kualitas produk coran
DESCRIPTION
PRODUK CORANTRANSCRIPT
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CASTING QUALITY
Dr. Ir. Dwi Rahmalina, MT
Casting Quality
! Banyak kemungkinan kesalahan yang terjadi selama operasi pengecoran, sehingga menimbulkan cacat produk.
! Cacat / defects dapat diklasifikasikan sebagai berikut : ! Cacat umum yang dapat terjadi selama proses
pengecoran dengan berbagai teknik ! Cacat yang terjadi selama proses pengecoran
pasir cetak.
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Benda cor telah selesai mengalami solidifikasi sebelum mengisi seluruh rongga cetakan.
Cacat Umum: Misrun
Dua bagian dari aliran logam cair bergabung tetapi tidak terjadi penyatuan sempurna karena premature freezing
Cacat Umum : Cold Shut
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Percikan logam terjadi selama penuangan dan menimbulkan bentuk bulatan padat dan terperangkap dalam cetakan.
Cacat Umum: Cold Shot
Kerusakan pada bagian permukaan atau cacat dalam yang disebabkan oleh penyusutan selama solidifikasi akibat terbatasnya jumlah logam cair yang tersedia pada bagian akhir pembekuan.
Cacat Umum: Shrinkage Cavity
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Rongga gas berbentuk balon yang disebabkan oleh pelepasan gas dari cetakan selama penuangan.
Cacat Sand Casting : Sand Blow
Terbentuknya rongga gas kecil pada daerah dekat permukaan.
Cacat Sand Casting : Pin Holes
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Jika fluditas dari logam cair terlalu tinggi, maka logam cair akan berpenetrasi ke dalam cetakan pasir atau inti, menghasilkan permukaan cor yang terdiri dari campuran butiran pasir dan logam.
Cacat Sand Casting : Penetration
Ketidaksesuaian benda cor pada bagian parting line yang disebabkan oleh displacement relatif dari cope and drag
Cacat Sand Casting : Mold Shift
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Metode Inspeksi pada Foundry
! Inspeksi Visual untuk mendeteksi cacat yang jelas terlihat seperti misruns, cold shuts, and cacat-cacat permukaan lainnya
! Pengukuran dimensi untuk memenuhi syarat toleransi yang diinginkan.
! Uji komposisi kimia dan metalurgi, sehubungan dengan kualitas dari cast metal
! Uji sifat mekanis " hardness, strength ! Deteksi Cacat " Non Destructive Test (NDT)
Penggunaan teknik noninvasive untuk menentukan integritas dari material, komponen atau struktur
atau pengukuran kuantitatif dari beberapa karakteristik produk
i.e. Inspeksi atau pengukuran tanpa merusak produk.
Pengertian dari NDT
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Metode-metode NDT Visual
Liquid Penetran
t
Magnetic Particle
Eddy Current
Ultrasonic
X-ray
Microwave
Acoustic Emission
Thermography
Laser Interferometry
Replication
Flux Leakage
Acoustic Microscopy
Magnetic M
easuremen
ts
Tap Testing
6 Metode NDT yang Umum Digunakan
Visual Liquid Penetrant
Magnetic Ultrasonic
Eddy Current X-ray
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Metode inspeksi dasar dan umum digunakan.
Menggunakan Tools : fiberscopes, borescopes,
magnifying glasses dan mirrors.
Robotic crawlers permit observation in hazardous or
tight areas, such as air ducts, reactors, pipelines.
Portable video inspection unit with zoom allows
inspection of large tanks and vessels, railroad tank
cars, sewer lines.
Inspeksi Visual
Suatu cai ran dengan karekters i t ik yang t inggi dar i kemampubasahan permukaan (high surface wetting characteristics) diaplikasikan ke permukaan benda kemudiaan didiamkan beberapa saat agar masuk ke surface breaking defects.
Liquid yg meluap dipindahkan dari permukaan Developer (serbuk) diberikan di permukaan untuk menarik penetrant
yang terperangkap. Inspeksi Visual sebagai tahao akhir process. Penetrant yg
biasa digunakan : fluorescent dye and inspkesi dilakukan dibawah sinar UV untuk meningkatkan sensitivitas uji.
Inspeksi Liquid Penetrant
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Inspeksi Magnetic Particle
Benda dimagnetisasi. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.
