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1 沖壓變形 沖壓變形工藝可完成多種工序 其基本工序可分為分離工序和變形工序兩 大類 分離工序是使坯料的一部分與另一部分相互分離的工藝方法 主要有落料 沖孔 切邊 剖切 修整等 其中有以沖孔 落料應(yīng)用最廣 變形工序是使坯 料的一部分相對另一部分產(chǎn)生位移而不破裂的工藝方法 主要有拉深 彎曲 局部成形 脹形 翻邊 縮徑 校形 旋壓等 從本質(zhì)上看 沖壓成形就是毛坯的變形區(qū)在外力的作用下產(chǎn)生相應(yīng)的塑性 變形 所以變形區(qū)的應(yīng)力狀態(tài)和變形性質(zhì)是決定沖壓成形性質(zhì)的基本因素 因 此 根據(jù)變形區(qū)應(yīng)力狀態(tài)和變形特點進行的沖壓成形分類 可以把成形性質(zhì)相 同的成形方法概括成同一個類型并進行系統(tǒng)化的研究 絕大多數(shù)沖壓成形時毛坯變形區(qū)均處于平面應(yīng)力狀態(tài) 通常認為在板材表面上 不受外力的作用 即使有外力作用 其數(shù)值也是較小的 所以可以認為垂直于 板面方向的應(yīng)力為零 使板材毛坯產(chǎn)生塑性變形的是作用于板面方向上相互垂 直的兩個主應(yīng)力 由于板厚較小 通常都近似地認為這兩個主應(yīng)力在厚度方向 上是均勻分布的 基于這樣的分析 可以把各種形式?jīng)_壓成形中的毛坯變形區(qū) 的受力狀態(tài)與變形特點 在平面應(yīng)力的應(yīng)力坐標系中 沖壓應(yīng)力圖 與相應(yīng)的兩 向應(yīng)變坐標系中 沖壓應(yīng)變圖 以應(yīng)力與 應(yīng)變坐標決定的位置來表示 也就是說 沖壓 應(yīng)力圖與沖壓應(yīng)變圖中的不同位置都代表著不同的受力情況與變形特點 1 沖壓毛坯變形區(qū)受兩向拉應(yīng)力作用時 可以分為兩種情況 即 0 t 0 和 0 t 0 再這兩種情況下 絕對值最大的應(yīng)力都是拉應(yīng)力 以下 對這兩種情況進行分析 1 當 0且 t 0時 安全量理論可以寫出如下應(yīng)力與應(yīng)變的關(guān)系式 1 1 m m t t m k 式中 t 分 別 是 軸對稱沖壓 成 形時 的 徑向 主 應(yīng)變 切向主 應(yīng) 變 和厚度方向上的主 應(yīng)變 t 分 別 是 軸對稱沖壓 成 形時 的 徑向 主 應(yīng) 力 切向主 應(yīng) 力和厚度 方向上的主 應(yīng) 力 m 平均 應(yīng) 力 m t 3 k 常數(shù) 在平面 應(yīng) 力 狀態(tài) 式 1 1 具有如下形式 3 2 3 2 t 3 t t k 1 2 因為 0 所以必定有 2 0 與 0 這個結(jié) 果表明 在 兩向 2 拉應(yīng) 力的平面 應(yīng) 力 狀態(tài)時 如果 絕對 值 最大 拉應(yīng) 力是 則在這個方向上的主 應(yīng)變一定是正應(yīng)變 即是伸長變形 又因為 0 所以必定有 t 0 與 t2 時 0 當 0 的變化范圍是 0 在雙向等拉力狀態(tài)時 有 式 1 2 得 0 及 t 0 且 t 0 時 有式 1 2 可知 因為 0 所以 1 定有 2 0 與 0 這個結(jié)果表明 對于兩向拉應(yīng)力的平面應(yīng)力狀 態(tài) 當 的絕對值最大時 則在這個方向上的應(yīng)變一定時正的 即一定是 伸長變形 又因為 0 所以必定有 t 0 與 t 0 當 0 的變化范圍是 0 當 時 0 也就是 在 雙向等拉 力 狀態(tài)下 在 兩個拉應(yīng) 力方向 上產(chǎn) 生 數(shù) 值相同的伸 長變形 在受 單 向拉應(yīng) 力 狀態(tài)時 當 0 時 2 也就是說 在受 單向拉應(yīng) 力 狀態(tài) 下 其 變形 性 質(zhì) 與一般的 簡單 拉伸是完全一 樣 的 這種變形與受力情況 處于沖壓應(yīng)變圖中的 AOC 范圍內(nèi) 見圖 1 1 而 在沖壓應(yīng)力圖中則處于 AOH 范圍內(nèi) 見圖 1 2 上述兩種沖壓情況 僅在最大應(yīng)力的方向上不同 而兩個應(yīng)力的性質(zhì)以及 它們引起的變形都是一樣的 因此 對于各向同性的均質(zhì)材料 這兩種變形是 完全相同的 1 沖壓毛坯變形區(qū)受兩向壓應(yīng)力的作用 這種變形也分兩種情況分析 即 t 0 和 0 t 0 1 當 0 且 t 0 時 有式 1 2 可知 因 為 0 一定有 2 0 與 0 這個結(jié) 果表明 在 兩向壓應(yīng) 力的平面 應(yīng) 力 狀態(tài)時 如果 3 絕對 值最大 拉應(yīng) 力是 0 則在這個方向上的主應(yīng)變一定是負應(yīng)變 即是壓 縮變形 又因為 0 與 t 0 即在板料厚度方 向上的 應(yīng)變 是正的 板料增厚 在 方向上的變形取決于 與 的數(shù)值 當 2 時 0 當 2 時 0 當 0 這時 的變化范圍是 與 0 之間 當 時 是雙向等 壓 力狀態(tài) 時 故有 0 當 0 時 是受 單 向 壓應(yīng) 力 狀態(tài) 所以 2 這種變形情況處于沖壓應(yīng)變圖中的 EOG 范圍內(nèi) 見圖 1 1 而在沖壓應(yīng)力圖 中則處于 COD 范圍內(nèi) 見圖 1 2 2 當 0 且 t 0 時 有式 1 2 可知 因為 0 所以 一定有 2 0 與 0 這個結(jié)果表明 對于兩向 壓 應(yīng)力的平面應(yīng)力狀 態(tài) 如果絕對值最大是 則在這個方向上的應(yīng)變一定時負的 即一定是壓 縮變形 又因為 0 與 t 0 即在板料厚度方 向上的 應(yīng)變 是正的 即 為壓縮變形 板厚增大 在 方向上的變形取決于 與 的數(shù)值 當 2 時 0 當 2 0 當 0 這時 的數(shù)值只能在 0 之間變化 當 時 是 雙向 等壓力狀態(tài) 所以 0 這種變形與受力情況 處于沖壓應(yīng)變圖中的 GOL 范圍內(nèi) 見圖 1 1 而在沖壓應(yīng)力圖中則處于 DOE 范圍內(nèi) 見圖 1 2 1 沖壓毛坯變形區(qū)受兩個異號應(yīng)力的作用 而且拉應(yīng)力的絕對值大于壓應(yīng) 力的絕對 值 這種變形共有兩種情況 分別作如下分析 1 當 0 時 由式 1 2 可知 因 為 0 所以一定 有 2 0 及 0 這個結(jié) 果表明 在異 號 的 平面 應(yīng) 力 狀態(tài)時 如果 絕對 值最大 應(yīng) 力是 拉應(yīng) 力 則在這個絕對值最大的拉應(yīng) 力方向上應(yīng)變一定是正應(yīng)變 即是伸長變形 又因為 0 所以必定有 0 0 0 時 由式 1 2 可知 用與前 項相同的方法分析可得 0 即在異 號應(yīng) 力作用的平面 應(yīng) 力 狀態(tài)下 如果 絕 對 值最大 應(yīng) 力是 拉應(yīng) 力 則在這個方向上的應(yīng)變是正的 是伸長變形 而在 壓應(yīng)力 方向上的應(yīng)變是負的 0 0 0 時 由式 1 2 可知 因 為 0 所以一定有 2 0 及 0 0 必定有 2 0 即在 拉應(yīng) 力方向上 的 應(yīng)變 是正的 是伸長變形 這時 的變化范圍只能在 與 0 的范圍內(nèi) 當 時 0 0 0 時 由式 1 2 可知 用與前 項相同的方法分析可得 0 0 0 0 AON GOH 伸長類 AOC AOH 伸長類 雙向受壓 0 0 EOG COD 壓縮類 0 MON FOG 伸長 類 LOM EOF 壓縮類 異號應(yīng)力 0 COD AOB 伸長類 DOE BOC 壓縮類 7 變形區(qū)質(zhì)量問題的表 現(xiàn)形式 變形程度過大引起變形區(qū) 產(chǎn)生破裂現(xiàn)象 壓力作用下失穩(wěn)起皺 成形極限 1 主要取決于板材的塑 性 與厚度無關(guān) 2 可用伸長率及成形極 限 DLF 判斷 1 主要取決于傳力區(qū)的 承載能力 2 取決于抗失穩(wěn)能力 3 與板厚有關(guān) 變形區(qū)板厚的變化 減薄 增厚 提高成形極限的方法 1 改善板材塑性 2 使變形均勻化 降低局 部變形程度 3 工序間熱處理 