Moulding dies
Index
- Aluminium because
- Aviometal because
- Aluminium when
- Technological properties
- Mechanical and physical properties
- Machining
- Materials
- Availability ex stock
Aluminium because
Aluminium alloys are used since many years for the manufacturing of low to medium pressure injection moulding dies, and additionally dies for blow forming, Resin transfer moulding, expansion forming, of technical polymers and rubbers.
The earlier exercises were relevant to applications for prototypic or small series production, where paramount importance is associated to minimising non recurring costs (manufacturing cost of dies) and total manufacturing time of tools, whilst problems related to wear and mechanical and thermal fatigue of dies are marginal.
The availability of high strength alloys, developed originally for aerospace, and the development of specific materials for moulding dies performed by the main mills on the basis of such alloys, allows the possibility of advantageous usage of aluminium for the manufacturing of moulding dies for medium and mass series production, in the field of many hundred thousands closures of the dies.
The competitiveness of aluminium dies versus traditional steel dies comes from the following main factors:
- Much better machinability, in terms both of cutting speed and of Volume of metal removed per unit time and of wear of tools, and additionally the machined surfaces can be easily polished.
- Specific gravity about one third of steel, and therefore much easier handling, transportation and set ups.
- Heat transmission coefficient more then 3 times higher than traditional steels for mould making, and so possibility to reduce up to 50% the cooling time after injection in the mould, with consequent increase of production rate.
- Hardness at room temperature comparable to traditional tool steel for moulds, and so comparable capability to stand abuses during handling and transportation.
- Resistance to oxidation inn typical workshop area generally better than tool steels.
- Possibility to apply simple and well known surface treatments in order to further improve properties in terms of corrosion and wear resistance.
- Possibility to repair through welding.
Cost
The above mentioned factors set a favourable costs trade-off for the manufacturing of aluminium moulding dies wherever it is allowed by the solution of the technical problems connected to the injection technology (process parameters, design of dies, selection of proper material):
For prototypical and small series productions this is due mainly to lower non recurring machining costs of dies, as shown in the following graph, referring to total cost of parts for small series (cost of tools + workmanship, excluded cost of polymer).
Productivity
For medium and mass production the benefits coming from elevated thermal conductivity of aluminium alloys become of importance, since it allows faster injection cycles, with time reductions up to 35%, so that the aluminium solution becomes profitable even in the limit situation of re-making of dies after some hundreds thousands closures, as shown in the following graph, showing the total cost of parts for medium and mass production (cost of tools + workmanship, excluded cost of polymer).
Time to market
Machining time reduced compared to traditional tool steels and ease of work reduce to about one half the time required for dies manufacturing, and allow to consistently reduce the time to market; this is of paramount relevance in case of prototypical productions and for certain products families.
Aviometal because ...
Aviometal, who are on the market since more than 50 years as supplier of aerospace companies, besides of the machinery industries, not only selects and delivers blocks for moulding dies cut to size in Just In Time environment, but also make available to customers their experience and knowledge of aluminium alloys and relevant technologies for machining, joining, surface protection for the best selection of optimum material for the most critical and special applications.
Aluminium when ...
The use of aluminium moulding dies is absolutely advisable for moulding processes performed at medium-low pressure (not exceeding 600 Bar); for processes operating at very high pressures and temperatures or for resins with hard fillers a tailored design of the die and selection of the alloy are required.
For the typical injection moulding process the appropriateness of using dies in aluminium alloys and the number of closures achievable comes from the following factors:
- Injection pressure of resin
- Injection temperature of resin
- Operating temperature of die
- Use of fillers in resin.
Injection pressure shall match compressive strength of die material at the injection temperature of resin, in order to avoid premature problems of distortion of internal surface of die and premature wear.
Additionally, in conjunction with the operating temperature of die, it id the basis for static and fatigue stress analysis.
The following table gives an example of the limit operating conditions for a die in a medium strength aluminium alloy suitable for elevated temperatures (2219-T851); Pi and Ti are the maximum injection temperature and pressure not to be exceeded at the shown die operating temperature Ts.
Should any filler be used, the wear phenomena of the inner surface of the die could speed up.
Therefore it is always strongly advisable to operate the process using values of injection pressure and temperature and of die operating temperature as low as possible, provided that moulded parts can be correctly obtained.
