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: 

      To design base unit by following the design constraints of each part with base unit

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

A typical Base unit and its parts

The typical parts of the base unit are as follows:

1)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.

base plate

2)Pedestal: Pedestal is part 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.

3)Trunking Channel: Trunking channel a duct or tube that carries all the electrical wire and pneumatic pipe connections for units of the different tool and units. 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.

truning channel

4)Valve box: Valve Box is a standard part which contains all the valves for the pneumatic units. It is a kind of control unit The valve box is the box which includes different solenoid valves which is used to control the vales. 

Typical valve box

5)Measuring hole cover : The measuring hole is drilled over the base plate which having exact cordinates and acts as reference for the other holes. Due to irregular shape of the car panel the holes coordinates are not nominal like 250.0, 310.0 But it like 250.62,310.84. These holes are covered by using some plate to protect against dust, damage etc.

Eyebolt: 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 purpose, sometimes forklift holes will be provided.

Typical eye bolts

6)Floor Plate: They are also known as foundation plate. They are grounded by using a fixed bolt. minimum of 10 mm clearance should be given between pedestal base plate and floor plate.

7)Weld bar: Weld bars are used after the levelling is done by levelling screw. Weldbars are steel plates along the sides of the base plate of a pedestal. Weld bars are used to position the positions permanently.

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:

pin unit

retractable pin unit

clamp units

swivel clamp units

rest unit

base plate

pedestals and square tubes

base unit and fixture assembly

Base unit and fixture assembly with plate

Conclusion:

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