What are the surface quality requirements for the processing of injection-molded parts for household appliances?

The surface quality of injection-molded parts of household appliances directly affects the aesthetics, functionality and user experience of products, so there are strict requirements for surface quality during processing. The following are common surface quality requirements and related instructions:

First, the appearance defect control

1. No obvious shrinkage marks.

Definition: The depressions or wrinkles formed on the surface of plastic parts due to uneven shrinkage of internal materials.

Requirements:

Visible appearance (such as shell, panel) is not allowed to have visible shrinkage marks;

Non-external surfaces (such as internal structural members) can be slightly shrunk, but the assembly and function should not be affected.

2. No weld marks (mold closing line)

Definition: Linear trace formed by the rejoining of molten plastics after shunting in the mold.

Requirements:

The weld marks on the appearance surface shall be controlled in the width ≤0.1mm, the depth ≤0.05mm, and the color shall be consistent with the periphery;

Precision parts (such as transparent parts and high-gloss parts) need to eliminate weld marks as much as possible through mold design (such as adding cold cavities) or process adjustment (increasing injection pressure).

3. No burr and flash

Definition: Excess material edge at the edge or parting surface of plastic parts.

Requirements:

All visible surfaces and assembly surfaces must be completely deburred and feel smooth and scratch-free;

The flash of gaps or hidden places should be controlled at a thickness of ≤0.03mm to avoid affecting the fitting of parts (such as buckles and slots).

4. No bubbles and air lines

Definition: bubbles or lines along the material flow direction formed by gas retention on the surface.

Requirements:

Bubbles with a diameter greater than ＞0.5mm are not allowed on the appearance surface, and dense bubbles (such as pits) need to be completely eliminated;

The air pattern length should be controlled outside the visible area of the appearance surface (for example, by adjusting the position of the glue inlet or increasing the exhaust slot).

Second, the surface roughness and texture

1. Roughness requirements

High-gloss surfaces (such as home appliance panels and decorative parts):

Ra (arithmetic average roughness) ≤0.2μm, which needs to achieve mirror effect, and is commonly used in acrylic, PC/ABS and other materials;

It needs to be achieved by mold polishing (such as manual polishing after EDM) or surface plating (such as electroplating and vacuum evaporation).

Matte surface (such as remote control housing, rice cooker handle):

Ra=1.6~6.3μm, which is delicate and non-reflective, and needs to be realized by pattern biting (sandblasting, chemical corrosion) or surface spraying matt paint;

The texture should be uniform, and there is no local difference between too deep and too shallow.

2. Special texture requirements

Imitation of metal texture: mirror surface or wire drawing effect can be achieved by electroplating (such as nickel and chromium), water transfer printing or metallic paint spraying, and the adhesion of the coating should be ensured (such as reaching the standard by grid method);

Leather/fabric texture: The texture is reproduced by die embossing process, requiring clear details and no deformation at the edges, which is common in household appliance handles or decorative strips.

Third, the consistency of color and gloss

1. Color accuracy

Color difference control:

It shall conform to the color cards specified by customers (such as Pantone and RAL), and the △E (color difference value) shall be ≤1.5 (the difference is hard to be detected by naked eyes);

In mass production, it is necessary to control △E≤0.8 for the same batch of products and △E≤1.2 for different batches to avoid "yin and yang color".

Color uniformity:

Uneven local color depth (such as discoloration caused by uneven material temperature) is not allowed, especially for large-area solid color parts (such as white refrigerator panels).

2. Gloss consistency

Gloss range:

High gloss parts: glossiness (measured at 60) ≥85GU (gloss unit), and the difference between different areas of the same part ≤ 5Gu;

Matte parts: Glossy ≤20GU, with uniform surface haze and no local reflection difference.

Fourth, functional surface requirements

1. Scratch resistance

Hardness standard:

The appearance surface must pass the hardness test (such as pencil hardness ≥2H) to avoid scratching in daily use;

The hardness can be improved by surface coating (such as UV paint) or material modification (adding glass fiber reinforcement).

2. Antistatic and easy to clean

Antistatic requirements:

The shell of household appliances (such as televisions and air conditioners) often needs a surface resistance of ≤ 10 9 Ω to prevent dust adsorption, which can be achieved by adding antistatic agents.

Easy to clean:

Kitchen appliances (such as microwave oven panels) need a smooth surface without pores, and stains can be easily wiped. Oil-repellent coatings (such as Teflon treatment) are often used.

3. Accuracy of assembly surface

Smoothness of mating surface:

The surface flatness tolerance of assembly areas such as screw holes and snap positions shall be ≤0.1mm to avoid assembly looseness caused by warping or deformation;

It is necessary to control the internal stress of plastic parts by optimizing the mold cooling system or adjusting the pressure keeping process.

V. Means of detection and control

Visual inspection: Observe the surface defects at a distance of 30cm under a standard light source (such as D65 light source), which must meet the AQL (Acceptable Quality Limit) standard (such as appearance surface AQL = 1.0);

Instrumental measurement:

Roughness meter (such as Mitutoyo SJ-210) detects Ra value;

A color difference meter (such as Konica Minolta CR-400) measures the △E value;

Glossy instrument (such as BYK-Gardner 4440) measures the GU value of glossiness;

Destructive test: Scratch and drop tests are carried out on the sampled products to verify the surface adhesion and impact resistance.

summary

The surface quality requirements of injection-molded parts of household appliances are both aesthetic (such as color and luster) and functional (such as scratch resistance and easy cleaning), which need to be comprehensively guaranteed by mold design, material selection, process parameter optimization (such as temperature, pressure and cooling time) and strict quality inspection. The surface standards of different products (such as white goods and small household appliances) will be further refined due to different usage scenarios. For example, kitchen appliances pay more attention to oil resistance and high temperature resistance, while consumer electronics pay more attention to appearance exquisiteness.