Magnetic Particle Crack Indications
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Radiography Menggunakan radiasi yg mempunyai energi lebih
tinggi (shorter wavelength) dari gelombang electromagnetic seperti cahaya yg terlihat.
Radiasi dapat berasal dari X-ray generator atau sumber radiasi lain.
High Electrical Potential
Electrons - +
X-ray Generator or Radioactive Source Creates Radiation
Exposure Recording Device
Radiation Penetrate the Sample
Film Radiography
Top view of developed film
X-ray film
The part is placed between the radiation source and a piece of film.
The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation.
= more exposure
= less exposure
The film darkness (density) will vary with the amount of
radiation reaching the film through the test object.
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Radiographic Images
Conductive material
Coil Coil's magnetic field
Eddy currents
Eddy current's magnetic field
Eddy Current Testing
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Eddy Current Testing
Pengujian arus Eddy sesuai untuk mendeteksi retak pada permukaan serta dapat digunakan untuk membuat konduktivitas listrik dan
pengukuran ketebalan lapisan. Here a small surface probe is scanned over the part surface in an attempt to detect a crack.
Gelombang suara berfrekuensi tinggi diberikan ke material dan direfleksikan kembali dari cacat atau permukaan.
Reflected sound energy is displayed versus time, and inspector can
visualize a cross section of the specimen showing the depth of features that reflect sound.
f
plate crack
0 2 4 6 8 10
initial pulse
crack echo
back surface echo
Oscilloscope, or flaw detector screen
Ultrasonic Inspection (Pulse-Echo)
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Ultrasonic Imaging
Gray scale image produced using the sound reflected from the front
surface of the coin
Gray scale image produced using the sound reflected from the back surface of the coin (inspected from heads side)
High resolution images can be produced by plotting signal strength or time-of-flight using a computer-controlled
scanning system.
Inspeksi of Raw Products
!Forgings, !Castings, !Extrusions, !etc.
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!Cracking !Corrosion !Erosion/Wear !Heat Damage !etc.
Inspeksi untuk In-Service Damage
Power Plant Inspection
Probe Signals produced by
various amounts of corrosion thinning.
Periodically, power plants are shutdown for inspection.
Inspectors feed eddy current probes into heat exchanger tubes to check for corrosion
damage.
Pipe with damage
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Wire Rope Inspection
Electromagnetic devices and visual inspections are used to find broken wires and other
damage to the wire rope that is used in chairlifts, cranes and
other lifting devices.
Storage Tank Inspection
Robotic crawlers use ultrasound to inspect
the walls of large above ground tanks for signs of thinning
due to corrosion.
Cameras on long
articulating arms are used
to inspect underground storage tanks for damage.
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! Simpel dari segi Geometri: ! Although casting can be used to produce
complex part geometries, simplifying the part design usually improves castability
! Avoiding unnecessary complexities: ! Simplifies moldmaking ! Reduces the need for cores ! Improves the strength of the casting
Pertimbangan dalam Desain Produk
! Sudut pada benda cor: ! Sharp corners and angles should be avoided,
since they are sources of stress concentrations and may cause hot tearing and cracks
! Generous fillets should be designed on inside corners and sharp edges should be blended
Pertimbangan dalam Desain Produk
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! Draft Guidelines: ! In expendable mold casting, draft facilitates
removal of pattern from mold ! Draft = 1 for sand casting
! In permanent mold casting, purpose is to aid in removal of the part from the mold ! Draft = 2 to 3 for permanent mold processes
! Similar tapers should be allowed if solid cores are used
Pertimbangan dalam Desain Produk
Draft
! Minor changes in part design can reduce need for coring
Figure 11.25 Design change to eliminate the need for using a core: (a) original design, and (b) redesign.
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! Toleransi Dimensi dan Penyelesaian Permukaan : Significant differences in dimensional accuracies and finishes can be achieved in castings, depending on process:
! Poor dimensional accuracies and finish for sand casting
! Good dimensional accuracies and finish for die casting and investment casting
Pertimbangan dalam Desain Produk
Pertimbangan dalam Desain Produk
! Allowances pada Proses Pemesinan: ! Almost all sand castings must be machined to
achieve the required dimensions and part features
! Additional material, called the machining allowance, is left on the casting in those surfaces where machining is necessary
! Typical machining allowances for sand castings are around 1.5 and 3 mm (1/16 and 1/4 in)