In hot runner systems, based on number of injection points, they can be divided into single-point nozzle injection, multi-point open or pin-point injection, or needle valve injection. In multi-point injection systems, a manifold is required. Manifold is a core distribution and temperature control unit located between main nozzle and secondary nozzles. Its primary function is to precisely distribute and guide melt entering main nozzle to each secondary nozzle, then from there to gates to complete injection molding process. Simultaneously, it ensures uniform heat distribution and minimal pressure loss throughout melt flow path.

 

As "central hub" of hot runner system, splitter plate's core functions can be summarized into three main aspects:
Precise Melt Distribution: Single stream of melt from self-contained nozzle is evenly and precisely distributed to inlets of each secondary hot nozzle through internal runner system, ensuring consistent material feeding to each cavity;
Precise Management: Through embedded heating strips or heating tubes combined with insulation design, plastic melt within runner is maintained at a constant process-set melting temperature, with temperature fluctuations controlled within ±3℃.
Mechanical load-bearing and sealing: Maintain structural rigidity of hot runner system while ensuring absolutely reliable sealing interfaces between manifold and each nozzle and main nozzle, eliminating material leakage at its source.
Core technical control point for this component is thermal expansion and flow balance. Taking an S136 or P20 manifold as an example, when heated from room temperature (20℃) to an operating temperature of 250℃, linear expansion can reach 1.0-1.5mm. If this expansion is not properly guided and compensated, it will translate into huge thermal stress, directly leading to sealing surface failure, template deformation, or damage to positioning system.

 

Manifold design is far more than a simple "drilling and wiring" process; it is a systematic engineering project integrating rheology, thermodynamics, and mechanical design. Its core revolves around two key aspects: "flow balance" and "thermal expansion compensation," ensuring both melt flow and structural stability meet requirements.

Core objective of flow channel system design is to achieve melt flow balance and minimize pressure loss and melt retention. Specific design principles and requirements are as follows:
Layout Principles: Prioritize natural balance layouts (such as H-shape, X-shape, I-shape) to ensure complete symmetry in length, number of bends, and geometry of flow channels from main nozzle to each secondary nozzle. This layout is simple to debug and highly reliable, making it preferred solution for automotive component molds (such as multi-cavity symmetrical parts like door panels and pillar trim panels).

 

When cavity layout cannot be symmetrical due to product structure, a rheological balance design is required: by adjusting diameter or length of each branch runner, time and pressure of melt reaching all gates are kept consistent. This design must be verified, optimized, and confirmed using mold flow analysis.
Runner Diameter Calculation: Runner diameter (D) is a key parameter balancing pressure loss and melt residence time, and needs to be determined in two steps:
Initial Value Estimation: Estimated based on plastic type and injection volume per runner. For general plastics such as ABS and PP, initial range for main runner diameter is 8-16mm;
Final Value Verification: Verified by shear rate to ensure shear rate of melt in runner is controlled between 500~1500 s^-1, avoiding excessive shear heat generation leading to melt degradation, or excessive shear causing cold material problems.
Runner Geometry Requirements:

 

Cross-section Type: A fully circular cross-section must be used to minimize internal surface area and flow resistance, reducing risk of melt stagnation.
Corner Design: All turns must have rounded transitions (R≥3mm preferred) to completely eliminate dead zones and facilitate color changes and melt flow.
Material Compatibility: To avoid internal corrosion of hot runner, high-chromium mold steel is preferred for processing runner, especially suitable for processing corrosive or glass fiber reinforced plastics.

