AAA MOULD's Medical Device Injection Moulding

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In the field of plastic injection molding production, short shots are among the most common and destructive quality defects. A short shot refers to a situation where molten plastic fails to fully fill the mold cavity during the filling process, resulting in problems such as material shortage, incomplete edges, and filling gaps in thin-walled areas of the molded product. These issues directly affect the structural integrity, assembly accuracy, and appearance quality of the product.


A case from a new energy vehicle manufacturer shows that a short shot problem in thin-walled bumpers alone caused the customer's production line to shut down for 8 hours, resulting in direct economic losses exceeding 500,000 yuan (Note: If converting to a foreign currency is more contextually appropriate, "over 70,000 US dollars" can be used, with the conversion rate based on the average market rate around 2024).


Starting from the essential mechanism of short shots, this article will systematically break down the four core causes, provide comprehensive solutions covering materials, molds, processes, and equipment, and illustrate the implementation paths with practical cases.

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I. The Nature of Short Shots: Dynamic Disruption of Flow Balance

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The formation of short shots is not caused by a single factor; its essence lies in the disruption of the dynamic balance between the "propulsive energy" and "flow resistance" of the molten plastic during the filling process. From a microscopic mechanism perspective, for the melt front to complete cavity filling, it must overcome three core types of resistance:
1. Viscous resistance of the melt itself: Generated by material viscosity and runner friction;
2. Pressure decay: The pressure loss of the melt from the gate to the end of the cavity increases exponentially with the length of the flow path;
3. Temperature gradient: Cooling of the melt leads to a sharp rise in viscosity—for every 10°C drop in temperature, the viscosity can increase by 2.3 times (per the Arrhenius equation).


When the sum of these resistances exceeds the propulsive force provided by the injection system, the melt front solidifies before fully filling the cavity, resulting in the short shot defect.


Typical manifestations of short shots include:
● Progressive material shortage (gradual thinning from the gate to the end of the part);
● Intermittent flow interruption (appearance of "bamboo joint-like lines" on the surface);
● Overall under-filling (insufficient filling of the entire cavity);
● Local material shortage (unfilled complex structures or mesh areas).
Different manifestations correspond to different combinations of causes.



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II. Four Core Causes: Full-Chain Tracing from Materials to Equipment

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(1) Material Properties: Innate Limitations on Flow Capacity
Materials are the fundamental factor affecting short shots, with core issues focusing on two aspects: flowability and purity.


High-viscosity materials (e.g., PC, PPO, PC + 20% mineral filler) exhibit high melt flow resistance. Particularly in thin-walled products (≤2mm) or long-flow-path products (flow ratio > 100:1), short shots are highly likely to occur due to insufficient flow. Impurities, unmelted particles, or excessive lubricants in raw materials further exacerbate the problem: impurities can block runners and form "flow obstacles," while excessive lubricants may cause melt slippage, reducing effective filling pressure.


In addition, for glass fiber-reinforced materials (e.g., PP + 30% GF), the reorientation of glass fibers increases flow resistance. Areas with concentrated long fibers may even form a network structure, hindering melt advancement.


(2) Mold Design: Structural Defects in Flow Paths
The rationality of mold design directly determines the smoothness of melt flow. Common design issues include:


● Improper runner and gate design (excessively thin runners, offset gate positions, or undersized gates), leading to excessive pressure loss;
● Poor cavity venting: Trapped air cannot escape, forming back pressure that obstructs melt filling;
● Unreasonable cooling system layout: Local overcooling causes the melt to solidify prematurely;
● Complex product geometry (e.g., dense meshes, narrow ribs): Increases flow resistance and easily forms flow stagnation zones.


For example, the mesh area of a notebook (NB) bottom cover has a large contact area and rapid heat dissipation—it is not only a high-risk area for short shots but also prone to flash defects due to the high pressure required for filling.


