moulding masterclass | Moving moulds part 4
Figure 1: Key specifi cation data for three moulding machines, A, B and C
Clamp capacity
Injection unit classifi cation Screw diameter Screw geometry L/D ratio
Specifi c injection pressure
kN 2,100 430
mm 40
Machine A Machine B Machine C 2,100 600 40
Standard Standard 20
20
Maximum cylinder head volume cm3 Maximum shot weight (PS) Maximum injection rate Plasticising rate (PS) Maximum screw stroke Nozzle sealing force
g Number of heating zones
bar 2,025 231 210
cm3/s 224 g/s
52
mm 184 kN 80 4
Screw cylinder heating capacity kW 11.1
2,423 231 210 187 32
184 80 4
11.1
2,000 750 40 -
25.2
2,500 251 228 153 39.4 -
50 5
15.54
Source: Data from Sumitomo SHI Demag (Machine A: Systec 210/580-430; Machine B: Systec 210/580-600) and KraussMaffei (Machine C: KM CX200-750)
Figure 2: A
process setting chart bringing together key specifi cation data for all
machines in the plant will help achieve smooth mould transfers
fl atness and dimensional requirements. The differences between Machines A & B (2,100kN) and C (2,000kN) are quite apparent from the specifi ca- tion data. It is, therefore, important for the process setter to have a good knowledge and understanding of each machine’s attributes by having at least a hard copy of the specifi cations for reference prior to attempting to transpose process settings derived in Machines A & B, or before optimising moulding parameters to replicate performance from both box and lid mould tools. Naturally, the processing conditions selected for Machine C will be somewhat different to those em- ployed for either the box or lid mould tools in Machines A and B due to the differences in shot capacity, screw stroke, injection rate, injection pressure availability, and hydraulic pump pressure. Another notable difference is the L:D ratio of the 40 mm screw for Machine C compared to the value for both Machines A & B. Such a differ- ence will affect both the melt homogeneity and resultant melt temperature. Another scenario, might be to
consider a fourth machine of different make or type possessing a dissimilar screw diameter. Certain process parameters will be transferrable from Machines A and B – for example injection time, holding pressure, holding pressure time, screw surface speed –
30 INJECTION WORLD | April 2014
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whereas others will have to be determined to accommo- date the attributes of the specifi c plasticising unit. Put simply, replication of the original processing
conditions will not reproduce base and lid components to the previous quality and output rates. In certain circumstances, for example where the screw diameter is larger than that in either Machine A or B but provides a comparable injection pressure, then an increase in output rates can sometimes be achieved. More often than not, however, the melt homogeneity and mainte- nance of a consistent shot volume is necessary together with other process parameter changes to ensure comparability of performance. Previous articles in this series have stressed the
importance of fully scoping original conditions so that replication of component quality and cycle time can be achieved and, as demonstrated above, this is particularly important where different moulding machines and screw diameters are involved. In conclusion, when moving a mould tool from one machine to another – regardless of the make and type – it is extremely important that full details of the process are taken from the original machine for replication. Generally the process setter will not have to hand the required specifi cation so, to enable greater vision, a comprehensive chart showing the important attributes of all machines in the workshop is often derived (an example is shown in Figure 2).
About the author: Moulding Masterclass series author John Goff is a chartered engineer (CEng), Fellow of the Institute of Materials, Mining and Metallurgy (FIMMM), and CEO of injection moulding process consultancy and G&A Moulding Technology (
www.gandamoulding.co.uk), which provides consultancy services on all aspects of process setting, optimisation and control, including hot runner technology, and developed and markets its own Pro-Op process optimisation software tool. You can read the most recent instalments in this series here, here and here.
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