DESIGN OF FLANGE COUPLING USING CATSCRIPT

DESIGN OF FLANGE COUPLING USING CATSCRIPT

Neerajkumar D. Wayzode

Student (M.E)

PRMITR, Badnera
wayzodeneeraj@gmail.com

Prof. Nitin.A. Wankhade

Associate Professor

PRMITR, Badnera

nawankhade@mitra.ac.in

ABSTRACT

This paper explores computer aided approach to the design of Shaft Coupling i.e. how the 3D solid modeling softwares (like CATIA V5) can be used to automate design tasks by using CATScript (programming language), and visual basic as event driven programming. This approach utilizes standard design equations of the various Shaft Coupling and links them together. The user has to supply some basic requirements of the coupling. Also, the program checks the design for its safety. The calculated data is used to generate part model of shaft coupling in part modeling environment of CATIA V5. This part model can be used to draft different views of the coupling which can directly be used for manufacturing processes.

Keywords

Design of Coupling, CATScript, CATIA V5

1.     INTRODUCTION

A coupling is termed as a device used to connect  two  shafts  together  at  their  ends  for  the  purpose  of transmitting power.

It may be used to connect two units such as a motor and a generator or it may be to form a long line shaft by connecting shafts of standard lengths say 6-8m by couplings. Coupling may be rigid or they may provide flexibility and compensate for misalignment.

However there are two main types of couplings: Rigid couplings are used for shafts having no misalignment while the Flexible couplings can absorb some amount of misalignment in the shafts to be connected.

Theoretically, the design and analysis of shaft couplings has been written extensively by several authors and the result put together in textbooks for use by the engineers.

CATScript

It can be used to develop a macro (program) for calculating design data and that data can be use as input for generating part model in CATIA.

2.     RELATED WORD

The  work  by  María  Gloria  Del  Río-Cidoncha  and  co-authors  describes  about  how automation  in solid  modeling  can  be  approached  by  means  of  macros  for  some  tasks  using CATIA  V5.  Modelling  of  solids  in  CATIA  V5  can  be  done  by  three  tools  viz.  PowerCopy, UserFeature and Macros. CATIA V5 offers the possibility of automating tasks (customization of software for particular task) using the above mentioned tools [2].

With  the  help  of  these  three  tools  user  can  customize  /  automate  CATIA  V5.  Since Macros has advantage over other two macros are used widely.  Visual  Basic  Script  offer  increased  flexibility  and complexity  through  implementation  of  user interface forms and module[3].

1.     DESIGN OF COUPLING

Flange Coupling:

It is a very widely used rigid coupling and consists of two flanges keyed to the shafts and bolted. The two flanges are coupled together by means of bolts and nuts. The flange coupling is adopted for heavy loads and hence it is used for large shafting.

Consider a flange coupling as shown in figure 

Fig 1: Flange Coupling

      d = diameter of shaft or inner diameter of hub,

       D = outer diameter of hub,

       d1 = Nominal or Outside diameter of bolt,

       D1 = Diameter of bolt circle,

       n = number of flange,

       t_f = thickness of flange,

       τ_s,  τ_b and τ_k = allowable shear stress for shaft, bolt and key material respectively.

       τ_c = allowable shear stress for flange material,

σ_cb and σ_ck = allowable crushing stress for bolt and key material respectively.

The flange coupling is designed as discussed below:

1.1     Design of hub

The hub is designed by considering it as a hollow shaft, transmitting the same torque (T)

as that of a solid shaft.    

The outer diameter of hub is usually taken as twice the diameter of shaft. Therefore from the above relation, the induced shearing stress in the hub may be checked.

The length of hub (L) is taken as 1.5 d.

1.2     Design of key

The key is designed with usual proportions and then checked for shearing and crushing stresses. The material of key is usually the same as that of shaft

1.1     Design of Flange

The flange at the junction of the hub is under shear while transmitting the torque. Therefore, torque transmitted,

T = Circumference of hub × Thickness of flange × shear stress of flange × radius of hub

1.2     Design of Bolts

The bolts are subjected to shear stress due to torque transmitted. The number of bolts (n) depends upon the diameter of shaft and the pitch circle diameter of bolts (D1) is taken as 3 d.

We know load on each bolt
Total load on all bolts
and torque transmitted,

From this equation, the diameter of bolt (d₁) may be obtained. Now the diameter of bolt may be checked in crushing.