(3) Process Parameters: Imbalanced Matching of Molding Conditions
Process parameters are the most direct cause of short shots, with the core lying in the triangular matching of temperature, pressure, and speed.


● Insufficient injection pressure or speed results in inadequate melt propulsive force; conversely, excessively high speed may trap air, while excessively low speed causes the melt to solidify prematurely.
● Low melt temperature or mold temperature significantly increases melt viscosity. For instance, the flowability of PP material at 200°C is much lower than that in its optimal temperature range (220–240°C).
● Improper holding pressure settings (e.g., delayed switchover timing, insufficient pressure) fail to compensate for melt shrinkage, leading to material shortage at the part's end.


The "one-size-fits-all" constant-speed injection strategy in traditional processes cannot adapt to the pressure decay law of long-flow-path products, which is also a key cause of progressive short shots.


(4) Equipment Performance: Insufficient Precision in Energy Transfer
The performance of injection molding machines directly affects the stability of "energy supply," and short shot occurrences vary significantly across machines of different brands. For electric injection molding machines, key influencing factors include pressure transfer accuracy, flow rate stability, and temperature field uniformity:


● Fanuc machines have a high flow rate decay rate (up to 60%), which easily leads to progressive material shortage;
● Response delays in the holding pressure switching valve of Sumitomo machines may cause intermittent flow interruption;
● Speed fluctuations in Haitian machines result in pressure instability, leading to overall under-filling.
In addition, equipment defects such as empty hoppers, blocked feed inlets, and worn check valves can cause a drop in actual injection pressure or pressure leakage, further worsening short shot issues.


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III. Comprehensive Solutions: A Systematic Strategy from Prevention to Eradication

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(1) Material Optimization: Enhancing Flow Capacity at the Source
The core of material adjustment is to reduce flow resistance, which can be achieved through three approaches:
1.Replace with resin grades of better flowability: Select materials with higher Melt Flow Rate (MFR) to reduce the injection pressure required for filling;
2.Raw material modification: Improve melt flowability by adding plasticizers, reducing the proportion of fillers, or optimizing the length distribution of glass fibers;
3.Raw material pretreatment: Strictly control impurity content and fully dry hygroscopic materials to avoid viscosity fluctuations caused by moisture.


For glass fiber-reinforced materials such as PP + 30% GF, the screw compression ratio and the length of the mixing section can be adjusted to reduce glass fiber breakage and lower flow resistance.


(2) Mold Optimization: Building a Smooth Flow System
Mold improvement requires precise optimization combined with CAE mold flow analysis:
● Runner and gate design: Expand runner size, optimize gate position (e.g., changing from side gating to center gating), and balance the filling time of each cavity. A certain automotive component achieved a 20% increase in filling rate through this method;
● Ventilation system: Add venting grooves (depth ≤ 0.02mm, width 5-10mm) at the end of the cavity and air accumulation areas, or use porous steel inserts to eliminate the impact of back pressure;
● Cooling system: Avoid local overcooling; for long-flow-path products, additional heating rods can be installed at the end to maintain melt temperature;
● Complex-structured products: Optimize product geometry through CAE simulation, such as thickening thin-walled areas or simplifying flow paths, to reduce flow resistance.


(3) Process Optimization: Achieving Precise Process Control
The key to process adjustment is to establish a dynamic matching relationship among "temperature, pressure, and speed":
● Temperature control: Appropriately increase melt temperature (e.g., raising PP temperature from 200°C to 220-240°C) and mold temperature to reduce melt viscosity, while avoiding material degradation caused by excessively high temperatures;
● Pressure and speed control: Adopt a segmented injection strategy and dynamically adjust parameters based on flow path length. For example, use high pressure and high speed in the initial stage to quickly establish a pressure gradient, maintain pressure in the middle stage to compensate for pressure decay, and reduce speed in the final stage to avoid flash. At the same time, use a gradually decreasing holding pressure to prevent sudden pressure changes;
● Parameter adjustment principle: Follow the "small and gradual" principle—adjust injection pressure by 5%-10% each time to avoid new defects caused by drastic parameter changes.


(4)Equipment Optimization: Ensuring Stable Energy Transfer
Equipment-level optimization includes:
● Regularly calibrate injection pressure and flow rate accuracy to ensure the accuracy of pressure transmission;
● Inspect and replace worn check valves to prevent pressure leakage;
Develop differentiated parameters based on the characteristics of machines from different brands. For example, Fanuc machines need to focus on compensating for flow rate decay, Sumitomo machines require optimizing holding pressure switching timing, and Haitian machines need to control speed fluctuations;
● For long-flow-path and thin-walled products, select equipment with higher stability in injection volume, pressure, and speed to avoid short shots caused by insufficient equipment capacity.






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IV. Practical Cases: The Path from Mass Short Shots to 95% Yield

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Case 1: Solution to Short Shots in Thin-Walled Bumpers for New Energy Vehicles
A certain automotive manufacturer produced thin-walled bumpers made of PP + 30% GF (wall thickness: 1.8mm, flow ratio: 120:1). All three electric injection molding machines experienced mass short shots, with a material shortage of 2-5mm at the end of the parts. The traditional method of increasing injection pressure only improved the issue by 15% and caused severe flash.

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Solution: A coupled optimization strategy of "equipment characteristics - material behavior - process parameters" was adopted:
● For Fanuc machines: Segmented injection was implemented (initial stage: 140MPa/200mm/s → middle stage: 120MPa/150mm/s → final stage: 100MPa/100mm/s). Additional heating rods were installed at the end of the runners to increase the temperature at the end from 185°C to 220°C, reducing viscosity by 48%;
● For Sumitomo machines: The holding pressure switching timing was optimized to shorten the response delay to 0.05 seconds, and the R-angle at the runner bends was expanded to 1.5mm;
● For Haitian machines: The length of the screw mixing section was adjusted to reduce the uneven dispersion of glass fibers, and the speed fluctuation was controlled within ±1rpm.


Ultimately, the short shot defect was completely resolved, the yield increased from 70% to 95%, and the flash volume decreased by 80%.


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Case 2: Collaborative Solution to Short Shots and Flash in the Mesh Area of NB Bottom Covers
A certain notebook (NB) bottom cover (wall thickness: 1.2mm, PC + 20% mineral filler) had coexisting short shots and flash due to dense meshes. Three adjustments to the gate showed no significant improvement. CAE mold flow analysis revealed that the mesh area had high flow resistance and concentrated pressure.

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Solution:
● The mesh was optimized using an equivalent wall thickness correction model, adjusting the wall thickness of the mesh area to 1.05mm;
● The gating system was redesigned: changing from four-point gating to two-point symmetric gating, and expanding the diameter of the cross-runner to 8mm;
● Micro venting grooves (depth: 0.015mm) were added in the dense mesh area;
● Process parameters were adjusted: increasing the melt temperature from 260°C to 275°C, and adopting the "low-speed filling - high-pressure holding" strategy.


After optimization, the short shot defect was eliminated, and the flash defect rate dropped from 35% to 2%.

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V. Conclusion: Core Logic of Short Shot Prevention and Control

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The short shot problem in injection molding is essentially a mismatch between the flow system, energy transfer, and material properties. Preventing and controlling short shots requires establishing a closed-loop system of "prevention - diagnosis - optimization":
● Potential risks are prevented in the design stage through CAE mold flow analysis;
● The causes are accurately diagnosed based on defect manifestations;
● A radical solution is achieved through the collaborative optimization of materials, molds, processes, and equipment.


With the increasing popularity of precision injection molding today, short shot prevention and control has evolved from simple parameter adjustment to a multi-dimensional systems engineering. Only by mastering its core mechanism and combining it with practical experience can we effectively improve product yield and reduce production costs.

