we must first make a sketch. So, I started with creating a simple rectangular base sketch for creating the tab. Other than tab, various sketches are also made on different planes or faces for creating another different part during design.

Tab:

A tab is the first parent feature in sheet metal designing using the Siemens NX tool. All the other features are usually based on a tab. In this casing design, I created the tab by using the sketch on the XY plane

Flange:

The flange is used to add extra material to the existing edge at any angle and of any size. For this project of box assembly design, I added four flanges on different edges, firstly I added two flanges with a 200 mm length normal to the XY plane and then another two flanges with a length of 70 mm were added normally to XZ plane.

Closed corner:

The close corner feature is used to close a corner where two adjacent flanges meet by extending the bends and flanges. For this box assembly, I used the closed corner feature twice to close the open corners at the bottom side of the flanges.

Flange for fastening:

For fastening or connecting the two flanges on side of the box assembly I first created a flange without length and then another flange having a dimension of 6.5 mm length with an outside bend.

Hem flange:

Hem flange feature is used to modify the model by folding the edge of a flange. The main purpose of this feature is to increase the stiffness and for safe handling. For this box assembly, I created the hem flanges with a 0.5mm bend radius and a length of 4 mm.

Mirror body:

As of now half part of the box assembly was designed remaining half part was designed by using the mirror body feature, which saves a lot of time. I used to mirror the body feature to mirror the half body about the YZ plane.

Unite:

Unite feature is used to combine two different bodies which are in contact. I used to unite feature to combine the body before the mirror and after the mirror feature.

Dimple:

Dimple is the feature that lifts the area of the model inside the sketch that simulates a stamping tool. Generally, it helps to strengthen the flat structure. For this box assembly, I first created an appropriate sketch, and then I used the dimple feature to create the final dimple on one side of the box assembly. The same dimple was mirrored on the other side of the box. One rectangular dimple was also added at the bottom of the box assembly for the purpose of a perfect landing.

Beads:

Beads are similar features to dimples the only difference is that by using dimples we lift an area while in beads we lift the contour of the sketch. It is also added to strengthen the component. For this project, one small bead was created near the top left corner having a diameter of 15 mm. then it was mirrored along the XZ plane and YZ plane to obtain the four beads on each corner.

Hem flange:

At this stage, the hem flange is used to create a rounded edge at the top which helps in easy handling.

Lid creation:

For creating the lid for the box, a datum plane was created at a distance of 202 mm from the XY plane. The sketch was created by taking the reference of the edges from the top view of the box design. Then the base tab was created with the sketch to create the lid.

Flanges:

For a closing box with proper alignment flanges having a web length of 3 mm were added to both sides.

Tab for hinge:

A rectangular tab was created on the YZ plane.

Break Corner:

The break corner feature is used to smoothen or chamfer the sharp edges of the sheet metal part. This action helps to prevent stress concentration and fracture breaking. For this box assembly, I used a blend with 10 mm.

Flanges:

For obtaining the required result two flanges of 40-degree bend each of length 4 mm were created adjacent to each other.

Hem flange:

For creating the hinge for the box lid an open bend outside type flange with a radius of 5 mm and sweep angle of 325 degrees was added at the end of the previous flange.

Unbend:

Unbend feature is one of the most powerful features in NX. In industry, we have to mark all the marking and sketch on flat sheet metal before it went to actual operations, so this unbend feature allows us to do that activity in Siemens NX software. For this project of box assembly design, I used this feature 2 times to mark the further operations/sketches.

Normal cutout:

The normal cutout feature uses cutting material by projecting a sketch onto the model and then removing material perpendicular to the faces intersected by the projection. For this box assembly, I used the normal cutout feature to remove two rectangular areas which leads to forming the hinge barrels on both sides.

Rebend:

Rebend feature is used to restore the unbend feature to its previous bent state along with any features added after the unbend feature. This is done by using rebend feature and selecting all the bends carefully in the order they unbent.

Mirror body:

After that, the body of the hinge was mirrored about the YZ plane, and a similar one formed on the other side.

Tab for creation of upper hinge:

A single rectangular tab was created on the top surface of the lead.

Flanges:

Similar to the bottom hinge, a flange was also added to the upper tab at 45 degrees with a length of 13 mm.

Hem flange:

Like the earlier process, an open hem flange of radius 5 mm with an angle of 325 degrees was created.

Normal cutout:

As per the required material is removed in the form of four rectangles by using the normal cutout feature for creating the hinge barrel.

Rebend:

Part of the upper tab which was unbent for creating the hinge barrel was rebended and the design for box assembly completes.

Flat Pattern:

The flat pattern feature allows us to convert 3D sheet metal components into 2D form in Siemens NX software. By using this flat pattern feature we can easily avoid errors like interference or collision.

Drafting:

After designing 3-d model for further process of manufacturing we have to convert the entire sheet metal component into 2D form for easy interpretation. For this project of box assembly, a drawing is created out of the flat pattern.