鈑金件的抽牙加工,包括沖孔,翻孔,攻牙的過程,在孔徑計算時,先確定翻孔內徑d1,然后依材料的圓孔翻邊系數kt,求得沖孔直徑d0,螺紋加工分為有屑加工及無屑加工. 有屑加工是以切削的方式,將材料去除,形成螺紋.因要去除材料,故坯料要保留較多,底徑d取較小值.無屑加工是以擠壓的方式,使材料塑性變形,形成螺紋.因無需去除材料,坯孔內的材料只作塑性流動,故坯料保留較少,底徑d取較大. 鈑金件的螺紋加工大多采用無屑加工,底徑計算以無屑加工方式確定.依設計所要求加工的螺紋型號,查表1,2,3,4,得該螺紋的標稱直徑D.螺距P.則翻孔內徑d1=D-P/2 (1) 表1,2,3,4分列了10mm以下公制粗牙,細牙及UNC UNF螺紋的規格尺寸.若為有屑加工,則d1=D-P (2)表1.公制粗牙螺紋(1/8)圖一: H=0.866025 P d2=d-0.649519 p H1=0.541266 P d1=d-1.082532 p D=d D2=d2 D1=d1 D1=d1螺紋之標稱(1)螺距P內螺紋根徑D有效徑D2內徑D1123外螺紋外徑d有效徑d2根徑d1M1M1.2M1.10.250.250.251.0001.1001.2000.8380.9381.0380.7290.8290.929M1.6M1.4M1.80.30.350.351.4001.6001.8001.2051.3731.5731.0751.2211.421M2M2.5M2.20.40.450.452.0002.2002.5001.7401.9082.2081.5671.7132.013M3*0.5M4*0.7M3.50.50.60.73.0003.5004.0002.6753.1103.5452.4592.8503.242M5*0.8M6M4.50.750.814.5005.0006.0004.0134.4805.3503.6884.1344.917M8M7M911.251.257.0008.0009.0006.3507.1888.1865.9176.6477.647M101.510.0009.0268.376表2 公制細牙螺紋之基本尺寸圖二.JIS公制螺紋(4/8) H=0.866025 P d2=d-0.649519 p H1=0.541266 P d1=d-1.082532 p D=d D2=d2 D1=d1 螺紋之標稱螺距p內螺紋根徑D有效徑D2內徑D1外螺紋外徑d有效徑d2根徑d1M1*0.2M1.1*0.2M1.2*0.2M1.4*0.2M1.6*0.2M1.8*0.20.20.20.20.20.20.21.0001.1001.2001.4001.6001.8000.8700.9701.0701.2701.4701.6700.7830.8830.9831.1831.3831.583M2*0.25M2.2*0.250.250.252.0002.2001.8382.0381.7291.929M2.5*0.35M3*0.35M3.5*0.350.350.350.352.5003.0003.5002.2732.2733.2732.1212.6213.121M4*0.5M4.5*0.5M5*0.5M5.5*0.50.50.50.50.54.0004.5005.0005.5003.6754.1754.6755.1753.4593.9594.4594.959M6*0.75M7*0.750.750.756.0007.0005.5136.5135.1886.188M8*1M*0.7510.758.0008.0007.3507.5136.9177.188M9*1M9*0.7510.759.0009.0008.3508.5137.9178.188M10*1.25M10*1M10*0.751.2510.7510.00010.00010.0009.1889.3509.5138.6478.9179.188表三 JIS美英統一制粗牙螺紋(1/2)圖三. P = 25.4/n H=(0.866025/n)*25.4 d=(d)*25.4 H1=(0.541266/n)*25.4 d2=(d-0.649519/n)*25.4 D=d D2=d2 D1=d1 d1=(d-1.082532/n)*25.4螺紋之標稱螺紋數(每25.4mm)n螺距P(參考)內螺紋根徑D有效徑D2內徑D1外螺紋外徑d有效徑d2根徑d112參考No.2-56 UNCNo.1-64 UNCNo.3-48 UNC0.0730-64UNC0.0860-56UNC0.0990-48UNC6456480.39690.45360.52921.8542.1842.5151.5981.8902.1721.4251.6941.941No.4-40 UNCNo.5-40 UNCNo.6-32 UNC0.1120-40UNC0.1250-40UNC0.1380-32UNC4040320.63000.63500.79382.8453.1753.5052.4332.7642.9902.1562.4872.647No.8-32 UNC 10-24 UNCNo.12-24 