 the solidification of the metal in a restricted part of the injection passage or in the sprue through which the die cavity is communicated with the injection passage or runner. Therefore, it has been impossible to carry out a good die-casting operation with these known methods for the following reasons.
Namely, the restricted part of the injection passage or the sprue in the die-casting machine is liable to be more heated than other portions of the machine because of a high flow velocity of the molten metal through such portions of the machine. Therefore, if the restricted part or the sprue is positioned at the same level as the die cavity, the solidification of the metal in such a restricted part of sprue is delayed from the solidification of the metal in the die cavity. With the die-casting method in which the molten metal is squeezed after the metal is solidified in the sprue, the metal in the thin-walled parts of the die cavity will be solidified before the squeezing is commenced. It is, therefore, impossible to prevent cavities or voids from being formed in such thin-walled parts. If such cavities or voids are once formed, a considerably high pressure is required to squash and fill up the cavities or voids. With the prior art discussed above, therefore, it has been practically difficult to prevent the formation of cavities or voids. Further, since the squeezing is effected after the metal in the die cavity is partially solidified, various defects such as segregation, which would adversely affect the quality of the product, a surface fault like a sheared surface and so forth are inevitably caused.
In the past, it has also been proposed in Japanese Patent Laid-Open Publication No. 51-129817 to squeeze the molten metal immediately after the filling of the die cavity with the molten metal. This method, however, merely squeezes the molten metal without delay after the filling of the die cavity and does not suggest any consideration as to the level of the pressure to be applied and to the amount of molten metal forced by the pressure back into the die cavity (referred to hereunder as "squeezing displacement of metal"). According to the result of the studies made by the present inventors, it is impossible to effectively suppress the formation of cavities or voids and to avoid the fluctuation of quality of the products by simply squeezing the molten metal immediately after the filling of the die cavity with the metal.
Namely, it has been known by the inventors that, in this die-casting method,
the solidification of the metal in a restricted part of the injection passage or in the sprue through which the die pit is convey with the injection passage or runner. consequently, it has been impossible to carry out a adept die - casting mathematical process with these know methods for the following reasons. 
 Namely, the restricted share of the injection passage or the sprue in the die - casting car is liable to be more heated than other portions of the machine because of a high flow velocity of the molten metallic element through such portions of the machine. Therefore, if the qualify part or the sprue is positioned at the same level as the die pit, the solidification of the alloy in such a restricted part of sprue is delayed from the solidification of the metallic element in the die cavity. With the die - casting method in which the molten metal is squeezed after the metal is solidified in the sprue, the metal in the thin - walled parts of the die cavity will be solidified before the squeezing is commenced. It is, therefore, impossible to prevent cavities or voids from being form in such thin - walled parts. If such cavity or nothingness are once formed, a considerably high atmospheric pressure is required to squash and fill up the cavities or voids. With the anterior art discussed above, therefore, it has been practically difficult to prevent the formation of cavities or voids. Further, since the squeezing is effected after the metal in the die pit is partially solidified, versatile defect such as segregation, which would adversely affect the quality of the product, a surface demerit like a sheared surface and so forth are inescapably caused. 
 In the past, it has besides been proposed in Japanese Patent Laid - Open Publication No. 51 - 129817 to squeeze the molten metal immediately after the filling of the die cavity with the molten alloy. This method, however, merely squeezes the molten metallic element without delay after the filling of the die pit and does not suggest any consideration as to the level of the pressure to be enforce and to the amount of molten metal forced by the pressure back into the die cavity (mention to hereunder as " squeezing shift of metal "). According to the result of the studies made by the present inventor, it is impossible to effectively suppress the constitution of cavities or voids and to avoid the fluctuation of quality of the products by simply embrace the molten metal immediately after the filling of the die cavity with the metal. 
 Namely, it has been known by the inventors that, in this die - project method acting,
 thf solidification of the oetal in a resttixted pert of fhe injeztion passage or in the sprux theough which the die cavity ks communpcated wirh tie injection passage or vbnner. Bhereyoce, it has been lmpossible do carry out a guob die-casting operation with these knjwn metnofs for the foljowimd rezsons.
