Reverse engineering of machining operation planning

Reverse engineering of machining operation planning

Author-X. YANy, K. YAMAZAKIy and J. LIUy

Introduction

Today’s rapid production development and production processes demand highly automated Computer-Integrated Manufacturing (CIM) systems. This kind of system is an integration of Computer-Aided Design (CAD), Computer-Aided Manufacturing (CAM) and Computer-Aided Process Planning (CAPP) subsystems. To automate operation planning through machining features, two major problems need to be solved: feature recognition from product models and machining database generation from successful machining operations. To generate automatically the feature-based machining know-how database from successful daily machining operations, two main tasks need to be performed: machining feature recognition and machining operation data extraction.  

To extract the machining know-how data from NC programs, a system called Autonomous Machining Process Analyzer (AMPA) has been developed . This system is used to extract the machining knowledge or know-how of the skilled operators and machinists, which is implied in successful NC programs, and automatically export it into the know-how database. Using this machining know-how database will drastically quicken the actualization of automating operation planning

1.Machining operation

Machining operation is the kernel process for creating a product. Operation planning is a subtask of process planning and is knowledge intensive. The machining operation includes the following tasks-

  1. Selection of cutting tools (type and diameter). 
  2. Selection of cutting conditions (parameters). 
  3. Selection of tool motion mode such as cutting mode (tool path pattern) and machining type.

2.Cutting conditions

Axial and radial depths of cut-

In three-axis milling, the depths of cut are in two directions: axial and radial.the difference between the last and the current Z levels in the workpiece is defined as ’axial depth of cut’ .distance between the side surface machined and the side surface to be machined,measured on the X±Y plane, is defined as `radial depth of cut’ .

Material removal rate

The material removal rate is defined as the volume of the material removed in the unit time. It is a critical parameter in the determination of the machining productivity and electric power.

3.Tool motion mode

The tool motion mode describes how the tool moves in machining the workpiece.It has two kinds of parameters. One is cutting mode (or tool path pattern), which describes the tool motion in the plane being machined (generally X±Y plane), and the other is machining type, which describes the tool motion in the axial direction (generally Z-axis).

Machining type

In milling, the machining type can be classified into the following-
 1.Z level machining or constant Z level machining
 2.Non Z level machining or variable Z level machining
 3.Drilling

The machining type can be recognized through a check of the coordinates in the part of the NC program for the machining element.

Cutting mode

In milling, the cutting mode or tool path pattern can be classified primarily into the following: 
1. Unilateral zigzag in X-, Y-axis or inclined direction 
2. Bilateral zigzag in X-, Y-axis or inclined direction 
3. Contouring or contour line, inward or outward 

4.Machining operation sequence

In the process of recognition of machining elements, the operation sequence of the elements is obtained from the NC program. In constructing a machining feature, the machining elements that belong to the feature will be recognized by the Boolean relations of their cut contours and Z levels .Once the elements of a feature are recognized, the operation sequence of the machining feature will be known. It is the order of the machining elements in machining time sequence.

5.Implementation of machining operation data extraction

System architecture-The above recognition algorithms of machining operations have been implemented

in the prototype of the AMPA system, developed under Windows NT/95.

Machining know-how database structure

To hold the extracted data for future operation planning.

Verifcation of machining operation data extraction

With the developed prototype, NC programs for machining a variety of features have been analysed, and machining operation data associated with the machining features have been extracted successfully.

Conclusion

To capture the machining know-how from daily machining operations, reverse engineering methodology has been proposed, and the prototype of the AMPA system has been developed for extracting machining features and their associated operation data from NC programs. The extraction of the operation data has been successfully verified through an analysis of a variety of NC programs. The generated machining know-how database will be applied in future operation planning.