In product design, electroplating, with its proven and stable metallic finish, has become a key tool for enhancing product aesthetics and performance. Especially in plastic parts, proper structural and mold design are crucial for determining electroplating quality. This article will systematically analyze key structural design points and mold design principles for electroplated plastic parts, providing engineers with practical technical guidance.

Electroplating utilizes electrolysis to uniformly and densely deposit a metal or alloy on a workpiece surface, forming a well-bonded metal coating. Simply put, an electric current drives metal ions to settle on workpiece surface, ultimately creating a metallic finish with a high gloss or matte finish.

Electroplating not only enhances product appearance but also imparts special properties to workpieces. It can be categorized into three main categories, as shown in table below:

Plastic electroplating requires activation of substrate. Activation requirements vary significantly for different plastics. Currently, ABS is the most commonly used material in industry due to its strong coating adhesion and low cost. Typical process is as follows:
Substrate pretreatment: ABS plastic part surface is cleaned to remove oil, dirt, and impurities.
Activation: Chemically enhances plastic part surface's ability to absorb metal ions.
Coating deposition: Copper (priming, enhancing adhesion), nickel (corrosion protection, increasing hardness), and chromium (for decorative effects) are sequentially deposited. Ideally, the total coating thickness is approximately 0.02mm. In actual production, due to variations in substrate quality, thickness often needs to be increased to 0.05-0.08mm.
Post-treatment: Check coating's flatness and adhesion, and remove any excess impurities.
In addition, localized electroplating can be achieved through "two-color injection molding." ABS and PC (non-electroplating-reactive) are injection-molded in a two-color mold. During electroplating, coating forms only on ABS area, achieving desired localized metallic effect.

Different electroplating effects require specific mold treatments and coating processes. Specific correspondence is as follows:
High-gloss plating: Mold surface requires a high-gloss finish, and a "bright chrome finish" is used when plating plastic part, resulting in a mirror-like metallic effect.
Matt plating: Mold surface also requires a high-gloss finish, and a "sub-chrome finish" is used when plating plastic part, resulting in a matte metallic texture.
Pearl chrome: Mold surface requires a high-gloss finish, and a special coating process (with addition of pearl powder particles) creates a metallic effect with a delicate shimmer.
Texture plating: Mold surface is first textured (e.g., sand or leather grain), and a bright chrome finish is used when plating plastic part, resulting in a "metal base + texture" composite effect.

Structural design directly determines success of electroplating, as well as performance and appearance of final product. Strict control is required across four dimensions: substrate selection, surface quality, structural details, and special requirements.

ABS is preferred: ABS has 2-3 times adhesion of plating to ordinary plastics and costs only 60% of PC/ABS alloy, making it the most cost-effective solution.
Zero-defect plastic surface: Electroplating can magnify injection molding defects (such as bubbles, flow marks, and shrinkage). Therefore, during injection molding, ensure:
Plastic material is thoroughly dried (moisture content ≤ 0.1%) to avoid surface pores;
Use of mold release agents is prohibited (they can impair plating adhesion and cause plating to fall off);
Surface flatness tolerance ≤ 0.05 mm/m, with no scratches or flash.

