Week 7:- Base Unit Design Challenges 1

Q-1 WHAT IS THE BASE UNIT ? WHAT ARE THE TYPICAL PARTS OF BASE UNIT?

- A base unit is a unit designed to mount all the other units of the tool such as Clamp unit , Pin unit , Rest unit & also other parts necessary for a tool like Pnewmatic valve box , Truncking channel

Floor etc.

TYPICAL PARTS OF BASE UNIT :

- Trunking Channel

- Base Plate

- Valve box

- Measuring hole cover

- Eye bolt

- Pedestal

- Weld bars

- Floor plate

1. Trunking channel :

- A trunking channel is a duct which accommodates all the pnewmatic & electical hoses and wires for the units of the tool.

2. Base plate :

- A base plate is a machined plate of 25 - 40 mm thickness made of steel & alluminium on which the holes are drilled to mount the individual units.

2. Valve box :

- Valve box is standard part which will accomodates the pnewmatic valves for the units.

3. 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.

4. 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 diffrent height & 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.

5. Floor plate :

- Floor plate is grouted to the floor with the fixed bolt on the ground. Floor are also called as foundation plates.

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

Q-2 WHAT ARE THE POINTS NEED TO ACCOUNT WHILE DESIGNING THE BASE UNIT?

1. Working Height :

- It depends on the nature of the manual or robotics fixtures.

- For manual fixtures working height of 850 - 1100 mm is needed to be considered , depending upon the working height of the worker standard specific country will apply.

- If the base structure is made with base plate having tubular structure welded below it then we can reach to height of 100 to 250 mm. In this case to reach the working welding height we need to provide

additional some leg structure which may have top plate welded to tube.

- Try to study gun ergonomics properly then design the unit height & then base top height.

2. Base plate or welded structure :

- Depending upon the component size & weight of the total units we can decide whether we need fabricated base or just plate.

- Mostly fabricated bases are used made of square or rectangular tube with plate.

3. Selection of eye bolt :

- As a designer it is important to know how big base plate or base welded structure will be handled during the fabrication & handling process.

- Depending upon the weight eye bolt is selected for lifting holes on the base plate.

4. Base plate:

- There are few OEM'S , line builders use only thick base plate. Few OEM's recommend thick base base plate 40mm or 50mm for the child part assembly.

- If we go for higher thickness it will not bend after machining & will have good flatness.

5. Number of measuring holes required :

- We would need 3 holes to define the plane.

- Most of the OEM makes 4 dowel hole at 4 corners & put small aluminium plate marking X , Y & Z co-ordinates of dowel holes.

- If the base length is too long few OEM's follow the mythology of having dowel holes at 500 mm distance.

Q-3 WHAT IS A DUMP UNIT ?

- When we have some geometrical constrains then we cannot mount normal units like clamp unit , pin unit etc in this case Dump unit is used.

- Dump unit is cpmplex unit to design due to space contrains there is less space available & have to adjust all the parts in available space.

- It consist a dump cylinder to perform the operation of clamping & unclamping the car panel.

Q-4 WHAT ARE THE POINTS TO NEED TO CONSIDER WHILE DESIGNING DUMP UNIT ?

- Following points to be consider while designing dump unit :

1. Dump units are used when we cannot use normal units like clamp unit , pin unit etc due to some space contraints. The design parts should be small in size but can do their functions effectively.

2. It contains the dump cylinder which will be heavier part in all unit , The riser & Blade should have enough strength to bear the load of the cylinder & all unit as well. The riser & blade thickness

should be more in this type of units.

3. The parts should be designed by considering the open condition of the unit. In the open condition of the unit the part should not fall on the other unit.

4. We can use any cylinder in this case which suits our requirments.

Q-5 WHAT IS A SLIDE UNIT ?

- Slide units are positioning units which are used to position the fixtures , weld gun , Units , Robots into position for furthur operations.

They are as follows :

1. Hardened guide ways.

2. LM guide way

Slide units can be classified into three types on the base of prime mover used :

1. Manual slides

2. Hydraulic / Pnewmatic slides

3. CNC slides

It may also classified depending on applications as :

1. Horizontal slides

2. Vertical slides

3. Angular slides

Q-6 WHAT ARE THE POINTS TO BE CONSIDER WHILE DESIGNING THE SLIDES UNIT ?

- Following points to be consider while designing the slide unit :

1. LM guide ways are prefered over hardened guide ways due to least co-efficient of friction.

2. Slide unit essentially consist of LM guides , Linear cylinder , Front & rear stopper , Front & rear shock absorber , Two proximity switch / Reed switchs for sensing the two end position , Bellows or protection

cover for rails.

3. Center trunnion / rear clevis mounted cylinders are ideally used for slide unit application as this allows for some float to take up miss - alingment.

4. Reverse stroke of 10 mm to be consider for both forward & retracted condition.

5. Cylinder & LM guides to be validated for load & stroke.

6. LM guide rail length to be standard & should be more than the actual stroke.

7. Mechanical hard stop to be considered for both extended & retracted condition.

8. Shock absorber to be used for both the conditions.

9. The two end limits to sensed externally by proximity switch.

10. The shock absorber should be mounted such that it is perpendicular to the pivot at mid stroke or within +/- 5 degree.