The table below shows typical data for various resin materials.
| Resin | Closures max | |||
|---|---|---|---|---|
| 103 | 104 | 105 | >105 | |
| Low Density Poly Ethylene | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| High Density Polly Ethylene | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Poly Propylene | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Poly Styrene | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| High Impact Poly Styrene | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Styrene Acrylo Nytrile | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Acrylonitrile Butadiene Styrene | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Poly Vynil Chloride | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Cellulasics | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Poly Amide 6 | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XX |
| Poly Amide 11 | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XXXXXXXX |
| Poly Amide 6/6 | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | XX |
| Poly Amide 6 filled glass | XXXXXXXXX | XXXXXXXXX | ||
| Poly Phenilene Oxide | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | |
| Poly Methyl Metacrylate | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | |
| Poly Acetals | XXXXXXXXX | XXXXXXXXX | XXXXXXXX | |
| Poly Carbonate | XXXXXXXXX | XXXXXXXXX | XXXX | |
Technological properties.
Aluminium alloys for moulding dies are delivered in form of plates or blocks coming from casting or hot working (rolling or forging), heat treated (where applicable) in order to achieve optimum properties, and (where applicable) mechanically stress relieved through stretching or cold compression in order to achieve optimum stability after machining.
Since these products are basically the same alloys used in aerospace, or anyway very close to these materials, the demanding quality standards applied can assure high consistency of properties, absence of surface and internal defects, minimum levels of established mechanical and technological properties.
Mechanical and physical properties
Mechanical and physical properties of aluminium products depend on factors like:
- Alloy (chemistry)
- Thermo-mechanical treatments
- Primary working technology (hot rolling, forging, etc.)
- Thickness of semi-finished product
- Grain direction (all wrought aluminium alloy products show phenomena of anisotropy of properties, at various degrees)
And are influenced by operating temperatures, even in the field of temperatures typical of processing of polymers and elastomers.
During design phase it is advisable, whenever possible, to address minimum guaranteed values for each individual product instead than "typical" values.
The following table refers to some products currently available in stock at Aviometal, and specifically to rolled plates, 100 mm thick; the mechanical properties are for LT direction (parallel to rolling).
For detailed figures see technical data sheets of specific products.
Alloy Properties |
AUQG (2219) |
AJQY (5083) |
AJQ4 (50XX) |
ARQF (6082) |
AZQI (7010) |
AYQK (7075) |
Ultimate strength (Mpa) |
414 |
275 |
275 |
295 |
540 |
456 |
Yield strength (Mpa) |
304 |
|
100 |
240 |
490 |
373 |
Elongation (%) |
5 |
|
7 |
7 |
5 |
3 |
Brinell hardness |
130. |
86 |
86 |
89 |
175 |
150 |
Young's modulus (Mpa) |
72500 |
71000 |
71000 |
69000 |
72000 |
71100 |
Specific gravity (g/cm3) |
2,85 |
2,66 |
2,66 |
2,70 |
2,83 |
2,80 |
Thermal conductivity (W/m °C) |
117 |
117 |
117 |
200 |
153 |
131 |
Linear thermal expansion coefficient (mm/mm °C) |
22 x 10^-6 |
24 x 10^-6 |
24 x 10^-6 |
23 x 10^-6 |
24 x 10^-6 |
23 x 10^-6 |
Machining
Machinability of aluminium alloys is much better than traditional tool steels, and allows reductions of machining times from 30% up to 50%.
In order to optimise the benefits coming from use of these materials in terms of machining time, during rough cutting it is generally advisable to use high cutting speeds and feeds, and to reduce the depth of cut to match the power of the machine, whilst for finish cutting high cutting speed and low feed are used to optimise surface finish.
For machines designed for machining steel the upper limit for the cutting speed is in general the maximum available speed of the spindle; special-to -type machines are available for machining aluminium alloys, with spindle speeds of more than 20000 RPM.
It is advisable to use cutting fluids, mineral or emulsified, with pH whenever possible neutral and in any case between 5 and 8, chloride free, in order to avoid corrosion in case of no or late removal from the surface of finished parts.
Tool life is in any case at least 20 times longer than for steel.
Milling
To improve removal of the great volume of chips per unit time it is advisable to use tools with number of cutters reduced respect to steel (1 or 2 cutters for end mills).
Recommended cutting parameters are shown in the following tables.
