A red hot connection
17.06.2013 - Oliver Hagenlocher
The composite camshaft is still gaining ground in the marketplace. The main reason for this is the considerable weight reduction it brings, compared to its one-piece rival. The composite version is by now also widely used in the HGV sector. However, a quite considerable disadvantage of many assembly processes are the high joining forces applied, which create unacceptable tolerances in positioning and alignment of the cams. By contrast, the patented heat shrink assembly process from EMAG offers a decisive advantage, as it ensures that „ready-to-fit“ camshafts, gear shafts and other precision composite units can be produced without problem.
The advantages of the composite camshaft are well known: less expense, less weight, the possibility to use different materials for the various constituent components, greater flexibility in production and the ability to implement new cam geometries, such as negative radii, with ease. The necessary reductions in petrol consumption – and with it those of CO2 emissions – are easier to achieve with an increasing use of composite camshafts. Alternative processes for the joining of cam and shaft have one serious disadvantage: the two components cannot be joined with the necessary accuracy to avoid a subsequent finish grinding process. In many cases, the joining of cam to tube is carried out using a form-fit process like press-fitting, knurling and / or spline / serrated gearing. The joining forces required for these processes can deform the components and result in unacceptable tolerances in cam position and orientation.
The heat shrink assembly process from EMAG means precision joining
Thermal joining, i.e. the heat shrinking of cam onto tube, ensures that the required tolerances are achieved with a reaction force-free process. The know-how to tightly control the process parameters “temperature” and “time” – and the mechanical design of the joining equipment – are of the utmost importance in this. An optimal combination of robot and special-concept gripping technology allows for fusion gaps of < 15 µm to be achieved safely. The concept’s great flexibility allows camshaft designers much freedom in their designs and ensures that the process can also be used for medium batch sizes, where frequent component type changes are the order of the day. The high degree of precision of the composite camshaft drastically reduces the need to subsequently grind the cams or – where precision cams are used – does away with the requirement completely. A further advantage of this process lies in the possibility to use different materials for the composite shaft. This includes forged cams, for instance in 100Cr6, or finish-ground cams, even dimensionally accurate sintered cams that do not require a downstream finish-grinding operation. Secondary components, such as bungs and endpieces, can – just like the actual shaft itself – be made of more advantageous materials. All this allows for the camshaft to be made to suit the requirements of the engine and to optimise it in terms of load bearing capacity and manufacturing costs.
And now one step further:
Where the camshaft needs to be ground after heat shrink assembly, the joining machine can be linked up to a grinder. This is particularly easy when using an EMAG grinding centre of the VTC DS series. With this, the joining machine robot transfers the assembled camshaft directly to the loading position on the grinding centre. The advantages of this process from EMAG also apply to the machining of other components. When machining gear shafts, ground gears can be joined tightly on the shaft, without having to take account of the grinding wheel overrun at the design stage. It also minimises the length of the shaft and makes the whole unit more compact.
The EMAG process is characterised by only a very few machining components being in direct contact with the workpiece. It allows for the machines to be reset in the shortest possible time (less than 15 minutes).
Joining in seconds and achieving the highest possible quality
The heat shrink assembly process offered by EMAG combines flexibility with productivity, whilst freedom of design and choice of production technologies ensure a short cycle time. Whilst one cam is heat shrunk, the next one is already being preheated. Equipping the heat shrinking machine with a number of preheating units allows for the optimal application of this technology to the task in hand. It is these advantages that may well be the reason why so many firmly established manufacturers of camshafts and other precision assemblies are showing such a great interest in the new process, are asking for machining tests, or are already applying the process under production conditions. In the ideal case, the customer will take advantage of the synergy provided by the EMAG Group and ask for a complete concept to be prepared that covers everything from premachining to heat shrinking and endmachining.
The advantages of the heat shrink process:
- Great accuracy, requires no downstream processing after heat shrinking
- Saves on material and offers weight reduction
- No deformation after heat shrinking
- Allows the use of a combination of different materials
- Freely selectable component sequence
- Freely selectable angular and axial position
- Fast resetting in case of product changes
The advantages of the composite camshaft:
- Less expensive
- Less weight
- Cams can be made of different materials
- Greater flexibility in production
- New cam geometries – such as negative radii – can be implemented easily