CNC Programming

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CNC Programming
KP3213 CAD/CAM
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CNC Programming

• Detailed list of instructions need to be executed
  by MCU
• Instruction broken down into small elements
• Written in specific format understood by MCU

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Part Programming Fundamental

• Process planning
• Axes selection
• Tool selection
• Cutting process parameters planning
• Job and tool setup planning
• Part program writing
• Part program proving

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Process planning

• Machine tool used
• Fixtures required
• Sequence of operations
• For each operation
• Cutting tools required
• Process parameter
• Page 323

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Axes selection

• All CNC machine tools rely on the axes system for
  describing axes motion
• Axes system for CNC machines have fixed datum
  position
• Absolute datum may not be very convenient for
  setting up job, thus floating datum

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Tool Selection

• Choice of cutting tool is a very important
  function
• A choice is may be feasible and economical than
  the other
• Speeds (removal rate) and finishes also factors
• Eg. Tapered end mill or slot drill would make the
  machining very simple in generating draft surface
  of dies and mold, otherwise a draft angle may
  take a large amount of programming

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Cutting process parameter

• Appropriate parameters to be selected
• From handbook supplied by cutting tool
  manufacturer or based on experience
• In CNC, feeds and speeds should be as high as
  possible to reduce machining time
• As long as quality or finishes are acceptable

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• Job and tool set up planning
• Aimed at setting the job on the machine tool and
  adjusting the cutting tool to the correct
  position
• Important because accuracy of geometry is
  dependant on set up
• Machine path planning
• Knowledge of machining operation is important
• It ensures the requisites manufacturing specs are
  achieved at lowest costs
• Part program writing
• Actual witting of programs
• Part program proving
• Once program are made, should be verified
• Faulty program can cause damage to tool,
  workpiece and machine
• Trial run can be done without workpiece
• Position of the clamps should be taken into
  account
• By sequence (block by block). Manual press for
  next block

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Documentation of NC

• Documentation is important in CNC manufacturing
  proactive
• Checklist as follows
• Component drawing
• Process planning sheet
• Tools cards show each tool in assemble form
• Setup sheet show all tool required with Ids
• Programming sheets
• Punched paper tape, if this is the input form used

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Turning Center Programming

• Comparison between machining center and turning
  center
• Axes system were X, Z but turning C, w and Y
• Tools used generally single point cutting tool
  such as turning and boring
• Multiple cuts the blanks for turned jobs are
  normally solid material (rolled stock) which
  require large amount for clearing, need planning
• Internal and external features there are
  identical features in these jobs with internal
  and external equivalents such as turning and
  boring, programming are similar but with care!

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Turning Center Programming

• More than one tool post, presently there are
  single post
• Different G and M codes
• Tool nose radius in machining center, program
  are done with center of spindle. Turning center
  center of tool nose radius
• Work rotation
• Tool indexing
• Diameter programming

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Axes System for Turning Center
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Case Study

• Prepare a complete and detailed process planning
  of a component for machining on a lathe. This
  part to be machined from a rolled stock of
  diameter 40mm.

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Case Study 1
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Case Study 2

• Prepare a complete and detailed process planning
  of a component for machining on a conventional
  machine. Tolerance for parts with diameter 80mm
  is 0.01mm and other parts is 0.1mm.

Ø50
60
Ø30
30
Ø80
Ø70
Ø8 T
30
4 Ø6 T
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Case Study 2
S2
S3
S1
S4
Setup1 (Turning machine) Chuck work-piece
exposing 30mm Turn S2 into 80mm diameter Face
S1 Setup2 (Turning machine) Chuck work-piece on
S2 Turn S3 into tapered surface for 30mm and the
other 30mm into 30mm diameter Face S5
Setup3 (Drilling machine) Chuck work-piece S5 and
S1 Drill 8mm diameter Setup4(Drilling
machine) Chuck work-piece on S2 Drill 4nos. of
6mm holes
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Homework

• Prepare a complete and detailed process planning
  of a component for machining on a conventional
  machine. Tolerance for parts with diameter 80mm
  is 0.01mm and other parts is 0.1mm.

Ø20 T
Ø80
40
Ø70
30
15
100