Small Home Appliance Structure - Plastic Part Screw Stud Design (Design Template)
Time：2025-11-07 08:09:44 / Popularity： / Source：
In plastic product manufacturing, screw studs are both fundamental and crucial. Their design quality directly impacts stability of connections and overall performance, making in-depth research on this topic highly worthwhile and necessary.
Connection and Fixing: This is primary function of screw studs. They tightly connect multiple plastic parts or plastic parts to components of other materials, forming a stable structure.
In electronic products, motherboard and casing are fixed using screw studs and screws, ensuring stability of internal components and preventing poor circuit contact due to movement.
Precise Positioning: During assembly, screw studs help components to be accurately positioned. By rationally designing position and spacing of screw studs, other components can be guided to be installed in predetermined positions, improving assembly accuracy.
Stress Dispersion: When plastic parts are subjected to external forces, screw studs can disperse stress, preventing stress concentration at a single point that could lead to breakage.
On plastic casings subjected to significant external forces, screw studs, in conjunction with screws, distribute external force evenly, enhancing the overall strength and durability of plastic parts. Easy to repair and disassemble: Plastic parts connected with screw studs are relatively easy to disassemble when repair or replacement is needed. Simply unscrew screws to separate components without damaging the overall structure.
This is particularly advantageous in scenarios such as electronic product repair and mechanical equipment maintenance, reducing maintenance costs and difficulty.
Adaptable to different material combinations: Screw studs can connect plastic parts with other materials such as metal and wood.
In some electronic products, connecting a plastic casing to a metal heat sink using screw studs leverages insulating and lightweight properties of plastic while utilizing excellent heat dissipation properties of metal.
Common Types of Screw Studs
Stud with Standard Screws:
Structural Features: This is the most basic type, generally cylindrical with an open top and internal threads for screw insertion or smooth holes. Threads are usually standard specifications, such as metric or imperial threads.
Application Scenarios: Widely used in various plastic products, such as assembly of electronic product casings, like connecting back cover and mid-frame of a mobile phone using ordinary screw studs; and in home appliances, such as fixing casing of a television to internal circuit board bracket.
Structural Features: A metal nut is pre-embedded inside screw stud. Metal nut can be a copper nut, stainless steel nut, etc., and it bonds tightly to plastic. This design utilizes high strength and wear resistance of metal nut.
Embedded nuts mainly include thermosetting nuts, injection-molded nuts, and ultrasonic nuts; this article mainly discusses design of self-tapping screw studs, and embedded nut screw studs will be discussed in a later article.
Application Scenarios: Suitable for applications requiring resistance to large tensile forces, torques, or frequent disassembly. For example, connecting plastic parts around a car engine; due to vibrations generated during engine operation, embedded nut screw studs ensure a stable connection and prevent loosening.
Dimensional Parameters: Diameter, height, and thread specifications of screw stud have a significant impact on its performance.
We need to study how these dimensions are determined in different application scenarios and relationships between them.
For example, screw studs for large plastic equipment housings may have larger diameters and heights to withstand greater external forces, and thread specifications must also be adapted.
Wall Thickness Design: Analyze relationship between screw stud wall thickness and the overall wall thickness of plastic part.
Appropriate wall thickness ensures strength of screw stud while avoiding shrinkage and deformation problems caused by uneven wall thickness.
If wall thickness is too thick, shrinkage marks are likely to occur; if it is too thin, strength will be insufficient.
Material Properties: Different shrinkage rates of plastic materials will cause changes in dimensions of the screw studs after molding and cooling.
Materials with high shrinkage rates may lead to large dimensional deviations in screw studs, affecting precision of fit with screw.
For materials like PE, which have relatively high shrinkage rates, it is necessary to allow for appropriate shrinkage allowance when designing screw studs, or to compensate for shrinkage through optimized mold design to ensure dimensional stability of screw studs.
Structural Strengthening: This research investigates how to enhance strength and stability of studs by adding reinforcing ribs, fillets, and other structural elements.
It explores impact of parameters such as shape, number, and location of reinforcing ribs, as well as fillet radii, on stud performance.
For example, adding a fillet of appropriate radius at the base of stud can distribute stress and prevent cracking.
Basic Principles of Stud Design
Stud Dimensioning:
What is appropriate distribution of outer and inner diameters?
How should height and wall thickness of stud be designed?
How should mating dimensions between stud and screw be given?
Here, I'll provide a design dimension template that I've found very useful in my own learning and work. Using this template as a reference during design will generally prevent major problems!
1. Screw stud and hole dimensions are designed according to standard ABS material. Adjustments should be made appropriately for other materials.
2. Screw types are limited to PA and PB.
3. Minimum screw stud height is 3.5mm for 1.0-1.7mm diameters and 4.0mm for 2.0-3.0mm diameters.
4. Reinforcing ribs should be considered when the total screw stud length exceeds 10mm.
5. H1, H2, and d1 are minimum dimensions; d2 must have positive tolerance.
Stud Fitting Issues
Chamfered Stud Mouth: This facilitates alignment during assembly, preventing misalignment during initial screw tightening; it also prevents material compression during screw driving, which can cause deformation and bulging of stud end face, affecting assembly accuracy and causing screw hole breakage. Chamfer size is generally 0.5, depending on stud size.
How to Add Reinforcing Ribs?
How to Determine Size and Shape?
Reinforcing Ribs: Adding reinforcing ribs around or inside stud enhances its strength and rigidity. Shape, number, and position of reinforcing ribs must be designed based on stress conditions of stud. Triangular reinforcing ribs strengthen stud and allow for smoother material flow.
Rounded Corners: Rounded corners at the base of stud disperse stress, preventing stress concentration and cracking. Fillet radius is typically a certain proportion of plastic part's wall thickness, such as 0.25-0.5 times.
During injection molding and cooling of plastic parts, uneven shrinkage due to differences in wall thickness is main cause of stud shrinkage. Long studs have a large height-to-diameter ratio, and wall thickness at root tends to accumulate, resulting in slow cooling and formation of depressions or pores.
For materials like ABS, shrinkage rate is 0.5%-0.7%. If wall thickness at stud root exceeds 1.2 times that of adjacent area, risk of shrinkage increases significantly.
Sink Relief Structure: By designing a recessed area at stud root, local wall thickness is reduced, balancing cooling rate.
Depth of sinker is typically 20%~30% of stud's outer diameter.
For example, for a screw stud with an outer diameter of 5mm, crater depth is 1~1.5mm, and diameter is about 60%~70% of outer diameter.
For further reading, please refer to Small Home Appliance Structural Design – Plastic Part Wall Thickness (with Mind Map and Material Lis.
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