We know that area resisting crushing of all the bolts
And crushing strength of all the bolts
Torque,

With the help of Visual Basic programming and above equations we can obtained the required dimensions of a coupling for generating a three dimensional modal in CATIA V5

2.     CATIA V5

CATIA (Computer Aided Three dimensional Interactive Application) is a multi-platform CAD/CAM/CAE commercial software suite developed by French company Dassault Systems and it is marketed world-wide by IBM. CATIA is the world's leading CAD/CAM/CAE software. CATIA V5 is an open system for developing advanced macros for special needs. A macro is a piece of code (written in a certain programming language) which groups a set of operations that define a certain task. These macros may be useful for creating, analyzing, measuring, modifying, translating, optimizing surfaces, solids, wireframes and more. Macros are also useful for assembly operations, CAM operations and all multidisciplinary applications. Macros are developed using VBScripts and VBA. In order to develop a macro in CATIA V5 all we need is the inputs, outputs and necessary supporting data from the user.

2.1     CATScript

Access to the CATIA object model is provided using scripts in different ways depending on the operating system and on the applications that can share their own objects with CATIA.

The CATScript language is a CATIA specific language which was designed to allow compatibility between the Unix Basic Script engine and the Windows VBScript engine. As CATIA does'nt anymore hosts the Basic Script engine on Unix since V5R7, it has only been kept for compatibility purpose. It is actually processed by a VBScript engine after removal of the typing information. 

2.2     CATIA Customization/Automation Objects

In CATIA the part objects, which are used for developing part model i.e. three dimensional object are structured under a tree as shown in the following figure. As and when needed the part object can be extracted with the macro programming for customization or automation of CATIA V5 .

Fig 2: Part Modeling Object Tree

The PartDocument object aggregates, or includes, the part tree structure starting with the Part object located at the top of the part specification tree.

These PartDocument objects are: OriginElement, GeometricElements, Bodies and Part objects are: Constraints, Relations, Parameters, Factory3D, ShapeFactory (Sketches, GeometricElements, Shapes)

1.     METHODOLOGY
Generation of Part Model

Part model is generated by few inputs given by designer. The designer has to select type of coupling, Material for coupling, input Power and Revolution. The parameters for coupling design are then calculated by the formulas, which is invoked by, calculate button on the main form. Also the design is checked weather it is safe or not, if it is safe, click on generate button. With this all design parameters are send to a subroutine to generate part model of Coupling. With this, part model of coupling is completed. If required the user can get different views of the coupling i.e. orthographic views along with isometric view for use while manufacturing.

Implementation Scheme in CATIA (Flow Chart)

The following figures give an overview about how the customization of CATIA V5 looked

Fig 3: Input Parameter Form

Fig 4: 3D View of Flange Coupling (Part Modeling)

Fig 5: Drafted View of Flange Coupling

6.   COMPARATIVE VIEW OF THE RESULTS

The means to excellently validate the package developed is to compare the results obtained.

Consider the following example for design of coupling

Example: Design a cast iron protective type flange coupling to transmit 15 kW at 900 r.p.m. from an electric motor to a compressor. The following permissible stresses may be used:

Shear stress for shaft, bolt and key material = 40 MPa

Crushing stress for bolt and key = 80 MPa, Shear stress for cast iron = 8 MPa. Draw a neat sketch of the coupling. Both results are nearly the same. This implies that the macro is excellently packaged.

7.     CONCLUSION

The objective was to customize CATIA V5 for design of a shaft coupling with minimum user requirements (inputs). With the help of this customization/automation a Coupling is generated. Also the time required for generating part model (three dimensional model) of Coupling is reduced to few minutes. This part model can be used to draft different views of the coupling which can directly be used for manufacturing processes. Thus, this automation / customization will increase productivity of the designer with increase in quality of design which in turn reduces lead time for design of shaft coupling.

8.     REFERENCES

1)      R.S.Khurmi & J.K.Gupta. A textbook of Machine Design, S Chand Publications.

2)      María Gloria Del Río-Cidoncha, Juan Martínez-Palacios, Francisco Ortuño-Ortiz, (2007),"Task automation for modelling solids with Catia V5", Aircraft Engineering and Aerospace Technology, Vol. 79 Iss: 1 pp. 53 - 59

3)      Nathan Clark and Tom Schneider, “Working With the CATIA/Visual Basic Interface” Vought Aircraft Industries, Inc.

4)      Adeyeri Michael Kanisuru, Adeyemi Michael Bolaji, Ajayi Olumuyiwa Bamidele & Abadariki Samson Olaniran “Computer Aided Design of Couplings”, International Journal of Engineering (IJE), Volume (5): Issue (5): 2011 pp 313-332

5)      http://www.maruf.ca/files/caadoc/CAAScdInfTechArticles/CAAInfInvoking.htm

6)      http://www.cax-services.com/index.php?option=com_content&view=article&id=56:catia-v5macros&catid=40:application-development&Itemid=65