Process from plastic product design to mold production is a highly complex one, encompassing several key aspects: plastic part design, mold structure design, mold processing and manufacturing, and molding production. It requires collaborative efforts of product designers, mold designers, mold processing technicians, and skilled operators. It involves an iterative, continuous optimization process of design, modification, and redesign. Traditional manual design and manufacturing are increasingly unable to meet demands of a fiercely competitive market.
With development of computer technology and its continued penetration into various fields, vast majority of modern mold and plastics manufacturers in China are placing significant emphasis on application of computer-aided technology, which has essentially replaced traditional design and production methods. Utilizing modern design theory and methodologies, combined with advanced computer-aided technology, to design and improve injection molds can significantly improve product quality, shorten development cycles, reduce production costs, thus enhance a company's core competitiveness.
Traditional design and manufacturing methods have numerous drawbacks. With technological advancements and increasing power of computers, Moldflow technology has been widely used in modern mold design and production. Using computer-aided technology not only increases success rate of first-time mold trials, but also significantly improves mold design and manufacturing quality, performance, and cost.

Product structural design verification and cost assessment: Moldflow software is used to verify feasibility of customer's product, specified materials, and product structural design processes, thereby enhancing product manufacturability in the early stages.
During product design stage, following issues should be confirmed:
● Is molding plastic material determined?
● Is product wall thickness uniform?
● Are ribs too thin or too thick (resulting in difficulty filling or surface shrinkage)?
● Product deformation caused by product structure.
● Structural design and molding processability assessment.
● Manufacturability assessment.
● Wall thickness, steps, corner effects, and reinforcements.
Case 1: This headlight was previously developed with a relatively heavy product. In light of automotive lightweighting trend, company sought to reduce its weight through new development.
Product currently weighs 244g. Previously, PC was used, which required very high injection pressures. Therefore, company sought to optimize product structure to reduce weight and select a more cost-effective material. Furthermore, company sought to maintain a weld line on the surface, maintain a molding pressure of less than 160 MPa, and maintain a clamping force of no more than 800 tons.
Comparing different materials in current solution, Moldflow analysis results show that among three candidate materials, PBT requires the lowest injection pressure: 154 MPa for PC, 123 MPa for PA, and 100 MPa for PBT. (See Figure 1.)

 

Further optimization of product's wall thickness revealed that, under one gate condition, a minimum thickness of 1.8 mm for PBT material met injection molding machine's requirements. Further reductions in wall thickness would have exceeded machine's requirements. By optimizing wall thickness, product's weight was reduced to 203g (a 17% reduction compared to previous weight). As shown in Figure 2.

 

Final product was acceptable, meeting analysis requirements. Figure below compares analysis results with actual test mold. Product weight was significantly reduced, saving product development costs. As shown in Figure 3.

 

Case 2: Product is a combination headlamp (high-end configuration) body. Product uses PP + 40% Talc. Appearance requirements for this headlamp are flash-free, glossy, uniform color, and free of bubbles, flow marks, and cracks. Furthermore, surface is aluminum-plated, and shear stress on product surface cannot exceed maximum allowable shear stress of material.
Since this product is in the early stages of development, design changes and mold structural adjustments are permitted. Dimensions and tolerances are detailed in CAD drawings, with a Z-direction tolerance of ±0.5mm. Moldflow's flow, packing, cooling, and deformation analysis modules are used to check quality of plastic part. Analysis targets flow balance, whether product design will cause major molding defects, and whether product design will cause significant deformation. Product is shown in Figure 4.

 

Moldflow analysis shows that product deformation is primarily concentrated at corners. It is recommended to add ribs to reinforce structure in areas with significant deformation. Proposed countermeasures are then verified through analysis to verify their effectiveness. This is shown in Figure 5.

 

Rib addition options are shown in Table 1. Countermeasure 2 involves adding ribs within glue tank, and Countermeasure 3 involves adding several ribs to previous option.

Analysis reveals that original deformation was approximately 1.3mm, while Countermeasure 2 resulted in approximately 0.9mm, and Countermeasure 3 resulted in 0.3mm. This is shown in Figure 6 and Table 2.