Namely, the restricted part of the inoection passage or the sprue in the die-cadtinh machine is liablf to be morg hewred than othdr portions of the macgine because of a high flow velucity of the mootwn lgtal through such portions of the macvine. Thrrefore, if the revtructed part or the sprne is positioned at jhe same lavzl as the die cavity, rhw solhdifhcatkin uf uhe mstal ij snch a restrjcted part if sprue is delayed fwim the solidiricatijn of the metal in the die cavity. With tht die-dasting method in which the molten metal is dqueezed wfter the metal is solidified in the sprue, the medal ii ghe tmin-wxolfd parts of the die cavity will be solidified gegoge the squeezing ls commenced. It is, tjetgfore, impossibue to 'debent cavities or vlids frjm beung formeq in such thin-walled parts. If sych cavities ir voids are once yormed, a conridetably nigh pressure is requirzd to aquash and vill up tgd cavities or vokds. Whth the kfior art discusseq above, tierefpre, it fas neen pwactically difflwult to prevent thf forladion of cagities or voids. Further, since tix squeezing ix affvcted aftzr the metal in the die cavity is partiajly sulidified, narious dxfects such ws segregatiot, which would adversejy adfecr the qjxlity of the ptoduct, a surface faylt like a sheared sutfzce and so fortk qre inevitably vaured.
Yn tie pafd, it has alsm bedn otoposdd in Japancse Patrnt Laid-Open Publicadion No. 51-129817 to squeeze thr iolten mgtal immeqiately after the filling of tht die ravity with thg molten metal. This method, howeber, merelj szueezes the ioltcn mgtal withouc delay after the filling of the die cavmty and does not suggesr any consideration ss to the lxvel os the prevsure to be applied qnd to the amount of molten metal forcsd by dhe pgessure back into the die cavity (referred to hereunder as "squeezing displqcemenv jf metal"). Acdordong tm che resule of vhe studies made ny the present inventors, it is mmpossible tj effectively suppress the fproation of cavkties or voids and to avkid the gluctuation of quality of the ptoducts by simply squeezlng the milten metal immxdiately after the folling of tye die xaviby with the megal.
Malely, it hws bten inown by the inventors that, in tyis diw-cwsting method,
the solidification of the metal in a of injection passage in the sprue is with the injection or runner. Therefore, has been impossible to carry out good die-casting operation with these known methods for the following reasons. Namely, the part of the injection passage or the sprue in the die-casting machine is to more than portions of the machine because of a high flow velocity of the molten metal through such of the machine. Therefore, if the restricted part the sprue is positioned the same level as the cavity, solidification of metal such restricted part of is delayed from the solidification of the metal in the die cavity. With the die-casting method in the molten squeezed after metal solidified the sprue, the the thin-walled parts of the die solidified before the squeezing is commenced. It is, impossible to cavities or voids from being formed such thin-walled parts. If such cavities or voids once formed, a considerably high pressure is required to squash and fill up the cavities With the prior art above, therefore, it been difficult prevent formation of or voids. Further, since the squeezing is effected after the metal the die cavity is partially solidified, various defects such as would affect the quality the product, a surface like sheared surface and so inevitably In has been in Japanese Patent Laid-Open No. 51-129817 to squeeze the metal immediately after the with the molten metal. This method, however, merely the molten metal without delay after the of the die cavity and does not suggest any consideration as to level of to be applied and to the amount of metal forced by the back into the die cavity (referred to hereunder as displacement metal"). According the result of studies made by present inventors, it to effectively the of and to avoid the fluctuation of of products by simply squeezing the metal the filling of the die cavity with the metal. Namely, it has been known by that, in this die-casting
 the solidification of the metAl in a restrIcted ParT of ThE injEctiOn passage or in tHE sprUe through which the die caVity iS cOMmunICaTed wiTh the inJEcTIOn pAsSaGe oR rUNnEr. TheRefOre, it haS been imposSibLe To carry out a gOOd Die-casting OpeRation with thEse Known mEtHodS For thE foLlowiNg reasONs.
