Lecture 13

hello and welcome back to this uh lecture on Microsystems fabrication by Advanced manufacturing processes so a quick recap of what we had done in the last uh class we were trying to figure out the the tool shape uh on a function mapping basis from the work piece to the to and supposing there is a geometry of the workpiece which is defined uh by any cat package in terms of uh lines straight lines curves different curvatures or for example fits like basier fit or U any other beastline or H missan uh fit so the idea is that how you can map uh by dividing the surfaces into uh small small parts and finding out what is the corresponding negative shape which would be there on the tool surface which would be able to sort of dis sync the whole shape into a workpiece surface so uh we actually did a problem uh for 2D based curvature this is Illustrated here and then we also uh learned about the fact that the other important issue uh which actually comes in ECM is the electrolyte flow and the way it has designed one of the basic fundamentals of electrolytic flow uh had been seen before when we were talking about designing of the electrolyte velocity between the the tool and the workpiece and uh we figured out that this velocity is a key component because uh the amount of heat that is injected into the uh the the moving electrolyte by virtue of the electrical power transferred onto the electrolyte from the electrodes has to be equal to the heat dissipated and there would be a equilibrium in terms of a temperature state which is uh achieved because of this whole process and that temperature should never go beyond the boiling point of the electrolyte okay so we designed for that and then with that Optimum velocity where the temperature just is is is just below the boiling point we tried to find out what is the active pressure on the electrode so that is one aspect that what are the parameters of the flow but the very important second aspect which we'll in fact talk today in our lecture is uh how to place the flow or position the flow uh or where can be the inlets and the outlets associated with The Tool uh so that you can safely C carry the electrolyte injection almost always along with the tool as it moves along the surface which has to be machined and um for doing this uh you know you have to introduce uh concepts by really looking at the overall design the amount of leftover area of the workpiece based on whatever tool area you are using and there would be some very nice illustrations and figures which we talk about where the flow has to be planned in a manner uh the flow has to emanate out of the electrode in a manner so that full coverage of the workpiece surface can happen Okay so uh the other important aspect is the the description of uh uh Machining plants which would do the ECM process and uh then we'll see the effects of ECM on some other materials uh of interest and correspondingly study about some other processes associated with the ECM like the ECG the electrochemical grinding the electro stream drilling ESD and so on so forth okay and uh after all the review of this fundamental level electrochemical Machining processes we will then start over again and try to apply some of this technology to the fabrication of Microsystems uh like for example micro needles uh small very small super fine High aspect ratio structures uh used for other applications which are almost always used in the area of mems or Microsystems can be fabricated using such Machining protocols uh by localized deposition of material at a certain place which we'll talk about a little bit later uh once the applications slides begin on the applications of chemical electrochemical Machining on Microsystems so let's look at what we did in the 2D case uh just uh reviewing what uh you know uh we said in the last few lectures uh that supposing there is a certain uh tool surface for example this is the tool surface so the the workpiece surface with a certain topology which is mapped by some function let's say y = to 5 of X and these are all the so-called work piece coordinates and then you want to imprint it or embed it into a uh so sort of looking it at a reverse an analogy tool surface okay so in other words conventionally it is the tool which will embed and produce a dncing operation on the work piece so the work piece moves towards the the tool surface we do not know what the shape of this and we'll have to somehow estimate the tool shape based on this y equal to 5x relationship for the work piece shape and we already know that in such a situation uh the D5 by DX is or the slope is very important uh basis for finding out a relationship between YT and YW this uh point right here is XT YT and the xw and XT which is actually equal to x w + Lambda by f d fxw by d x w okay so this uh actually becomes equal to YT by Lambda plus Lambda by F this becomes equal to x uh W + Lambda by f * of slope so as we have already seen for the 2D case if supposing y w was related by an equation a + b x w + c x w² uh in that event the slope d5x W by dxw would be twice would be BX B+ tce c x w and simultaneously uh the final equation which would emerge would be corresponding to Y = to a + BX + CX and these are all tool coordinates okay so this is the sort of uh functional relationship between the the Y and X on the tool surface on this point which would map then this surface the tool surface and this comes out to be equal to uh a plus b XT plus C XT minus Lambda by F minus Lambda by F times of b + t c x t² uh divided by 1 + T C Lambda by F okay so this is how you