High Speed Tool Steel mills |
||
Parameter |
Rough |
Finish |
Cutting speed (m/min) |
70 ¸ 90 |
100 ¸ 120 |
Feed rate (mm/cutter) |
0,1 ¸ 0,3 |
0,03 ¸ 0,1 |
Cutting depth |
(1) |
£ 0,5 |
Edge angle (°) |
20 |
20 |
Rake angle (°) |
6 ¸ 10 |
6 ¸ 10 |
Carbide tipped tools |
||
Parameter |
Rough |
Finish |
Cutting speed (m/min) |
400 ¸ 1500 |
400 ¸ 3000 |
Feed rate (mm/cutter) |
0,1 ¸ 0,3 |
0,03 ¸ 0,1 |
Cutting depth(mm) |
(1) |
£ 0,5 |
Edge angle (°) |
15 |
20 |
Rake angle (°) |
6 ¸ 10 |
6 ¸ 10 |
Depending on power available.
Drilling
Generally drilling operations do not raise particular problems; the recommended cutting parameters are shown in the table below.
Parameter |
HSS tools |
Carbide tools |
Cutting speed (m/min) |
40 ¸ 60 |
150 ¸ 300 |
Feed rate (mm/round) |
0,02 ¸ 0,6 (1) |
0,02 ¸ 0,6 (1) |
Edge angle (°) |
120 ¸ 140 |
120 ¸ 140 |
Helix angle °) |
25 ¸ 40 |
25 ¸ 40 |
Rake angle °) |
8 ¸ 10 |
8 ¸ 10 |
(1) Higher values refer to bigger diameters.
Reaming
Reaming operations are performed both manually and mechanically, with straight or spiral flute reamers; the recommended cutting parameters are shown in the table below.
Parameter |
HSS tools |
Carbide tools |
Cutting speed (m/min) |
20 ¸ 40 |
80 ¸ 150 |
Avanzam.(mm/giro) F < 25 25 < F < 40 F > 40 |
0,03 ¸ 1,0 0,1 ¸ 0,2 0,2 ¸ 0,3 |
0,05 ¸ 0,2 0,1 ¸ 0,3 0,2 ¸ 0,4 |
Edge angle (°) |
5 ¸ 7 |
5 ¸ 7 |
Helix angle (°) |
10 ¸ 15 |
10 ¸ 15 |
Rake angle (°) |
6 ¸ 8 |
6 |
To obtain better surface roughness use lower values of cutting speed and feed rate.
Tapping
It is recommended to use ground taps, without clearance surface; the recommended cutting parameters are shown in the table below.
HSS tools |
|
Parameter |
Value |
Cutting speed (m/min) |
15 ¸ 20 |
Rake angle °) |
18 |
Grinding
Grinding operations are seldom required, since usually proper machining with metal or carbide tools, performed with the right parameters, can give the required surface properties.
In case of prismatic parts, the part can be fixed on the magnetic worktable between two steel blocks, after applying two sided adhesive paper on the surface in contact with the worktable.
To avoid scratches due to presence of hard foreign particles, pay attention to the following:
- Do not use wheels formerly used to grind other metals, steel in particular; whenever possible use wheels with very porous structure.
- Should the machine have been formerly used for other metals, remove all cutting fluid, wash the relevant circuit, change filter, then refill with new cutting fluid.
Polishing
Polishing, both manual and mechanical, allows to obtain mirror-like surfaces, with roughness down to 0.1 µm, and working effort of only 25 to 30% respect to steel.
It is recommended to start polishing with 320 abrasive paper, and then to go on with increasing finer meshes, till 1200; if required polishing can be complete with clothes and diamond paste from 2 to 6 µm
Electrical Discharge Machining
MThrough EDM results not worse than those obtained with steel can be achieved, with working times lower from 20 to 50%.For shaped electrode EDM the same tools typical of steel parts can be used; to improve the surface finishing it is recommended to reduce the metal removal rate in finishing phase.
Turning
The upper limit of the cutting parameters is limited only by the power of the machine and stiffness of the cutting tool; the recommended cutting parameters are shown in the tables below.
