[转载]熔模铸造十大经常被问到的问题
The Top 10 Frequently Asked Questions
About&&Investment
Casting& &&
1. What is an Investment Casting?
The term "investment" may bring dollar signs before the eyes of
those who are not familiar with the process. Actually, it refers to
the ceramic materials that are used to build a hollow shell into
which molten metal is poured to make the castings. The origin of
the term investment comes from the solid mold process where a
plaster type material is poured or "invested" into a container that
holds a clustered tree of small plastic patterns that are identical
to the casting being produced. After the plaster has set, the
disposable patterns are burned out leaving a hollow cavity into
which the metal is poured. The same hold true for the investment or
"lost wax" casting process. Wax is injected into an aluminum die to
produce a pattern that is an exact replica of the part to be
produced. For every casting, a wax pattern must be manufactured.
The patterns are then clustered around a coated sprue and
repeatedly dipped into an agitated vat of ceramic and allowed to
dry. After a shell thickness of approximately 3/8" has been built,
the molds are dewaxed by either flash firing at high heat (1400
degrees F) or autoclaving (pressure and steam). The hollow shells
are then preheated to 800 - 2000 degrees F depending on the alloy
to be poured and the molten metal cast immediately into the hot
shell. After cooling, the ceramic is vibrated and blasted off the
metal parts and discarded. The balance of the cleaning operations
(cut off, grind, heat treat, straightening, blast) are straight
forward and quite similar to the other casting processes.
2. What alloys can be poured as an investment casting?
Generally, all ferrous and non-ferrous materials can be investment
cast. On the ferrous side, carbon, tool and alloy steel along with
the 300, 400, 15-5PH and 17-4Ph stainless steels are most commonly
poured. most aluminum, copper base, and other non-ferrous materials
can be cast. In addition, there are the "exotic" alloys used
primarily in the aircraft engine industry to produce blades and
vanes. These alloys are primarily composed of nickel and cobalt
with a variety of secondary elements added to achieve specific
strength, corrosion and temperature resistant properties.
3. What size range of parts can be produced by the investment
casting process?
Investment castings can be produced in all alloys from a fraction
of an ounce (such as dental brace for a tooth) to over 1,000 pounds
(complex aircraft engine parts). Of the approximately three hundred
investment casting foundries nationwide, most cast parts fall in
the ounces to 20 pound range. Presently, a larger number of
foundries are increasing their capability to pour larger parts, and
pieces in the 20-120 pound range are becoming quite common.
4. What are the "as cast" dimensional tolerances I can
Typically, a linear tolerance of +.005 in/in is standard for
investment casting. This varies depending on the size and
complexity of the part. Subsequent straightening or coining
procedures often enable even tighter tolerances to be held on one
or two specific dimensions. A concerted initial effort between the
customer's and the foundry's engineering staff can often result in
an investment casting drawing for a part that substantially reduces
or completely eliminates the previous machining requirements to
produce an acceptable part.
5. What type of surface finish can I expect from an investment
Because the ceramic shell is built around smooth patterns produced
by injecting wax into a polished aluminum die, the resultant
casting finish is excellent. A 125 micro finish is standard and
even finer finishes (63 or 32) are not uncommon on aircraft engine
castings. Each foundry has its own standards for surface blemishes
(positives, negatives). These are discussed and agreed upon with
the customer based on the function and cosmetic requirements of the
part prior to release of the tooling order.
6. Aren't investment castings expensive? And if so, how can they
save me money?
While investment castings are generally more expensive than forged
parts or those produced by other casting methods, they make up for
higher cost through the reduction of machining achieved through the
near net shape tight tolerances that can be held as cast. Many
parts that require milling, turning, drilling, and grinding to
finish can be investment cast with only .020-.030 finish stock.
Again, it is imperative for the engineering staff of the foundry
and customer to get together and discuss what can or cannot be cast
to determine final finishing requirements and the potential cost
7. How many pieces do I need to make buying an investment casting
practical?
Not as many as you think! Tooling amortization is a key factor in
determining whether or not an investment casting is practical. The
machine tool industry will often specify an investment casting on
25 pieces of a new part. This is bought once and after that only
one or two pieces at a time for replacements. Conversely,
quantities exceeding 100,000 parts per month are produced by some
foundries largely for automotive use. The bulk of investment
castings produced fall in the 100 - 10,000 piece annual
8. What type of tooling or pattern equipment is necessary?
Typically, a split cavity aluminum die is manufactured that is the
"female" mold from which the "male" wax patterns are produced.
Depending on the complexity of the casting, carious combinations of
aluminum, ceramic or soluble cores may be employed to yield the
desired configuration. Most tooling for investment castings falls
in the $1,000 - $10,000 category.
9. What about the integrity of an investment casting?
Will I have problems with porosity and shrinkage that are usually
non-existent in bar stock or forgings? Investment castings are used
for many critical applications that require the parts to be x-rayed
and meet definite soundness criteria. The integrity of an
investment casting can be far superior to parts produced by other
10. What are the lead times I can expect when ordering an
investment casting?
Nothing varies more than lead times depending on part complexity
and foundry capacity. Generally 6-12 weeks is typical for tooling
and sample casting and 6-12 weeks for production.
