The importance of clamping jig
A clamping jig is specially designed and manufactured to hold the parts during the FSW welding operation. The quality of the weld depends on the performance of this clamping jig. It performs four functions:
- A backing positioned under the workpiece to offset the vertical pressure exerted by the welding operation,
- Z-clamping to ensure that the workpieces are not lifted,
- XY clamping to prevent the parts from slipping,
- XY clamping to prevent the parts from moving apart.
We will expand on these four functions and explain why it is important that your clamping tool is efficient.
How do you clamp your parts during a friction stir welding operation?
Backing: the first part of a successful clamping jig
In friction stir welding, a vertical force is applied to the workpiece. The so-called forging force, between 1 and 2 kN/mm to be welded. The risk: the workpiece breaks or crushes on itself. There are two possible scenarios. On the one hand, the workpiece is self-supporting and can withstand the forging force thanks to its design. On the other hand, the shape of the workpiece is not sufficient to take up the welding force. In this case, a backing must be placed under the workpiece. The support points between the backing and the workpieces must be large enough to allow the backing to take up the welding load instead of the workpiece. The higher the clean surface area in contact, the lower the pressure on the workpiece.
Backing of a welded part by FSW
The backing material also has a role to play in the FSW process. The backing material must be able to withstand the heat generated when welding the parts. The melting temperature of the backing must therefore be much higher than the melting temperature of the aluminium parts to prevent the parts from sticking to the backing and the backing from expanding too much. Attention must therefore be paid to the thermal conductivity of the backing, which can strongly influence the welding parameters. Also, the chosen material must be rigid so that it is able to withstand the welding forces. For welding aluminium parts, the ideal material for a backing is steel because of its rigidity and melting point, which is about twice as high as aluminium, and its relatively low price.
How to counter longitudinal force?
In friction stir welding, the tool enters the material and moves forward. This can lead to slippage of the workpieces to be welded. The solution: position the stops to prevent the workpieces from slipping and being dragged along by the tool movement. These stops block the movement of the workpieces while welding and thus counteract the longitudinal force of the FSW tool.
Stops of clamping jig
The spread of parts: a trap to avoid during the welding operation
With the backing the pieces can’ t crush on themselves and thanks to the stops they can’ t slip. However, the workpieces can still move apart when the tool is passed through. Therefore, they must be clamped at the sides to counter the transverse force of the welding process. The solution: fix stop points on the sides of the workpiece. These stop points will block the movement of the workpieces during the welding operation.
Stopping points to block parts during FSW operation
Clampes: the last part of a powerful clamping jig
One point of attention remains: the lifting of the parts during the welding operation. Indeed, when we weld, a vertical force is applied to the parts, which can cause them to lift. It is therefore necessary to add clamps that will hold the parts from above and always as close as possible to the weld seam because this is where the forces are applied. The vertical pressure exerted on the parts by the clamps will prevent the parts from being lifted upwards. Depending on the welding configuration, this last clamping may not be necessary. For example, in transparency welding, clamps are not required.
The last step of a clamping jig: clamps
What are the different types of clamping jigs?
There are two main categories of clamping jig: manual and automatic. Manual clamping jigs are preferred for small series or prototypes. They are less expensive than automatic clamping jigs and therefore preferable for lower speed operations. However, the development of an automatic clamping jig is necessary when welding larger series and is more cost-effective. There are two types of clamping jig: pneumatic and hydraulic. Pneumatic clamping jig operates with pressurised air which allows the piston to move up or down. Hydraulic clamping jig works on the same principle except that the air is replaced by oil to move the pistons up and down.
For your clamping system to be efficient, you must take into account the clamping force, the number of support points, the geometry of the workpiece, the tool wear and of course the tool path. These elements are very important as your clamping system influences the production rate and the quality of the welds. Thus, the clamping jig fulfils several functions: it supports the vertical force exerted when the FSW tool plunges into the workpieces, it counters the longitudinal and transverse force and prevents the workpieces from lifting. Clamping workpieces with backing, stops, stop points and clamps guarantees optimum quality of the FSW weld.
Stirweld, an expert in the field of friction stir welding, offers you its know-how for the design of your clamping jigs. Striweld designs and manufactures the backing and clamping jigs necessary to obtain a good quality weld.
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