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From Concept to Mass Production: Solving Dimensional Precision & Assembly Looseness
1. Project Background & Early Involvement
In the transition from 3D modeling to physical injection molding, modular products face unique challenges. We received an inquiry regarding the development of a plastic plant-like splicing product. Unlike static decorative items, this product required users to splice multiple stems and leaves together manually.
The client provided preliminary 3D STEP models with a clear mandate: the final molded parts must ensure a stable, tight fit. If the splicing joints were too loose, the “plant” would collapse; if too tight, assembly would be impossible for the user.
Proactive DFM Analysis
During the initial review phase, our engineering team conducted a comprehensive DFM (Design for Manufacturing) analysis. We identified that the long, thin geometry of the plant stems would be prone to uneven shrinkage, posing a high risk to the precision of the splicing interfaces.
We subsequently presented this risk assessment report based on data rather than sales pitches. This proactive technical communication established trust, and the project was officially launched.
KEY STEP
Risk Assessment & DFM
2. The Challenge: Assembly Gaps in T0 Trial
Despite thorough preparation, the issue appeared as predicted during the T0 (initial) mold trial: the “splicing joint” area of the plant stem exhibited significant assembly looseness.
The interlocking parts could not hold their weight, causing the assembled structure to wobble. This was not a design flaw, but a typical physical phenomenon in injection molding—uneven cooling shrinkage affecting the mating surfaces. Since our engineers had already identified this area as a critical tolerance control point, we immediately initiated a parameter optimization plan.
3. Deep Engineering Analysis & Solutions
To solve the assembly looseness in this splicing product, we needed to find a precise balance between “dimensional shrinkage” and “cooling solidification.” Below is our root cause analysis.
Issue: Connector Deformation
The Phenomenon
The mating connector pins on the stems were experiencing excessive shrinkage, consequently yielding dimensions that fell below the lower tolerance threshold.
Root Cause Analysis
The ejection force was prematurely applied while the material was still in a semi-solid state due to insufficient cooling time. This rapid action caused micro-deformation and excessive shrinkage after ejection.
The Solution
Locked cooling cycle time at 45 seconds.
Ensured the plastic achieved structural rigidity inside the mold before ejection, stabilizing the basic shape of the connectors.
Issue: Loose Splicing Fit
The Phenomenon
The "Dimensional Paradox." Although basic dimensions were stable, the female receiving holes remained slightly too large, preventing a tight grip.
Root Cause Analysis
Counter-intuitively, extending cooling time caused the plastic around the core pin to "freeze" too early against the mold steel, restricting its natural inward shrinkage. This left the hole larger than required for a friction fit.
The Solution
Fine-tuned localized cooling parameters.
We managed localized shrinkage to allow the hole to shrink just enough to create the perfect interference fit for splicing.
4. Results and Delivery
After rigorous parameter corrections and physical verification, the dimensional deviations of the mass-production samples were all controlled within tolerance limits. The splicing assembly feel met the design expectations perfectly—firm enough to hold the structure, yet smooth enough for assembly.
Timeline
On Schedule
Quality
Perfect Fit
5. Summary: Beyond the Drawing
“In precision injection molding, especially for splicing products, there is no such thing as a ‘perfect drawing,’ only ‘controllable tolerances.'”
This case reaffirms Zetar's core philosophy: True precision control is not just about making a product, but about converting uncontrollable manufacturing variables (like shrinkage and deformation) into manageable process parameters.
The ability to translate a drawing into reality largely depends on when the supplier gets involved. We do not simply execute drawings; we act as a "Technical Partner" in design. Through early flow analysis, structural optimization suggestions, and Root Cause Analysis during trials, we help clients avoid mass production risks and reduce trial-and-error costs.
For Zetar, this was not just a product delivery, but a complete technical realization of the original industrial design intent.
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