CRP Technology became the FIRST to use Rapid Casting for really hard to cast shapes, such as F1 uprights and gearboxes, and alloys, such as Titanium alloys.
The Experience: Minardi Gearbox
In 1998 CRP began to work alongside the Minardi F1 Team, supplying them the engineering process, the manufacturing process optimization and finally the manufacturing of front and rear uprights: they began from the study of the Titanium Rapid Casting process.
Rapid Casting procedure
“Rapid Casting” is based on the combination of Rapid Prototyping technology, to manufacture the disposable pattern, and Investment Casting technology (investement casting).
After the uprights, CRP and Minardi applied successfully the same technology to the Gearbox manufacturing.
On the left: Minardi Titanium Rapid Casting Gearbox 2000; on the right: Minardi Titanium Rapid Casting Gearbox 2001
This allowed CRP Technology to become the FIRST to use Rapid Casting for really hard to cast shapes (such as F1 uprights and gearboxes) and alloys (such as Titanium alloys).
On the basis of the gearbox developed in 2003 and used in the 2004 season, Minardi started work on developing a new gearbox for the 2005 season.
The goal of the study was to optimise the interior structure but most of all its volumes.
The targets are numerous:
- reduce the quantity of oil used
- improve gearbox lubrication
- reduce the power dissipated
- make the casting even more rigid and lightweight
So Minardi’s aim was to change the position of the gearbox oil pump from inside the sump to the outside of it which gives us a dry sump gearbox.
Minardi and CRP Technology have worked together on this project, preparing the road of evolution towards the new 2005 gearbox in 3 main steps:
- Minardi opted for SLA technology due to its transparent characteristics since the aim was to “visually” assess and verify the effectiveness of the gearbox lubricating system. But the results were unsatisfactory which was actually due to the technology used. To overcome these problems, Minardi turned to CRP Technology and the SLS Technology.
- Minardi and CRP Technology make the same gearbox with the SLS Technology using the composite material Windform GF. It managed to complete the scheduled tests thanks to this.
- the implementation of the new Cast gearbox using the Rapid Casting technique.
The first step started with some Dyno tests with the gearbox case made with the sterolithography technique.
The result in SLA tested on the dyno does have a fundamental characteristic that puts it apart from the standard version: in fact the volumetric pump installed inside the oil sump was replaced with one installed on the outside.
The first dyno test
The dyno test, fitted out especially for this purpose, consisted of the following elements:
- The 2003 gearbox with the centre case obtained by means of rapid prototyping, driven by a 5 HP electric motor. The gearbox has no bottom oil sump so we have “dry sump” lubrication;
- volumetric pump with external gears driven by a 2 HP electric motor;
- Dyno measuring instruments for flow rate, pressure and temperature;
- Operator Fluid: hydraulic oil;
Gearbox mounted on the dyno (traditional spacer in cast titanium, gearbox case in epoxy resin, rear traditional cover in cast titanium)
The aim of the test was to “visually” assess the effectiveness of the working of the gearbox lubricating system with an external volumetric pump and reduced capacity so as to reduce the power absorbed.
It was decided not to use the usual straw-yellow coloured lubricating oil but the bright red coloured hydraulic oil instead, in the vehicle’s hydraulic circuit. From all the different kinds of oil available this one was chosen after comparing its specifications with those of the traditional oil.
The hydraulic oil, at a temperature of 30 to 35°, has the same kinematic viscosity as the usual lubricating oil at 60°C.
The main values obtained only at limited revs in virtue of the low mechanical characteristics of the case made with the stereolithography technique are given in the following table.
As you can see in the following pictures and considering that the limit of this test was dictated by the low structural characteristics of the material, we decided to keep drive shaft revs under 3,000 during the test.
Lubricating the bearings of the 3rd shaft – zoom of the two side Plexiglas covers with the gearbox at a standstill.
Subsequent to a very thorough visual inspection/analysis of how the gearbox lubricating circuit works, we were able to see how the flow of oil that lubricates the two bearings of the 3rd shaft is much greater than we had ever imagined.
In fact is quite clear that the oil flowing by gravity from the two side bearings is far greater than what “falls” from the differential on the rear “bottom” of the case.
The aim is to check the working of the system after a significant alteration had been made to the 3rd shaft user point. And, just as happened in the first test, we saw that the flow of oil to the bearings of the third shaft of the gearbox is much greater than what we had always thought. So what we want to do is try to reduce this flow of oil to the benefit of the differential user point to make it much safer.
The first change was to reduce the size of this hole, of the oil passage on the cover of the 3rd shaft, which entailed reducing it from 2 mm to 1 mm. This reduces the oil runoff area up to ¼ of the standard value.
Seeing the table, it’s clear that modifying the oil passage lubricating of the third shaft (throttling the runoff areas) we have an increase in the system pressure at the same flow rate supplied by the pump!
The aim was to verify optimisation of the oil level with a test using the bottom sump of the standard gearbox, with the pump mounted inside the sump.
With these tests we wanted to “visually” assess the effectiveness of the working of the gearbox lubricating system with different quantities of oil.
The “lines” drawn on the outer surface of the case are clearly visible, indicating the different levels: each line corresponds to another ½ litre of oil added.
Gearbox in static conditions with “only” 2 litres of oil inside
With the third test we had the confirmation that the system needs only 1 litre of oil to maintain circulation in the oil passage. The quantity of oil was increased for this purpose (Oil volume = 1.5 litres).
From the picture it is quite clear that of all the oil put inside the gearbox case, 1 litre is circulating round the system while the remaining ½ litre, subject only to the force of gravity, stays at the bottom sump.
This confirms then that the minimum quantity of oil required to start the system is 1 litre and this quantity can in no way guarantee correct lubrication of the gearbox elements.
