Week 7:- Base Unit Design Challenges 1

1.What is the Base Unit? What are the typical parts of the Base Unit?

BASE UNIT

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

FUNDAMENTALS OF BASE PLATE DESIGN

• A base plate size should cover all the units with its outer periphery inclusding 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 base plate.

• Datum holes should be drilled at nominal values of coordinates,and in terms of 50 and 100 in general.

• Example - X=100,Y=-600,Z=250

• Datum holes should be drilled with dia 100 mm away from outer units.

• Datum holes should be covered with cover plates.

Below are the some parts of abase unit in general.

• Trunking channel

• Base Plate

• Valve box

• measuring Hole Cover

• Eye Bolt

• Pedestal

• Weld Bars

• Floor plate

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 cased 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 sizes of the base plate,The number of pedestal varies for load distribution.

A pedestal are of different types with different inclinations.

Trunking Channel

Trunking channel is a duct which accommodates all the pneumatic and electrical hoses and wires for the units of the tool.

(or)

Trunking channel is a duct that carries all the electrical and pneumatic connections like wires and pipes for units of the tool.

It has a thickness of few millimetres.

VALVE BOX

Valve box is a standard part which contains all the valves for the pneumatic units.

• A valve box is basically a box which supplies air to all the other pneumatic cylinders. it's it's a device which includes a lot of other solenoid valves, so it will have one inlet and one outlet and from that one inlet, all the other solenoid valves will be attached to it. And each solenoid valves will have the input, and then again supplied to the separate cylinder, then again the output will be collected, while this solenoid valves, and again given back to the valve box.

MEASURING HOLE COVERS

Measuring Hole covers is on the base unit which is for measuring purpose.

• 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 and these holes are covered by using some plates to protect against from dust damage etc.

EYEBOLTS

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.

• It is to drag the entire unit and relocated.

(or)

• Eye bolts are the bolts that are used to lift the fixture for transportation by inserting hooks into them.

• For Example we usally use M20 Bolts that are bolted on the base plate.Used for transportation purpose and sometimes forklift holes will be provided.

WELD BARS

Weld bars are to mount it to the floor.

FLOOR PLATE

They are also known as foundation plate.They are grounded by using a fixed bolt 10mm clearance should be given between pedestal base plate and floor plate.

• Weld bars need to use after the levelling is done by levelling screw.

• Weld bars are steel plates along the sides of the base plate of a pedestal.

• Weld bars are used to position the positions permanently.

2.What are the points need to account while designing a base unit?

• A base plate size should cover all the units with its outer periphery inclusding opening.

• A base plate is preferred to be designed with respect to BCS coordinates.

• Working height depends on the nature of the manual or robotic welding fixture and for manual fixture we need to consider the working height be 850 - 1100mm and its depending upon the working height of the worker or its about ergonomics.It differs by countries.

• 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 base plate.

• Depending upon the Weight of the fixture design unit we need to select the eyebolt size for lifting the base plate.While shifting the fixture units from one place to another they will not damage or damaging any other units.

• Datum holes should be drilled at nominal values of coordinates,and in terms of 50 and 100 in general.

• Example - X=100,Y=-600,Z=250

• Depending upon the component size and weight of the total units you can decide whether you need a fabricated base or a plate.Mostly fabricated bases are used and made of square or a rectangle tube with the plate.

• Datum holes should be drilled with dia 100 mm away from outer units.

• Datum holes should be covered with cover plates.

• The base Unit of the fixture must be strong enough so that deflection of the fixture is as mimum as possible during welding,This Deflection is caused by the forces of welding and while clamping of the panel.

• The base unit of the fixture should prevent vibrations and chatter.

3.What is a Dump unit?

DUMP UNIT

A dump unit is a unit where you actually assemble a component which if you have certain constraints.

(or)

Dump unit is the complex unit to design due to space constains there is less space avilable & have to adjust all the parts in available space.

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

• Sometimes its hard to reach panels and which cannot be fixed by simple units,In such cases to fix them by using a dump unit.

• A dump unit can have more than one cylinder to perform such operation.

Functions Of Dump Unit

• If you have particular constraint and you cannot assemble in a normal way to use this use it in different ways again it has same dumb cylinder and and it has open position and closed position.and it has Clamp Cylinder Unit too.

• That is why this are very complex and design.

• Dump unit can have a slide cylinder or a clamp cylinder attached to it,Cylinder validation is more important in case of a dump unit as the weight can be too heavy for cylinder to dump,In such a case calculations are done and force exerted by the cylinder is checked againest the weight of the load being carried,If cylinder force is more,It is validated or we use more powerful cylinder.

• If you have any geometrical constraints, you can use this dampener to constrain your components.

• Proper resting of panel being welded and to restrict its motion.

• There is NO ROTATION in the panel to fix this either by pins or side blocks or magnets.

• It does not move while doing welding because of enough clamping force.

4.What are the points you need to consider while designing a Dump unit?

Dump Unit Cylinder Validation

Cylinder Validation is an Important aspect of the dump Unit or any clamp unit design because the cylinder able to push the load for operation and then pull it back after the operation is complete.

• measuring Interia - Mass - Create Geometry - Create a New Cat Part number - Select Product -Cetre of Gravity - Select Axis System - Press OK

• While calculating the centre of gravity of moving parts or assekbly by knowing the Longest perpenducular distance from a vertical line that passes through the center of gravity and the pivot center.

• The longest perpenducular distance could be in the work or rest position of anywhere in between In millimeters.

Idle Time For loading and Unloading

• The time for loading and Unloading of the clamp should be atleast as possible and this will depend on the power of the cylinder and the weight of assembly being dumped.

