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Metallurgy and Materials Engineering Department
University of Indonesia
Semester Genap 2013-2014
Introduction to CastingProcess
Prof. Dr.-Ing. Bambang SuharnoKuliah Pembentukan Logam
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Produk barang-barang manufaktur
(casting)
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Casting (Pengecoran Logam)
proses pembentukan
logam (ferrous dan
non ferrous) dengan
cara memasukanlogam cair kedalam
cetakan berongga
dan dilanjutkan
dengan prosespembekuan
(pendinginan) logam
tersebut
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Principle of mold filling
quick& quiet
airmetal
air entrap
oxidation
turbulence
solidification
gravityLogam Cair
Cetakan
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Keuntungan Casting
bentuk produk (sederhana rumit dan berongga)
tingkat presisi (longgar sangat ketat)
jumlah produk (satuan massal)
berat produk (beberapa gram ton) proses pengerjaan akhir dapat minimum
mengurangi biaya dan waktu proses
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Kelemahan Casting
Kekuatan (strength) kurang, karena terbentuk struktur
dendrit pada metal cor (ferrous dan non ferrous)
Cacat lubang halus (pin hole, shrinkage, dll) dapat
berpengaruh besar pada sifat mekanis. Beberapa diperlukan proses Heat Treatment untuk
memperbaiki sifat mekanis
Perlu ketrampilan khusus pada proses foundry untuk
mendapatkan benda cor yang baik dengan variabel : temperatur,
komposisi,
kondisi cetakan dan cairan logam
casting design.
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Struktur Dendrite dan Cacat Porositas
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Klasifikasi Metode Casting
Berdasarkan material cetakan
Cetakan pasir,
Cetakan Keramik
Cetakan logam Berdasarkan tekanan (pressure) yang diberikan pada
saat logam cair mengisi cetakan
gaya gravitasi (gravity casting),
tekanan rendah (low pressure die casting) < 20 MPa tekanan tinggi (high pressure die casting) 2080 MPa
gaya setrifugal (centrifugal casting),
Vakum
Cari di web video atau animasi metode-metode casting
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Klasifikasi Metode Casting
Cetakan permanen atau cetakan logam
untuk pengecoran gravitasi dan pengecoran
dengan tekanan (pressure die casting)
dipakai berulang-ulang produksi massal Pada proses dengan cetakan expendable
cetakan pasir, cetakan kulit (shell moulding)
dan cetakan invesment/keramik (investment
mold) sekali pakai
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Summary of Casting Processes
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Characteristics of Casting
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Pengecoran Logam Skala Industri
4 proses teknologi pengecoran logam yang sangat
populer yakni:
pengecoran cetakan pasir (sand casting)dan
pengecoran invesment (investment casting)
untukproses pengecoran logam ferrous seperti besi cor
(cast iron) dan berbagai baja cor paduan (alloy steel
casting).
pengecoran gravitasi (gravity casting)dan
pengecoran dengan tekanan (pressure die casting)
yang banyak dipergunakan untuk logam non ferrous
dengan titik lebur relatif rendah terutama paduan
aluminium dan magnesium
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Proses Pengecoran Skala Industri
Baca: http://www.diecasting.org/faq/
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Produk Pengecoran Logam
Komponen industri otomotif
Komponen Industri elektronik dan rumah tangga
Component or Spare Part for industries:
Mining
Oil and Gas
Metal Treatment
Cement
Petrochemical
Power Plant Steel Mill
Fertilizer
Pulp and Paper
Glass and Rubber
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Typical Cast Parts
Figure 11.1 (a) Typical gray-iron castings used in automobiles, including the transmission
valve body (left) and the hub rotor with disk-brake cylinder (front). Source: Courtesy of
Central Foundry Division of General Motors Corporation. (b) A cast transmission housing.
(c) The Polaroid PDC-2000 digital camera with a AZ191D die-cast high-purity magnesium
case. (d) A two-piece Polaroid camera case made by the hot-chamber die-casting process.
Source: Courtesy of Polaroid Corporation and Chicago White Metal Casting, Inc.
(a)
(b)
(c)
(d)
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Examples of cast parts
Metal: Aluminum
Process: Die Cast
Weight: 14.6 lbs
Size: Large(over 12X12)
Market: Automotive
Description: Transmission Gear Case
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Metal: Magnesium
Process: Die Cast
Weight: 90 gramsSize: Medium(3X3 to 12X12)
Market: Computer/Electronics
Description: Military Hand Held Radio Housing
Examples of cast parts
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Metal: Zinc
Process: Die Cast
Weight: 0.39 lbsSize: Medium(3X3 to 12X12)
Market: Automotive
Description: Police/Commercial Spot Light Hsng.
