1. Define Purpose of Analysis
Before starting mold flow analysis, purpose of analysis must be clearly defined. For new molds, analysis can avoid potential problems and ensure rationality of design; for existing molds, analysis can help solve practical problems, such as incomplete filling and warpage.
2. Data Collection
Collect all relevant design and process data, including 3D model of product, mold structure, material properties, and process parameters.
Table 1 Injection Molding Process Parameters

 

Fit material properties to a UDB file and then import it into flow analysis software. This includes data such as material rheology, thermal conductivity, PVT, and filler aspect ratio.

 

Figure 1 Material Property Parameters
Click to obtain: National High-Tech Materials Analysis and Testing Center - National Integrated Service Platform for Polymer Materials Testing and Scientific Research
3. Select Appropriate Mold Flow Analysis Software
Select appropriate mold flow analysis software according to project requirements, such as Moldflow, Moldex3D, etc.
4. Mesh Generation
Mesh is core of mold flow analysis; a high-quality mesh directly affects accuracy of analysis. Ensure mesh generation meets following requirements: No free boundaries. For double-sided flow analysis, mesh matching rate of upper and lower surfaces must reach 90%. Side length ratio of triangular elements: average <3:1, maximum <6:1. No intersections or overlaps between meshes. Mesh size.
5. Material Parameter Definition
Accurately define material parameters, such as melt flow index, coefficient of thermal expansion, etc.
6. Injection Parameter Setting
Set injection parameters according to actual performance of injection molding machine, including injection speed, pressure, holding pressure, etc.

1. Filling Analysis: Filling analysis is the first step in mold flow analysis, focusing on how melt fills mold cavity. Note that injection/holding pressure switching point should be between 95% and 99% of injection volume.
If injection volume is less than 95% of part volume, it can lead to insufficient holding pressure. That is, some areas will have defects such as shrinkage marks and material shortages due to insufficient filling.
2. Pressure Distribution Check: Inspect pressure distribution at mold flow tip to ensure it is balanced and symmetrical, avoiding excessive pressure that could lead to inconsistent material shrinkage or insufficient holding pressure.
3. Melt Tip Temperature Monitoring: Monitor temperature changes at melt tip to prevent excessive temperature fluctuations that could cause internal residual stress and warpage.
4. Cooling Analysis: Focus on efficiency of mold's cooling system to ensure uniform cooling of plastic part and prevent deformation.
5. Warpage Deformation Analysis: Predict potential deformation of plastic part during cooling and solidification, providing a basis for mold design corrections.
Rationality of gate location; Size of gate and runner; Rationality of cooling water channel design; Understanding rationality of product's molding cycle; Magnitude of clamping force, confirming size of injection molding machine in advance; Identifying air trapping areas in product, preparing venting system in advance; Identifying whether there is shrinkage on product surface, optimizing and reducing material loss in advance; Identifying location of weld lines on product surface during molding; Identifying whether there are flow marks and spray marks on product surface; Identifying whether there are areas of incomplete filling in product; Identifying whether there are deformed areas in product, adjusting for deformation during material removal!

 

Design range of male and female mold core dimensions during plastic mold design

 

Note: When designing molds, designers are required to use integer values for mold core dimensions; therefore, safety distance is not a fixed value and can be adjusted according to product (part) dimensions.

 

540 + 2 * 45 = 630 Mold core width
310 + 2 * 45 = 400 Mold core length
120 (female mold core thickness) * 1.68 = 201.6 Female mold core thickness
110 (male mold core thickness) * 1.8 = 198 Male mold core thickness

 