• Generaly it takes 1 to 3 sec to Loading the panel and 1 to 3 secs to Unloading the panel.

• If it takes 2 seconds to loading the panel means for that time we will not able to Unloading the panel which will increase the cycle time resulting in more idle time.

Material Used

• In Dump Unit We using two materials Steel and aluminium.

• After designing the dump unit,Choose Moving parts for steel like pin unit,Pin retainer,Blocker,Rest mylar,Clamp Mylar etc.

• we used Aluminium for Dump Cylinder.

Measure Inertia

We taking little bit more mass value as mentioned for the factor of safety.

• Make sure that the assembly being dumped should have less weight as possible without compromising on the strength of the assembly.

• Lesser the weight lesser will be the force required to push or pull the assembly by using Cylinder.

• We taking little bit more mass value as mentioned for the factor of safety.

5.What is a Slide unit?

SLIDE UNIT

A slide Unit can have a clamp or a pin or a rest unit attached to it and which slides forward and performs the required operation then it slides backward.

• It has a cylinder which pushes the assembly forward and which pulls the assembly.

• Slide unit contains Sensor unit,stopper,guide block,locking units,slide cylinders etc.

• Sensnor units in the extreme ends of the slide unit to sense the position.

• Opening and closing of the slide should not fowl.

• Sliding units are basically used in places where you have a lot of constraints or space constraints, when you cannot use different types of units to design the entire assembly. So, here you will use this sliding Only.

• Sliding cylinder has One open position and One closed position, which has to guide rails direction to the entire panel is going to move.

• Position locking unit which will lock the position at that particular point doesn't allow the entire plate to move.

• Sensors need to sense whether this entire component has reached here or not.

• Stopper blocks as I said initially to control the entire panel moving and it's a moving part.

• Slide units are used at where there are space constraints and places where there is less accessibility.

• Sometimes there is too small panels near each other and there is not enough space as each panel requires resting location using clamping,sensing.

• This becomes more difficult when the panel is at angles.To solve this problem,A slide unit mounts rest,Clamp or pin unit or all of them on a slide using guide rails,Guide BLocks,A cylinder,Locking mechanis, Stoppers and sensors.

• When the panel is to be welded,This slide unit moves forward,unload the panel or place the panel at one place or it completes its operation then it slides to backward.

• After that it locked at its position similarly same is done for other remaining panels.

Maintainence Of Sliding unit

• Guide rails should be Lubricated well.

• Choosing Good quality lubricant.

• Applying lubricant minimizes friction while loading and unloading or while traveling.

• Applying lubricant Reduces wear.

• Covers the metal surface to prevent rust formation.

6.What are the points you need to consider while designing a Slide unit?

Sliding units

Sliding units are basically used in places where you have a lot of constraints or space constraints, when you cannot use different types of units to design the entire assembly. So, here you will use this sliding Only.

Sliding cylinder

Sliding cylinder has One open position and One closed position, which has to guide rails direction to the entire panel is going to move.

Stroke

We need to select the lenght of stroke based on the work area we want to get cleared.

position locking unit

Position locking unit which will lock the position at that particular point doesn't allow the entire plate to move.

Locking Mechanism

The locking mechanism ensures that the slide does not move while it is at open or retract position.

• If the slide moves while welding,It can damage the panel as the positional accuracy will be hampered or position of slide unit in progress.

Sensor Unit

Sensors need to sense whether this entire component has reached here or not.

• Sensor unit helps to check the position of the slide,When the operation is going to start,The operator pushes the button and the slide moves forward.

• In that the sensor gives the signal to the PLC then it performs the next operation.

Stopper blocks

Stopper blocks as I said initially to control the entire panel moving and it's a moving part.

Points need to consider while designing a Slide unit

1.Slide Units are positioning units which are used to position the car part,fixture,weld gun,Units,Robots into position for furthur operations.

2.Slide Units may be classified into two types based on the types of Guide ways used as hardened guide way and LM guide way.

3.Slide units may further be classified into three types based on the prime Mover used as Manual slides,Hydraulic/pneumetic slides and CNC slides.

4.It may be further classified as horizontal,Vertical and angular slide units depending on the application.

5.LM guide ways are preferred over hardened guide ways due to the least co_efficient of friction.

6.Slide unit essentially consists of LM guides,Linear cylinder,Front and rear Stoppers,Front and rear Shock absorbers,Two proximity switches/Reed Switches for sensing the two end positions,Bellows or protection covers for rails.

7.Center trunnion/ Rear Mounted Cylinders are ideally used for slide unit application as this allows for some float to take up mis alignment.

8.Reserve stroke of 10 mm to be considered in both forward and retracted condition.

9.Cylinder and LM guides to be validated for load and stroke.

10.LM guide rail length should be standard and should be more than the actual stroke.

11.Master Guide way to be constrained and the subsidiary guide way to be free.

12.Mechanical hard stop to be considered for both extended and retracted condition.

13.Shock absorber to be used for both extended and retracted conditon to reduce impact load.

14.Slide to be locked or Clamped in the working position.

15.Slide to be locked with a safety pin in the retracted position during transportation.

16.The two end limits to be sensed externally by a proximity switch.

17.The LM rails should always be covered to protect against weld spatter and dust by a bellow or sheet metal cover.

18.The design to be checked for screw accessibility,ease of assembly,machinability of parts.

19.The LM guide and rail are integral assemblies and should not be separated at any cost.

20.The shock absorber should be mounted such that it is perpendicular to the pivot at mid stroke or with in positive or negative 5 degree.

21.LM guideways to be lubricated for extended life.

22.LM guide and rail can be ordered separately or as a single package based on the customers requirement and the make of LM guide.

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