Examples of cast parts
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Metal: Aluminum
Process: Die Cast
Weight: 19 lbs
Size: Large(over 12X12)
Market: Automotive
Description: Lower crankcase
Examples of cast parts
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Metal: Zinc
Process: Die Cast
Weight: 0.244 oz
Size: Very Small(1X1)
Market: Computer/Electronics
Description: A shielded cable header for
housing electrical connector pins
Examples of cast parts
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Metal: Aluminum
Process: Die CastWeight: xx
Size: Medium(3X3 to 12X12)
Market: Sports/Recreation
Description: wankel snowmobile engine rotor housing
Examples of cast parts
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Product : automotive component for domestic
and regional market
ADC12, AC2B,AC4B, AC8H
Cylinder Head, PistonCrankcase,Plate Oil SeparateCylinder ComShock Breaker
All St l C ti I d t
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Alloy Steel Casting Industry
Product
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Semester Genap 2013-2014
Cetakan (Mold)
Prof. Dr.-Ing. Bambang Suharno
Kuliah Pembentukan Logam
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Cetakan
Fungsi : memberikan bentuk dan
dimensipada benda yang akan diproduksi.
Tidak ada hasil benda cor yang lebih baik dari
kondisi cetakannya. Untuk mendapatkan benda cor yang baik,
maka cetakan harus lebih baik lagi.
Cacat pada benda hasil cor yang terjaditerutama diakibatkan kondisi cetakan yang
kurang sempurna (bermasalah).
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1. Cetakan Pasir (Sand Mold)
Pasir (silika, chromit, zircon dll)
Murah (silika)
Dapat dipergunakan kembali
Bersifat isolator, pendinginan lambat(hasil butir kasar dibandingkan dengancetakan logam)
Hasil permukaan : kasar mulus
Sifat produksi : satuan masal
Dimensi kurang akurat, harus finishingseperti machining (bubut, frais, bor dll)
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Syarat Pasir Cetak
Memiliki sifat mampu bentuk dan mampu menahan
logam cair waktu dituang kedalamnya
Permeabilitas yang cocok agar gas atau udara yang
terjadi dalam cetakan waktu penuangan, dapat keluar
dan tidak masuk kedalam logam cair/produk
Distribusi besar butir pasir yang cocok, butir halus
akan memperhalus permukaan namun dapat
menghambat gas keluar sehingga berakibat cacat
Tahan panas terhadap temperatur logam yang
dituang (perlu komposisi kimia dan senyawa ikutan
yang cocok)
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Pasir silika
Berasal dari : Bangka, Tuban
atau Sukabumi.
Umumnya berwarna putih
dengan kandungan clay
yang rendah. Lokasi bisa
dipantai, gunung, kali dll.
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Bahan Pengikat (Binder)
bentonit (clay: secarafisik)
furan atau pep-set(secara kimia)
Ada juga menggunakanpasir silika denganresin (resin coated
sand) yang digunakansebagai cetakan kulit(shell moulding) ataupasir inti (core).
Bahan pengikat bentoni t
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Production Steps in Sand-Casting
Figure 11.2 Outline of production steps in a typical sand-casting operation.
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Sand Casting
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Sequence of
Operationsfor
Sand-
Casting
Figure 11.8 Schematic illustration of the sequence of operations for sand casting. (a) A
mechanical drawing of the part is used to generate a design for the pattern. Considerations suchas part shrinkage and draft must be built into the drawing. (b-c) Patterns have been mounted on
plates equipped with pins for alignment. Note the presence of core prints designed to hold the core
in place. (d-e) Core boxes produce core halves, which are pasted together. The cores will be
used to produce the hollow area of the part shown in (a). (f) The cope half of the mold is
assembled by securing the cope pattern plate to the flask with aligning pins and attaching inserts to
form the sprue and risers. Continued on next slide.
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Sequence of
Operations
for Sand-
Casting,
Cont.
(g) The flask is rammed with sand and rthe plate and inserts are removed. (h) The drag half is
produced in a similar manner with the pattern inserted. A bottom board is placed below the drag
and aligned with pins. (i) The pattern , flask, and bottom board are inverted; and the pattern iswithdrawn, leaving the appropriate imprint. (j) The core is set in place within the drag cavity. (k)
The mold is closed by placing the cope on top of the drag and securing the assembly with pins.
The flasks the are subjected to pressure to counteract buoyant forces in the liquid, which might lift
the cope. (l) After the metal solidifies, the casting is removed from the mold. (m) The sprue and
risers are cut off and recycled, and the casting is cleaned, inspected, and heat treated (when
necessary). Source: Courtesy of Steel Founders Society of America
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Sand Casting
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Vertical Flaskless Molding
Figure 11.7 Vertical flaskless molding. (a) Sand is squeezed between two
halves of the pattern. (b) Assembled molds pass along an assembly line
for pouring. (c) A photograph of a vertical flaskless molding line. Source:
Courtesy of American Foundry Society.
