You work for a company manufacturing small high precision mechanical devices in large quantities, using scaled down conventional machining and forming processes. The sales department has seen the financial advantage of entering the market for true micro-mechanical devices. The production director is aware that in order to carry out machining processes involved in meeting < 0.1 mm sized components then non-mechanical means of material removal are going to be required, particularly in view of the complex shapes often required.
You have been asked to produce a report to describe the typical processes involved in non-mechanical material removal and the type of equipment required in order to produce micro-mechanical - sub 0.1 mm - parts of complex shapes.
a)You will be expected to describe the principles of operation and specifications of such equipment, satisfying the criteria for LO3.1
b)The description of tooling, work holding and any specific health and safety requirements will satisfy the criteria for LO3.2.
c)The examination and comparison of more than one method of carrying out manufacturing processes of this nature will meeting the criteria for the merit.
d)The examination of developmental / experimental methods will meet the distinction.
LO3. Understand the use of less conventional machining techniques for a given component specification
LO3.1 Select suitable data and processes for component manufacture using a less-conventional machining process.
LO3.2 Explain the tooling and ancillary equipment requirements to manufacture a given component by a less-conventional machining process.
M2 Show that relevant theories and techniques have been applied, a range of methods and techniques have been applied and a range of sources of information has been used.
D3 Demonstrate convergent / lateral / creative thinking: ideas have been generated and decisions taken and self-evaluation has taken place.
The continued proliferation of miniature and the different micro products components had steadily increased the demand for their production to rise exponentially. Most manufacturers today are investing heavily in the micromachining technique in the production of precision wise equipment. With the ever decreasing feature size required from the conventional millimeters to tens of micrometers, the conventional mechanical machining technology cannot be trusted to handle such high precision. It is therefore imperative to switch to more non-mechanical means of material removal to be adopted by the company. This report describes briefly, the operations of the non-mechanical material removal tools(Kussul et al., 1996).
This section outlines the basic principles behind the operations of the non-traditional machining tools for deeper understanding, the industry specification for the different level of precision required. A comparison is done on the different tools used by the manufacturing industry and the sharp contrast between them, this will be vital in making the best decision on the way forward for the company in embracing the new technology.
Principles of Operation
Removal of materials from the work-piece using the non-mechanical approach generally are grouped into four principles primarily based on the source of energy used in the removal process of the material at the work-piece. These principles are hereinafter discussed in details. This will enable deeper comprehension of their modus operanda, which is vital is ensuring safety and health requirements are adhered to. The four basic principles are
- Electrochemical grinding (ECG)
- Electrochemical machining (ECM)
- Electrical discharge machining(EDM)
- Radiant Energy Material Removal Method.
The discussion below details their mode of operation and basic principle they use to achieve their desired efficiency and effectiveness.
Electrical Discharge (EDM)
This technique is the widely used non-mechanically machining technology to remove materials from the work-piece .it involves passing a low voltage but of high-frequency direct current which aims at removing the covering layers of the metallic material. This is done using an electrode which in most case is the brass. Care is taken such that the cross-sectional part of the container technically is supposed to be identical to the cavity to be machined. The dielectric fluid is used which provides the medium where the electrode and the part to undergo machining is immersed(Goswami, Mitra and Sarkar, 2009). For a medium to act as a dielectric in this method, it must meet the following minimums.
- The dielectric must have the ability to prevent the electric current from flowing in a centric manner.
- Ability to flash away the would be remains of the work-piece part.
- Ability to act as a coolant.
The figure below illustrates the principle behind its working,
Illustration 1: Electrical Discharge (EDM)
- The ability to apply machining has no independent of the strength of the mechanical components.
- It is possible to produce irregular shapes whose contours are intricate. This is achievable since the shape of the machined part entirely depends on the electrical configuration. This makes it easier to come up with accurate dimensions with a lot of ease(Curtis et al., 2009).
