The polishing effect of plastic moulds is affected by a variety of factors, which can be summarized into the following main categories:
1. Material factor
Steel quality: The hardness, purity and uniformity of the material are crucial. High-hardness steel is more wear-resistant but difficult to polish; Impurities or pores can easily lead to surface defects.
Heat treatment process: Improper heat treatment may cause uneven hardness, decarburization layer or residual stress, resulting in orange peel phenomenon or micro-cracks.
2. Manufacturing process
The hardening layer formed by EDM (about 20-30μm) needs to be removed by grinding or acid etching, otherwise it is easy to pitting after polishing.
Machining marks: Deep knife marks left by milling or grinding need to be treated before polishing, otherwise it is difficult to completely eliminate.
3. Polishing process parameters
Steps and tools: Follow the process from coarse to fine (e.g. 400#→1500# sandpaper), each step needs to completely remove the previous trace.
Polishing medium: Improper selection of grinding paste size (such as premature use of fine granularity) can lead to inefficiency or uneven surface.
Temperature control: Local overheating may cause material to soften or oxidize, affecting surface consistency.
4. Mold design
Geometric complexity: Areas with deep cavities, narrow grooves or sharp angles are difficult to evenly polish, and reachability needs to be considered during the design phase.
Parting line and insert structure: the joint is easy to produce uneven polishing, requiring special treatment.
5. Surface pretreatment
Cleanliness: Oil, rust or oxide should be completely removed by pickling or sandblasting, otherwise it will affect the polishing effect.
Welding repair: The hardness difference between the welding material and the substrate needs to be eliminated by tempering treatment (such as 300℃×2h).
6. Human factors
Handling skills: Inexperience can lead to cross scratches (such as not polishing in a single direction) or overthrowing (material removal > 0.01mm).
Quality inspection: Real-time monitoring is required using a 10x magnifying glass or roughness meter (Ra≤0.025μm).
7. Environmental control
Cleanliness: It should be operated in a dust-free workshop above ISO Class 6 (Class 1000) to avoid particles pressing into the surface.
Temperature and humidity: 23±2 ° C and 40-60% humidity are recommended to prevent tool rust.
8. Auxiliary devices
Polishing machine accuracy: spindle radial runout should be < 0.005mm, speed should be adjusted according to the process (rough polishing 800rpm, fine polishing 1200rpm).
Fixture design: It is necessary to ensure that the workpiece is firmly installed and avoid ripples caused by vibration (amplitude < 2μm).
9. Post-treatment process
Ultrasonic cleaning: Use a neutral solvent (pH6.5-7.5) at 40kHz for 10 minutes to completely remove the polishing residue.
Anti-rust treatment: Spray gas phase anti-rust agent (VCI) or nitrogen storage to prevent oxidation during storage.
Typical case analysis