1. Scrap Material Jumping into Cavities
Punch length is insufficient: Cut punch into die by one piece of material thickness plus 1mm, replace punch.
Die clearance is too large: Cut in insert to reduce clearance or use a calendering machine to reduce clearance.
Punch or die plate not demagnetized: Demagnetize punch or die plate with a demagnetizer.
2. Scrap Material Blocking into Cavities
Small blanking hole or misaligned blanking hole: Enlarge blanking hole to ensure smooth blanking.
Chamfered blanking hole: Enlarge blanking hole or remove chamfer.
No taper on cutting edge: Cut a taper or enlarge hole on reverse side to reduce length of straight wall section.
Excessively long cutting edge straight wall section: Drill a hole on reverse side to shorten cutting edge straight wall section.
Chipped cutting edge, causing large burrs, causing blockage; re-grind cutting edge.
3. Poor Burrs
Cutting edge is chipped, resulting in excessive burr. Re-grind cutting edge. Clearance between punch and die is too large; use wire-cutting inserts and readjust clearance. De edge has poor surface finish; polish die edge to ensure straight wall position. Clearance between punch and die is too small; re-finish die and readjust clearance. Ejector force is too large; pull burr out in reverse direction and replace spring to reduce ejector force.
4. Uneven cutting edge
Positioning misalignment; adjust positioning. One-sided forming; increase pulling force and adjust positioning. Design error causing uneven tool connection; re-wire-cut trimming insert. Inaccurate feeding; adjust feeder. Incorrect feeding step distance calculation; recalculate step distance and reposition tool connection.
5. Punch easily breaks
Following are common causes of punch breakage:
Closed Height Too Low: Punch cutting edge is too long. Adjust closed height.
Improper Material Positioning: Punch cuts on one side. Adjust positioning or feeding device. Uneven force causes breakage.
Scrap Material from Lower Die Blocks Cutting Edge, Causing Punch Breakage. Re-drill a larger blanking hole to ensure smooth material flow.
Refit or Re-cut Punch's Fixing Part (Clamping Plate) and Guide Part:Repair or re-cut insert block to ensure smooth punch movement.
Poor Punch Guide: Punch experiences uneven force on one side. Repair punch gap.
Punch Cutting Edge Too Short, Interfering with Punch. Replace punch and increase cutting edge length. Punch not properly fixed, moving up and down. Re-fix punch to prevent it from moving up and down. Punch cutting edge is not sharp. Re-grind cutting edge. Punch surface is scratched, uneven force during stripping. Replace punch. Punch is too thin, too long, or lacks strength. Replace punch type. Punch hardness is too high, punch material is incorrect. Replace punch material and adjust heat treatment hardness.
6. Iron filings
Misaligned ribs: Recalculate rib position or bend position.
Insufficient bending gap: Extruded iron filings; readjust gap, or grind forming block, or grind forming punch.
Bending punch too sharp: Repair R-angle.
Insufficient cutting edge material: Re-connect cutting edge.
Ribs too narrow: Re-grind ribs.
7. Poor drawing:
Center of budding hole does not coincide with center of budding punch, requiring accurate centering. This necessitates repositioning budding punch, potentially resulting in a budding-side-high-side-low or even breakage issue. Adjusting pre-punch position or positioning may also cause problems.
Uneven die clearance can lead to a budding-side-high-side-low clearance or even breakage.
Budding hole may not meet requirements, causing budding height issues. Recalculating hole diameter, increasing or decreasing pre-punch diameter deviation, or even breakage may occur.
8. Poor forming
Forming die punch is too sharp, causing material tearing. Adjust radius (R) of forming punch, and appropriately adjust R at cutting edge.
Insufficient forming punch length results in incomplete forming. Calculate correct punch length and adjust actual punch length to achieve forming requirements.
Forming punch is too long, causing material deformation at forming point, even leading to punch breakage.
Insufficient material at forming point causes tearing. Calculate and expand material, or adjust R angle, or reduce forming height.
Poor positioning causes poor forming. Adjust positioning or feeding device.
Insufficient forming gap causes tearing or deformation. Adjust spacing. Gap
9. Bending dimensions
Die not properly adjusted, causing angle error and dimensional deviation: Incorrect closing height or angle difference.
Insufficient spring force, causing angle error and dimensional deviation: Replace spring.
Material not meeting requirements, causing angle error and dimensional deviation: Change material or readjust clearance deviation.
