ComputerAided_Design_Engineering_amp_Manufactur.pdf
ComputerAided_Design_Engineering_amp_Manufactur.pdf
ComputerAided_Design_Engineering_amp_Manufactur.pdf
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1. A tool is searched for in the data base by three types of search calls:<br />
• Searching for the tool by a key parameter. The search succeeds if the key parameter matches with<br />
a field in the data base. This type of search is used for the hole-making tools and form tools (for<br />
ex<strong>amp</strong>le, the diameter of drills and the feature code of form grooves).<br />
• Searching for the tool which has a key parameter greater than or equal to the specified parameter.<br />
This type of search is used while matching the cutting edge length.<br />
• Searching for the tool which has a key parameter less than or equal to the specified parameter. For<br />
ex<strong>amp</strong>le, this search call is applied for grooving tools (whose width should be less than the width<br />
of the groove).<br />
2. The system has provision for maintaining an on-line dialogue with the user, thus informing about<br />
the status of the tool search. If a tool is not found, the user can specify the tool.<br />
3. General rules for discarding some of the selected tools are employed. Some of these are<br />
• Selection of a larger insert over a smaller one is preferred because it requires a smaller number<br />
of passes, thus reducing the machining time.<br />
• The tool holder, which is wider and has a shorter length, is preferred because it gives the tool a<br />
greater stiffness.<br />
• In addition to these guidelines, the production practices of the participating industry, such<br />
as using different tools for roughing and finishing operations, are included while choosing a<br />
tool.<br />
4. There can be a number of pockets attached to each setup. For each pocket, the tooling data<br />
base will deliver all tools that could accomplish the operation. The tool selection procedure<br />
initially keeps all these tools in a list. In the final stage, the number of tools can be minimized<br />
by extracting a common tool set. To summarize, this module tags each machinable pocket with<br />
a tool and a machining direction. In the current implementation of the system, the machining<br />
direction will be towards the head stock since it is assumed that the pockets lying on either side<br />
of the pocket will be machined in different setups. The results are written back to PPIR. These<br />
data are used to calculate the process parameters and the time estimates in the next stage of<br />
pocket processing.<br />
The functions of the tool selection module in Micro-GIFTS thus include (a) getting the necessary<br />
inputs from partial PPIR, PDIR and MRIR; (b) searching the cutting tool data base to decide the tools<br />
for machining each pocket; and (c) attaching the tool code to the pocket data in PPIR. The cutting tools<br />
available in a given shop floor are stored in the tools data base which is managed by Data-GIFTS. The<br />
selection of one of these tools involves the determination of the key parameters and searching the tool<br />
data base based on such key parameters.<br />
The execution of this module tags each machinable pocket with a tool and a machining direction. In the<br />
current implementation of the system, the machining direction will be towards the head stock since it<br />
is assumed that pockets lying on either side of the pocket will be machined in different setups. The results<br />
are written back to PPIR. These data are used to calculate the process parameters and the time estimates<br />
in the next stage of pocket processing.<br />
Process Parameter Selection<br />
Selection of proper cutting parameters is important as these affect the quality and cost of a machined<br />
component. An optimization module in GIFTS is based on mathematical models formulated with an<br />
objective function of minimizing the production time (Prasad, 1994). Practical limitations are imposed<br />
on speed, feed, and depth-of-cut through constraints. These constraints include the spindle power,<br />
workpiece rigidity, tolerances, and surface finish, apart from the permissible ranges of speeds, feeds, and<br />
depths of cut. The mathematical models are solved using a geometric programming technique.<br />
Optimization of process parameters is attempted only for primary operations. The parameters for<br />
secondary operations (such as grooving, threading, etc.) are specified as a fraction of the turning parameters.