铸造技术

我们可以提供离心铸造、砂型铸造、真空造型铸造和锻造工艺零件，并具备良好精细的加工能力以满足严格要求。

离心铸造

In centrifugal casting, a permanent mold is rotated continuously about its axis at high speeds (300 to 3000 rpm) as the molten metal is poured. The molten metal is centrifugally thrown towards the inside mold wall, where it solidifies after cooling. The casting is usually a fine-grained casting with a very fine-grained outer diameter, owing to chilling against the mould surface. Impurities and inclusions are thrown to the surface of the inside diameter, which can be machined away. Casting machines may be either horizontal or vertical-axis. Horizontal axis machines are preferred for long, thin cylinders, vertical machines for rings. Most castings are solidified from the outside first. This may be used to encourage directional solidification of the casting, and thus give useful metallurgical properties to it. Often the inner and outer layers are discarded and only the intermediary columnar zone is used. Centrifugal casting was the invention of Alfred Krupp, who used it to manufacture cast steel tyres for railway wheels in 1852.

离心铸造的特点

铸件几乎可以制成任何长度、厚度和直径。

相同尺寸的模具可生产不同壁厚的产品。

无需使用型芯。

耐大气腐蚀，这是管道的典型情况。

离心铸造的机械性能非常优异。

此工艺只能生产圆柱形零件。

尺寸限制为直径最大3米（10英尺），长度最大15米（50英尺）。

壁厚范围从2.5毫米到125毫米（0.1 - 5.0英寸）。

公差限制：外径可为2.5毫米（0.1英寸），内径可为3.8毫米（0.15英寸）。

表面光洁度范围为2.5毫米至12.5毫米（0.1 - 0.5英寸）均方根值。

离心铸造的优点

Cylinders and shapes with rotational symmetry are most commonly cast by this technique. "Tall" castings (in the direction of the settling force acting, usually gravity) are always more difficult than short castings. In the centrifugal casting technique the radius of the rotation, along which the centrifugal force acts, replaces the vertical axis. The casting machine may be rotated to place this in any convenient orientation, relative to gravity's vertical. Horizontal and vertical axis machines are both used, simply to place the casting's longest dimension conveniently horizontal. Thin-walled cylinders are difficult to cast by other means, but centrifugal casting is particularly suited to them. To the rotation radius, these are effectively shallow flat castings and are thus simple. Centrifugal casting is also applied to the casting of disk and cylindrical shaped objects such as railway carriage wheels or machine fittings where the grain, flow, and balance are important to the durability and utility of the finished product. Providing that the shape is relatively constant in radius, noncircular shapes may also be cast.

砂型铸造

砂型铸造，又称砂模铸造，是一种以砂为模具材料的金属铸造工艺。术语砂型铸造也可指通过砂型铸造工艺生产的物件。砂型铸件在称为铸造厂的专业工厂中生产。超过70%的金属铸件是通过砂型铸造工艺生产的。

砂型铸造相对便宜，且具有足够的耐火性，甚至可用于铸钢生产。除砂子外，还需混合或添加合适的粘结剂（通常为黏土）。混合物通常用水润湿，有时也用其他物质，以增强黏土的强度和可塑性，使骨料适合造型。砂子通常被容纳在称为砂箱的框架或模具箱系统中。型腔和浇注系统是通过将砂子紧实于模型或模样周围，或直接在砂中雕刻而成。

砂型铸造的图案

From the design, provided by an engineer or designer, a skilled pattern maker builds a pattern of the object to be produced, using wood, metal, or a plastic such as expanded polystyrene. Sand can be ground, swept or strickled into shape. The metal to be cast will contract during solidification, and this may be non-uniform due to uneven cooling. Therefore, the pattern must be slightly larger than the finished product, a difference known as contraction allowance. Pattern-makers are able to produce suitable patterns using Contraction rules (these are sometimes called shrink allowance rulers where the ruled markings are deliberately made to a larger spacing according to the percentage of extra length needed). Different scaled rules are used for different metals, because each metal and alloy contracts by an amount distinct from all others. Patterns also have core prints that create registers within the molds into which are placed sand cores. Such cores, sometimes reinforced by wires, are used to create under-cut profiles and cavities which cannot be molded with the cope and drag, such as the interior passages of valves or cooling passages in engine blocks.