1 采用多道工序成形 2 改變傳力區(qū)與變形區(qū) 的力學(xué)關(guān)系 3 采用防起皺措施 伸 長 類 成 形 脹 形 拉 深 翻 邊 壓 縮 類 成 形 壓 縮 類 成 形 擴 口 拉 深 脹 形 伸 長 類 成 形 縮 口 縮 口 擴口 4 4 翻 邊 圖 1 3 沖壓應(yīng)變圖 8 沖壓成形 極限 變形區(qū)的 成形極限 傳動區(qū)的 成形極限 伸長類 變 形 壓縮類 變 形 強 度 抗拉與抗壓 縮失衡能力 塑 性 抗縮頸 能 力 變形均 化與擴 展能力 塑 性 抗起皺 能 力 變形力及 其 變 化 各向異性 值 硬化性能 變形抗力 化學(xué)成分 組 織 變形條件 硬化性能 應(yīng)力狀態(tài) 應(yīng)變梯度 硬化性能 模具狀態(tài) 力學(xué)性能 值與 值 相對厚度 化學(xué)成分 組 織 變形條件 圖 1 3 體系化研究方法舉例 9 Categories of stamping forming Many deformation processes can be done by stamping the basic processes of the stamping can be divided into two kinds cutting and forming Cutting is a shearing process that one part of the blank is cut form the other It mainly includes blanking punching trimming parting and shaving where punching and blanking are the most widely used Forming is a process that one part of the blank has some displacement form the other It mainly includes deep drawing bending local forming bulging flanging necking sizing and spinning In substance stamping forming is such that the plastic deformation occurs in the deformation zone of the stamping blank caused by the external force The stress state and deformation characteristic of the deformation zone are the basic factors to decide the properties of the stamping forming Based on the stress state and deformation characteristics of the deformation zone the forming methods can be divided into several categories with the same forming properties and to be studied systematically The deformation zone in almost all types of stamping forming is in the plane stress state Usually there is no force or only small force applied on the blank surface When it is assumed that the stress perpendicular to the blank surface equal to zero two principal stresses perpendicular to each other and act on the blank surface produce the plastic deformation of the material Due to the small thickness of the blank it is assumed approximately that the two principal stresses distribute uniformly along the thickness direction Based on this analysis the stress state and 10 the deformation characteristics of the deformation zone in all kind of stamping forming can be denoted by the point in the coordinates of the plane princ ipal stress diagram of the stamping stress and the coordinates of the corresponding plane principal stains diagram of the stamping strain The different points in the figures of the stamping stress and strain possess different stress state and deformation characteristics 1 When the deformation zone of the stamping blank is subjected toplanetensile stresses it can be divided into two cases that is 0 t 0and 0 t 0 In both cases the stress with the maximum absolute value is always a tensile stress These two cases are analyzed respectively as follows 2 In the case that 0and t 0 according to the integral theory the relationships between stresses and strains are m m t t m k 1 1 where t are the principal strains of the radial tangential and thickness directions of the axial symmetrical stamping forming and tare the principal stresses of the radial tangential and thickness directions of the axial symmetrical stamping forming m is the average stress m t 3 k is a constant In plane stress state Equation 1 1 3 2 3 2 t 3 t t k 1 2 Since 0 so 2 0 and 0 It indicates that in plane stress state with two axial tensile stresses if the tensile stress with the maximum absolute value is the principal strain in this direction must be positive that is the deformation belongs 11 to tensile forming In addition because 0 therefore t 0 and t2 0 and when 0 The range of is 0 In the equibiaxial tensile stress state according to Equation 1 2 0 and t 0 and t 0 according to Equation 1 2 2 0 and 0 This result shows that