In the injection molding industry, weld lines (weld marks) are one of the most common, troublesome, and impactful surface defects affecting the quality of high-end plastic parts. When molten plastic flows through the mold cavity at high temperatures, it encounters ribs, pillars, holes, or multi-gate structures. The melt is divided into two or more streams, which then converge and fuse again after passing around. The interface between the two streams cannot be completely fused, resulting in a visible linear mark after cooling. This is what the industry commonly refers to as a weld line, seam line, or cold joint.


Weld lines not only severely damage the smoothness and consistency of the product's appearance but also significantly reduce the structural strength, impact resistance, and bending resistance of plastic parts. Especially suitable for products requiring both high-end appearance and durability, such as electronic casings, button panels, automotive interior parts, medical device components, and home appliance casings. Minor welds can affect subsequent surface treatments like pad printing, screen printing, spray painting, and laser engraving; severe welds can directly lead to batch scrap, rework, and repairs, increasing production costs and delaying delivery.


I.Core Causes of Injection Molding Welds



Weld formation is not caused by a single factor, but rather by the combined effect of five dimensions: mold design, plastic raw materials, injection molding process, product structure, and production environment:
1. Mold Design Factors: Excessive number of gates, unreasonable gate placement, uneven material flow paths; insufficient or blocked venting channels in the cavity, poor venting at the parting line; uneven cooling water distribution, and large local temperature differences in the mold can all lead to lower temperatures at the material flow convergence point, trapping gas and forming noticeable welds.
2. Plastic Raw Material Factors: Low melt flow index and poor fluidity of raw materials; excessive addition of fillers such as glass fiber and talc; inadequate drying of raw materials; excessive moisture content; excessive mixing of recycled materials; and mixing of multiple grades of materials all increase melt viscosity and reduce fusion performance.
3. Injection Molding Process Factors: Low barrel temperature, mold temperature, and nozzle temperature; slow injection speed and insufficient injection pressure; short holding time and insufficient back pressure; rapid cooling before melt convergence leads to poor fusion.
4. Product Structure Factors: Significant differences in wall thickness, excessively dense or thick ribs, numerous openings, and lack of rounded corners at right angles easily alter the material flow direction, artificially creating points of divergence and convergence.


II. Comprehensive Improvement Solution for Injection Molding Welds

To improve or even eliminate injection molding welds, a comprehensive solution must be adopted, encompassing early-stage design prevention, mid-stage process debugging, and post-stage surface finishing:
1. Mold Front-End Optimization: Optimize the gate design and layout, employing hot runners and valve needles for sequential injection, controlling the material flow convergence point; increase venting grooves and optimize venting angles in the weld line area; evenly distribute cooling water channels to stabilize mold temperature and delay melt cooling.
2. Standardized Raw Material Control: Select high-flow-compatibility raw materials; strictly control the filler ratio; thoroughly dry and dehumidify the material; limit the proportion of recycled material and eliminate the mixing of impurities.
3. Fine-tuning of Injection Molding Process: Appropriately increase material temperature, mold temperature, and nozzle temperature; increase injection pressure and mid-stage injection speed; increase back pressure and extend holding pressure and shrinkage compensation time to ensure full fusion of the material flow under high temperature and high pressure.
4. Pre-emptive Product Structure Avoidance: Design uniform wall thickness and use rounded corners; guide welds to non-visible surfaces, hidden side areas, and non-stressed areas.
5. Post-processing Finishing and Masking Minor, unavoidable weld seams can be treated with fine mold polishing, texturing, and spray painting for masking. Alternatively, they can be cleverly concealed using pad printing and screen printing patterns, without affecting the overall aesthetics or functionality.


