A few days ago, a client inquired about color variation issues among different plastic injection molded components and sought advice on better quality control measures for plastic color consistency.
The root of the client’s problem stems from their risk diversification strategy in procurement. They have distributed different plastic molds across multiple injection molding manufacturers.
While individual plastic components pass incoming quality inspection within the specified color tolerance range (between upper and lower limits), noticeable color discrepancies become apparent when all components are assembled into the final product.
From a procurement perspective, distributing molds across multiple plastic injection manufacturers is a reasonable strategy. This approach not only effectively mitigates risks but also strengthens negotiating power for better pricing.
While this distribution model may pose challenges for engineering quality control, we can implement specific measures to maintain both plastic quality and color consistency. Some of these methods require close collaboration with the procurement team to strike a balance between engineering quality and procurement profitability.
Here are several methods that our company has either implemented or is considering, which we believe could serve as valuable references:
Centralized Plastic Coloring Process:
While most companies standardize their resin suppliers, few regulate the coloring process. It’s crucial to centralize plastic coloring with a qualified masterbatch or coloring specialist. All injection molding suppliers should source colored resin from the same provider or send raw resin to the same coloring facility. Even slight variations in coloring batches from the same supplier can cause inconsistencies, let alone using multiple vendors. Centralization ensures color uniformity across different injection molding plants.
Ideally, the resin manufacturer should handle the coloring process. This approach maintains both resin quality and color consistency. However, this often requires significant order volumes, and not all resin manufacturers offer this service (e.g., Sabic does, while Polyone and Samsung do not). Resin manufacturers are less likely to compromise material properties or use recycled materials, ensuring mechanical integrity and quality.
Consolidate Molds for the Same Product:
While diversifying injection molding suppliers is beneficial, molds for the same product—especially matching components like upper and lower housings—should be placed at the same supplier. This minimizes color discrepancies and simplifies troubleshooting for dimensional issues.
Distributing molds for the same product across multiple suppliers doesn’t effectively mitigate risk; if one supplier fails, the entire product line may halt. However, if multiple molds are available, distributing them across suppliers can still be considered.
These strategies balance risk management with quality control, ensuring both consistency and reliability in production.
Refining Color Tolerance Standards:
If all plastic components meet the specified color tolerance limits but still exhibit noticeable color mismatches when assembled, the tolerance range is likely too broad.
While some companies apply a uniform tolerance across all colors for simplicity, human perception varies—especially for pure white and black, where even minor ΔE differences are easily noticeable. It’s recommended to define specific ΔE limits for each color to ensure consistency.
Design Strategies to Mitigate Color Mismatches:
If market conditions allow, consider designing upper and lower housings in intentionally different colors during the IDV phase. This approach makes potential color variations less noticeable to customers, reducing the risk of returns and eliminating color-matching issues.
Standardizing Color Management:
The team responsible for plastic molds should create standardized color swatches, updating them at least every two years. Store these swatches in black bags to prevent light-induced fading. Additionally, define and document the L, a, b, and ΔE values for each swatch, along with their acceptable Δ ranges, to minimize color variation over time.
These measures ensure tighter color control, improve product aesthetics, and reduce quality-related risks.
Adopting Industry-Standard Color Systems:
Initially, my company used custom-defined color standards, but each time the color swatches were replaced, the colors shifted, causing significant challenges for suppliers in matching our requirements. To resolve this, we transitioned to using the Pantone color system, which is widely recognized in the industry.
This change not only streamlined the color-matching process but also improved consistency and reduced supplier frustration. Adopting an established standard like Pantone ensures better color accuracy and simplifies communication across the supply chain.