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Injection molding is a high-precision manufacturing process that injects molten plastic into a carefully designed mold, where the plastic cools and hardens into the specified part or product. The piece is then ejected from the mold, either as the final product or as a near-final product that is sent on for secondary finishing.
The injection mold consists of two parts: the mold core and the mold cavity. The space that these two parts create when the mold is closed is called the part cavity (the void that receives the molten plastic). Depending on production needs, “multi-cavity” molds can be designed to create multiple identical parts (as many as 100 or more) during the same run. Injection mold design China is now obey these basics.
Designing the mold and its various components (referred to as tooling) represents a highly technical and often complex process that requires high precision and scientific know-how to produce top-quality parts with tight dimensions. For example, the proper grade of steel must be selected so components that run together do not wear out prematurely. Steel hardness must also be determined to maintain the proper balance between wear and toughness. Waterlines must be well-placed to maximize cooling and minimize warping. Tooling engineers also need to calculate gate/runner sizing specifications for proper filling and minimal cycle times, as well as determine the best shut-off methods for tooling durability over the life of the program.
During the injection molding process, molten plastic flows through channels called “runners” into the mold cavity. The direction of flow is controlled by the “gate” at the end of each channel. The system of runners and gates must be carefully designed to assure even distribution of plastic and subsequent cooling. Proper placement of cooling channels in mold walls to circulate water are also essential for cooling to create a final product with homogeneous physical properties, resulting in repeatable product dimensions. Uneven cooling may result in defects called “hot spots”—areas of weakness that affect repeatability.
In general, more complex injection-molded products require more complex molds. Now injection mold manufacturer China is able to solve these problems. These often must deal with features such as undercuts or threads, which typically require more mold components. There are other components that can be added to a mold to form complex geometry; rotating devices (using mechanical racks and gears), rotational hydraulic motors, hydraulic cylinders, floating plates, and multi-form slides are just some examples.
Stage 1: Manufacturability and Feasibility
In this initial stage, design engineers, tooling engineers, materials engineers, manufacturing engineers, quality engineers, and lab technicians work together to determine product specifications, mold component functionality, mold materials, operational constraints, and any needed product enhancements and improvements. The team especially looks for any potential problems in part geometry or tolerance that might result in poor steel conditions or require special tooling features such as lifters, slides, and threading/unthreading. The physical and chemical properties of the selected resin are also evaluated so that the proper mold steel can be selected and mold cooling be reviewed. Mold flow evaluation is also undertaken to determine the best type of gate and gate locations, in addition to determining proper vent locations.
Manufacturability review includes confirmation of standard plastic design practices and incorporation of tooling details to create the most robust design possible. Tooling specifications and tooling sources are finalized and purchased component sources qualified. A comprehensive process failure mode effects analysis (PFMEA) is also completed.
Stage 2: Design
Preliminary 2D and 3D design models are constructed to determine mold sides and steel sizes. Once these are reviewed and approved, the detailed design is finalized.
Stage 3: Final Design Specifications
The tool builder is given the tool design specifications for mold construction. Final adjustments and modifications are done in-house, with special attention given to manufacturability and critical dimensional requirements.
Stage 4: Construction of Primary and Secondary Tools
Detailed tool drawings are completed and construction standards are reviewed and verified. The tool builder’s progress is closely monitored and on-site meetings are held. The completed mold is inspected against a comprehensive checklist.
Stage 5: Bring the Tool In-House for the Initial Sample
A molding process is established that is acceptable to the manufacturing department. Processing parameters are recommended and established. Initial sampling using scientific molding practices is carried out; cavity pressure transducers in the mold accurately determine the filling profile over time. Sample parts are qualified.
Stage 6: Make Any Final Tool Corrections
Any needed process adjustments are made as required. Tool construction is verified and the process is detailed and documented so it can be used in the future with minimal setup time. Perfect parts are resampled and submitted to the customer. After final approval is obtained from the customer, the production process is launched.
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