UNC0.1640-32UNC0.1900-24UNC0.2160-24UNC3224240.79381.05831.05834.1664.8265.4863.6504.1384.7983.3073.6804.3411/4-20 UNC5/16-18 UNC3/8-16 UNC0.2500-20UNC0.3125-18UNC0.3750-16UNC2018161.27001.41111.58756.3507.9389.5255.5247.0218.4944.9766.4117.805表四 .JIS美英統一制粗牙螺紋(2/2)圖四. P = 25.4/n H=(0.866025/n)*25.4 d=(d)*25.4 H1=(0.541266/n)*25.4 d2=(d-0.649519/n)*25.4 D=d D2=d2 D1=d1 d1=(d-1.082532/n)*25.4螺紋之標稱螺紋數(每25.4mm)n螺距P(參考)內螺紋根徑D有效徑D2內徑D1外螺紋外徑d有效徑d2根徑d112參考No.0-80 UNFNo.2-64 UNFNo.1-72 UNF0.0600-80 UNF0.0730-72 UNF0.0860-64 UNF8072640.31750.35280.39691.5241.8542.1841.3181.6261.9281.1811.4731.755No.4-48 UNFNo.5-44 UNFNo.3-56 UNF0.0990-56 UNF0.1120-48 UNF0.1250-44 UNF5648440.45360.52920.57732.5152.8453.1752.2202.5022.7092.0242.2712.551No.6-40 UNFNo.8-36 UNFNo.10-32 UNF0.1380-40 UNF0.1640-36 UNF0.1900-32 UNF4036320.63500.70560.79383.5054.1664.8263.0943.7084.3102.8173.4013.9671/4-28 UNF5/16-24 UNFNo.12-28 UNF0.2160-28 UNF0.2500-28 UNF0.3125-24 UNF2828240.90710.90711.05835.4866.3507.9384.8975.7617.2494.5035.3676.7923/8-24 UNF0.3750-24 UNF241.05839.5258.8378.379確定d1,若螺紋規格小于M5.則簡便計算如下:d0=0.45d1 d0=翻孔前毛坯孔t1=0.65t t1=翻孔后豎邊壁厚h=2~2.5t或查表以確定翻孔系數kk=d0/Dm式中 d0---毛坯上圓孔的初始直徑 Dm---翻邊后豎邊的中徑圓孔翻邊的成形極限根據豎邊邊緣是否發生破裂來確定.如下圖所示,翻邊系數k與豎邊邊緣厚度減薄量的關系如下.圖五:T/t0=4√【(d02/(Dm2-t02)】=4√【(d0/Dm)2/【1-(t0/Dm)2】】=4√【K2/【1-(d0/Dm)2】】(3)若相對厚度d0/Dm較小,則t≒t0√K (4) 由式(3),(4)可知,K越小,豎邊孔緣厚度減薄愈大,容易發生破裂,故圓孔翻邊成形限受K值限制.表五是保証低碳鋼翻邊不發生破裂時允許的極限翻邊系Kl,通常可用它們反映圓孔翻邊成形極限,Kl越小,成形極限愈大.表五:低碳鋼極限圓孔翻邊系數Kl凸模形式孔的加工方法比值d0/t0100503520151086.5531球形凸模鑽孔 沖孔0.7 0.750.6 0.650.52 0.570.45 0.520.4 0.480.36 0.450.33 0.440.31 0.430.3 0.420.25 0.420.2 -圓柱形凸模鑽孔 沖孔0.8 0.850.7 0.750.6 0.650.5 0.60.45 0.550.42 0.520.4 0.50.37 0.500.35 0.480.3 0.470.25 - 影響圓孔翻邊成形極限的因素如下:(1) 材料延伸率和應變硬化指數n大,Kl小,成形極限大.(2) 孔緣無毛刺和硬化時, Kl較小,成形極限較大,為了改善孔緣情況,可采用鑽孔方法或在沖孔后行整修,有時還可在沖孔后退火,以消除孔緣表面的硬化.為了避免毛刺降低成形極限,翻邊進需預制孔有毛刺的一側朝向凸模放置.(3) 用球形,錐形和拋物形凸模翻邊時,孔緣會被圓滑地脹開,變形條件比平底凸模優越,故Kl越小,成形限越大.(4) 板料相對厚度越大, Kl越小,成形極限愈大.3.圓孔翻邊的毛坯計算主要是利用板料中性層長度不變的原則,用翻邊高度計算翻邊圓孔的初始直徑d0和翻邊系數計算可以達到的翻邊高度.(1) 一次翻邊成形翻邊高度不大時,可將平板毛坯一次翻邊成形.按圖五所示,一次翻邊成形時,翻邊圓孔的初始d0 ,翻邊高度h和翻邊系數Kl之間的關系如下:h=1/2*(Dm-d0)+0.43r+0.72t0 =Dm/2*(1-k)+0.43r+0.72t0 (5)需要指出,按式(3)計算翻邊高度時,必須滿足k≧Kl,否則不能一次翻邊成形.。