Question

QUESTION 2 a. When preparing a foundation for a heavy duty machine tool, discuss any four (4) statics machine characteristics to be considered. (12) b. State and explain briefly four (4) functions that a machine foundation should fulfill. (8)

Answer 1

Below is the Heavy duty Lathe of Skoda Company:

Heavy horizontal lathes equipped with NC controlling enable effective and precise machining of axial workpieces. Supplied with a wide range of accessories they can machine parts like crankshafts or turbine rotors including slotting.

MOOS

If we consider a normal heavy duty Lathe machine like this

The specifications pertaining to this are:

Automation Grade ...........................CNC

Max Swing Over Bed.......................500-750 mm

Max Turning Diameter......................1000-1500 mm

Height of Centre...............................175 - 400 mm

Range of Spindle..............................1200 rpm

The set of criteria defined for the Machine tools, which are used to apply the quantities which are slowly varying with time or mostly constant, i.e., do not vary with time, is called ‘static characteristics’.

Static Machine characteristics are where the performance criteria for the Machine Tolls of quantities that remain constant. Or vary only quite slowly.

Machine tools are an inherent part of manufacturing industries and indispensable particularly to those reliant on interchangeable components. A machine tool is a machine for shaping or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformation.

1. Accuracy of the Machine Tool

This the very most important Characteristic of the machine tool. Before etting up of any machine tool manufacturing unit the accuracy should be a major concern. As all the tools that are manufactured are then be treated as the output of the Heavy Machine Tool.

2. Linearity in the product line

The product line of the industry i.e., A product line is a group of related products produced by one manufacturer. For example, products that are intended to be used for similar purposes or to be sold in similar types of shops, should be in a linear operable way not be time consuming and intermixing of the path of travel.

3. Load bearing capacity

This also the major specification of a machine tool by ehichit classify. The amount of load that a machine tool bears will show many parameters like shear stress, strength, fatique, creep etc.

4. Torque of the machine

This is the amount of force multiplied by the distance of the operation. The torque per second gives out the power ratings of the machine tool. This also helps in evaluating the electrical characteristics as we know the power.

The Functions that a machine foundation have are:

Foundation, Machine is a structure used to receive and transfer to the ground the static load from a machine and the dynamic loads imposed during the operation of the machine as a result of imbalances in the moving parts.

Machine foundations are special types of foundations required for machines, machine tools and heavy equipments which have wide range of speeds, loads and operating conditions. These foundations are designed considering the shocks and vibrations (dynamic forces) resulting from operation of machines.

Functions are:

1. To prevent resonance between the machine and the adjacent soil, by achieving increased weight of foundation block in promotion to the power of the engines. Hence the mass of the foundation block performs the fuction to absorb the vibrations.

2. The foundation machine prevents the possibility of differential settlement, in the resultant force due to the weight of the machine and weight of the foundation mass that passes through the C.G. of the contact area

3. To minimise the bearing trouble by the deflection being a slightest, the foundation is enough to have necessary rigidity

4. To avoid transmission of vibration from the machine to the adjoining parts of the building, a gap should be left around the machine foundation to isolate it from the adjoining parts of the building.

5. To provide with reinforced running both ways along the surface of the concrete block of all the units of the foundation machine, and hence concrete cover to the reinforcement should not be less than 75 mm at the bottom, 50 mm on sides and 40 mm at the top. In case of foundation for stream turbo-generators, cover for the reinforcement at bottom side and top of the base slab should not be less than 100 mm

7. To maintaine The amount of reinforcement in foundation units not be less than 25 kg/m³ of concrete for impact type of reciprocating type of machines, 50 kg/m³ of concrete for the rotary type of machines and 100 kg/m³ of concrete for stream turbogenerators.

8. To use 150 m to 200 m grade of concrete in the foundations and as far as possible, the entire block should be concreted in one operation without construction joints.

When an owner selects a specific machine to meet the milling needs of their company, it is paramount to construct a foundation that properly supports the machine. Without a properly designed and built foundation, the machine will not function properly. Machine tool suppliers request the foundation to maintain deflections measured in microns, and with the cost of some foundations exceeding a million dollars, the design process needs to be carefully and precisely worked out.