电脑机箱侧板冲压模具设计【10张CAD图纸和文档全套】
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1 冲压变形 冲压变形工艺可完成多种工序 其基本工序可分为分离工序和变形工序两 大类 分离工序是使坯料的一部分与另一部分相互分离的工艺方法 主要有落料 冲孔 切边 剖切 修整等 其中有以冲孔 落料应用最广 变形工序是使坯 料的一部分相对另一部分产生位移而不破裂的工艺方法 主要有拉深 弯曲 局部成形 胀形 翻边 缩径 校形 旋压等 从本质上看 冲压成形就是毛坯的变形区在外力的作用下产生相应的塑性 变形 所以变形区的应力状态和变形性质是决定冲压成形性质的基本因素 因 此 根据变形区应力状态和变形特点进行的冲压成形分类 可以把成形性质相 同的成形方法概括成同一个类型并进行系统化的研究 绝大多数冲压成形时毛坯变形区均处于平面应力状态 通常认为在板材表面上 不受外力的作用 即使有外力作用 其数值也是较小的 所以可以认为垂直于 板面方向的应力为零 使板材毛坯产生塑性变形的是作用于板面方向上相互垂 直的两个主应力 由于板厚较小 通常都近似地认为这两个主应力在厚度方向 上是均匀分布的 基于这样的分析 可以把各种形式冲压成形中的毛坯变形区 的受力状态与变形特点 在平面应力的应力坐标系中 冲压应力图 与相应的两 向应变坐标系中 冲压应变图 以应力与 应变坐标决定的位置来表示 也就是说 冲压 应力图与冲压应变图中的不同位置都代表着不同的受力情况与变形特点 1 冲压毛坯变形区受两向拉应力作用时 可以分为两种情况 即 0 t 0 和 0 t 0 再这两种情况下 绝对值最大的应力都是拉应力 以下 对这两种情况进行分析 1 当 0且 t 0时 安全量理论可以写出如下应力与应变的关系式 1 1 m m t t m k 式中 t 分 别 是 轴对称冲压 成 形时 的 径向 主 应变 切向主 应 变 和厚度方向上的主 应变 t 分 别 是 轴对称冲压 成 形时 的 径向 主 应 力 切向主 应 力和厚度 方向上的主 应 力 m 平均 应 力 m t 3 k 常数 在平面 应 力 状态 式 1 1 具有如下形式 3 2 3 2 t 3 t t k 1 2 因为 0 所以必定有 2 0 与 0 这个结 果表明 在 两向 2 拉应 力的平面 应 力 状态时 如果 绝对 值 最大 拉应 力是 则在这个方向上的主 应变一定是正应变 即是伸长变形 又因为 0 所以必定有 t 0 与 t2 时 0 当 0 的变化范围是 0 在双向等拉力状态时 有 式 1 2 得 0 及 t 0 且 t 0 时 有式 1 2 可知 因为 0 所以 1 定有 2 0 与 0 这个结果表明 对于两向拉应力的平面应力状 态 当 的绝对值最大时 则在这个方向上的应变一定时正的 即一定是 伸长变形 又因为 0 所以必定有 t 0 与 t 0 当 0 的变化范围是 0 当 时 0 也就是 在 双向等拉 力 状态下 在 两个拉应 力方向 上产 生 数 值相同的伸 长变形 在受 单 向拉应 力 状态时 当 0 时 2 也就是说 在受 单向拉应 力 状态 下 其 变形 性 质 与一般的 简单 拉伸是完全一 样 的 这种变形与受力情况 处于冲压应变图中的 AOC 范围内 见图 1 1 而 在冲压应力图中则处于 AOH 范围内 见图 1 2 上述两种冲压情况 仅在最大应力的方向上不同 而两个应力的性质以及 它们引起的变形都是一样的 因此 对于各向同性的均质材料 这两种变形是 完全相同的 1 冲压毛坯变形区受两向压应力的作用 这种变形也分两种情况分析 即 t 0 和 0 t 0 1 当 0 且 t 0 时 有式 1 2 可知 因 为 0 一定有 2 0 与 0 这个结 果表明 在 两向压应 力的平面 应 力 状态时 如果 3 绝对 值最大 拉应 力是 0 则在这个方向上的主应变一定是负应变 即是压 缩变形 又因为 0 与 t 0 即在板料厚度方 向上的 应变 是正的 板料增厚 在 方向上的变形取决于 与 的数值 当 2 时 0 当 2 时 0 当 0 这时 的变化范围是 与 0 之间 当 时 是双向等 压 力状态 时 故有 0 当 0 时 是受 单 向 压应 力 状态 所以 2 这种变形情况处于冲压应变图中的 EOG 范围内 见图 