Navigator #7, March 2000
Impellers: Aluminum Investment Casting
Prototype aluminum casting is a great solution for functional testing. We created aluminum investment castings of an impeller design. Due to the complicated geometries and minute design differences, impellers and fan blades are two of the most challenging applications for functional testing if you’re looking for an inexpensive and expeditious method.
A combination of prototype aluminum casting and stereolithography, proved invaluable for functional tests in this case. The largest part prototyped using SLA was 14 inches (355mm) in diameter. Made of standard SLA resin, the impeller was tested at 4500 rpm. The aluminum investment castings were created based on the approved SLA pattern.
These tests allowed fine-tuning of the design before further testing it as a working prototype in a cast urethane. An entire family of impellers was eventually developed. The photo shows SLA impellers that were functionally tested. The parts were then created as prototype aluminum castings. Both QuickCast and active wax patterns were used. One of the benefits of testing with SLA parts is that they are so accurate that no additional balancing is necessary.
Open House
The open house was very interesting! Thanks to all our customers for allowing us to show their prototypes and applications. We displayed rib spreaders, notebook computers, surgical models, and woodburning fireplaces.
Thanks to all the customers who made the open house informational and to all of you who were able to attend the event. People even came from Israel.
Lastly, a special thank you goes out to our customers who donated gifts for raffle and door prizes. Donations ranged from water filters and boots to bundt pans and leaf blowers.
Guests attendees had the opportunity to see five SLA machines and an ACTUA machine running prototypes. Also, the guests were exposed to hands-on samples of RTV molding, rapid tooling, under-the-hood applications and metal castings.
Seasons greetings from all of us to all of you. Thanks for making 1999 a special year for Vista. Our best wishes to you and your as we enter the new millennium.
Rapid Prototyping Notes:
Keltool
Keltool is an extremely fast method of producing hard tool inserts for injection molding or die casting. The process starts with growing an SLA master pattern. The master pattern is not of the part, but it is a mold of the part (the core and cavity). After the SLA masters have been finished and polished to tolerance, they are put into a platinum-base, silicone rubber, soft mold. When the SLA masters are taken out of the rubber mold, they leave behind the negative pattern of the SLA mold.
An A-6 powder steel slurry, connected with a binder, is poured into the soft mold.
Once the slurry settles into the rubber and hardens, the insert is taken out and then put into a furnace. In the furnace, the binder is melted out in order to bring it to a green state. Once all the binder is out, the insert is then copper impregnated. This brings the tool to the consistency of 70% A-6 steel and 30% copper.
The tolerance of Keltool is +/- .002 inch per inch, with a tool insert size limitation of 6"x8"x4". There is a .006" shrink factor added to the SLA to offset the shrinkage rate of the Keltool process.The process of getting inserts takes between 8-10 days.
These inserts still need to have the parting lines matched, core pins and ejector pins added, and be ground to fit a Mudd set. If heat-treated, the inserts can become up to 45 Rockwell in hardness.
The Keltool process is owned by 3D Systems from Valencia, CA. These inserts have been used in production applications to produce over 1 million parts using a 35% glass-filled nylon. Keltool works best for low tolerance, highly detailed parts. The Keltool process also works for creating electrodes. Instead of using an A-6 steel slurry, a tungsten slurry is added for a strong electrode master.
New Software
Magics RP is a computer software system recently installed at Vista. This software, which is written by Materialise, will aid us in better serving our customer's needs. With Magics RP, Vista can now accept IGES files from any CAD system and turn them into STL files. (An STL file is what is needed to make a stereolithography part.)
Two of the basic operations Magics RP provides are measuring parts and rescaling parts. It also offers more difficult operations such as hollowing of parts and advanced cutting of parts.
One of the main features Vista uses is the importation of IGES files. When importing an IGES files, Magics RP automatically calculates all of the triangles needed to make an STL file. After the STL file is created, we can look at it more carefully to make sure all of the required details are there. If we find any problems with the STL file, we are able to manipulate it in several ways. We have the ability to fix flipped triangles or remove extra triangles. We can also fill holes and create new triangles where needed.
Magics RP allows us to hollow out a part giving it a specified wall thinkness. Doing this will cut down on the overall volume of the part, which saves the customer time and money by reducing build time and using less resin. When producing a hollowed out part, supports are generally left on the inside. This should not affect the exterior appearance of the part if this is what is needed for the prototype. Hollowing out a part will not work for all applications; but if a customer is interested in it, we can take a closer look and decide if a hollowed out part will work for them.
In the next year, Vista will be able to aid customers even more using Magics RP, since we will be going through software training. We will be trained on all of the features that relate to stereolithography. Some of the methods we will be learning are advanced cutting of parts, detailed support editing, and more efficient ways to manipulate STL files.
Quick Quip
"People forget how fast you did a job--but they remember how well you did it."
-Howard W. Newton
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