模具尺寸的確定方法

模(mo)具(ju)型腔和(he)型芯的(de)(de)加工尺(chi)寸(cun)除了(le)通過(guo)D=M(1+S)公(gong)(gong)式計(ji)算(suan)基本尺(chi)寸(cun)之外，還有(you)一(yi)個加工公(gong)(gong)差(cha)(cha)的(de)(de)問(wen)題。按照(zhao)慣例，模(mo)具(ju)的(de)(de)加工公(gong)(gong)差(cha)(cha)為塑(su)件(jian)公(gong)(gong)差(cha)(cha)的(de)(de)1/3。但由(you)于塑(su)料收縮率(lv)(lv)范(fan)圍(wei)和(he)穩(wen)定性各(ge)有(you)差(cha)(cha)異，首先必(bi)須合理化確定不同塑(su)料所成形(xing)(xing)塑(su)件(jian)的(de)(de)尺(chi)寸(cun)公(gong)(gong)差(cha)(cha)。即由(you)收縮率(lv)(lv)范(fan)圍(wei)較大(da)或收縮率(lv)(lv)穩(wen)定較差(cha)(cha)塑(su)料成形(xing)(xing)塑(su)件(jian)的(de)(de)尺(chi)寸(cun)公(gong)(gong)差(cha)(cha)應(ying)取(qu)得大(da)一(yi)些。否則就可能出現大(da)量(liang)尺(chi)寸(cun)超差(cha)(cha)的(de)(de)廢品(pin)。 為此(ci)，各(ge)國(guo)對塑(su)料件(jian)的(de)(de)尺(chi)寸(cun)公(gong)(gong)差(cha)(cha)專門(men)制(zhi)訂了(le)國(guo)家標(biao)(biao)(biao)準(zhun)或行業標(biao)(biao)(biao)準(zhun)。中國(guo)也曾制(zhi)訂了(le)部級專業標(biao)(biao)(biao)準(zhun)。但大(da)都(dou)無相應(ying)的(de)(de)模(mo)具(ju)型腔的(de)(de)尺(chi)寸(cun)公(gong)(gong)差(cha)(cha)。德國(guo)國(guo)家標(biao)(biao)(biao)準(zhun)中專門(men)制(zhi)訂了(le)塑(su)件(jian)尺(chi)寸(cun)公(gong)(gong)差(cha)(cha)的(de)(de)DIN16901標(biao)(biao)(biao)準(zhun)及相應(ying)的(de)(de)模(mo)具(ju)型腔尺(chi)寸(cun)公(gong)(gong)差(cha)(cha)的(de)(de)DIN16749標(biao)(biao)(biao)準(zhun)。此(ci)標(biao)(biao)(biao)準(zhun)在世界上具(ju)有(you)較大(da)的(de)(de)影(ying)響，因而(er)可供塑(su)料模(mo)具(ju)行業參(can)考。

關于塑件的尺寸公差和允許偏差

為(wei)了合理地確定不(bu)同收(shou)縮特性材(cai)料(liao)所成(cheng)形塑件的尺寸公差(cha)，讓標準(zhun)引入了成(cheng)形收(shou)縮差(cha)△VS這一概(gai)念(nian)。 △VS＝VSR_VST(4)

式中： VS－成(cheng)(cheng)形(xing)收縮(suo)(suo)差　VSR－熔料流動(dong)(dong)方向(xiang)的成(cheng)(cheng)形(xing)收縮(suo)(suo)率(lv)　VST－與熔料流動(dong)(dong)垂直(zhi)方向(xiang)的成(cheng)(cheng)形(xing)收縮(suo)(suo)率(lv)。

