Plastic Material Shrinkage Rate
1. Common Plastic Engineering Materials and Shrinkage Rates:
- ABS: 0.5% (Super Tough Plastic)
- PC: 0.5% (Bulletproof Glass Plastic)
- PMMA: 0.5% (Organic Glass)
- PE: 2% (Polyethylene)
- PS: 0.5% (Polystyrene)
- PP: 2% (Polypropylene)
- PA: 2% (Nylon)
- PVC: 2% (Polyvinyl Chloride)
- POM: 2% (Acetal)
- ABS+PC: 0.4%
- PC+ABS: 0.5%
- Engineering Materials: ABS, PC, PE, POM, PMMA, PP, PPO, PS, PET
2. Major Systems in Molds:
- Gating → Ejection → Cooling → Forming → Venting
3. Considerations in Mold Design:
- (1) Uniform wall thickness and adequate draft angles.
- (2) Gradual transitions and smooth corners to avoid sharp edges.
- (3) Gates and runners should be wide, short, and positioned considering shrinkage and cooling; cold slug wells may be necessary.
- (4) Mold surface should be smooth with low roughness (preferably below 0.8).
- (5) Adequate venting holes and slots to expel air and gases.
- (6) Except for PET, wall thickness should not be too thin, generally not less than 1mm.
4. Common Defects in Plastic Parts:
- Short shot → Flash → Bubbles → Shrinkage → Weld lines → Black spots → Streaks → Warping → Delamination → Peeling
5. Common Plastic Mold Steels:
- 45#, S50c, 718, 738, 718H, 738H, P20, 2316, 8407, H13, NAK80, NAK55, S136, S136H, SKD61
6. Steel for High Gloss Polishing:
- Commonly used high-hardness heat-treated steels, such as SKD61, 8407, S136.
7. Mold Base Structures:
- Clamping plate → A plate → B plate → Spacer block → Guide pin → Ejector plate → Ejector retainer plate → Bottom plate
8. Basic Types of Parting Surfaces:
- Flat → Inclined → Curved → Vertical → Arc-shaped
9. How to Hide in UG:
- Ctrl+B or Ctrl+Shift+B
Mold Processing Equipment and Techniques
10. Mold Processing Machinery:
- CNC machining center → Lathe → Milling machine → Grinding machine → Drilling machine
11. What is 2D and 3D?
- D stands for Dimension. 2D refers to two-dimensional planes, and 3D refers to three-dimensional space. In molds, 2D usually refers to CAD drawings, and 3D refers to three-dimensional models.
12. Default Precision in Pro/E and UG:
- Pro/E default precision: 0.0012mm, UG default precision: 0.0254mm.
13. Top Four Global Mold Base Manufacturers:
- Germany: HASCO, Japan: FUTABA, USA: DME, China: LKM.
14. Default Text Height in CAD:
- CAD default text height: 2.5mm.
15. What is a Shut-off and a Core?
- Shut-off refers to the mating surface parallel to the PL surface, and core refers to the mating surface not parallel to the PL surface.
16. Relationship between Tiao and Si:
- Both are units of length. Tiao is used in Taiwan, 1 Tiao = 0.01mm; Si is used in Hong Kong, 1 Si = 0.01mm. Therefore, 1 Tiao = 1 Si.
17. What is a Pillow Block?
- The edge of a shell plastic part often has notches for installing accessories, forming a pillow-shaped parting surface called a pillow block.
18. What is a Crater?
- The reduced material at the base of a boss, resembling a volcanic crater, is called a mold crater.
19. What is a Core?
- Core refers to the mold insert, commonly used in Hong Kong.
20. What is a Tiger Mouth?
- Tiger mouth, also known as a positioning block, is used for limiting positions.
21. What is Layout?
- The arrangement of products on a mold is called layout.
22. What is a Cavity?
- The hollow part of a product on a mold is called a cavity.
23. What is a Rib?
- The ribs on a product are called ribs.
24. What is a Boss?
- The columns on a product are called bosses.
25. What is Clearance?
- The gap on a mold is called clearance.
26. What is a Hook?
- The connecting hooks on a product are called hooks.
27. What is EDM Texture?
- The texture left after EDM (Electrical Discharge Machining) is called EDM texture.
28. What is a PL Surface?
- PL surface, also known as the parting surface, is the contact surface between the front and rear molds when closed.
29. What is a CNC Machining Center?
- CNC milling machines and machining centers.
30. What is a Copper Electrode?
- EDM often uses easily machinable copper as the discharge electrode, called a copper electrode or simply electrode. Copper electrodes are generally divided into rough, semi-finish, and finish electrodes, with finish electrodes also known as precision electrodes.
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