Appearance and Wall Thickness Design
Surface Protrusion Control: Protrusion height must match length, with a maximum protrusion height of 0.15mm or less per centimeter (e.g., for a 10cm long plastic part, maximum protrusion should not exceed 1.5mm) to prevent uneven coating thickness during electroplating.
Sharp Edge Treatment: All sharp corners must be rounded (R ≥ 0.5mm) to prevent "point discharge" during electroplating (resulting in excessively thick coating in certain areas) and to avoid scratches during use.
Wall Thickness Control: Wall thickness must be between 1.5-4mm. Too thin (<1.5mm) can cause deformation at high temperatures (60-70℃) during electroplating. Too thick (>4mm) can easily cause injection molding shrinkage and bubbles in coating. If thin-walled structures (e.g., 1.0-1.5mm) are required, reinforcing ribs (rib width 1/2-2/3 of the wall thickness, height no more than 3 times wall thickness) must be added to weak areas to prevent deformation during electroplating.
Hole and Slot Design
Blind hole depth limit: Depth of a blind hole must not exceed 1/2 hole diameter (e.g., for a φ5mm blind hole, depth should be ≤ 2.5mm). Otherwise, bottom of hole will not be fully exposed to plating solution, resulting in "no plating" or "uneven color." If a deep blind hole is necessary, indicate on drawing that "plating effect is not required at the bottom of hole."
Hole and slot spacing: Center-to-center distance between adjacent holes/slots should be ≥ 2 times hole diameter (e.g., for a φ3mm hole, spacing should be ≥ 6mm). This prevents residual plating solution from causing corrosion on hole wall.
Hanging and Sprue Design
During electroplating, workpieces must be suspended from a hanger. Structural design must reserve a dedicated hanging area:
Hanging Area Location: Preferentially located on non-exterior surfaces (such as inside or edges of product) to avoid damaging appearance due to hanging marks. Common designs include "square holes" or "bosses" (e.g., a 10×10mm square hole with a depth of ≥5mm).
Sprue Location: Sprue must be located away from exterior surfaces and have a diameter of ≥3mm to prevent breakage during electroplating, potentially causing workpiece to fall off. Furthermore, sprue must form a "support structure" with workpiece to enhance its resistance to deformation during high-temperature electroplating.
Avoiding Metal Inserts: Metal inserts are prohibited in plastic parts. Thermal expansion coefficients of plastics and metals differ significantly (ABS's is approximately 7×10⁻⁵/℃, while steel's is approximately 1.2×10⁻⁵/℃). At high electroplating temperatures, these differences in expansion and contraction allow plating solution to seep into gaps, leading to cracking in plastic part or loosening of insert.

Match Dimension Reserve (for Sliding Fits)
Electroplating increases workpiece size, so clearance reserves are required in advance:
Ideal plating thickness is 0.02mm, with a practical maximum thickness of 0.08mm. Therefore, single-sided clearance for sliding fits must be ≥ 0.3mm (for example, for a shaft-sleeve fit, shaft diameter must be at least 0.6mm smaller than hole diameter) to prevent sticking after electroplating.
Localized Plating Solutions
When only a portion of a product requires plating (e.g., a button arm that requires flexibility and cannot be hardened by plating), following three solutions can be used:

Mold design bridges gap between structural design and electroplating process. It must balance injection molding quality with electroplating requirements, focusing on key aspects such as glue feeding, cooling, parting, and materials.

Glue feed method directly affects surface quality of plastic parts and electroplating effect. Following principles must be followed:
Glue Feed Type: Prefer side, top, or slider glue feed. Latent glue feed is strictly prohibited (latent glue feed automatically cuts off when it is automatically cut off, generating powder that adheres to plastic part surface and causes plating to fall off during electroplating).
Glue Inlet Size: Inlet diameter should be ≥3mm (to prevent gate breakage during electroplating), and feed scar should be located on a non-appearance surface or in an area that does not affect assembly.
Number of Gates and Hot Runners: When slender parts (length > 100mm) require multiple gates, a sequential valve hot runner system must be used to control weld line location (plating is prone to pinholes at weld line).
Case Study: A slender trim strip originally designed with a single gate experienced insufficient holding pressure and shrinkage. After switching to a two-point sequential valve hot runner, shrinkage was eliminated and electroplating appearance met standards.

Shrinkage rate selection: Shrinkage rate for electroplated parts should be determined based on material properties and injection molding process. The lower end of material's shrinkage range should be selected (e.g., standard shrinkage rate for ABS is 0.5%-0.7%, so 0.5% is recommended for electroplated parts). This is because high temperature during electroplating causes slight shrinkage of plastic part, and high injection pressure (to eliminate shrinkage marks) reduces actual shrinkage rate.
Length allowance: For products with high length precision requirements (such as automotive trim strips), a "glue reduction allowance" should be designed at both ends (0.2-0.3mm per 100mm of length). Adjustments should be made based on actual dimensions after mold trials to avoid length deviations after electroplating.

Strength Design: Electroplated parts require injection molding using high-speed, high-pressure technology (to prevent shrinkage and air bubbles). Mold must possess sufficient impact resistance.
Mold Thickness: Thickness of movable and fixed mold plates should be ≥ twice maximum product height (e.g., if product height is 20mm, mold thickness should be ≥ 40mm).
Guide Pin Diameter: ≥ 1/8 mold thickness (e.g., if mold thickness is 40mm, guide pin diameter should be ≥ 5mm) to prevent misalignment during mold closing.
Mold Core Material Selection: Different mold cores require different hardnesses to avoid wear and damage:

Note: NAK80 was commonly used for front mold core in the early days, but its hardness (HRC40) makes it easily dented by slider, resulting in product flash. Switching to 2343 ESR solved this problem.

