Base Unit Design Challenges 2

AIM:

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

THEORITICAL PROCEDURE:

BASE UNIT:

A base unit is the 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 on to a base unit. And below are the 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.

Fig . Shows example of welded base structure.

TYPICAL PARTS OF BASE UNIT:

BASE PLATE:

The base plate is a plate of 25mm to 40mm thickness.

The base plate has no of holes on it which will act as mounting points for 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 or 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:

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:

Valve box is a standard part which will accommodates all the pneumatic valves for the unit. The valve box is the box which includes different solenoids valves. The trunking channel includes all the pressure inlet cables going to pneumatic parts of the fixture & protects them from damaging while operation is in process.

EYE BOLT:

Eye bolts are the bolts that are used to lift fixture 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.

FLOOR PLATE:

Floor plate is grounded to the floor with fixed bolt on the ground.

Floor plates are also called as foundation plates.

There will be a clearance of 10mm 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.

BASIC NEEDS TO DESIGN A 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 850-1100mm, depending upon the working height of the worker standard of a specific country will apply.
• If base structure is made with base palte having tubular structure welded below it. We can reach to height 100mm to 250mm. in this case to reach the working welding height we need to provide additional some leg structure which may have top & plate welded to the tube.
• As designer it is important to know how big base plate or bigger base welded structure will be handled during the fabrication & handling process. 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 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 OEM’s follow the methodology of having holes at 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 work piece.
• The base unit of the fixture should have the mass to prevent vibration & chatter.
• The base unit may be built from 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 provision of the height adjusting mechanism.

Fundamentals of Base unit:

• A base plate size should cover all the units with its outer periphery including opening.
• A base plate is always preferred to be designed with respect to BCS coordinated.
• A base plate should be drilled with datum holes / measuring holes in line with a pitch of 1000m in general.
• Number of datum holes is depend 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.

PRACTICAL PROCEDURE:

• We have to consider welding gun to designing a base unit. Because the welding gun has to flow through between panel and base plate. So first we have to measure the height between panel and base plate.
• The minimum space between the welding gun and base plate is 50 mm to 100 mm. because this is why we are creating the fixture.
• The base plate have to be strong and rigid to hold the entire fixture tool for welding process.
• In some cases the base unit is mounted on a trolley or it will fix to a slide bases unit.

FIG . TOP VIEW

 The base plate has diferent types of weldments and it varies when it comes from the customer. 

FIG .LEFT SIDE VIEW

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

In this project the base plate thickness is 20mm which is machined to maintained the parallelity which is very useful to when to mount the unit.

FIG . RIGHT SIDE VIEW

 The base unit should have the mass to prevent vibration and chatter.

The permanent parts like weldments has to be very strong enough to hold the all units and so do validity of the base unit will long.

FIG . ISO VIEW OF WHOLE TOOL

 The base unit should cover all the units with its outer periphery including opening positions.

FIG . RENDER VIEW

 the most important thing is once when we create the whole tool. the design have to move on to next stage to simulation. this process is also called as tool validation.

FIG . BOLT 

 This bolt is used to adjust the height of the base unit. The base unit should be parallel to the floo, to adjust the provision of height adjusting method. Here in this design we can adjust the height upto 10mm in upwards & downwards direction.

         

FIG . 3-2-1 PRINCIPLE

 In this project i have done the design to follow 3-2-1 principles. it is necessary to restrict all the degrees of freedom to weld the panel.

In this project the blue and orange panels are very small when consider to the yellow panel. i have created seperate units for pin unit. if we cannot achieve all the weld spots. we can unclamp some units to achieve those weld spots.

In this project the clamping positions are so near to the other units. So in standard we cannot achieve a weld spot it will be moved to re-spot station. But here the panel is too big. so the robots are not capable to operate this panel to achieve the weld spot.

For that we can unclamp some units to achieve those weld spots.

 In this project the whole tool name is P001_Z10_ST10_00_00.

CONCLUSION:

 Here as per the objective to design a base unit for the pin units and clamp units including swivel clamp unit with all weldments for the given car panel has been designed with 3-2-1 principle.