for the plane stress state with two tensile stresses when the absoluste value of is the strain in this direction must be positive that is it must be in the state of tensile forming Also because 0 therefore t 0 and t 0 and when 0 12 The range of is 0 When 0 that is in equibiaxial tensile stress state the tensile deformation with the same values occurs in the two tensile stress directions when 0 2 that is in uniaxial tensile stress state the deformation characteristic in this case is the same as that of the ordinary uniaxial tensile This kind of deformation is in the region AON of the diagram of the stamping strain see Fig 1 1 and in the region GOH of the diagram of the stamping stress see Fig 1 2 Between above two cases of stamping deformation the properties of and and the deformation caused by them are the same only the direction of the maximum stress is different These two deformations are same for isotropic homogeneous material 1 When the deformation zone of stamping blank is subjected to two compressive stresses and t 0 it can also be divided into two cases which are 0 t 0 and 0 t 0 1 When 0 and t 0 according to Equation 1 2 2 0 與 0 This result shows that in the plane stress state with two compressive stresses if the stress with the maximum absolute value is 0 the strain in this direction must be negative that is in the state of compressive forming Also because 0 and t 0 The strain in the thickness direction of the blank t is positive and the thickness increases The deformation condition in the tangential direction depends on the values 13 of and When 2 0 when 2 0 and when 0 The range of is 0 When it is in equibiaxial tensile stress state hence 0 when 0 it is in uniaxial tensile stress state hence 2 This kind of deformation condition is in the region EOG of the diagram of the stamping strain see Fig 1 1 and in the region COD of the diagram of the stamping stress see Fig 1 2 2 When 0and t 0 according to Equation 1 2 2 0 and 0 This result shows that in the plane stress state with two compressive stresses if the stress with the maximum absolute value is the strain in this direction must be negative that is in the state of compressive forming Also because 0 and t 0 The strain in the thickness direction of the blank t is positive and the thickness increases The deformation condition in the radial direction depends on the values of and When 2 0 when 2 0 and when 0 The range of is 0 When it is in equibiaxial tensile stress state hence 0 This kind of deformation is in the region GOL of the diagram of the stamping strain see Fig 1 1 and in the region DOE of the diagram of the stamping stress see Fig 1 2 3 The deformation zone of the stamping blank is subjected to two stresses with opposite signs and the absolute value of the tensile stress is larger than that of the compressive stress There exist two cases to be analyzed as follow 14 1 When 0 according to Equation 1 2 2 0 and 0 This result shows that in the plane stress state with opposite signs if the stress with the maximum absolute value is tensile the strain in the maximum stress direction is positive that is in the state of tensile forming Also because 0 therefore When then 0 0 0 according to Equation 1 2 by means of the same analysis mentioned above 0 that is the deformation zone is in the plane stress state with opposite signs If the stress with the maximum absolute value is tensile stress the strain in this direction is positive that is in the state of tensile forming The strain in the radial direction is negative When then 0 0 0 according to Equation 1 2 2 0 and 0 and 0 therefore 2 0 The strain in the tensile stress direction is positive or in the state of tensile forming The range