了解压铸

从发动机缸体到门把手，压铸是一种适用于大型或小型零件的快速、准确和可重复的金属生产技术。压铸件具有出色的表面光洁度，并且该工艺与多种有色金属兼容。

由于与压铸相关的高启动成本，该工艺通常用于大批量生产，其中制造规模弥补了高机械和工具成本。压铸原型和小批量生产更难获得，因为与下大宗订单的客户合作符合压铸公司的经济利益。然而，3ERP 目前为希望下小压铸订单的客户提供了独特的压铸解决方案。

本文深入探讨了金属压铸，解释了该工艺的合适材料、表面光洁度和应用。

什么是压铸？

压铸是一种金属铸件，它利用高压将熔融金属压入由两个模具形成的模腔中。它与注塑成型的塑料制造工艺具有共同的特点。

在更大的金属铸造领域中，压铸是最流行的技术之一，因为它具有准确性、高质量和详细程度。已经存在数千年的更广泛的金属铸造类别包含许多使用模具形成液态金属的不同工艺。从历史上看，这种工艺通常涉及借助重力将液态金属倒入模具中——许多金属铸造工艺仍然以这种方式工作。然而，压铸是 19 世纪引入的一种相对较新的金属铸造形式，它使用压力而不是重力来填充模腔。

压铸有时被称为高压压铸，因为压力（通常为 10-140 兆帕）用于迫使金属进入模腔。低压压铸（LPDC）的相关工艺不太常见。压铸通常分为两类之一：热室压铸和冷室压铸，它们适用于不同类型的金属。但是，还有其他更小众的压铸类型，例如半固态金属铸造 (SSM)。

压铸的工作原理

简单来说，金属压铸的工作原理是利用高压迫使熔融金属进入由两个硬化钢模具形成的模腔。一旦型腔被填满，熔融金属就会冷却并凝固，模具就会打开，这样就可以取出零件。但在实践中，工艺步骤较多，需要熟练的工程师操作压铸设备。

这里我们将压铸过程分为三个阶段：

1. 制模
2. 铸造
3. 后加工

如何制作压铸模具

压铸模具至少由两半组成：盖侧（安装在固定板上）和顶出侧（安装在可移动板上）。一些模具还具有其他部分，例如滑块和型芯，用于生产更复杂的零件，例如带有孔和螺纹的零件。

根据制造零件的尺寸，压铸模具可能有多个型腔，以便每个周期生产多个零件。这种模具要么有几个相同的型腔（多型腔模具），要么具有不同型腔的混合以生产不同的零件（单元模具）。

压铸模具除了具有良好的耐磨性和延展性外，还必须具有难以置信的强度和耐热性。因此，它们由高性能硬化工具钢制成（通常经过热处理），使其每小时可进行数百次铸造循环，并且在其整个使用寿命期间可进行多达 200 万次循环。压铸模具必须在非常高的夹紧力下保持性能。

制造压铸模具首先要结合使用特定铸件的设计和模拟工具的计算机辅助设计 (CAD)。与注塑模具一样，压铸模具必须具有浇道孔、流道和浇口，以允许熔融材料进入型腔。还必须结合锁定销和顶出销，以固定模具并促进顶出。模具的数字化设计允许创建复杂的形状和严格的公差。

CNC加工被广泛用于制造压铸模具。通常，压铸模具制造从模具形状的粗加工开始，然后是金属模具的热处理，最后是一轮精加工。原型级模具也可以使用快速工具制造，使用 CNC 加工或其他工艺，如选择性激光烧结 (SLS)。

如何铸造金属零件

与注塑类似，模具制作完成后，可以在压铸机中制作压铸件。压铸过程包括四个主要阶段：准备、填充、顶出和落砂。

但是，铸造工艺会根据使用的是热室还是冷室而略有不同。这两种高压压铸工艺具有不同的优势：一种适用于高速铸造，另一种适用于更广泛的铸造材料。

热室压铸

期间 热室压铸 ，金属 压铸机 包含将金属加热到熔融状态的必要设备。因为它是一个独立的系统，它比替代方案快得多，提供简短的 周期时间 ，虽然它只适用于选择的 铸造材料 ，包括锌、锡和铅 合金 .

