Direct shell sand rapid prototyping: from CAD to casting in days.

by:INDUSTRIAL-MAN     2019-09-27
Creating functional casting prototypes from CAD data, this new application of fast prototyping can open more doors for casting applications.
Current Science of rapid prototyping (RP)
About 10 years ago, when a fragile, inaccurate size \"touch and feel\" model was produced to help three
The dimension and psychological conception of the graph.
It is found that these models are useful in verifying the shape and fit of the part.
Today, the science of RP has evolved to the point where it is possible to use multiple materials to make very precise, durable parts using multiple prototyping methods.
With the improvement of the RP method, foundry workers have obtained more durable models, and for some applications, innovative modders have a new way to make patterns, even a tool.
Unfortunately, from the casting point of view, there is no RP method that can produce metal castings that simulate the sand casting production process.
For operating a foundry worker, successful prototyping means making a prototype metal part directly from his CAD file and using the metal and casting process for final production.
In order for foundry workers to be able to compete with other metal forming alternatives, a functional cast metal prototype must be produced quickly for testing.
Two of the most accepted methods for functional prototyping of cast metal parts are CNC machining and a variant of investment casting, before casting, various RP models will be made from ceramic shells
Unfortunately, these relatively high-cost manufacturing techniques do not provide a high-yield foundry who produces castings in the sand, and the sample parts have physical properties similar to those manufactured by resin
Sand casting process.
Another RP process close to sand casting is the Soligen process.
In this RP method, inorganic colloidal silica adhesive is sprayed on alumina after being treated with citric acid.
The reaction in the layering/construction process forms the gel mold, which is then sintering in the high temperature oven to produce the core and the mold.
This process produces precise, complex castings, but the use of inorganic adhesives (not common in the foundry) and the tendency of the mold to break further during the pouring process limit its use.
But a new process.
Rapid Forming of direct shell sand (DSS RP)-
It has emerged from the prototype method for the production of metal castings and can be used for accurate evaluation and testing.
Dss rp is a combination of three processes of computer-aided casting design;
Selective laser sintering is a closed laser sintering of molten powderlike material;
And Shell mold process.
Although each of these three processes is currently used by metal casters, combining them, the foundry worker can produce a metal casting whose physical and metallurgical properties are produced with sand cores and molds
In addition, dss rp supports extremely complex prototype castings
Manifold, cylinder head and even engine block-
Produce quickly and accurately for evaluation.
Dss rp was launched in Europe in 1995 with the title direct cutting laser-
Dss rp is a sintering process developed and sold outside the United StatesS.
Through the photoelectric system (EOS)-
Zeiss Group, Munich, Germany. In the U. S.
Dss rp technology is distributed by DTM company.
Austin, Texas, with the trademark name \"sand form \".
The process starts by converting CAD files to stereo printing (STL)file.
The prototype device is in STL format.
After the STL file is transferred to the prototype device, the prototype mold and/or core are formed by selective laser sintering of sand particles.
Dss rp can make sand cores and/or molds with pre-prepared silica or zirconium sandPainted with B-
Graded phenol/novolac resin. (A B-
Graded thermosolid plastic is a plastic that has been partially cured or aggregated and needs to reach the final curing stage or C-by being exposed to heat-Stage. )
By spreading the device, a thin layer of coated sand is applied on the entire surface of the construction area within the prototype machine.
After deposition, the sand that will become part of the mold and/or core is heated with C [O. sub. 2]laser beam [
Diagram omitted in figure 1].
When the coating melts on the outer surface of the sand, it is attached to the adjacent sand particles.
This time, the particles of the layer are combined with the shape of the reunion formed below.
When subsequent layers are combined and hardened, a specific shape is formed within the scope of the build volume.
With the application of each layer, the build platform is reduced to the machine until the height of the build is completed.
The total amount of material in the volume of the building consists of the specific bonded sand shape formed by the aggregated particles, surrounded and supported by uncured free flowing resin
Covered shell sand.
After the construction process is completed, the construction platform is lifted and the partially cured and uncured sand is removed from the machine.
Then, by simply brushing your teeth and blowing it away from the cured sand part, separate the cured sand mold and/or core from the loose sand.
After separation from the uncured sand, the partially cured mold and/or core is aftercured.
If you want to connect the sections together, this is at post-curing.
It is then set to fall.
It should be noted that any loose, non-bonded sand removed from the process is reusable and can be recycled back into the machine.
The standard aggregates currently used in dss rp are silica and zirconium sand.
However, almost any sand used in the \"standard\" Shell process can be used.
Usually, from about 90-
AFS/GFN and zirconium sand of about 110-100
120AFS/GFN is used.
Process Advantage * dss rp has little limitation on part complexity;
* Almost any geometry can be built within the size of the machine\'s build volume;
* Castings larger than the size of the machine construction volume can be manufactured by assembling the mold parts together;
* At the same time of mold manufacturing, the core can be built into the mold, so that the core in the mold can be accurately positioned (
Prevent inaccurate fine tuning and positioning size);
* The bottom can be built into the core and mold packaging;
* Draft angle is not required;
* Casting wall thickness as low as 1.
4mm production without any problems;
* The core can be formed in the unit for another casting process;
* Any metal used in the shell sand process can be used for dss rp.
Using traditional casting methods, even with the help of standard RP tools, the time required between CAD and first casting is usually 2-5 weeks.
Build time for dss rp, 1-
Cylinder head for two days, 4-
Cylinder head less than 1 week.