of is 0 When then 0 0 0 according to Equation 1 2 and by means of the same analysis mentioned above When then 0 0 0 0 AON GOH Tensile AOC AOH Tensile Biaxial compressive stress state 0 0 EOG COD Compress ive 0 MON FOG Tensile LOM EOF Compress ive State of stress with opposite signs 0 COD AOB Tensile DOE BOC Compress ive 20 Table 1 2 Comparison between tensile and compressive forming Item Tensile forming Compressive forming Representation of the quality problem in the deformation zone Fracture in the deformation zone due to excessive deformation Instability wrinkle caused by compressive stress Forming limit 3 Mainly depends on the plasticity of the material and is irrelevant to the thickness 4 Can be estimated by extensibility or the forming limit DLF 4 Mainly depends on the loading capability in the force transferring zone 5 Depends on the anti instability capability 6 Has certain relationship to the blank thickness Variation of the blank thickness in the deformation zone Thinning Thickening Methods to improve forming limit 4 Improve the plasticity of the material 5 Decrease local 4 Adopt multi pass forming process 5 Change the mechanics 21 deformation and increase deformation uniformity 6 Adopt an intermediate heat treatment process relationship between the force transferring and deformation zones 6 Adopt anti wrinkle measures Fig 1 1 Diagram of stamping strain tensile forming bulging deep drawing flanging compressive forming compressive forming expanding deep drawing bulging tensile forming necking necking expanding 4 4 flanging Fig 1 2 Diagram of stamping stress 22 Ten sile for ming Com pres sion for ming St re ngth Cap abil ity of an ti w rinkle und er t he t ensi le and com pres sive st re sses Plasticity Cap abil ity of an ti n ecking Def orma tion uniformit y an d ex te nsion ca pa bility Pl as ticity Cap abil ity of an ti w rinkle Def orma tion for ce a nd i ts Ani sotr opy valu e of r Har deni ng c hara cter isti cs Deformation r es is ta nc e Che mist ry c ompo nent Str uctu re Deformation c on di ti on s Har deni ng c hara cter isti cs Sta te o f st ress Gradient of s tr ai n Har deni ng c hara cter isti cs Die sha pe Mechanical pr oe rt y The value of t he n a nd r Relative th ic kn es s Che mist ry c ompo nent Str uctu re Deformation c on di ti on s Fig 1 3 Examples for systematic research methods 沖壓成形與板材沖壓 1 概述 通過模具使板材產(chǎn)生塑性變形而獲得成品零件的一次成形工藝方法叫做 沖壓 由于沖壓通常在冷態(tài)下進行 因此也稱為冷沖壓 只有當板材厚度超 過 8 100mm 時 才采用熱沖壓 沖壓加工的原材料一般為板材或帶材 故也 稱板材沖壓 某些非金屬板材 如膠木板 云母片 石棉 皮革等 亦可采 用沖壓成形工藝進行加工 沖壓廣泛應(yīng)用于金屬制品各行業(yè)中 尤其在汽車 儀表 軍工 家用電 器等工業(yè)中占有極其重要的地位 沖壓成形需研究工藝設(shè)備和模具三類基本 問題 板材沖壓具有下列特點 1 高的材料利用率 2 可加工薄壁 形狀復(fù)雜的零件 3 沖壓件在形狀和尺寸方面的互換性好 4 能獲得質(zhì)量輕而強度高 剛性好的零件 5 生產(chǎn)率高 操作簡單 容易實現(xiàn)機械化和自動化 沖壓模具制作成本高 因此適合大批量生產(chǎn) 對于小批量 多品種生產(chǎn) 常采用簡易沖模 同時引進沖壓加工中心等新型設(shè)備 以滿足市場求新求變 的需求 板材沖壓常用的金屬材料有低碳鋼 銅 鋁 鎂合金及高塑性的合 金剛等 如前所述 材料形狀有板材和帶材 沖壓生產(chǎn)設(shè)備有剪床和沖床 剪床是用來將板材剪切成具有一定寬度的 條料 以供后續(xù)沖壓工序使用 沖床可用于剪切及成形 2 沖壓成形的特點 生產(chǎn)時間中所采用的沖壓成形工藝方法有很多 具有多種形式餓名稱 但塑性變形本質(zhì)是相同的 沖壓成形具有如下幾個非常突出的特點 1 垂直于板面方向的單位面積上的壓力 其數(shù)值不大便足以在板面方 向上使 板材產(chǎn)生塑性變形 由于垂直于板面方向上的單位面積上壓力的素 質(zhì)遠小于板面方向上的內(nèi)應(yīng)力 所以大多數(shù)的沖壓變形都可以近似地當作平 面應(yīng)力狀態(tài)來處理 使其變形力學(xué)的分析和工藝參數(shù)的計算大呢感工作都得 到很大的簡化 2 由于沖壓成形用的板材毛胚的相對厚度很小 在壓應(yīng)力作用下的抗 失穩(wěn)能力也很差 所以在沒有抗失穩(wěn)裝置 如壓邊圈等 的條件下 很難在 自由狀態(tài)下順利地完成沖壓成形過程 因此 以拉應(yīng)力作用為主的伸長類沖 壓成形過程多于以壓應(yīng)力作用為主的壓縮類成形過程 3 沖壓成形時 板材毛胚內(nèi)應(yīng)力的數(shù)值等于或小于材料的屈服應(yīng)力 在這一點上 沖壓成形與體積成形的差別很大 因此 在沖壓成形時變形區(qū) 應(yīng)力狀態(tài)中的靜水壓力成分對成形極限與變形抗力的影響 已失去其在體積 成形時的重要程度 有些情況下 甚至可以完全不予考慮 即使有必要考慮 時 其處理方法也不相同 4 在沖壓成形時 模具對板材毛胚作用力所形成的約束作用較輕 不 像體積成形 如模鍛 是靠與制件形狀完全相同的型腔對毛胚進行全面接觸 而實現(xiàn)的強制成形 在沖壓成形中 大多數(shù)情況下 板材毛胚都有某種程度 的自由度 常常是只有一個表面與模具接觸 甚至有時存在板材兩側(cè)表面都 