冷室压铸

冷室压铸工艺 需要使用单独的熔炉来加热金属。这自然会减慢速度 生产率 ，作为 熔化的金属 必须带到 压铸机 用勺子。但是，因为单独的熔炉比 热室压铸机 ，可以铸造高熔点金属。这种方法适用于铝铸件。

无论是使用热室机还是冷室机，金属压铸过程通常如下进行：

1. 模具准备
2. 填充
3. 弹射
4. 震荡

在模具准备过程中，两个半模的内表面涂有润滑剂，以在铸件完成后促进脱模。然后可以关闭半模并用锁定销固定。

使用压力系统实现模具的填充。该系统在热室和冷室系统之间有所不同。在这两种情况下，最终结果是熔融金属被柱塞通过浇口强制进入模腔。高压——热室中高达 35 兆帕，冷室中高达 140 兆帕——确保快速和全面的填充，从而导致持续冷却，防止不均匀收缩和随之而来的零件变形。在冷却过程中保持压力。

打开两个半模，用顶针取出铸件。通常，模具随后会立即重新闭合，为下一次注射做好准备。与此同时，完成的铸件准备好进行落砂，这包括去除铸件的废料部分，例如浇口、流道和飞边（分型线上的材料渗漏）。这种材料去除可以使用手动工具、翻滚或液压修整模具来实现。

后加工

许多金属压铸件需要最少的二次操作。这是由于所涉及的高压导致高水平的细节和良好的表面光洁度。然而，许多净形和近净形铸件还需要对孔、螺纹和其他特征进行精密加工。一些铸造金属比其他金属更容易加工：例如，镁压铸和铝压铸非常适合后加工。

后加工压铸件的第二个好处是能够使用 CNC 机器的在机检测功能，让机械师能够验证零件。

压铸应用

压铸是一种功能强大、用途广泛的工艺，适用于从发动机部件到电子外壳等一系列零件。压铸具有多功能性的原因包括其较大的构建面积、多种材料选择以及制造详细、可重复的薄壁零件的能力。

• 汽车 ：铝压铸件在汽车行业很受欢迎，因为它可以生产轻质部件，如液压缸、发动机支架和变速箱壳体。锌压铸适用于燃料、制动器和动力转向部件，而镁压铸适用于面板和座椅框架。
• 航天 ：与汽车行业一样，航空零件供应商使用铝压铸件制造具有高耐热性和耐腐蚀性的轻质零件。轻量化部件可减少燃料消耗。
• 能源 ：石油和天然气领域的压铸件包括阀门、过滤组件和叶轮。风力涡轮机叶片等可再生能源部件也可以压铸成型。
• 电子 ：压铸在电子产品中很普遍，因为它用于外壳、外壳和连接器等物品。压铸部件也可以设计有集成散热器，这对于许多设备都是必需的。薄壁 RFI EMI 屏蔽组件普遍采用镁压铸，而 LED 灯组件采用铝压铸则很普遍。 （LED 外壳的压铸通常使用 A383 等合金。）
• 构造 ：建筑行业将铝压铸件用于建筑框架和窗框等大型结构。
• 工程 ：起重设备、机床和其他设备通常包含压铸部件。
• 医疗 ：在医疗保健领域，压铸可用于监测设备组件、超声系统和其他物品。