Despite the enormous advantages, this method display some disadvantage. This is explained below,
- Their is chances the machined part will crack along the boundaries due to relatively low fatigue strength compared to the parts machined
This method consist of passing through a direct current through an electrolyte which separates the surface of the would be machined parts from an electrode. In this arrangement, the part will be used as an anode whereas the electrode takes the role of cathode. The chemical reaction caused by the electric current lead to the dissolution of the anode which is the part to be machined(Kozak, Budzynski and Domanowski, 1998).
Electrochemical Grinding (ECG)
This method looks similar to the ECM in principle, however, in this method, electrode I made from a grinding wheel whose role is twofold. The electrode does two roles, first by virtue of being a cathode, it causes anodic dissolution of surface layers of the part to be removed. Second, being a grinding wheel, it further enhances metal removal through grinding (Levinger and Malkin, 1979).
It uses the principle of high energy which can be in form of a laser or an electron beam which is focused on the surface of the would be removed surface of the metals, a process called vaporization. This method is ideal for those work-piece with high melting points. Its ability to focus the laser on a particular part makes it possible to reach the area which would otherwise be inaccessible (Steigerwald and Meyer, 1969).
Various tools can be used in cutting and removal of parts of the work-piece. This section highlight some of the known non-mechanical machining tools.
Water Jet Cutting
It uses use the high velocity of water focused on the work surface hence causing cutting
Abrasive Jet Cutting
Removal of materials is due to the impingement of some fine abrasive particles onto the surface part of the work-piece. The typical abrasive material is 0.025mm in the diameter.
Health and Safety Requirements
Despite their continued adoption, the non-mechanical methods of machining pose serious health and safety issues to the human operating them. This section highlights some of this safety threat and how much can be mitigated by providing requirements for the non-mechanical machining tools to fulfill. The first obvious safety concern is the high light intensity from the laser beam which if get in contact with skin can be cancerous. Ionizing radiations in form of X-rays and microwave are equally very dangerous to human. They cause skin rashes. To mitigate some of this risks, the organization shall enforce access controls policy to monitor who uses what. Regular maintenance is also vital for their continued work delivery(Hutter, 2001).
The non-traditional machining technology requires a non-mechanical machining technology to speed up the manufacturing process of microscopic work-pieces. The various principles the technology are discussed. Despite their promising usage, the above tools have serious health and safety implications on the operator and various ways to mitigate the risk are outlined. The future seems bright for non-mechanical removal of work-piece parts.
Curtis, D.T., Soo, S.L., Aspinwall, D.K. and Sage, C., 2009. Electrochemical super abrasive machining of a nickel-based aero-engine alloy using mounted grinding points. CIRP Annals, 58(1), pp.173–176.
Goswami, R.N., Mitra, S. and Sarkar, S., 2009. Experimental investigation on electrochemical grinding (ECG) of alumina-aluminum interpenetrating phase composite. The International Journal of Advanced Manufacturing Technology, 40(7–8), pp.729–741.
Hutter, B.M., 2001. Regulation and risk: occupational health and safety on the railways. Oxford University Press on Demand.
Kozak, J., Budzynski, A.F., and Domanowski, P., 1998. Computer simulation electrochemical shaping (ECM-CNC) using a universal tool electrode. Journal of Materials Processing Technology, 76(1–3), pp.161–164.
Kussul, E.M., Rachkovskij, D.A., Baidyk, T.N. and Talayev, S.A., 1996. Micromechanical engineering: a basis for the low-cost manufacturing of mechanical microdevices using micro equipment. Journal of Micromechanics and Microengineering, 6(4), p.410.
Levinger, R. and Malkin, S., 1979. Electrochemical grinding of WC-Co cemented carbides. Journal of Engineering for Industry, 101(3), pp.285–294.
Steigerwald, K.-H. and Meyer, E., 1969. Machining process using radiant energy. Google Patents.