有于模具接觸的變形部分 在這種情況下 這部分毛胚的變形是靠模具對其 相鄰部分施加的外力實現(xiàn)其控制作用的 例如 球面和錐面零件成形時的懸 空部分和管胚端部的卷邊成形都屬這種情況 由于沖壓成形具有上述一些在變形與力學(xué)方面的特點 致使沖壓技術(shù)也 形成了一些與體積成形不同的特點 由于不需要在板材毛的表面施加很大的 單位壓力即可使其成形 所以在沖壓技術(shù)中關(guān)于模具強度與剛度的研究并不 十分重要 相反卻發(fā)展了學(xué)多簡易模具技術(shù) 由于相同原因 也促使靠氣體或液體壓力成形的工藝方法得以發(fā)展 因 沖壓成形時的平面應(yīng)力狀態(tài)或更為單純的應(yīng)變狀態(tài) 與體積成形相比 當 前對沖壓成形匯中毛胚的變形與 力能參數(shù)方面的研究較為深入 有條件運 用合理的科學(xué)方法進行沖壓加工 借助于電子計算機與先進的測試手段 在 對板材性能與沖壓變形參數(shù)進行實時測量與分析基礎(chǔ)上 實現(xiàn)沖壓過程智能 化控制的研究工作也在開展 人們在對沖壓成形過程有離開較為深入的了解 后 已經(jīng)認識到?jīng)_壓成型與原材料有十分密切的關(guān)系 所以 對板材沖壓性 能即成形性與形狀穩(wěn)定性的研究 目前已成為沖壓技術(shù)的一個重要內(nèi)容 對 板材沖壓性能的研究工作不僅是沖壓技術(shù)發(fā)展的需要 而且也促進了鋼鐵工 業(yè)生產(chǎn)技術(shù)的發(fā)展 為其提高板材的質(zhì)量提供了一個可靠的基礎(chǔ)與依據(jù) 3 沖壓變形的分類 沖壓變形工藝可完成多種工序 其基本工序可分為分離工序和變形工序 兩大類 分離工序是使胚料的一部分與另一部分相互分離的工藝方法 主要 有落料 沖孔 切邊 剖切 修整等 其中又以沖孔 落料應(yīng)用最廣 變形 工序是使胚料的一部分相對于另一部分產(chǎn)生位移而不破裂的工藝方法 主要 有拉深 彎曲 局部成形 脹形 翻邊 縮徑 校形 旋壓等 從本質(zhì)上看 沖壓成形就是毛胚的變形區(qū)在外力的作用下產(chǎn)生相應(yīng)的塑 性變形 所以變形區(qū)內(nèi)的應(yīng)力狀態(tài)和變形特點景象的沖壓成形分類 可以把 成形性質(zhì)相同的成形方法概括成同一個類型并進行體系化的研究 絕大多數(shù)沖壓成形時毛胚變形區(qū)均處于平面應(yīng)力狀態(tài) 通常認為在板材 表面上不受外力的作用 即使有外力作用 其數(shù)值也是較小的 所以可以認 為垂直于板面方向上的應(yīng)力為零 使板材毛胚產(chǎn)生塑性變形的是作用于板面 方向上相互的兩個主應(yīng)力 由于板厚較小 通常都近似地認為這兩個主應(yīng)力 在厚度方向上是均勻分布的 基于這樣的分析 可以把各種形式?jīng)_壓成型中 的毛陪變形區(qū)的受力狀態(tài)與變形特點 在平面應(yīng)力的應(yīng)力坐標系中與相應(yīng)的 兩向應(yīng)變坐標系中以應(yīng)力與應(yīng)變坐標決定的位置來表示 4 沖壓用原材料 沖壓加工用原材料有很多種 它們的性能也有很大的差別 所以必須根 據(jù)原材料的性能與特點 采用不同的沖壓成形方法 工藝參數(shù)和模具結(jié)構(gòu) 才能達到?jīng)_壓加工的目的 由于人們對沖壓成形過程板材毛胚的變形行為有 了較為深入的認識 已經(jīng)相當清楚的建立了由原材料的化學(xué)成分 組織等因 素所決定的材料性能與沖壓成形之間的關(guān)系 這就使原材料生產(chǎn)部門不但按 照沖壓件的工作條件與使用要求進行原材料的設(shè)計工作 而且也根據(jù)沖壓件 加工過程對板材性能的要求進行新型材料的開發(fā)工作 這是沖壓技術(shù)在原材 料研究方面的一個重要方向 對沖壓用原材料沖壓性能方面的研究工作有 1 原材料沖壓性能的含義 2 判斷原材料沖壓性能的科學(xué)方法 確定可以確切反映材料沖壓性能的 參數(shù) 建立沖壓性能的參數(shù)與實際沖壓成形間的關(guān)系 以及沖壓性能參數(shù)的 測試方法等 3 建立原材料的化學(xué)成分 組織和制造過程與沖壓性能之間的關(guān)系 沖 壓用原材料主要是各種金屬與非金屬板材 金屬板材包括各種黑色技術(shù)和有 色金屬板材 雖然在沖壓生產(chǎn)中所用金屬板材的種類很多 但最多的原材料 蛀牙是鋼板 不銹鋼板 鋁合金板及各種復(fù)合金屬板 5 板材沖壓性能及其鑒定方法 板材是指對沖壓加工的適應(yīng)能力 對板材沖壓性能的研究具有飛行重要 的意義 為了能夠運用最科學(xué)與最經(jīng)濟合理的沖壓工藝過程與工藝參數(shù)制造 出沖壓零件 必須對作為加工對象的板材的性能具有十分清楚的了解 這樣 才有可能充分地利用板材在加工方面的潛在能力 另一方面 為了能夠依據(jù) 沖壓件的形狀與尺寸特點及其所需的成形工藝等基本因素 正確 合理地選 用板材 也必須對板材的沖壓性能有一個科學(xué)的認識與正確的判斷 評定板 材沖壓性能的方法有直接試驗法與間接試驗法 實物沖壓試驗是最直接的板材沖壓性能的評定方法 利用實際生產(chǎn)設(shè)備 與模具 在與生產(chǎn)完全相同的條件下進行實際沖壓零件的性能評定 當然能 夠的最可靠的結(jié)果 但是 這種評定方法不具有普遍意義 不能作為行業(yè)之 間的通用標準進行信息的交流 模擬試驗是把生產(chǎn)中實際存在的沖壓成形方法進行歸納與簡單化處理 消除許多過于復(fù)雜的因素 利用軸對稱的簡化了的成形方法 在保證試驗中 板材的變形性質(zhì)與應(yīng)力狀態(tài)都與實際沖壓成形相同的條件下進行的沖壓性能 的評定工作 為了保證模擬試驗結(jié)果的可靠性與通用性 規(guī)定了私分具體的 關(guān)于試驗用工具的幾何形狀與尺寸 毛胚的尺寸 試驗條件 沖壓速度 潤 滑方法 壓邊力等 間接試驗法也叫做基礎(chǔ)試驗法 間接試驗法的特點是 在對板材在塑性 變形過程中所表現(xiàn)出的基本性質(zhì)與規(guī)律進行分析與研究的基礎(chǔ)上 進一步把 它和具體的沖壓成形中板材的塑性變形參數(shù)聯(lián)系起來 建立間接試驗結(jié)果 間接試驗值 與具體的沖壓成形性能 工藝參數(shù) 之間的相關(guān)性 由于間 接試驗時所用試件的形狀與尺寸以及加載的方式等都不同于具體的沖壓成形 過程 所以它的變形性質(zhì)和應(yīng)力狀態(tài)也不同于沖壓變形 因此間接試驗所得 的結(jié)果 試驗值 并不是沖壓成形的工藝參數(shù) 而是可以用來表示板材沖壓 性能的基礎(chǔ)性參數(shù) Characteristics and Sheet Metal Forming 1 The article overview Stamping is a kind of plastic forming process in which a part is produced by means of the plastic forming the material under the action of a die Stamping is usually carried out under cold state so it is also called stamping Heat stamping is used only when the blank thickness is greater than 8 100mm The blank material for stamping is usually in the form of sheet or strip and therefore it is also called sheet metal forming Some non metal sheets such as plywood mica sheet asbestos leather can also be formed by stamping Stamping is widely used in various fields of the metalworking industry and it plays a crucial role in the industries for manufacturing automobiles instruments military parts and household