88 Essential Mold Design Basics: The Ultimate Guide for Mold Makers

Whether you are a seasoned mold designer or a new engineer, having a solid grasp of fundamental concepts is crucial. This guide compiles 88 essential knowledge points regarding plastic materials, mold structures, processing techniques, and industry terminology.

Section 1: Materials & Properties

#	Topic	Details
1	Common Plastics & Shrinkage	• ABS: 0.5%• PC: 0.5%• PMMA: 0.5%• PE: 2%• PS: 0.5%• PP: 2%• PA (Nylon): 2%• PVC: 2%• POM: 2%• ABS+PC: 0.4%• PC+ABS: 0.5%
2	Recommended Wall Thickness	• ABS: 1.8 – 3 mm• PC: 2 – 3.5 mm• POM: 1.5 – 2.5 mm• Noryl: 2 – 3.5 mm
3	Flash Values (Tolerance)	• ABS: 0.04 mm• PC: 0.06 mm• PA: 0.015 mm• POM: 0.04 mm• PP: 0.03 mm• PE: 0.02 mm• PVC: 0.07 mm

Section 2: Mold Structure & Systems

#	Topic	Details
1	5 Major Systems	1. Gating System2. Ejection System3. Cooling System4. Forming System5. Venting System
2	Mold Base Components	Top Clamp Plate → A-Plate → B-Plate → Support Block → Guide Pins → Ejector Plates → Bottom Clamp Plate.
3	Parting Line (PL) Forms	Straight, Angled, Curved, Vertical, Stepped.
4	Shut-off vs. Interlock	• Shut-off: Parallel to PL plane.• Interlock: Angled/Non-parallel to PL plane.
5	PL Plane Definition	The contact surface between the front (cavity) and rear (core) molds when closed.
6	Global Standards	• HASCO: Europe• DME: USA• LKM: China/Asia• FUTABA: Japan
7	Gating Methods	Direct Sprue, Tab Gate, Edge Gate, Ring Gate, Submarine (Tunnel) Gate, Pin Point Gate, Cashew Gate, Fan Gate.
8	Runner Shapes	Circular, Semicircular (Trapezoidal), T-Shape, Hexagonal.
9	Mold Classification	• By Material: Plastic vs. Non-Plastic (Stamping, Die Casting).• By Gating: 2-Plate, 3-Plate, Hot Runner.
10	Gating System	Channel from nozzle to cavity: Sprue → Runner → Gate → Cold Slug Well.

Section 3: Design Principles & Calculations

#	Topic	Details
1	Design Considerations	• Uniform wall thickness.• Sufficient draft angles.• Smooth transitions (no sharp corners).• Wide/short runners.• Surface roughness < 0.8.• Adequate venting.
2	Why Draft Molds?	To prevent scratching or damage during ejection.
3	Screws & Fasteners	• Function: Fixing/Clamping.• Engagement Length: 1.5x to 2x screw diameter.
4	Slider Angles	• Slider Wedge: 20°• Angle Pin: 18°
5	Cold Slug Well	Captures cool plastic at the start of injection to prevent blockage.
6	Locating Ring	Centers the mold with the injection machine nozzle.
7	Inserts Function	Saves material, aids venting/polishing, easy replacement of worn parts.
8	Clamping Force	Must be greater than internal cavity pressure to prevent flashing.
9	Deformation	• Elastic: Returns to shape.• Plastic: Permanent deformation.

Section 4: Industry Terminology (The "Lingo")

#	Term	Definition
1	Tiao / Si	Unit of length. 1 Tiao = 1 Si = 0.01 mm.
2	Pillow	Stepped parting surface for housing edges.
3	Volcano	Recess at base of Boss to prevent sink marks.
4	Heh-Zhi	Hong Kong slang for Mold Insert (Core/Cavity).
5	Tiger Mouth	Interlock mechanism for alignment.
6	Layout	Arrangement of cavities in the mold.
7	Cavity	The void in the mold forming the part.
8	Rib	Reinforcing wall on the plastic part.
9	Boss	Cylindrical post for screws/assembly.
10	Clearance	Gap between components.
11	Snap Fit	Plastic hook for assembly.
12	Spark Pattern	Texture from EDM process.
13	Electrode	Copper/Graphite tool for EDM (Roughing/Finishing).
14	Spark Gap	EDM gap: Roughing (0.1-0.5mm), Finishing (0.05-0.15mm).
15	Wanddicke	Thickness of the plastic part ("Meat").
16	Integral Core	Core machined from one block (no inserts).
17	Weld Lines	Line where two melt flows meet.
18	Jetting	Snake-like flow mark from high speed entry.
19	LKM	Long Ji Mold Base standard.
20	Undercut	Feature preventing direct ejection.
21	Poka-Yoke	Fool-proofing design (e.g., unique alignment pins).
22	Beer Machine	Slang for Injection Molding Machine.
23	Beauty Line	Cosmetic line to hide parting lines.
24	Fly Mold	Fitting/matching process.
25	Light Knife	Final CNC finishing pass.
26	Opening Frame	Machining pocket for inserts in mold base.
27	Photo Etching	Adding logos/text via film process.
28	Reverse Core	Inverted molding orientation.
29	Floating Core	Small insert for undercut ejection.
30	Core Stick	Part sticking to the core side.
31	Stress Marks	White marks from excessive ejection force.
32	Gate Vestige	Mark left by submarine gate.
33	Clamping Block	Wedge tool for assembly.
34	Overcut	Machining error (removing too much material).
35	Core Pull	Internal slider/lifter action.
36	Tapping	Cutting threads.

Section 5: Software & Machinery

#	Topic	Details
1	UG Shortcuts	Hide/Unhide: `Ctrl+B` or `Ctrl+Shift+B`.
2	Machinery	CNC Mill, Lathe, Milling, Grinding, Drilling, EDM.
3	2D vs 3D	• 2D: CAD Drawings.• 3D: Solid Models (NX, Pro/E).
4	Default Accuracy	• Pro/E: 0.0012 mm• UG: 0.0254 mm
5	CAD Text Height	2.5 mm.
6	Surface Drafting	Single surfaces cannot be drafted; Surface Sets (Quilts) can.
7	Projection Angles	• 1st Angle: Left view on Right (Europe/Asia).• 3rd Angle: Left view on Left (USA).
8	Paper Sizes	A0 (1189x841), A1 (841x594), A2 (594x420), A3 (420x297), A4 (297x210).
9	CAD Spaces	• Model Space: Geometry creation.• Layout Space: Sheet arrangement.

Section 6: Defects & Troubleshooting

#	Defect	Beschreibung
1	Short Shot	Incomplete filling of the cavity.
2	Flash	Excess plastic leaking at parting lines.
3	Air Bubbles	Trapped air pockets inside the part.
4	Sink Marks	Depressions from thick wall cooling.
5	Weld Lines	Visible lines at flow front intersections.
6	Black Spots	Contamination or burnt material.
7	Warpage	Bending/twisting after cooling.
8	Delamination	Layers peeling apart.

Section 7: Hardness & Steel

#	Topic	Details
1	Mold Steels	• Pre-hardened: P20, 718, NAK80.• Hardened: S136, H13, SKD61.• Base: 45#, S50C.
2	Mirror Polish Steel	High hardness steels like S136, 8407, SKD61.
3	Hardness Scales	Brinell (HB), Rockwell (HRC), Vickers (HV).
4	Mold Base Material	Medium Carbon Steel (45# Steel / "Wang Steel").

Section 8: Process & Workflow

#	Topic	Details
1	Double Color Molds	Used for two materials or two colors in one part.
2	Design Workflow	Product Analysis → Material Selection → 3D Parting → Gating → Structure → Detail Drawings → BOM.
3	Demolding	• Smooth: Standard ejection.• Force: Stripping (for flexible plastics like PP).
4	Springs	Provide rebound force for mechanisms.
5	Fits	Clearance, Transition, Interference (Press).
6	Cooling Lines	Straight-through, Loop, Fountain (Bubbler), Spiral.
7	Injection Machines	Vertical/Horizontal; by Shot Size (mg to kg); by Clamping Force (Tons).
8	Mold Sizes	• Small: 15-30 series.• Medium: 30-50 series.• Large: 50+ series.
9	Cooling Function	Controls mold temperature.
10	Mold Definition	Tool to shape materials via pressure.
11	Reverse Engineering	3D scanning → Surface reconstruction → CAD data generation.

Fazit

Mastering these 88 points provides a solid foundation for any career in mold design and manufacturing. From understanding the subtle shrinkage differences between ABS and PC to navigating complex CAD standards, attention to detail is what separates a good mold from a great one.

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