Step-by-step guide
Definitions
Let's start with a few definitions.
A mold is a 3D negative part of an object with the goal of capturing all geometric features of the original part.
Moldmaking is the process of creating the 3D negative space to allow for creating reproductions that are identical to the original part.
A cast is the reproduction of the original part. Casts can be made from different materials depending on the requirements.
Casting is the process of reproducing the original part. The process consists of filling the mold cavity (or cavities) with materials that hardens (typically polymers - more on materials in Mold Materials, Mold Processes) and then removed from the mold once cured. Depending on the mold materials, casting can occur multiple times within the same mold.
The process of curing is the hardening of polymer materials.
Casting Production Cycle:
- Preparation of Material
- Filling the Cavity
- Curing Processing time
- Cooling/solidifying of the cast
- Ejection from mold
(For the purposes of Midnight Sun, we use molds (styrofoam, MDF, or others) to create the aerobody using materials such as carbon fiber.)
Design Considerations
In general, considerations must be made for mold design in any application, especially in mass manufacturing.
Repeatability: The mold should be able to be used multiple times, each producing a replica of the original part.
Efficiency: uses the available technology to minimize waste, optimize production, and reduce time.
Quality: These are the standards set by an industry or policies. In any case, quality is the ratio of value to cost. Does the product create enough value to the user for its cost?
Tolerances: This is the allowable margin of error or variations that is acceptable for reproductions of the original part. This would impact assemblies of objects, enclosures, open parts, and others.
Regardless of what type of mold and process is used, the reproduced part must be able to be removed from the mold. The more complicated the design is, the more difficult it gets to remove, thus designs must account for these properties.
Draft angles, the angle of taper away from the perpendicular (degrees), that are added to SolidWorks models to aid the removal of the object. More drafts are added depending on the complexity and textures in the design.
Fillets are rounded edges included in designs to facilitate the smooth flow of the cast material into the mold. Otherwise, issues such as air bubbles and will add stress to the part.
Vents are built in (depending on the casting process used) to allow for air to be better displaced by the casting material.
Creating Molds in SolidWorks
(Finally here, eh?)
Let's start with some simple models in SolidWorks to create molds out of. The method we are using is to create the negative space around the part. This would include intersecting the part with a "block" and removing the intersected space.
Simple Mold (with a symmetrical shape)
You can use any simple shape (sphere, rectangular prism, block, etc.) but for the purposes of this section, we will be using a sphere.