Week 7:- Base Unit Design Challenges 1

Week 7:- Base Unit Design Challenges 1

QUESTIONS:-

1. What is the Base Unit? What are the typical parts of the Base Unit?
2. What are the points need to account for while designing a Base unit?
3. What is a Dump unit?
4. What are the points you need to consider while designing a Dump unit?
5. What is a Slide unit?
6. What are the points you need to consider while designing a Slide unit?

ANSWER NO:-1.

BASE UNIT is the unit designed to mount all the other units (clamp unit, pin unit, rest unit, etc.) of the tools, also other parts necessary for a like pneumatic value box, trunking cable path will also be mounted on to a base unit. the base unit also mounts the components like valve bank, junction box, eye bolts, trunking cable path, etc.

TYPICAL PARTS OF THE BASE UNIT:-

BASE UNIT: A flat supporting plate or frame at the base of a column, designed to distribute the column's weight over a greater area and provide increased stability. the base plate has no of holes drilled on it which will act as mounting points for the clamp unit, pin unit and so on .base plate is a machined plate made of steel or aluminum of thickness 25mm to 40mm on which the holes are drilled to mount different units like rest units, pin unit, etc.

PEDESTAL:

• The pedestal is a part of an assembly (welded structure) that joins the base plate to the floor plate.
• The pedestal can be a standard part of a make part, depending on the size and height of the fixture.
• standard pedestals are available at different heights.
• Pedestals are also available in different inclinations depending on the size of the base plate, the number of pedestals for a fixture can vary for load distribution.

TRUCKING CHANNEL:

• The Trunking channel is a duct that carries all the electrical and pneumatic connections (wires and pipes) for a unit of the tool.
• it has a thickness of new millimeters.

VALVE BOX:- valve box is a standard part that contains all the valves for the pneumatic unit. the valve box is the box that included different solenoid valves. the pneumatic fixture work on air pressure provided to it. so the arrangement of air pressure inlet & outlet is done within this valve box. the trunking channel includes all the pressure inlet cables going to the pneumatic parts of the fixture & protects them from damage while the operation is in process.

MEASURING HOLE COVER: The measuring hole is drilled over the base plate which has exact coordinates and acts as a reference for the other holes due to the irregular shape of the car panel the coordinates of the hole are not norminal like 250.0,310.0 but it is like 250.62,310.84. these holes are covered by using some plate to protect against dust, damage, etc

EYEBOLT:

• Eye bolts are the bolts that are used to lift the fixture for transportation by inserting hooks into them
• for example, we usually use M20 bolts that are bolted on the base plate.
• used for transportation purposes, sometimes forklift holes will be provided.

FLOOR PLATE:

• They are also known as foundation plates. they are grounded by using a fixed bolt.
• 10 mm clearance should be given between the pedestal base plate and the floor plate.
• weld bars need to use after the leveling is done by leveling 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.

ANSWER NO:-2.

The following point needs to be taken into account while designing the base unit

1. working height:-

• it depends on the nature of the manual or robotic welding fixture.
• for manual fixtures we need to consider the working height of 850-1100mm, depending upon the working height of the worker standard of a specific country will apply (in few countries human height is higher or lower e.g. us, japan).
• If the base structure is made with a base plate having a tubular structure welded below it we can reach a height of 100 mm to 200 mm.
• In this case to reach the working welding height we need to provide additional leg structure which may have a top plate welded to the tube.

2. As a designer it is important to know how the base plate we a bigger base structure will be handled during the fabrication and handling process. special care needs to take care of flatness if the base size is very big.

3. Depending upon the weight eyebolt size is selected for lifting holes on the base plate. generally, 4 eye bolts provision is made. you also need to select the location of the eye bolt considering the rope/ belts/ used while shifting the structure or complete fixture are not damaging any units (rest, clamp, or location unit) nearby.

4. only base plate or welded structure

• Depending upon the component size and weight of the total units you also decide whether you need a fabrication base or just a plate.
• mostly fabricated bases are used made of square or rectangular tubes with the plate.

5. Most the OEMs makes 4 dowel holes at 4 corners and puts small aluminum plate marking the X, Y & Z coordinate of dowel holes. if the base length is too long few OEMs follow the methodology of having dowel holes at a 500mm distance.

6. The base unit of the fixture must be strong enough so that the deletion of the fixture is as minimum as possible. this deflection of a fixture is caused because of the force of welding, and clamping of the workpiece.

7. The base unit of the fixture should have a mass to prevent vibration and chatter.

8. The base unit may be built from the simple selection so that other units may be fastened with screw or welded whenever necessary those parts of the fixture that remains permanently with the fixture may be welded. those parts that need frequent changing may be held with the screw.

9. The base unit should cover all the units with its outer periphery including the opening.

10. The base unit should be parallel to the floor, to adjust this there should be the provision of the height adjusting mechanism.

ANSWER NO:-3.

when we have some geometrical constraints then it is difficult to place units like clamp unit, pin unit, etc. in this case the dump unit is used. dump unit is a complex unit to design due to space contains there is less space available & have to adjust all the parts in available space. it consists of a dump cylinder to perform the operation of clamping & unclamping the car panel. the first cylinder dumps the assembly carrying clamp mylar, and pins, and then this assembly performs the required operation. In this unit, we should make sure that in the open position of the panel, we should be able to remove the panel.

