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Our project work, Abrasive Jet Machining (AJM) presents the working of abrasive jet machining and removing materials from the brittle and heat sensitive materials by the application of a high speed stream of abrasive particles carried by a gas medium through the nozzle. In particular drilling of holes of minimum diameter and maximum depth is also possible in AJM with greater accuracy and surface finish. Since no heat is induced while machining the surface, the workplace is not subjected to thermal shocks.
The abrasive jet machining apparatus can be used for determining the material removal rate (MRR) for materials like glass, ceramics and aluminium sheet by varying the parameters like pressure, nozzle tip distance (NTD) and size of the abrasive flow rate. In this project we have designed and fabricated the Abrasive jet machining apparatus for drilling holes and cutting glass, ceramic plates and aluminium sheet.
Rapid technology development in the field of new materials and alloys with increasing strength, hardness, toughness, heat resistance and wear resistance has imposed many problems and difficulties during the machining by conventional means.
Machining intricate and complicated shapes of this and fragile components and accurate and economical forming of very hard, high strength materials which are being extensively used in airplanes and nuclear industries have forced the scientist, engineers and technologists search for new techniques of machining which can readily provide an effective solution to these problems.
As a research and development for the last forty years, several new methods of machining have emerged. Among the new methods we are going to deal with the Abrasive Jet Machining. The conventional techniques like turning, drilling, milling, etc., are well known and involves the use of mechanical power between the workpiece and the tool, whereas in this method need not be the case with unconventional on advanced machining techniques.
Abrasive jet machining (AJM) removes material through the action of a focussed stream of abrasive-laden gas. Micro-abrasive particles are propelled by inert gas at velocities of up to 300 m/Sec. When directed at a workpieces, the result in erosion can be used for cutting, etching, cleaning, deburring, polishing, and drilling.
Material removal occurs through a chipping action, which is especially effective on hard, brittle materials such as glass, silicon, tungsten, and ceramics. Soft, resilient materials, such as rubber and some plastics resist the chipping action and thus are not effectively processed by AJM.
No work piece chatter or vibration occurs with this process because the large enables AJM to produce fine, intricate detail extremely brittle objects. The AJM processed eggshell provides a graphic example of the delicate nature of the process. In addition, because heat carried away by the abrasive propellant gas, workpieces experience no thermal damage.
The manufacturer prepares a reusable rubber stencil for each model panel. The rubber stencil is then placed on the surface of the panel and the abrasive jet is used to etch the exposed areas providing permanent marking. In this particular use, the Abrasive Jet Machining (AJM) costs only 1/3 of the cost required for label method of production.
A variety of diverse jobs has been successfully performed by AJM. These include cutting threads into glass rods, deflation small castings, die and mound touch up, cutting titanium fink and drilling glass wafers.
The AJM has been successfully employed to manufacture small electronic devices consisting of a 0.38 tungsten disk. After the two materials were were brazed together. The silicon wafer must be trimmed and beveled without harming the tungsten disk. To accomplish the task an AJM nozzle is mounted at the desired angle and directed at slowly rotating part with this technique the unwanted silicon is trimmed off each part in less than one minute.
An example of debugging plastic parts with AJM is cited by Lacourte (1979) in an application involving the manufacture of small biomedical analysis packages. Small plastic cubes are cross drilled with two 0.34mm diameter holes. Tiny burrs are created internally at the intersection of the two holes must be removed without providing scratches. It is not only able to meet this difficult quality requirement, but it also was able to reduce devouring time by 80% when compared with the old method of debarring.
AJM provides cool cutting action, no heat damage occurs to the delicate work materials.
Cutting action is shockless.
Ability to cut fragile and heat sensitive materials without damage.
Ability to cut intricate hole shapes in materials of any hardness and brittleness.
No variation due to surface irregularities and tool wears as in conventional machining.
Low capital cost.
AJM units are easy to operate and maintain.
Stray cutting is unavoidable if not properly controlled.
AJM yields low material removal rates.
Nozzle life is limited.
Replacement of rubber hoses which carry abrasives may be necessary.
A suitable dust collection system is required to prevent pollution.
Embedding of the abrasive on the workpiece surface may occur while machining softer materials.