Case study Rapid Casting
CRP state-of-the-art casting work (1996 – 2007) with CastForm products
INTRODUCTION
CRP Technology
CRP has been instrumental in the success of many winning racing teams. From F1, to MotoGP, WRC (World Rally Championship), American Le Mans Series, Rally Raid (Paris –Dakar) we offer a high level of support throughout the entire project, including the manufacturing process.
What makes this company different are the partnerships we have formed with the different teams. CRP is involved at the earliest design and development stages and our innovative approach to the use of new materials and technology is widely recognised by the race car industry.
CRP Technology is therefore considered a unique service point for several different technologies and engineering activities.
The main activities are:
- HQ & HSM CNC (high speed and high quality machining with 3, 4 and 5 axis)
- Rapid Casting (lost wax casting with RP patterns) in Titanium, Aluminium, Steel alloys or Superalloys
- Rapid Manufacturing and Rapid Prototyping services
- Rapid Manufacturing & Rapid Prototyping composite materials production and sales
- Total Quality Management
- R&D: continuous research on materials like metallic alloys, plastic materials and new manufacturing processes development
- Reverse Engineering
CRP RP Department
In particular, CRP manages innovative projects, such as high precision titanium alloy castings and hard to work materials machining of complex shapes.
The Machining Department is therefore characterized by CNC milling centres, suited in particular to hi-tech materials machining.
WINDFORM® materials, developed by CRP’s internal R&D Department, are commercialized worldwide.
Technological patent pending and trademarks were done.
In Particular, WINDFORM® PRO and PRO B, by now, are covered by US patent and registered trademarks!!
The Procedure
In 1998 CRP Technology began to work alongside the Minardi F1 team, supplying them the engineering process, the manufacturing process optimization and the manufacturing of front and rear uprights: they began from the study of the Titanium Rapid Casting process.
F1 Upright –Titanium Rapid Casting
Rapid Casting is based on the combination of Rapid Prototyping technology, to manufacture the disposable pattern, and Investment Casting technology (Investement casting).
Disposable pattern: laser sintering and red wax infiltration
The RP disposable pattern is made by a consecutive overlapping of layers, using the Selective Laser Sintering technology. The system doesn’t require any support because the piece is held up by the non sintered powders, therefore giving complete freedom of shape.
The Rapid Casting procedure is composed of a number of steps:
- A disposable pattern is made through RP technique
- The pattern undergoes wax infiltrations (immersion and capillarity) to increase its strength (to avoid handling breaks);
- The pattern is immersed in a ceramic bath:
- Slurries and stuccoing and exsiccation;
- The lost pattern is evacuated: dewaxing with flash firing or in an 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
Example of disposable pattern, ceramic shell and casting
The casting structure is formed of an aggregate of grains or polyhedral crystallites which produce isotropy compensation, while in a solid metal they are anisotropic: it is obvious that isotropy has great advantages, for instance, FEM calculations are very close to the real behaviour of the part thanks to the isotropy of the piece.
Micrography in which it's possible to see the alpha-beta structure in the grain center and the typical annealed alpha structure at the grain border.
Moreover, Rapid Casting with laser sintered patterns allows complete shape conception freedom: thus reducing undercut and tool path problems during CNC machining.
It’s therefore 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). It’s what we can call DFFF: Design For Functionality & Fun, thus allowing you to think about what you need and not how to machine it (Design for Functionality instead of Design for Manufacturing).
The Materials
CastForm®, the material used nowadays for Rapid Casting patterns, was developed from the cooperation between DTM Corp. and CRP in 1998.
CRP began in fact in 1997 to study Laser Sintering technology to manufacture disposable patterns, using Polycarbonate and Trueform materials.
A schematic drawing of an SLS process
By the way, these materials were absolutely not suitable for Titanium alloys’ pouring, despite they seemed to be perfect for steel and aluminium alloys. This was the reason why CRP and DTM decided to create a new material, developed for Titanium alloys casting. CRP’s goal was to use Rapid Casting for very high performance parts, primarily for F1, therefore having very complicated shapes and geometries, and 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.
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).
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| Minardi Titanium Rapid Casting gearbox 2000 |
F1 Upright – Titanium Rapid Casting |
The Ti-6Al6V is the most widely used alloy in motorsport and aerospace markets, particularly the one used by CRP. It contains 6% aluminium and 4% vanadium, an excellent combination of stress resistance and toughness, with optimal wear resistance.
