Cost Reduction Plan for Plastic Part Material Replacement: Material Switching Path Without Performance Degradation
1. Locking of Performance and Boundary Conditions Before Material Replacement
Material replacement is a common way to reduce plastic part cost, but many projects only compare unit price and ignore long-term performance, resulting in cracking, aging, dimensional drift and assembly failure after mass delivery. Before material replacement, a complete baseline material file shall be sorted out, including core performance indicators such as tensile strength, impact strength, flexural modulus, heat deflection temperature, shrinkage rate, chemical resistance, temperature resistance, flame retardancy and compliance standards. The actual working conditions of products shall be collected, such as long-term continuous working temperature, contact medium, buckle plugging times, drop requirements and vibration environment. Shrinkage rate is a key point that is easy to be ignored. If the shrinkage difference between new and old materials is too large, it will directly cause out-of-tolerance size, warpage and assembly interference. The adaptability of the existing mold, hot runner and cooling system shall be confirmed to reduce subsequent mold modification investment.
2. Equivalent Material Classification and Cost Reduction Direction
There are several material replacement paths, and the scheme with the smallest modification shall be preferred. The first is replacement of different grades with the same base material, such as switching from imported high-melt-flow PP grades to domestic grades with the same specification, with small changes in molding window and shrinkage rate and low verification workload. The second is adjustment of filling modification. Under the premise of meeting impact and rigidity requirements, the proportion of glass fiber and mineral filling can be optimized in the performance redundancy area. The third is base material downgrade replacement, which has a large cost reduction range but obvious performance differences, and requires complete reliability verification. The fourth is regrind blending, adding qualified primary regrind within the customer’s permission, and strictly controlling ash content, impurities and melt index fluctuation.
3. Material Benchmarking and Physical Property Screening
After obtaining the physical property reports of candidate materials, the full physical property curve shall be compared instead of only checking single-point indicators. For impact-resistant materials, the difference between room temperature impact and low-temperature impact shall be distinguished. For glass fiber reinforced materials, the glass fiber content and fiber length retention rate shall be checked. For flame retardant materials, the test standard and sample thickness of flame retardant grade shall be verified. The batch stability of raw materials shall be checked, and suppliers with mature modification process and small melt index fluctuation shall be preferred.
4. Molding Simulation and Mold Adaptation Prediction
After selecting 2 to 3 candidate materials, mold flow analysis is carried out to compare the filling pressure, shear rate, cooling time, shrinkage and warpage trend of new and old materials. If the viscosity of new material is higher, the filling pressure will rise, and the gate and runner need to be evaluated for enlargement. If the viscosity is lower, the flash risk will increase. The crystallization rate of crystalline materials such as POM, PA and PP is different. Slow crystallization materials need to extend holding and cooling time, which may offset the benefit of raw material price reduction. The weld line strength of low-cost materials is easy to decay, which shall be focused on the stress fulcrum position.
5. Small Sample Trial Mold and Short-term Performance Verification
After simulation, trial molding shall be carried out with a fixed baseline process. The key assembly dimensions, hole positions and datum planes shall be measured and compared with the baseline. Appearance comparison shall be carried out to check color difference, gloss, floating fiber, silver streaks and stress cracking. Mechanical tests such as tensile, bending and impact are carried out on the same batch of samples, and the allowable fluctuation range shall be confirmed with customers in advance.
6. Long-term Reliability and Environmental Aging Verification
Qualified short-term physical properties do not mean stable long-term use. Aging tests such as thermal aging, damp heat aging, high and low temperature cycle, chemical immersion and UV aging shall be arranged according to working conditions. Buckle products shall be tested for plugging durability, and outdoor products shall focus on weathering attenuation. Low-cost modified materials with low-grade additives often have a sharp drop in impact strength after aging. Solvent immersion method can be used to check the internal stress of products.
7. Small Batch Trial Production, Process Solidification and Mass Production Switching
After reliability verification, small batch trial production is arranged to track multi-cavity products continuously, confirm the process window, and update the operation instruction sheet. Samples shall be sent to customers for assembly test. A phased switching plan shall be formulated, new and old materials shall be stored separately, and a plan to switch back to the original material shall be reserved.
8. Comprehensive Cost Accounting of Material Replacement Projects
Cost accounting shall not only consider raw material unit price. If the new material has longer molding cycle, higher defect rate or faster mold wear, the cost reduction benefit will be offset. Glass fiber filled materials will accelerate the wear of screw, barrel and parting surface, and the drying of some materials will increase energy consumption. The essence of material replacement cost reduction is to find cost redundancy within the performance boundary, rather than sacrificing product reliability for low price. Complete verification links can realize stable cost reduction without performance loss.