金属进入模具型腔的路径构成浇注系统，包括直浇道、维持良好金属补缩的各种补料口，以及将浇注系统连接到铸造型腔的内浇口。铸造过程中产生的气体和蒸汽通过透气性砂型或冒口排出，冒口可添加在模型本身上，或作为独立部件。

砂型铸造的模具箱及材料

A multi-part molding box (known as a casting flask, the top and bottom halves of which are known respectively as the cope and drag) is prepared to receive the pattern. Molding boxes are made in segments that may be latched to each other and to end closures. For a simple object—flat on one side—the lower portion of the box, closed at the bottom, will be filled with a molding sand. The sand is packed in through a vibratory process called ramming, and in this case, periodically screeded level. The surface of the sand may then be stabilized with a sizing compound. The pattern is placed on the sand and another molding box segment is added. Additional sand is rammed over and around the pattern. Finally a cover is placed on the box and it is turned and unlatched, so that the halves of the mold may be parted and the pattern with its sprue and vent patterns removed. Additional sizing may be added and any defects introduced by the removal of the pattern are corrected. The box is closed again. This forms a green mold which must be dried to receive the hot metal. If the mold is not sufficiently dried a steam explosion can occur that can throw molten metal about. In some cases, the sand may be oiled instead of moistened, which makes possible casting without waiting for the sand to dry. Sand may also be bonded by chemical binders, such as furane resins or amine-hardened resins.

砂型铸造的激冷

为了控制金属的凝固组织，可以在模具中放置金属板或冷铁。局部快速冷却会形成更细的晶粒结构，并可能在这些位置形成硬度稍高的金属。在黑色金属铸件中，其效果类似于锻造中的淬火工艺。发动机气缸内径通过冷铁芯使其硬化。在其他金属中，冷铁可用于促进铸件的定向凝固。通过控制铸件的凝固方式，可以防止铸件内部出现气孔或缩松缺陷。

砂型铸造的型芯

为了在铸件内部形成空腔——例如用于发动机缸体和气缸盖的液体冷却——使用负形来制造砂芯。砂芯通常采用砂模成型，在取出模型后插入铸造箱中。由于额外的设置时间和更高的成本，设计时尽可能避免使用砂芯。

在适当的湿度下完成模具后，装有砂型的砂箱被定位，准备注入熔融金属——通常是铁、钢、青铜、黄铜、铝、镁合金，或各种含铅、锡、锌的压铸合金。注入液态金属后，砂箱被放置一旁，直到金属冷却至足够强度。随后去除砂子，露出粗糙的铸件，若是铁或钢铸件，可能仍呈红热状态。当铸造比型砂重得多的金属（如铁或铅）时，砂箱通常需用厚板覆盖，以防止出现称为“浮模”的问题。浮模现象是指金属压力导致型腔上方砂层变形，从而造成铸造失败。

铸件浇铸后，通过拉杆或钢丸破碎型芯并将其从铸件中清除。浇口和冒口的金属从粗铸件上切除。可采用多种热处理方式消除初始冷却产生的应力，并增加硬度——对于钢或铁制件，可通过水淬或油淬实现。铸件还可通过表面压缩处理（如喷丸强化）进一步增强，从而提高抗拉裂能力并平滑粗糙表面。

砂型铸造的设计要求

The part to be made and its pattern must be designed to accommodate each stage of the process, as it must be possible to remove the pattern without disturbing the molding sand and to have proper locations to receive and position the cores. A slight taper, known as draft, must be used on surfaces perpendicular to the parting line, in order to be able to remove the pattern from the mold. This requirement also applies to cores, as they must be removed from the core box in which they are formed. The sprue and risers must be arranged to allow a proper flow of metal and gasses within the mold in order to avoid an incomplete casting. Should a piece of core or mold become dislodged it may be embedded in the final casting, forming a sand pit, which may render the casting unusable. Gas pockets can cause internal voids. These may be immediately visible or may only be revealed after extensive machining has been performed. For critical applications, or where the cost of wasted effort is a factor, non-destructive testing methods may be applied before further work is performed.

