22-10-2016, 03:23 PM
1460580260-1.NCPS.pdf (Size: 4.66 MB / Downloads: 3)
Machine Tool Capabilities
• Holding and supporting the workpiece
• Holding and supporting a cutting tool
• Imparting a suitable movement (rotating or
reciprocating) to the cutting tool or the work
• Feeding the cutting tool or the work so that the
desired cutting action and accuracy will be achieved
Machine Tool Categories
• Four broad categories
– Chip-producing machines
– Non-chip-producing machines
– New-generation machines
– Multi-tasking machines
Non-chip-producing Machines
• Form metal to size and shape by pressing,
drawing, punching, or shearing
• Produce parts by compressing granular or
powdered metallic materials
New-Generation Machines
• Perform operations that cannot be done on
chip- or non-chip-producing machines
• They are also known as Non-Traditional
Machining.
Multi-tasking Machines
• Combined machining and turning center
• Can produce virtually any shape part from
rough to finish
• Consists of turning center with two
independent spindles and vertical machining
center with rotary tool spindle
• Combine Information Technology (IT) and
Manufacturing Technology (MT)
Numerical Control (NC) Defined
Numerical control(NC) can be defined as a form of programmable
automation in which the mechanical actions of machine tool are
controlled by alphanumeric data. In NC, the numbers and
alphabets form a program of instructions designed for a particular
workpart or job.
Operating principle of NC is to control the motion of the
workhead relative to the workpart and to control the sequence in
which the motions are carried out.
BASIC COMPONENTS OF NC SYSTEM
1. Program of
instructions
• 2. Controller unit,
also called a machine
control unit (MCU)
• 3. Machine tool or
other controlled
process
Program of instructions
• It is the detailed step-by-step set of directions which tell the
machine tool what to do. It is coded in numerical or symbolic
form on some type of input medium that can be interpreted
by the controller unit. The most common input medium is
punched tape. (Punched Card, Magnetic Tape)
• There are two methods of input to the NC system . The first is
by manual entry of instructional data to the controller unit
known as Manual Data Input(MDI) and second one is Direct
Numerical Control (DNC)
Controller unit (MCU)
• The typical elements of a conventional NC controller
unit include the
• Tape reader
• Data buffer
• Signal output channels to the machine tool
• Feedback channels from the machine tool and
• The sequence controls to coordinate the overall
operation.
• A block of information usually represents one complete step
in the sequence of processing elements.
• The signal output channels are connected to the servomotors
and other controls in the machine tool. Through these
channels, the instructions are sent to the machine tool from
the controller unit.
• To make certain that the instructions have been properly
executed by the machine, feedback data are sent back to the
controller via the feedback channels.
Sequence controls coordinate the activities of the
elements of the controller unit.
• The control panel or control console contains the
dials and switches by which the machine operator
runs the NC system.
• It may also contain data displays to provide
information to the operator.
Machine Tool
• It is the part of the NC system which performs useful work.
• The machine tool consists of the worktable and spindle as
well as the motors and controls necessary to drive them.
• It also includes the cutting tools, work fixtures, and other
auxiliary equipment needed in the machining operation.
Problems with Conventional NC
Part Programming Mistake
• Non optimal speeds and feeds
• Punched Tape
• Tape reader
• Controller