III. Value of Professional Mold and Injection Molding One-Stop Service AAA MOULD specializes in precision mold design, injection molding, and surface decoration services. We intervene in weld line risk prediction from the early stages of product development, optimizing across all dimensions from product structure and mold runners to venting and cooling, and injection molding processes. This reduces weld seam formation at the source and allows for aesthetic enhancement through post-processing techniques such as pad printing, screen printing, and spray painting, balancing product structural strength, appearance, and mass production stability. This helps customers reduce scrap, save costs, and maintain consistent quality.

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Silver streaks are one of the most common and typical surface defects in injection molding. Characterized by silvery, needle-like, striped or cloudy marks along the melt flow direction on plastic parts, these flaws not only compromise surface flatness and glossiness but also degrade local mechanical properties. They frequently cause batch rework, product rejection and customer complaints, severely affecting production yield and brand reputation. This article comprehensively elaborates on the classification, root causes, targeted solutions and routine prevention measures of silver streaks, providing practical technical guidance for injection molding manufacturers.



1. Definition and Common Types of Silver Streak Defects
Silver streaks refer to silvery strip defects formed on the part surface when internal moisture, air or impurities fail to escape completely during mold filling and solidification, and are stretched and squeezed within the molten plastic. Based on formation mechanisms and morphological features, the four most prevalent types in mass production are summarized as follows:


Moisture-induced Silver Streaks: Fine and uniform random streaks widely distributed on part surfaces, primarily caused by excessive moisture in raw materials. This is the most common type of silver streak defect.
Air-trap Silver Streaks: Intermittent streaks concentrated at melt flow ends, dead corners and wall thickness transition areas, resulting from insufficient mold venting.
Degradation-induced Silver Streaks: Coarse, opaque and heavy silvery marks often accompanied by slight scorching near the gate, generated by gas released from overheated material degradation.
Impurity-induced Silver Streaks: Irregular streaks with uneven width and scattered white spots, caused by contaminated raw materials or excessive impurities in recycled resin.



2. Root Causes of Silver Streaks
Silver streaks are rarely caused by a single factor but result from the superposition of abnormalities in materials, processes, molds and equipment. Accurate cause identification is critical for effective defect resolution.



2.1 Material Factors (Primary Cause)
Most engineering plastics (ABS, PC, PA, PMMA, modified PP, etc.) are hygroscopic and absorb ambient moisture during storage and transportation. Insufficient drying before production leads to instant water vaporization under high melting temperature. The vapor trapped in the melt is stretched during filling and forms visible silvery stripes after cooling and solidification. In addition, dust, oil contamination, mixed foreign materials or excessively degraded recycled resin will produce volatile gas and impurities at high temperatures, further triggering silver streaks.

2.2 Improper Injection Process Parameters
Unbalanced process parameters aggravate gas generation and entrapment. Excess barrel and nozzle temperature, insufficient screw back pressure and fast plasticizing speed lead to material thermal degradation and uneven melt mixing, making internal gas difficult to discharge. Excess injection speed and pressure cause turbulent flow and air entrapment, wrapping air inside the melt. Insufficient holding pressure and short holding time fail to compact the part surface, allowing internal gas to precipitate and form streaks.

2.3 Mold Design and Venting Abnormalities
Poor mold venting is the main cause of localized silver streaks. Shallow, blocked or improperly positioned vents fail to exhaust trapped air and melt gas at flow ends, rib positions, pillar areas and thin-thickness transitions. Low mold temperature accelerates melt cooling, freezing gas inside the part before it escapes. Undersized gates and narrow runners increase flow resistance, causing local overheating, material degradation and gate-area silver streaks.

2.4 Equipment and Operational Issues
Worn screws and barrels result in poor plasticization and material retention, causing local overheating and degradation. Incomplete barrel cleaning leaves residual old materials that generate volatile contaminants. Unsealed hoppers, open material storage and inaccurate dryer parameters cause secondary moisture absorption and insufficient drying, continuously inducing silver streak defects.

3. Targeted Solutions for Silver Streak Defects
Practical and mass-production-friendly solutions are proposed covering material control, process optimization, mold improvement and equipment management to eliminate silver streaks effectively.



