he use of simulation programs saves

he use of simulation programs saves time and
reduces the costs of the casting system design. At the
same time it is possible to meet stringent product quality.
Simulation can make a casting system optimal: it enables
the producing of sound, high-quality castings with fewer
experiments. Furthermore environmental savings and
economical use of materials can be achieved when the
number of test castings is reduced.
Foundries use now widely simulation codes that are
based on a thermal conduction model where thermal
conduction in the melt and liberation of latent heat during
solidification are considered.
Fluid flow simulations are less used. However, e.g.
aluminium die casting is so complicated in which flow
momentum plays a crucial role in the mould filling process
due to the high velocity of the liquid metal. Inertia effects
may cause splashing, jetting or undesirable filling of the
metal flow into mould cavity. When considering complex
parts, the accurate prediction of mould filling behaviour
using empirical knowledge is nearly impossible.
In most of the industrial nations, about70% of the
diecast parts go to the automotive industry. Aluminium
diecastings are gaining importance in the production of
lightweight vehicle bodies, as for example used in new
model Audi cars. Therefore, it is even more vital today
that these castings can be produced with the high quality
methods. In this context the simulation is becoming more
essential in the designing process.
This paper describes the advantages of the Shot
Sleeve simulations to attain better casting system design
in HPDC castings. Filling analysis is used to determine
the size and location of the gate as well as proper runner
system design for ensuring a complete and balanced
filling of the part. Shot sleeve simulations in High Pressure
Die Casting process ensures the minimum air entrapment
during the pre-filling phase.
.
Introduction
Computer simulations of various kinds are gradually
becoming widely recognised tools in numerous design
processes. Simulation codes are widely used in the
foundry industry. Computer simulation of the casting
process began with solidification modelling. For this
reason, the codes are used, in most cases, for heat
transfer calculations in order to predict hot spots and to
avoid porosity in castings
1
.
Fluid flow simulations are less widely used. One of
the reasons is that only a few of the codes can adequately
simulate highly dynamic flows. On the other hand, all of
the known methods require a significant degree of human
effort during the pre-processing phase of the simulation
process. This excludes the everyday practical use of such
methods, when complicated geometries are utilised: The
enmeshing process takes simply too long and often
calculation meshes must be fixed in order to achieve
converged solutions. Furthermore, although the casting
geometry has been received from the workshop, adding
the channels may involve considerable effort. For these
reasons, many foundries tend to trust to their empirical
knowledge
2
. However, fluid flow simulations should be
used in many instances, e.g. in aluminium die casting,
which is particularly because flow momentum plays a
crucial role in the mould filling process due the high
velocity of the liquid metal. Inertia effects may cause
splashing, jetting or undesirable filling of the metal flow
into mould cavity. When considering complex parts, the
accurate prediction of mould filling behaviour using only
empirical knowledge is virtually impossible
3
.
It is commonly accepted that shrinkage and gas are two major causes of porosity. The shrinkage porosity is associated with the hot spot in the casting. The gas
porosity has four different reasons: 1) Trapped air that is entrained in the injection system and cavity: 2) Gas generated from burned lubricants; 3) Gas generated from water that may be in cavity and 4) Hydrogen gas. The gas porosity due to the trapped air is an unwanted byproduct
of relatively high velocity injection method used. Gas
entrapment is caused by turbulent flow pattern generated
during metal injection process. The location, size and total
volume of contained gas porosity are influenced by the
method chosen to fill cavity with molten alloy. In high
pressure die casting, some efforts have been made to
reduce air entrapment by the modification of conventional
injection shot profile taking advantages of the
development of advanced and reliable control systems.
The paper describes Shot Sleeve simulations for the High
Pressure Die Casting Process. Different process
parameters were tested and plunger speed was optimised
by using simulation.
Shot Sleeve simulation
In the cold chamber die casting process, molten
metal is injected into the die cavity by means of a plunger,
which forces the metal flow through a horizontallymounted cylindrical shot sleeve. Usually, the shot sleeve
is only partially filled with molten metal, the amount of
metal depending on the volume of the casting piece and
its system. The remaining volume of the shot sleeve is
filled with air. Theoretical and experimental research work
has shown that the motion of the plunger, the shot sleeve
dimensions and the initial amount of metal in the sleeve
all affect the types of waves which are created during the
shot and furthermore, the amount of air which may
become entrapped
3
.
Fluid flow simulations should start in the sleeve and
comprise the moving boundary of the plunger. With this
model, the simulation of wave formation in the shot sleeve
and all of its effects, such as air entrapment, is possible. It
is not only desirable to define the critical velocity of the
plunger, but also to achieve optimal plunger acceleration
because this will help to create a stable wave front and at
the same time keep both turbulence and air entrapment to
a minimum. Theoretical research has shown that both
plunger velocity and acceleration affect wave formation
and air entrapment. By expanding the simulation model to
include the parameters and attributes of the die casting
machine, it is possible to simulate the filling process more
accurately.
In principle, the casting process can be divided into
three phases:
- pre-filling phase
- mould filling phase
- final pressure phase
The pre-filling phase serves the purpose of moving
liquid metal in the cold chamber towards the gate,
preferably without entrapping the air in the cold chamber.
The low velocity of the plunger enables the air to escape
via parting line or vents. The plunger velocity during the
pre-filling phase must be adjusted to a value that develops
a banked up wave that fills up the complete cold chamber
cross section. If the velocity is too low, the resulting wave
will not be sufficiently high, whereas too high a velocity
results in a surging wave that traps air. Mould filling phase
the plunger is accelerated to a high velocity. In this short
mould filling phase venting of the die cavity is practically
impossible.
In industry and in theoretical papers have been
suggested that some various degrees of cavity pre-fill is
preferrable. This means that the casting cavity is partially
filled with molten metal using slow shot velocity before
fast shot starts. These practises have shown equal or
superior quality of castings in terms of porosity and
surface finish compared to castings made by conventional
approach when fast shot begins immediately after the
shot sleeve and runner system are full of molten metal by
slow shot. However, injection parameters for machine set
points, such as pre-fill percentage and plunger
acceleration rate from slow to fast shot for the maximum
quality castings in terms of air entrapment are not known.
Most injection profiles used in industry are determined by
trial and error method
4
.
Several simulations were carried out using different
combinations of plunger speed and movement to
demonstrate importance of right plunger movement
profiles. Figures 1 to 4 shows a situation in which the
plunger is moving first of all at a constant speed and then
accelerated to high speed. Constant speed causes the
first wave which is quite shallow; however, when the
plunger speed is accelerated, it causes a very strong
splashing effect which reaches the shallow wave before
the end of the cylinder. These two waves entrap a
considerable quantity of air.

Hasil (Bahasa Indonesia) 1:

Dia menggunakan program simulasi menghemat waktu danmengurangi biaya desain sistem casting. Disaat yang sama mungkin untuk memenuhi kualitas produk yang ketat.Simulasi dapat membuat sistem pengecoran yang optimal: memungkinkanmemproduksi coran suara, berkualitas tinggi dengan lebih sedikitpercobaan. Penghematan selanjutnya lingkungan danekonomis penggunaan bahan dapat dicapai ketikaJumlah tes coran berkurang.Peleburan menggunakan sekarang banyak kode simulasi yangBerdasarkan model konduktor panas mana termalkonduksi di mencair dan pembebasan panas laten selamasolidifikasi dianggap.Aliran fluida simulasi kurang digunakan. Namun, misalnyaaluminium die casting begitu rumit di mana aliranmomentum memainkan peran penting dalam cetakan proses pengisiankarena kecepatan tinggi logam cair. Inersia efekdapat menyebabkan mengisi percikan, terbang atau tidak diinginkanaliran logam ke dalam rongga cetakan. Ketika mempertimbangkan kompleksBagian, prediksi yang akurat dari cetakan mengisi perilakumenggunakan pengetahuan empiris hampir mustahil.Di sebagian besar negara-negara industri, about70% dariDiecast bagian pergi ke industri otomotif. Aluminiumdiecastings mendapatkan penting dalam produksibadan-badan kendaraan ringan, misalnya digunakan dalam barumodel Audi mobil. Oleh karena itu, hal ini bahkan lebih penting hari inibahwa coran ini dapat diproduksi dengan kualitas tinggimetode. Dalam konteks ini simulasi ini menjadi lebihpenting dalam proses desain.Makalah ini menjelaskan keuntungan dari tembakanLengan simulasi untuk mencapai lebih baik desain sistem castingdi HPDC coran. Mengisi analisis digunakan untuk menentukanukuran dan lokasi gerbang serta tepat pelaridesain sistem untuk memastikan lengkap dan seimbangmengisi bagian. Simulasi tembakan lengan dalam tekanan tinggiProses Die Casting memastikan jebakan udara minimalselama fase pra-mengisi..PendahuluanSimulasi komputer berbagai macam yang secara bertahapmenjadi secara luas diakui alat dalam berbagai desainproses. Simulasi kode secara luas digunakan dalamindustri pengecoran. Simulasi komputer castingproses dimulai dengan solidifikasi pemodelan. Untuk inialasan, kode yang digunakan, dalam kebanyakan kasus, untuk panasmentransfer perhitungan untuk memprediksi hot spot danmenghindari porositas di coran1.Aliran fluida simulasi kurang banyak digunakan. Salah satualasan adalah bahwa hanya beberapa kode dapat secara memadaimensimulasikan arus yang sangat dinamis. Di sisi lain, Semuayang dikenal metode memerlukan gelar signifikan manusiausaha selama fase pra-pemrosesan simulasiproses. Hal ini akan mengecualikan penggunaan praktis sehari-hari sepertimetode, ketika sedang dimanfaatkan oleh rumit geometri:enmeshing proses mengambil hanya terlalu lama dan seringperhitungan jerat harus tetap untuk mencapaikonvergensi solusi. Selain itu, meskipun castinggeometri telah diterima dari bengkel, menambahkansaluran mungkin melibatkan banyak upaya. Untuk inialasan, banyak peleburan cenderung percaya untuk mereka empirispengetahuan2. Namun, aliran fluida simulasi harusdigunakan dalam banyak kasus, misalnya di aluminium die casting,yang merupakan terutama