The essential guide
There are two types of fixtures. Assembly fixtures hold all components as loose items,
which are then separately clamped. When a product is too large or is produced in
low volumes it is best to pre-
In this case the robot fixture can be very simple indeed locating on some key features of the product. When designing an assembly fixture you should consider the following points:
If there are certain features within the product that have critical tolerances, shim the location surfaces to compensate for any distortion due to heat input. Sometimes the components have to be set away from nominal to get an accurate part. Incorporate local shielding if weld spatter is an issue in certain areas.
Customers in general industry tend to have welding fixtures with clamps that are manually applied. These represent the lowest cost and often work the best. In this example the fixture is for welding gates. Because the product features welding on both sides, it is necessary to rotate the assembly using a positioner. The fixture is mounted from a strong back, that spans across the fixture discs of the positioner. The strong back has a series of locations to accept a range of other fixtures. The strong back needs to be very rigid so that the joints will be accurately positioned.
Customer is in the automotive industry tend to have either automatic fixtures or
semi automatic fixtures (manually applied clamps, pneumatic backup and pneumatic
release). There will be sensors that monitor part presence and clamp open/close condition.
This information is mapped through to the robot control system or a PLC. If any of
the sensors is not made an error will be flagged up. These requirements are usually
the result of the automotive manufacturers insistence on quality control and traceability.
Automatic fixtures are also faster to operate and will show an improvement in productivity
when a large number of components and clamps need to be handled. The use of sensors
in fixtures greatly increases the electrical engineering cost associated with mapping
the sensor information and additional hardware such as a Human Machine Interface
(HMI), PLC and bus system. Whilst customers in the automotive sector often do not
have a choice, general industry customers should carefully consider the cost implications.
In addition, this type of fixturing tends to make a cell more dedicated and any subsequent
fixtures will need to be electrically integrated at a high on-
When welding very large assemblies it is generally too expensive to use assembly
fixtures and in this case the assembly is pre-
Manual welding fixture