electrical appliances etc The process equipment and die are the three foundational problems that needed to be studied in stamping The characteristics of the sheet metal forming are as follows 1 High material utilization 2 Capacity to produce thin walled parts of complex shape 3 Good interchangeability between stamping parts due to precision in shape and dimension 4 Parts with lightweight high strength and fine rigidity can be obtained 5 High productivity easy to operate and to realize mechanization and automatization The manufacture of the stamping die is costly and therefore it only fits to mass production For the manufacture of products in small batch and rich variety the simple stamping die and the new equipment such as a stamping machining center are usually adopted to meet the market demands The materials for sheet metal stamping include mild steel copper aluminum magnesium alloy and high plasticity alloy steel etc Stamping equipment includes plate shear punching press The former shears plate into strips with a definite width which would be pressed later The later can be used both in shearing and forming 2 Characteristics of stamping forming There are various processes of stamping forming with different working patterns and names But these processes are similar to each other in plastic deformation There are following conspicuous characteristics in stamping 1 The force per unit area perpendicular to the blank surface is not large but is enough to cause the material plastic deformation It is much less than the inner stresses on the plate plane directions In most cases stamping forming can be treated approximately as that of the plane stress state to simplify vastly the theoretical analysis and the calculation of the process parameters 2 Due to the small relative thickness the anti instability capability of the blank is weak under compressive stress As a result the stamping process is difficult to proceed successfully without using the anti instability device such as blank holder Therefore the varieties of the stamping processes dominated by tensile stress are more than dominated by compressive stress 3 During stamping forming the inner stress of the blank is equal to or sometimes less than the yield stress of the material In this point the stamping is different from the bulk forming During stamping forming the influence of the hydrostatic pressure of the stress state in the deformation zone to the forming limit and the deformation resistance is not so important as to the bulk forming In some circumstances such influence may be neglected Even in the case when this influence should be considered the treating method is also different from that of bulk forming 4 In stamping forming the restrain action of the die to the blank is not severs as in the case of the bulk forming such as die forging In bulk forming the constraint forming is proceeded by the die with exactly the same shape of the part Whereas in stamping in most cases the blank has a certain degree of freedom only one surface of the blank contacts with the die In some extra cases such as the forming of the blank on the deforming zone contact with the die The deformation in these regions are caused and controlled by the die applying an external force to its adjacent area Due to the characteristics of stamping deformation and mechanics mentioned above the stamping technique is different form the bulk metal forming The importance or the strength and rigidity of the die in stamping forming is less than that in bulk forming because the blank can be formed without applying large pressure per unit area on its surface Instead the techniques of the simple die and the pneumatic and