can correlate the YT and the XT and uh similar case can be repeated for the three-dimensional problem so in case the equation of the work piece is a three-dimensional equation so YW in this case is related to let's say a + b x w + C X w² plus some D ZW so we are including both all the three coordinates here X Y and Z so it's a cartisian coordinate uh system dxw dzw + E Z w² Plus GX w ZW so the required tool geometry which is then calculated in a similar manner but of course for the relationship between the YW and xw and YW and ZW independently okay so you'll have to do partial derivatives uh of all these and then find out what is the corresponding relationship on a three-dimensional plane between two points xw YW ZW and XT YT ZT in a similar manner as you have done for the two dimensional curvature case Okay so this is actually a plain surface that we are talking about and how you map that surface uh into the tool surface so this is of more practical importance to the ECM process typically because all the features or structures that you're trying to dis sync into the work piece are three-dimensional surfaces or Surface topologies so here the find uh relationship which comes out between the YT XT and x uh or ZT uh the position coordinates of the tool surface is basically a + b XT plus cxt s + d z t + e z t² + G XT ZT minus Lambda by F minus Lambda by F of this whole term here which is B + tce cxt plus GT ZT square plus d + tce e t+ g XT squ divided by the term 1 + T C + e Lambda by F so that's how the three-dimensional relationship would exist between the YX and Zed on the tool side if a given relationship socalled uh YW in terms of some function f of xw ZW exists okay so you have to really uh look at uh in the same manner uh following the same algorithm as we have done before for the curvature case and I leave it for food for thought for you guys to be able to see how you can derive the tool equation on this 3D surface or how you can map the topology of a work piece uh surface topology of a work piece onto the tool surface using such a uh you know fundamental equation given here in this slide okay so some of the important points uh to remember particularly when we talk about this uh so-called ECM process uh that uh it should be remembered that the method used to solve for y value uh is typically applicable for smooth surfaces okay with some gentle variations one of the reasons why smooth surfaces uh are the point of uh discussion here is that if the surface is too rough then there would be uh A variation a local variation of the electric field and in our uh approach Ro that we have used or the algorithm we have developed really that variation for electri electric field is not accommodated we still assume the electric field to be constant depending on the function of the inter electrode Gap okay and the Lambda the way Lambda is defined is really uh for a constant field case where we assume that the lines of forces are fully parallel to one another the the field is homogeneous all through the two electrodes the work piece and Tool so on so forth if the field is locally varying which is the case when there are surface topologies of small size uh which would create coiling of the lines of forces uh in that case we cannot use uh the simple you know homogeneous electric field solution to Define uh the functional mapping between the work piece and Tool so there would be a complication uh which is imposed because of the roughness of both the surfaces if it is above a certain value so for more complex uh shapes and surfaces particularly involving sharp curves this is something that you have to be look out on uh and sudden changes the first thing that we really need to establish is a solution for the electric field itself so you should have a solution compare uh considering all the uh the sharp corners of the surface topology and all the coiling of the lines of forces and that relationship of field when it so would exist uh would be automatically translated to find out the Lambda value okay and uh that way the the equilibrium Gap g can be calculated as Lambda by F so it would be a more accurate uh assumption uh to to incorporate into the function mapping strategy okay so when the closed form expression for work piece surface is not available one option could be that you divide the surfaces into small straight or curved segments of known geometry and then within this local domain if you assume the field to be constant then you can still be able to translate some of these equations uh in for for mapping between the tool and the the work piece so instead of uh the strategy followed earlier which was uh about uh just having a single curvature to define the whole surface we would be able to split up the surface into various parts okay and uh I think I've Illustrated this before that c package can really these days uh convert the whole surface in terms of fits uh in terms of uh various various uh uh parametric or non-parametric Curves and uh segments or planes and so the whole surface uh can be localized to a local domain and then each domain's functional map on the tool surface can be estimated that way you can assume that you are avoiding the corners or you don't need a close form solution of the electric field okay you can assume for that local small area the electric field is homogeneous so these are some of the important points to remember when you do function mapping okay so the other aspect I would like to really illustrate for the ECM process is the design for electrolyte flow okay so one aspect we've already