Monday, June 29, 2009
Home-based learning exercise
Due to H1N1, this week we do not need to go to campus but instead we study at home using the Heucampus to communicate with our tutors. Also, the lab or practical lesson is canceled.
Turning machine
Although my goal is only aimed for the grinding machine but my this blog will touch on the turning machine as the lesson of the grinding machine had ended.
This week we learned the structures and the functions of turning machine which was teached by Mr Tay. As other people told me, once started the lesson, he introduced many formulae. First was the cutting speed(v), which depends on the material of the work piece and the cutting tool being used. If the material of the work piece was soft, for example, plastic, and the cutting tool was diamond, which is the hardest substance in the world, the cutting speed need to be increased and vice versa.
Next was the spindle speed(n). Spindle is the wheel that clamps the work piece while cutting. Its formula is
n=(1000v)/(π x d)
where v =cutting speed
d=diameter of the work piece
There are differences in calculating the diameter for different process although the work pieces may are of the same dimensions.
For facing,
d=d' x(2/3)
For side cutting,
d=d'
where d'=original of the diameter of the work piece
And finally was the feedrate, which is the speed of x-axis and z-axis moving when they are set into automatic mode. These two axes can be moved manually or automatically. To determine this feedrate, we need to refer to the turning machine manual which lists all the feedrates for different work pieces and tools or sometimes to save time, Mr Tay will tell us. The speed of the feedrate can affect the surface of the workpiece. The slower the feedrate, the flatter the finishing of the work piece's surface.
These were all told by Mr Tay this week and the week after common test, we will have to start to use the turning machine on our own.
This week we learned the structures and the functions of turning machine which was teached by Mr Tay. As other people told me, once started the lesson, he introduced many formulae. First was the cutting speed(v), which depends on the material of the work piece and the cutting tool being used. If the material of the work piece was soft, for example, plastic, and the cutting tool was diamond, which is the hardest substance in the world, the cutting speed need to be increased and vice versa.
Next was the spindle speed(n). Spindle is the wheel that clamps the work piece while cutting. Its formula is
n=(1000v)/(π x d)
where v =cutting speed
d=diameter of the work piece
There are differences in calculating the diameter for different process although the work pieces may are of the same dimensions.
For facing,
d=d' x(2/3)
For side cutting,
d=d'
where d'=original of the diameter of the work piece
And finally was the feedrate, which is the speed of x-axis and z-axis moving when they are set into automatic mode. These two axes can be moved manually or automatically. To determine this feedrate, we need to refer to the turning machine manual which lists all the feedrates for different work pieces and tools or sometimes to save time, Mr Tay will tell us. The speed of the feedrate can affect the surface of the workpiece. The slower the feedrate, the flatter the finishing of the work piece's surface.
These were all told by Mr Tay this week and the week after common test, we will have to start to use the turning machine on our own.
Saturday, June 6, 2009
Final week
This week was really a critical week.
We learned a new technique of grinding, that is punching. We placed the thicker side of the work piece against the stopper on the magnetic table. According to what Mr Teng said, this was important due to safety reason. It prevents accident from occurring. It was because if we ground the thinner side first, there might be some students forgot to move the grinding wheel forward and after turn the work piece over to the thicker side, they just move the work piece inside, then the grinding wheel will hit the work piece and it might fly out due to huge impact. Punching is a technique that moves the y-axis slowly, 10 mm at a time. It was different from what we had done last time. Last time, we either moved the y-axis continuously or did not move it at all. But now is move y-axis gradually.
Also, we learned to grind the vertical surfaces of the 'U' shape. To do this, we could just grind them using the back side of the grindning wheel. There is a step at its back side in order to grind such vertical surfaces.
Luckily, in this final week I did not make mistake.
And next week, I am going to learn turning machine, which many people said it is really hard as there are many formulae involved. Hope that I can cope with it and no accidents occur.
We learned a new technique of grinding, that is punching. We placed the thicker side of the work piece against the stopper on the magnetic table. According to what Mr Teng said, this was important due to safety reason. It prevents accident from occurring. It was because if we ground the thinner side first, there might be some students forgot to move the grinding wheel forward and after turn the work piece over to the thicker side, they just move the work piece inside, then the grinding wheel will hit the work piece and it might fly out due to huge impact. Punching is a technique that moves the y-axis slowly, 10 mm at a time. It was different from what we had done last time. Last time, we either moved the y-axis continuously or did not move it at all. But now is move y-axis gradually.
