Two successful Moulding applications
Using aluminium mould technology for creating thermoplastic parts
At times the opportunity to develop a long-coveted and tenaciously pursued project may present itself. However, a sudden acceleration of events may also compromise the possibility of carrying the project out.
In fact, a plastic part featuring considerable size and uncommon difficulties for its construction does not combine well with haste.
These few lines serve as an introduction to an extraordinarily successful application the importance of which regard the advantages and results which can be obtained using aluminium mould technology for creating thermoplastic parts.
To the left is a segment of the composter container where the many stiffening ribs can be seen.
The material used to construct the mould is CERTAL®SPC aluminium, a series 7xxx alloy derived from the field of aeronautics and specially developed with the aim of satisfying the needs of die-sinkers with regard to machinability, size stability, weldability and mechanical characteristic constancy from the exterior to the core of the plate.
In the case referred to, the advantages obtained thanks to the use of aluminium equipment can be summed up as follows:
- Rapid mould construction.
- Possibility of making simple and rapid changes.
- Electroerosion operations reduced to a minimum - All stiffening ribs have been made by milling.
- Thanks to high thermal exchange all moulding operations are considerably simpler.
- Considerable cost reduction in comparison with the same equipment in steel.
This slide shows the milling carried out to create the stiffening ribs.
The possibility of carrying out thin and deep (up to 20 times the diameter of the tool) milling has definitely made the die-sinker's task much easier as electroerosion working has been avoided. In this way it was possible to avoid electrode construction operations and subsequent finish milling.
The wear of the tools, which is absolutely negligible, allows the drastic reduction of costs for their purchase and allows machine tool working operations without the prolonged attendance of an operator.
The high thermal exchange value of aluminium (higher that that of copper-beryllium) does not require a sophisticated conditioning network for the mould. The passage channels can be made in 20÷25 mm diameters and be sufficiently distant from the figure.
Before obtaining the final version of the moulded part, plugs were used to make a number of changes to the geometry and shape of the mould components. These operations were made easier by the excellent machinability of the aluminium and were carried out in rapid time.
Finally, aluminium's specific weight - equal to 1/3 that of steel - was particularly appreciated by the die-sinker and the moulder, who were able to move the equipment with great ease, in shorter time with a saving of energy that could not be quantified but which was certainly impressive.
Technical Specifications of the application.
| Item |
Composter |
| Processing Technique |
Milling on OMV HS 320 machine |
| Mould material |
Certal®SPC |
| Mould size |
1200 x 900 x 1200 mm. |
| Mould weight |
3500 kg. |
| Undercuts |
Moving parts made of Bronze on Aluminium |
| Plastic material |
Copolymer polypropylene |
| Part weight |
3400 grams |
| Plastic material size |
9400 cm ³ |
| Mould contruction time |
40 days |
| Expected life |
500.000 % 700.000 pieces |
| Mould constructor |
Tagliabue modelli |
| Moulder |
Plasteva |
| % savings in terms of equipment construction costs between Aluminium and Steel 30 - 50% |
| % savings in terms of equipment construction time between Aluminium and Steel 50 - 60% |
Frame for a medical chair made of HIS- PUR
The application illustrated in the photo refers to a frame for a medical chair made of HIS- PUR (High impact resistance polyurethane).
The process used is RIM overmoulding on a steel core.
The series of parts manufactured equalled 15,000 pieces.
The following comparative table between Certal® Aluminium and Ck45 Steel emerges from the economic analysis of the mould construction and utilisation phase (not including the savings in press cycle time).
Cost assessment Aluminium / Steel
| Criteria |
Certal® |
Steel Ck45 |
Difference |
| Material costs |
540 Kg x 7 €/Kg
= 3.780 € |
1.540 Kg x 1,5 €/kg
= 2.310 € |
+ 1.470 € |
| Machining costs |
50 hours x 70 €/h
= 3.500 € |
150 hours x 70 €/h
=10.500 € |
- 7.000 € |
| Energy costs (*) |
89.200 x 0,08 €/Kwh
= 7.140 € |
135.900 x 0,08 €/Kwh
= 10.870 € |
- 3.730 € |
| TOTAL COSTS |
14.420 € |
23.680 € |
- 9.260 € |
(*) = See energy consumption
Energy use
| Criteria |
Notes |
Certal® SPC |
Steel Ck45 |
| Blocks transportation |
Given a transport of 500 km, and a ratio of 1,5 litre/ton/100 km and of 39 MJ/litre with a Diesel truck. |
158 MJ |
459 MJ |
| Machining |
12 Kwh power Milling Machine |
5.712 MJ |
17.136 MJ |
| Handling/Fixing/Demoulding |
Steel: 12 Kwh needed
Certal®: 8 Kwh needed |
285.600 MJ |
428.400 MJ |
| Mould heating |
Steel: Cm = 0,11 kcal/kg.K
Certal®: Cm = 0,22 kcal/kg.K |
29.700 MJ |
43.170 MJ |
| TOTAL |
|
321.170 MJ =
89.200 Kwh |
489.165 MJ =
135.900 Kwh |
Notes
Block weight: Steel 1570 kg, Aluminium 540 kg
Conversion: 1 kWh = 3.6 MJ
For heating, the energy equals Cm (mass heat) x mould mass x difference in temperature / 1 kcal = 4.18 kJ
Work weeks considered: 150
Conclusion
Despite the greater initial cost of the material used for constructing the mould (+40%), the total savings (material + machining + energy) equalled approximately 40% with respect to the equivalent solution in steel. The die-sinker also noticed the following other advantages:
- No thermal treatment was necessary after machining (the alloy was already tempered and de-stressed)
- Reduction of cooling time and therefore of the cycle's rhythm
- Maintenance made easier thanks to weight reduction
- No mould corrosion during storage
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From Old Tooling 