The aim of the last test was to observe the working of the system under working conditions where, in effect, there are 2.5 litres of oil in the case.
This is a picture of the system where the primary shaft is turning at a speed of 3,000 rpm
If you compare this picture with those in the previous figures you will see how the quantity of centrifuged oil inside the case has increased with respect to the cases already examined.
Due to the particular shape of the inside of the gearbox, the oil “centrifuged” by the interior elements of the gearbox reaches areas that are wet needlessly and which are too far away from the pump inlet orifice of the pump in the sump.
The standard rate of oil used to lubricate the bearings of the third shaft is far too much so we suggest modifying the oil passage of such user points until their inside diameter is 1 mm (see TEST 2).
In TEST 2, the external volumetric pump is enough to guarantee correct lubrication of all gearbox elements.
Thanks to the last test illustrated it was possible to show how the shaking inside of the oil is such to send the fluid to areas of the gearbox that do not require it. For this reason it is necessary to optimise the interior volumes optimise the interior volumes.
At this point, we would like to check if the results and advantages obtained visibly could also be obtained under conditions closer to real working conditions in terms of revs of the gearbox’s primary shaft.
The stereolithography technique, due to its limited mechanical characteristics, prevented us coming anywhere near the actual rotation speed.
Minardi decided for the powder Laser Sintering Technology utilising material produced by CRP Technology, Windform GF.
Thanks to the SLS technology it was possible to come closer to the actual conditions and thus make the necessary modifications to the shape of the gearbox for the final one for the 2005 season, taking full advantage of all the benefits we saw in the dyno tests with the SLA technology.
So Minardi began redoing the first dyno test, already described, taking engine rotation speed up to 6,000 revs.
These results show the correlation with the previous results and, therefore, the validity of the test!
The next step is to verify the alterations made to the oil passage, using the SLS technology up to 6000 revs.
The important aspect that we can see is the reduction of the interior volumes with the aim of minimising the quantity of oil circulating around the gearbox which, as a result, means less weight, less heat and less power dissipated.
This was done by exploiting different interior shapes in successive evolutions which, after several bench tests, led to an optimum shape as can be seen in the exploded view of the main gearbox case in Windform GF.
The RP technology has therefore allowed us to assess in advance the highly important functions of the gearbox at the design phase, such as lubrication, structure shape, interior volumes to minimise the quantity of oil circulating and, consequently, assess the mechanical pressure pump and minimise its displacement.
This approach to the problem was made possible thanks to the use of the Selective Sintering Laser technique, of which the CRP Technology in Italy was a precursor!
Rapid Casting Technology was the next step used.
The RP technique was also used for the complete production of the gearbox case 2005.
Once all the geometries and surfaces of the box were defined with CAD, a disposable pattern was then built in RP utilising the Rapid Casting technique with CastForm® material.
After the uprights, CRP and Minardi applied successfully the same technology to the Gearbox manufacturing.
Minardi Titanium Rapid Casting Gearbox 2005
CastForm®, the material used nowadays for Rapid Casting patterns, was developed from the cooperation between DTM Corp. and CRP in 1998.
- use Rapid Casting for very high performance parts (primarily for F1), therefore having very complicated shapes and geometries
- using the best alloy available for the casting procedure: Ti-6Al4V
Thanks to CastForm, the production of ash during the evacuation of the ceramic shell has been reduced: the ash, when in contact with the titanium, produces chemical reactions that damages the casting, and have therefore to be eliminated before pouring the cast metal in the ceramic shell.
The RP disposable pattern is made using the Selective Laser Technology (SLS).
CastForm® is the material used for Rapid Casting patterns.
- The pattern undergoes wax infiltrations to increase its strength
- It is then immerged in a ceramic bath
- Slurries and stuccoing and exsiccation
- The lost pattern is evacuated: dewaxing with flash firing or autoclave and subsequent sintering of the ceramic shell
- Alloy casting with inductor or voltaic arc
- Pouring, cooling, reduction of the shell, shot peening, gate cutting, heat treatments
The casting structure is formed of an aggregate of grains or polyhedral crystallites which produce isotropy compensation.
FEM calculations are very close to the real behaviour of the part thanks to the isotropy of it.
It’s possible to create the product along its mechanical stress axes, and to obtain a perfect reproduction of all details of the RP pattern, with tolerances and surface finishing of a very high quality (such as fully machined parts).
Rapid Casting with laser sintered patterns allows complete shape conception freedom: thus reducing undercut and tool path problems during CNC machining .
The Rapid Casting Procedure provided significant advantages:
- possibility to have a best post-stress control of the piece compared to carbon laminated parts
- durability and reliability of the detail (a casting is naturally isotropic for compensation)
- fewer design limitation
- the possibility to lightener (adding pockets) and get stiffer (adding ribs) the part during the racing season
From a direct comparison between Minardi Titanium Rapid Casting Gearbox 2005 and a gearbox produced in magnesium, the results are:
- weight saving is about 20-25%
- dimensions saving is about 20%
- torsional stiffness is double
- gear wear is reduced
- friction loss reduced
- with possibility to run higher oil temperature and lower viscosity
The collaboration with CRP Technology and its Rapid Casting Technology has resulted in several advantages, such as:
- a reduction in the volume of oil and the possibility of using oil at higher temperatures, hence at a greater viscosity;
- lower power dissipated in the pump;
- optimising the shape meaning a smaller gearbox case;
- reducing gearbox case weight;
- greater torsional rigidity;
- the possibility of integrating the supports for the suspension couplings inside the gearbox case without having to put additional mechanical elements in between which is how it was done in the past in gearbox cases made in aluminium and/or magnesium alloy (therefore giving us a better overall tolerance, just the one structure which is even more “solid” and making the gearbox corner even lighter).