Challenge

Week 7- Base Unit Design Challenges 2

PPaluvaie Chandra Sekhar Reddy7 Jul 2022

*Designing a Base Unit for a BiW Fixture Units.

Given Panel:

INTRODUCTION

The base unit is designed to mount all the other units like clamp unit, pin unit, rest unit, etc of the tool, also other parts like pneumatic valve box, trunking cable path will also be mounted on the base unit.

The parts of the base unit are as follows:

Valve box
Trunking Channel
Measuring hole cover
Eyebolt
Pedestal
Floorplates

Base Plate

It is the machined plate of 25to 40 mm thickness, made of Steel or Aluminium on which all the other units are mounted.

Valve box

A valve box is used to supply compressed air to the pneumatic cylinders assembled in the fixture.
The valve box consists of solenoid valves with an inlet and outlet which controls the supply of air to the cylinder.

Truncking channel

Trunking channel is a hollow passage that guides and covers the pneumatic and electrical linings.

Measuring hole cover

The measuring hole cover the coordinates of the measuring holes are mentioned. These coordinates are used as references for placing the other units and also for the CMM inspection purposes.

Eyebolts

Eyebolts are placed in the base unit in order to lift the base unit and move it from one place to another.

Pedestal

The pedestal is a stand-like structure where the entire unit of the base will be mounted.

Floorplates

Floorplates are used to mount the entire base on the floor.

The above image shows the structure of the base unit.

Points to be considered while designing the Base unit

A base unit should cover all the units with its outer periphery including the opening.
A base unit is preferred to be designed with respect to BCS Coordinate
A base plate should be drilled with datum holes measuring holes in line with a pitch of 1000mm in general.
The number of datum holes must depend upon the size of the base plate.
The datum holes must be drilled at nominal values of coordinates and in terms of 50 and 100.
Datum holes must be drilled with a diameter of 100mm away from other units.
Datum holes must be covered with cover Plates.
The height of the base unit depends upon the type of the welding fixture and the standard height of the worker of the specific country. It is usually 850-1100mm.
The 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 changes may be fastened.

3-2-1 Principle

The 3-2-1 method is a work-holding principle where three pins are located on the 1st principle plane, i.e. either XY, YZ, ZX. And two pins are located on the 2nd plane which is perpendicular to the 1st plane, and at last one pin on the plane which is mutually perpendicular to the 1st and 2nd planes. The ultimate goal is to constrain the movement of the workpiece along all three axes.

3.Minimum

From the above figure, We can see three locator blocks positioned at the primary locating surface. These three locators restrict the axial upward and downward movement along with it the two radial movements both clockwise and Anti clockwise are also restricted. So, a total of four radial movements is restricted to the two mutually perpendicular axes.

The three locators, on the whole, have restricted six Degrees of freedom.

2.Round Locating Pin

The pin added in the location of the hole restricts the axial movements of two perpendicular axes (both positive and negative). Thus, restricting Four Degrees of freedom.

1.Round Locating Pin

The round locating pin is added to the slot in order to restrict the remaining radial movement in both clockwise and anti-clockwise. This, therefore, restricts the remaining two degrees of freedom.

Thus, the 3-2-1 principle is used to restrict the 12 degrees of freedom of a part.

BASE UNIT: