▁effect ▁of ▁the ▁beam ▁depends ▁on ▁the ▁particular ▁combination ▁of ▁these ▁parameters . ▁Action ▁of ▁the ▁beam ▁at ▁low ▁power ▁density ▁or ▁over ▁a ▁very ▁short ▁time ▁results ▁in ▁mel ting ▁only ▁a ▁thin ▁surface ▁layer . ▁A ▁def oc used ▁beam ▁does ▁not ▁pen et rate , ▁and ▁the ▁material ▁at ▁low ▁w eld ing ▁spe eds ▁is ▁he ated ▁only ▁by ▁condu ction ▁of ▁the ▁heat ▁from ▁the ▁surface , ▁producing ▁a ▁hem is pher ical ▁m elt ed ▁zone . ▁At ▁high ▁power ▁density ▁and ▁low ▁speed , ▁a ▁deeper ▁and ▁slightly ▁con ical ▁m elt ed ▁zone ▁is ▁produced . ▁In ▁the ▁case ▁of ▁very ▁high ▁power ▁density , ▁the ▁beam ▁( well ▁focused ) ▁pen etr ates ▁deeper , ▁in ▁proportion ▁to ▁its ▁total ▁power . ▁ ▁The ▁w eld ing ▁process ▁ ▁W eld ability ▁For ▁w eld ing ▁thin - w alled ▁parts , ▁appropriate ▁w eld ing ▁a ids ▁are ▁generally ▁needed . ▁Their ▁construction ▁must ▁provide ▁perfect ▁contact ▁of ▁the ▁parts ▁and ▁prevent ▁their ▁movement ▁during ▁w eld ing . ▁Usually ▁they ▁have ▁to ▁be ▁designed ▁individually ▁for ▁a ▁given ▁work pie ce . ▁ ▁Not ▁all ▁materials ▁can ▁be ▁w eld ed ▁by ▁an ▁electron ▁beam ▁in ▁a ▁vac u um . ▁This ▁technology ▁cannot ▁be ▁applied ▁to ▁materials ▁with ▁high ▁v ap our ▁pressure ▁at ▁the ▁mel ting ▁temperature , ▁like ▁z inc , ▁cad m ium , ▁mag nes ium ▁and ▁pract ically ▁all ▁non - met als . ▁ ▁Another