3.1 Material Control: Eliminate Moisture and Impurities at the Source
Follow standardized drying specifications for different resins: dry ABS and PP at 70-80℃ for 2-4 hours; dry highly hygroscopic materials including PC, PMMA and PA at 90-120℃ for 4-6 hours to meet moisture requirements. Keep hoppers and barrels sealed during production to prevent secondary moisture absorption. Reject damp, contaminated or deteriorated raw materials, and control the proportion of recycled materials with sufficient filtration and re-drying. Regularly clean hoppers, loaders and dryers to avoid impurity contamination.

3.2 Process Optimization: Reduce Gas Generation and Air Entrapment
Optimize thermal parameters by properly lowering barrel front and nozzle temperatures to avoid thermal degradation. Increase screw back pressure and reduce plasticizing speed to achieve uniform melt mixing and full gas release. Adopt low-speed filling to avoid turbulent flow and air entrapment. Appropriately increase holding pressure and extend holding time to compact the part surface and suppress gas precipitation. Shorten material residence time in the barrel to prevent long-term high-temperature degradation.

3.3 Mold Optimization: Improve Venting Performance
Optimize the venting system by deepening and widening vents at gas-prone positions including flow ends, ribs and pillars, with a standard vent depth of 0.02-0.05 mm for smooth gas discharge. Regularly clean mold parting surfaces and vents to remove carbon deposits and resin residues. Moderately increase mold temperature to slow down cooling and reserve sufficient time for gas escape. Optimize gate and runner designs to reduce flow resistance and avoid local overheating.

3.4 Equipment Maintenance and Standardized Operation
Establish periodic equipment maintenance schedules to inspect and repair worn screws and barrels for stable plasticization. Thoroughly clean barrel residuals before production and complete purging during material changes. Calibrate dryers and temperature control devices regularly to ensure accurate drying parameters. Standardize operational procedures: avoid open material storage and seal hoppers after shutdowns to eliminate human-induced defects.

4. Routine Prevention and Mass Production Control
The core of silver streak management is prevention and closed-loop control. Implement incoming material inspection to test moisture content and purity, rejecting unqualified batches. Standardize drying and injection parameters for each material grade and form unified process specifications to prevent arbitrary parameter adjustment. Develop daily vent cleaning and weekly full mold maintenance plans. Sustain regular equipment calibration and maintenance to ensure stable production.

5. Conclusion
As a frequent surface defect in injection molding, silver streaks involve the entire production chain including materials, processes, molds and equipment. The core root causes are residual moisture, trapped air, material degradation and poor venting. Most silver streak issues can be thoroughly resolved through four key measures:precise material drying, venting system optimization, process parameter calibration and standardized equipment maintenance. For injection molding enterprises, refined and standardized full-process control is essential to reduce defect rates, improve surface quality, stabilize mass production, guarantee on-time delivery and enhance market competitiveness.

Injection mold dimension calculation is a core process of mold design, which directly determines the dimensional accuracy and mass production qualification rate of plastic products. Plastic products shrink after cooling and forming. Therefore, mold dimensions cannot be directly copied from product drawings. Scientific formulas are required to compensate for shrinkage, combined with tolerance, structure and production conditions for correction. This article briefly introduces the standard calculation logic, core formulas and practical key points of injection mold dimensions, providing references for the design and manufacturing of various injection molds.



1. Core Principle of Dimension Calculation

Plastic melt undergoes volume shrinkage during high-temperature injection molding and normal-temperature cooling. If the mold is manufactured according to the nominal product size, the final product size will be generally smaller. The core logic of mold dimension calculation is to enlarge the mold forming size in advance based on the plastic shrinkage rate to offset the cooling shrinkage of products, and make corrections in combination with product tolerance, machining error and mold wear to ensure the finished product dimensions are within the qualified range.



