模(mo)具尺(chi)寸的確定(ding)方法

模(mo)(mo)具型(xing)腔和型(xing)芯的(de)(de)(de)加工尺(chi)(chi)寸(cun)除了通過(guo)D=M(1+S)公(gong)(gong)(gong)(gong)式計算(suan)基本(ben)尺(chi)(chi)寸(cun)之(zhi)外，還有一個加工公(gong)(gong)(gong)(gong)差(cha)(cha)的(de)(de)(de)問題(ti)。按照慣(guan)例(li)，模(mo)(mo)具的(de)(de)(de)加工公(gong)(gong)(gong)(gong)差(cha)(cha)為塑(su)(su)(su)件公(gong)(gong)(gong)(gong)差(cha)(cha)的(de)(de)(de)1/3。但(dan)由(you)于塑(su)(su)(su)料(liao)收(shou)(shou)縮(suo)率范(fan)圍和穩定性各有差(cha)(cha)異，首先(xian)必(bi)須(xu)合理化確定不同塑(su)(su)(su)料(liao)所成形塑(su)(su)(su)件的(de)(de)(de)尺(chi)(chi)寸(cun)公(gong)(gong)(gong)(gong)差(cha)(cha)。即(ji)由(you)收(shou)(shou)縮(suo)率范(fan)圍較大或(huo)收(shou)(shou)縮(suo)率穩定較差(cha)(cha)塑(su)(su)(su)料(liao)成形塑(su)(su)(su)件的(de)(de)(de)尺(chi)(chi)寸(cun)公(gong)(gong)(gong)(gong)差(cha)(cha)應(ying)(ying)取得大一些。否(fou)則(ze)就可能出現(xian)大量尺(chi)(chi)寸(cun)超(chao)差(cha)(cha)的(de)(de)(de)廢(fei)品。 為此，各國對塑(su)(su)(su)料(liao)件的(de)(de)(de)尺(chi)(chi)寸(cun)公(gong)(gong)(gong)(gong)差(cha)(cha)專門(men)制訂了國家標(biao)(biao)(biao)(biao)準(zhun)(zhun)(zhun)(zhun)或(huo)行業(ye)標(biao)(biao)(biao)(biao)準(zhun)(zhun)(zhun)(zhun)。中國也曾制訂了部(bu)級專業(ye)標(biao)(biao)(biao)(biao)準(zhun)(zhun)(zhun)(zhun)。但(dan)大都無相應(ying)(ying)的(de)(de)(de)模(mo)(mo)具型(xing)腔的(de)(de)(de)尺(chi)(chi)寸(cun)公(gong)(gong)(gong)(gong)差(cha)(cha)。德(de)國國家標(biao)(biao)(biao)(biao)準(zhun)(zhun)(zhun)(zhun)中專門(men)制訂了塑(su)(su)(su)件尺(chi)(chi)寸(cun)公(gong)(gong)(gong)(gong)差(cha)(cha)的(de)(de)(de)DIN16901標(biao)(biao)(biao)(biao)準(zhun)(zhun)(zhun)(zhun)及相應(ying)(ying)的(de)(de)(de)模(mo)(mo)具型(xing)腔尺(chi)(chi)寸(cun)公(gong)(gong)(gong)(gong)差(cha)(cha)的(de)(de)(de)DIN16749標(biao)(biao)(biao)(biao)準(zhun)(zhun)(zhun)(zhun)。此標(biao)(biao)(biao)(biao)準(zhun)(zhun)(zhun)(zhun)在世界上具有較大的(de)(de)(de)影響，因而可供塑(su)(su)(su)料(liao)模(mo)(mo)具行業(ye)參考。

關于塑件的尺寸公差和允許偏差

為了合理地確(que)定(ding)不(bu)同收縮特性材(cai)料所成(cheng)形(xing)塑件的尺寸(cun)公(gong)差，讓標準引(yin)入了成(cheng)形(xing)收縮差△VS這一概念。 △VS＝VSR_VST(4)

式中： VS－成(cheng)形收縮(suo)差(cha)　VSR－熔(rong)料流動(dong)方(fang)向(xiang)的成(cheng)形收縮(suo)率　VST－與熔(rong)料流動(dong)垂直方(fang)向(xiang)的成(cheng)形收縮(suo)率。