discussed is how the velocity and pressure could be calculated from before the the other uh very important uh method or the other the very important part of the layout that we have to plan is how you flow in the electrolyte to begin with okay so for example in this particular figure here there is a concentric Channel which is available on the tool electrode and uh this is having uh an option that the electrolyte can be pumped in and uh you can see that because this Gap is very small the curvature here is a smooth so it makes the electroly flow in streamline shapes so typically these are very high uh these are very small gaps uh meaning thereby that sometimes the the renolds number is very low because it is dominated by the the de effective or the effective diameter and uh it's microscale phenomena so almost always sometimes the almost always the uh the flows are laminar or creepy okay in such gaps so therefore what we need to ensure as a design engineer is that the sufficient electrolyte flow should be there between work piece and Tool uh and uh of course that's because it needs to carry a away the Heat and the products of Machining the flow is needed for that purpose in any case as we have seen before and uh you can also have an assistance to the whole Machining process uh so you can have suitability in the surface finish that you obtain or you know at a certain rate you are trying to produce uh the Machining or you are intending for certain yield of Machining which is defined by this feed rate so even for that uh the amount of heat carrying away carry away is very critical but however when you are talking about the flow of electrolyte particularly past the surface which it is Machining uh there is of course problems additional problems that the flow impose one is cavitation stagnation and Vortex formation so cavitation happens because of uh Bubbles as you know that this Electro uh electrochemical Machining is all about uh the carrying away of the de material as precipitate there is a and and there are certain gases which are sometimes produced in the process there is always a a scope for bubbles of Micron size which may grow up to some macro size between the tool and the work piece okay and so when that bubbles happen there is a pressure difference because of which some uh effect can be felt back on the Machining rates because of this gravitation so the electrolyte moving although it carries the bubble away uh very fast but cavitation is a major problem uh which would come that bubble formation and uh the influence on the material removal rate because of the bubble formation you have seen that in USM case this cavitation happens because of the vibrating tool head at a very high frequency so the uh the fluid can no longer follow that tool head and there are thousands and thousands of bubbles which are created because of that because the air typically bleeds out uh uh and fulfills the Gap done by that vibrating tool head in the ECM case the same bubble is generated electrochemically okay by the system so then there can be a possibility of stagnation of the flows okay so there are maybe certain it's a creepy flow it's a laminer flow so if supposing there are certain nooks and Corners in the workpiece where sometimes because of extremely uh low let's say discharge rate uh the perfect streamlining happens so supposing there is a Surface like this that you are trying to machine with this tool okay and this tool is uh shaped in this particular manner with the electrolyte flow across the center of the tool concentrically so if this shapes are perfectly streamlined there may be a case that the fluid molecules go into this local region and there is some rotation or vorticity or Vortex formation which happens here and although the remaining part of the flow moves smoothly this local flow remains on one place okay for example let's just blow it up and see what happens let's say this is the laminarity of the flow at this particular place okay and there is a big gap here so what would happen is if the flow goes inside the flow would start to rotate in this particular region without being affected even though the up the flow which is on the top of it is flowing in a streamlined and nice manner so these are uh the formation of local vortices of wpes oh this can be dangerous to the ACM process because number one the local conductivity here is really a function function of the amount of debris which is coming into this uh so-called local well poool uh we can assume that the debris gets confined here in this particular Zone you know it doesn't get moved ahead the remaining debris which is generated from let's say for example this surface or the other surfaces here would get carried away but this local debris formulation here doesn't go ahead anymore okay so there is a change in conductivity there is a change in Machining rate there's a change in so many parameters which are associated with this vortex formation so we should by and large aoid uh by designing a flow in a manner so that these voes don't exist as such so as as low Corners as low as possible uh such corners or crevices uh should be kept in designing uh the system okay so stagnation and Vortex formation are a major a major problem while considering the electrolyte flow so one basic rule that is followed that is that there should not be any sharp Corners in the flow path all Corners in the flow path should have a radius of at least about 700 to 800 microns for example you can see there is a chamfering here at the corner just for introducing uh this concept of sort