& 什么是熔模精密铸造？
在人们没有熟悉这个工艺流程之前，“投资”这个词是一种美元的标志。实际上，它涉及的用陶瓷性材料形成空的型壳，用于熔化的金属液浇注进去从而形成铸件.熔模精密铸造来源于实心型壳工艺过程，在该过程中，一种熔融的金属熔体被浇注或倾倒在一个容器中，形成一系列可塑的模型，也等同于铸件的形成。当涂料胶凝结壳后，通过脱蜡去掉蜡料，从而形成金属液浇注的空腔。同样的铸造工艺适用于“熔模”或“失蜡”。熔融的蜡料被注射到铝材的模具中，压制出一个精确的复制品出来。对以每一个铸件，蜡模都必须先被制造出来。蜡模被组合在浇道周围，，然后放入盛有搅拌涂料的陶瓷大缸中，待干燥，然后重复上一过程。在模壳厚度接近3/8”形成后，该模壳可以进行脱蜡，可以通过热水脱蜡，也可以通过高压蒸汽脱蜡处理。然后脱完蜡的模壳进行高温焙烧，该焙烧温度取决于合金的浇注温度；焙烧后，把熔融的金属液立即浇注的型腔中。待其冷却后，通过振动和清壳，除去铸件表面的模壳。铸件清理工序（如，切割浇冒口、打磨、热处理、矫正、喷丸）按上述过程依次进行；并且和其他铸造的工艺流程十分相似。
2.熔模精密铸造适用于哪些合金呢？
一般地，所有的黑色金属及有色金属均可适用于熔模铸造。就黑色金属而言，对碳钢、工具钢、不锈钢300, 400,
15-5PH（马氏体、析出硬化、铬镍铜不锈钢）和17-4Ph（铜、铌/钶构成的沉淀、硬化、马氏体不锈钢）是最常见的。大部分的铝基和铜基合金及其他的有色合金适用于熔模铸造。另外，有一种高性能的合金主要用于航空发动机工业生产叶片。这些合金主要由镍和钴元素组成，并增加各种辅助元素以增强该类合金特定的强度性能、抗
腐蚀度和耐高温性能。
3、熔模铸造工艺可生产铸件的尺寸范围大多少呢？
所有用于熔模铸造的合金铸件重量从几十克（牙科专用的矫正器）到1000镑（复杂的飞机发动机部件）。接近有300家铸造厂分布在全国各地，大部分铸件的重量在几十克到20镑之间。现在，一大部分的铸造厂在增添自己的生产能力以便能生产更大的铸件，对于生产20-120
磅范围中的铸件变得十分的普通了。
4、作为熔模铸件，我期望的尺寸公差范围是多少呢?
通常的，熔模铸造的线性公差标准在+0.005英寸范围之中。公差变化取决于铸件的尺寸和复杂程度。对重要的线性尺寸或重要过程控制尺寸经常会对其中的一两个尺寸的公差精度要求更高。根据客户和铸造工程人员达成初步的一致性意见可以依零件绘制出铸件图，然后再根据情况，适当减少或完全去除先前的工艺机加要求，从而生产出两者认可的零件。
5熔模铸造中，我可以得到哪种程度的表面粗糙度（表面光洁度）。
通过注射蜡进入抛光铝质的模具中，从而在蜡模光滑的外形形成陶瓷型壳，最终铸件表面的光洁度非常好。R3.2是标准的值，甚至更小的(R1.6或R0.8)在航空发动机上很常见。每个铸造厂都有他们自己的标准作为表面质量的参考。同客户商量讨论后，参照铸件的功用和表面要求优先于铸件的&&&&
6.熔模铸造成本昂贵么？如果是，我们该如何节约成本呢？
然而熔模铸件一般都比锻件或其他铸造方式生产的铸件的成本要高，该方法的组成成本较高，尽管铸件是净形状公差，能减少机加要求。很多铸件需要铣削、车削、钻削和磨削去完成，通过熔模铸造铸出的铸件只有.020-.030的利润。再次，急切需要铸造工程技术人员和客户共同商量如何决定铸件最终的交付要求和节约潜在的成本消耗。
7、我需要多少件去购买熔模铸造的实践工艺？
不是你想想的那么多？模具工装是决定熔模铸造批量生产的关键因素。机加工行业经常指定新零件生产中的25件。这个一旦购买，在这之后就仅仅有一个或两件在一定的时间内需要取代。相反的，部分铸造厂的月产量超过10000件大部分是由于自动生产线。熔模铸件生产的大部分在
100-10000 件每年的范围内。
8.对于熔模铸造来说，大部分工具的价格范畴在$1,000 - $10,000之间。
9 关于精密铸件质量的完美程度如何？
我有一个问题就是在锻件或原材料中不存在缩孔和缩松么？熔模铸件用于很多重要的部位，该部位要求进行X光透视和并和标准进行比对。熔模铸件的完好性优先于通过其他铸造方法生产的。
10．当我想订购熔模铸件时，我可以期望的时间是多久呢？
影响交货的时间取决于铸件复杂程度和工厂的生产能力。一般的。6-12周时准备工装和交付样品件的时间，然后通过6-12周可以交付铸件。
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