压铸材料

制造商在选择压铸材料时必须考虑某些因素和变量。其中包括：

• 材料是否适合热室压铸
• 材料成本
• 间接材料成本（例如所需的任何额外后处理）
• 材料结构特性
• 实力
• 重量
• 表面处理
• 可加工性

在为零件或原型选择压铸材料时，应考虑所有这些因素。

压铸铝合金

铝是主要的压铸金属之一，铝合金用于冷室压铸。这些合金通常含有硅、铜和镁。

铝压铸合金重量轻，尺寸稳定性好，这使其成为复杂、精细零件的理想选择。铝铸件的其他优点还包括良好的耐腐蚀性、耐温性、导热性和导电性。

常见的压铸铝合金有：

• 380 ：兼顾铸造性和良好机械性能的通用铝合金。它用于各种各样的产品，包括发动机支架、家具、电子外壳、框架、把手、变速箱和电动工具。
• 390 ：耐磨性和耐振动性优异的合金。它专为汽车发动机缸体的压铸而开发，也适用于阀体、叶轮和泵壳。
• 413 ：铸造性优良的铝合金。 It has good pressure tightness and is therefore used for products like hydraulic cylinders, as well as architectural parts and food and dairy industry equipment.
• 443 :The most ductile of die casting aluminum alloys, this alloy is suitable for consumer goods, especially those that require plastic deformation after casting.
• 518 :A ductile aluminum alloy with good corrosion resistance. It is used in a variety of products, including aircraft hardware fittings, ornamental hardware, and escalator components.

Magnesium die casting alloys

Magnesium is another very popular die casting material. It is even lighter than aluminum, with the added advantage of being highly machinable — making it suitable for cast parts that require additional machined details or machined surface finishing.

A major advantage of magnesium die casting alloys is their suitability for hot-chamber die casting, making them easier to use than die casting metals like aluminum. Other elements in magnesium alloys include aluminum, zinc, manganese, and silicon.

Common magnesium die casting alloys include:

• AZ91D :A general-purpose alloy with good castability, corrosion resistance, and strength-to-weight ratio. Applications include mechanical and power-train components.
• AM60 :An alloy with good castability, strength, vibration dampening, and ductility. It is used in automotive components such as seat frames and panels.
• Rare earth alloys AS41B and AE42 :Alloys with superior temperature resistance, as well as good creep resistance, corrosion resistance, and ductility. Both alloys are found in engine parts.

Zinc die casting alloys

Another major category of die casting metals is zinc alloys. Castable in a hot-chamber die casting machine, zinc casting is the most manufacturer-friendly die casting option and offers other benefits like impact strength, ductility, and suitability for plating. Due to its castability, it also results in minimal die wear.

Zinc is heavier than aluminum and magnesium and is usually alloyed with aluminum, copper, and magnesium.

Common zinc die casting alloys include:

• Zamak  3 :A general-purpose zinc alloy that is easy to cast and offers excellent dimensional stability. In North America, more than two thirds of zinc die castings use Zamak 3. Example uses include ceiling fans and plumbing components.
• Zamak 2 :A slightly stronger and more expensive alloy with added copper content. This zinc casting alloy is often used to produce tooling for plastic injection molding.
• Zamak 5 :A zinc alloy close in composition to Zamak 3 but with greater tensile strength and lower ductility. Popular for products like automotive parts and wheel balancing weights.

Other die casting alloys

Other die casting materials include copper, silicon tombac, lead, and tin alloys, in addition to zinc-aluminum alloys.

Copper alloys exhibit high strength, hardness, and corrosion resistance, in addition to excellent dimensional stability. Meanwhile lead and tin alloys are very dense and can be resistant to corrosion. Zinc-aluminum alloys are recognizable by the ZA prefix; those with a lower aluminum content can be hot-chamber die cast, but those with 11% or more typically cannot.

Die casting finishing options

High-pressure die casting produces parts to a high standard, and finishing options can often be kept to a minimum. However, there are many functional and cosmetic finishing options available for die casting parts.

Deburring

A standard finishing procedure is deburring, which can be thought of as a continuation of the shakeout stage. Deburring involves the removal of imperfections caused by the manufacturing process and is deployed to normalize the appearance and function of the part without adding any specific texture or color.

Methods of deburring include:

• Manual deburring with abrasive materials (can also be automated)
• Vibration deburring with tools like rollers and sandblasting
• Trimming with a punch die

Secondary finishing options

Once imperfections have been removed from the metal die casting parts using a deburring process like sandblasting or manual sanding, it is possible to perform secondary finishing options to transform the surface finish of the castings. These finishing techniques adjust the texture or color of the die casting parts.

