Capp System

Process planning consists of preparing a set of instructions that explain how to fabricate a part or build an assembly which shall satisfy engineering design specifications. The resulting set of instructions might include any or all of the following: operations sequence, materials, tolerances, machines tools, cutting or operating parameters, processes (such like how to heat treat), jigs, fixtures, time standards, methods ,setup details, gauges, inspection criterion and graphical representations of the part in various stages of completion. It is clear that process planning might be very complex and time consuming job requiring a big amount of data. In addition, various people may participate in developing a process plan, because no one person may have the complete expertise required. It is further complicated by the fact that the process planning is a critical element in making the part correctly & economically.

Process planning received little attention till the late year 1970s. Informally process planning has been performed for hundreds of years - ever since someone primary developed instructions to make something. Though, industrial revolution fostered a required to formalise process planning in the manufacturing environment. At first, manufactured parts had few components & were made up by few workers. In this kind of setup, formal process plans were not needed. As the number of parts & complexities increased, a need for formal process plans was identified. Nevertheless, till the 1970s the importance of process planning was understood primarily through those closely involved in making the individual parts. As a result, little was done to automate this process.

Current manufacturing environment has become extremely competitive & complex. This complexity is a function of more intricate parts, and factors, such like manufacturing technologies that allow making several parts in different ways, small lot sizes that do not permit long setup times, enhanced government regulations that needed documentation of process plans, several types of materials that might require special tools and/or processes, and less skilled workers. These factors combined with enhanced emphasis on decreasing the manufacturing costs have affirmed the importance of process planning and corroborated that substantial savings might be achieved by automating the preparation of process plans. As a result this function has been receiving widespread attention.

The benefits that have been reported from successful application of automating some of process planning functions are impressive and contain one of the shortest pay-back periods of all CAD/CAM technologies. Some typical benefits include following

• 50% increase into process planner's productivity.
• 40% increase in capacity of present equipment.
• 25% reduction in setup costs.
• 10% reduction in scrap and rework.
• 10% reduction in shop labour.
• 6% reduction in work-in-process inventory.
• 4% reduction in work material.

Some of the benefits might not appear to be related to the automation of process planning. Though, this permits the process planners to:

1. Spend more time on methods improvement and cost reduction activities.

2. Routing can be consistently optimised.

3. Manufacturing instructions can be prepared in more detail.

4. Pre-production lead times can be reduced.

5. Responsiveness to engineering changes can be improved.

Objectives

After studying this unit, you will be able to understand

• The role of process planning in CAD/CAM integration,
• Different approaches to process planning for machining operations, and
• The criteria for selecting the CAPP system for a particular application.