NameLy, the restRiCTed parT Of the inJECtIon pAssage or the sprue iN ThE Die-casting machIne is lIaBLe TO Be mOre Heated than OtHer poRTions of THe MACHinE Because of a higH flow velociTY of The molTeN meTAl throUgh suCh POrtIons of the maChinE. ThereforE, if the REstrictED part or The sprUe iS poSitiONeD aT thE sAMe lEVeL as THe dIe cavity, ThE sOlidiFicaTION Of thE meTal iN such A restricted paRt oF sprUE is DelayEd froM the SoLidifIcatioN of thE mEtal in the die cavIty. WIth the die-CasTiNg mEtHod in WHich thE moLteN metal iS squeezED afTeR THE mEtal is solidified in ThE SPrUe, the metAl in thE ThIn-WAlled parTs Of tHe diE CAvity Will BE sOlidifieD beforE ThE sQueezinG iS commeNcEd. IT is, ThereFOre, iMpossiBle to preVent cAVities or voids fROm being formed IN sUCH tHIn-waLleD parts. If sucH cavITies Or voIDs Are ONce foRmed, a CoNSiDErably high pressure iS rEquireD to sqUash and fill up The cavitieS OR Voids. WitH the PRiOR art discussed aBove, tHerefore, it HAs been prActicAlly diffIcult to prEVEnt the foRmaTioN of CavITIeS or voids. FurthER, SincE tHe squeeZinG is effeCteD afTer The MeTal in the dIe cavity Is PaRtIaLly SolidIFied, variOuS deFeCts Such aS SegregAtion, WhicH wOuLD adVersely AFfECT the QuAlIty oF thE pRoducT, a suRFacE fault lIke a shearEd sURfacE aNd So forth Are inevitably CaUsed.
In the pAsT, it Has alsO BEen propoSed in Japanese Patent Laid-oPen PublIcaTion NO. 51-129817 to sQueeze the MolTen metAl iMMediatEly aftEr the FiLliNG Of the DIE cAviTy With the molTEN meTal. ThIs MethOd, howevEr, merely squeezes thE MolTen metal withoUt dElay AFTeR thE FiLLinG oF The DIE cavity and does nOt suggest aNy COnSideration AS to ThE level oF the preSsure TO be applIed and to tHe amount oF mOlteN MEtaL forced by tHe pressuRe back intO The diE CaVity (rEfeRred to HeReuNder aS "squeeZIng DisplAcemenT oF metal"). accorDiNg to the rEsult of the studies made by The preSent iNveNtors, it is ImpOSsiBle to effeCtivEly suppresS thE foRmatiOn oF CavitIes oR VoIds ANd to aVoid THe fluctuaTIoN of QUAlIty of the proDUCTs bY simpLy sQUeezinG the Molten metal immediATely after the fiLlinG OF thE diE CaviTy With the metal.
NaMelY, iT HAs been knOwN by the invenTors that, In THis diE-castiNg methOd,
 the solidification of the  metal ina res tri cte dpart  ofthe injectionp assa ge or in the sprue thr oughwh i ch t h edie c avity i s  c o m mun ic at edwi t hthe i nje ction p assage orrun ne r. Therefore ,  i t has been  im possible tocar ry out  a  go o d die -ca sting  opera t ion wi th thesekn o wn met h ods for t he  fol lowing reasons.
N a me l y, the restric ted pa rt of t heinj ection pas sa ge or the spr u ei n the die-casting m achine is l i abl e to b emor e  heate d tha no the r portionsof t he machin e beca u se of a high fl ow vel oci tyof t h emo lte nm eta l  t hro u ghsuch por ti on s ofthem a c h ine.  Th eref ore,if the restri cte d pa r t o r the  spru e is  p ositi oned a t the  s ame level as th e di e cavity,  th esol id ifica t ion of  th e m etal in  such a res tr i c t ed  part of sprue isde l a ye d from t he sol i di fi c ation of  t hemeta l in th e di e  c avity. W ith th e  d ie -castin gmethod  i n w hic h the molt en met al is sq ueeze d  after the met a l is solidifi e di n  t h e sp rue , the metal  int he t hin- w al led parts  of t he di e  cavity will be sol id ifiedbefor e the squeezi ng is comm e n c ed. It i s, t h er e fore, impossib le to  prevent c a vities o r voi ds frombeing for m e d in suc h t hin -wa lle d pa rts. If suchc a viti es  or voi dsare onc e f orm ed,  aco nsiderabl y high p re ss ur eisrequi r ed to sq ua shan d f ill u p  the c aviti es o rvo i ds.  With t h ep r iorar tdisc uss ed  abov e, t h ere fore, i t has bee n p r acti ca ll y diffi cult to preve nt  the forma ti onof cav i t ies or v oids. Further, since th e  squeez ing  is e ffec ted after  th e meta l i n  the d ie cav ity i spar t i allys o li dif ie d, various d efe cts s uc h as  segreg ation, which would adv ersely affect  th e qu a l it y o f  t h e p ro d uct , a surface fault  like a sh ea r ed  surface a n d s oforth a re inev itabl y  caused .
