Institute for Systems Research Technical Reports

The research presented in this thesis focuses on improving machining accuracy using a systems engineering approach. A conventional lathe during machining is taken under consideration as a machining system. The tool post is identified as a critical component in the machining system to achieve the defined machining accuracy. Smart material made actuators are used to design a new tool post structure that is capable of carrying out an active vibration control during machining.

In this thesis research, the fabrication of the designed tool post is completed. Results obtained from the initial tests strongly demonstrate its capability to attenuate tool vibration during machining in an active and intelligent way. Thus, the smart tool post system fulfills the design objective of achieving microscopic level machining precision on a low-cost conventional machine tool platform. Suggestions on the actuator specifications are made for further improvement on vibration compensation.

Evaluating the manufacturability of a proposed design involves determining whether or not it is manufacturable with a given set of manufacturing operations - and if so, then finding the associated manufacturing efficiency. In this research, the design is represented as a solid model. The tolerance and surface finish information is represented as attributes of various faces of the solid model. Machining features are used to model the available machining operations Since there can be several different ways to manufacture a proposed design, this requires considering alternative ways to manufacture it, in order to determine which one best meets the design and manufacturing objectives.

The approach developed in this thesis is based on the systematic exploration of various machining plans. The first step is to identify all machining features which can potentially be used to machine the given design. Using these features, different machining plans are generated. Each time a new plan generated, it is examined to find whether it can produce the desired design tolerances. If a plan is found to be capable of meeting the tolerance specifications, then its rating is computed. If no machining plan can be found that is capable of producing the design, then the design cannot be machined using the given set of machining operations; otherwise, the manufacturability rating of the design is computed. Since various alternative ways of machining the part are considered in this approach, the conclusions about the manufacturability are more realistic compared to the approach where just one alternative is considered.

It is anticipated that this research will help in speeding up the evaluation of new product designs in order to decide how or whether to manufacture them. Such a capability will be useful in responding quickly to changing demands and opportunities in the marketplace.

Given an interpretation of the design as a collection of machinable features, our approach is to generate alternate machining features by making geometric changes to the original features, and add them to the feature set of the original part to create an extended feature set. The designer may provide restrictions on the design indicating the type and extent of modifications allowed on certain faces and volumes, in which case all redesign suggestions generated by our approach honor those restrictions.

By taking combinations of features from the extended feature set generated above, we can generate modified versions of the original design that still satisfy the designer's intent. By considering precedence constraints and approach directions for the machining operations as well as simple fixturability constraints, we can estimate the setup time that will be required for each design. Any modified design whose setup time is less than that of the original design can be presented to the designer as a possible way to modify the original design.