NUMERICAL CONTROL (NC) MACHINES AND COMPUTER NUMERICAL CONTROL (CNC) MACHINES

NC  MACHINE

WHAT  IS  NUMERICAL  CONTROL  MACHINE

NC  machines  is  very  commonly  used  in  machines  tools.It   is  the  form  of  programmable  automation,in  which  process  is  controlled  by  number,letter  and  symbols.In  case  of  the  machine  tools  this  programmable  automation  is  used  for  the  operations  of  machines.The  numerical  control  machine  is  defined  as  the  machine  that  is  controlled  by  the  set  of  instruction  called   as  the  program.The  NC  technology  can  be  applied  to  variety  of   operation  like  drafting,assembling,sheet  metal  operation.It  is  more  used  in  various metals   like  turning,drilling,milling  and  shaping.

COMPONENTS  OF  NC  MACHINES

There  are  three  components  of  NC  machines.These  are  

1. Program  of  instruction
2. Controller  unit  also  called  the  machine  control  unit (MCU)
3. Machine  tool

1. PROGRAM  OF  INSTRUCTION

The  typical  desktop  program  gives  the  instruction   to  the  computer  to  perform  certain  function.The  set  of  instruction  are   codded  in  numerically  or  symbolically  form  or  written  on  certain  medium  that  can  interpreted  by  the  controller  unit  of  NC  machines.

2. CONTROLLER  UNIT  

The  controller  unit  is  the  vital  parts  of  the  NC  or  CNC  machines.The  controller  unit  is  made  of  electronic  components.It  reads  and  interpreted  the  program  of  instruction  and  converts  them  into  mechanical  tools.The  controller  unit  forms  an  important  link  between  program  and  machines tools.All  the  modern  NC  machines  are  equipped  with  the  microcomputer  that  acts  as  the  controller  unit.

3. MACHINE  TOOLS

It  is  the  machine  tools  that  performs  a  machining  operations.The  machine  tool  can  be  any  types  like  milling  machine, drilling  machine etc.The  microcomputer  operates  the  machine  as  per  set  of  instruction  or  program.The  NC  machines  have  the  control  panel that  contains  the  dials  or  switches  which  the  operator  runs  the  NC  machines.Most  of  the  NC  machines  also  called  the  CNC  machines.

CNC  MACHINE 

WHAT  IS  COMPUTER  NUMERICAL  CONTROLLED  MACHINE

The  CNC  machines  comprises  of  the  mini  computer  or  the  microcomputer  that  acts  as  the  controller  unit  of  the  machine. In  CNC  machine  the  set  of  program  is  fed  directly  into  the  computer.In  CNC  machines  the  program  is  stored  in  the  memory  of  the  computer.The  programmer  can  easily  right  the  codes and  edit  the    program  as  per  requirements.These  program  can  be  used  for  different  parts  and  they  dont have  to  repeat  again  and  again.

HOW  THE   CNC  MACHINE  WORKS

The  CNC  machines  comprises  the  computer  in  which  the  program  is  fed  for  the  cutting  of  the  metal  of  the  job  as  per  requirements.CNC  machine  works  like  the  robot,  which  has  to  be  fed  with  the  program  and  it  follows  all  the  instruction.Some  of  the  common  machine  tools  that  can  run  on   the  CNC  machines  like  Lathe,  drilling  etc.The  main purpose  of  these  machines  is  to  remove  some  of  the  metals  as  to  give  it  the  proper  shaped  such  as round  or  rectangular  etc.

ADVANTAGES  OF  CNC  MACHINES 

1. Part  Program  tape  and  tape  recorder
2. Editing  the  program
3. Metric  conversion
4. Highly flexible
5. Easier  programming

APPLICATION  OF  CNC  MACHINES

1. Industries  for  removing  metals
2. Industries  for  fabricating  metals
3. Electrically  discharge  machining  industry
4. Others  industries  where  CNC  machines  are  used. 

TURBINES

FRANCIS TURBINES

DEFINITION

• It  is  type  of  water  turbine.
• It  is  an  inward  flow  reaction  turbine  that  combines  radial  and  axial  flow  concepts.
• They  operate  in  a water  head  from  40 to 600 m.
• Primirly  used  in  electrical  power  production.
• The  speed of  this  turbine  is  75 to 1000 rpm.
• It  is  always  mounted  with the shaft.

  

COMPONENTS

1. Spiral casing
2. Guide wanes
3. Runner blades
4. Draft tube

1.  SPIRAL CASING

The spiral casing around the runner of the turbine knows as scroll  case.It  converts pressure energy  of  the  fluid  into  momentum  energy.The  cross sectional  area  of  casing  decreases with uniformly along  the  circumstances.

2. GUIDE WANES

The primary function of this guide  wanes  is to  convert  pressure  energy  into  momentum  energy.It also serve  to  direct the  flow  at  design  to  the  runner  blades.

3. RUNNER  BLADES

Runner blades  are  the  hearts  of  any  turbines  as  these  are  centre  where  fluids  are  stricks  . In this  parts  one   has  careful  about  the  blades  angles  of  inlet  or  outlet  as  these  are  the  major  affecting  of  power  production.

4. DRAFT  TUBE

The  draft  tube  is  a  conduict  which  connects  the  runner  exist  to  the  tail  race  where  the  water  is  being  discharge  from  turbines.The  primary duty  of draft  tube  is  used  to  reduce  the  velocity  of  discharge  water  to  minimise  the  loose  of  kinetic  energy  at  the  outlet.

APPLICATION

Frances  turbine  may  be  design  for  wide  range  of  head  and  flow.Because  of  his  high  efficiency  it  become  the  most  widely  used  turbines  in  the  world.Francis type units  cover  a  head  of  40 to  600m

STRESS AND STRAIN

STRESS

•  The force across a small boundary per unit area.

• Derived from physical fundamental quantity like velocity,energy torque.

• Stress is a macroscopic concept.

• Its matter must be described by the tensor.

• The dimension is that of pressure.

• Stress is a material body due to multiple physical causes like internal influence etc.

• In some solid material such stress will generate a internal elastic stress.

• Stress that exceeds certain strength of the material will result in permanent deformation.

• It is the internal resistance set up by body when it deformed.

• It is measure in n/m2

TYPES

1. Tensile
2. compressive
3. shearing

TENSILE STRESS

COMPRESSIVE  STRESS

• If the bar is subjected to axial compresion rather then axial tension then the stress developed called stress compression

SHEAR STRESS

• It is also called tangential stress and denoted by q
• Q=r/a

     

STRAIN

• Strain is the measure of deformation representing the displacement particles of the body.
• It is generally a tensor quantity.
• It has a dimensionless quantity.
• It expressed in the form of decimal fraction or a percentage etc.
• Shrain can be decompose into normal and shear component

TYPES OF STRAIN

1. Longitudinal strain
2. Volumatric strain
3. Shearing strain

LONGITUDINAL STRAIN

It is defined as the change in length of the body to the original length of the body.

VOLUME STRAIN

• It is defined as the change in volume to the original volume.

SHEAR STRAIN

• It is the ratio of the displacement of the layer to its distance from fixed layer.

STRESS AND STRAIN EQUATION

• Hooke's law gives a relationship between strain and stress.According to hook's law,with in the elastic limit,strain produced in a body is directly proportional to the stress produced.