1 1 而在冲压应力图 中则处于 COD 范围内 见图 1 2 2 当 0 且 t 0 时 有式 1 2 可知 因为 0 所以 一定有 2 0 与 0 这个结果表明 对于两向 压 应力的平面应力状 态 如果绝对值最大是 则在这个方向上的应变一定时负的 即一定是压 缩变形 又因为 0 与 t 0 即在板料厚度方 向上的 应变 是正的 即 为压缩变形 板厚增大 在 方向上的变形取决于 与 的数值 当 2 时 0 当 2 0 当 0 这时 的数值只能在 0 之间变化 当 时 是 双向 等压力状态 所以 0 这种变形与受力情况 处于冲压应变图中的 GOL 范围内 见图 1 1 而在冲压应力图中则处于 DOE 范围内 见图 1 2 1 冲压毛坯变形区受两个异号应力的作用 而且拉应力的绝对值大于压应 力的绝对 值 这种变形共有两种情况 分别作如下分析 1 当 0 时 由式 1 2 可知 因 为 0 所以一定 有 2 0 及 0 这个结 果表明 在异 号 的 平面 应 力 状态时 如果 绝对 值最大 应 力是 拉应 力 则在这个绝对值最大的拉应 力方向上应变一定是正应变 即是伸长变形 又因为 0 所以必定有 0 0 0 时 由式 1 2 可知 用与前 项相同的方法分析可得 0 即在异 号应 力作用的平面 应 力 状态下 如果 绝 对 值最大 应 力是 拉应 力 则在这个方向上的应变是正的 是伸长变形 而在 压应力 方向上的应变是负的 0 0 0 时 由式 1 2 可知 因 为 0 所以一定有 2 0 及 0 0 必定有 2 0 即在 拉应 力方向上 的 应变 是正的 是伸长变形 这时 的变化范围只能在 与 0 的范围内 当 时 0 0 0 时 由式 1 2 可知 用与前 项相同的方法分析可得 0 0 0 0 AON GOH 伸长类 AOC AOH 伸长类 双向受压 0 0 EOG COD 压缩类 0 MON FOG 伸长 类 LOM EOF 压缩类 异号应力 0 COD AOB 伸长类 DOE BOC 压缩类 7 变形区质量问题的表 现形式 变形程度过大引起变形区 产生破裂现象 压力作用下失稳起皱 成形极限 1 主要取决于板材的塑 性 与厚度无关 2 可用伸长率及成形极 限 DLF 判断 1 主要取决于传力区的 承载能力 2 取决于抗失稳能力 3 与板厚有关 变形区板厚的变化 减薄 增厚 提高成形极限的方法 1 改善板材塑性 2 使变形均匀化 降低局 部变形程度 3 工序间热处理 1 采用多道工序成形 2 改变传力区与变形区 的力学关系 3 采用防起皱措施 伸 长 类 成 形 胀 形 拉 深 翻 边 压 缩 类 成 形 压 缩 类 成 形 扩 口 拉 深 胀 形 伸 长 类 成 形 缩 口 缩 口 扩口 4 4 翻 边 图 1 3 冲压应变图 8 冲压成形 极限 变形区的 成形极限 传动区的 成形极限 伸长类 变 形 压缩类 变 形 强 度 抗拉与抗压 缩失衡能力 塑 性 抗缩颈 能 力 变形均 化与扩 展能力 塑 性 抗起皱 能 力 变形力及 其 变 化 各向异性 值 硬化性能 变形抗力 化学成分 组 织 变形条件 硬化性能 应力状态 应变梯度 硬化性能 模具状态 力学性能 值与 值 相对厚度 化学成分 组 织 变形条件 图 1 3 体系化研究方法举例 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 与 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 冲压成形与板材冲压 1 概述通过模具使板材产生塑性变形而获得成品零件的一次成形工艺方法叫做冲压。由于冲压通常在冷态下进行,因此也称为冷冲压。只有当板材厚度超过8100mm时,才采用热冲压。冲压加工的原材料一般为板材或带材,故也称板材冲压。某些非金属板材(如胶木板、云母片、石棉、皮革等)亦可采用冲压成形工艺进行加工。冲压广泛应用于金属制品各行业中,尤其在汽车、仪表、军工、家用电器等工业中占有极其重要的地位。冲压成形需研究工艺设备和模具三类基本问题。 板材冲压具有下列特点: (1)高的材料利用率。(2)可加工薄壁、形状复杂的零件。(3)冲压件在形状和尺寸方面的互换性好。(4)能获得质量轻而强度高、刚性好的零件。(5)生产率高,操作简单,容易实现机械化和自动化。冲压模具制作成本高,因此适合大批量生产。对于小批量、多品种生产,常采用简易冲模,同时引进冲压加工中心等新型设备,以满足市场求新求变的需求。板材冲压常用的金属材料有低碳钢、铜、铝、镁合金及高塑性的合金刚等。如前所述,材料形状有板材和带材。冲压生产设备有剪床和冲床。剪床是用来将板材剪切成具有一定宽度的条料,以供后续冲压工序使用,冲床可用于剪切及成形。 2 冲压成形的特点生产时间中所采用的冲压成形工艺方法有很多,具有多种形式饿名称,但塑性变形本质是相同的。冲压成形具有如下几个非常突出的特点。 (1)垂直于板面方向的单位面积上的压力,其数值不大便足以在板面方向上使板材产生塑性变形。由于垂直于板面方向上的单位面积上压力的素质远小于板面方向上的内应力,所以大多数的冲压变形都可以近似地当作平面应力状态来处理,使其变形力学的分析和工艺参数的计算大呢感工作都得到很大的简化。 (2)由于冲压成形用的板材毛胚的相对厚度很小,在压应力作用下的抗失稳能力也很差,所以在没有抗失稳装置(如压边圈等)的条件下,很难在自由状态下顺利地完成冲压成形过程。因此,以拉应力作用为主的伸长类冲压成形过程多于以压应力作用为主的压缩类成形过程。 (3)冲压成形时,板材毛胚内应力的数值等于或小于材料的屈服应力。在这一点上,冲压成形与体积成形的差别很大。因此,在冲压成形时变形区应力状态中的静水压力成分对成形极限与变形抗力的影响,已失去其在体积成形时的重要程度,有些情况下,甚至可以完全不予考虑,即使有必要考虑时,其处理方法也不相同。 (4)在冲压成形时,模具对板材毛胚作用力所形成的约束作用较轻,不像体积成形(如模锻)是靠与制件形状完全相同的型腔对毛胚进行全面接触而实现的强制成形。在冲压成形中,大多数情况下,板材毛胚都有某种程度的自由度,常常是只有一个表面与模具接触,甚至有时存在板材两侧表面都有于模具接触的变形部分。在这种情况下,这部分毛胚的变形是靠模具对其相邻部分施加的外力实现其控制作用的。例如,球面和锥面零件成形时的悬空部分和管胚端部的卷边成形都属这种情况。 由于冲压成形具有上述一些在变形与力学方面的特点,致使冲压技术也形成了一些与体积成形不同的特点。由于不需要在板材毛的表面施加很大的单位压力即可使其成形,所以在冲压技术中关于模具强度与刚度的研究并不十分重要,相反却发展了学多简易模具技术。由于相同原因,也促使靠气体或液体压力成形的工艺方法得以发展。因冲压成形时的平面应力状态或更为单纯的应变状态(与体积成形相比),当前对冲压成形汇中毛胚的变形与 力能参数方面的研究较为深入,有条件运用合理的科学方法进行冲压加工。借助于电子计算机与先进的测试手段,在对板材性能与冲压变形参数进行实时测量与分析基础上,实现冲压过程智能化控制的研究工作也在开展。人们在对冲压成形过程有离开较为深入的了解后,已经认识到冲压成型与原材料有十分密切的关系。所以,对板材冲压性能即成形性与形状稳定性的研究,目前已成为冲压技术的一个重要内容。对板材冲压性能的研究工作不仅是冲压技术发展的需要,而且也促进了钢铁工业生产技术的发展,为其提高板材的质量提供了一个可靠的基础与依据。 3冲压变形的分类 冲压变形工艺可完成多种工序,其基本工序可分为分离工序和变形工序两大类。分离工序是使胚料的一部分与另一部分相互分离的工艺方法,主要有落料、冲孔、切边、剖切、修整等。其中又以冲孔、落料应用最广。变形工序是使胚料的一部分相对于另一部分产生位移而不破裂的工艺方法,主要有拉深、弯曲、局部成形、胀形、翻边、缩径、校形、旋压等。从本质上看,冲压成形就是毛胚的变形区在外力的作用下产生相应的塑性变形,所以变形区内的应力状态和变形特点景象的冲压成形分类,可以把成形性质相同的成形方法概括成同一个类型并进行体系化的研究。绝大多数冲压成形时毛胚变形区均处于平面应力状态。通常认为在板材表面上不受外力的作用,即使有外力作用,其数值也是较小的,所以可以认为垂直于板面方向上的应力为零,使板材毛胚产生塑性变形的是作用于板面方向上相互的两个主应力。由于板厚较小,通常都近似地认为这两个主应力在厚度方向上是均匀分布的。基于这样的分析,可以把各种形式冲压成型中的毛陪变形区的受力状态与变形特点,在平面应力的应力坐标系中与相应的两向应变坐标系中以应力与应变坐标决定的位置来表示。4.