GUIDE TO PRODUCING INVESTMENT CASTING MOLDS WITH 3D PRINT N SCAN
Investment casting is a process used to cast metal components.
PolyJet models produced by 3D Print N Scan can be used to create a master model, which is then dipped in a ceramic slurry to produce the shell, which the final part will be cast in.
After the shell has been created, the PolyJet model can be burnt out, leaving a pattern to pore molten metal into, creating the final part.
3D printed patterns can be printed in a much quicker time, at a lower cost, and easily adjusted, saving time and money in comparison to the cost of metal tooling.
The cost of storing this traditional metal injection molding tooling is gone, and the space allowed to be re utilized for other organizational needs.
2. BENEFITS OF POLYJET TOOLING
A PolyJet mold saves money on the traditional costs associated with the manufacture of molds, with the cost saving of not having to produce injection mold tooling, the extra work involved in calculating the expansion and contraction of the mold and wax master pattern.
Savings in the storage and rack space needed is also gone, with no injection molding tooling required.
Minor adjustments can be easily made to the CAD file for the next part to account for shrinkage of the metal when cooling, leading to very accurate parts.
Once metal injection molding tooling has been manufactured at a cost of £3,000+ trying to add or remove material, to adjust the geometry of the final part is a costly process.
The cost of low volume production is greatly reduced with one offs and even volumes of parts in the hundreds, and is well suited for small runs of parts.
PolyJet patterns can also be produced in rapid time, in hours or a day or two, to have a part cast, where you can be looking up to 12 weeks to have a mold made by traditional methods.
3. DESIGN OF POLYJET PATTERNS
With traditional patterns there are several design considerations to take into account, but depending on the volume of parts you require, will depend if you need to go for the more expensive metal molds or use 3D Print N Scan to produce a PolyJet pattern for you!
- Draft angles – to aid the release of parts – These are not required with a PolyJet pattern, as the part does not need to be removed from a mold, so you can have a part produced square as intended.
- Parting lines & wear and tear – Over time injection molding tooling will wear changing the geometry of your final part, eventually leading to new tooling being required, Parting lines are also visible on injection molded parts where post processing of each part is required, to remove the flashing created around the edge of the pattern, this does not occur with a PolyJet part! Because there is no tooling to wear and no tooling to create a split line.
- Complex geometry – The production and associated cost of complex geometry, and costly tooling in producing holes, pins, undercuts, bridges and spirals, the list goes on! Is no longer an issue with a PolyJet mold pattern! As the part does not need ejector pins, sliding gates, plugs, guides or inserts, with 3D Printing the part is printed how you want it to look at a fraction of the cost.
- When Producing a PolyJet pattern all our standard materials can be used, but the preferred material is Vero Black, this is because of its low ash content at 0.02% in comparison to our other materials at 0.3%, this material offers strength for the remaining processes after 3D Printing.
- When designing your parts good practices in the design are still required, so your part forms properly in the mold, and material can flow correctly.
- Knife edges should be avoided, and a 0.25mm fillet should be added to all edges.
- General fillets should be a minimum of 0.8mm radii.
- Wall thicknesses should be a minimum of 1.5mm.
- The part as a whole should be shelled out, so all features have a 1.5mm wall thickness, to allow the part to burn out and not expand and crack the ceramic mold.
e.g. a 10mm wall should have a void of 7mm at its core.
- Shrinkage of the final metal part should be accounted for in the design also.
- Parts should be designed, so they get printed without the use of support material inside the part, this will require the part to be shelled out to the minimum wall thickness, and split into 2 or more parts.
The part will require keys or some type of feature to index the part and allow it to be assembled and bonded together after printing.
Tolerance of these keys or indexing features will need to be incorporated into the design, so the parts mate correctly after printing, with the male insert being 0.1mm smaller than the female part, outside surfaces should remain as per the original design.
Understanding how to design PolyJet parts for casting parts in the desired metal you require, can be a practical and extremely cost-effective solution for prototypes and small batches.
By utilizing the 3D Printing Service, 3D Print N Scan have to offer, and these design principles you can enable and start to enjoy the benefits and the design freedom associated, and get your designs produced in the minimal amount of time and into the market place.
STRATASYS. www.stratasys.com/-/media/files/design-guides/dg_pj_investmentcasting_1217a.pdf. 12TH August 2017.