of laminarity of the the flow which is guided from this corner so the initial shape of the component generally does not comply with the tool shape and only a small fraction of the area is close to the tool surface at the beginning and that results in another very interesting problem where you have to actually restrict the flow you know so you are going more towards stagnation there but then that there is a reason why we do that so in such a situation where uh The Tool uh in its first approach to the workpiece is covering very small amount of the work piece area you have to somehow ensure that the flow is is guided throughout the inter electrode Gap okay so that uh Machining can start at some point of time okay once the electric field is good enough uh for the material removal to take place so you have the concept of flow restrictors which you put in such a situation uh and just to ensure that the the supply of the electrolyte uh is properly guaranteed over the the whole workpiece surface so you artificially restrict the flows by creating some Dam like structures so that it can go past the whole surface and cover the whole surface okay so one issue about electrochemical Machining is that you want to have the electrolyte spread out to over the whole area of Machining and the other issue is how to get the field to be of substantial value so that dissolution can start taking place okay so this is a problem which would you would hit upon when you are talking about Flow Design that sometimes the areas are not fully covered because the tool shape initial uh initially at the beginning of the Machining may not be uh at all uh uniform or un even with respect to the workpiece shape so there is a possibility of a lot of workpiece area remaining as such uncovered okay so that's uh another issue you have to take care of for while doing flow designing so in many situations for example when initial uh work shape confirms to the tool shape for example in this particular case uh you see that this is the tool okay and there is a boss uh on this workpiece which has somehow come into the path of the electrolyte flow okay so there is a small shamer corner of this uh tool and there is a concentric uh coaxial channnel which is available for for the electrolyte flow and the boss has somehow the boss on the surface which was existing from before has somehow uh sort of come in alignment with this coaxial fluid path which has been artificially made in the tool surface okay so what will it result in so if such a uh Ridge or a boss comes in the path of the flow the first obvious reaction that a designer would have is to somehow remove it okay or make it non-aligned otherwise if the flow keeps on continuing here the boss shape would remain because there is no electric field which is actually trying to remove or dissolve away this this boss uh because the electric field happens between the tool and the workpiece here okay and this zone is far far away from the electric field so you'll have to design the the flow in a manner so that these uh problems uh like existence of such boss or ridges uh may not Hamer the overall strategy of Machining that you are following for developing the whole uh workpiece surface so a tool with an electrolyte Supply slot is pretty simple to manufacture but uh there is a downside that these leave ridges or bosses on the workpiece when you talk about uh such concentrically uh you know so such concentric tool Lings with with uh flows which are coming axially out of the tool surface itself so one option can be that uh The Ridges can be made very small by making the slot sufficiently narrow okay so instead of doing this whole width here W you go for a much narrower slot that is let's say w W Dash w- is much much smaller in comparison to W okay so that would ensure that the ridge or the boss has minimum size if possible but then the fall of having a very narrow slot is that sometimes the flow may not be enough so that the whole area on this other part of the work piece may be covered with the flow okay so uh the slot width should be designed with an idea of of how much it would leave in terms of boss or ridges on the surface and also with an idea of how much electrolyte really is needed to be dispensed per unit time so that the whole area of the workpiece surface may be covered so the flow typically from a slot takes place in a direction perpendicular to the slot and uh the flow at the end is poor so velocity of the flow is highest here where it is Ting out and the velocity here is comparatively lesser because there is frictional effect between this point and this point okay so that's another issue that the uh the um flow is different in terms of velocity as it emanates or as it goes away from the uh workpiece Zone therefore the slot should be terminated near the corners of the workpiece uh so that there is always a possibility of a dam formation as if the the the fluid is going all the way up to the corner and then emanating out uh between the corner and the the tooling as can be Illustrated here so you can see these are these flow restricted dams which uh have been talking about so that uh the the flow of the electrolyte May ooze out from these Corners thus uh the question of stagnation because of low velocity at the corners would be avoided number one because there is a continuous Supply and there is a continuous uh sort of fluid bed which is permanently present on the surface of the work piece so some of these strategies can be intelligently designed for such a system when you are designing uh the tools for with