Week 7:- Base Unit Design Challenges 1
Que no. 1
Base Unit
A base Unit is a machined Plate of 25 to 40 mm thickness made of steel and aluminium on to which the hole is drilled to mount individual units like clamp unit pin unit etc of a tool.
Fundamentals of Base Plate Design
- A Base plate size covers all the units with its outer peripheral individual opening
- A Base plate is preferred to be designed with respect to BCS coordinates.
- A Base plate should be drilled with datum holes / measuring holes in line with a potch of 1000mm in general.
- Number of datum holes depends on the size of the base plate.
- Datum holes should be drilled at the nominal value of co-ordinates and on terms of 50& 100
eg. x=100 , y=600 , z=250.
- Datum holes should be drilled with a diameter of 100mm away from other units.
- Datum holes should be covered with a core plate.
Parts of Base Unit
1] Pedestal - A pedestal is a plate is a part that connects the base plate to the floor plate. A pedestal is a standard part in general and in some cases, it can be welded frame integrated with a base plate.
- A standard pedestal can be of different heights & different sizes.
- Depending on the side of the base plate the number of pedestals varies for the load distribution.
- A pedestal are of different types with different inclination.
2] Trunking channel - A trunking channel is a duct that accommodates all of the pneumatic and electrical hoses and wires for the unit of the tool.
3] Valve box - The valve box is a standard part that will accommodate the pneumatic valves for the units.
4] Eyebolt - Eyebolts are used for the transportation of the tool, using lifts hooks, forks lift holes will also be provided in some cases for transporting purposes.
5] Floor Plate - is grouted to the floor with fixed bolt on the ground floor plates are called foundation plate.
These will a clearance of10mm maintain between the pedestal base plate and the floor plate. This clearance will be used by the levelling screws, for levelling and the entire tool. Weld bars are being used to weld the position permanently after levelling is done. A weld bar is a palate that aligns the sides of the base plate of the pedestal.
Que 2nd Ans:-
1] Working Height - It depends on the nature of the manual or robotic welding fixture. For manual fixtures, we need to consider the working height of 850mm to 1100mm depending on the working height of a specific country.
2] Depending on the weight eyebolt size is determined for liting holes on a base plate. Most of the time 4 eye bolts are selected for lifting holes on the base plate.
3] Base unit should cover all the units in it and also include some openings for free movement of workers.
4]The base unit must be strong so that movements of the fixture is minimum. This movement occurs because welding workpiece or the clamping,
5] Base unit should not vibrate therefore it should have enough amount of mass to prevent the vibration.
6] while designing the base plate it is very important to know how big the base plate should we need and also should consider the flatness of the base plate.
Que 3 Ans:-
Dump Unit
It happens that there are some hard to reach panels that cannot be fixed by simple units. To fix them we use a dump unit.
-A dump unit can have more than one cylinder to perform such operations.
-The first cylinder dumps the assembly carrying clamps mylars, pins and then this assembly performs the required operations. In this unit, we should make sure that in the operation of the panel we should be able to remove the panels.
-A dump unit can have a slide cylinder or a clamp cylinder attached to it. Cylinder validation is important in the case of a dump unit as the weight can be too heavy for the cylinder to dump.
-If cylinder force is more it si validate or we use a more powerful cylinder.
Que 4th Ans:-
1]Dump units are used when we cannot use normal units like clamp units, pin units etc. Due to some space constants.
2] It contains the demo units cylinder which will be the heavier part in all units the riser and blade should have done enough strength to bear the load of the cylinder and all the units as well.
3] We can use any cylinder in this case that suits our requirements we can use both clamp and hinge cylinders.
4] The parts should be designed by considering the open condition of the unit.
5] In the open condition of the unit the parts should not fall to another unit
6] The Design parts should be small in size but can do their functions effectively.
7] Thew riser and blade thickness should be more in this type of unit.
8] We can use any cylinder in this case that suits our requirements we can use both clamp and hinge cylinders.
Que 5th Ans:-
Slide units are positioned units are used to position the fixtures weld gun, units, robots into position for further operations they are as follows:
1]LM guideways.
2] Hardened guideways.
Classified into 3 parts:-
1] CNC Sliders
2] Hydraulic or pnumatic slieders.
3] Manual sliders.
Depend on application
1] Horizontal slide
2] Vertical slide
3] Angular slide
Slide units are used when we have some space constraints so we don't have space to design different special units to assemble in those cases slide unit is used.
6th Ans:-
1] The two end limits are to be sensed externally by a proximity switch.
2]LM guides ways are prefered over hardened guideways due to the least coefficient of fiction.
3] Cylinders and LM guide to be validated for load and stroke.
4] Shock absorbers are used to be both extended and retracted conditions.
5] the shock absorbers should be mounted such that it is perpendicular to the pivot at mid-stroke or within negative or positive 5 degrees.
6]Reverse stroke of 10 mm to be considered in both forward and retracted conditions.
7]Mechanial hard stop to be considered for both forward or retracted conditions.