Advanced Sheet Metal Design Using NX Cad Challenge_2_Box Assembly

Tittle : To design and modelled Box assembly using siemens NX-CAD

Objective :    

                       1.) To understand the concept behind design 

                       2.) To get familiar with NX-CAD sheet metal workbench

Introduction :  

 Sheet Metal : It is a comprehensive cold working process for sheet metal (Usually below 6mm).Thicknesses of this sheet  can vary significantly extremely thin to the thicker sheets,  thinner sheets are generally considered as foil or leaf and pieces thicker than 6 mm (0.25 in) are considered plate steel. There are many different metals that can be made into sheet metal, such as aluminium, brass, copper, steel, tin, nickel and titanium. Sheet metal is used in automobile and truck (lorry) bodies, airplane fuselages and wings, medical tables, roofs for buildings (architecture), and many other applications. Generally there are two types of region in any sheet metal are web and bend region. COMMON BENDING OPERATIONS GENERALLY used are Press brake forming, Air bending ,Roller bending , Beading,Flanging , Hemming , Roll forming , Stretch forming,Deep drawing.

NX-CAD Sheet metal Workbench : With Sheet metal CAD tools, you can apply standard values, such as material thicknesses and bend radii, based on industry or company best practices. With folding and unfolding capabilities, you can work with models at any stage of the fabrication process. Sheet metal parameters create accurate flat patterns for documentation and manufacturing.

Methodology : 

                            To achieve a final product the methodology is followed is 

                                                                                                                              

                                                                                                                                                                                                                  fig.1

Features Used : 

1.TAB: Usually this feature is the first feature  used to create a base feature by extruding a sketch along a vector by a thickness value or adding a material to a plane face. The sketch can be of any shape only if it has to be closed. The thickness to the base plate is automatically determined by the metal parameters which in sheetmetal workbench it refers to as a global value, we can add different thickness manually as a local value. 

                                                                                                                              

                                                                                                                                                                                                                           fig.2

2.FLANGE:  This feature adds a flange/wall on edge; it can be at an angle to a planar face and adds a bend between the two adjacent edges. First we need to select the edge then specify height and angle. Thickness in this feature is automatically assigned by its base plate and bend radius is also predefined in sheet metal parameters.If it is required to change bend radius we need to select on advance flange. For web region length of the flange and angle at which flange is situated for example if the flange is perpendicular to base plate then the angle we need to specify is 90 degree. There are many types of flange for example we can start the flange from the centre or we can give some offset values from both the ends and many more.

                                                                                                                       

                                                                                                                                                                                                                         fig.3

3.DIMPLE: It is a punching tool in which it lifts an area of the model inside a closed sketch. The depth of this punching is given according to its application. Other parameters that needs to be added is punch radius and die radius, punch radius is in the upper side and die is situated at the bottom of the base plate. 

                                                                                                                        
                                                                                                                                                                                                                            fig.4

4.UNBEND: Usually this feature is used to create some additional features on the flanges by flattening a bend by first selecting the flat surface and then clicking on the bend region. 

                                                                                                                       
                                                                                                                                                                                                                     fig.5

5. BREAK CORNER:  For better manufacturing process and to make part more handy.In this it Rounds a sharp corner by selecting an edge and then specifying the radius of it. 

                                                                                                                   
                                                                                                                                                                                                                          fig.6

6. NORMAL CUTOUT: This command is a cutting tool, it removes the material. It cuts the sheet metal part by sketching the profile for cutout and then it cuts the sheet perpendicular direction to the sketch plane.

                                                                                                                   

                                                                                                                                                                                                                              fig.7

7. Hole : First step is to locate the point by sketching on the plane the points are the centre of the hole. Then click on hole feature on the ribbon tab and select the point that you sketch earlier and give the diameter.

                                                                                                         

                                                                                                                                                                                                                               fig.8

8. REBEND: Once all the features are done on the flanges then in order to rollback this command is used.It restores the bend by just selecting the bend region.

                                                                                                                           

                                                                                                                                                                                                                                                fig.9

9. BEAD: It is a stamping tool that lifts a material along a counter of a sketch that simulates stamping a tool. In these parameters like depth of the stamping, radius of the stamping and die radius need to be specify correctly in order to work on this properly.

                                                                                                   

                                                                                                                                                                                                                                 fig.10

10. FLAT PATTERN: Creates flat pattern feature from the formed sheet metal part. It is generally used for adding a flattern view of this sheet on the drafting environment.So that when the part is ready the manufacturer will have an idea of cutting the shape of sheet that needs to be cut and its dimensions.

                                                                                                     

                                                                                                                                                                                                                                      fig.11

11. Closed corner :  While modelling any sheet metal part the software has a tendency to automatically create a relief or some gaps between the flanges. So in order to fill the gaps, a closed corner is being used.For this we first need to select the adjacent bend region and click on “ok”. 

                                                                                        

                                                                                                                                                                                                                                           fig.12

Stepwise explanation of modelling the box assembly : 

1. Step 1: 

                    To start with double click on NX-Cad software icon and open it,once all the modules loaded click on new then select sheet metal module. Select sketch and then click on x-y plane to draw a new profile. To create the base plate I sketched a rectangle by keeping its width symmetric to x-axis. By right clicking on any empty space in the working area one command pops up to finish the sketch. Once the sketch is done now we have to add sheet metal parameters. This is done by clicking menu-preferences-sheetmetal and then setting up the values of sheet metal parameters. 

                                                                                                  

                                                                                                                                                                                                                                           Fig.13

1.  Step 2 : 

                            Select the sketch and click on the tab to add its base plate with the thickness value that we specified earlier as 1mm. 