with sharp corners for ECM process you have to follow some thumb rules for example the distance between the tip of a slot and the corner so you're talking about this distance okay from this tip to the corner and that should be at least uh 1.5 mm for obvious reasons that there has to be sufficient so there there may be some electrochemical Machining of the tooling itself although the tooling is chosen in a manner so that it doesn't happen but then one has to ensure that the slot doesn't go all the way to the side of the tool pH uh and therefore there has to be a gap okay and uh also uh the slot with a width of typically width of 700 to 800 Micron is recommended as I earlier uh told also and when the work piece corner is rounded uh the slot end should be made larger for example you can see a particular case here this is a rounded Corner okay and uh you are deliberately making the slot and larger because you want the flow to reach in all the directions if the slot were narrow here maybe the flow would not have uh been able to reach sufficiently the holy fully chamfered corner so you have to ensure that the floor reaches okay so maybe some shape equivalence between the uh chamfering here and the Sham of the corner of the slot is needed and uh the shape and location of the slot should be such that every portion of the surface is supplied and there is no passive area for example see this uh very nice problem here so you have a straight slot cut at a particular angle on this particular tool and you can see that the electrolite although it emanates from uh the slot uniformly is not able to spread it to the ho whole area so this area remains passive okay similarly in this case it remains passive here so a better design of such electrode would be for example to change the slot into a curve curvature with a certain curvature so that you can guide the flows okay so in this particular case there may be a flow coming out here there may be a flow coming in this direction okay there may be a flow coming in this direction as already Illustrated this direction perpendicular to the slot is already Illustrated and so the idea is that the curvature of the slot has been designed in a manner so that the full area can be supplied with the the electrolyte same is the case here okay you have just taken that slot which was earlier a straight edge or a combination of straight edge here and have just introduced a small curvature so when you introduce the curvature you see that there is a coverage of the elect assuming that the electrolyte emanates perpendicularly to the the slot and it goes and covers the whole surface okay so some of these strategies need to be developed intelligently by looking at the the work piece shape that you really want to machine and uh it is a job of a designer to also while designing the tool consider that the flow of the electrolyte should be uniform and it should at least cover all the surface that one is trying to machine so we have talked about uh FL restrictors we have talked about how the slot shape and size can be changed what are the thumb rules which are followed particularly for Designing slots near Corners uh if the corner is shamer what is the thumb rule followed all these aspects of Designing of how uh the flow can be uh emanated out of the tool have been looked upon and these are some practical problems related to ECM just because it is a uh time based process that as the electrolyte keeps on circulating uh the debris would be generated and the work piece would slowly get machined off so the other issue which is needed for uh considering ECM is how to develop good insulation on the tool and there are good number of reasons for developing insulation for example let's say this uh figure here considers uninsulated a completely non-insulated tool so there would be CCM carried out between uh the tool and the workpiece in this direction which is what we need or what is intended for but then also there would be ECM carried out between the sides of the tool and the workpiece okay and therefore as you can see here that if we were intending for a some size of the hole okay that we were trying to drill with ECM maybe the hole has gotten extended and there is a lateral cut th ensuring that the the hole is broader in size and so one way to prevent this from happening is to somehow stop the field you cannot stop the flow of the electrolyte because it goes and covers all the surface but you somehow stop the field uh to go and take out the material at the corners by designing this uh insulation okay on the tool surface which would typically mean that the current now the current density Vector which is responsible for all the electrochemical movement is only confined to this portion of the surface okay the remaining portion is insulated now and so there is no field loss as such from this portion of the surface onto the other portion of the work piece here and uh that ensures that uh the size of the hole that was intended while doing let's say the drilling operation with cm is uh met so another example of insulation can be uh seen here in fact look at the difference that it creates between the shape here and here just by adding these two insulations on the electrodes so because it's a die syncing process and it goes into the the this a case where the tool is actually physically going into the workpiece thus trying to uh make a matching of you know the topology of the uh tool surface itself onto the workpiece surface it is very important that uh we get rid of all those stray effects which would happen between