Thermal expansion compensation is core of manifold mechanical design. Design goal is to ensure precise alignment of axes of all mating runners across the entire operating temperature range, with sealing surfaces always tightly fitted, without gaps or offset.
Expansion Calculation:
Basic Calculation Formula: Expansion = Length * Temperature Difference * Expansion Coefficient
Three key parameters must be clearly defined during calculation: characteristic length of manifold in calculation direction, linear expansion coefficient of mold steel, difference between operating temperature and assembly room temperature.
Core Compensation Strategies (Combined use of three strategies)
Center Positioning, Surrounding Floating: Typically, only one tight-fitting locating pin is set at the center of manifold, while remaining positioning uses clearance-fitting anti-rotation pins, allowing manifold to expand freely radially from center outwards.
Pre-reserved Thermal Gap: An air insulation gap larger than calculated expansion amount ΔL must be reserved between manifold and surrounding mold plates (fixed mold plate, backing plate) (usually 1.5-3.0 mm on one side). This gap also serves as insulation.
Axial (Nozzle Direction) Pre-compression: Through precise height calculation of pressure ring/pad, a pre-compression (typically 30%-50% of the total axial expansion) is achieved between manifold and nozzle system during room temperature assembly. During operation, thermally expanded portion releases this pre-compression force, ensuring consistent sealing surface contact while preventing excessive thermal stress from being transferred to mold plate.

 

(Common manifold layouts shown in image above: two-point feed splitting plate, four-point feed splitting plate, twenty-four-point feed splitting plate; appropriate layout can be selected based on number and arrangement of cavities.)

Core principle of manifold selection is to find optimal solution between technical performance, project cost, and delivery cycle. This requires comprehensive consideration from three dimensions: heating system, main material selection, and standard/customized component selection, while also developing a selection plan based on project scenario.

Heating Power Calculation: Heating power needs to be calculated comprehensively based on mass of manifold, target temperature rise, heating time, and heat loss (radiation, conduction, convection). Empirical estimation standard: For a steel manifold operating at 200-300℃, heating power required to maintain temperature is approximately 40-60 W/kg (heating power needs to be increased by 2-3 times based on this, and can be adjusted according to actual heating time requirements).
Heating Element Arrangement: Heating rods (tubes) should be evenly arranged as close as possible to flow channel, ensuring good contact between heating element and mounting hole wall. If air gaps exist, they must be filled with thermal paste to ensure efficient heat transfer.
Thermocouple Arrangement: Temperature measuring points need to be accurately set in critical hot zones and temperature-depleted areas, such as end of flow channel, heating blind zones, and intersection of multiple flow channels, to achieve accurate and sensitive detection of melt temperature, ensure accuracy of closed-loop temperature control.

Main material for manifold needs to be selected based on plastic processing temperature, plastic type (whether it contains abrasive fillers), and product appearance requirements. There are two main categories:
2311 (P20 Modified): Pre-hardened to 28~30 HRC at factory, with excellent processing performance, requiring no subsequent heat treatment to avoid deformation during processing; good thermal conductivity, moderate cost, suitable for molding most general-purpose plastics (PP, PE, ABS, PS, etc.), with a working temperature typically ≤250℃, making it the most commonly used and economical preferred material in industry;
2316 (S136 Modified)/H13: Requires heat treatment to 48-52 HRC, with higher hardness, better wear resistance and corrosion resistance, suitable for processing temperatures >300℃, long production cycles, high appearance requirements, or engineering plastics containing abrasive fillers such as glass fiber/minerals (e.g., PPS, PPA, LCP, etc.). Although procurement cost is higher than 2311, advantages in mold life and maintenance cycle are significant.

Practical Advice for Purchasing and Cost Engineers:
Early Intervention: During mold quotation stage, require mold engineers to clearly define manifold selection scheme and incorporate selection costs and timelines into the overall mold evaluation;
Prioritize Standardization: Use standard products whenever possible, never choose custom parts (general plastic conventional molds / (Suitable for symmetrical multi-cavity molds); If initial design leans towards customization, fine-tuning of design is required in collaboration with mold and product engineers. Gate position offset should be within ≤5mm, and cavity layout symmetry deviation within ≤3°. Standard manifolds should be prioritized for adaptation; minor design changes can significantly save costs and reduce risks.
Exceptions for high-end scenarios: For high-precision parts (such as high-gloss interior parts) and molds for special working conditions, customized manifolds can reduce mass production defect rates. A comprehensive evaluation of initial design costs and long-term mass production costs is necessary.
Scientific supplier selection:
Standard parts: Prioritize mainstream hot runner brands (imported: YUDO (automotive-specific, high temperature control accuracy), Synventive (high-precision electronic components/...) High-gloss parts have strong adaptability; HASCO/DME (complete standard parts system), etc.; Domestic: Maxtor (multi-cavity symmetrical manifold, high cost performance), etc., with rich standard product series, stable supply chain, and comprehensive technical support;
Custom parts: Focus on evaluating supplier's non-standard design capabilities and past successful cases, rather than just focusing on processing capabilities; Domestic custom parts can prioritize Best (needle valve type hot runner manifold, excellent sealing performance), Hotes (short customization cycle, adaptable to special layouts of automotive molds), etc., while verifying their R&D capabilities, quality control system, and delivery capabilities.

