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Ten Steps of Plastic Mold Design
发布日期：2021.11.12 类别：Industry News
I. Receiving the Task Brief
The task brief for forming plastic parts is usually proposed by the part designer, and its contents are as follows:
1. Formal part drawings that have been reviewed and signed, specifying the plastic grade, transparency, etc.
2. Instruction manual or technical requirements for the plastic part.
3. Production volume.
4. Samples of the plastic part.
Usually, the mold design task brief is proposed by the plastic part process engineer based on the part brief. Mold designers use both as the basis for designing the mold.
II. Collecting and Organizing Information
Collect information regarding part design, molding processes, equipment, machining, and specialized processing for use during design.
5. Digest the plastic part drawing: Understand the part's application, analyze manufacturability, dimensional accuracy, and other technical requirements. For example, what are the requirements for appearance, color, transparency, and performance? Is the geometry, draft, and insert placement reasonable? Determine the allowable degree of defects like weld marks and sink marks, and check for post-processing requirements like painting or plating.
6. Digest process data: Analyze whether the molding method, equipment, material specifications, and mold type proposed are appropriate and feasible.
7. Determine the molding method: Compression, transfer, or injection molding.
8. Select molding equipment: Familiarize yourself with the performance and specifications of the equipment (injection capacity, clamping pressure, mounting dimensions, ejection stroke, etc.). Estimate the mold's overall dimensions to ensure it fits the selected machine.
9. Specific structural scheme:
(1) Determine the mold type: e.g., injection mold, compression mold (open, semi-closed, closed), etc.
(2) Determine the main structure: Select the ideal structure based on technical and economic requirements (geometry, surface finish, accuracy, cost-effectiveness, and service life).
III. Factors Influencing Mold Structure and Systems
The factors influencing mold structure are complex and include:
10. Cavity layout: Determine the number and arrangement of cavities based on geometry, accuracy, volume, and cost.
11. Determining the parting surface: The position should facilitate machining, venting, demolding, and surface quality.
12. Gating and venting systems: Define the shape, position, and size of the sprue, runners, gates, and vent grooves.
13. Ejection and core-pulling: Choose the ejection method (pins, sleeves, stripper plates) and core-pulling mechanism for undercuts.
14. Cooling and heating: Decide on the method, channel shape, and installation of heating elements.
15. Dimensions and strength: Based on material and strength calculations, determine part thicknesses, overall dimensions, and the layout of connection/positioning/guiding components.
16. Structural form of main molding and structural parts.
17. Strength considerations: Calculate working dimensions for molding parts.
Once these are resolved, prepare the structural sketch for formal drawing.
IV. Drafting the Mold Layout
Drawings must follow national standards while incorporating factory-specific conventions. Before the assembly drawing, create a process drawing reflecting the part requirements. If no machining other than flash removal is needed after molding, the process drawing is identical to the part drawing.
V. Drafting the Assembly Drawing
Use a 1:1 scale where possible. Start from the cavity and draw multiple views simultaneously.
18. Mold forming structure.
19. Gating and venting system structure.
20. Parting surface and part removal method.
21. External structure, fasteners, positioning, and guiding components.
22. Dimensions (cavity height and overall dimensions).
23. Auxiliary tools (removal, calibration tools).
24. Numbering all parts and completing the Bill of Materials (BOM).
25. Technical requirements and operating instructions.
VI. Technical Requirements in Assembly Drawing
26. Performance requirements for systems (e.g., assembly requirements for ejection or sliders).
27. Requirements for assembly processes (e.g., parting line fit gap < 0.05mm, parallelism of platens).
28. Usage, assembly, and disassembly methods.
29. Anti-oxidation, numbering, marking, oil sealing, and storage requirements.
30. Requirements for mold testing and inspection.
VII. Drafting Part Drawings
Extract parts from the assembly drawing in order: inside to outside, complex to simple, molding parts first, then structural parts.
31. Graphics: Accurate projection and reasonable view selection. Keep graphics consistent with the assembly drawing for clarity.
32. Dimensioning: Unified, concentrated, and complete. Annotate primary dimensions and draft first, then fit dimensions, then all others.
33. Surface roughness: Use a general note for common roughness and specific symbols for others.
34. Other details: Part name, mold number, material grade, heat treatment/hardness, surface treatment, scale, and technical notes.
VIII. Proofreading and Review
(I) Self-Proofreading:
35. Relationship with part drawings: Check if materials, hardness, and accuracy meet requirements.
36. Plastic part aspects: Check if flow, sink marks, or draft affect performance. Verify shrinkage rate selection.
37. Equipment compatibility: Verify injection volume, pressure, clamping force, and nozzle contact.
38. Mold structure: Check parting surface, flashing risks, ejection method (pins/stripper plate), cooling/heating channel effectiveness, and core-pulling mechanisms.
39. Drawing accuracy: Check numbering, BOM, material callouts, tolerances, and projection correctness.
40. Machinability: Ensure all parts are designed for efficient manufacturing.
41. Auxiliary tools: Re-calculate working dimensions.
(II) Professional Review: Focus on structural principles, processability, and safety.
(III) Signing: Design and tool manufacturing departments must review and sign off.
(IV) Process Card: Technical personnel prepare manufacturing process cards and prepare for production.
IX. Mold Testing and Modification
After manufacturing, perform mold trials to verify part quality. If defects appear, perform detailed analysis. Since molding conditions are easier to change, always adjust process parameters before considering mold modifications. Mold modifications should be handled with extreme caution as they are often irreversible.
X. Data Archiving
If the mold is not in use, clean it, apply anti-rust oil, and store it. Systematically organize, bind, and archive all technical documents generated—from the task brief to trial records. This data is invaluable for future maintenance and new designs.
The task brief for forming plastic parts is usually proposed by the part designer, and its contents are as follows:
1. Formal part drawings that have been reviewed and signed, specifying the plastic grade, transparency, etc.
2. Instruction manual or technical requirements for the plastic part.
3. Production volume.
4. Samples of the plastic part.
Usually, the mold design task brief is proposed by the plastic part process engineer based on the part brief. Mold designers use both as the basis for designing the mold.
II. Collecting and Organizing Information
Collect information regarding part design, molding processes, equipment, machining, and specialized processing for use during design.
5. Digest the plastic part drawing: Understand the part's application, analyze manufacturability, dimensional accuracy, and other technical requirements. For example, what are the requirements for appearance, color, transparency, and performance? Is the geometry, draft, and insert placement reasonable? Determine the allowable degree of defects like weld marks and sink marks, and check for post-processing requirements like painting or plating.
6. Digest process data: Analyze whether the molding method, equipment, material specifications, and mold type proposed are appropriate and feasible.
7. Determine the molding method: Compression, transfer, or injection molding.
8. Select molding equipment: Familiarize yourself with the performance and specifications of the equipment (injection capacity, clamping pressure, mounting dimensions, ejection stroke, etc.). Estimate the mold's overall dimensions to ensure it fits the selected machine.
9. Specific structural scheme:
(1) Determine the mold type: e.g., injection mold, compression mold (open, semi-closed, closed), etc.
(2) Determine the main structure: Select the ideal structure based on technical and economic requirements (geometry, surface finish, accuracy, cost-effectiveness, and service life).
III. Factors Influencing Mold Structure and Systems
The factors influencing mold structure are complex and include:
10. Cavity layout: Determine the number and arrangement of cavities based on geometry, accuracy, volume, and cost.
11. Determining the parting surface: The position should facilitate machining, venting, demolding, and surface quality.
12. Gating and venting systems: Define the shape, position, and size of the sprue, runners, gates, and vent grooves.
13. Ejection and core-pulling: Choose the ejection method (pins, sleeves, stripper plates) and core-pulling mechanism for undercuts.
14. Cooling and heating: Decide on the method, channel shape, and installation of heating elements.
15. Dimensions and strength: Based on material and strength calculations, determine part thicknesses, overall dimensions, and the layout of connection/positioning/guiding components.
16. Structural form of main molding and structural parts.
17. Strength considerations: Calculate working dimensions for molding parts.
Once these are resolved, prepare the structural sketch for formal drawing.
IV. Drafting the Mold Layout
Drawings must follow national standards while incorporating factory-specific conventions. Before the assembly drawing, create a process drawing reflecting the part requirements. If no machining other than flash removal is needed after molding, the process drawing is identical to the part drawing.
V. Drafting the Assembly Drawing
Use a 1:1 scale where possible. Start from the cavity and draw multiple views simultaneously.
18. Mold forming structure.
19. Gating and venting system structure.
20. Parting surface and part removal method.
21. External structure, fasteners, positioning, and guiding components.
22. Dimensions (cavity height and overall dimensions).
23. Auxiliary tools (removal, calibration tools).
24. Numbering all parts and completing the Bill of Materials (BOM).
25. Technical requirements and operating instructions.
VI. Technical Requirements in Assembly Drawing
26. Performance requirements for systems (e.g., assembly requirements for ejection or sliders).
27. Requirements for assembly processes (e.g., parting line fit gap < 0.05mm, parallelism of platens).
28. Usage, assembly, and disassembly methods.
29. Anti-oxidation, numbering, marking, oil sealing, and storage requirements.
30. Requirements for mold testing and inspection.
VII. Drafting Part Drawings
Extract parts from the assembly drawing in order: inside to outside, complex to simple, molding parts first, then structural parts.
31. Graphics: Accurate projection and reasonable view selection. Keep graphics consistent with the assembly drawing for clarity.
32. Dimensioning: Unified, concentrated, and complete. Annotate primary dimensions and draft first, then fit dimensions, then all others.
33. Surface roughness: Use a general note for common roughness and specific symbols for others.
34. Other details: Part name, mold number, material grade, heat treatment/hardness, surface treatment, scale, and technical notes.
VIII. Proofreading and Review
(I) Self-Proofreading:
35. Relationship with part drawings: Check if materials, hardness, and accuracy meet requirements.
36. Plastic part aspects: Check if flow, sink marks, or draft affect performance. Verify shrinkage rate selection.
37. Equipment compatibility: Verify injection volume, pressure, clamping force, and nozzle contact.
38. Mold structure: Check parting surface, flashing risks, ejection method (pins/stripper plate), cooling/heating channel effectiveness, and core-pulling mechanisms.
39. Drawing accuracy: Check numbering, BOM, material callouts, tolerances, and projection correctness.
40. Machinability: Ensure all parts are designed for efficient manufacturing.
41. Auxiliary tools: Re-calculate working dimensions.
(II) Professional Review: Focus on structural principles, processability, and safety.
(III) Signing: Design and tool manufacturing departments must review and sign off.
(IV) Process Card: Technical personnel prepare manufacturing process cards and prepare for production.
IX. Mold Testing and Modification
After manufacturing, perform mold trials to verify part quality. If defects appear, perform detailed analysis. Since molding conditions are easier to change, always adjust process parameters before considering mold modifications. Mold modifications should be handled with extreme caution as they are often irreversible.
X. Data Archiving
If the mold is not in use, clean it, apply anti-rust oil, and store it. Systematically organize, bind, and archive all technical documents generated—from the task brief to trial records. This data is invaluable for future maintenance and new designs.