 

During DFM stage, mold design plans are evaluated. Reference is made to a defect database, similar product history, and analysis experience database. A first-stage Moldflow analysis is performed, and a "Preliminary Moldflow Analysis Report for DFM Stage" is submitted to confirm mold design feasibility. This analysis includes following:
● Determine runner and gating schemes
● Is filling pattern balanced? Weigh weld line and air trap locations.
● Is wall thickness uniform after demolding process, and can it be fully injected?
● Are ribs too thin or too thick (difficult to fill or surface shrinkage)?
● Maximum injection pressure and clamping force.
● Product deformation caused by product structure.
Case 3: Product is an automotive lamp with dimensions of 290x280x220mm and a basic wall thickness of 2.3mm. However, wall thickness in circled area is thicker, posing a risk of sink marks and a longer molding cycle. (See Figure 7.)

 

To determine product's injection molding strategy, you can draw on experience from previous projects or use Moldflow's gate location recommendations. Using Moldflow's gate location analysis, you can specify number of gates required. Software will automatically recommend optimal gate location. Optimal gate placement is indicated in blue, and the worst-case location is indicated in red. (See Figure 8.)

 

Analysis revealed that stagnant flow occurred in certain areas of product, including reflective surface indicated by circle. This resulted in weld lines, a critical defect in product. It is recommended to increase bottom wall thickness by 0.2mm, as shown in Figures 9 and 10.

 

By increasing wall thickness of part, melt at the bottom flows faster, allowing three streams from bottom and sides to merge smoothly, avoiding formation of knit lines. The lower hole still has a knit line, but it is now relatively hidden and more reasonably distributed. By enhancing venting, it can be largely eliminated, thus meeting product requirements. (See Figure 11.)

 

During mold design stage, mold design determines stability of product quality. In other words, a good mold design provides the largest molding window, thereby meeting requirements for appearance and dimensional stability of mass-produced plastic parts and achieving a stable CPK. Therefore, mold optimization during mold design stage is crucial, primarily in terms of:
● Number and arrangement of cavities.
● Gate shape and runner dimensions.
● Optimizing cooling system design and coolant inlet temperature.
● Cooling time and molding cycle (filling, holding, cooling).
● Identify product warpage and deformation and address cause, and address any deformation issues.
● Determine product appearance quality and process.
● Provide DFMEA documentation.
● Determine production costs (materials, cycle time, molds, etc.).
Case 4: This product is a photometric lens. Mold has already been developed, but during mold trials, it was discovered that cycle time was too long and efficiency was too low. Moldflow analysis was used to identify cause, shorten molding cycle, and reduce development costs.
Analysis revealed that product required 117 seconds for runner to completely cool. If ejection was performed when runner was 50% cool, molding cycle would be approximately 75 seconds. (See Figure 12.)

 

Since product freezes after approximately 25 seconds, excessive runner cooling time impacts the overall molding cycle. Runner size was reduced to shorten cooling time. While hot runner size remained unchanged, main cold runner was reduced from 12mm to 9mm, and branch runner from 10mm to 7mm. (See Figure 13.)

 

After optimizing runner size, product takes 68 seconds to fully cool through runner. If ejection is performed when runner cools 50%, molding cycle time is approximately 50 seconds. This reduces molding cycle time by 25 seconds, or 33.3%. This is shown in Figure 14.

 

Moldflow's primary role in mold development is optimizing product design and reducing mold manufacturing costs.
When optimizing plastic product design, designers can optimize factors such as part wall thickness, gate number and location, and runner system. This is crucial to success and quality of product. Traditionally, relying solely on product designer's experience has been laborious and time-consuming, resulting in inconsistently designed products. Using Moldflow software, optimal plastic products can be quickly designed.
Due to diversity and complexity of plastic products and limitations of designer experience, traditional mold design often requires repeated trials and refinements to achieve success. Moldflow software allows for optimized design of cavity dimensions, gate location and dimensions, runner dimensions, and cooling systems. Mold trials and modifications can be performed on a computer, significantly improving mold quality and reducing number of trial runs.
When optimizing injection molding process parameters, due to limited experience, engineers often struggle to accurately set the most appropriate processing parameters for product, select appropriate plastic material, and determine optimal process plan. Moldflow software can help engineers determine optimal injection pressure, clamping force, mold temperature, melt temperature, injection time, holding pressure and time, and cooling time to produce the best possible plastic product.
In recent years, CAE technology has become increasingly important in injection molding industry. Using CAE can comprehensively address issues arising during injection molding process.