冲压用原材料 冲压加工用原材料有很多种,它们的性能也有很大的差别,所以必须根据原材料的性能与特点,采用不同的冲压成形方法、工艺参数和模具结构,才能达到冲压加工的目的。由于人们对冲压成形过程板材毛胚的变形行为有了较为深入的认识,已经相当清楚的建立了由原材料的化学成分、组织等因素所决定的材料性能与冲压成形之间的关系,这就使原材料生产部门不但按照冲压件的工作条件与使用要求进行原材料的设计工作,而且也根据冲压件加工过程对板材性能的要求进行新型材料的开发工作,这是冲压技术在原材料研究方面的一个重要方向。对冲压用原材料冲压性能方面的研究工作有(1)原材料冲压性能的含义。(2)判断原材料冲压性能的科学方法,确定可以确切反映材料冲压性能的参数,建立冲压性能的参数与实际冲压成形间的关系,以及冲压性能参数的测试方法等。 (3)建立原材料的化学成分、组织和制造过程与冲压性能之间的关系。冲压用原材料主要是各种金属与非金属板材。金属板材包括各种黑色技术和有色金属板材。虽然在冲压生产中所用金属板材的种类很多,但最多的原材料蛀牙是钢板、不锈钢板、铝合金板及各种复合金属板。5板材冲压性能及其鉴定方法 板材是指对冲压加工的适应能力。对板材冲压性能的研究具有飞行重要的意义。为了能够运用最科学与最经济合理的冲压工艺过程与工艺参数制造出冲压零件,必须对作为加工对象的板材的性能具有十分清楚的了解,这样才有可能充分地利用板材在加工方面的潜在能力。另一方面,为了能够依据冲压件的形状与尺寸特点及其所需的成形工艺等基本因素,正确、合理地选用板材,也必须对板材的冲压性能有一个科学的认识与正确的判断。评定板材冲压性能的方法有直接试验法与间接试验法。 实物冲压试验是最直接的板材冲压性能的评定方法。利用实际生产设备与模具,在与生产完全相同的条件下进行实际冲压零件的性能评定,当然能够的最可靠的结果。但是,这种评定方法不具有普遍意义,不能作为行业之间的通用标准进行信息的交流。 模拟试验是把生产中实际存在的冲压成形方法进行归纳与简单化处理,消除许多过于复杂的因素,利用轴对称的简化了的成形方法,在保证试验中板材的变形性质与应力状态都与实际冲压成形相同的条件下进行的冲压性能的评定工作。为了保证模拟试验结果的可靠性与通用性,规定了私分具体的关于试验用工具的几何形状与尺寸、毛胚的尺寸、试验条件(冲压速度、润滑方法、压边力等)。 间接试验法也叫做基础试验法。间接试验法的特点是:在对板材在塑性变形过程中所表现出的基本性质与规律进行分析与研究的基础上,进一步把它和具体的冲压成形中板材的塑性变形参数联系起来,建立间接试验结果(间接试验值)与具体的冲压成形性能(工艺参数)之间的相关性。由于间接试验时所用试件的形状与尺寸以及加载的方式等都不同于具体的冲压成形过程,所以它的变形性质和应力状态也不同于冲压变形。因此间接试验所得的结果(试验值)并不是冲压成形的工艺参数,而是可以用来表示板材冲压性能的基础性参数。Characteristics and Sheet Metal Forming1 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 8100mm. 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 shapeand 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. 2Characteristics 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. 3Categories 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. 4Raw materials for stamping formingThere 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. 5Stamping forming property of sheet metal and its assessing methodThe 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.
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