Week 7- Base Unit Design Challenges 2

DESIGN OF BASE UNIT

OBJECTIVE:

To design a base unit for the pin unit and clamp units including swivel clamp unit with all weldments fr the given car panel.

SOFTWARE USED:

CATIA V5

BASE UNIT:

A base unit is a unit designed to mount all other units (clamp unit,rest unit, pin unit) 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 also mounts the componenets like Valve bank,junction box,eye bolts , trunking cable.etc.

PARTS OF BASE UNIT:

• Base plate:A flat supporting plate or frame at the base of a column,designed to distribute the coluimn's weight over a greater area and provide increased steablity.The base plate has number of holes drilled on it which will act as mouting points for clamp unit,pin unit and so on.Base plate is machine plate made ofsteel or aluminium of thickness 25mm to 40mm on which the holes are drilled to mount different units like rest unit,clamp unit,pin unit etc.
• Pedestal:Pedestal is a part of an assembly (welded structure) That joins the base plate to the floor plate.pedestal can be a standard part,depending on size height of the fixture.Standard pedestals are available at different heights.pedestals also available in different inclinations.Depending on the size of base plate ,the number of pedestal for a fixture can vary for load distribution.
• Trunking channel:Trunking channel is duct that carries all the electrical and pneumatic connections(wire and pipes) for units of the tool.It has a thickness of few millimeters.
• Valve box:Valve box is a standard part which contains all the valves of the pneumatic units.The valve box is the box which includesdifferent solinoid valves.The pneumatic fixture work on air pressure provided to it.So the arrengement of air pressure inlet cablles going to the pneumatic parts of the fixture& protects them from damaging while operation in process.
• Eyebolt:Eyebolts are the bolts that are used to lift the fixture for transportation by inserting hooks into them.
• Floor plate:Floor plate is grouted to the floor with xed bolt in the ground.Floor plates are also called foundation plates.There is a clearence of 10mm between pedestal base and floor plate.This gap is used to level the entire tool using leveling bolts.Weld bars are used to position the positions permanently.Weld bars are steel plates along the side of base plate of pedestal.

DESIGINING OF BASE UNIT:

• Working height: It depends on nature of the manual or robotic welding fixture.For manual fixturewe need to consider the working height 500-1100mm.depending upon the working heightof the workerstandard of specific country will apply(In few countries humman height is higher or lower e.g.US,Japan).If base structure is made with base plate having tubular structure welded below it you can reach to height 100mm to 250mm.In this case to reach working welding height you need to give aditional some leg like structure which may have top and plate welded to the tube.Study the gun ergonomic properly then design the unit height and then base to top height.The total height of the fixture should be lies between 900 to 1000mm.
• Eyebolt size:It is important to knoe how big base plate or bigger base welded structure will be handed during the fabrication and handling process. Depending upon the weight of eyebolt size are selected for lifting hole on base plate.Generally 4 eye bolt provisions is made.It 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.
• Plate Thickness:Few OEM's recommend thick base plate 40mm or 50mm for child part assemblies(eg.BMW).40/50mm plates makes a very heavy structure but som OEM's follow methodology.

Depending upon the component size and weight of the total units you can decide wheather you need fabricated base or just plate.

The base unit of the fixture must be strong enough so that deflection of the fixture is as minimum as possible.The deflection of a fixture is caused because of forces of welding ,clamping of workpiece.

The base unit of fixture should have the mass to prevent vibration and chatter.The base unit must be built from simple sectionsso that other u its fastened with screws or welded whenever necessary.Those parts of fixture that remain permanently with the fixture may be welded.Those parts That need frequent changing may be held with the screws.

The base unit should cover all the units with its outter pheriphery including the opening.

The base unit should parellel to the floor , To adjust this ,there should be the provisions of the height adjusting mechanism.

3-2-1 PRINCIPLE:

The best and most effective method of part location is referred to as 3-2-1 method.

3-Three locator blocks to establish part plain.Three locators or supports are placed under the workpiece.The three locators usually positioned on the primary locating surface.THis restricts one axial movements.Together the three locators restricts 5 DOF.

2-Round locating pin on a round hole that defines location in four directions (4-way)perpendicular to the plane previously established.THis restricts 4 axial movements.

1-Round locating pin a slot that defines two of the directiions of the other pin (2-way).This restricts two axial movements.

In this project there are 5 parts which needs to be joined together and these parts must achive 3-2-1 principle.I designed pin unit , clamp unit which holds those parts and achived 3-2-1 principle.

from the above picture it shows 2 pin units and 1 clamp unit holds the one part of the panel.

2 pin units restricts the 4 translational movements and 2 rotational movements

1 pin unit restricts = +X

-X

+Y

-Y

2 Pin unit together restricts = CROT AROUND Z AXSIS

ACROT AROUND Z AXSIS

1 clamp unit restricts 2 translational movements and 4 rotational movements

-Z

CROT AROUND X AXSIS

ACROT AROUND X AXSIS

CROT AROUND Y AXSIS

ACROT AROUND Y AXSIS

FIXTURE DESIGN:

FRONT VIEW

SIDE VIEW

TOP VIEW

MULTIPLE VIEW

ISOMETRIC VIEW WITH PANEL

ISOMETRIC VIEW WITHOUT PANEL

BASE UNIT

DESIGN TREE STRUCTURE

CONCLUSION:

Hence, Base unit is designed for the pin units and clamp units including swivel clamp unit with all weldments for the given panel.