Material thickness deviation causing angle error and dimensional deviation: Determine material thickness, change material or readjust clearance difference.
Improper positioning causing dimensional deviation: Adjust positioning to achieve OK dimensions.
Design or processing errors causing gaps between bending manifold parts: Weld and grind to eliminate gaps between parts, resulting in smaller bending dimensions.
Forming manifold without R-angle: Under normal angle and other conditions, bending height is too small when forming manifold's R-angle is adjusted.
Both sides bending dimensions are too large: Add pressure ribs.
Single-sided bending with material pulling causes dimensional instability: Increase spring force and adjust positioning.
Unreasonable clearance causing angle error and dimensional deviation: Adjust clearance.
Insufficient bending knife height: Bending punch is too short when engaging bending knife. Increase bending knife height to ensure bending punch engages as much as possible. Folding knife misalignment causes more angle defects.
Excessive bending speed causes deformation at bend root; adjust speed ratio control and select an appropriate speed.
Inadequate structure; folding knife not inserted into fixed mold plate. Re-mill groove and insert folding knife into mold plate. During stamping, this causes a larger gap.
Insufficient heat treatment hardness of forming die causes pressure lines to break or require remaking forming die and flattening pressure lines.
10. No unloading.
Improper positioning or feeding: Adjust positioning or feeding device.
Insufficient clearance: Grind clearance.
Inner guide post damage causing poor platen movement: Replace inner guide post.
Punch scratches or uneven surface: Replace punch.
Ejector pin misalignment: Reposition ejector pin.
Insufficient ejector force or stripping force: Replace ejector spring or stripping spring.
Improper punch-clamp fit: Repair ejector plate and clamp to ensure proper punch fit.
Improper forming slide fit: Repair slide and guide groove to ensure proper fit.
Improper heat treatment of forming plate: Deformation after stamping period: Re-grind forming plate and correct deformation.
Punch too long or ejector pin too short: Increase ejector pin length or replace with a punch of appropriate length.
Broken punch: Replace punch.
Die plate not demagnetized: Demagnetize die plate as workpiece is moved upwards.
11. Feeding irregularities:
Mold not properly aligned, causing strip to be misaligned with feeder and mold. Re-align mold or adjust feeder.
Uneven strip: Adjust leveling machine or change material.
Failure to unload causes feeding problems. Refer to solutions for failure to unload.
Positioning too tight: Adjust positioning.
Guide pin too tight or straight wall too long: Adjust guide pin.
Punch not properly fixed or too long, interfering with strip. Replace with a punch of appropriate length and re-fix.
Ejector pin too short, causing interference between strip and forming block. Adjust ejector pin length to avoid interference.
Improper placement of floating blocks: Adjust floating block position.
12. Poor Riveting
Improper mold closing height; riveting not in place. Adjust closing height.
Workpiece not placed correctly; positioning deviation. Adjust positioning.
Before riveting, confirm workpiece defects, including burr hole. Refer to burr hole defect solutions.
Check if riveting hole is chamfered; if not, add a chamfer.
Insufficient riveting punch length; replace with a punch of appropriate length.
Riveting punch does not meet requirements; confirm and use a suitable riveting punch.
13. Missing or Incorrect Installation
Accidentally misinstalled punches during assembly.
Punches without directional markings; mark directional punches.
14. Incorrect Screw Installation
Unknown template thickness; template too long or too short.
Insufficient attention to detail; lack of experience. Use appropriate screws.
15. Mold assembly/disassembly:
Pin holes not cleaned properly: Clean pin holes and pins thoroughly. When disassembling mold, remove locating pins first as they are easily damaged. When assembling mold, use screws to guide pins first, then drill locating pin holes.
Incorrect mold assembly/disassembly procedure: Do not damage pin holes when knocking out pins.
16. Locating pins:
Roughness or scratches on hole wall causing excessive tightness: When assembling mold, carefully check if pin holes are rough. If not, re-ream pin holes that cannot be drilled.
Pin hole misalignment or lack of escape hole: Add locating pin escape holes.
17. Spring too long:
Failure to pay attention to spring hole depth: Measure spring hole depth carefully, calculate spring compression, and reselect a spring that cannot be compressed to correct depth.
Insufficient attention and experience: Choose a suitable spring with appropriate bottom dead center.