                                                                                       

                                                                                                                                                                                                                                fig.14

1.  Step 3 :  

                            Select the flange command on the ribbon bar and then select parallel longitudinal edges to specify the flange length and angle must be 90 degree from the base plate as we want it to be pendicular to it.(Tip :Here we need to reuse the command multiple times so we will click on “apply” instead of “ok” so that we will not go out of command and there is no need to click on flange command repeatedly.) Length reference must be inside this is because it will measure the flange length from the top of base plate and material must also be inside the reason behind this the length of base plate will remain as it is. 

                                                                                 

                                                                                                                                                                                                                  fig.15

1.  Step 4 : 

                            To create more walls on the boundary of edges select flange and all the edges of the flange that we created earlier one by one. (Tip :Here we need to reuse the command multiple times so we will click on “apply” instead of “ok” so that we will not go out of command and there is no need to click on flange command repeatedly.)Specify the length of flange make sure both the flange don't intersect each other because later we are adding a clamp to it. Flange condition remains the same length reference will be inside and material is also                                                                                              

                                                                                                                                                                                           fig.16

1.  Step 5 : 

                       When we look at our modeled part we will see that there are some gaps between the base plate and flange that we created earlier. Now to fill these gaps between the walls there is command called “Closed Corner” located on the ribbon toolbar. Select the closed corner and click on two adjacent bend region of the flanges and click on “Apply”.  Repeat the same procedure one more time for the other side. 

                                                                                        

                                                                                                                                                                                                                              fig.17

Step 6: 

                     Once again there is a gap between two collinear flanges so to fix this we are clamping onto one another by creating flanges on them. To start with again click on the flange tool and select any of the edges while doing this make sure that bend radius is zero (Tip: When there is variation in bend radius use command advance flange) and flange length is as short as possible and it should not be that short so that it will not create trouble in selecting the edge of it. Once this is done create another flange of some bend radius (0.5mm) and length of 6.5mm. Repeat the same procedure on the other side of the flange. To close this use hem flange and in type choose open hem flange and select the edge specify bend radius and length and make sure the material is added outwards. Repeat the same thing for the edge. Adjust the length if its need to be changed just make sure in the final result its not overlapping. 

                                                                                           

                                                                                                                                                                                                              fig.18

Step 7: 

                        At this stage we modeled half part of the box and then mirror it by using a midplane. This helps to model the part at very less time and error free environment. And then unite both the parts using boolean operations(Unite).

                                                                                                  

                                                                                                                                                                                                             fig.19

Step 8 : 

                    In the group called punch there is a punch tool called “Dimple” select the sketch icon and click on the outer edge of the wall. Create the sketch with the help sketch commands and define dimensional constraint and geometrical constraint if required and finish the sketch. Specify depth of the punch and give punch radius and die radius if needed then mirror the same feature. 

                                                                                              

                                                                                                                                                                                                                 fig.20

Step 9 :  

                 For the bottom part of the model again sketch a rectangle on the bottom plate, add some fillets to its edges and specify the depth of the punch and give the radius. There is another punch tools called “Bead” click on the command select sketch icon and draw circular profile thnen finish the sketch and define the parameters. We need to create this punch on every corner so to do this select bead and then mirror along x-z plane, then select both the feature click mirror feature and select y-z plane. 

                                                                                                        
                                                                                                                                                                                                           fig.21

Step 10 :

                                             To make the part more handy and make it more user freindly its sharp edge are removed by either adding fillet to its edges or adding hem closed flange towards it. So in these edge hem flange of 2mm is used because fillet cannot be appropriate in these situation. 

                                                                               

                                                                                                                                                                                                                          fig.22

Step 11 : 

                            To design the lid of the box,sketch on the new datum plane that we will create at the offset of 203mm distance from the top plane and make the boundary of the lid and create new base tab of 1mm thickness and then add a hem flange to outer edges so that it coincide with the bottom box. 

                                                                                                                     
                                                                                                                     

                                                                                                                                                                                                                                       fig.23

Step 12 : 

                                      Select the left edge of the box and sketch the rectangle on it then give appropriate dimensions to it and finish the sketch once the sketch is fully constrained. Click on tab and create a base plate on the flange of the box of thickness 1mm, add fillet to bottom left corner of the rectangle. 

                                                                                                                             

                                                                                                                                                                                                                                fig.24

Step 13 : 

                             To create the hinges first we need to add some flanges to the tab we created earlier for the appropriate height and then create the hem flange of an open loop with 5mm of bend radius. To make some gap between these hinges first unbend the flanges by selecting tab and then selecting on bend region. All the flanges are now flatten, sketch the cutout part and close the sketch and select the cutout tool on the ribbon toolbar. Then rebend it by just clicking on bend region and mirror all the new features using midplane. 

                                                                                                               

                                                                                                                                                                                                                    fig.25

Step 14 : 

                                In the last step we are going to create a tab feature on the lid by sketching a rectangle. Then add some flanges on the tab and create a spiral geometry by using hem flange and make sure these spirals are concentric with previous one if not make some changes to achieve final results.Unbend all the flanges are now flatten, sketch the cutout part and close the sketch and select the cutout tool on the ribbon toolbar. Then rebend it by just clicking on the bend region.

                                                                                                          

                                                                                                                                                                                                                       fig.26

 

                                                                                                                                                              Standard View Images 

                                                                                                            

                                                                                                                                                                                                                   fig.27

                                                                                                               

                                                                                                                                                                                                                                               fig.28

                                                                                                          

                                                                                                                                                                                                                                     fig.29

                                                                                                            

                                                                                                                                                                                                                                fig.30

                                                                                                       

                                                                                                                                                                                                                       fig.31

                                                                                                                                        

                                                                                                                                                                                                                         fig.32

 

Conclusion : 

                             Thus, the box assembly has been created using siemens NX-Sheet metal and various features executed successfully