the walls of the Tool uh which is away from the surface of the tool okay uh onto the workpiece so insulation can be uh done by securing uh reinforced or solid plastic material to the tool with epoxy resin uh cement and sometimes plastic screws in fact uh one has to be careful the the moment the term insulation or the moment the term insulated pads come into picture they have to be very well pasted onto the surface of the Tool uh a little bit of gap between the the insul insulation as such and the tool surface would result in number one incomplete finishing uh because bosses or ridges May formulate because of that gap on the surface at the same time it can also take away the insulation with time because water because there's a continuous action of the electrochemical action which is going on into whatever portion is uninsulated and left over of the tool side so therefore um typically you have to secure the insulation very firmly onto the sides of the tool also you can actually insulate by applying synthetic rubber coating on the artificially oxide oxidized tool surface this is a very prominent technique particularly for copper tools okay so you can give a coating by masking the tool appropriately and giving coating so that later on when you remove the mask the portions which are Beneath The Mask uh would be not Co okay and so you have a very clearly demarcated uh insulated and non-insulated region iion on the tool surface the boundaries of the insulation layer should uh not be exposed to high velocity of electrolyte flow uh because sometimes the tier of the glued layers as I already told you and this automatically by virtue of the fact that insulation is needed mostly towards the end okay uh in in designs uh where the tool has the concentric is the capability of delivering the um the electrolyte coaxially this is really not a major issue because the velocity seems tends to drop from the center to the side of the particular tool okay but in cases where electrolytes are flown like in this particular case electrolytes are flown from one side to other one needs to ensure that the insulation is properly glued onto the uh workpiece surface let's now look at uh the other part that is electrolytes which you need to design for ECM systems so let's uh just first find out what are the basic functions associated with an electrolyte so one it allows the completion of the electrical circuit between the tool and the work piece okay so this is the only conducting means between the tool and the workpiece and it should allow uh flow of large currents so that those current density is typically account for the material transport from the workpiece surface onto the the electrolyte itself also the electrolyte should have Ways and Means to sustain the required electrochemical reaction which is going on and it should be a good carriage for the heat which is generated by the electrical power that is pumped on from the electrode the tool electrode onto the work piece okay and also to carry away the waste products in turn so it should be able to somehow locally carry away whatever debris is generated and it should also be able to carry out the heat that is pumped in from the uh the to tool side to the work piece side okay by the i squ r power that it is delivering onto the electrolyte so what are the requirements so the first function should require that the electrolyte be uh of large electrical conductivity okay and uh the second function should require that it should continuously dissolve work material at the anode so it should sustain the electrochemical reaction at the anode anode is the work piece in this particular case and it should discharge or or it should discharge the the metal ions uh that come in by virtue of some chemical reactions thus leaving no residue on the tool surface okay so whatever uh ions are IM manting from the workpiece surface should be able to get chemically dissolved within the electrolyte system so electrolyte is a sort of barrier between the material that gets transported from the the workpiece and the tool otherwise there would be a coating on the tool although you cannot prevent 100% coating there may be instances where there is some formulation of oxide or something on the tool with time but then one has to ensure that the choice of electrolyte being in a way that whatever comes out of the work piece gets precipitated and doesn't get deposited onto the other uh electrode so the dissolution of the uh anode should be sustained at a high level of efficiency uh by the electrolyte and uh there are some other cic constituents of the electrolyte like hydrogen ammonia or alkaly Metals uh which should be part of the regular process of the electrolyte so whatever the tool generates is either a gas okay or something which again creates a reaction with with the the electrolyte itself the electrolyte of course must have good chemical stability so it should not degrade with time uh and uh it should be as inexpensive and safe environmentally safe as possible because it should not create any toxic Vapors or fumes for uh the operator to get exposed so in a nutshell good conductivity of the electrolyte the ability to dissolve away the workpiece by precipitating whatever is coming out or whatever cic reactions are happening at the tool side or the cathode side uh is supported by imation of a gas like hydrogen or ammonia something like that and the Very fact that it should be of a highly sustained nature or as far as the um the electrochemical operation of the work piece goes so these are all necessarily included uh for