根據塑料(liao)△VS值(zhi)，將各種塑料(liao)的(de)(de)收縮特(te)性(xing)(xing)(xing)分為4個組(zu)(zu)(zu)(zu)(zu)(zu)。△VS值(zhi)最(zui)小(xiao)的(de)(de)組(zu)(zu)(zu)(zu)(zu)(zu)是高(gao)精度組(zu)(zu)(zu)(zu)(zu)(zu)，以此類推(tui)，△VS值(zhi)最(zui)大(da)的(de)(de)組(zu)(zu)(zu)(zu)(zu)(zu)為低精度組(zu)(zu)(zu)(zu)(zu)(zu)。 并按照(zhao)基本尺(chi)(chi)(chi)寸(cun)(cun)編(bian)制(zhi)了精密技術、110、120、130、140、150和(he)(he)(he)160公(gong)(gong)(gong)差(cha)(cha)(cha)組(zu)(zu)(zu)(zu)(zu)(zu)。并規定(ding)(ding)，用(yong)(yong)收縮特(te)性(xing)(xing)(xing)最(zui)穩定(ding)(ding)的(de)(de)塑料(liao)成(cheng)(cheng)(cheng)形塑件(jian)(jian)(jian)(jian)(jian)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)公(gong)(gong)(gong)差(cha)(cha)(cha)可選(xuan)(xuan)用(yong)(yong)110、120和(he)(he)(he)130組(zu)(zu)(zu)(zu)(zu)(zu)。用(yong)(yong)收縮特(te)性(xing)(xing)(xing)中等穩定(ding)(ding)的(de)(de)塑料(liao)成(cheng)(cheng)(cheng)形塑件(jian)(jian)(jian)(jian)(jian)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)公(gong)(gong)(gong)差(cha)(cha)(cha)選(xuan)(xuan)用(yong)(yong)120、130和(he)(he)(he)140。如果(guo)用(yong)(yong)這類塑料(liao)成(cheng)(cheng)(cheng)形塑件(jian)(jian)(jian)(jian)(jian)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)公(gong)(gong)(gong)差(cha)(cha)(cha)選(xuan)(xuan)用(yong)(yong)110組(zu)(zu)(zu)(zu)(zu)(zu)時，即可能出大(da)量尺(chi)(chi)(chi)寸(cun)(cun)超差(cha)(cha)(cha)塑件(jian)(jian)(jian)(jian)(jian)。用(yong)(yong)收縮特(te)性(xing)(xing)(xing)較差(cha)(cha)(cha)的(de)(de)塑料(liao)成(cheng)(cheng)(cheng)形塑件(jian)(jian)(jian)(jian)(jian)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)公(gong)(gong)(gong)差(cha)(cha)(cha)選(xuan)(xuan)用(yong)(yong)130、140和(he)(he)(he)150組(zu)(zu)(zu)(zu)(zu)(zu)。用(yong)(yong)收縮特(te)性(xing)(xing)(xing)最(zui)差(cha)(cha)(cha)的(de)(de)塑料(liao)成(cheng)(cheng)(cheng)形塑件(jian)(jian)(jian)(jian)(jian)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)公(gong)(gong)(gong)差(cha)(cha)(cha)選(xuan)(xuan)用(yong)(yong)140、150和(he)(he)(he)160組(zu)(zu)(zu)(zu)(zu)(zu)。 在使用(yong)(yong)此公(gong)(gong)(gong)差(cha)(cha)(cha)表時，還需注意以下各點(dian)。 表中的(de)(de)一(yi)般公(gong)(gong)(gong)差(cha)(cha)(cha)用(yong)(yong)于不注明公(gong)(gong)(gong)差(cha)(cha)(cha)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)公(gong)(gong)(gong)差(cha)(cha)(cha)。直接(jie)標注偏差(cha)(cha)(cha)的(de)(de)公(gong)(gong)(gong)差(cha)(cha)(cha)是用(yong)(yong)于對(dui)塑件(jian)(jian)(jian)(jian)(jian)尺(chi)(chi)(chi)寸(cun)(cun)標注公(gong)(gong)(gong)差(cha)(cha)(cha)的(de)(de)公(gong)(gong)(gong)差(cha)(cha)(cha)帶。其(qi)上、下偏差(cha)(cha)(cha)可設計人員(yuan)自行確(que)定(ding)(ding)。例(li)如公(gong)(gong)(gong)差(cha)(cha)(cha)帶為0.8mm，則(ze)可以選(xuan)(xuan)用(yong)(yong)以下各種上、下偏差(cha)(cha)(cha)構成(cheng)(cheng)(cheng)。0.0;-0.8;±0.4;-0.2;-0.5等。 每一(yi)公(gong)(gong)(gong)差(cha)(cha)(cha)組(zu)(zu)(zu)(zu)(zu)(zu)中均有(you)A、B兩(liang)組(zu)(zu)(zu)(zu)(zu)(zu)公(gong)(gong)(gong)差(cha)(cha)(cha)值(zhi)。其(qi)中A是由模(mo)具零(ling)件(jian)(jian)(jian)(jian)(jian)組(zu)(zu)(zu)(zu)(zu)(zu)合(he)形成(cheng)(cheng)(cheng)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)，增加了模(mo)具零(ling)件(jian)(jian)(jian)(jian)(jian)對(dui)合(he)處不密合(he)所形成(cheng)(cheng)(cheng)的(de)(de)錯(cuo)差(cha)(cha)(cha)。此增加值(zhi)為0.2mm。其(qi)中B是直接(jie)由模(mo)具零(ling)件(jian)(jian)(jian)(jian)(jian)所決定(ding)(ding)的(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)。 精密技術是專門(men)設立的(de)(de)一(yi)組(zu)(zu)(zu)(zu)(zu)(zu)公(gong)(gong)(gong)差(cha)(cha)(cha)值(zhi)，供具有(you)高(gao)精度要求(qiu)塑件(jian)(jian)(jian)(jian)(jian)使用(yong)(yong)。 在此用(yong)(yong)塑件(jian)(jian)(jian)(jian)(jian)公(gong)(gong)(gong)差(cha)(cha)(cha)之前，首先必須知道所使用(yong)(yong)的(de)(de)塑料(liao)適用(yong)(yong)哪幾個公(gong)(gong)(gong)差(cha)(cha)(cha)組(zu)(zu)(zu)(zu)(zu)(zu)。