Positive aspects of Ti-6Al4V are:
- lightness (density 4,43 g/cm3)
- high specific Ultimate Tensile Strength (225,73 MPa/(g/cm3)) (UTS 1000 Mpa)
- bio-compatibility
- low thermal and electrical conductivity
- corrosion and stress-corrosion resistance (SCC)
Advantages given by heat treatment of the casting are:
- stress reduction
- ductility
- workability
- dimensional and structural stability
Minardi Titanium Rapid Casting gearbox 2001
Titanium casting has a really high reactivity and that’s the reason why it needs in addition:
- Chemical milling, to remove the alpha case created when the metal touches the ceramic shell;
- HIP: Hot Isostatic Pressure applied in an inert atmosphere (argon) to eliminate micro-porosity and shortage of material inside the casting;
- TIG Weld repair in inert atmosphere to fill in porosity or HIP hollows, tested with real time RX inspections;
- Shot peening: under-control shot peening to reduce stress and increase fatigue resistance.
The Minardi uprights
The first Titanium parts made for Minardi were the Cast Titanium front and rear uprights. The upright is the connecting part of the wheel where the hub transmits the engine rotational power to the tires. The suspension brackets, the front steering bracket, the rear convergence tie-rod and the brake callipers are connected to the uprights.
The required properties of the uprights therefore are: lightness (it is a non-suspended mass, therefore need no resonant bumps given by heavy wheels), stiffness (any deformation compromises the kinetics of the suspension and braking) and reliability, (as one of the safety components).
The uprights were usually manufactured through a long and complicated process of forming and cutting steel sheets, which included welding, heat treatment, CNC machining and finally painting to protect against corrosion. This process can’t optimize the mechanical performances of the piece, making the uprights heavier than they should have been. Moreover, being a welded piece, it presents a structural anisotropy that shortens its lifespan, and therefore its reliability and life expectancy.
In the beginning the classic cast alloys were tested, like aluminium ones, but almost immediately CRP decided to make the big jump and study the Titanium Rapid Casting.
In 1998 the study began for the Minardi F1 team, Marc Gené driving the test car, and the first uprights were produced in 1999.
Titanium Rapid Casting was therefore introduced in F1 by CRP Technology as a world première, in 1999.
Complex geometries were achievable only with this process, saving weight, increasing stiffness and reliability, besides giving cheaper costs than the other solutions.
In 2000 and 2001, Cast Titanium front and rear uprights were produced for other F1 Teams whose names have to be kept confidential.
In 2002 and 2003, The Cast Titanium front upright was studied and produced also for the Jaguar Racing F1 Team, driven by Eddie Irvine. Later on more or less all F1 teams used Titanium cast uprights, and nowadays it remains one of the best solutions and the safest back-up in case of need.
The Minardi gearbox
In 2000, CRP also developed the Minardi Titanium Gearbox.
Titanium gearbox: season 1999 (Magnesium), 2000 and 2001 (Titanium)
After the titanium fabricated g/box (’97 Ferrari) and the carbon fibre case (’98 Arrows/’98 Stewart), the Titanium Rapid Casting Gearbox was the latest evolution in this field and is currently one of the few providing such a high performance, as shown by the significant imitations following its introduction on the 2000 Minardi.
The requirements are the same as those of the uprights, however in this case the complexity of the piece’s design and dimensions increases.
From a direct comparison between our solution and a gearbox produced in magnesium, the results are:
- 20-25% of weight saving
- approximately 20% of dimensions saving
- double torsional stiffness
- less wear on the gears and lower power absorption, thus allowing the use of special lubricants, able to run at a higher temperature and with lower viscosity.
General advantages
Rapid Casting technology was immediately highly appreciated by customers because it provided significant advantages.
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For example:
- the possibility of maximum post-stress control of the components 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.
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Outside F1
After having consolidated with success its innovative transformation technologies, CRP decided in 2002 to begin the first cooperation out of the F1 circuit. The intention was, and is, to introduce into other motor series new hi-tech solutions, in order to increase mechanical performance and reliability.
CRP has cooperated in many different series using Titanium Rapid Casting first, and, being Titanium banned in some series in 2003, Steel special alloys Rapid Casting later.
Mitsubishi Dakar
In WRC and Rally Raid, CRP Technology strongly cooperated from the first design stage, in order to optimize the part project together with the constructors’ technical staff, and this alliance was finally rewarded.
