Week 7- Base Unit Design Challenges 2

Aim: 

      To design a base unit with all weldments for the given Car Panel & Design all the other remaining Units required for this Fixture assembly.

Objective: 

      1. Design a Base Unit for the units designed for the above challenges with all weldments for the given Car Panel.

      2. Design the complete Fixture assembly. Make all the 5 Panels given in the CAD data fully constrained with the 3-2-1 principle.

Introduction & theory:

      A base unit is the unit 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. Base unit is the fundamental component of the fixture because all other components are mounted over it so every fixture have base unit. The base unit design is different according to the panel design of clamp system, location system etc.

Base Unit: 

Base unit is the unit of the 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 componet of the fixture because all other components are mounted over it.so every fixture have base unit. The base unit design is different according to the panel, Design of clamp system, location system etc.

Parts of the Base Unit:

• Base plate Pedestal
• Trunking channel
• Valve box
• Eye bolt
• Floor plate

1. BASE PLATE:

Base plate is a machined plate of 25 to 40mm thickness made of steel and aluminum on which the holes are drilled to mount individual units like clamp unit, pin unit, rest unit etc.

2. 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 millimetres.

3. PEDESTAL:

A pedestal is a part which connects the base plate to the floor plate. A pedestal is a standard part in general and in some cases it can be a welded frame integrated with the base plate.

• A standard pedestal can be of different height and different sizes.
• Depending on the size of the base plate, the number of pedestal varies for load distribution.
• Pedestals are of different types with different inclinations.

4. 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 fixtures work 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.

5. Eye Bolts:

Eye bolts are used for the transporting of the tool, using lift hooks, fork lift holes will also be provided in some cases for transporting purpose. For example, we usually use M20 bolts that are bolted on the base plate.

When installing lifting eye bolts it is critical to ensure face is in firm contact with the mating surface. These lifting rings are intended for linear pulling loads in the direction of the thread.

They are not intended for use where the load is perpendicular to the thread. This is because in these instances the bolt could unscrew and move or it could be twisted and break

6. Floor Plate:

Floor plate is grouted to the floor with fixed bolt on the ground. Floor plates are also called as foundation plates.

• There will be a clearance of 10 mm maintained between the pedestal base plate & floor plate.
• This clearance will be used by the leveling screws, for leveling the entire tool.
• Weld bars are be 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.

Points to be considered while designing Base unit:

• Working height 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 specific country will apply.
• If base structure is made with 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 plate welded to tube.

     The base unit of fixture must be strong enough so that deflection of the fixture should be minimum. This deflection of 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 and chatter.

     Base unit may be built from simple sections so that other units may be fastened with screws or welded whenever 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 the screws.

     The base unit should cover all the units with its outer periphery including opening. The base unit should be parallel to the floor, To adjust this there should be the provision of height adjusting mechanism.

Design of Base unit and fixture assembly:

1. Pin unit  

2. Retractable pin unit

3. clamp units

4. Swivel clamp units

Base plate

Pedestals and square tubes

Base unit and fixture assembly

Base unit and fixture assembly with plate