Copy and contour machining: Comparison
Copy machining is where the end mill moves linearly following the workpiece cross-sectional geometry. Contour machining is when an end mill machines around the workpiece at the same depth, then sinks deeper repeats the operation shown in the image.
Contour machining is advantageous over copy machining because machining on level surfaces means that any changes in cutting resistance are even and easily manageable. However, contour machining has a disadvantage that the cutting points are concentrated in one area and therefore large tool wear can occur.
Copy machining
Contour machining
Copy and contour machining: Copy machining
Copy machining includes run-up (or up-copy) machining and run-down (or down copy) machining. As shown in the image, when run-down machining, the chip thickness is largest near the centre of the cutting edge where the cutting speed is the lowest, but this can cause abnormal damage on the end mill.
Up-copy milling
Down-copy milling
At the cutting edge
where cutting speed is
fastest, the chip thickness becomes largest.
Abnormal damage is
likely to occur to the tool.
Near the centre of the cutting edge where cutting speed is slowest, chip thickness becomes largest.
Abnormal damage is
likely to occur to the tool.
Copy and contour machining: Contour machining
When contour machining, an end mill cuts the workpiece axially from top to bottom at a fixed depth of cut as shown in the image and only the lower part of the cutting edge suffers from wear. Measures to prevent this include a method to first rough cut large portions using the whole cutting edge as shown in the image, and then to go on to perform the finishing. This is called one-shot roughing and contour run-up machining. The use of this machining method will lengthen the interval between tool replacements, increase roughing efficiency and shorten machining times.
Ramping
Many indexable insert end mills do not have a centre cutting edge. Therefore, when pocketing with these end mills, vertical plunging is impossible so ramp machining is used instead. This allows pocketing with a single tool, enabling tool consolidation and shorter machining times.
End mills for ramping need a minor edge inside the wiper edge. End mills without this type of insert geometry cannot be used for ramping. The maximum ramping angle is determined by the angle of a line connecting the innermost point of the minor edge and the innermost point of the wiper on the opposite corner.
Maximum ramping angle
Ramping angle
Maximum ramping angle
Rib slotting: Ribs
Ribs are the reinforcing parts of thin moulded components an example of which is shown in the image. The ribs of moulds are usually produced using electric discharge machining (EDM). However, the electrodes need to be manufactured and the machining of these electrodes can be time consuming. So, replacing electric discharge operations with machining using end mills can shorten the overall manufacturing time.
Rib
Rib slotting: Rib slot type
However, for rib slotting, thin, long end mills have to be used that can easily bend and vibrate, making a good surface finish less likely to be achieved.
Rib slot type
Through rib
Blind rib
Trochoidal and helical machining:
Slotting by trochoidal and conventional method
Trochoidal machining is a method that continuously repeats an arc type cutter path as shown in the image. The move does not strictly follow a true trochoidal curve, but it is close to it and therefore called trochoidal machining.
When conventional slotting, the end mill machines the slot when in contact with its full diameter. This full diameter contact means that the cutting loads on the end mill are high, in comparison to trochoidal machining where contact with the workpiece is short. This reduces the cutting load and allows for high-speed cutting.
Trochoidal and helical machining:
Pocketing with trochoidal method
Trochoidal machining is also used for pocketing as shown in the image.
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Trochoidal and helical machining:
Helical method
Helical machining is a method used to drill or form a hole with an end mill moving in a spiral direction as shown in the image. The cutting load is lower than when vertical feed milling, thereby reducing the cutting resistance and allows high-speed cutting because the chips are broken into shorter lengths.
Furthermore, higher accuracy holes can be machined by using a low feed in the vertical direction that reduces cutting resistance. This method also makes it possible to machine holes of different diameters with the same tool, allowing tool consolidation and thereby reducing costs.
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Helical plunge cutting
x
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Copy and contour machining:
Rib slotting:
Trochoidal and helical machining: