1. Selection of tooling material: NewMat elastomer...
1. Selection of tooling material: NewMat elastomers are environmentally-friendly materials with no chemical corrosion. Ordinary tooling steel or beryllium copper alloy can be used as tooling material. If the high transparency is required for finished products, stainless steel is recommended.
2. Runner Design:
A. Sprue: The sprue should be as short as possible with a draft angle of at least 30 degrees, polished to the direction of demolding. A cold slag added at the bottom of the runner and a design of undercut will facilitate the release of the part, otherwise it will likely cause mold sticking or a breakage of sprue.
B. The Shape and Arrangement of Runners: circular cross sections are the best runner shape. Runners should be arranged evenly. Cold slags and ventilation should be added at runner ends to guarantee an even plastic flow. There are a few options in tooling design. The first option: each cavity hosts the same product. Second option: parts with similar shape, size, and wall thickness may be placed in the same mold. Third option: each part of the same figurine is placed in one mold. The third option is most challenging in terms of quality control and should be avoided unless absolutely necessary.
3. Gate Design:
A. Position: The gate should not face the cavity position where high thickness and high volume parts will be formed. This will likely produce flow marks and spray marks and other injection flaws. The gate should be placed very close to the side of the cavity wall. Specifically: plastic should be injected into the paws of animal figurines. Injecting plastic through two or more gates is not recommended.
B. Shape of gate: The gate should ideally adopt a circular cross-section with a diameter of at least 2mm. Rectangular cross-sections are also acceptable, and should be at least 2x2mm. The thicker the figurine, the bigger the gate; Point gates are not recommended as they are prone to cause flow marks and spray marks.
<p>4. Mold Venting: Runner ends should have venting design. Trapped gas in the product should be released by venting. The depth of the venting grooves should be between 0.015-0.03mm.
5. Mold Cooling: The mold must have sufficient cooling channels. Cooling channels must be able to reach the mold core. If done on a template, the cooling effect will be poor. Cooling must be near the nozzle, otherwise there may be breakage near the gate.
6. Selecting Ratio of Mold Shrinkage: The shrinkage rates vary with different TPR grades and hardness. They differ greatly and the range is very wide. For specific shrinkage rates, refer to the specifications of the TPR product.
1. Selection of Injection Molding Machine: The pressure of each injection should be at 30%-80% of the machine capability. Injection machines with high pressure should not used for low pressure molding. The best choice is to choose a machine with a multi-speed control system.
2. Drying: under normal circumstances, injection do not require drying. If the resin has been placed in a humid environment for medium to long-term storage, it should be dried at 60℃ for 2-3 hours.
3. Clamping Force: 1.5-3 tons/sq. in.<p/>
4. Hopper Temperature Setting: General Principle: The greater the resin hardness, the higher the temperature.
Hardness below 70A: (Actual material temperature 180℃- 190℃)
|180℃ - 190℃
||170℃ - 180℃
||160℃ - 170℃
||150℃ - 160℃
Hardness above 70A: (Actual material temperature 200℃ - 220℃)
|200℃ - 210℃
||180℃ - 210℃
||170℃ - 190℃
||160℃ - 180℃
5. Injection Tuning Parameters: (Speed, positioning and timing are of utmost importance)
A. Stage One Speed: Can be a little faster; fill all runners; can inject resin into the gates of the entire mold cavity; generally at a speed of 10-50%.
B. Stage Two Speed: Can be a little slower; fill to 1/5-1/3 of the product, for thick figurines, the plastic striker should be spherical rather than a spiral or complex shape. Generally use a speed of 5-30%.
C. Stage Three Speed: A slightly faster speed to fill the mold cavity, generally at a speed of 30-50%. Use plastic injection for packing or the packing function of the injection machine for packing.<p/>
D. Injection pressure: the injection or packing pressure should not be too high, only provide sufficient pressure to fill the cavity; otherwise too high pressure will cause demolding problem and thus deformation. It is not advisable to increase pressure in addressing the issues of watermarks or gas lines.
E. Injection time: generally speaking, 15-30 seconds injection time and 25-35 seconds cooling time for thick figurines.<p/>
F. Melting speed: a high-speed melt is recommended to improve flowability. Control it between 50%-90%. Back pressure should be appropriate and not too high; plastic pumping should not be too large. The buffer layer should about 10-30mm, not too large.
6. Machine water is generally used for mold cooling. Mold temperature is controlled at about 20-45℃. Cold water may be used for cooling when necessary. Overly-high molding temperatures will lead to a long cycle time and lower productivity.
7. Runner Reused: Recommend the limit of about 20% although some customers may accept up to 50% of runner material. Follow quality requirements.
8. Color matching: For SBS materials, polystyrene based carrier is recommended. For harder SEBS composites, low density polyethylene (LDPE) or ethylene vinyl acetate copolymer (EVA) can be used. For softer products, PP based carrier is not recommended as the hardness of the composite material will be affected. For some overmolding applications, the use of polyethylene (PE) based carrier may adversely affect the adhesion to the substrate. For specific overmolding material, adhere to the coloring recommendations of the product’s technical datasheet.
1. TPR rubber oil is commonly used. PVC oil is not recommended. According to the expert experience in the ink/paint industry, it is difficult to coat the objects of hardness below 30A and hardness between 70 to 80A. Coating is difficult in places where the shape of a figurine may accumulate the ink. This area may burn because of the extra ink. For specific issues, consult the ink/paint supplier.
2. Poor injection quality are likely to cause coating issues; for example, if products are injected with some glossy surface and some matted surfaces, the matted area will likely burn. Coating will not only unable to conceal the appearance defects, but explore them further.
3. Warpage and shrinkage during demolding will adversely affect coating. The result could be jagged edges of coating effect due to the loose fitting of steawwncil. Consistent control of production parameters is recommended in order to maintain consistent dimension for the finished products.
4. The use of demolding agent or oil stain inside the cavities must be treated by cleaning solution. The products should be thoroughly cleaned before painting.