A Simple Guide to Design Screw Bosses - Guidelines, Challenges and Solutions
Before installing screw bosses on your injection molded parts, it’s best for you to follow the best design guidelines to create them. The primary function of the screw bosses is to help strengthen your injection-molded parts’ structure. However, if you are not careful, screw bosses can also break your injection-molded parts.
Basic Guidelines to Design Screw Bosses
There are various aspects you need to consider before creating a design for screw bosses. Here are some basic guidelines to design screw bosses:
●Diameter of Screw Bosses.
How long should the diameter of the screw bosses be? The diameter of the screw bosses must at least be the same as the injection-molded parts’ wall thickness and size. This is to provide the necessary support for the injection molding.
●Size.
The screw boss size should also follow the overall design of the injection molded parts, meaning that you should create a balanced proportion when you consider the screw boss size. Larger size will help you give more strength to the injection-molded parts, but you need to avoid creating oversized screw bosses.
●Location.
Where will you locate the screw bosses? This is also another important question when designing the screw bosses. Different locations will need to have different designs, depending on the surrounding area of the injection-molded parts. The best locations you can put the screw bosses are around the areas where the primary stresses for the injection-molded parts reside. This way, the screw bosses can provide an additional strength around these areas.
●Material.
Another important consideration is the material that you use for the screw bosses. It’s best to use the same primary material for the screw bosses as the materials of the injection-molded parts. This can help prevent any material incompatibility problems.
●Screw Bosses Factor or Thickness Selection.
Each material you can use to build screw bosses has their thickness selection recommendations. So, you can refer to the thickness selection or boss factor recommendations for each material. For instance, ABS has 2.00 Boss Factor, whereas PET has 1.80 Boss Factor.
●Spacing.
How many boss screws are you planning to install? It’s important to consider the spacing between each boss screw. Make sure that the spaces between screw bosses are not too thin, as it can be counterproductive for the plastic injection molding parts you are working on.
●Draft angle.
The draft angle guideline for screw bosses is quite simple. You need to set at least 0.5 draft angle for the outer screw bosses surface. This is to simplify the ejection process of the screw bosses later, as not to cause any damage to the injection-molded parts.
Challenges in Designing Screw Bosses
In designing screw bosses, there are some challenges you need to know, which can potentially put your design into jeopardy. Here are some challenges in designing screw bosses:
●Tight spacing.
Tight spacing between screw bosses is a common challenge in the screw boss design, as it can cause various problems within the injection-molded part. For instance, tight spacing can create unnecessary pressures in too many areas around the screw bosses, which can lead to material damage.
●Damages around screw bosses area.
When you install screw bosses around the injection-molded parts, you might damage the surrounding area if you are not careful. Screw bosses that are too tight might cause damages in the surrounding areas, which can be difficult to fix.
●Sink marks.
Sink marks often appear around the screw bosses’ bottom area if you don’t follow the design guidelines carefully. The sink marks are characterized by the sinking appearance of the ground around where you install the screw bosses.
●Different cooling times on screw bosses.
Sometimes, there will be different cooling times between the upper part and bottom part in the injection molding services. Thus, when you install screw bosses and the injection-molded part has different cooling times between the upper area and lower area, it will result in extended lead times for the injection molding process, which can cost more money for your production.
●Shrinkage.
Shrinkage can also happen when you apply screw bosses, whether it is the shrinkage of the screw bosses or the injection-molded parts. It can be a challenge to deal with shrinkage, as it will change the overall shape of the screw bosses later.
●Compatibility between materials.
Between screw bosses’ materials and the injection-molded parts’ materials, there might be incompatibility. When this happens, you might not be able to get the result you want from installing the screw bosses.
Solutions to Create the Best Screw Boss Design
●Aim for the best material compatibility.
Material incompatibility can cause various problems for the injection-molded parts, such as weak support for the structure and bad screw boss performance. Check the materials before making the screw bosses and see whether it will be compatible with the injection-molded parts or not.
●Change the screw bosses size and geometry.
It’s best for you to design screw bosses for the best strength, so that it can hold the injection-molded parts well. If you think that the screw bosses are too weak, too thin, or might be subject to shrinkage, it’s best for you to change the size and geometry of the screw bosses.
●Pick the best screw boss locations.
The screw boss locations need to be considered well, as you can’t put too many screw bosses and line them up too close. Pick the right locations for these screw bosses to strengthen the structure of the injection molding(overmolding, insert molding, and silicone rubber molding).
●Rapid prototyping the screw bosses.
Before releasing the screw bosses and installing them on your injection-molded parts, you need to do some testing first. Thus, to avoid any mistakes in the screw boss design, it’s best for you to create some prototypes of the screw bosses and test them to see which one is best to support the injection-molded parts.
●Add metal materials as inserts.
Another solution you can try to strengthen the screw bosses is to add metal materials as inserts when you make them. A small metal insert can strengthen the structure of the screw boss, which can then help strengthen the overall structure of the injection-molded part.
Conclusion of designing screw bosses
The guidelines to make screw boss design can be quite complicated, but unless you follow the guidelines, problems can happen when you install the screw bosses. It’s best to stick to the guidelines and use the best solutions to prevent any problems in your screw boss installation.
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