Feature Mapping

The proximity feature attributes, as discussed above should make it possible to segregate feature clusters which interact. The current CAPP system method, generatcProcess, segregats features on the basis of their machining datum plane and Ls as follows:

C lan : Component Method: generate Process

"Reason the feature instances of the component instance to generate a machining process"

[addDatumld parent Features addFtrsSamcDatum highest i t | (curProduct isMembeiOf: Component)

ifFalsc: [self error: 'Select Component instance']. "1. Clear previously generated Auto process" curProduct reselAu to Process.

" 2 . R e a d the d a tu m id o f ad d itiv e fe a tu re in s ta n c e s " a d d D a t u m ld := S e t n e w .

c u r P r o d u c t w ith A llC h ild re n do: [reach | (e a c h i s K in d O f: A d d itiv c F e a tu re )

if T ru e :[a d d D a tu ra I d a d d : e a c h d a tu m ]].

" 3 . S e le c t sa m e d a tu m ad d itiv e p e a re n tF e a tu r e in sta n ce s" a d d F trs S a m e D a tu m := O rd e re d C o lle c tio n n ew . a d d D a t u m ld d o : [:e a c h D a tu m |

c u r P r o d u c t w ith A llC h ild re n d o : [:e a c h | (e a c h is K in d O f: A d d id v e F e a tu re ) ifT ru e :[(e a c h d a tu m = e a ch D a tu m ) if T n ie :[a d d F tr s S a m e D a tu m ad d : e a c h ]]]. " 4 . W h ile a d d F trs S a m e D a tu m is n o t e m p ty , F o r e a c h a d d F trs S a m e D a tu m , g e n e ra te a p ro c e s s ” [a d d F trs S a m e D a tu m is E m p ty ] w h ile F a ls e :[ h ig h estF t := a d d F trs S a m e D a tu m s h o w H ig h Z . h ig h e s tF t a d d M c P ro c e s s . a d d F trs S a m e D a tu m re m o v e : h ig h estF t. it Class: AddiUveFeature Method: addMcProcess " g e n e ra te s a m e p ro c e s s f o r a s in g le a d d itiv e p aren t in sta n ce . A ls o re q u e s ts a p ro c e s s fo r its s u b tra c tiv e c h ild fe atu re in s ta n c e s "

[s u b C h ild re n n e x tS u b C h ild re n a llS u b C h ild re n a D a turn d a tu m s |

datums := # (T O P ’FRONT ’RIGHT 'BOTTOM’ ’LEFT TUGHT). nextSubChildren := OrderedCollection new.

d a tu m s d o :[:a D a tu m | s e lf m fg M e th o d : a D a turn.

s u b C h ild re n := s e lf g e tS u b C h ild re n S a m e D a tu m .a D a tu m . a llS u b C h ild re n := s e lf g e tA H S u b C h ild re n S a m e D a tu m : a D a tu m . [a llS u b C h ild re n isE m p ty ]

w h ile F a ls e : [s u b C h ild r e n d o :[:a F e a tn r e | a F e a tu re m fg M e th o d .

(a F e a tu re w ith A U C h ild re n ) isE m p ty ifF a ls e :[n e x tS u b C h ild re n ad d A ll: ( a F e a t u r e g e tS u b C h ild re n S a m e D a tu m :a D a tu m ) ].

i

a llS u b C h ild re n re m o v e A ll: su b C h ild re n . s u b C h ild re n := n e x tS u b C h ild re n ]].

As illustrated above, the generateProcess which basically segregates the additive features, will remain the same. However, the additive feature plan generation method, addMcProcess, will have to be modified to segregate the additive features into single additive feature or additive feature clusters, based on proximityFcature attributes. Similarly, subtractive features or subtractive feature clusters should be segregated. Here, the term, ‘feature cluster’ is being referred to as a set of interacting features.

As discussed in section 7.5.1, the current machining methods (mfgMethod) are not valid for side interacting features. The interaciing additive and subtractive type of feature clusters should be machined either by pocket milling or by pocket milling with

island. For this reason, the additive and subtractive cluster pocket milling methods should be developed for the EndMilling class.

The proximityFeature sub-attributes may not be able to recognise the precise topology of interacting feature clusters. However they would help in determining the overall size. Moreover, the shape of a cluster depends on the feature instance size attributes. From the designers viewpoint, feature based modelling is a subset of parametric modelling and hence the design modifications are likely to be implemented by changing the feature size attributes. Therefore, any feature cluster machining method should first check the validity of a cluster and then apply the appropriate machining method. It should respond to different types of machining methods, e.g., pocket milling, stepped pocket milling, pocket milling with island, open profile, closed profile, etc.