karena aliran momentum memainkanperanan penting dalam cetakan mengisi proses karena tinggikecepatan logam cair. Inersia efek dapat menyebabkanpercikan, terbang atau mengisi tidak diinginkan aliran logamke dalam rongga cetakan. Ketika mempertimbangkan bagian kompleks,prediksi yang akurat penggunaan cetakan mengisi perilaku hanyaempiris pengetahuan hampir mustahil3.Secara umum diterima bahwa penyusutan dan gas adalah dua penyebab utama porositas. Porositas penyusutan ini dikaitkan dengan hot spot di casting. Gasporositas memiliki empat alasan yang berbeda: 1) terjebak udara yang entrained di sistem injeksi dan rongga: 2) Gas yang dihasilkan dari pelumas dibakar; 3) gas yang dihasilkan dari air yang mungkin dalam rongga dan 4) Hydrogen gas. Porositas gas karena terjebak udara adalah produk sampingan yang tidak diinginkanmetode injeksi kecepatan relatif tinggi digunakan. Gasjebakan disebabkan oleh pola aliran turbulent yang dihasilkanselama proses logam injeksi. Lokasi, ukuran dan totalvolume gas yang terkandung porositas dipengaruhi olehmetode yang dipilih untuk mengisi rongga dengan paduan cair. Tinggitekanan die casting, beberapa upaya telah dilakukan untukmengurangi jebakan udara dengan modifikasi dari konvensionalinjeksi ditembak profil mengambil keuntungan daripengembangan sistem kontrol canggih dan handal.Kertas menjelaskan simulasi tembakan lengan tinggiTekanan Die Casting proses. Proses yang berbedaparameter diuji dan pendorong kecepatan dioptimalkandengan menggunakan Simulasi.Ditembak lengan simulasiDi ruang dingin die casting proses, cairlogam disuntikkan ke dalam rongga mati dengan sebuah pendorong,yang memaksa aliran logam melalui horizontallymounted silinder lengan ditembak. Biasanya, lengan ditembakhanya sebagian diisi dengan logam cair, jumlahtergantung pada jumlah bagian pengecoran logam dansistemnya. Volume sisa sleeve ditembakdiisi dengan udara. Pekerjaan penelitian teoritis dan eksperimentaltelah menunjukkan bahwa gerakan plunger, lengan ditembakdimensi dan jumlah awal logam di lenganSemua mempengaruhi jenis gelombang yang diciptakan selamamenembak dan selanjutnya, jumlah udara yang mungkinmenjadi terperangkap3.Aliran fluida simulasi harus mulai di lengan danterdiri dari batas bergerak plunger. Dengan inimodel, simulasi pembentukan gelombang di lengan ditembakdan semua efek, seperti jebakan udara, mungkin. Ituini tidak hanya diinginkan untuk menentukan kecepatan kritispendorong, tetapi juga untuk mencapai percepatan optimal plungerkarena ini akan membantu untuk menciptakan gelombang yang stabil depan dan disaat yang sama menjaga turbulensi dan jebakan udara untuka minimum. Theoretical research has shown that bothplunger velocity and acceleration affect wave formationand air entrapment. By expanding the simulation model toinclude the parameters and attributes of the die castingmachine, it is possible to simulate the filling process moreaccurately.In principle, the casting process can be divided intothree phases:- pre-filling phase- mould filling phase- final pressure phaseThe pre-filling phase serves the purpose of movingliquid metal in the cold chamber towards the gate,preferably without entrapping the air in the cold chamber.The low velocity of the plunger enables the air to escapevia parting line or vents. The plunger velocity during thepre-filling phase must be adjusted to a value that developsa banked up wave that fills up the complete cold chambercross section. If the velocity is too low, the resulting wavewill not be sufficiently high, whereas too high a velocityresults in a surging wave that traps air. Mould filling phasethe plunger is accelerated to a high velocity. In this shortmould filling phase venting of the die cavity is practicallyimpossible.In industry and in theoretical papers have beensuggested that some various degrees of cavity pre-fill ispreferrable. This means that the casting cavity is partiallyfilled with molten metal using slow shot velocity beforefast shot starts. These practises have shown equal orsuperior quality of castings in terms of porosity andsurface finish compared to castings made by conventionalapproach when fast shot begins immediately after theshot sleeve and runner system are full of molten metal byslow shot. However, injection parameters for machine setpoints, such as pre-fill percentage and plungeracceleration rate from slow to fast shot for the maximumquality castings in terms of air entrapment are not known.Most injection profiles used in industry are determined bytrial and error method4.Several simulations were carried out using differentcombinations of plunger speed and movement todemonstrate importance of right plunger movementprofiles. Figures 1 to 4 shows a situation in which theplunger is moving first of all at a constant speed and thenaccelerated to high speed. Constant speed causes thefirst wave which is quite shallow; however, when theplunger speed is accelerated, it causes a very strongsplashing effect which reaches the shallow wave beforethe end of the cylinder. These two waves entrap aconsiderable quantity of air.