Advanced Sheet Metal Design Using NX Cad Challenge_2_Box Assembly

SHEET METAL BOX ASSEMBLY USING SIEMENS NX

Objective: To learn sheet metal design process and to design a sheet metal box assembly on Siemens NX CAD software.

Introduction:

Sheet metal is most versatile materials in the manufacturing industry. It’s made from steel, aluminium, brass, copper, tin, nickel, titanium etc., Sheet metal is a metal with a small thickness ranging from 0.5-6mm.Sheet metal is one of the most versatile in the manufacturing industry.

Design methodology:

The box assembly is created in a single part document as different bodies. The box consists of different bodies like the box, the lid and the hinges. The box assembly consists of repeated features like flanges, bends, cut-outs, holes, dimples and beads. The design methodology used for the box assembly can be summarized as flow chart below:

Description of the features:

• Sketch
• Tab
• Flange
• Hem Flange
• Break Corner
• Closed corner
• Unbend
• Normal Cut Out
• Dimple
• Bead
• Rebend
• Mirror Body
• Mirror feature
• Unite
• Flat Pattern
• Draft

• Sketch:

Sketches are the basic clement or we can say the foundation of a design model. A base sketch is needed to perform most of the operations in Sheet Metal designing including Tab, Dimple, Bead, Hole, Contour Flange etc. The sketches can be created using the various sketch tools provided top left corner of the interface.

• Tab:

Normally tabs are the Basic feature in NX sheet metal designing process. Tab Command extrude a sketch along a vector by a thickness value or by adding material to existing face and bend regions of a sheet metal part

• Flange:

A flange feature consists of a face and bend connected to an existing face along a straight edge. To add a flange feature, we select one or more edges. and specify the size and position of the material added.

• Hem:

Flange Hemming is a sheet metal forming operation in which the edge of the sheet is folded back on itself. It serves several purposes: to fasten two sheet metal parts to improve the appearance of edges and to increase the part stiffness.

• Mirror Body:

Mirror body feature allows the solid body to get copied and mirrored with respect to a plane Here, the design made till this stage is a half part of the box which is then mirrored with respect to YZ plane. A black edge appears on the face of the side flange representing the separation between two bodies

• Unite:

After the mirror of the body is completed, it results in two separate bodies which is not the intended one. Unite allows us to combine the bodies and make one single body. After applying the Unite feature, the black edge on the face disappears.

• Break Corner :

The command used to break or round the corners in a solid body in order to avoid accidents by the sharp edges

• Closed :

Corner The command use to close the corners in between two flanges or bends is the closed corner feature.

• Unbend:

Use the Unbend tool to unbend one or more curved surfaces such as Bends or Curved walls to a flat configuration in a Sheet Metal part .For performing a Unbend feature its must to define a fixed planar face or edge. We can either select bend geometry individually or automatically select all the bend geometry.

• Normal Cut Out:

Normal Cut out command extract volumes from sheet metal by using sheet metal production principles. Cutting faces will be perpendicular to the sheet metal surface

• Dimple:

Use this command to create a raised dimple feature in a sheet metal part. The dimples can be placed on any flat face including flanges and will extend in the direction of the face. The dimple feature will be governed by the settings defined in the Options Form. Dimple also helps the sheet mcatal part to increase its stiffness

• Bead:

Beads are the features added in sheet metal components in order to increase the stiffness of the component. Beads require a sketch in order to apply the feature. It can be either an open or closed profile. For this casing design project. four small beads are applied in the symmetric positions as shown in the image below.

• Rebend :

Command use to re bend the un bended parts along with the feature applied after the Unbend. After addition sketches and features the sheet metal is to be re bended to its required shape. This operation is done by box selecting all the features and clicking the ReBend command.

• Flat Pattern:

Flat pattern is the representation of the entire sheet metal component in the 2D form with all the bends, cut-outs, holes, and additional features in the form of lines or edges. The flat pattern ensures the ability to cut the sheet metal out of the raw sheet metal plate. It removes the possible errors such as interference or collision within the same component.

• Draft:

After the modelling the manufacturing of the component a technical 2D drawing of the component with accurate dimensions or scales denoted. For achieving this we are using the command Draft.

Procedure:

The Box assembly is created as different bodies such as

• Box
• Lid
• Hinge 1
• Hinge 2

The following is the procedure to obtain the desired results:

• Create a Base sketch of rectangle of 150*200 and perform the Tab feature with 1 mm thickness.

• Create Flanges from the 2 edges with 200mm length and 10 mm bend radius as shown

• Create another flanges from the edge of the earlier created flanges with 70 mm length and same 10 mm radius.

• Close the two corners using the closed corner set the type to corner and relief.

• Create two flanges one over the other on the edge and apply length of 5mm and 0.5 bend radius.Do the same operation on the opposite edge.

• Create two hem flanges on the edges of the previously created flanges with 5 mm length. Set the flange type to open.

• Mirror the body about the YZ plane and ensure all the option in the feature menu is ticked.

• Unite the mirrored parts in to one.

• Using proper sketch create a dimple with required depth on the side face of the box

• Mirror it to the opposite side.

• Create another dimple on the bottom side using the sketch

• Unbend and rebend the body also can use flat pattern this would complete the box part

• Using circle create a bead on one of the bottom corner and mirror it to all three corners

• Apply Hem Flanges on the top outer edges of the box

• Create a datum plane with 203 mm away from origin, linear to XY plane and create a sketch of the lid by converting the upper edges of the box and create a tab of 2 mm thickness

• Then create 2 flanges on the 2 edges of the lid with a length as shown and it completes the lid part.

• Create a Tab using sketch of 55 mm height and 20 mm width on the right side face of the box

• Break the corner with 10 mm radius using Break corner command

• Create 2 flanges with 4 mm length & angle as required shown in figure.

• Create a open loop type hem flange on the edge of newly created flange with a sweep angle 325 degree and bend radius as required.

• Unbend the body and perform normal cut out with given sketch.

• Rebend the body and mirror the body to opposite side this completes the hinge-1.

• Create a new tab on top surface of the lid using a rectangle and use break corner.

• A flange of required length and angle is created on the edge of the new tab.

• Create a open loop type hem flange of 325 degree sweep and required bend radius.

• Unbend the body and create a normal cut out using proper sketch.

• Rebend the body back to its required shape.

• Flat pattern and its drafting is shown below:

• The modelling of box assembly is completed here. The different view are given below

Conclusion:

We have succesfully created the box assembly using Siemens NX CAD.