Design of a circular rod fits in drilled hole

As an extremely simple example of how such process can be applied, consider the case of the design of a circular rod which fits into a hole drilled into a part. One of the first steps is to choose the material of the rod, attribute ROD.MATERIAL, which might be equated to the part material or chosen by a rule such as the given:

IF         ROD.ENVIRONMENT IS CROSSIVE

THEN ROD.MATERIAL IS STAINLESS-STEEL ELSE ROD.MATERIAL IS CARBON-STEEL

These rules specify the rod material uniquely, depending on the values of the described condition. This is also possible to choose the rod material from a list of available materials contained in the database.

The rod diameter might be determined from the strength needs, to satisfy a given allowable stress. Rules can be utilized to select the applicable code or other services needs, as like:

IF         <Condition A is true>

AND     <Condition B is true>

.

.

.

AND     <Condition N is true>

THEN   CODE is SAME

IF PART.SERVICE IS CRITICAL AND CODE IS SAME

AND     ROD.MATERIAL IS STAINLESS-STEEL

.

.

.

AND <Condition N is true>

THEN   ROD>SAFETY_FACTOR IS 3

The minimum rod dia or diameter to meet specified loads, safety factors, and etc. may be found from familiar strength of materials formulas that may be written in the form of rules. Additional rules and database needs can immediately select the rod size that is available and meets the strength requirements, if the stainless steel rods available in the inventory are stored in the database by the manufacturing inventory management system.

Additionally to setting attributes uniquely, rules can be used also to propagate constraints on attributes. The rod chosen by the above rules with diameter ROD.DIAMETR, must fit into a hole along with the diameter HOLE.DIAMETER. For ease in manufacturing, there must be some finite gap, or play, among the rod and the hole. For manufacturability, such gap cannot be less than ROD.PLAY.MINIMUM. Such minimum value may be assigned with the rule as like:

IF         ROD.MATERIAL IS STAINLESS - STEEL AND   ROD.ASSEMBLY IS MANUAL

.

.

AND     <Condition N is true>

THEN   ROD.PLAY.MINIMUM IS 0.0001*ROD.DIAMETER

For suitable functioning of the pair, the play among the hole and rod cannot be controlled by rules as like:

IF         <Condition A is true> AND                  <Condition B is true>

.

.

.

AND     <Condition N is true>

THEN   ROD.PLAY.MAXIMUM IS 0.005*ROD.DIAMETER

Additional rules may be utilized to modify the constraints, for illustration, making them tighter as:

IF ROD.PLAY.MAXIMUM > 0.01

THEN ROD.PLAY.MAXIMUM IS 0.01

After these rules has been applied, the expert system must choose hole diameter among the minimum value ROD.DIAMETER plus two times ROD.PLAY.MINIMUM and the maximum value ROD.DIAMETER plus two times ROD.PLAY.MAXIMUM. The hole diameter must be standard drill diameter assume that standard drill size are stored as attribute SIZE in the table DRILL.TABLE. Then a database query is utilized to find the hole diameter equal to a standard drill diameter lying among these constraints as:

EXECUTE SQL SELECT FROM DRILL.TABLE 'SIZE' WHERE 'SIZE' >

'ROD.DIAMETER'+2*'ROD.PLAY.MINIMUM' AND     'SIZE'   <

'ROD.DIAMETER'+2*ROD.PLAY.MINIMUM' INTO 'HOLE.DIAMETER'

At last, a rule base can be utilized to create the geometric feature for the hole or to write an error message to the user if there is no standard drill diameter inside the tolerances as:

IF HOLE.DIAMETER IS NOT NULL

THEN CALL CREATE.GEOMETRY(HOLE,HOLE.DIAMETER, HOEL.DEPTH)

ELSE WRITE MESSAGE ("here is no standard drill diameter inside the prescribed tolerances for the rod and hole. Do you wish to employ a nonstandard drill or to override the standard tolerances?")

In this type of case, if the database quarry returns the value NULL. There is no standard drill bit to drill a hole inside the constraints set by rod diameters and the minimum play and the maximum play. In an interactive CAD session, the expert system shows a message on the CAD screen, asking the designer to resolve the problem, which may include the overriding one of the manufacturing standards or redesigning the rod in that a way that the standards can be met.

A standard drill bit has been determined that meets the derived constraints, and a geometric construction routine is named as to create the hole part in the model geometry, if the results of the database query are not NULL.