Computer Control of Z-axis of Drilling Machine that making Hole at Micron Accuracy
Abstract
Drilling operations are used widely in industrial applications. In these operations several drill bits having different drill geometry and different tool materials such as HSS and WC are used to obtain the holes at desired surface quality and tolerances. The big problem in drilling operations with drill bits is to achieve a hole diameter at micron accuracy. In order to be able to drill at desired accuracy the main factor is that the drill bit must be moved at constant feed speed and can be adjusted. In this experimental study, a standard workbench based drilling machine have been used and the computer controlled mechanism have been set up to adjust the Z-axis to drive the drill bit at constant speed, so the drilling diameter will be kept at desired tolerance and at the drill axis. The parameters such as feed speed, drilling length, entering and exit speed related to drilling machine tools are adjusted the software written in Visual Studio C#. Communication between step motor control and computer is provided by control card constituted with microprocessor. Also, operation parameters are saved to the memory by EEPROM installed on the circuit and the working of the system is realized without computer connection. By the installed system the drilling holes at micron accuracy (0.18-0.25µ) were achieved in drilling operations carried out at different feed speeds and drilling lengths on the computer controlled Z-axis drilling machine tools.
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Introduction
Developing technology and workpiece demand at high accuracy in manufacturing technology require micro machining. Machine tools and workpieces machined are miniaturized with micro machining and also material and power consumption are reduced to the lowest level. In worldwide, by means of this industry that getting expanding high efficiency is obtained in source and time usage. Many type of drill bits are widely used in industrial applications. The most important problem in drilling applications is drilling of micro scaled holes and to fix the parts in desired coordinates. The main factor in drilling micro-hole around 0.18-0.25µ at micron accuracy in small diameter is that feed speed must be at constant and also adjustable.
There are several micro hole creating methods are claimed by many authors in their investigations. The holes at too small diameters are formed with. Micro-electro discharge machining (EDM) using water as a working fluid is systematically studied to find its characteristics. As a result, the unique advantages of high removal rate, low electrode wear and consequently higher working efficiency, without formation of carbonaceous materials are found under optimum experimental conditions, as compared with the case when kerosene is used. This was achieved by the choice of suitable combinations of electrode and workpiece materials and electrode polarity. Use of a tungsten electrode with straight polarity is exceedingly good with respect to high removal rate and low electrode wear. This makes it possible to obtain a non-tapered straight microhole around 0.1 mm in diameter with a certain anticipative working gap. The advantageous properties of this machining method are effectively utilized to drill deep micro-holes with a ratio of depth to diameter of the order of 10–17 as in the case of 2.9 mm depth and 0.17 mm diameter, which is superior to the limits achievable with both electro discharge drilling (EDD) using kerosene and mechanical drilling with a micro-drill [1].
Conclusion
As a result of the experimental study, a standard workbench type drilling machine used for drilling of unsusceptible holes is converted into the drilling machine being controlled and making the holes accurately. The spindle of the drilling machine (Zaxis) is driven by step motor that having 3.6º in one step. By the designed interface program feed speed, drilling distance, exit speed related to the drilling machine can be controlled and adjusted depends on drilling conditions. As a result of experimental study performed it is seen that the holes drilled on the drilling machine have desired surface quality and distance, expected surface roughness and the deviation of the hole diameter is within tolerance.