HSS steel tools |
||
Parameter |
Rough |
Finish |
Cutting speed (m/min) |
100 ¸ 120 |
400 ¸ 1500 |
Feed (mm/round) |
0,2 ¸ 0,6 |
0,05 ¸ 0,2 |
Cutting depth (mm) |
3 ¸ 15 |
0,3 ¸ 3 |
Edge angle (°) |
20 |
20 |
Rake angle (°) |
6 ¸ 8 |
6 ¸ 8 |
Carbide tipped tools |
||
Parameter |
Rough |
Finish |
Cutting speed (m/min) |
400 ¸ 1500 |
400 ¸ 1500 |
Feed (mm/round) |
0,3 ¸ 0,6 |
0,05 ¸ 0,2 |
Cutting depth (mm) |
3 ¸ 15 |
0,3 ¸ 3 |
Edge angle (°) |
25 |
25 |
Rake angle (°) |
6 ¸ 8 |
6 ¸ 8 |
Materials
Below the technical data sheets of materials recommended for the manufacturing of moulding dies and accessories.
The mechanical properties listed are, if not differently specified, minimum guaranteed properties, and are relevant to the nominal thickness of products; actually the typical properties of products are generally about 10% higher.
NThe data sheets refer to the thickness range of practical interest for the manufacturing of dies; lower thickness, that could be used for miscellaneous workshop tooling, show generally higher properties.
The US terminology is adopted, where
Ftu ultimate tensile strength
Fty yield tensile strength (conventional, 0.2% permanent deformation)
Fcy yield compressive strength (conventional, 0.2% permanent deformation)
Fsu ultimate shear strength
Fbru ultimate bearing strength
Fbry yield bearing strength
e elongation after rupture
E Young's modulus, tensile
Ec Young's modulus, compressive
G Shear elastic modulus
The physical properties are generally typical values, drawn from official documents or indicated by materials manufacturers.
The technological properties refer to the following rating:
very good
good
fair
poor
The elevated temperatures mechanical properties are given as a percentage of the mechanical properties of the product at room temperature for different holding times at indicated temperature; attention shall be paid to the fact that in certain intervals the reduction of properties increases with increasing holding times.
To obtain the value of the property at the indicated temperature, multiply the value of such property at room temperature, for the intended thickness, by the value coming from the curves, and divide by 100.
Successive exposures cumulate the effect.
The fatigue properties are shown using the US terminology; the curves are for room temperature, and show the value of maximum alternating stress Smax versus number of cycles to failure.
The curves refer to pulsing fatigue (R = 0, where R= Smin/Smax), to alternating fatigue (R = -1) and to other two typical cases (R = ± 0,5); the test results are for unnotched (Kt = 1) and notched test pieces, with different notch sensitivities (Kt > 1).
Availability ex stock
Thickness Material |
140 | 150 | 160 | 180 | 200 | 220 | 240 | 250 | 260 | 300 | 350 | 400 | 500 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| AUQG | # | # | # | # | |||||||||
| AJQY | # | # | # | # | # | # | # | # | # | # | # | ||
| ARQF | # | # | # | # | # | # | |||||||
| AZQK | # | # | # | # | # | ||||||||
| AYQK | # | # | # | # | # | # |
Technical data sheets
In the following data sheets the materials were identified with the internal Aviometal codes.
General features
General purpose material, it is an Al-Mg alloy with medium mechanical properties, very good corrosion resistance, good weldability, high dimensional stability.
Supplied in form of rolled plates up to 250 mm thickness, and in form of cast and machined plates up to 350 mm thickness.
Typical uses
Machinery components, tools, even if very large and medium stressed, where elevated starting thickness is required.
Large moulding dies, for forming technologies where forming pressure is not very high, or for prototypes and small series.
Parts to be embodied into welded assemblies.
Minimum mechanical properties at room temperature
Thickness mm from to a |
100 150 |
151 250 |
251 350 |
Rm (MPa) L LT |
275 275 |
240 240 |
220 220 |
Rp0.2 (MPa) L LT |
105 105 |
100 100 |
100 100 |
A5 LT |
8 |
7 |
6 |
E (MPa) |
71000 |
||
Ec (MPa) |
71700 |
||
G (Mpa) |
26400 |
||
Physical properties
Specific gravity: 2.70 g/cm3
Thermal conductivity: at 20 °C 120 W/m °C
Specific heat: at 20 °C 0.215 Cal/kg °C
Linear thermal expansion coefficient: at 20 °C 22.3 x 10-6 mm/mm °C
From 20 to 100 °C 24,2
From 20 to 200 °C 25,0
From 20 to 300 °C 26,0
Technological properties:
Machining: very good
Polishing: fair
Welding: good (TIG - MIG)
Available sizes
- Full plates, 950, 1050, 1130, 1220, 1350, 1430, 1530, 1700 mm width and up to 4000 mm length.