Secondary die casting finishes include:

• Polishing with manual equipment to achieve a high-shine finish
• Painting to alter the color of the castings
• Powder coating to alter the color and texture of the castings
• Metal plating to add a surface coating of a different material, either for cosmetic or functional purposes (e.g. plating an electronic component with a more electrically conductive metal).

Strategy for selecting a die casting manufacturer

Die casting is a common manufacturing process used by a broad range of companies. However, finding a die casting manufacturer is much more difficult than finding, for example, a machinist or 3D printing service provider. This is because die casting is typically used by large parts suppliers for high-volume production.

For small and medium-size companies that require metal die casting parts, selecting a die casting manufacturer poses challenges. Typically, manufacturers in this domain will fall into one of the following four categories:

1. Die casting companies that make die casting molds and die casting parts but do not offer post-machining
2. Die casting companies with a few CNC machines but who stipulate much longer lead times for post-machined parts due to their limited machining capacity
3. Die casting companies with a large number of CNC machines for post-machining but who work almost exclusively with large companies placing large orders
4. CNC machining companies who can carry out post-machining of die casting parts but who cannot themselves make die casting molds or die casting parts

Clearly, this makes it hard for smaller companies to find a die casting partner. If post-machining is required, such companies often accept the longer lead times offered by the second category of die casting partner.

But there is another option:by working with a small or medium-size metal die casting partner and a dedicated machining partner like 3ERP — combining options 1 and 4, in effect — companies can order smaller volumes of die casting parts with post-machining with surprisingly short lead times.

At 3ERP, we have a selection of trusted die casting partners with whom we work to provide a seamless casting and finishing service, getting quality cast parts manufactured and delivered in a short timeframe.

Die casting design guidelines

As with most manufacturing processes, high-pressure die casting comes with its own set of design rules and constraints. These include parting line considerations, draft angles, and wall thickness limitations.

Parting line

A die casting part is made using two hardened steel dies. The line where the two dies meet is called the parting line, and this line is often visible after casting in the form of flash — a thin extrusion of excess material that has escaped the cavity at the parting line due to insufficient clamping force.

During die casting design, the designer must find a suitable location for the parting line, i.e. decide where the mold will be split in half. Doing so depends on several factors, including:

• Material flow:The inlet for metal flow must be located along the parting line to ensure optimal filling of the mold cavity.
• Cosmetic features:Cosmetic features should not be located near the parting line, since they may be obstructed by gates and vents.
• Post-machining:The parting line area of the casting will likely require the most machining and finishing, so it should be located to provide easy machine tool access.

Small amounts of flash are inevitable, so designers should prepare for the necessity of trimming it after the casting is removed from the mold.

Wall thickness

As with other casting and molding processes, die casting parts are suited to consistent wall thicknesses, as this encourages consistent filling and cooling of the metal castings, reducing the likelihood of uneven shrinkage and warping.

Draft

Metal die casting parts require a small amount of draft — tapered sides of the mold cavity — so the castings can be easily ejected from the dies without damaging them. All surfaces parallel with the die opening direction require draft.

Inner surfaces like untapped holes require a greater draft angle than external walls (which naturally shrink away from the inside of the mold).

Fillets and radii

Fillets are rounded internal corners that increase the load-bearing capacity of die castings. They are also easier to manufacture than sharp internal corners, so should be incorporated into die casting designs as standard. Using an equal radius across fillets is preferable to fillets with varying radii.

Radii are rounded external corners and play a different but equally important function, helping to improve metal flow in the mold cavity.

Ribs

Ribs are small protrusions from the die casting part that serve to increase strength and stiffness without resorting to thicker walls and increased material usage. They also improve metal flow. Note that ribs require their own fillet and radius considerations for maximum strength and flow.

With our network of trusted manufacturing partners, 3ERP offers a comprehensive die casting process even in low volumes.联系我们获取免费报价。