(c)
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Cetakan Pasir
Cetakan pasir menggunakanmoulding machine dengan
ukuran yang besar, meng
gunakan tenaga hidrolik.Cetakan ini digunakan dalam
jumlah yang besar (mass pro-
duction) yang menggunakan
pola dari logam (aluminium)
agar tidak cepat rusak.
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Pattern atau Pola untuk Cetakan Pasir
Pola Kayu Pola Stereform
E d bl M ld C ti
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Expendable Mold Casting -
Expanded Polystrene Mold
Pattern made from Polystrene and vaporized when in contact withmolten metal. The pattern can include the sprue and runner. No cope /drag is needed.
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2.Cetakan Keramik
Agak relatif lebih mahal (bahan import misalpasir Zirkon)
Tidak dapat direklamasi
Bersifat isolator Permukaan : mulushalus
Sifat produksi : massal
Untuk benda cor yang cukup rumit
Methode: investment/precision casting
I C i
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Investment Casting
Mould for wax patterns Wax patterns Mould, dewaxedand fired
Pouring Casting as-demoulded, withsprue and runners
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Investment Casting Process
Figure 11.13 Schematic illustration of investment casting (lost-wax) process.
Castings by this method can be made with very fine detail and from a variety
of metals. Source: Courtesy of Steel Founders Society of America.
3 C t k L
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3. Cetakan Logam Logam (baja, besi tuang, kuningan dll)
Mahal (terutama pembuatan dan design).
Bersifat non isolator, pendinginan cepat: menghasilkan
struktur yang halus meningkat sifat mekanis
Permukaan : halus sangat halus.
Sifat produksi : harus massal.
Menggunakan coating (pelapis) agar permukaan cetakan
retak atau tererosi.
Coating juga berfungsi sebagai isolator sehinggapermukaan cetakan tidak overheating
Pendinginan cepat menghasilkan struktur yang halus
meningkat sifat mekanis.
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Cetakan Logam
1. Preheat mold and spray-coating
2. Insert core and close mold
3. Pour molten metal
4. Finished part
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Cetakan Logam
Benda hasil corberupa manifold
dikeluarkan dari
cetakan, secara
Manual (bantuantangan).
Benda cor dengan
pertolongan pin
keluar dari
cetakan.
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High Pressure Die Casting
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Hot-Chamber Die-Casting
Figure 11.17 Schematic illustration of the hot-chamber die-casting process.
C ld Ch b Di C ti
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Cold-Chamber Die-Casting
Figure 11.18 Schematic illustration of the cold-chamber die-casting process.
These machines are large compared to the size of the casting, because high
forces are required to keep the two halves of the dies closed under pressure.
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Semester Genap 2013-2014
Dapur Peleburan
(Furnace)
Prof. Dr.-Ing. Bambang SuharnoKuliah Pembentukan Logam
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Reverberatory
(Hearth Furnace) misal peleburan Aluminium
Reverberatory
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Reverberatory
(Hearth Furnace)
Jenis dapur tertua Menggunakan sistem pembakaran langsung
melalui burner ke arah umpan hingga umpanmeleleh
Umpan (bahan baku) diletakkan di bagianbawah, sumber api berapa di atas kemudianpanasnya dapat diteruskan melalui konveksiataupun radiasi ke arah umpan
Effesiensi panasnya rendah
Kapasitasnya bervariasi umumnya besar danoperasi non-stop untuk menekan biaya bahanbakar (panas sesudahnya dapat digunakankembali)
Plant ie
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Plant viewPlant view
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Rotation Reverberatory
Circular moving
Horizontal moving
Plant view
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Plant view
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Crucible Furnace
Menggunakan krusibel atau kowi dari bahan
refraktori (batu tahan api) ataupun logam
sebagai penampung umpan dan logam cair
Sumber panasnya bisa dari bahan bakar(internal atau external) ataupun energi listrik
Panas dari sumber panas sebagian besar
dialirkan dengan cara konveksi melalui krusible
Kapasitasnya sangat bervariasi dari beberapagram sampai ukuran ton
Effisiensinya panasnya cukup baik
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Crucible Furnace
Simple, external, fixed, coke or coal firedcrucible furnace
Melting Proses
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Melting ProsesDapur Krusibel
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Fixed type
Tilting and moving type
I d ti C ibl F
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Induction Crucible Furnace
Melting Proses
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Melting ProsesDapur Induction
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Holding Furnace
Digunakan :
Menahan temperatur logam cair
Proses Alloying
Proses Degassing, dll
Biasanya digunakan dapur induksi ataupun
dapur pemanas listrik yang menggunakan
elemen Dapat juga dilakukan di dalam ladle yang
menggunakan pemanas baik berupa burner
ataupun elemen
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Degassing furnace
Fixed holdingfurnace
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Arc Furnace
Horizontal Arc Furnace Vertical Arc Furnace
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Kupola
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