模具的制造公差

德國國家標(biao)準(zhun)針對塑(su)件(jian)公(gong)(gong)差(cha)(cha)制(zhi)訂了相應模具制(zhi)造公(gong)(gong)差(cha)(cha)的(de)(de)(de)(de)標(biao)準(zhun)DIN16749。該表中共設4種(zhong)(zhong)公(gong)(gong)差(cha)(cha)。不論何種(zhong)(zhong)材料的(de)(de)(de)(de)塑(su)件(jian)，其中不注明尺寸(cun)(cun)公(gong)(gong)差(cha)(cha)尺寸(cun)(cun)的(de)(de)(de)(de)模具制(zhi)造公(gong)(gong)差(cha)(cha)均使用序號(hao)(hao)(hao)1的(de)(de)(de)(de)公(gong)(gong)差(cha)(cha)。具體(ti)公(gong)(gong)差(cha)(cha)值由基本尺寸(cun)(cun)范圍確定。 不論何種(zhong)(zhong)材料塑(su)件(jian)中等(deng)精度尺寸(cun)(cun)的(de)(de)(de)(de)模具制(zhi)造公(gong)(gong)差(cha)(cha)為序號(hao)(hao)(hao)2的(de)(de)(de)(de)公(gong)(gong)差(cha)(cha)。不論何種(zhong)(zhong)材料塑(su)件(jian)較高精度尺寸(cun)(cun)的(de)(de)(de)(de)模具制(zhi)造公(gong)(gong)差(cha)(cha)為序號(hao)(hao)(hao)3的(de)(de)(de)(de)公(gong)(gong)差(cha)(cha)。精密技術相應的(de)(de)(de)(de)模具制(zhi)造公(gong)(gong)差(cha)(cha)為序號(hao)(hao)(hao)4的(de)(de)(de)(de)公(gong)(gong)差(cha)(cha)。

可(ke)以合理地確定(ding)各(ge)種材料塑件的合理公差和相應(ying)的模(mo)(mo)具制(zhi)造公差，這不僅給(gei)模(mo)(mo)具制(zhi)造帶來方便，還可(ke)以減(jian)少廢品，提(ti)高(gao)經濟效期益。