真空成型铸造

Vacuum molding (V-process) is a variation of the sand casting process for most ferrous and non-ferrous metals, in which unbonded sand is held in the flask with a vacuum. The pattern is specially vented so that a vacuum can be pulled through it. A heat-softened thin sheet (0.003 to 0.008 in (0.076 to 0.203 mm)) of plastic film is draped over the pattern and a vacuum is drawn (200 to 400 mmHg (27 to 53 kPa)). A special vacuum forming flask is placed over the plastic pattern and is filled with a free-flowing sand. The sand is vibrated to compact the sand and a sprue and pouring cup are formed in the cope. Another sheet of plastic is placed over the top of the sand in the flask and a vacuum is drawn through the special flask; this hardens and strengthens the unbonded sand. The vacuum is then released on the pattern and the cope is removed. The drag is made in the same way (without the sprue and pouring cup). Any cores are set in place and the mold is closed. The molten metal is poured while the cope and drag are still under a vacuum, because the plastic vaporizes but the vacuum keeps the shape of the sand while the metal solidifies. When the metal has solidified, the vacuum is turned off and the sand runs out freely, releasing the casting.

V法铸造工艺因无需拔模斜度而闻名，因为塑料薄膜具有一定的润滑性，且在砂箱内抽真空时会轻微膨胀。该工艺具有高尺寸精度，首英寸公差为±0.010英寸，之后每英寸公差为±0.002英寸。可实现的截面最小厚度为0.090英寸（2.3毫米）。表面光洁度极佳，通常介于150至125微英寸均方根之间。其他优势包括无水分相关缺陷、无需粘结剂成本、优异的透气性，以及燃烧粘结剂时无有毒烟雾。最后，由于砂子不与模型接触，模型不会磨损。主要缺点是工艺速度比传统砂型铸造慢，因此仅适用于中低产量生产，每年约10至15,000件。然而，这使其非常适合原型制作，因为塑料模型易于修改。

锻造

锻造是已知最古老的金属加工工艺之一。传统上，锻造由铁匠使用锤子和铁砧完成，但12世纪水力被引入铁的生产和加工后，锤子和铁砧逐渐被淘汰。经过数百年发展，铁匠铺或锻造厂已演变为拥有工程化工艺、生产设备、工装、原材料和产品的设施，以满足现代工业需求。

现代工业锻造通常使用压力机或由压缩空气、电力、液压或蒸汽驱动的锻锤进行。这些锻锤的往复重量可达数千磅。较小型的动力锻锤（往复重量为500磅（230公斤）或以下）和液压压力机在艺术锻造车间中也很常见。部分蒸汽锻锤仍在使用，但随着其他更便捷动力源的出现，它们已逐渐被淘汰。

锻造的优缺点

锻造可以生产出比同等铸造或机加工零件更坚固的工件。在锻造过程中，金属成型时其内部晶粒会随零件整体形状发生变形，从而使晶粒在整个零件中保持连续性，最终形成具有更优强度特性的工件。

某些金属可以冷锻，但钢铁几乎总是热锻。热锻可防止冷锻导致的加工硬化，而加工硬化会增加对工件进行二次机械加工的难度。此外，虽然加工硬化在某些情况下可能有利，但其他硬化方法（如热处理）通常更经济且更易控制。适用于沉淀硬化的合金（如大多数铝合金和钛合金）可先热锻，再进行硬化处理。

生产锻造涉及机械、模具、设施和人员方面的重大资本支出。在热锻情况下，需要高温炉（有时称为锻炉）来加热钢锭或坯料。由于大型锻锤和压力机及其可生产零件的巨大规模，以及处理热金属固有的危险性，通常需要专门的建筑来容纳该操作。在落锻操作中，必须采取措施吸收锻锤产生的冲击和振动。大多数锻造操作使用金属成形模具，这些模具必须精确加工并仔细热处理，以正确成形工件，并承受所涉及的巨大力量。

锻造工艺

锻造工艺种类繁多，但主要可分为三大类。

拉长：长度增加，横截面减小

镦粗：长度减小，横截面增大

在闭式压缩模具中挤压：产生多向流动

常见的锻造工艺包括：辊锻、旋锻、拔长、自由锻、模锻、压力机锻造、自动热锻和镦粗。