Q: Can scientific molding techniques be implemented in Liquid Silicone Resin molding?
A: Yes, the importance for documentation would still apply.

Q: Can these techniques be used for MIM?
A: Yes, the basics of the process are very similar, and the importance of machine independent documentation is universal

Q: Can you please repeat how the viscosity is determined for the plastics.
A: The 'Relative Viscosity' can be determined by multiplying: (peak plastic pressure at transfer) X (1st stage fill time)

Q: Can you re-clarify how you measure mould deflection?
A: Mold deflection is measured by the movement of the injection unit during mold filling and packing.

Q: One problem is most molders have several different sizes of machines from different suppliers; as a consequence, the tool needs to be re-developed each time - have you any comments?
A: You should generate a mold specification guide for all tools being produced... possibly consider an interchangeable tool system. If necessary, you can also refit your tools to standardized clamping plates for your machines.

Q: Should you relieve tool edges so that the clamp force is concentrated over the mould contact faces and projected area of components?
A: The mold cavity and core blocks should be left 'proud' meaning they should stick out from the mold base a little to create preload and concentrate the clamping force.

Q: How many cycles should be run to validate individual changes?
A: Simple changes such as injection speed will take place within one or two shots. Changes that affect the mold or melt temperature may take as long as half an hour to stabilize depending on the size of your mold and machine.

Q: How can I determine plastic pressure?
A: Multiply the Hydraulic Pressure times the amplification ratio. Your injection molding machine or manual may also have a conversion chart.

Q: In a scientific molding process can we change inputs but having the same outputs?
A: There are many cases where a change in the inputs may have little or no affect on the actual process... For example, if the process was pressure limited, a change in the injection speed will have no affect on the process. This is why the documentation of process outputs is critical.

Q: Do you continue to choose a fill rate at a faster rate on the right side of the viscosity curve until you see a defect related to fill then back off a bit and that’s your ideal fill rate?
A: There are many factors that contribute to the selection of a final fill rate. You typically want to find a range of fill rates to the right of the thinning, and select a speed in the middle of that range. Choosing the fastest rate may reduce the robustness of your process.

Q: Is scientific molding applicable to high speed packaging machine where injection fill time and hold are around 0,5s for and overall cycle time of 3sec?
A: Yes, you should always document the process outputs... especially since any change in your process is virtually imperceptible to the human eye, and can only be identified through process outputs.

Q: Explain the check ring test more in depth.
A: Basically (1) you mold ten short shots (2) measure and record the shot weight and (3) determine the percentage of imbalance.

Q: Explain how to calculate shear rate.
A: For any process the 'Apparent Shear Rate' = 1 ÷ (fill time)

Q: How long should a sample mold be run before accepting the process as stable?
A: A typical molding process takes 15-30 minutes to stabilize.

Q: During rheology curve, should we use close loop or open loop option, what's difference?
A: You should always prefer closed loop over closed loop. If your machine is only open loop, you may want to make a note on the documentation so since the apparent shear rate is based on the average speed of the decelerating screw.

Q: In the molding process what is the most important tool, machine, process or die.
A: (1) part design (2) mold (3) process (4) machine - A good machine cannot compensate for a bad process, a good process cannot compensate for a bad mold, and a good mold cannot compensate for a bad part design.

Q: Relation between Injection & Holding
A: Injection should be used to fill the mold ~95% - Packing & Hold is used to complete fill and compensate for material shrinkage until the gate freezes.

Q: Talk about open loop vs. closed loop molding
A: Basically, when the operator enters the process inputs into an open loop controller and the process outputs are not monitored for adherence. When the operator enters the process inputs into a closed loop controller and the process outputs are monitored for adherence and the process is adjusted to ensure accuracy.

Q: We do in line strip molding, difficult to practically trim and weigh during processing, any suggestions?
A: You may consider performing a variation of this when starting or completing a spool.

Q: What is the difference between pack and hold?
A: Ideally, pack is used to compensate for shrinkage and hold is used to prevent material back flow until the gate freezes. To simplify the process, many injection molders use one pressure to perform both functions successfully.

Q: When checking the platen deflection of a new machine, what is the normally allowed deflection for the platens?
A: This is very machine specific... The most important factor is to measure the deflection so that you have a basis for comparison when situations arise.

Q: When establishing a process in a valve gated tool, how does one determine when to close the valve gate?
A: You can use a gate seal worksheet to determine when the part weight increase stabilizes over time.

Q: Why do you check fill ONLY part weight then fill and pack weight, then final weight?
A: When combined with the times for fill, pack, and hold... you can develop a machine-independent picture of the process.