Also, we learned to grind the vertical surfaces of the 'U' shape. To do this, we could just grind them using the back side of the grindning wheel. There is a step at its back side in order to grind such vertical surfaces.
Luckily, in this final week I did not make mistake.
And next week, I am going to learn turning machine, which many people said it is really hard as there are many formulae involved. Hope that I can cope with it and no accidents occur.
Mistake again
I think I already have phobia in grinding due to last week mistake. So this week. I amde mistake again!
When zero sets the work piece, which means bring the grinding wheel juzt touches the work piece before starting grinding, I turned the wheel that control the z-axis too fast, so it results in cutting too deep on the work piece and a burn mark can be seen clearly on my work piece. Because of this, the grinding wheel also being affected, so I need to dress the wheel once more. Again, Mr Teng was so kind. He did not scold me. He just said that next time must be more careful and do not make the same mistake again. Then, I proceed to grind other surfaces with extra care. Therefore, I did not mistake again.
This week i was able to complete all surface and square grinding.
At the end of the lesson, Mr Teng told us nest week would be the final and most critical week for grinding. This made me feel worry. I was afraid that I would make mistake again.
When zero sets the work piece, which means bring the grinding wheel juzt touches the work piece before starting grinding, I turned the wheel that control the z-axis too fast, so it results in cutting too deep on the work piece and a burn mark can be seen clearly on my work piece. Because of this, the grinding wheel also being affected, so I need to dress the wheel once more. Again, Mr Teng was so kind. He did not scold me. He just said that next time must be more careful and do not make the same mistake again. Then, I proceed to grind other surfaces with extra care. Therefore, I did not mistake again.
This week i was able to complete all surface and square grinding.
At the end of the lesson, Mr Teng told us nest week would be the final and most critical week for grinding. This made me feel worry. I was afraid that I would make mistake again.
Friday, June 5, 2009
New work piece
This week we got a new work piece as shown in the photo above.Similarly, we grind the parallel surfaces first. But this week I made a big mistake! I was supposed to grind 0.12mm, which 120 microns on each of the parallel surfaces to a dimension of 16.55mm and to reach the total width of 36mm and also to achieve symmetry. However, after I ground the first surface and took out the work piece and checked its dimension, I forgot which side I had ground and which had not. I just simply place the ground side on top thinking that if was not ground yet. Then, when I took the measurement again, I only realised that I ground the same side! Now, one side is 16.44mm which was out of dimension already! And I could not grind the other side to the same dimension. It was because if I did so, the total width of 36mm will be affected. Luckily, Mr Teng did not scold me but just said, "Never mind. Now, what you need to do is grind the other surface to keep the total dimension of the width, just ignore the symmetry." So, I did what he told me but still felt very sad because of my silly mistake.
Surface K and surface H
This week we need to grind the surface H and surface K as shown in the diagram above. It was more really challenging. To do so, we put the work piece on the platform of the machine with 3 square blocks, acting as a support to the work piece. This was to prevent the work piece from flying away during the grinding process as the surface of the work piece that was in contact with the platform was too small, so it was not very stable when being magnetised on the platform. After that, we placed the grinding wheel very close to the surface K but it must not touch the surface k and tightened the knob that control the y-axis. This is also the main difference between the technique we learned in the previous week and this week. Normally, we will move the y-axis, so that all the surface is well ground but now due the small surface, but now we need not move the y-axis and just keep the x-axis moving. Then, we started grinding. First, we only ground 20 to 30 microns. This is to clean the the surface in order to make sure that the surface is flat before we could take an accurate measurement and grind to the dimension required. When the required dimension was reached, the value of z-axis was then reset to zero. Without moving the y-axis, the work piece was turned to the other site to be ground in the same way. At this time, we need not measure the workpiece again, we could just grind to the zero value of the z-axis that we had reset earlier. In such way, we could make sure that both side had equal height.
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