Machine Tools: Elements and Parts

• A machine tool is defined as one that can remove metal from a workpiece while holding the cutting tools to generate the requisite job of a given size, configuration, and finish.
• It is different from a machine, which essentially converts the source of power from one form to the other.
• The machine tools are the mother machines since, without them, no components can be produced in their finished form.
• The machine tool is required to support the workpiece and cutting tools and provide motion to one or both of them in order to generate the required shape on the workpiece.
• The form generated depends on the type of the machine tool used.
• A machine tool is designed to perform certain primary functions, but its flexibility is measured by the extent to which it can be exploited to perform secondary functions.
• Generally, the use of special attachments increases the flexibility of the machine tool, thereby increasing productivity.

Lathe can be generally specified by

• Swing, the largest work diameter that can be swung over the lathe bed.
• Distance between tailstock and headstock
• Sometimes both of the above.

Basic elements of Machine tools:

The various components that are used in machine tools are discussed under:

1. Work holding device:

Work holding devices are used to hold the work-piece in the correct orientation to achieve the required accuracy in manufacturing.
Example: chuck.

2. Tool holding device

Tool holding devices hold the cutting tool in the correct position with respect to the workpiece and provide enough holding force to contract the cutting forces acting on the tool.
Example: Tool post.

3. Work motion mechanism

The work motion mechanism is generally used to provide the necessary speed to the workpiece for generating the required surface.
Example: headstock.

4. Tool motion mechanism

A tool motion mechanism is generally used to support all the mechanisms, maintain their relative positions with respect to each other, and allow for relative movement between the various parts.

5. Support structures

Support structures are used to support all the mechanisms, maintain their relative positions with respect to each other, and allow for relative movement between the various parts.
Example: Bed.

Some common parts in machine tools and their features:

1. BED:

Important considerations in the bed design are rigidity, alignment, accuracy and damping qualities.

Functions:

1. It acts as a rigid support.
2. It is used to absorb vibrations induced during machining.
3. It will act as a house.

Material used:

Generally, grey cast iron material is used.

Manufacturing process used:
Generally, casting will be used to manufacture the beds.

Shape of the bed:
The bed's shape is selected so that the reduction in rigidity will be minimal and should provide the maximum amount of free space. Examples: X,I, H cross-section shapes, etc.

2. Lead screw:

Function:
A lead screw is used for feeding the cutting tool in a direction parallel to the axis of rotation, and this will convert rotational movement into translation motion.

Material used:
The material used for making lead screws must have wear resistance.
Brass is used for lengths less than 2 meters. Stainless steel is used for Lengths 2 to 10 meters. For lengths above 10 meters, rack and pinion is used.

Manufacturing process:
Thread rolling or thread machining process will be employed to manufacture lead screws.

Shape:
Square threads are preferable because they are highly efficient in power transmission, and buttress and acme threads can also be used as the second choice.

3. Guide ways:

Function:
Guideways are used to guide and allow the other parts to move in their directions relative to other parts.

Material used:
Generally, high-carbon steel will be used.
As guide ways subjected to many forces during machining low ductile like brass and high hard like stainless steel will not be preferable because of having the localized hardening.

Manufacturing process:
The final manufacturing process used in manufacturing the guideways is flame hardening, which gives the hardened, localized surface required for guideways to avoid wearing.

Shape:
Rectangle-shaped guideways have the highest bearing area, but aligning is difficult.

‘V’ shaped guides are even aligned automatically, but the bearing area is less, so a combination of ‘V’ and rectangular guideways, i.e., dovetail-shaped guideways, will be employed.

4. Prime Mover:

Whatever energy is required for the machining operation is obtained from the Prime mover.
Types of Prime Mover:

1. IC Engine: They are obsoleted due to some disadvantages of IC engines.
2. Electrical motor: The induction motor is the most commonly used motor. The cost of the induction motor is less compared to other motors. No reciprocating parts and no noise. So, to get variable speeds for the job, even though the motor is rotating at only one speed, we will use a mechanical transmission system.