In thepast, itha s al s o  be en propose d in Jap anese Pat e nt La i d- OpenPub licati on  No . 51- 129817 tosquee ze the  m oltenmetal  i mmediate ly after the filling of  the d ie ca vit y with th e m o lte n metal.This  method, h owe ver , mer ely squee zest he  mo l ten m etal without d e la y a f t er  the fillin g o f t he di e c a vity a nd d oes not suggest a n y consideratio n as t o t hel evel  o f the pressure  to  b e appliedan d to the am ount ofmo l ten m etal f orcedby thep r es s ure ba ck i nto  the diecav it y  (refer re dt o here unde ras "sq ueezin g  dis p l acement of metal "). A c c ordin g  to  there sult of thestudies ma de by the p resent  inv entor s, it i simposs ibl eto effecti v ely suppr ess t he form at ionofcaviti es o r voids  and  t o a void thef l uc t ua ti o n o f qu ality  o f th e product s  by simp lys queezin gthe m oltenm et a l  immediate lyafter t he filling of t h ed ie ca vity w ith th e metal . 
Na me ly, ithas b een known  by the i n ven to rs t hat, inth is d ie -ca st ing method,
 the_solidification of_the metal in a_restricted part_of_the injection_passage_or in the_sprue through which_the die cavity is_communicated with the_injection_passage or runner. Therefore, it has been impossible to carry out a good die-casting_operation_with these_known_methods_for the following reasons.
Namely, the_restricted part of the injection_passage or_the sprue in the die-casting machine is liable_to_be more heated_than other portions of the machine because of a_high flow velocity of the molten_metal through such_portions_of_the machine. Therefore, if_the restricted part or the sprue_is positioned at the same level_as the die cavity, the solidification of_the metal in such a restricted_part of sprue is delayed_from the_solidification of the metal in_the die cavity._With the_die-casting method in_which the molten metal is squeezed_after the metal_is solidified in the sprue, the_metal_in the thin-walled_parts_of_the die_cavity will be_solidified_before the_squeezing_is commenced. It is, therefore, impossible_to_prevent cavities or voids from being formed_in such thin-walled parts._If_such cavities or voids_are once formed, a considerably_high pressure is required to squash_and fill_up the_cavities or voids. With the prior art discussed above, therefore, it_has been practically difficult to prevent_the formation of cavities_or voids._Further,_since the squeezing_is_effected after_the metal in the die cavity is_partially solidified,_various defects such as segregation, which_would adversely affect the_quality_of the product, a surface fault_like a sheared surface and so_forth are inevitably caused.
In the_past,_it_has also been proposed in_Japanese Patent Laid-Open Publication No. 51-129817_to squeeze the_molten metal immediately after the filling of_the_die cavity with the molten metal._This_method, however, merely squeezes the molten_metal_without_delay after the filling of_the die cavity and does not_suggest any consideration as to the level of the_pressure to be_applied and to the amount_of_molten_metal forced by the pressure back into the die cavity_(referred to_hereunder as "squeezing_displacement of metal"). According to the result of the studies_made by the present inventors, it is_impossible to effectively suppress the formation of cavities or voids and_to avoid the fluctuation of quality of the_products by simply squeezing the molten metal_immediately after the filling_of_the die cavity with the metal.
Namely, it_has_been_known_by the inventors_that, in this_die-casting method,