Turning & Types of Turning Process

Turing is one of the basic machining processes. It is used to remove the work piece material with the help of the cutting tool. By using the turning process we can produce wide variety of products.

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The turning operation is performed on the lathe machine.

Turing is used to produce typically rotational and axis- symmetric parts that have amenities such as threads, grooves, holes, contoured surfaces, tapers, and various diameter steps.

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Cyclic process:

Loading and unloading time: Mainly the load time depends upon the weight size, type of fixtures and complexity of the work piece material. Time required for loading the material, fixed the material in the turning machine and the required for unloading the machine is known as loading and uploading time.

Cut time:

In the process the cutting tool is used to perform all the cutting operation on the work piece. The cutting time is calculated by dividing the total cut length and the feed rate. The tool speed is related to the work piece.

Ideal time:

Ideal time is also known as non-productive time. In the process cycle if one of the machine processes comes to an end, and waiting for another tool or work material process to begin, the difference time is considered as ideal time. The ideal time consist of the tool approaching and withdraw from the work piece. Movement of the tool between the features, machine settings and tool changing depends on the ideal time.

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Replacement time required for tool

We can see the tool replacement when tool damage takes place. We never see the tool replacement in very cycle after the completion of life time the tool must be replaced.

Different types of turning operations that are performed internally and externally

  • Face turning or facing
  • Straight turning
  • Eccentric turning
  • Shoulder turning
  • Tapper turning
  • Grooving
  • Thread cutting
  • Cut-off
  • Drilling
  • Boring
  • Tapping
  • Reaming

Face turning or facing

Face turning is also known as facing operation. The work piece material is fixed in between the chucks that are mounted on the lathe machine. The chucks rotate in the shaft direction. The tool is rotated along the perpendicular direction to the axis of the work piece material. This process is used to produce a square surface at the end of the work piece material or to get a chosen length.

Straight turning

In this process of straight tuning the work piece is fixed in between the chucks, with the help of tool feed that is provided along the longitudinal direction with required depth of cut. Straight turning operation is used to produce a cylindrical surface by removing the excess materials by providing the required depth.

Eccentric turning

If the work piece material has more than one axis of rotation at that case the axis is parallel to one another but never coincides. Cylindrical operation is performed on the different surfaces which is called eccentric turning.

Shoulder turning

Shoulder turning is also known as step turning operation. On the work piece material with different diameters are used for the performance, at that instance shoulder turning operation is used. There are different types of the shoulder turning they are beveled shoulder, radius shoulder and squared shoulder.

Tapper turning

Tapper turning is used to produce tapper surface on the cylinder. With the help of the tapper turning conical shapes are produced.

Grooving

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With the help of the single point cutting tool, to the sides of the material tool moves radially. To make the groove, large multiple cuts are made on the work piece material. To do the same special tools and tool width are used with different geometries.

Thread cutting

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The thread cutting tool moves along the axial direction and they are with an angle of 60 degrees. With the multiple pass of the tool toward the work piece we get the threads. The threads are arranged on the work piece material with specific pitch and specific length.

Cut-off

It is also similar to the grooving. In this process single point cutting tool moves along the side of the work piece. The cut off process is performed until it reaches the center of the work piece.

Drilling

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The drill bit enters into work piece axially and makes a hole which is equal to the diameter of the drill bit.

Boring

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A single point cutting tool is entered into the material axially to perform the operations like chamfers, tapers, step turning etc. Boring operation is performed after the drilling. To enlarge the diameter of the hole boring is required.

Tapping

In the existing holes, to perform the internal threads, tapping process is used. After the completion of the drilling process tapping is operated.

Reaming

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The tool should be placed into the work piece axially to expand the holes. In the reaming process we can see the minimum amount of the metal removal rate. Mainly the process is used to enlarge the existing holes, by using this process we find a good internal finish with accurate diameters.

Cutting parameters

The parameters are selected based on the tool material size and work piece material. The parameters are

  • Cutting feed
  • Cutting speed
  • Radial depth of cut
  • Axial depth of cut
  • Spindle speed

Equipment used in the turning process:

  • Turning operation is mainly performed on the lathe machines. The lathe machine consists of bed, head stock, tail stock, carriage, cross slide,
  • Bed: Bed is a base arranged on the ground. All the components are arranged on the bed.
  • Head stock: Head stock is attached to the bed. The head stock consists of spindle, motor, hydraulic drive and power system. Chucks are arranged to the head stock, with the help of the spindle the work piece must rotate.
  • Tail stock: Tail stock is arranged on the opposite side of the head stock which is mounted on the bed. The tail stock is used to support the other end of the work piece material where it allows rotating. From the end of the work piece the material is removed.

Materials used are:

  • Before selecting the material one needs to consider some factors they are strength of the material, cost, wear resistance and machinability.
  • Turning operations are performed on various materials. Common materials used in the process are brass, aluminum, nickel, magnesium, steel, zinc, titanium, thermoset plastics etc.

Cutting speed for different metals

Material type                MPM            SFM
steel 15 to 18 50 to 60
Cast iron 18 to 24 60 to 80
Alloy steels 20 to 37 65 to 120
Carbon steels 21 to 41 70 to 130
Stainless steel 23  to 40 75 to 130
bronze 24 to 45 80 to 150
Mil steel 30 to 38 100 to 125
Free cutting steels 35 to 69 115 to 225
Aluminum 75 to 105 250 to 350
Brass 90 to 210 300 to 700
Leaded steel 91 300

 

Cutting speed for turning

The cutting speed for machining is represented as surface velocity of the work piece material in the motion.

V=  \pi \times D \times \frac {N}{1000} \:\:\:\frac {m}{min}

Where,

V= Cutting speed

D= diameter of the work piece (mm)

N= speed required to rotate the shaft

Cutting velocity is selected by using the following factors

  • Based upon the cutting tool material property
  • Depth of cut and feed given during the process
  • Physical properties like ductility, brittle ness, hardness of the work piece material
  • Capacity and rigidity of the cutting tool to struggle the cutting forces

 Defects that occurred are:

The defects that we are seen in the turning process are improper cutting parameters, unsafe work piece and Dull cutting tools.

Advantages:

  • In turning operation all types of materials are used for the process.
  • Short lead times
  • Very good tolerance

Disadvantages:

  • Several operations are performed
  • Equipment cost is high
  • Scrap content is large
  • Significant tool rate
  • Limited to rotational parts

click here to know more about: Milling & Types of Milling Machines

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