根據塑(su)(su)(su)(su)(su)(su)(su)料(liao)△VS值(zhi)，將各(ge)種(zhong)塑(su)(su)(su)(su)(su)(su)(su)料(liao)的(de)(de)(de)(de)(de)收縮(suo)特性(xing)(xing)分(fen)為(wei)4個組(zu)(zu)。△VS值(zhi)最小的(de)(de)(de)(de)(de)組(zu)(zu)是高(gao)精(jing)(jing)度(du)(du)組(zu)(zu)，以此(ci)(ci)類推，△VS值(zhi)最大(da)的(de)(de)(de)(de)(de)組(zu)(zu)為(wei)低精(jing)(jing)度(du)(du)組(zu)(zu)。 并按照(zhao)基(ji)本尺(chi)(chi)(chi)寸(cun)(cun)(cun)編制了精(jing)(jing)密技(ji)(ji)術(shu)、110、120、130、140、150和160公(gong)(gong)差(cha)(cha)(cha)組(zu)(zu)。并規定，用(yong)(yong)收縮(suo)特性(xing)(xing)最穩定的(de)(de)(de)(de)(de)塑(su)(su)(su)(su)(su)(su)(su)料(liao)成(cheng)形塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)公(gong)(gong)差(cha)(cha)(cha)可選用(yong)(yong)110、120和130組(zu)(zu)。用(yong)(yong)收縮(suo)特性(xing)(xing)中等穩定的(de)(de)(de)(de)(de)塑(su)(su)(su)(su)(su)(su)(su)料(liao)成(cheng)形塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)公(gong)(gong)差(cha)(cha)(cha)選用(yong)(yong)120、130和140。如(ru)果用(yong)(yong)這類塑(su)(su)(su)(su)(su)(su)(su)料(liao)成(cheng)形塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)公(gong)(gong)差(cha)(cha)(cha)選用(yong)(yong)110組(zu)(zu)時，即可能出大(da)量尺(chi)(chi)(chi)寸(cun)(cun)(cun)超差(cha)(cha)(cha)塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)。用(yong)(yong)收縮(suo)特性(xing)(xing)較差(cha)(cha)(cha)的(de)(de)(de)(de)(de)塑(su)(su)(su)(su)(su)(su)(su)料(liao)成(cheng)形塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)公(gong)(gong)差(cha)(cha)(cha)選用(yong)(yong)130、140和150組(zu)(zu)。用(yong)(yong)收縮(suo)特性(xing)(xing)最差(cha)(cha)(cha)的(de)(de)(de)(de)(de)塑(su)(su)(su)(su)(su)(su)(su)料(liao)成(cheng)形塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)公(gong)(gong)差(cha)(cha)(cha)選用(yong)(yong)140、150和160組(zu)(zu)。 在使(shi)用(yong)(yong)此(ci)(ci)公(gong)(gong)差(cha)(cha)(cha)表時，還需注意(yi)以下各(ge)點。 表中的(de)(de)(de)(de)(de)一般(ban)公(gong)(gong)差(cha)(cha)(cha)用(yong)(yong)于不注明公(gong)(gong)差(cha)(cha)(cha)的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)公(gong)(gong)差(cha)(cha)(cha)。直接標注偏差(cha)(cha)(cha)的(de)(de)(de)(de)(de)公(gong)(gong)差(cha)(cha)(cha)是用(yong)(yong)于對塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)尺(chi)(chi)(chi)寸(cun)(cun)(cun)標注公(gong)(gong)差(cha)(cha)(cha)的(de)(de)(de)(de)(de)公(gong)(gong)差(cha)(cha)(cha)帶。其(qi)(qi)上、下偏差(cha)(cha)(cha)可設計人員(yuan)自行確定。例如(ru)公(gong)(gong)差(cha)(cha)(cha)帶為(wei)0.8mm，則可以選用(yong)(yong)以下各(ge)種(zhong)上、下偏差(cha)(cha)(cha)構成(cheng)。0.0;-0.8;±0.4;-0.2;-0.5等。 每一公(gong)(gong)差(cha)(cha)(cha)組(zu)(zu)中均(jun)有(you)A、B兩組(zu)(zu)公(gong)(gong)差(cha)(cha)(cha)值(zhi)。其(qi)(qi)中A是由模具零(ling)件(jian)(jian)(jian)(jian)(jian)(jian)組(zu)(zu)合形成(cheng)的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)，增(zeng)加了模具零(ling)件(jian)(jian)(jian)(jian)(jian)(jian)對合處不密合所形成(cheng)的(de)(de)(de)(de)(de)錯差(cha)(cha)(cha)。此(ci)(ci)增(zeng)加值(zhi)為(wei)0.2mm。其(qi)(qi)中B是直接由模具零(ling)件(jian)(jian)(jian)(jian)(jian)(jian)所決(jue)定的(de)(de)(de)(de)(de)尺(chi)(chi)(chi)寸(cun)(cun)(cun)。 精(jing)(jing)密技(ji)(ji)術(shu)是專門設立(li)的(de)(de)(de)(de)(de)一組(zu)(zu)公(gong)(gong)差(cha)(cha)(cha)值(zhi)，供(gong)具有(you)高(gao)精(jing)(jing)度(du)(du)要求(qiu)塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)使(shi)用(yong)(yong)。 在此(ci)(ci)用(yong)(yong)塑(su)(su)(su)(su)(su)(su)(su)件(jian)(jian)(jian)(jian)(jian)(jian)公(gong)(gong)差(cha)(cha)(cha)之前，首先必(bi)須知(zhi)道所使(shi)用(yong)(yong)的(de)(de)(de)(de)(de)塑(su)(su)(su)(su)(su)(su)(su)料(liao)適(shi)用(yong)(yong)哪(na)幾個公(gong)(gong)差(cha)(cha)(cha)組(zu)(zu)。

