Week 7:- Base Unit Design Challenges 1

Q) What is the Base Unit? What are the typical parts of the Base Unit?
- A base unit is the unit 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 on to a base unit.

Base unit has a base plate which can be of different shapes. The shape of the base plate should be such that all the units can be mounted without any space
constraints. Sometimes, if the fixture weights too heavy, base plate can be given pockets to reduce some weight.

Typical parts of base unit are given as follows:
Base Plate: Base Plate is a machined plate made of steel or Aluminium of thickness 25mm to 40mm on which the holes are drilled to mount diffrent units like
rest units, clamp units, pin units etc.
Pedestal is a part or an assembly (welded structure) that joins the base plate to the floor plate. Pedestal can be a standard part or a make part, depending on
size and height of fixture. Standard pedestals are available in different heights. Pedestals are also available in different inclinations.Depending on the size of
base plate, the number of pedestal for a fixture can vary for load distribution.

Trucking 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 millimetres.

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 fixtures work on air pressure provided to it. So the arrangement of air pressure inlet & outlet is done within this valve box

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.

Floor Plates is grouted to the floor with fixed bolt on the ground. Floor plates are also called foundation plates. There is a clearance of 10mm between pedestal
base plate and floor plate. This gap is used to level the entire tool using leveling bolts. Weld bars are used to position the positions permanently. Weldbars are
steel plates along the sides of base plate of pedestal.

Q).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
1)Working Height:-
It depends on the nature of the manual or robotic welding fixture.
For manual fixture we need to consider the working height 850-1100 mm, 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 100 mm to ~250 mm.
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.
2)As a designer its is important to know how big base plate or bigger base welded structure will be handled during the fabrication and handling process. Special
care needs to be taken care of flatness if the base size is very long.

3) No. of datum holes to be drilled depends on the size of base plate.
4) Datum holes should be drilled outside a diameter of 100mm of unit.
5) Datum holes should be nominal and should be in multiples of 50 and 100.
For example; X=250;Y=-150;Z=100
6) Datum Holes should be covered with hole cover plates.

Q). What is a Dump Unit?

Sometimes, It happens that there are some hard to reach panels and which cannot be fixed by simple units, in such cases, to fix them, we use a dump unit. A
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 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 are 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.

Q).What are the points you need to consider while designing a Dump unit?

1) 3-2-1 principle
Once we have designed the rest mylars, pins and clamps and added a cylinder for clamping. We will 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. The
positional accuracy of the panel is of utmost importance.

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

3) Time of opening and closing
We also need to keep in mind that the time of opening and closing of clamp should be least possible and this will depend on the power of cylinder and the
weight of assembly being dumped

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

Q).What is a Slide unit?
- Slide units are positioning units which are used to position the fixture, weld gun,units,robots into position for further operations.
- Slide units can be calssified into two types on the base of the type of guide-ways used as
1)hardened guide ways
2)LM guide way
- Slide units can be calssified into three types on the base of the prime mover used
1)Manual slides
2)Hydraulic/pneumatic slides
3)CNC slides
- It may also be classified depending on application as
1)Horizontal slide
2)Vertical slide
3)Angular slide

Q. What are the points you need to consider while designing a Slide unit?

1) Weight carrying Capacity
There are different kinds of guide rails available in the market, each having a diifferent load capacity. Hence, we calculate the weight of our assembly and
calculate the weight capacity of the rail. Hence, we choose the rail based on its load carrying capacity.
2) 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 an inclination.
3) Locking Mechanism
Locking mechanism ensures that the slide does not 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.
4) Stopper Blocks
Stopper blocks are used to stop the slide at required postition. It is important as if the slide unit has rest mylars and pins, they need to be stopped at their
respective postion for prper resting and location. Without a stopper, it may dentthe panel.
5) Sensor Unit
Sensor unit helps to check the position of the slide. When the operation is going to start, the operator pushes the button and the slide moves forward, sensor
gives this signal of presence of unit to the PLC which then performs the next operation.
6) Stroke
We need to select the length of stroke based on the work area we want to get cleared.
7) Open position
The only moving parts are that one the slides, so we need to check the fowling with gun or other unit nearby. Only after this has been checked that we can
approve the design.