Week 7:- Base Unit Design Challenges 1

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

ANSWER:

• 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 Pneumatic 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 the 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:

• 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 pedestal base plate and the floor plate.
• This clearance will be used by the leveling 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 the base unit.

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 to 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.
• Datum holes should be covered with cover plates.

3. What is a dump unit?

• 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.

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

ANSWER:

• 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.
• 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.

Time of opening & closing:

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

Cylinder Validation:

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

ANSWER:

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

• 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 slide 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 ensures the slide 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 slide 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 a slide unit are,

Weight carrying capacity:

• There are different kinds of guide rails available in the market each having a different load capacity.
• Hence we calculate the weight of our 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 & pull forces & check if it enough to push & pull the whole assembly slide especially when the slide is at an inclination.

Locking Mechanism:

• The locking mechanism ensures that the slide does not move while it is in an open or closed position. If the slide moves while designing 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 slide unit has rest mylars & pins, they need to be stopped at their respective position for proper resting & locations or else it may dent the panel.