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Up Milling and Down Milling:
Let’s first understand the Milling Machine which I also written separate articles just check out. I will drop the link below.
- This machine perhaps most widely used in manufacturing industries after the lathe machine.
- However, In the case of lathe machine, the tools used there single point cutting tool but In the case of the milling machine, the tools used are multi-point cutting tools.
- The milling is a process of metal-removing by feeding the work past a rotating multipoint cutter. The diagram is shown below:
- This machine can hold one or more, number of cutters at a time and rotates at high speed to remove the metal at a faster rate.
- The metal removal rate is faster as compared to a lathe machine.
- This machine is used to make gears like Spur gears, and also drill the workpiece bore, and produce slots.
Parts and its brief details:
- It is the foundation part of a milling machine and all other parts are joined on it.
- It carries the entire load so it should have high compressive strength and it is made up of cast iron.
- It is mounted vertically on the base.
- It supports the knee, table, etc. Work as housing for all the other driving member.
- it is a hollow member which contains driving gears and sometimes motor for the spindle and the table.
- It is a casting that supports the saddle and table.
- All gearing mechanism is enclosed within the knee.
- It is fastened to the column by dovetail ways.
- The knee is supported and adjusted by a vertical positioning screw (elevating screw).
- The elevating screw is used to adjust the knee up and down by raising or lowering the lever either with the help of hand or power feed.
- It is placed between the table and the knee, and work as an intermediate part between them.
- It can moves transversally to the column face.
- It slides over the guideways provided situated on the knee which is perpendicular to the column face.
- The main function is to provide motion in a horizontal direction to the workpiece.
- It is also made by cast iron.
- It is a rectangular casting which is present on the top of the saddle.
- The table is situated over the knee.
- It is the part of a machine which holds the workpiece while machining.
- It is made by cast iron and has T slot cut over it.
- It provides vertical motion by moving the knee up and down.
- It provides horizontal motion by the feed screw.
- It provides a horizontal (transverse) motion by moving the saddle.
- The overarm is used to fastened arbor support.
- It may consist of one or two cylindrical bars which slide through the holes in the column.
- It is made by cast iron.
- The spindle is the main part of the machine which holds the tool in the right place.
- The spindle provides the drive for arbors, cutters, and attachments used on a milling machine.
- It is a mechanical part, on which is used as an extension part of the spindle in a horizontal milling machine.
- It is fitted on the spindle whenever it’s required.
- It holds the tool and moves it in the correct direction.
- There are generally two types of arbor supports used in the milling machine. The first one has a small diameter bearing hole, 1-inch in maximum diameter.
- And the other one has a large diameter bearing hole, usually up to 23/4 inches.
- The arbor support has an oil reservoir that lubricates the bearing surfaces.
- It can be clamped anywhere on the overarm.
- The arbor support is used only in the horizontal types of milling machine
- It is the upper section of a vertical milling machine.
- It consists of a spindle, driving motor and other controlling mechanisms.
- One end of the arm is attached to the column and other ends to the milling head.
- The ram can be a moved transversally ( in and out) on the column by a hand lever.
Column and knee type machine:
- It is the very common milling machine types.
- In this machine, a vertical column is attached to the bed which consists of all gear drives which rotate the knee and saddle.
- A knee is situated on the base which provides vertical motion to the workpiece or which moves up and down.
- A saddle is attached to the upper section of the knee which can move in the transverse direction.
- The table is placed over the which can hold the workpiece by use of climbing bolts.
In this there are several machines like:
Vertical milling machine:
- The spindle if this machine is in the vertical position.
- No arbor is required in this machine.
- The cutter tool has the cylindrical shape and the cutting edges are situated at the circumference of the cylindrical face.
- The up milling is also called as conventional milling or Climb up milling.
- In which the cutter and feed moves in the opposite direction i.e the rotary cutter moves against the feed.
- With reference to the adjacent figure, the cutter rotates in the anti-clockwise direction, while the direction of feed is from right to left.
- So, due to this opposite motion, the width of the cutting chips gradually increases from minimum to maximum.
- There is massive friction between the cutter and workpiece which results in generating a large amount of heat.
- This is a safe operation because It has no tendency to drag the workpiece into the cutter.
- The up milling is generally used for milling of casting and forging.
- The down milling is also called a Climb down milling.
- In case of down milling, the cutter rotates in the same direction as that of the feed.
- In down milling, there is less friction involved between the cutter and the workpiece as both.
- Therefore, the cutter and feed are moving in the same direction. This small amount of friction results in the generation of minimum heat.
- Here, the thickness of the chip varies from a maximum to minimum during the process.
- This machine poses a longer tool life.
- This machine produces a good surface finish.
- This type of machine generally used for finishing the operation like sawing, grooving, keyway cutting, etc.
Difference between Up and Down Milling Machine:
|Sl.No||Up Milling||Down Milling|
|1.||This machine is also called as conventional milling or climb up milling.||Down milling is also called a climb down milling.|
|2.||The cutting forces act upward.||The cutting forces act downward.|
|3.||Up milling is mostly used for rough cutting operations.||Down milling is used for finishing operations.|
|4.||Due to more tool wear rate, the durability of the tool is less.||Due to less tool wear rate, the durability of the tool is more.|
|5.||Tool wear rate is more, as the direction of the rotary cutter is against the feed.||Tool wear rate is less, as the direction of a cutter is the same direction as the feed.|
|6.||This process is mostly used in the conventional way of cutting the surface.||Nowadays, down milling is a better operation choice then up milling machine.|
|7.||Effective cooling is not required during cutting action.||Effective cooling is possible during cutting action.|
|8.||Cutter rotates against the direction of travel of the workpiece during metal cutting.||Cutter rotates in the same direction of travel of the workpiece during metal cutting.|
|9.||Poor surface finish.||Good surface finish.|
|10.||It requires a large amount of force compared to down milling.||For down milling, there is a requirement of less force.|
|11.||This machine is mostly used cutting of brass, bronze, and ferrous materials.||And whereas this is applicable to aluminum and aluminum alloys.|
|12.||Chip thickness starts at zero and increases towards the end of the cut.||Chip thickness is maximum initially and reduces to zero at the end of the cut.|
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