2. Core Parameter: Plastic Shrinkage Rate

The calculated shrinkage rate is uniformly adopted in mold design and serves as the basic basis for dimension verification. The formula is as follows:

Calculated Shrinkage Rate (S) = (Mold Dimension at Room Temperature – Product Dimension at Room Temperature) / Product Dimension at Room Temperature × 100%



Reference shrinkage rates of common plastics:

- Low shrinkage (precision parts): ABS, PC, PMMA, 0.3%~0.8%

- Medium shrinkage (general parts): PP, PE, PS, 1.0%~2.0%

- High shrinkage (structural plastics): POM, PA6, PA66, 2.0%~3.5%

- Glass fiber reinforced modified materials: 0.2%~1.0%

Value Selection Principles: Select a slightly lower value for precision appearance parts to reserve fine-tuning space; select a slightly higher value for thick-walled and large-size parts. For modified materials and special working conditions, prioritize the parameters provided by material manufacturers or test mold data.



3. Standard Calculation Formulas for Core Mold Dimensions

Mold dimensions are divided into three categories: cavity dimension, core dimension and center distance dimension, with corresponding independent calculation formulas. The mold manufacturing tolerance (δ) is uniformly set to 1/3~1/4 of the product tolerance.

3.1 Cavity Dimension (Product External Dimension)

Applied to external dimensions such as product shells, outer contours, length, width and outer diameters, adapting to the negative tolerance rule of product external sizes.

Formula: A = (A0 + A0×S - 3/4Δ) ± δ

Parameters: A = Mold cavity dimension; A0 = Nominal product dimension; S = Plastic shrinkage rate; Δ = Product dimensional tolerance; δ = Mold manufacturing tolerance.



3.2 Core Dimension (Product Inner Hole/Inner Groove Dimension)

Used for internal dimensions such as product holes, clamping grooves and inner cavities, adapting to the positive tolerance rule of product internal sizes to compensate for the shrinkage and reduction of inner holes after molding.

Formula: B = (B0 + B0×S + 3/4Δ) ± δ

The parameter definitions are consistent with those of cavity dimensions.



3.3 Center Distance Dimension (Hole and Pillar Spacing)

The center distance features uniform shrinkage and symmetrical tolerance, mostly used for the design of screw hole spacing and positioning pillar spacing.

Formula: C = (C0 + C0×S) ± δ/2



4. Practical Dimension Correction Key Points

- Structural Correction: Appropriately increase the shrinkage rate for thick-walled products, and finely adjust local areas such as thin walls and rib glue accumulation positions to improve shrinkage and deformation.

- Wear Correction: Reserve a wear allowance of 0.02~0.05mm for molds with an annual output of more than 100,000 pieces to extend mold service life.

- Process Correction: Products formed under high pressure holding and high mold temperature have lower shrinkage, allowing a slight reduction of the shrinkage rate value.

- Precision Part Correction: Avoid applying standard shrinkage rates directly for high-precision products; revise mold dimensions reversely based on actual shrinkage data from test molding.



5. Common Calculation Errors

- Adopting a single fixed shrinkage rate for the entire mold without zoning adjustment according to wall thickness and structure;

- Only calculating theoretical dimensions while ignoring mold machining tolerance with no fine-tuning allowance;

- Mixing up cavity and core calculation formulas, resulting in unqualified internal and external dimensions and assembly failure;

- Applying shrinkage rates of raw materials directly without adapting to glass fiber reinforced, flame retardant and other modified plastics.



6. Conclusion

The core of injection mold dimension calculation is taking the shrinkage rate as the basis, adopting differentiated calculations for cavity, core and center distance dimensions, and making corrections combined with product structure, tolerance and mass production conditions. Accurate dimension calculation is the key to ensuring product precision, reducing defect rates and realizing stable mass production. In design practice, it is necessary to combine theoretical formulas with actual test molding effects to continuously optimize dimensional parameters.