Plastic Injection Molding Manufacture In China

Titoma has years of experience in designing molds and complex plastic assemblies and ensure optimal manufacturability and adherence to requirements. During the mold design stage, Titoma engineers will formulate the appropriate mold making strategy for the project by doing an in-depth evaluation of the product’s enclosure and designing the most cost effective mold and production process to ensure optimal manufacturing based on—

- surface finish required

- plastic material

- precision requirements

- number of parts you want to produce

- your budget

An Introduction to Molds for Plastic Injection

An injection mold (or tool) will be necessary for an electronic project that requires a custom plastic or metal enclosure (housing). A mold is a hollowed-out block of steel that is injected with molten material such as plastic, which then hardens to take on the counterpart shape of the mold.

Molds can be made from a variety of steels. In the West, people tend to opt for higher quality steel since it constitutes a lower percentage of total cost of the mold, whereas in Asia, it comprises significantly more since labor costs are lower.

Examples of some common steels used in plastic injection include P20, NAK80, H13, and S7. Each vary in terms of—

- hardness

- wear resistance

- compression strength

- corrosion resistance

- machining ease

- polishability

- weldability

Plastic Injected Enclosures

Custom plastic enclosures give your electronic products the greatest freedom in shape and the lowest cost per unit. It begins to make financial sense to invest in a mold at quantities of 250 pieces and up. And once you have invested in molds, the more you produce the more you save. In fact, plastic enclosure is the cost component on which you can realize the largest cost difference between Asia and the West.

Some Common Plastics Used in Enclosures

PC(Polycarbonate)

ABS(Acrylonitrile Butadiene Styrene)
PP(Polypropylene)

Description:
Polycarbonate has excellent impact strength, clarity, and optical properties and can be molded to tight tolerances.

Description:
ABS plastic has good mechanical toughness, dimensional stability, chemical resistance, and ease of fabrication.

Description:
Polypropylene is widely used and inexpensive but is difficult to mold to precision.

Advantages:
High impact resistance
Clarity
Good flammability performance
Dimensional stability
Chemical resistance (PC blends)

Advantages:
Good impact resistance
Excellent processability and appearance

Advantages :
Excellent moisture resistance
Good impact strength
Inexpensive

Disadvantages:
Subject to stress cracking Yellowing after long term

Disadvantages
Poor solvent resistance Melts easily

Disadvantages
Degraded by UV

 

Plastic Injection Problems

Injection molding is an art in itself. While a good mold design will increase the chance of getting well-molded enclosures and parts, it is also essential to use the correct plastic injection parameters appropriate to the parts being produced and material used; otherwise the parts may come out defective.

Common Molded Part Defects
Defect Description Cause
Burn marks Burnt areas at furthest points from injection gate Injection speed likely too high; mold lacks venting
Flash Excess material Too much injection speed/material injected; parting line on the tool may be damaged; clamping force too low.
Flow marks Wavy lines or patterns Injection speed too slow
Knit lines Small lines on parts Caused by the plastic flowing around an object; can be minimized or eliminated with a mold-flow analysis.
Sink marks Depressions Time and pressure too low; cooling time too short; enclosure walls may be too thick.
Short shot Incomplete parts Injection speed or pressure too low
Splay marks Lines/Marks Gas or moisture flow along the part during injection process
Warping Warped part Cooling time too short; material is too hot

 

Metal Enclosures

Metal enclosures contribute tremendously to giving your device a high-end quality look and feel. A custom metal enclosure made in China or Taiwan can become cost effective at quantities as low as 200 pieces. We have at our resources fast turn-around milled (CNC) metal enclosures for electronics at reasonable prices. Once you get to quantities of 500 units, you can significantly lower the unit cost by going for a stamped metal housing produced using a progressive die. Alternatively, to get more form freedom you could go for die-cast housings in zinc or magnesium.

 

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