hydraulic forming are developed Due to the plane stress or simple strain state in comparison with bulk forming more research on deformation or force and power parameters has been done Stamping forming can be performed by more reasonable scientific methods Based on the real time measurement and analysis on the sheet metal properties and stamping parameters by means of computer and some modern testing apparatus research on the intellectualized control of stamping process is also in proceeding It is shown that there is a close relationship between stamping forming and raw material The research on the properties of the stamping forming that is forming ability and shape stability has become a key point in stamping technology development but also enhances the manufacturing technique of iron and steel industry and provides a reliable foundation for increasing sheet metal quality 3 Categories of stamping forming Many deformation processes can be done by stamping the basic processes of the stamping can be divided into two kinds cutting and forming Cutting is a shearing process that one part of the blank is cut from the other It mainly includes blanking punching trimming parting and shaving where punching and blanking are the most widely used Forming is a process that one part of the blank has some displacement from the other It mainly includes deep drawing bending local forming bulging flanging necking sizing and spinning In substance stamping forming is such that the plastic deformation occurs in the deformation zone of the stamping blank caused by the external force The stress state and deformation characteristic of the deformation zone are the basic factors to decide the properties of the stamping forming Based on the stress state and deformation characteristics of the deformation zone the forming methods can be divided into several categories with the same forming properties and be studied systematically The deformation zone in almost all types of stamping forming is in the plane stress state Usually there is no force or only small force applied on the blank surface When is assumed that the stress perpendicular to the blank surface equals to zero two principal stresses perpendicular to each other and act on the blank surface produce the plastic deformation of the material Due to the small thickness of the blank it is assumed approximately the two principal stresses distribute uniformly along the thickness direction Based on this analysis the stress state and the deformation characteristics of the deformation zone in all kinds of stamping forming can be denoted by the points in the coordinates of the plane principal stresses and the coordinates of the corresponding plane principal strains 4 Raw materials for stamping forming There are a lot of raw materials used in stamping forming and the properties of these materials may have large difference The stamping forming can be succeeded only by determining the stamping method the forming parameters and the die structures according to the properties and characteristics of the raw materials The deformation of the blank during stamping forming has been investigated quite thoroughly The relationships between the material properties decided by the chemistry component and structure of the material and the stamping forming has been established clearly Not only the proper material can be selected based on the working condition and usage demand but also the new material can be developed according to the demands of the blank properties during processing the stamping part This is an important domain in stamping forming research The research on the material properties for stamping forming is as follows 1 