Today’s metal processing industries are often interested to induce compressive residual stresses in the several components which they will come across in fabrication processes daily. The conventional methods of finishing process viz. grinding, broaching used to improve the surface finish of the metallic components, but the burnishing process which is having same role to play in finishing process has many advantages associated with it fulfilling above said requirement successfully. This paper presents results of the study about design and developmental issues of Ball burnishing tool. This tool is used to perform burnishing process successfully by controlling different parameters.
The burnishing process consists of pressing hardened steel rolls or balls into the surface of the workpiece and imparting a feed motion to the same. Ball burnishing of a cylindrical surface is illustrated in Fig.
During burnishing considerable residual compressive stress is induced in the surface of the workpiece and thereby fatigue strength and wear resistance of the surface layer increase.
How is the surface quality improved in ball burnishing?
In this process, a hardened steel ball presses the workpiece surface. The surface finish is markedly improved. In addition, a residual compressive stress is developed on the surface, which in turn improves the fatigue resistance. The work hardening effect, as a result of burnishing, also enhances wear resistance of the surface. Therefore, by ball burnishing the overall quality of the workpiece surface is significantly improved.
It is observed that the conventional machining methods such as turning and milling leave inherent irregularities on machined surfaces and it becomes necessary to very often resort to a series of finishing operations with high costs. However, conventional finishing processes like grinding, honing and lapping are traditionally used finishing processes, but these methods essentially depend on chip removal to attain the
desired surface finish, these machining chips may cause further surface abrasion and geometrical tolerance problems. Accordingly, burnishing process offers an attractive post-machining alternative due to its chip less and relatively simple operations . Many researchers have done their works by developing different types of burnishing tools i.e. ball and roller burnishing and making them ready to use with conventional machine tools viz. Lathe and milling.
DESIGN OF BURNISHING TOOL
As it was decided to carry out the ball burnishing process in present work among two process of burnishing, the first and foremost work is to design and develop the ball burnishing tool by selecting suitable materials, dimensions and proper design such that the process and the tool is simple, cheaper and requires minimum time consumption with minimum cost. The tool developed in this work can be used on convectional machine tools like lathe. Fig. shows the tool developed in this work to carry out ball burnishing process with interchangeable roller burnishing tool assembly. This option increases flexibility of the tool and allow us to carry out both the processes.
The burnishing tool designed in above said manner consists of parts namely ball holder, square casing, lock pins and threaded lock support and spring. The design of tool is made in consideration with the parameters to be selected and to be controlled in the work. The experimental work is planned to conduct mainly considering four different parameters and burnishing force is one among the parameters. So, the force is measured by means of spring deflections in the tool. The work piece material will be 60/40 Cu-Zn and the maximum force applied on the work piece during experiment is 30kgf.
APPLICATION OF BURNISHING TOOLS
Burnishing tools are being used in sectors like Automobile, Aircraft, Defence, Spacecraft, Railways, Textile, Machine Tool, Motors and Pump Industry, Hydraulic and Pneumatic Farm Equipment, Home Appliances etc., and areas where close tolerance and superior surface finish is required.