3D Print for Durable, Accurate Patterns
Sand casting patterns can be 3D printed with PolyJet or FDM Technology for substantial savings in cost, labor and time, ultimately speeding new product development.
Sand Casting With PolyJet and FDM Patterns
The green sand casting process uses a mold made by pressing a pattern into a sand mixture. The pattern leaves a cavity into which molten metal is poured. This process works well for low–volume production. With automated equipment, it can be efficient for high–volume production. Three common types of sand casting patterns are:
- Loose patterns, which simply replicate the cast piece; patterns are not connected to other patterns or mounted on a plate.
- Cope and drag patterns, or split patterns, are like loose patterns with a gating system added and a split along the parting line.
- Matchplates are similar to cope and drag patterns except the cope and drag sides are combined into a single piece.
Producing sand molds and cast metal parts is relatively straightforward and suitable for automated methods that can reduce cycle time and labor. However, fabricating the patterns is often difficult, time-consuming and expensive. The most common approach is to produce aluminum patterns using CNC machining. The biggest problems with this approach are the high cost and lengthy lead time. The potential for problems, such as incorrect shrink compensation and design flaws, means the initial pattern often must be redone, which adds to the expense and lead time. It is not usually practical to machine the intricate gate and runner systems on CNC machines because testing is required to finalize the design. Instead, the gate and runner system is cut from Ren board or a similar material and then hand–carved and sanded to the finished shape. Constructing the gating system adds expense and lead time.
Because of the problems associated with traditional pattern production, foundries have long been interested in 3D printing (also called additive manufacturing). With 3D printing systems available from Stratasys, foundries can fabricate patterns with either inkjet-based technology or FDM Technology. This results in substantial savings in cost, labor and time, ultimately speeding new product development.
PolyJet or FDM patterns are a best fit for sand casting when:
- Molds are intended for prototype or production use
- Casting designs need verification
- Gate and runner refinements are likely
- Castings will be complex or large
Benefits of PolyJet and FDM patterns for sand casting include:
- Pattern cost reduction of 50 to 70 percent
- Lead-time reduction of 30 to 70 percent
- Faster design revisions
- Interchangeable gate and runner system
- 3D print the master: In CAD, design a master that will maximize the capabilities of inkjet or FDM. Print the master, which will become the pattern, with the best build parameters for the desired surface finish and strength.
- Accommodate parting: Mount the pattern on parting-line elements (which can be FDM or inkjet 3D-printed fixtures). The parting line helps avoid issues with undercuts.
- Mount the casting pattern and parting line elements on a wooden plate. The parting–line elements will be fixed in place to the plate.
- Apply a surface release agent on the 3D-printed master pattern.
- Create the mold: Pour sand around the pattern and parting line element and remove the pattern. A cavity appears in the shape of the pattern, the upper half forming the cope and the lower half forming the drag.
- Use the mold: Pour the molten metal in the cavity. Once it cools, it can be removed and finished.
Application Outline — PolyJet
FullCure materials, which work with Stratasys inkjet 3D printing systems, have good mechanical properties, allowing them to endure foundry environments and last longer. Sand casting facilities use inkjet technology to create mold patterns when they want high-resolution printing with exceptionally fine details and smooth surfaces right out of the printer, and because inkjet 3D printing offers materials that fit the requirements of this niche application. When using inkjet materials, a lacquer significantly hardens the pattern surface without affecting the finish. Check with a Stratasys application engineer for lacquer recommendations.
Application Outline — FDM
All of the thermoplastics that FDM technology uses have the high compressive strength required for green sand casting patterns. The surface finish of the FDM master can be optimized through build orientation and/or through a secondary process such as sanding. The Finishing Touch Smoothing Station uses a semi–automated process to smooth FDM parts to near–injection-molded quality. This also seals the mold surface, which keeps the release agent from penetrating and sand from sticking. The ability to build highly accurate, large, complex patterns fast and inexpensively makes FDM a clear advantage over traditional methods.
How does FDM compare with traditional tooling methods?
|CNC Matchplates||$5,000||3-4 weeks|
|FDM Tooling Matchplates||$2,000||1.5 weeks|
|SAVINGS||$3,000 (60%)||1.5-2.5 weeks (37%-62%)|
Tools Without Tooling
3D printed tools, molds and tool masters add a new layer of cost efficiency and flexibility to the factory floor. Not only can you cost-effectively produce tools for prototype testing and manufacturing low volumes of final parts, you can create made-to-order assembly tools customized for each task. In addition, you can create a leaner manufacturing environment, enabling quick production of tools, when and where they’re needed to speed the manufacturing process and reduce costs.
Optimized assembly tools, made to order
Improve manufacturing efficiency with job-specific jigs and assembly fixtures, 3D printed on demand in just hours. 3D printing tools directly from CAD data, on-demand, saves time, lowers costs and reduces inventory requirements. In addition, you can easily create customized lightweight, ergonomic tools that increase workflow efficiency.
3D printed Injection molds
Imagine producing injection molds without costly CNC tools. With Stratasys thermoplastics and photopolymers, you can quickly 3D print injection molds to evaluate prototype parts or produce low volumes of end use parts. This is especially useful to test the design, fit and function of products before mass production. If changes are required, new mold iterations can be 3D printed in just a few hours at minimal cost.
3D print customized, low volume durable parts with fine details and smooth surface finishes
Stratasys additive manufacturing enables you to 3D print strong, functional final parts on demand directly from CAD data. Because the part is created digitally layer by layer, complex geometries and sophisticated features that would be difficult to produce using traditional manufacturing methods are now easily achieved with Stratasys additive manufacturing. Producing end use parts with Stratasys technology not only dramatically reduces your production costs and delivery times, it also reduces inventory while creating exciting new supply chain efficiencies and new business models.