Design of a shock absorber

for printing it on a RP machine

Design of a shock absorber for printing it on a RP machine

2 Prof. Dr.-Ing. Dirk Hennigs

Table of contents

1 Introduction .......................................................................................................... 3

1.1 The task ......................................................................................................... 3

1.2 What is Rapid Prototyping? ........................................................................... 3

1.3 Problems ....................................................................................................... 3

2 Design of the shock absorber .............................................................................. 3

2.1 Overview of the methods ............................................................................... 3

2.2 Method A ....................................................................................................... 4

2.3 Method B ....................................................................................................... 4

2.4 Method C ....................................................................................................... 5

elaborated by

Björn Wiegand

Design of a shock absorber for printing it on a RP machine

3 Prof. Dr.-Ing. Dirk Hennigs

1 Introduction

1.1 The task In this workshop the task is to design a shock absorber in a small measuring unit with the CAD-Software Catia. With the help of sets of drawings the shock absorber has to be created in a 3D model. In the next step this model will be exported into so-called stl-files. This Surface Tesselation Language data is a three dimensional illustration of the model, which is formed out of triangles. These in Catia generated files provide the basis for generative manufacturing methods. Therefore the theoretical desingned model can easily be generated into a plastic and realistic 3d model. Finally the task is not only to design a common component but also to manufacture it with the help of state-of-the-art technologies.

1.2 What is Rapid Prototyping? The mentioned generative manufacturing method is also called ‘Rapid Prototyping’ (RP). In simple terms the RP-technology is a three dimensional printing process. A special plastic material is applied in thin layers to reconstruct the geometry of the building element from the bottom to the top.

1.3 Problems In this context the most essential problem of the RP technology is to rebuild screw threads, because the CAD software only displays a thread texture on a pin. Therefore a real and plastic thread has to be modeled.

2 Design the shock absorber

2.1 Overview of the methods There are three possibilities to design the shock absorber: One with two connection assemblies, one with a connection assembly on top and a real modeled thread on the buttom and one with two threads. There are sets of drawings for each of the options. For those who want a simple and easy mountable model the author recommends version A with the building element numbers sa_AXX. A demonstrative but more challenging model is version B (sa_BXX) with one real modeled screw thread. This is a construction that refers more to the real shock absorber. The last and equal challenging version C (sa_CXX) needs to be designed with two real threads. This version is not recommended because of the second and very small internal screw thread that demands a lot of flair after the printing process although it represents to most impressive RP model.

Design of a shock absorber for printing it on a RP machine

4 Prof. Dr.-Ing. Dirk Hennigs

2.2 Method A In this Version there is no special advice needed, because there is not any thread in it. To get a sufficient thrust bearing, the contact areas are modeled in nominal size.

2.3 Method B The Version B uses a metric M12x1 ISO fine pitch thread. As the CAD software does not create a real thread it is the user’s task to craft one. This article is not a tutorial, it is just a collection of tips and tricks for creating real screw threads. The first step is to build the internal screw thread in the tail end (sa_B01):

� Create a negative extrusion with a diameter of 12mm and a depth of 10mm

� Create a new drawing on top and in the middle of the extrusion like in the picture on the right

� Draw a trapezium with the lengths and angles of the graphic on the right (this trapezium represents the basis of M12x1 thread)

� Model a coil with a material creating (positive extrusion) option with an elevation of 10mm and a flank lead of 1mm

� It is possible that there is too much material on top of the tail end. This problem can be fixed with the help of a simple negative extrusion

In the next step the external screw thread has to be created at the end of the cylinder (sa_B02):

� The cylinder has to be modeled with the nominal size of 12mm in diameter

� Like in the tail end create a drawing at the middle and end of the cylinder as it is shown in the picture

Design of a shock absorber for printing it on a RP machine

5 Prof. Dr.-Ing. Dirk Hennigs

� Draw the geometry of the graphic on the right

� Model a coil with the negative extrusion option turned on (elevation 10mm, flank lead 1mm)

After modeling the internal and external screw thread the real thread is modeled and will successfully be printed on the RP machine. The connection between the piston and the cap is like in Version A.

2.4 Method C To design version C please read the tips of version B. Additionally there is a real M4 screw thread to connect the piston with the cap. For this purpose please use the following graphics:

� For the internal M4 thread:

Design of a shock absorber for printing it on a RP machine

6 Prof. Dr.-Ing. Dirk Hennigs

� For the external M4 thread:

The elevation for these M4 threads is 7mm and the flank lead is 0,7mm.

Please notice, that, after the shock absorber was printed, it needs some time after the threads work properly.