What should be the Ideal relationship between Total Tonnage of Injection Moulding Machines in any Injection Moulding shop and Tons of Plastic Material Processed monthly?

It really depends on what material you are running, size of parts, equipment maintainence and scheduling, etc.

Another important thing is the quantity of injection mold cavities
if you have to much cavities for example you need also more
Pressure of course.

For each square inch projected area .

3.0 to 3.5 tonnes For PE,PP,ABS, Acetal, Acrylics

3.5 to 4.5 tonnes For material Nylon, polycabonate, polyester,

Material viscosity is also one of factor that considered

Rule of thumb was 3 to 4 ton per square inch of the projected area that is being acted directly upon in the clamp plane.

This is totally dependant on the viscosity of the material, the flow path length, wall section, type of material, mould temperature, processing temperature. I have found as little as 1.5ton per square inch is adequate but have also found that on long flowpath thinwall products it can be neeccessary to go to 5 ton per square inch.

Tonnage is related to Projected Area of the Mold (or ) exposed to Injection Pressure. And Plastic RM is related to Design of the mold , Runner and Gate Balancing , Processing Temperature. Hereby Tonnage related to RM is possible to balance by the above factors to a particular range. For ex. An 110 Tons Requirement mold can be adjusted to run on an 100 Ton Machines if the mold can be accomadated Physically by doing the above changes to run on a smaller machine too.

Molding component's [part] wall thickness also is major factor for tonnage, Injecting pressure increases when the component thickness decreases, as usually the injecting pressure decreases when the component thickness increases.