Flow Lines, Metal Flake Orientation
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This section of metallic molded-in-color rocker molding show appearance defects caused by flow lines and metal flake alignments formed around the attaching hole pins.
Molding Issues and Common Defects
Mold Expansion / Part Shrinkage
• Thermoplastics shrink as they cool and solidify during the molding process and after part ejection. • The mold cavity is machined larger than the final desired part size in order to compensate for part shrinkage as the part cools. • Mold shrinkage data for the specific plastic material can be used to calculate the amount of mold expansion needed. • Mold shrinkage units are expressed as length-per unitlength, or as a percentage, and is calculated using the following formula:
Injection Molding Press
The injection molding press operation includes a means to: Open and close and clamp the injection mold. Measure, melt, and inject the plastic resin. Cool the molten plastic in the mold. Eject the finished part from the mold. Computer control system.
Core with lifter
Cavity
Design Terminology
Part and Tool Design Terminology
Part and Tool Design Terminology
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- Die Angles & Draft Angles, 拔模角 - A Surface, B Surface, etc. A 面, B 面 - Parting Lines, Lifter Lines, 分模线 - Doghouses, Ribs, Flanges 安装支座,加强筋,翻边 - True Holes, Molded Holes, 注塑孔 - Tooling Considerations, 注塑模考虑 ....
Traveling Angled Lifter
Forms rib with flange
*Actually, the cavity is stationary, and the core side moves to open the tool when mounted in the molding machine.
Hot Runner Manifold & Multiple Valve Gates
The manifold in a large mold heats and delivers the hot plastic from the molding machine to the gate locations on the part.
Injection Mold Components
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Cavity Core Clamp Plates Ejector Plate & Pins Lifters Slides Water Lines Gates and Sprues Hot Runner System, etc
Injection Molding and Design 注塑成型与设计
• Injection Molding Process Overview • Part and Tool Design Terminology
• Common Molding Defects
• Molded Part Design Best Practices
We generally use minimum 3 degrees draft per side.
More draft is needed for grained surfaces.
Cavity 'A' surface vs. Core 'B' surface
Do you know the difference? Does your supplier and tool shop? Did you indicate it clearly in your math data file?
Revised Part, eliminate pins on A surface
Oops! Original Part, tooled wrong, core/cavity. Ejection pins on show surface (A surface).
Molding Issues and Common Defects
Injection Molding Process Overview
Injection Molding Process ew
• Injection molding is used to produce most of our complex plastic parts. • Injection molding is a process which involves forcing molten plastic into a machined mold cavity under high pressure.
Core With Slide
Cavity With Horn Pin
Cavity and Core with Lifter and Pin
Cam Operated Core Pin
Forms hole in flange
Cam
Plastic Part
Ejection Pin
Injection Sprue
Die Angle & Parting Line
Cavity
Part (2 cavity) Die Angle (Die Vector) Mold opening direction Parting Line – where the core, cavity, and part meet together. Core
Draft Angles
Parts must have open draft angles in the part geometry design. Part draft angle is measured relative to the die opening angle. If there is no draft angle, the part will cool and shrink onto the tool and will be difficult or impossible to remove without damage.
(mold dimension – part size) / mold dimension = Shrink Factor
Molding Issues and Common Defects
• Dimensional Size Errors (too long, too short, too thin, too thick, etc.) • Dimensional Warpage, Distortion, & Stress • Sink & Shrink Marks • Lifter Line Read-Through • Flow Lines, Weld (Knit) Lines • Metallic Flake Orientation • Porosity • Non-isotropic Behavior (different behavior in different directions)
Flow Line & Metal Flake Orientation
Gate
Flow Obstruction
Weld Lines (Knit Lines)
Weld (knit) lines are appearance and structural defects which are formed when the molten plastic must divide to go around an obstruction and then rejoin itself. We often find this problem on doghouses and also at attaching holes near a part edge.
Injection Mold
• The injection mold forms both the show (A) side and the back (B) side of the part. • The show side of the part is generally the cavity side of the tool, and the back side is the core side. • The interface between the cavity and core is the parting line. • The number of cavities is the number of parts produced per cycle.