Scientific Molding
A Systematic Approach
System Benefits
Defect Prevention: Consistent part quality based on understanding polymer rheological behavior.
Controlled Process: Based on hard data, not "black magic".
Part Discrimination: The process of knowing the part is good or defective in real time. Allows us to segregate suspect parts as molded, true process control.
Scheduling Flexibility: Allows us to produce parts of consistent quality, regardless of the molding machine. Process parameters are derived from the plastic variables, not machine variables.
Successful Plastics Application
Key Components of Any Application:
- Part Design
- Tool Design & Construction
- Material Selection and Handling
- Processing
Definition: Scientific Molding is a disciplined, systematic approach to part processing based on what is happening to the plastic during the injection molding process. The focus is based on controlling what ishappening to the material melt and is defined by controlling the viscosity of the material.
Process Control Objectives
Control of Key Plastic Processing Variables: A machine-independent process that provides four (4) basic parameters to optimize the molding process.
- Plastic Temperature: We measure plastic temperature – not barrel temperature..
- Velocity of Injection (Viscosity or flow rate): The objective is to push the same amount of materials at the same rate each machine cycle. Viscosity changes as the flow rate changes. When the flow rate changes, the viscosity changes. When the viscosity changes – the parts will vary. The greater control there is over the material viscosity - the easier it becomes to have a consistent the molding process and part quality.
- Plastic Pressure: Measure & monitoring of cavity pressure, hydraulic pressure and pack and hold pressures
- Cooling: We monitor cooling by measuring the coolant temperature inside and outside of the tool.
Control of the processing variables enables Empire to have a locked process, and run the same cycle shift after shift.
Scientific Molding Process
- We correlate good parts with the process measurements and then lock in the process. Data derived from pressure transducers inside the cavities is used to activate part segregation.
- A rheology study is performed (study of flow and deformation of matter) with a series of short shots. Data from these shots is used to derive a rheology curve, which is used to establish optimum velocity for the first-stage injection. This velocity assures we mold at the best possible viscosity for this mold.
- Mold Optimization: A thorough analysis is performed on injection pressure, injection velocity, transfer position, fill time, pack, and hold pressure and then we conduct a gate seal study to determine pack time.
- Once the process is stabilized and acceptable parts are produced, basis data is recorded for the mold in Empire's Propritary Process Analysis Program. Processes are specific to the mold, not the machine.
This becomes the “Locked Process” for this mold and correlates to the parts submitted to the customer for approval