2002
In 2002 Peugeot Cast Titanium front and rear uprights were studied and produced for the Peugeot WRC Official Team and MARCUS GRONHOLM won the World Rally Championship with these Titanium uprights made by CRP. This solution had cheaper costs compared to the other ones made in Titanium alloy.
In 2002 CRP began also to use 17-4 PH, a steel alloy with high mechanical characteristics.
“Process and production of mechanical parts through investment casting made by 17-4PH steel alloy did allow us first to gain a weight saving, second to obtain a structural behavior with higher efficiency, as well as much better final quality”, Franco Cevolini, CRP Technology’s Chairman, explains. “The perfect synergy between our partners’ and CRP technical offices has always facilitated co-design of the component, obtaining an excellent mechanical performance, respecting the foundry requirements”.
CRP therefore made the study and production of the Cast 17-4 PH front and rear uprights for the 3GR Cadillac official ALMS Team.
2004
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In 2004, CRP studied the same kind of uprights for the Mitsubishi official Rally Raid Team (Paris-Dakar). CRP also studied and produced prototypes of the Cast Titanium front and rear uprights for the Citroen Official WRC Team.
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2005
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In 2005, Mitsubishi Repsol Official Rally Raid Team and with LUC ALPHAND won the Lisbon-Dakar Rally Raid with 17-4PH Steel uprights made by CRP.
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2006
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In 2006, CRP Technology made the study and production of the Cast Titanium 17-4 PH front and rear uprights for the Mitsubishi Repsol Official Rally Raid Team and the study and production of the Cast Titanium front and rear uprights for an Official Le Mans Team.
Once again, it was a great success for Repsol-Mitsubishi in the Dakar 2006.
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The winning synergy
The last part that CRP made for Mitsubishi is for the 2007 Mitsubishi Pajero / Montero Evolutions. It is again the racing wheel upright for Rally Raid car, which is the typical part holding the wheel hub bearing and formed with various mountings and brackets for suspension attachment (wishbones and damper), and in addition various analysis sensors.
After validation from Mitsubishi engineers, CRP has begun the productive cycle involving its internal Rapid Prototyping department. After full inspection, these sintered PS lost patterns have been used for the casting process. The CNC (Continuous Numerical Control) service has completed various tests on the parts, including NDT (Non Destructive Test) inspection and 3D tests, allowing the uprights to be fully finished in short time period for car building.
“The opportunity of being able to decide between different manufacturing processes inside the same company is fundamental to guarantee the best result. The flexibility of a highly selected staff assures, moreover, reliability and respect of the total timing” indicates Franco Cevolini. “This is one of the reasons why Mitsubishi has decided to renew the winning synergy with CRP Technology”.
The extreme conditions of an event like the Dakar Rally highlights the talent of those who work for you, leaving no margin of error, and rewarding the best collaborations.As for the ’07 event, further optimization will be considered on these mechanical components, following the same process, with similar goals, i.e. further weight saving and increased stiffness.
Upright design trends – Mitsubishi Pajero/Montero Evolutions (2007)
Example - Lower mounting point
New design for the cage to get uniform wall thickness all around in order to improve casting quality and to save weight, together with a new distribution of the ribs for better response to the mechanical requirements caused by stress.
The “cap type” structure is a direct response to the structural calculation made on the model, and thanks to this new morphology, the result was a more uniform stress distribution and obvious weight savings. This was especially the case in one of the key areas of the upright.
All this is possible solely thanks to the very long experience that CRP has made during the last 11 years, what we call the “CRP METHOD”. So many years of study, improvement and optimization, allowed us to reach the highest level worldwide. The necessary know-how of Rapid Prototyping (creation of lost patterns), casting technology, design optimization (being able to adapt the design to the casting technology, with its needs), materials, alloys, and so on. A very high level thanks to a very long and deep experience.
It is very important also to understand the needs of the clients and the parts (loads, work conditions of the part, etc.) thus implying the maximum collaboration between the customer and the supplier (CRP) in order to adapt the part to this technique.
CRP will continue to study new materials and work alongside the racing teams in order to find always the best solution for each partner, helping the teams’ staff on engineering, right materials choices, right design suited for the right material and relative manufacturing process, manufacturing process optimization, quality and short delivery times, as motor sport industry requires and as only a lean and flexible company can do: It boosts production and choice, whilst still remaining a small, managerially agile company.
This is for sure a winning strategy, because racing teams need exactly a “KEY IN HAND” product, immediately ready for the race.
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