EDMUS-Cross process innovation Full report
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16-02-2010, 12:29 PM
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EDMUS-A Cross process innovation
Advanced difficult-to-machine materials
Stringent design requirements
Cross Process Innovations
Todayâ„¢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 work pieces. 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 work piece 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 work piece 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.
Cross process innovation
The technological improvement of machining process can be achieved by combining different physical/chemical actions on the materials being treated.
The reasons for developing cross machining processes are
to make use of the combined or mutually enhanced advantages
to avoid or reduce some adverse effects the constituent processes produce when they are individually applied.
General Issues in Cross Process Study
The performance characteristics of the cross processes must be considerably different from those that are characteristic for the component processes, when performed separately.
There are generally two categories of Cross Machining Processes:
Processes in which all constituent processes are directly involved in the material removal, and
Processes in which only one of the participating processes directly removes the material while the others only assist in removal by changing the conditions of machining in a positive direction from the point of view of improving capabilities of machining.
The general issues in cross process study is to integrate different processes, making use of their individual advantages while avert their adverse effects.
The first step is to understand the interactions involved in various machining processes.
To develop a practical process for industry, the overall feasibility should also be evaluated.
Normally the cross process is more complex than the individual processes. The benefits should be big enough for the industry to accept it as a feasible solution to their problems.
Electro-Discharge Machining with Ultrasonic Assistance
The vibrating movement of the tool electrode or the workpiece, improves the slurry circulation and the pumping action by pushing the debris away and sucking new fresh dielectric, which provides ideal condition for discharges and gives higher removal rate.
The ultrasonic assistance helps in improved flushing and metal removal from the surface craters
Structure modifications are minimized
Less micro-cracks are observed
Fatigue life is increased
These process conditions are significant for micro drilling and production of slots and grooves.
Micro-Hole Drilling using EDMUS
The introduction of ultrasonic vibration to the micro-EDM process has more than 60 times increased the machining efficiency, without significantly increasing the electrode wear.
The efficiency improvement is attributed to the strong stirring effect caused by ultrasonic vibration, which results in an excellent flushing in the micro-EDM process.
The introduction of UV to the micro-EDM of Nitinol has more than 60 times increased the machining efficiency, without significantly increasing the electrode wear.
A greater UV amplitude results in a higher efficiency and a smaller electrode wear.
A higher applied voltage leads to a higher efficiency, as well as a larger electrode wear.
The larger pre-set sparking gap has helped the flushing in the gap, and thus resulted in a higher machining efficiency. However, the electrode wear is also larger.
A larger electrode has a higher machining efficiency, but has little effect on the tool wear.