FUNCTION OF THE DUMP UNIT:

• To ensure proper resting of the panel being welded and to restrict its motion.
• to ensure there is no rotation in the panel and to fix it either by pin or side blocks to magnets.
• To ensure there is enough clamping force in the cylinder so that it doesn't move to weld.
• The dump unit should have correct shimming for adjustment of the panel.

CONSIDERATIONS FOR THE DUMP UNIT:

A dump unit can have a slide cylinder or a clamp cylinder attached to it. cylinder validation is important in the case of a dump unit as the weight can be too heavy for the dump in such case, calculations are done and the force exerted by the cylinder is checked against the weight of the load being carried. if cylinder force is more, it is validation or we use a more powerful cylinder.

ANSWER NO:-4

The following are the points to be considered while designing the dump unit otherwise it results in error and waste of time and money.

3-2-1 PRINCIPLE: once we have designed the rest of mylar, pins, and clamp and added a cylinder for clamping. we will check the resting and clamping of the panel being welded. this will be done by assembly being dumped onto the panel to operate. it is important because it is the reason why we are creating a dump unit. the positional accuracy of the panel is of utmost importance.

MASS CONSIDERATION: The assembly being dumped should have as less weight as possible without a reduction in the strength of the assembly. this is because the lesser the weight, the lesser will be the force required to push and pull the assembly we have to consider the factor of safety as well.

TIME OF OPENING AND CLOSING: The time of opening and closing of the clamp should be less. This basically depends on the power and capacity of the weight of the assembly being dumped. we need to keep it less because if it takes say 2 seconds to open then for that time we will not be able to unload the panel which will increase the cycle time resulting in more idle time.

CYLINDER VALIDATION: Cylinder validation is an important aspect of the dump unit or any clamp unit design because the cylinder should be able to push the load for operation and then pull it back after the operation is complete the center of gravity of the unit and the distances between the cylinder center lines and end effectors.

OPEN CONDITION: We need to also check the open condition after the cylinder validation because the panel should not fowl with the unit while removal.

ANSWER NO:-5

A SLIDE UNIT can have a clamp or a pin or a rest unit attached to it which slides forward and performs the required operation. on completion of the operation, the slide moves back. it has a cylinder that pushes the assembly forward. assembly is mounted on a plate, which is attached to guide rails. there are sensors on the extreme ends of the slides to sense the position of the slide.it has stop docks on either side to stop the cylinder at the required position. it has a locking mechanism that ensures that the slide does not move in a particular position as it may affect the welding quality and may damage the panel. slide unit is commonly used in places where there are space constraints.

Slide units are used at places where there are space constraints and places where there is less accessibility . sometimes, there are too many small panels near others and there is not enough space as each panel requires resting, location using 2 pins, clamping, and sensing. this becomes even more difficult when the panel is at angles. to solve this problem, a slide unit mounts a rest, clamp, or pin unit or all of them on a slide using guide rails, guide blocks, a cylinder, locking mechanism, stop blocks, and sensors. when a particular panel is to be welded, this slide moves forward, fixes the panel, and on completion of the operation, the slide moves back and gets locked at its position similarly, the same is done for other panels.

THERE ARE TWO TYPES OF SLIDE UNITS:

1. Hardened guideways
2. LM guideway

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

1. MANUAL SLIDES
2. HYDRAULIC /PNEUMATIC SLIDES
3. CNC SLIDES

It may also be classified depending on the application as follows:

1. HORIZONTAL SLIDES
2. VERTICAL SLIDES
3. ANGULAR SLIDES

ANSWER NO:-6

A sliding unit comes under the category of a complex unit. few point that need to be considered while designing a slides unit are:

1. WEIGHT CARRYING CAPACITY: There are different kinds of guide rails available in the market, each having a different load capacity .hence we calculate the weight of our assembly and calculate the weight capacity of the rails. hence, we choose rail based on its load-carrying capacity.
2. PUSH AND PULL FORCES: We need to check the push and pull forces and check if it is enough to push and pull the slides especially when the slide is at an inclination.
3. LOCKING MECHANISM: The locking mechanism ensures that the slide does not move while it is at the open or retracted position. if the slide moves while welding, it can damage the panel ad the positional accuracy will be hampered.
4. STOPPER BLOCKS: Stopper blocks are used to stop the slide at the required position. it is important as if the slide unit has rest mylar and pins they need to be stopped at their respective position for proper resting and location. without a stopper, it may dent the panel.
5. STOPPER UNIT: The sensor unit helps to check the position of the slides. when the going to start the operator pushes the button and the slides move forward the sensor gives this signal of the presence of the PLC which then perform the next operation.
6. SENSOR UNIT: we need to select the length of stoke based on the work area we want to get cleared.
7. OPEN POSITION: Theo only moving parts are that on the slides. so we need to check the following with a gun or other unit nearby. only after this has been checked that we can approve the design

THANKS