Week 7:- Base Unit Design Challenges 1

What is the base unit & what are the typical parts of the base unit?

ANSWER:

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

fig shows example of welded base structure

TYPICAL PARTS OF BASE UNITS:

BASE PLATE:

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

PEDESTRAL:

• It is used to connect the base plate with a floor plate.
• The pedestral can be a standard part of a make part, depending on the size and height of the fixture.
• Standard pedestrals are available in different heights.
• Pedestrals are also available in different inclinations.
• Depending on the size of the base plate, the number of pedestral 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 millimet

Fig. Trunking channel

VALVE BOX:

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

Fig. Valve box

EYEBOLT:

• 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.
• Used for transportation purpose, sometimes forklift holes will be provided.

Fig. Eyebolt

FLOOR PLATE:

• The floorplate is grounded to the floor with a fixed bolt on the ground.
• Floor plates are also called foundation plates.
• There will be a clearance of mm maintained between the pedestral base plate and the floor plate.
• This clearance will be used by the levelling screw, for leveling the entire tool.
• 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.

2.What are the points need to account while designing a base unit?

ANSWER:

• The following points need to be taken into account while designing base unit.

Working heights:

• It depends on the nature of the manaul or robotic welding fixture.
• For manaul fixtures we need to consider the working height 850-1100mm, depending upon working height of the worker standard of a specific country will apply.
• If the base structure is made with the base plate having a tubular structure welded below it. we can reach the heigt of 100mm to250mm. 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 importanto know how big plate or bigger base welded structure will be handled during fabrication and 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 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 aluminium 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 base unit of the fixture must be strong enough so that deflection of fixture is as minimum as possible. This deflection of the 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 screwa or welded necessary.
• Those parts of the fixture that remains 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 adust this there should be 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 preffered to be designed with respect to BCS coordination.
• A base plate sould be drilled with datum holes/ measuring holes inline with a pitch of 1000mm in general.
• The number of datum holes depends on the size of 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

• Datum holes should be covered with cover plates.

3. What is a dump unit?

• Dump unit is mostly used on difficults panels where the weld 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 dunp unit should have two cylinders one is to clamp the mylars at the localized point and the other cylinder is 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 to function dump unit.Because when the two cylinders move at the same time if 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 case, calculations are done and force exerted by the cylinder is checked against thre weigh of the load being carried.

4. What are the points you need to consider while designing dump unit?

ANSWER:

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

Fig. Pivot point

3-2-1 Principle

• This will be done by the assembly being dumped into 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 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 weight. Because mass is an important role to play dump units.

Time of opening & closing:

• We also need to keep in the mind thst opening and closing of clamp will cause damages to other units or assembly. The timing of the cylinder in dump unit should always warry. Because the tiing will be the same the panel will get damage.

Cylinder Validation:

• Cylinder validation is the most important things to create dump unit. Because the cylinder should able to push the load from one place to another and then pull it back after the operation has done. Pivots points are impotant to lift the whole assembly by using cylinder.

Open condition:

• We need to also check the open condition after cylinder validation because the panel should not fowl with the unit while removal.

5. What is slide unit?

ANSWER:

• A sliding unit is majority used for difficult panel like(tunnel assembly) to be weld. Slide unit can have a clamp or a pin or a rest unit attached to which slides forward and performs the required operations. On completion of the operation, the slide moves back.

Fig- Slide unit

• It has a cylinder that pushes the assembly forward.
• Assembly is mounted on a plate, which is attached to guide rails.
• There are sensors on the extreme end of the side to sense the position of the slide whether it is in an open state or close state to identify.
• It has a locking system that ensure the side does not move from that place and it gives welding quality.
• Slide units are commonly used at places where are space constraints. The opening and closing of the side should not fowl.

Guide rails should be lubricated well.

The lubricants have the following roles.

• Minimizes friction in the traveling unit to prevent seizure and reduce
• Forms oil on the raceway to decrease stress acting on the surface and extend rolling
• Covers the metal surface to prevent rust.

6. What are the points you need to consider while designing a slide unit?

ANSWER:

Slide unit comes under the category of complex units, few points that need to be considered while designing slide unit are:

Weight carrying capacity:

• There are different kinds of guide rails available in the market each having different load capacity.
• Hence we calculate the weight of assembly & calculate the weight capacity of the rail. Hence, we choose rail based on its load- carrying capacity.

Push & Pull Forces:

• We need to check the push and pull forces & check if it enough to push and pull the whole assembly side especially when the slide is at an inclination.

Locking Mechanism:

• The locking mechanism ensure that hte slide does not move while it is in an open or closed position, if the slide moves while designin it can damage the panel as the positional accuracy will be hampered.

Stopper Block:

• Stopper blocks are used to stop the slide at the required position. It is important as if the side unit has rest mylars and pins, they need to be stopped at their respective position for proper resting and locations or else it may dent the panel.