Parting line and core pulling method affect post-electroplating appearance and require specific control:
Parting Line: Electroplating can magnify "bulges" (protrusions on the edge of plastic part) at parting line. Therefore:
Preferably, use large sliders or concealed pull-out sliders to reduce number of parting lines (for example, at the bottom buckle position of product, using a large slider pull-out instead of multiple small bevels can reduce number of parting lines from three to one);
Parting lines must be avoided from exterior surface. If avoidance is unavoidable, a "parting line concealment structure" should be designed (for example, placing parting line within a groove on part edge).
Core Pulling Method: For core pulling near exterior A surface, beveled pulls are strictly prohibited (beveled pulls move in mold opening direction, which can easily lead to uneven product edges, which is more obvious after electroplating). Slider core pulling is required;
Multiple small sliders/beveled pulls should be combined into a "large slider/large beveled pull-out" to avoid multiple mold split lines (which can easily cause plating discontinuities at mold split lines).

Ejection method must avoid damaging part surface and affecting electroplating effect:
Ejector Component Selection: Ejector blocks and flat ejector pins are preferred. Conventional ejector pins are prohibited (ejector pins tend to leave "ejector pin marks" on part surface, which cannot be concealed after electroplating).
Preventing Whitening: Case Study: A product was ejected using a flat ejector pin. Whitening occurred after increasing injection pressure. This was because high pressure pushed flat ejector pin downward, deforming ejector plate. After pressure was released, ejector plate rebounded, causing whitening.
Solution: Replace flat ejector pin with an insert and add auxiliary flat ejectors around perimeter of part to distribute ejection force.
Ejector Pin Details: Tip of ejector pin should be rounded (R ≥ 0.2mm) to prevent sharp edges from causing localized "non-plating" (discharge from tip affects plating deposition).

Slender parts (such as moldings and grilles) are prone to deformation due to uneven cooling during injection molding before electroplating. Therefore, cooling water circuits must meet following requirements:
Layout: Perpendicular to length of part (e.g., for a 100mm long molding, water circuits should be arranged along width) to ensure uniform cooling;
Segmented circuits: Utilize "segmented inlet and outlet" (e.g., one independent water circuit for every 50mm of length) to independently adjust temperature of each section and control product warpage;
Water channel distance: Center of water channel should be 15-20mm from part surface, with 30-40mm spacing between them to avoid cooling dead spots (which can cause uneven shrinkage in plastic part and cause deformation after electroplating).

Reserve Vent Holes: Design vent holes (diameter 0.5-1.0mm, depth 0.1-0.2mm) at weld lines and closed areas (such as bottom of blind holes) to prevent air marks and pockets during injection molding, which can affect electroplating adhesion.
Mold Draft Angle: Mold draft angle for all exterior surfaces should be ≥1.5°, and for non-exterior surfaces ≥1° to prevent surface damage during demolding (scratches will be magnified after electroplating).
Avoid Corner Design: All corners of mold parts that require quenching (such as mold cores and sliders) should be rounded (R ≥0.5mm) to prevent cracking during quenching.
Hanging Points: Mold should have "electroplating hanger points" (such as bosses or square holes) on non-exterior surfaces of plastic part. Diameter of hanger points should be ≥5mm to ensure stable suspension of workpiece during electroplating and prevent deformation.
Surface Texture: For parts that do not require a high gloss finish, mold surface can be treated with a "pear dot or embossed pattern" (texture depth). 0.05-0.1mm), which can not only improve coating adhesion but also cover minor injection molding defects.

Even if you master design principles, problems can still easily occur in real-world projects. Following are common mistakes and solutions:

Design of plastic electroplated parts is result of a synergistic combination of "structure, mold, and electroplating process." Core logic is as follows:
Structural Design: With goal of "preventing deformation and maintaining surface finish," control wall thickness, hole depth, and hanging position, and reserve clearance.
Mold Design: With goal of "improving quality and adapting to electroplating," we optimize injection molding process, cooling, and ejection, and select appropriate mold core material.
Process Collaboration: Communicate with electroplating plant in advance to clarify coating thickness, localized electroplating requirements to avoid disconnects between design and process.
Only by integrating technical details throughout the entire design process can we ensure the final product possesses both excellent appearance and performance, while also improving production yield and reducing costs.