Manufacturing quality of manifold is physical basis for its design function. Core processing requirements are to ensure quality of flow channel, dimensional accuracy, and integrity of sealing surface. Standardized processing procedures must be followed, process parameters of each process must be strictly controlled, full-process inspection and testing must be carried out.

 

Core Process: Deep Hole Drilling (Gun Drill)
Purpose: To machine circular flow channels with a large length-to-diameter ratio, ensuring straightness of flow channels;
Requirements: Hole wall surface roughness Ra ≤ 0.8 μm (Ra ≤ 0.4 μm when machining glass fiber/mineral reinforced plastics), small straightness error, no obvious drilling spiral marks or intermediate tool steps;
Key Points: Use 4-10MPa high-pressure cooling oil for internal cooling and chip removal, with a cooling oil flow rate ≥ 20L/min to ensure sufficient drill bit cooling and timely chip removal, avoiding scratching of hole wall or drill bit wear; after machining, a 100% internal inspection using an industrial endoscope is required to check for hole diameter deviations, tool steps, and other problems.
Flow Channel Polishing: After deep hole drilling, flow channels are subjected to fluid polishing (abrasive flow) or electrolytic polishing to further reduce hole wall roughness to Ra 0.2-0.4μm, ensuring smooth melt flow, no stagnation, no degradation, and facilitating color change.
High-precision machining of mating holes
Heating rod fixing groove: CNC machined to ensure uniform contact with heating tube. A copper or aluminum strip is pressed onto top surface and precision ground to designed dimensions to improve heat transfer efficiency.
Positioning pin hole: Center positioning hole requires precision machining to ensure accurate alignment with mold plate. Anti-rotation pin hole is machined according to clearance fit requirements, allowing for expansion space.
Precision machining of sealing surfaces: All sealing surfaces in contact with nozzle and main nozzle are precision ground, with a flatness requirement of ≤0.01mm. Sealing surfaces are also guaranteed to be free of scratches and dents, structurally ensuring sealing reliability and preventing material leakage.
Heat treatment and surface treatment (as needed): For processing glass fiber/mineral reinforced plastics and other easily worn conditions, or scenarios requiring high hardness and high corrosion resistance, manifold can be subjected to overall quenching and tempering or surface nitriding treatment to improve surface hardness and wear resistance, extending mold's service life.
Final Inspection and Testing (100% Inspection, No Omissions)
Dimensional and Geometric Tolerance Inspection: A coordinate measuring machine (CMM) is used for full-dimensional inspection, focusing on key parameters such as position of each flow channel outlet, flatness of sealing surface, and coaxiality of locating pin holes.
Pressure Testing: Assembled manifold is subjected to a 4MPa high-pressure gas pressure test for leak detection to ensure no leakage at sealing surface.
Electrical Testing: Resistance and insulation performance of all heating circuits and thermocouple circuits are checked one by one to verify normal functioning of temperature control system and ensure there are no short circuits or open circuits.

Manifold is a core component in a hot runner system where "technology determines cost, and details determine success or failure." Every detail of its design, selection, and processing directly affects mass production stability of mold, product qualification rate, and the overall production cost.
In mass production fields like automotive parts, where reliability, consistency, and cost control are paramount, focusing on standardization in design, balancing performance and cost in component selection, strictly controlling precision and quality in manufacturing are essential professional qualities for every mold design, procurement, and process engineer.
Only by clarifying core design and selection principles of each independent component in a hot runner system, mastering its technical essence and practical points, can one truly understand nature of hot runner technology and lay a solid foundation for successful design, procurement, and mass production of every mold project.