Week 7- Base Unit Design Challenges 2
AIM/OBJECTIVE
1. Design a base unit for the units designed for the above challenge with all weldmates for the given car panel.
2. Design all the other remaining units required for this fixture assembly.
SOFTWARE USED
CATIA V5
BASE UNIT DESIGN
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 valave box,trunking cable path will also be mounted on to a base unit.
Below are the some parts of a base unit in general
- Trunking channel
- Base plate
- Valve box
- Measuring hole cover
- Eye bolt
- Pedestal
- Weld bars
- Floor plate
BASE PLATE
Base plate is a machined plate of 25 to 40mm thickness made of steel and aluminium, on to which the holes are drilled to mount the individual units like clamp unit, pin unit etc. of a tool.
FUNDAMENTALS OF 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
A pedestal is apart which connects the base plate to the floor plate. A pedestal is a standard part in general and in some cases it can be welded frame integrated with the base plate.
FUNDAMENTALS OF 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.
TRUNKING CHANNEL
A trunking channel is a duct which accomodated all the pneumatic and electrical hoses and wires for the units of the tool. The trunking channel includes all the pressure inlet cables going to the pneumatic parts of the fixture and protects them from damaging while operation is in process.
VALVE BOX
Valve box is standard part which will accomodates the pneumatic valaves for the units. It is kind of control unit. The unit valave box is the box which includes different solenoid valaves which is used to control the valaves.
EYE BOLT
Eye bolts are used for the transporting of the tool using lift hooks, fork lift holes willl also be provided in some cases for transporting purpose. We usually use M20 bolts that are bolted on the base plate, used for transportation purpose,sometimes forklift holes will be provided.
MEASURING HOLE COVER
The base plate has some drills to mount various units like clam,rest,pin etc. and every drill have some coordinates to define the exact location of the hole.Due to irregular shape of the car panel the drilled holes coordinates are not like 110.0,150.0 but like 110.62,150.84. The measuring hole is drilled over the base plate which having exact coordinates so that all other holes can take reference from it.The measuring hole number depends on the size of base plate.These holes are covered by using some plate to protect against dust,damage etc.
FLOOR PLATE
Floor plate is grouted to the floor with fixed bolt on the ground. Floor plates are also called as foundation plates.
FUNDAMENTALS OF 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 aplate along the sides of the base plate of the pedestal.
THE POINTS NEED TO ACCOUNT WHILE DESIGNING A BASE UNIT
a) 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.
b) 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.
Fundamental of 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.
c) 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.
d) 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. Moatly fabricated bases are used made of square or rectangualr tube with the plate.
e) 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.
f) 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.
g) The base unit of the fixture should have the mass to prevent vibration and chatter.
h) 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.
i) The base unit should be paralled to the floor, to adjust this there should be provision of the height adjusting mechanism.
j) The 3-2-1 principle of location (six point location principle) is used to constrain the movement of work-piece along the three axes XX,YY, and ZZ. This is achieved by proving six locating points. 3 pins in the base plate, 2 pin in verticle plane and 1 pin in a plane which is perpendicular to the first two planes.
- (3) Minimum three locator blocks to establish part plane. Three locators or supports are placed under the work piece. The three locators are usually positioned on the primary surface. This restricts one axial movement downwards and four radial movements together the three locators restrict five degrees of freedom.
- (2) Round locating pin in a round hole that defines location in four direction ( 4- way) perpendicular to the plane previously established. This restricts four axial movements.
- (1)Round locating pin in a slot that defines two of the direction of the other pin (2-way). This restricts two axial movements.
Degree of freedom controlled by 3-2-1 location principle.
In this method,9 degree of freedom is controlled.
- Pins A,B,C on the base plane restrict the rotation of componenet about X axis and Y axis. It also limit the downward movement of component along Z axis. i.e. 1,2,3,4 and 5 degree of freedom is restricted.
- Pin D,E is in plane parallel to the plane containing X and Z axis. It prevent the rotation of component about Z axis ( 6,7 degree of freedom) and the movement of body in Y axix towards one direction (8 degree of freedom)
- The last pin F is in plane parallel to plane contains Y and Z axis. It restrict the movement component along X axis in one direction.
The remaining degeree of freedom 10,11 and 12 is unrestricted. It allows the loading of component in fixture. this degeree of freedom is restricted after loading of component by using clamping.
DESIGN METHODOLOGY
The Base unit is divided into two products.
a) Weld_01
b) Weld_02
Design Tree
Weld_01
Weld_02
Weld_01 consist of eye bolt X 4 , base plate, square tube X 5 and plate X4 where Weld_02 consist of plate X4 , sqaure tube X4 and ground plate X4.
EYE BOLT DESIGN (M24 EYE BOLT)
Specifications
Thread lengh= 48mm
Stack lengh= 64mm
Internal Diameter= 46mm
Outer Diameter= 92mm
Rod Diameter= 24mm
BASE PLATE
Base plate of length 1800mm and width 1400mm with padding of 20mm.
Base plate is provided with 4 holes of diameter 24mm to fix eye bolt.
SQUARE TUBE
To support and give strength to the base plate we have provided 5 square tube of different dimentions.
Square tube of length 1360mm X 2 provided on width side of base plate where as of length 1560mm X 2 provided on length of base plate.
To maximize the strength we have provided the square tube at middle of the base plate.
Cross section of dimention 100mm X 100mm of thickness 4mm.
We have aligned the tubes 20mm inside from each side of the base plate.
PLATE
Support plate is provided below the square tube of dimention 300mm X 3OOmm (4 no.) with pad of 20mm.
Weld_02 consist of plate, square tube and ground plate.
PLATE
Support plate is provided below the square tube of dimention 300mm X 3OOmm (4 no.) with pad of 20mm.
SQUARE TUBE
Square tube (4 no.) of length of 400mm and thickness of 8mm provided as a leg to support whole weight of the components.
Cross section dimention is 100mm X 100mm.
GROUND PLATE
Ground plate of dimention 150mm width and 250mm length with thickness 20mm.
It is provided with threaded hole of M27.
FINAL DESIGN OF BASE UNIT
Isometric View
Front View
The various units that are mounted on the base unit with their positions to the car panels.
1) Fixed Pin unit
2) Retractable Pin Unit
3) Clamp unit
4) Swivel clamp unit
5) Rest unit
All units placed together on base unit without car panel
Isometric View all the units mounted to the base unit without car panel
All units placed together on base unit with car panel
Isometric View of all the units mounted to the base unit with car panel
CONCLUSION
Thus a base unit is designed with all the weldmates for a given car panel and all the other remaining units have been designed for the given car panel and fixed its movement using the 3-2-1 Principle.