the choice of electrolytes let's look let's look at some of the systems which uh are existing typically for uh some conventionally used allo of engineering importance so for iron based systems the electrolyte that is normally used is chlorine Solutions in water you know brine solution comparing or consisting of kitchen salt and water uh 20% concentration is typically used for iron uh based uh work pieces for electrochemical Machining for nickel based uh samples you use uh either hydrochloric acid or a mixture of again salt water and h204 for titanium based uh constituents can use a combination of 10% hydrochloric acid 10% HCL hydrochloric acid and then 10 nitric acid for a Cobalt chromium tungsten based system people have tried again Salt Solutions and for uh tungsten carbide uh which is very often used for tooling applications strong alkaline Solutions so these are typically some of the electrolytes which are used uh for the ECM Machining process we now look at the ECM plant uh the way that the electrolyte is circulated and all this Machining happens so this is a very nice schematic of what all goes into an ECM system so you should have a uh electrolyte pumping mechanism this is a electrolyte storage and uh basically have a pumping mechanism and a discharge mechanism so normal operation you can keep this valve on so that whatever pumps out goes in back and if it is uh switched off then the electrolyte can get circulated into the system so the electrolyte goes through a filter uh this right here is the filter and uh it is injected into the tool this is a coaxial tool where you can see the electrolyte coming out of the tool in a very uh small slot at the end of the tool here right here and uh then the electrolyte flows on both directions okay into over the the work piece surface as such uh it discharges whatever hydrogen or gases come out or IM manate of the tool s side uh there should be a capability of uh blowing them out so uh this environment being closed whatever hydrogen uh is generated or ammonia is generated as a subprocess of the tool side okay so where all the iron transport would happen because of the generation of the gas that gas can be discharged so there should be a discharge port for uh the the byproducts of the chemical reaction coming out and then of course U uh there can be a way that you can recirculate the electrolyte so you can basically either precipitate and uh do a sludge discharging okay so that whatever electrolyte you can recover here can be recirculated back although it's really not a very good idea to do that and then of course you should have a very strong stage uh which uh should have enough rigidity to sustain uh the deflection of the tool as I already have Illustrated before this Zone here of uh flow is so small that the viscous forces provided by the flowing electrolyte sometimes gives huge amount of pressures and force uh is basically pressure times area so whatever interfacial area is there on the tool surface that uh kind of gets influenced by the force that it feels and so if the tool is not rigid enough it is amenable to wobbling sometimes particularly when you are feeding and that may create a local Zone which is much more uh in its Dimensions than the intended dimensions of that zone okay so therefore one has to be careful about the uh the holder the tool holder it should be of sufficient amount of rigidity and uh a change of temperature may also cause uh relative displacement and somehow this design should be able to take care of this aspect also so if need be sometimes the tool needs to be cooled so that there is no tool needs to be cooled so that the uh the relative displacement between the the tool and the work piece don't happen because of temperature uh gradients or thermal gradients also to avoid corrosion wherever possible uh non-metallic material should be used which is not amenable to the electrochemical Machining process as such uh the workpiece holder is very much prone to anodic attack therefore it needs to be surface passivated uh sometimes with ti tum or a stable any other stable metal as most of the components are in close proximity to the electrolyte even they are exposed to corrosion it's a electrochemical process okay so wherever there is a electrolyte and wherever there is a field there is corrosion so the material should be chosen in a manner so that identical electrochemical Behavior comes of all these materials so in a nutshell uh the job of a designer of a electrochemical plant is really to look at uh the Machining system from an overall standpoint so the the main idea is that whatever electrochemical changes are happening should be limited to either the tool or the work piece okay and that also on a very minuscule basis on the tool side the remaining components which are participating in this electr chemical Machining process and is amenable to attack uh because of the reach of the coolant or reach of the field they should be passivated in a manner so that they don't influence the the electrochemical process of Machining going on uh so that's in a nutshell what the electrochemical Machining unit should look like we will talk about some other aspects of uh this electrochemical Machining in our next uh lecture and we'll try to cover uh some additional processes like electr stream drilling or electrochemical grinding or even electrochemical drilling okay so ECG or ecd ESD as they are commonly known as and we'll try to then wrap off uh by saying or or by looking at the applications that such systems may have to Microsystems Engineering thank you