Week 7:- Base Unit Design Challenges 1

1) What is the Base Unit? What are the typical parts of the Base Unit?

• Base unit is the unit of fixture which is designed as such so that other units of the fixture can be mounted on it.
• Apart from these units, other necessary tools like pneumatic valve box, trunking cable path will also be mounted on the base unit.
• Base unit is the fundamental component of the fixture because all other components are mounted over it and so every fixture has base unit.
• The base unit design is different according to the panel, Design of clamp system, location system.

PARTS OF THE BASE UNIT

1. Base plate
2. Trunking channel
3. Valve box
4. Eye bolt
5. Floor plate

BASE PLATE

• Base plate is a plate of 25mm to 40mm thickness.
• Base plate has no of holes drilled on it which will act as mounting points for clamp unit, pin unit and so on.

PEDESTAL

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

TRUNKING CHANNEL

• 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.

EYEBOLTS

• Eye bolts are the bolts that are used to lift the fixture for transportation by inserting hooks into them.
• For example, we usually use M20 bolts that are bolted on the base plate.
• Used for transportation pupose, sometimes forklift holes will be provided.

FLOOR PLATE

• They are also known as foundation plate.
• They are grounded by using a fixed bolt.
• 10mm clearance should be given between pedestal base plate and floor plate.
• Weld bars need to use after the leveling is done by leveling screw.
• Weld bars are used to position the positions permanently.

VALVE BOX

• Valve box is a standard part which contains all the valves for the pneumatic units.
• The valve box is the box which includes different solenoid valves.
• The pneumatic fixture works on air pressure provided to it. So the arrangement of air pressure inlet & outlet is done within this valve box.
• The trunking channel includes all the pressure inlet cables going to the pneumatic parts of the fixture & protects them from damaging while operation is in process.

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

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 fixture we need to consider the working height 850-1100mm, depending upon the working height of the worker standard of a specific country will apply (in few countries human height is higher or lower e.g. US, Japan).
• If the base structure is made with a base plate having tubular structure welded below it we can reach to height 100mm – 25mm.
• In this case to reach the working welding height we need to provide additional some leg structure which may have top and plate welded to the tube.

BASE PLATE OR WELDED STRUCTURE

• Depending upon the component size and weight of the total units we can decide whether we need fabricated base or just plate.
• Mostly fabricated bases are used made of square or rectangular tube with plate.

EYEBOLT

• As a designer, it is important to know how big base plate or biggest base welded structure will be handled during the fabrication and handling process.
• Depending upon the weight of the eye bolt size is selected for lifting holes on the base plate.
• Generally 4 eye bolt provision is made. We also need to select the location of eye bolt considering the rope or belts used while shifting the structure or complete fixture not damaging any units (rest clamp or location units) nearby.

BASE PLATE

• There are few OEMs, Line builders use only thick base plate.
• Few OEMs recommend thick base plate 40mm to 50mm for the child part assemblies.(e.g BMW).
• 40 or 50 mm plate makes a very heavy structure but it varies upon customer to customer

FUNDAMENTS OF BASE PLATE DESIGN

• A base plate should cover all the units with its outer periphery including opening.
• It is to be designed with respect to BCS coordinates.
• Base plate should be drilled with datum holes/ measuring holes in line with a pitch of 100mm in general.
• Number of datum holes depends on the size of the base plate.
• Datum holes should be drilled at nominal values of coordinates and in terms of 50 and 100 and in diameter of 100mm away from other units.
• Datum holes should be covered with cover plates.

3) What is a dump unit?

• The dump unit is used when we have any constraints and we cannot use our normal units like clamp unit and pin unit etc.
• Sometimes, it happens if they are hard to reach the panel and which cannot be fixed by simple units.
• In such cases to fix them, we use dump unit.
• Dump unit can have more than one cylinder to perform such operation.
• The first cylinder dumps the assembly carrying clamp mylars, pins and then this assembly carrying clamp mylars, pins and then the 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 THE DUMP UNIT

• To ensure proper resting of the panel being, welded and to restrict its motion.
• To ensure there is no rotation in the panel and to fix it either by pins or side blocks or magnets.
• To ensure there is enough clamping force in the cylinder so that it doesn’t move while welding.
• Dump unit should have correct shimming for adjustment of the panel.

4) What are the Points you need to consider while designing a Dump unit?

• Dump units is the complex unit which has lot of parts, so we need to give more importance while designing the dump unit because if any mistake we make in the design can result in errors that can create wastage of time and money. Points which should be considered for designing a dump are given as follows.

1) 3-2-1 Principle

• After designing clamp, clamp mylars, pins, after adding a cylinder, we should check the resting location and clamping of the panel being welded.
• This will be done by the assembly being dumped onto the panel to operate.
• It is important because it is the reason why we are creating a dump unit.

2) MASS

• We need to make sure that the assembly being dumped should have as less weight as possible without compromising on the strength of the assembly.
• This is because the lesser the weight, lesser will be the force required to push and pull the assembly.

3) OPENING AND CLOSING

• It is required to keep in consideration that the time of opening and closing of the clamp should be least possible and this will depend on the power of the cylinder and the weight of the assembly being dumped.

4) CYLINDER VALIDATION

• Cylinder validation is an important aspect of the dump unit or any clamp unit design because the cylinder should be able to push the load for operation and then pull it back after the operation is complete.

5) What is a slide unit?

• Similar to dump unit, sliding unit is also used where we have space constraints.
• It consist guide block, guide rails, sensor unit, stopper block, position locking unit and slide cylinder.

1) SLIDE CYLINDER

This helps in actuation of the platform from closed position to open position and vice versa.

2) SENSOR UNIT

This unit senses if the panel has is at its position or not.

3) GUIDE RAILS

This helps in movement of platform between open and close position.

4) POSITION LOCKING UNIT

It locks the open or closed position.

5) STOPPER

It restricts the further motion when in open position.

CLASSIFICATION OF SLIDE UNIT

Based on type of guide ways

• LM Guide way
• Hardened guide way

Based on prime mover used

• Manual slides
• Hyraulic/ pneumatic slides
• CNC slides
• Base

Based on application

• Horizontal slide
• Vertical slide
• Angular slide

6) What are the points you need to consider while desigining a slide unit?

• A sliding unit comes under the category of complex units. Few points that need to be considered while designing a slide unit are.

A) WEIGHT CARRYING CAPACTIY

• There are different kinds of guide rails available in the market, each having different load capacity.
• Hence we calculate the weight of our assembly and calculate the weight capacity of the rail.

B) PUSH AND PULL FORCES

We need to check the push and pull forces and check if it is enough to push and pull the slide especially when the slide is at in inclination.

C) LOCKING MECHANISMS

• The locking mechanism ensures that the slide doesn’t move while it is at open or retract position.
• If the slide moves while welding, it can damage the panel as the positional accuracy will be hampered.

D) STOPPER BLOCKS

• Stopper blocks are used to stop the slide at the required position.
• It is important as if the slide unit has rest mylars and pins, they need to be stopped at their respective position for proper resting and location.
• Without a stopper, it may dent the panel.

E) STROKE

• We need to select the length of the stroke based on the work area we want to get cleared.

F) OPEN POSITION

• The only moving parts are that one the slides, so we need to check the fowling with a gun or other unit nearby.
• Only after this has been checked that we can approve the design.