Challenge

Week 7- Base Unit Design Challenges 2

TTushar Rastogi20 Jun 2022

AIM :

a)- Design the base unit for the units designed for the above challenges with all the weldments for the given car panel.

b)- Design all the other remaining units required for this fixture assembly.

BASE UNIT:

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

FUNDAMENTALS OF BASE PLATE DESIGN

A base plate 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 1000 mm in general, for example X = 100 Y= 600 Z = 250
Datum holes should be cover with cover plates.

PARTS OF BASE UNIT

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

b) 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.
Depends on the size of the base plate, the number of pedestal varies for load distribution.
A pedestal are of different types with different inclinations.

c) Valve box : Valve box is a standard part which will accomodates all the pneumatic valves for the units.

d) Eye bolt: 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.

e) Floor plate : Floor plate is grouted to the floor with fixed bolt on the ground. Floor plates are also called as Foundation plates.

f) Trunking channel : It is duct that carries all the electrical and pneumatic connections (wires and pipes) for units of the tool.

It has very minimal thickness.

IMAGES OF BASE UNIT

2- PIN UNIT

THEORY OF PIN:

Pin unit consists of Pin, Pin retainer, L Block, Shims, Blade and Riser.

Further it is classified into two types:

a)- Fixed Pin unit.

b)- Retractable pin unit.

1- Pin: It is used to fix the car panel by arresting DEGREE OF FREEDOM of car panel.

There are four cases arise due to the different combination of hole and pin.

a)- Circular hole with circular pin. ----------- 4 DOF arrested.

b)- Circular hole with diamond pin.---------- 2 DOF arrested.

c)- Slot with circular pin.---------- 2 DOF arrested.

d)- Slot with diamond pin.--------- 4DOF arrested.

2)- Pin retainer: It is used to support the pin.

3)- Shims : Due to the deviation in the diemension because of Man, machine and materials we provide shim pack in order to correctly locate the pin in the hole of the respective panel.

4)-Blade : It gives you the flexibility to use the same riser for different heights of the hole positions.

5)-Riser : It is a component used to support all the other component and it is attached to the base.

Types of pin unit

Fixed pin unit: Here pin is fixed because of the pin retainer and riser.

Retractable pin unit : Here we provide any mechanism for up and down motion of pin.

Design consideration of pin

1- It is must to use two pin to locate the car panel, one pin is going to arrest 4 translational motion and another pin is going to arrest 2 translational motion of the car panel.

2- Pin must be protuding 3 to 5 mm from the hole diemension.

3- Depending on the shape of the hole we have to use specific shape of the pin to arrest 4 translational motion first and then arrest 2 translational motion of the car panel.

4- Axis of hole and axis of pin must coincide.

Manufacturing consideration of the pin

a) The mounting surface of the pin should be finely machined i.e, mounting surface of the pin should be smooth.

b) Pin must have a step collar with surface exactly match with the wall of pin retainer to arrest the rotation about the axis of the pin.

c) A pin must be hardened ( Heat treated ) and Black oxide finished in general.

d) Pin must have the provision like tapped hole from the bottom or a v groove from the side.

Tolerance of pin

a) Geo pin -0.15mm.

b) Respot pin -0.28mm.

Fixed pin unit design images

a) With T riser

b) With L riser

Retractable pin unit design images

a) With T riser

b) With L riser

Overall design of fixed pin unit.

Overall design of retractable pin unit.

3-) CLAMP UNIT:

It is a unit which is used to hold the car panel with the help of fingers, Mylar using Pneumatic cylinder

It consists of Riser, Plate, Shims, Pneumatic cylinder, Clamp arm and Mylar.

Riser

Shims

Pneumatic cylinder

Clamp arm

Mylar

Blade

Design considerations

We have to make L block of simple shapes mostly of square cross section 15 * 15 or 20*20 or 25*25.
We have to provide the height of the riser not more than 450 mm in order to prevent break because of the weight of the cylinder.
We have to provide stiffner where the height of the riser is large.
Shim have to be of E shape for easy access.

Rest unit

This unit is used to support the panel by touching the lower surface of the panel.

Rest unit 1

Rest unit 2

Image of car panel with Complete rest unit

Power clamp unit

This unit is used to hold the panel with pressure delivered by the Pneumatic cylinder known as power clamp cylinder.

Power clamp unit 1

Power clamp unit 2

Power clamp unit 3

Image of panel with support to rest unit and power clamp unit

SWIVEL CYLINDER CLAMP UNIT : It is a unit to hold the car panel using Mylars which exerts force on the car panel by means of swivel cylinder

PARTS OF SWIVEL CYLINDER CLAMP UNIT

1- Mylars : It is a L block with square cross section which is used to hold the car panel by exerting direct pressure on the top of the car panel.

2- One way shim pack : It is used to adjust the position of Mylar finger in one direction (" here vertical direction ").

3- Clamp arm : It is a slender bar of rectangular cross section which is directly pivot to the swivel cylinder oscillating in the YZ plane (here in design) used to exert pressure on the MYLAR.

4- Stopper : It is used to support the clamp arm and prevent the clamp arm from excessive deflection also in order to restrict the linear motion of the stopper on the clamp arm we made a cut out of required diemension to limit the motion of the stopper.

5- Pivot arm : It is a link attached between the clamp arm (welded / pivoted) and blade (pivoted / welded) the main function of it is to limit the opening angle of clamp arm (upto 90 deg) and also help to maintain the required motion.

6- Swivel cylinder : It is a Pneumatic cylinder which govern the rotation of clamp arm and also provide the required force to hold the car panel.

7- Blade : It is a component which is attached to the riser and all the parts are attached to it because of this component we can use same riser for different height requirement for fixture.

8- Riser : It is a stand which supports all the above components.

9- Bush : It is used to avoid the wearing and tearing of elements if there is a relative motion exists between them.

10-Lock pin : It is used to connect the pivot arm to the blade and allow the rotation of pivot arm with respect to the blade.

PARTS OF SWIVEL CYLINDER PIN CLAMP UNIT

Besides above mentioned parts we have Pin (round and Diamond), Pin retainer, two way shim pack , 2 L brackets which are directly attached to blade and L block as shown below.

1- Pin

a) Round pin.