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Collect all relevant data and assemble it for evaluation. The main sources of information are the part print, process sheets, and machine specifications. Make sure that part documents and records are current. For example, verify that the shop print is the current revision, and the processing information is up-to-date. Check with the design department for pending part revisions.
An important part of the evaluation process is note taking. Complete, accurate notes allow designers to record important information. With these notes, they should be able to fill in all items on the "Checklist for Design Considerations." All ideas, thoughts, observations, and any other data about the part or fixture are then available for later reference. It is always better to have too many ideas about a particular design than too few.
Four categories of design considerations need to be taken into account at this time: workpiece specifications, operation variables, availability of equipment, and personnel. These categories, while separately covered here, are actually interdependent. Each is an integral part of the evaluation phase and must be thoroughly thought out before beginning the fixture design.
Workpiece specifications usually are the most important factors and have the largest influence on the fixture's final design. Typically, these considerations include the size and shape of the part, the accuracy required, the properties of the part material, the locating and clamping surfaces, and the size of the run.
Operation variables include the type of
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operations required to make the part, number of operations performed, sequence of operations, inspection requirements, and time restrictions.
Availability of equipment required to machine, assemble, and inspect a part often determines whether the fixture is designed for a single part or multiple parts. A process engineer sometimes selects the equipment to machine parts before the tooling designer begins the design. The tooling designer should verify what equipment will be used for each operation.
A vertical milling machine, for example, is well suited for some drilling operations. But for operations that require a drill jig, a drill press is the most cost-effective machine tool. Typically, equipment criteria include the following factors: types and sizes of machines, inspection equipment, scheduling, cutting tools, and plant facilities.
Personnel considerations deal with the end user, or operator, of the equipment. Fixture designers should put themselves in the machine operator's shoes and consider all the operational scenarios they can. Designers should consider not only correct usage of the fixture, but also possible incorrect usage. They must ask, "Is there any way for me to hurt myself while operating this equipment?"
Additional factors usually considered in this category are operator fatigue, efficiency, economy of motion, and the speed of the operation. The designer also must know and understand the general aspects of design safety and all appropriate government and company safety rules and codes. |
