Non-Mechanical Machining Flashcards
Explain the basic principles of operation, capabilities, and limitations of electrical discharge machining (EDM), noting relative merits between sink/ram EDM and wire EDM. Explain the reasoning behind tooling materials and the functional roles of dielectric fluid in EDM
o EDM: Based on the erosion of metals due to spark discharges (very high temp locally), a shaped tool and the work piece are connected to power supply and placed in a dielectric fluid, once potential difference is high enough a spark discharges through the fluid and removes a very small amount of metal from the work piece, good for hard materials, deep small diameter holes, narrow slots. Disadvantage is only works on conductive materials
o Sink/Ram EDM: The electrode is either copper or graphite (good conductivity), the electrode has all the features that will be transferred to work.
o Wire EDM: The wire moves slowly around a prescribed path cutting the work piece, good for cutting plate material, main advantage is wire is always replenished new (important because some material is removed from tool as well)
o Dielectric fluid: Act as insulator until the potential is high enough, provide a cooling medium, act as a flushing medium and carry away debris
Explain the basic principles of operation, capabilities, and limitations of laser machining, noting distinctions among carbon dioxide, Nd-YAG, and excimer types.
o Laser machining: highly focused, high-density energy source melts and evaporates portions of the work piece in a controlled manner, capabilities include drilling and cutting metals, nonmetallic, ceramics, composites, small holes with high aspect ratios are possible. Disadvantages are sharp corners are hard to produce, deep cuts will have tapered walls, reflectivity of surface is an important consideration.
o Carbon dioxide: medium performance, medium power
o ND-YAG: high performance, high power
o Eximer: no heat affected zone
Explain the basic principles of operation, capabilities, and limitations of chemical machining. Explain what in particular is meant by photochemical machining.
o Chemical: works on principle of chemical dissolution, etchants remove material temperature and agitation control are important for uniform depth removal, maskants are used to prevent removal of material in unwanted areas good for shallow removal on large flat or curved plates, low tooling and equipment costs, good for low production runs, limitations are that the process is relatively slow and is only usable for shallow material removal.
o Photochemical: A photosensitive material is placed on the object, it is exposed to ultraviolet light which hardens the exposed areas, this produces the mask in the wanted areas (the rest of the photosensitive material is washed away), then it is placed in a chemical bath and proceeds just like standard chemical machining.
Explain the basic principles of operation, capabilities, and limitations of electrochemical machining. Explain the role of electrolyte.
o Electrochemical: an electrolyte acts as current carrier and high rate of electrolyte movement washes metal ions away from work piece (anode) before they have a chance to plate onto the tool (cathode). The cavity produced is based off the tool shape (reverse of electroplating). Advantages are it leaves burr free, bright surfaces and causes no thermal distortion or any distortion created by the contact with the tool, can produce complex shapes. Disadvantage can’t produce sharp corners; controlling electrolyte flow is difficult for irregular cavities.
o Electrolyte role: Current carrier completes connection between part and tool.
• State relative advantages of the various non-mechanical machining processes, not only compared to each other, but also with respect to mechanical machining processes
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