模具的制造公差

德國(guo)國(guo)家標準針對塑(su)件公(gong)(gong)(gong)差(cha)(cha)(cha)制訂了相(xiang)(xiang)應(ying)模(mo)(mo)(mo)具(ju)(ju)(ju)制造(zao)公(gong)(gong)(gong)差(cha)(cha)(cha)的(de)(de)(de)標準DIN16749。該表中(zhong)(zhong)共設4種(zhong)公(gong)(gong)(gong)差(cha)(cha)(cha)。不(bu)(bu)論何(he)種(zhong)材(cai)料的(de)(de)(de)塑(su)件，其中(zhong)(zhong)不(bu)(bu)注(zhu)明尺寸(cun)(cun)公(gong)(gong)(gong)差(cha)(cha)(cha)尺寸(cun)(cun)的(de)(de)(de)模(mo)(mo)(mo)具(ju)(ju)(ju)制造(zao)公(gong)(gong)(gong)差(cha)(cha)(cha)均使用序(xu)號(hao)(hao)1的(de)(de)(de)公(gong)(gong)(gong)差(cha)(cha)(cha)。具(ju)(ju)(ju)體(ti)公(gong)(gong)(gong)差(cha)(cha)(cha)值由基本(ben)尺寸(cun)(cun)范圍確(que)定(ding)。 不(bu)(bu)論何(he)種(zhong)材(cai)料塑(su)件中(zhong)(zhong)等(deng)精(jing)(jing)度(du)尺寸(cun)(cun)的(de)(de)(de)模(mo)(mo)(mo)具(ju)(ju)(ju)制造(zao)公(gong)(gong)(gong)差(cha)(cha)(cha)為(wei)(wei)序(xu)號(hao)(hao)2的(de)(de)(de)公(gong)(gong)(gong)差(cha)(cha)(cha)。不(bu)(bu)論何(he)種(zhong)材(cai)料塑(su)件較高精(jing)(jing)度(du)尺寸(cun)(cun)的(de)(de)(de)模(mo)(mo)(mo)具(ju)(ju)(ju)制造(zao)公(gong)(gong)(gong)差(cha)(cha)(cha)為(wei)(wei)序(xu)號(hao)(hao)3的(de)(de)(de)公(gong)(gong)(gong)差(cha)(cha)(cha)。精(jing)(jing)密(mi)技術相(xiang)(xiang)應(ying)的(de)(de)(de)模(mo)(mo)(mo)具(ju)(ju)(ju)制造(zao)公(gong)(gong)(gong)差(cha)(cha)(cha)為(wei)(wei)序(xu)號(hao)(hao)4的(de)(de)(de)公(gong)(gong)(gong)差(cha)(cha)(cha)。

可以(yi)合(he)理地確定各種(zhong)材料(liao)塑件的合(he)理公差和(he)相應(ying)的模具制(zhi)造公差，這不僅給模具制(zhi)造帶(dai)來(lai)方便，還可以(yi)減少廢品，提高經濟(ji)效期益。