Definition of the stamping property of the material 2 Method to judge the stamping property of the material find parameters to express the definitely material property of the stamping forming establish the relationship between the property parameters and the practical stamping forming and investigate the testing methods of the property parameters 3 Establish the relationship among the chemical component structure manufacturing process and stamping property The raw materials for stamping forming mainly include various metals and nonmetal plate Sheet metal includes both ferrous and nonferrous metals Although a lot of sheet metals are used in stamping forming the most widely used materials are steel stainless steel aluminum alloy and various composite metal plates 5 Stamping forming property of sheet metal and its assessing method The stamping forming property of the sheet metal is the adaptation capability of the sheet metal to stamping forming It has crucial meaning to the investigation of the stamping forming property of the sheet metal In order to produce stamping forming parts with most scientific economic and rational stamping forming process and forming parameters it is necessary to understand clearly the properties of the sheet metal so as to utilize the potential of the sheet metal fully in the production On the other hand to select plate material accurately and rationally in accordance with the characteristics of the shape and dimension of the stamping forming part and its forming technique is also necessary so that a scientific understanding and accurate judgment to the stamping forming properties of the sheet metal may be achieved There are direct and indirect testing methods to assess the stamping property of the sheet metal Practicality stamping test is the most direct method to assess stamping forming property of the sheet metal This test is done exactly in the same condition as actual production by using the practical equipment and dies Surely this test result is most reliable But this kind of assessing method is not comprehensively applicable and cannot be shared as a commonly used standard between factories The simulation test is a kind of assessing method that after simplifying and summing up actual stamping forming methods as well as eliminating many trivial factors the stamping properties of the sheet metal are assessed based on simplified axial symmetric forming method under the same deformation and stress states between the testing plate and the actual forming states In order to guarantee the reliability and generality of simulation results a lot of factors are regulated in detail such as the shape and dimension of tools for test blank dimension and testing conditions stamping velocity lubrication method and blank holding force etc Indirect testing method is also called basic testing method its characteristic is to connect analysis and research on fundamental property and principle of the sheet metal during plastic deformation and with the plastic deformation parameters of the sheet metal in actual stamping forming and then to establish the relationship between the indirect testing results indirect testing value and the actual stamping forming property forming parameters Because the shape and dimension of the specimen and the loading pattern of the indirect testing are different from the actual stamping forming the deformation characteristics and stress states of the indirect test are different from those of the actual one So the results obtained form the indirect test are not the stamping forming parameters but are the fundamental parameters that can be used to represent the stamping forming property of the sheet metal