Even if the casting and gate system of the mold requires additional design time, the total processing time of the new cylinder head can be significantly reduced.
In addition to time-saving considerations, dss rp-
The cylinder head produced is almost the same as sand in all metallurgical and mechanical aspects
Casting parts that will be produced in the production phase.
This means that the test engine can be evaluated using parts with physical, mechanical and metallurgical properties similar to those that will be manufactured during the final production phase of manufacture.
Despite the benefits of technology, dss rp equipment may be costly for the foundry.
However, the foundry interested in this process has the option to use the service bureau.
These resources usually have expertise in equipment and operating equipment.
The service bureau also has a variety of processes and applications that allow the foundry to do some-stop shopping.
As with most RP-generated surfaces, another limitation of the technology is the obvious \"staircase-
Step on the outside of the part as the height increases. Stair-
Step type is applied by layer sand in z-
The way the axis is layered is that the new layer does not have the layer width below.
When the narrower layer is cured, a step is formed between the edge of the previous layer and the top edge of the new layer.
These steps continue along all the concave and convex surfaces, but the stairs can be eliminated almost by directional parts
Strengthen during the planning phase, or minimize by building with thinner layers.
Unfortunately, the thinner storey building extends the construction time and the thickness is limited to the diameter of the thickest coated sand.
Another solution is to polish the sharp edges, which can minimize the jagged appearance of the stairsstepping.
While the dss rp doesn\'t have a lot of limitations on part complexity, it does have a clear limit on mold and/or core dimensions based on build volume. The two-
Laser EOS machine with X, Y and Z build volume size 28X15X15-in. respectively.
The volume size of the DTM machine operated using a single laser is 13-in.
Diameter 15-in. in height.
The restrictions caused by the mold size limit do not constitute insurmountable obstacles.
If the goal is to make the part larger than the manufacturing volume size, the multi-core and mold parts can be fixed together before pouring, as shown in the mold assembly of BMW and VAW Mandl & Berger (
See the result of dss rp sidebar).
Prior to the recent introduction of dss rp, a breakthrough for RP was that most casting prototypes required secondary tools to produce prototype parts.
This results in the casting metal prototype assembly being manufactured only through a series of steps, which often results in a large amount of time delay.
Other metal forming processes such as welding parts and manual manufacturing can be produced and evaluated quickly.
This puts the sand casting supplier at a disadvantage, as customers are usually not in a hurry to start again once the testing procedure is started.
The development of dss rp allows sand casting plants to compete at a faster level and quickly translate the mold and/or core concepts into functional sand casting prototypes to evaluate their physical properties, metallurgical properties and parts properties.
General Advanced Development Lab show Step-by-
Steps to make a prototype casting using dss rp gm power system, introduced dss rp into its Advanced Development Laboratory (ADL)in January.
Its goal is to reduce lead time and cost associated with the development of Foundry products.
The laboratory has installed the DTM Sinterstation 2000, which is used with shell sand materials.
The universal power system selects this new process to avoid some of the previous secondary operations encountered by its investment casting prototype method.
Here is a step. by-
Step by step look at a compressor housing developed in the laboratory.
1 initially, on the CAD system, develop the compressor housing model with the mold inside the mold envelope.
The mold is split in order to remove the excess non-bonded sand after the mold/core construction is completed.
The metal feed path and cavity vent are added.
The STL file from the CAD system then applies the mold build, scale and direction parameters when sent to the machine to build the mold and core package.
Once the mold is made of phenol resin-
The zirconium sand is coated by laser sintering process to lift it from the building cylinder.
Then, remove the excess infinite sand from the cavity.
3 then put the mold and core into the curing furnace for latercuring.
The mold and the core are behindcured at 485F (250c)for 15-16 min.
Once cured, the half part of the mold is installed together and prepared for the molding operation by placing a bead glue around the joint to prevent the half part from being separated or displaced.
The construction volume of the DTM machine limits the casting size to 13-in. diameter by 15-in.
Height, so once the mold is cured, it is put into the room temperature nobake sand type containing the standard Gate, debris and runner.
Before pouring into our mold, close and prepare to cope with and drag the mold in a traditional way.
After pouring, the solidified mold enters a stable state.
Part of the laser in the mold-
Sintering has been further solidified due to exposure to molten metal.
So it\'s harder than the sand that contains it.
6 after removing the shell sand, the casting is completed in a conventional way.
The main benefit of this technology for the laboratory is the integration of dss rp into its current casting processes, materials and products.
Special tools are not required (
Other than dss rp devices)
, Customers receive accurate casting in a short period of time.
The daily use of dss rp produces experimental castings that exceed competition in terms of casting quality and responsiveness.
The following are the three stages of the dss rp mold assembly for the air-cooled aluminum motorcycle engine cylinder head.
The project was developed by BMW in Munich, Germany, and VAW Mandl and Berger in Linz, Austria.
As shown in Step A, the mold is very complex because the air-cooled wing piece is 2mm thin and must be formed by the horizontal wall of the outer mold section.
The entire mold assembly consists of six segments and a small core for the oil channel.
The gate and the risering system are integrated into the mold section.
As shown in Step B, the inlet and outlet channel cores are firmly integrated into adjacent external mold segments, allowing for tighter tolerances due to the lack of additional clearance between the channel core and the external mold segment.
The partial assembly of the mold in Step C shows how the mold section is assembled together.
Add a large section from above that contains the entrance and the riser and close the mold.
10 days after receiving the CAD date, two complete molds ready for casting are delivered.
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