University of Nevada Las Vegas

MEG426/626 Manufacturing Processes

Department of Mechanical Engineering

Fall Semester 2000

　

Machining Centers

　

Machining center is an automated machine tool capable of performing multiple machining operations under computer numerical control in one setup with minimal human attention.

Features: automatic tooling changing.

pallet shuttles that can be automatically transferred to the spindle to machine the workpart, therefore, the nonproductive time can be reduced.

automatic workpart positioning.

Category: horizontal machining center,

vertical machining center,

universal machining center.

　

Usually contains a control unit, measuring units, A/D converters, and feedback unit.

　

NC Control

Fixed automation: the processing steps and their sequence are fixed by the equipment configuration.

Programmable automation: the equipment is designed with the capability to change the process steps and/or their sequence so that different product styles can be produced.

FMS: flexible manufacturing systems.

Numerical Control (NC): is a form of programmable automation in which the mechanical actions of a piece of equipment are controlled by a program containing coded alphanumeric data.

Components of a NC System:

      1. part program,

      2. machine control unit, and

      3. processing equipment.

Part program is the code inputted by the machine operator to the machine. The code specifies each motion of the spindle and the tool, and also the sequence of motions.

Machine control unit is a microcomputer that stores the program and executes it by converting each command into actions by the processing equipment.

This is the control center.

Processing equipment accomplishes the sequence of processing steps to transform the starting workpart into a completed part.

It is the hardware that takes actions.

Open-loop Control System: no feedback

Close-loop Control System: feedback is used to adjust the control parameters.

　

NC Part Programming

It requires the programmer to define the points, lines, and surfaces of the workpart in the axis system and to control the movement of the cutting tool relative to these defined part features.
  1. Manual part programming,
  2. Computer-aided part programming, APT and FAPT.

    3. APT = automatically programmed tooling,

    Geometry input,

    Used in 1960-80.

    Compiling.

    　

  3. CAD/CAM-aided part programming.

Using CAD/CAM software to generate mechanical drawing, then automatically create NC code for each machine.

Graphic input,

Widely used software: AutoCAD, PRO/E, CADKEY, MasterCAM, and DP Technology.

Created by Dr. Wang