Injection molding solutions for screw holes in plastic parts

author: Universe plastic

2024-05-21

During the injection molding process of plastic parts, designing and manufacturing parts with screw holes is a common but challenging task. Screw hole injection molding needs to consider many aspects such as the functionality, strength and manufacturing process of the part. The following are suggestions from Universe Plastics engineers on screw hole injection molding design and process:

Screw hole design suggestions

Reasonable location: Screw holes should be designed in areas with smaller stress concentration and avoid weak areas.

Proper spacing: Proper spacing should be maintained between screw holes and between screw holes and the edge of the part to avoid stress concentrations and cracking.

Symmetrical layout: Try to use a symmetrical layout to disperse stress and improve the strength and stability of the parts.

Reserved hole diameter: Design an appropriate reserved hole diameter to facilitate subsequent thread processing.

Thread type: Choose a thread type appropriate for the plastic material, such as self-tapping or insert threads.

Mold screw hole design

Insert design: Design inserts in the mold to facilitate processing of threaded holes, and inserts are easy to replace.

Slider and ejector pin: For complex screw hole structures, use a slider and ejector pin design for smooth demoulding.

Uniform cooling: Ensure that the cooling system of the mold is properly designed to avoid uneven cooling in the screw hole area, which may lead to deformation.

Cooling channels: The cooling channels should be close to the screw hole area to provide effective cooling.

Injection molding material selection for products with screw holes

Mechanical strength: Choose plastic materials with high mechanical strength and toughness, such as polycarbonate, nylon, polybutylene terephthalate, etc.

Thermal stability: Choose materials with good thermal stability to ensure dimensional stability during injection molding.

Creep resistance: Choose materials with good creep resistance to prevent screw holes from deforming after long-term stress.

Injection molding process optimization

Injection pressure: Optimize the injection pressure to ensure complete filling of plastic melt and avoid material shortage at the screw hole.

Injection speed: Control the injection speed appropriately to avoid bubbles or burns caused by too fast and uneven cooling caused by too slow.

Holding time: Adjust the holding time to ensure that the screw holes are fully filled to avoid shrinkage and deformation.

Mold temperature: Control the mold temperature to ensure even cooling of the screw hole area and avoid deformation.

Barrel temperature: Optimize the barrel temperature to ensure good fluidity of the plastic melt and complete filling.

Post-processing and quality inspection

Thread processing: For screw holes that require high-precision threads, secondary thread processing, such as tapping, can be performed after injection molding.

Insert installation: For parts requiring high-strength threads, metal inserts can be installed during or after the injection molding process.

Dimensional inspection: Use tools such as vernier calipers and micrometers to inspect the aperture and thread accuracy of screw holes.

Pull-out test: Carry out a pull-out test to detect the strength and firmness of the screw holes.

Visual inspection: Use a microscope or high-definition camera to inspect the screw holes for surface quality and defects.

Example application

1. Electronic product casing

Material: Choose ABS or PC.

Design: The screw holes are designed near the structural reinforcement to ensure strength.

Process: Use slider design to ensure smooth demoulding of screw holes.

2. Automobile interior parts

Material: Choose PA or PBT.

Design: The screw holes are designed in thicker areas to ensure impact resistance.

Process: Insert installation after injection molding to improve thread strength.

Summarize

Screw hole injection molding involves many aspects from design, material selection, mold manufacturing to injection molding process optimization. By rationally designing the position and shape of screw holes, selecting appropriate materials and mold structures, and optimizing injection molding process parameters, problems encountered during screw hole injection molding can be effectively solved and the quality and performance of the final product can be ensured.

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