Week 8:- 3D Finishing Challenge 2

3D-FINISHING:

3d Finish is a process where the design is finished and to be ready for final simulation and 2d detailing.

• While finishing the design, the nominality is checked, ensuring the easy assembly of all the units.
• The hole concentricity and hole sizes are checked which ensures the assembly of different parts.
• The gaps between the different units are checked to ensure the proper individual working of different units.
• