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Cutting Tools

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Video 1: Single Point Cutting ToolSo, now we are moving to the cutting tools this is the second chapter that we are going into. And as you can see the turning process which is a single point cutting tool process the simple process we consider is a basic turning process. In the turning process we have 2 things one is Generatrix, another one is a Directrix, you can see here Generatrix and Directrix. So, whenever you are  considering the turning process the rotary motion will generate the surface that is called Generatrix and the direction that you are giving in the feed are the feed direction that will called as a Directrix; that means, the cutting speed whatever the arrow that you are seeing here generate the Generatix at the same time this one will give the Directrix. Normally it is a circle generatix is a circle and the directrix is a line. So, indirectly you will get a cylindrical surface that is about the generatix and the directrix we are going to study in detail about the cutting tool. Normally 2 important phases are the surfaces in a cutting tool are Rakes face or rake surface and Flank face . So, we goin detail about these things before going to these we should know also what are the input conditions in the turning process, that is a single point machining process the basic input parameters are cutting speed feed and depth of cut. These are the basic 3 inputparameters that one give and the cutting edge that is a most important thing which separates the work piece and the chip. This is the overview of tool geometry. The tool geometry will have many things some of the important things are shown in this slide the tool shank, this is the tool shank and the tool angles different tool anglesare there on the different different faces of the tool and different different faces the faces will have this angles and the edges cutting edge and principal cutting edge, auxiliary cutting edge and all those things and the axises, how you are referring to the axises and all those things also we see in the tool signatures. If you see this picture it will have a one is the rake face this is called a rake face the cutting edge normally this is a principal cutting edge which normally involve in the cutting process. So, back rake angle nose radius this is the flank surface this is the flank surface this is the rake surface and this is the, another flank surface that is called some people it called as a auxiliary flank surface, this is called principal flank surface. So, there are different terminologies are there that are used by the different authors of the books and the researchers. So, relief angle, some people they say flank angle, some people they say clearance angle, some people they say relief angle. So, these are the samethe different books will give you different varieties, that is some people say relief, some people say clearance, some people say flank angles. So, tool geometry if you see the tool geometry normally tool geometry has angles now we are going to see only the tool angles. So, if the 2 angles on the rake surface are nothing, but the rake angles one is the back rake angle, another one is side rake angle see this is the rake surface. The rake surface will have this is the backrake angle and the side rake angle this is the side rake angle. So, these are the 2 angles that is on the rake surface let me is explain you how it looks like in the normal sample that we fabricated specially for you using a single point cutting tool. So, this is a single point cutting tool and this is the rake surface and this is the principalflank surface some people say this is end flank surface and this auxiliary flank surface this rake surface will define 2 rake angles one is the back rake angle another one is side rake angle. This is the surface which is defined by a back rake angle like this at the same time if you see it is having a slantness here so, this is called side rakeangle. So, at the same time this is my cutting edge another one is this is another one cutting edge. So, this cutting edge will have one angle if you put a plane like this it will have certain angle that is called one of the cutting edge angle. If you put a plane like this it will have certain angle so, these are the 2 cutting edge angles if you call it as a principal cutting edge then it is called principal cutting edge angle or end cutting edge angle if you say this is the side cutting edge if you put a plane like this, this is called side cutting edge angle, at the same time this is my one flank surface or the clearance surface or the relief surface this is another one flank surface. Normally in this course we take it as a flank surface so, this a one flank surface, another one this is another flank surface this alsomakes some slantness that is called one of the flank angle this also make the some slantness that is called another flank angle this flank angles always use to avoid the rubbing action with the final product. Coming to the slide we can see the cutting edge angle one is side cutting edge angle and end cutting edge angle. So, if you considerthis is principal then this angle is the end cutting edge angle if you consider this as a side cutting edge then it is called side cutting edge angles. ASA system follow one nomenclature, ORS system follow another nomenclature that why there is slightly confusion. So,relief angle or the clearance angle or the flank angle this surfaces has some slantness and those are the flank angle. So, we see rake surface and it is angles flank face and it is angles rake face directs a chip flow this is the rake face whenever you are cutting the material it will flow like this; that means, that it will directs the flow of newly formed chip. So, that is the rakes face function and it can be 0 rake angle it can be positive rake angle, it can negative rake angle also when it called 0 if it is parallel to the shank it is called as 0, normally if you take like this, this is called positive if it is filled like this, like this, it is called negative rake angle so, this is about the rake angle. The flank angle provides the clearance as I said if I am if I have a work piece and I am cutting the work piece in this type. So, if I am cutting this is the clearance this is the clearance or this is the flankangle this flank angle provides to the tool because to avoid the rubbing action. Assume that it is the same distance then what will happen it will rub so, to avoid the rubbing action normally the flank angle is provided. Importance of the rake angle so, if you can see as I said this is my rake angle back rake angle. So, if the rake angle is increased; that means, I am going to increase like this. This is my new rake angle. So, if I am going to increase my tool become much sharp. So, if it is sharp assume that I have knife with high sharp what will happen it is very easy to cut a vegetables and all those things. That means the force required for by a person to cut the vegetables is les; that means, lower forces required at same time it alsoimprove the surface finish. In terms of if I say the vegetables cuttingit will you can slice it properly without any much disturbance or no change in the surface roughnesses. So, if my forces are less in a cutting tool to machine a material because of increase in the rake angle what will happen power consumption also goes down because power consumption is nothing, but F c into V, if my cutting force decreases; obviously, cutting force multiplied by cutting velocity will also goes down so, the power consumption will be less. But the basic problem if I am going to increase rake angle like this, what will happen tools strength goes down because I have very less tool to cut the work piece material that is the problem. So, at the same time if I have a less material to cut what will happen temperature is continuously going into tool from the chip side from the shearing side from the work piece side and all 3 sides because of whichif my conducting area is very less, what is happening is it thermal softening of the tool takes place and it may fail at early stages. So, these are the 2 drawbacks if I increase the back rake angle. However it is good from the point of our consumption as well as less forces, this is a side rake angle as I we can see the from the tool thatwe have seen there are mainly 2 types of rake angles one is back rake angle and side rake angle . So, normally as I said we have a 3 types of a rake angles, one is positive rake angle this is called positive rake angle where chip can be easily flown on top of it, another one is zero rake angle as I said it is parallel to the tool shack and the negative rake angle if you see the negative rake angle it is like this. This is the negative rake angle, this is the positive rake angle and here angle is 0. So, 0 are negative rake angle or employed in the carbide ceramics and similar hard tools. Basically the hard tools are used to machine the hard materials if you want to machine very hard materials with positive rake angles as we have discussed in the earlier slides, the tool material to counter the machining is very less from that point of view the thermal softening or the strength of the tool will be less that is why always at the most of times the researchers uses the negative or 0 rake angle whenever the researchers want to cut the hard materials at the same time if the tool material is also ceramics or brittle materials. It increases the tool forces, but keeps the tool in compression and provides added support to the cutting edge, this is the positiveness about the 0 or the negative rake angles important thing is performing a intermittent cuts if there is a intermittent cuts; that means, that there is a gap between cutting and cutting what will happen there will be a shack . So, if it is positive rake angle there is a tendency of bending or catastrophic failure if you are taking a brittle tool material that is a another problem in a positive that is why you go or the people prefer 0 rake angle or negative rake angle positive rake angles are provided to the ductile tool materials like HSS the rake angle ranges from 5 to 15 degrees and lower values for the harder materials. So, flank angles normally flank angles as I said that it uses for minimizing the rubbing or eliminating rubbing nothing in this worldis 100 percent elimination. So, you try to minimize only so, normally you will provide a flank angle as you can see in this picture this is the clearance. So, that this particular tool would not touch this particular work piece so, this is the flank angle. So, that the clearance will be given and this is the final product that we are going to get whichwe want at a good level or the good surface finish good tolerance and all those things. We do not want to any type of disturbanceon the surface. So, if the flank angle is 0 what will happen this continuously rubs and the final product will be like this. So, we do not want the rubbing of this one higher flank angles will also reduce the strength if I am increasing the flank angle what will happen, my tools strength goes down again as we have seen in the rake angle type, but if you increase what will happen the rubbing action will reduce this is my tool new tool. So, my rubbing action will reduce; however, the tool strength goes down the flank angles have no influence on cutting forces and power. So, the large angles have are selected. So, it may not have much affect I cannot say 0 affect, but it may not have much effect on tool or the cutting forces the machining forces that are there involved during the machiningprocess so, you can choose the optimum not maximum, optimum so, that the rubbing action can be minimized normally 5 to 12 degrees were chosen for HSS tool and the lower for the brittle materials were chosen. So, there are 2 types of flank angles oneis end flank angle another one is a side flank angle whatever you are seeing is end flank angle in one way of system it is end flank angle. If you consider it has as a side flank face it is side flank angle. So, it is depend on system to system ASA system ORS system and all.
Video 2: Cutting Edge Angles and Nose Radius