Rule-based feature recognition methods borrowed those of expert system’s concepts.For different features, rules can be written for detecting directly the underlining features.Templates are normally defined first for both general and specific features. Then rules are constructed for each of the feature template. For example,
//recognise a 2.5D pocket//
If ((a face has an internal loop made up of a number of edges) +
(all faces sharing these edges also share another common face))
Then (there exists a pocket)
End If
More often than not, both geometric and topological conditions are tested.Therefore,rule-based methods can detect features that graph-based and syntax-based methods cannot.It is also easy to construct and alter rules when necessary. The above rule can be modified to detect a (close) pocket and (blind or through) hole,
//recognise a 2.5D pocket or hole//
If (a face has an internal loop)
If (the loop has one edge)
If (the face sharing the edge also shares another common face)
Then (there exists a blind circular hole)
Else(there exists a through circular hole)
Else if (all faces sharing these edges also share another common face)
Then (there exists a pocket)
Else (there exists a general through hole)
End If
Rule-based method has been widely used together with other types of methods for feature recognition.
(Xun Xu, Integrating Advanced Computer-Aided Design, Manufacturing, and Numerical Control:Principles and Implementations, pages 95-96)
Hydroforming
Hydroforming is similar to the Guerin process; the difference is that it substitutes a rubber diaphragm filled with hydraulic fluid in place of the thick rubber pad.Thşs allows the pressure that forms the workpart to be increased to around 100Mpa thus preventing wrinkling in deep formed parts.In fact, deepr drawss can be achieved with the hydroform process than with conventional deep drawing.This is because the uniform pressure in hydroforming forces the work to contact the punch throughout its length, thus increasing friction and reducing the tensile stresses that cause tearing at the base of the drawn cup.
(M.Groover. Fundamental of Modern Manufacturing,third edition
page 461)
Tig welding(GTAW)
Gas tungsten arc welding(GTAW) is an AW process that uses a nonconsumable tungsten electrode and an inert gas for arc shielding.The term tig welding(tungsten inert gas welding) is often applied to this process(in europe, wig welding is the term-the chemical symbol for tungsten is W, for wolfram).The GTAW process can be implemented with or without a filler metal.When a filler metal is used , it is added to the weld pool from a seperate rod or wire, being melted by the heat of the arc rather than transferred across the arc as in the consumable electrode AW process.Tungsten is agood electrode material due to its high melting point of 3410 C.Typical shielding gases include argon, helium, or a mixture of these gas elements.
(M.Groover. Fundamental of Modern Manufacturing,third edition page 714)
Mig welding(GMAW)
Gas metal arc welding(GMAW) is an AW process in which the electrode is a consumable bare metal wire, and shielding is accomplished by flooding the arc wtih a gas.The bare wire is fed continuosuly and automatically from a spool through the welding gun.Wire diameters ranging from 0,8 to 6,5 mm are used in GMAW, the size depending on the thickness of the parts being joined and the desired deposition rate.Gases used for shieldind include inert gases such as argon and helium and active gases such as carbon dioxide.Selection of gases depends on the metal being welded, as well as other factors.Inert gases are used for welding aluminum alloys and stainless steels , while CO2 iscommonly used for welding low and medium carbon steels.the combination of bare electrode wire and shielding gases eliminates the slag covering on the weld bead and thus precludes the need for manual grinding and cleaning of the slag.The GMAW process is therefore ideal for makşng multible welding passes on the same joint
(M.Groover. Fundamental of Modern Manufacturing,third edition
page 711)
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