About Defining the Process Plan Work Flow
To define the part machining process plan work flow, the process planner may need to have access to:
1. A library of tools, holders, workcell and available fixtures.
One of the setup steps for process planning involves the documentation and inventory of all tools, fixtures, and holders for easy retrieval by the process planner. The library of machining tools are classified by function, size, and application. The process planner can create these fixtures, holders, and workcell as needed; that is, the database need not be complete before the work begins.
2. The design part as provided by the design department.
The design part is typically in the released format. The released model contains dimensions, tolerances—dimensional and geometric—and surface finish information.
3. The workpiece geometry as available from a supplier or manufacturing engineer.
The workpiece often represents an assembly of a part at some state of machining. It is possible that the starting workpiece for one process planner is the end result of a previous machining operation. Except for workpiece surfaces where the tolerance is sufficient to meet design requirements, the dimensional, surface or tolerance information associated with the design part is used by the process planner to decide on tools and fixtures.
To define the machining process plan work flow, the process planner may need to perform:
• An assembly of the workpiece and design model.
Given the workpiece and design model information, the process planner assembles the two parts in such a way as to provide sufficient machine allowance and co-locate critical features; such as an axis for a boss and reference datum planes.
Sometimes, the process planner or user creates just the casting model, and then creates the final design model through material removal. This way, the process planner or user can better model the design through the manufacturing process, because the design model incorporates limitations of the manufacturing process.
• An assembly of the workpiece into a relative fixture.
The process planner, or user, needs to define how the workpiece with the reference model assembled inside will be assembled relative to a fixture.
• The creation of a custom fixture.
If there are no preexisting fixtures, then the process planner, or user, passes the workpiece along with manufacturing instructions to the tools department for creation of a custom fixture.
• A simplification of the model representation.
The process planner, or user, often wishes to create a representation of a design part that is as simple as possible, yet contains all necessary details in the area to be machined.
• Workcell and tool definition and selection.
Based on process planing requirements such as material, stock allowance, surface finish, and tolerance, the process planner or user defines or retrieves a workcell and may choose a tool for each machining step or NC sequence.
• A representation of the workpiece with material removed.
The process planner or user needs this representation for input to the next machining step and also to document the process.
• Modifications to the machining steps.
After defining all steps, the process planner may reorder the machining steps, add or insert more steps, or delete some of the unnecessary machining operations.