The following are quick suggestions that will help ensure a mold performs optimally.
What’s your CAD file format?
3D printing/additive manufacturing systems often still use the .STL format to define the geometry of the part. .STL files describe a part’s surface primarily through the use of triangles. Many CAD file formats use curves to describe features. If you’re sending a part originally created for 3D printing, consider using the STEP file and then clearly define the desired thicknesses to avoid potential problems with the design of the mold.
Ensure you have sufficient draft
Draft is a simple, effective way to ensure a part can be easily removed from a mold. For some parts, it can improve overall moldability. A general rule of thumb is based on the depth of the mold—use 1-degree of draft per inch of depth.
Watch wall thickness
–If possible, don’t use varying wall thicknesses. Uniform wall thickness helps deliver a stronger part. Material choice plays a role here as some materials require specific thickness dimensions to maintain part strength.
–Some aspects of wall thickness to watch include if a wall is too thin, it can sink or warp. A thin wall should be no less than 40-60% of the width of adjacent walls.
–In addition, recommended practice is to move from thick to thin areas gradually. Otherwise, parts or segments of parts may be weak and/or sag.
–Parts need to cool after injection molding. Some cool a bit in the mold, most cool more after removal from the mold. Naturally, thin areas will cool faster than thick ones. Since cooling is not uniform, cooling differences could lead to weakness, sink and warp.
Notes on parting lines
Designers often try to make parting lines as unnoticeable as possible. Mold makers trying to accommodate this preference usually face manufacturing challenges. In addition, accommodating this desire will increase the cost of the mold. Parting lines affect the aesthetic and can affect the mechanical operation of a part. Recommendations are to watch various features close to the parting line, such as a radius. It can lead to undesirable results such as flash.
Radii can help material flow into a mold more easily, but they can also create problems. Recommendations are to use them only as necessary, for example in critical functional areas of a part, or for better customer experience when handling the final part. Well placed radii, such as in a corner, can create stronger parts.
Not only do undercuts cause challenges when ejecting parts from molds, they can increase manufacturing time. Part of this increase is due to the need for additional elements such as side-action cams or pickout inserts, which increase complexity.