When to change a screw-tip set, and what a worn one looks like
Shot weight variation that behaves like a process problem is often a mechanical one. Here is how to tell.
Sizing a vertical injection moulding machine for insert moulding
Why the tonnage figure is the last thing to decide, not the first, when the part has an insert in it.
Most vertical machine enquiries arrive as a tonnage. Tonnage is an output of the sizing exercise, not an input to it.
Start with the part
Projected area of the moulding, including runners, is what actually decides clamp force alongside the cavity pressure the material needs. A part that looks small can need more clamp than expected once the runner system is counted.
Shot weight against the machine’s injection capacity, with sensible headroom. Running a barrel near its maximum shot gives poor residence-time control; running it near its minimum degrades material.
Material decides required injection pressure and melt temperature, and therefore screw and barrel selection.
Then the insert
How the insert is held in the mould, and whether it needs the operator’s hands inside the area. This decides guarding and often decides the machine layout.
Loading method — manual, semi-automatic or robot. Manual loading on a single-station machine means the machine waits for the operator every cycle.
Whether a rotary table helps. With a rotary table the operator loads one station while the other moulds, so loading time comes off the cycle rather than adding to it. This is usually where the productivity argument for a vertical machine is won or lost.
Then the cycle and the volume
Required annual volume, working shifts and available cycle give the machines-required figure. It is common for a correct answer to be two smaller machines rather than one larger one.
What to send for a sizing exercise
- Part drawing or photograph, with material and shot weight
- Insert drawing, or at minimum a photograph with dimensions
- Required annual volume and shift pattern
- Whether loading is manual or automated
- Available floor space and ceiling height
- Existing mould details, if the mould already exists
The check worth doing
If someone quotes you a machine without asking about the insert and the loading method, they have sized it from the tonnage you gave them. That is not sizing.