Week 7- Base Unit Design Challenges 2

AIM

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

INTRODUCTION

BASE  UNIT

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

 

Typical parts of the Base Unit:

• Trunking channel
• Base plate
• Valve box
• Measuring hole cover
• Eye bolt
• Pedestal
• Weld bars
• Floor plate 

Points need to account while designing a Base unit

• 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 height of the worker stanadard of a specific country will apply( in few countries human  height is higher or lower eg.(US, Japan).  If base unit structure is made with base plate having tubular structure welded below it, we can reach to height 100mm to 250mm. In this case to reach the working working height we need to provide additional some leg structure which may have to and bottom 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 and handling process. Special care need to take care of flatness if the base size is very long.
• Depending upon the weight eyebolt size is selected for lifting holes on the base plate. Generally four eye bolt provision is made. You also need to select the location of eye bolt considering the rope/belt used while shifting the structure or complete fixture are not damaging any units (rest,clamp or location units) nearby.
• Only base plate or welded structure.  Depending upon the componenet size and weight of the total units you can decide whether you need a fabricated base or just plate. Mostly fabricated bases are used made of square or rectangualr tube with the plate.
• Most of the OEM makes 4 dowel holes at 4 corner and put small aluminium plate marking x,y and 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 fixyure 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 the work piece.
•  The base unit of the fixture should have the mass to prevent vibration and chatter.
• The base unit may be built from simple section so that other units may be fastened with screw 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 paralled to the floor, to adjust this there should be provision of the height adjusting mechanism.

BASE PLATE DESIGN

• A base plate size should cover all the units with its outer periphery including opening.
• A base plate is preferred to be designed with respect to BCS coordinates.
• A base plate should be drilled with datum holes/measuring holes in line with a pitch of 1000mm in general.
• Number of datum holes is depend on the size of the boxplate.
• Datum hole should be drilled at nominal value of coordinates and in terms of 50 & 100 in general Ex. X= 100, Y=-600, Z=250.
• Datum holes should be drilled with diameter 100mm away from the other unit.
• Datum holes should be covered with cover plates.

PEDESTAL DESIGN

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

FLOOR PLATE DESIGN

• There is a clearance of 10mm maintained between the pedestal base plate and the floor plate.
• This clearance will be used by the leveling screws for leveling the entire tool.
• Weld bars are to be weld the positions permanently after leveling is done.
• A weld bar is a plate along the sides of the base plate of the pedestal.

BASE PLATE - DESIGN

1. Base plate dimension is 2200*1450*30

2. Base plate have required  holes to mount  all units within  it.

3. Base plate has 4 eyebolt holes  on 4 direction

4. Base plate has 3 dowel holes. measurement  value of coordinates and in terms of 50 & 100 in general.

5.Datum holes should be drilled with diameter 100mm away from the other unit.

Base plate with square tube & weld plate. it has two square tube in middle to withstand the load on it

Total design with pedestal unit & floor plate

Base unit with all unit

Total working height is  900mm approximately.

base units should cover the all units within its outer periphery including opening.

Iso view

TREE STRUCTURE

Conclusion

Thus a base unit is designed with all the weldments for a given car panel and all the other remaining units have been designed for the given car panel