Week 7- Base Unit Design Challenges 2

AIM:- To design the base unit for the pin unit and clamp unit with swivel clamp unit all weldments for the given car panel.

SOFTWARE:- CATIA V5

BASE UNIT:-

• A base unit is designed to mount all other units(Clamp unit, pin unit, rest unit, etc) of the tool, also other parts necessary for a tool like Pheumatic valve box, trunking cable path will also be mounted onto a base unit. And below are some parts of a base unit in general.
• They are trunking channel, base plate valve box, measuring hole cover, eye bolt, pedestal, weld bars, and floor plate.

TYPICAL PARTS OF BASE UNIT

BASE PLATE

• The base plate is a plate of 25mm to 40mm thickness.
• The base plate has no holes on it which will act as mounting points for the clamp unit, pin unit, etc. of a tool.

PEDESTAL

• It is used to connect the base plate with a floor plate.
• The pedestal can be a standard part of a make part, depending on the size and height of the fixture.
• Standard pedestals are available in different heights
• Pedestals are also available in different inclinations.
• Depending on the size of the base plate, the number of a pedestal for a fixture can vary for load distribution.

TRUNKING CHANNEL:

• A Trunking channel is a duct that carries all the electrical and pneumatic connections (wires and pipes) for units of the tool. It has a thickness of few millimeters.

VALVE BOX

• The valve box is a standard part that will accommodate all the pneumatic valves for the unit.
• The valve box is the box that includes different solenoids valves. The trunking channel includes all the pressure inlet cables going to pneumatic parts of the fixture & protects them from damage while th operation is in process.

EYEBOLT:

1. Eyebolts are the bolts that are used to lift fixtures for transportation by inserting hooks into them. For example, usually we use M20 bolts that are bolted on the base plate.
2. Used for transportation purpose, sometimes forklift holes will be provided.

FLOOR PLATE:

1. The floorplate is grounded to the floor with a fixed bolt on the ground.
2. Floor plates are also called foundation plates,
3. There will be a clearance of mm maintained between the pedestal base plate and the floor plate.
4. This clearance will be used by the leveling screw, for leveling the entire tool.
5. Weld bars are used to weld the positions permanently after leveling is done. A weld bar is a plate along the sides of the base plate of the pedestal.

Working height:

• It depends on the nature of the manual or robotic welding fixture.
• For manual fixtures we need to consider the working height 850-1100mm, depending upon the working height of the worker standard of a specific country will apply.
• If the base structure is made with a base plate having a tubular structure welded below it. We can reach the height of 100mm&250mm.in this case to reach the working welding height we need to provide additional leg structure which may have top & plate welded to the tube
• As a designer, it is important to know how big base plate or bigger base welded structure will be handled during the fabrication & handling process. The special case needs to take care of flatness if the base size is very long Depending upon the weight eyebolts size is selected for lifting holes on the base plate. Generally, 4 eye bolt provision is made. You also need to select the location of the eye bolt considering the rope/belts used while shifting the structure or complete fixture are not damaging any units nearby.
• Most of the OEM makes 4 dowel holes & put small aluminum plate marking X, Y. & Z coordinates of dowel holes. If the base length is too long few OEMs follow the methodology of having holes at a 500mm distance.
• The best unit of the fixture must be strong enough so that deflection of the fixture is as minimum as possible. This defection of a fixture is caused because of forces of welding, clamping of the workpiece.
• The base unit of the fixture should have the mass to prevent vibration & chatter.
• The base unit may be built from a simple section so that other units may be fastened with screws or welded necessary.
• Those parts of the fixture that remain permanently with the fixture may be welded. those parts that need frequent changing may be held with screws.
• The base unit should be parallel to the floor, to adjust this there should be the provision of the height adjusting mechanism.

Fundamentals of Base unit

• A base plate size should cover all the units with its outer periphery including the opening
• A base plate is always preferred to be designed with respect to BCS coordination.
• A base plate should be drilled with datum holes/measuring holes in line with a pitch of 1000m in general. The number of datum holes depends on the size of the base plate.
• Datum holes should be drilled at nominal valves of coordinates and in terms of 50 and 100. Example X-100, Y--600, Z-250.

• Dump unit is mostly used on difficult panels where the welds are not achieved easily. Sometimes, it happens that there are some hard to-reach panels and which cannot be fixed by simple units, in such case, fix them we use a dump unit.
• The first cylinder dumps the assembly carrying clamp mylars, pins and then this assembly performs the required operation. In this unit, we should make sure that in the open position of the panel, we should be able to remove the panel.

Functions of Dump unit:

• To ensure proper resting of the panel being welded and to restrict its motion.
• A dump unit should have two cylinders one is to clamp the mylars at the localized point and the other cylinder used to dump the whole unit.
• In the dump unit, one assembly is fixed and that whole fixed assembly will mount on the dump unit cylinder.
• Programming is the main part of to function dump unit. Because when the two cylinders move at the same time it causes distortions to the panel so at that time programming will play the role.
• Cylinder validation is more important in the case of a dump unit as the weight can be too heavy for the cylinder to dump.
• In such a case, calculations are done and force exerted by the cylinder is checked against the weight of the load being carried. If cylinder force is more, it is validated or we use a more powerful cylinder.

DUMP UNIT:-

1. A dump unit is a complex unit which has a lot of parts. Hence, we need to be extra cautions while designing a dump unit because any mistake has happen in design can result a lots of errors that can create wastages of time and money. Hence we should check all the points that they are clearing all areas for all operations.
2. Most probably we should check it on with the simulation software like ROBCAD, DELMIA V5, and PROCESS SIMULATE if there any clash are hiding on catia these software will show the particular area of clashing.

3-2-1 Principle:

• This will be done by the assembly being dumped onto the panel to operate. It is very important to create a dump unit. The position of the panel orientation, pivot point, and PLP points are important to check while designing.

Mass:

• We need to ensure that the whole assembly being dumped should have less weight as possible without compromising on the strength of the parts. If we design the unit very little in weight there will be more possible to break the whole assembly. So design as much as possible to strengthen the design and more like reducing the weight. Because mass is an important role to play in the dump units.

PRACTICAL PROCEDURE:

• We have to consider welding gun to designing a base unit. Because the welding gun has to flow through between panel and base plate So first we have to measure the height between panel and base plate
• The minimum space between the welding gun and base plate is 50 mm to 100 mm. because this is why we are creating the fixture.
• The base plate have to be strong and rigid to hold the entire fixture tool for welding process. • In some cases the base unit is mounted on a trolley or it will fix to a slide bases unit.

TOP VIEW:

SIDE VIEW:-

FRONT VIEW & WORKING HEIGHT:-

ISO VIEW:-

3-2-1 PRINCIPLE:-

As per 3-2-1 principle all sub assembly part to be constraint

In this project i have done the design to follow 3-2-1 principles, it is necessary to restrict all the degrees of freedom to weld the panel. In this project the blue and orange panels are very small when consider to the yellow panel. have created seperate units for pin unit, if we cannot achieve all the weld spots, we can unclamp some units to achieve those weld spots.

in this project the clamping positions are so near to the other units. So in standard we cannot achieve a weld spot it will be moved to re-spot station. But here the panel is too big so the robots are not capable to operate this panel to achieve the weld spot

For that we can unclamp some units to achieve those weld spots

In this project the whole tool name is PO01 Z10 ST10_00_00

DESIGN METHODOLOGIES:-

As per welding station and zone tree of design shown as following,

CONCLUSION

Here as per the objective to design a base unit for the pin units and clamp units including swivel clamp unit with all weldments for the given car panel has been designed with 3-2-1 principle