Cross Process Innovations

Section 1. Introduction

Why Nontraditional Machining Processes are used?

Today’s manufacturing industry is facing challenges from advanced difficult-to-machine materials (tough super alloys, ceramics, and composites), stringent design requirements (high precision, complex shapes, and high surface quality), and machining costs.

Advanced materials play an increasingly important role in modern manufacturing industries, especially, in aircraft, automobile, tool, die and mold making industries. The greatly-improved thermal, chemical, and mechanical properties of the material (such as improved strength, heat resistance, wear resistance, and corrosion resistance), while having yielded enormous economic benefits to manufacturing industries through improved product performance and product design, are making traditional machining processes unable to machine them or unable to machine them economically. This is because traditional machining is most often based on removing material using tools harder than the workpieces. For example, polycrystalline diamond (PCD), which is almost as hard as natural diamond, cannot be effectively machined by traditional machining process. One of the most commonly used conventional techniques is diamond grinding. In order to remove the material from a PCD blank, the diamond layer of the grinding wheel must be renewed by turning or dressing operations resulting in rapid wear of the wheel, because the G-ratio (ratio of workpiece volume removal rate to grinding wheel volume wear rate) is 0.005 to 0.02. Thus, the grinding wheel wear rate is 50 to 200 times higher than the workpiece removal rate. Hence, classical grinding is suitable only to a limited extent for production of PCD profile tools. The high costs associated with machining ceramics and composites, and damage generated during machining are major impediments to the implementation of these materials. For example, the costs of machining structural ceramics (such as silicon nitride) often exceed 50% of the total production costs in the engine industry. In some cases, current machining methods cannot be used and innovative techniques or modifications of existing methods are needed.

In addition to the advanced materials, stringent design requirements also pose major problems in manufacturing industry. More and more complex shapes (such as an aerofoil section of a turbine blade, complex cavities in dies and molds, non-circular, small, and curved holes), low rigidity structure, and micromechanical components with tight tolerances and fine surface quality are often needed. Traditional machining is often ineffective in machining these parts. To meet these challenges, new processes need to be developed.

The purpose of this module

The technological improvement of machining processes can be achieved by combining different physical/chemical actions on the materials being treated. In particular a mechanical action, which is used in conventional material removal processes can be combined with respective interactions applied in unconventional manufacturing processes such as electrical discharge machining (EDM), electrochemical machining (ECM), and laser beam machining (LBM).

The reasons for developing a cross machining processes are to make use of the combined or mutually enhanced advantages, and to avoid or reduce some adverse effects the constituent processes produce when they are individually applied [1,2]. Some authors use the name Hybrid Machining Processes, which means more than machining processes or machining mechanisms. We feel that "Cross" has a broader sense than "Hybrid", since some processes integrated several techniques while the major machining mechanism doesn't change. For example, in pulsed ECM, which improves normal ECM, the mechining process is still similar to normal ECM.

Although some of the nontraditional machining processes have shown to be very effective in machining new and advanced materials and manufacturing of machine parts and tools, the research effort in cross processes and process innovations has been inadequate. More importantly, adequate theory and methodology to guide the research and development in the cross processes are needed.

The purpose of this module is to report some of the representative progress in cross process innovation in recent years. We will also discuss the methodology that consist main cross or hybrid processes with a description of its characteristics, physical and chemical phenomena and selected problems of the cross processes.

References

 

[1] Rajurkar, K. P., Zhu, D. McGeough, J. A., Kozak, J., De Silva A.: New Developments in Electro-Chemical Machining. Annals Annals of the CIRP, 1999 vol.48/2,p.569-579.

[2] Rajurkar, K. P., Ross, R.F., Wei, B., Kozak, J., and Williams, 1992, "The Role of Nontraditional Manufacturing Processes in Future Manufacturing Industries," Manufacturing International, 1992, ASME, pp. 23-37.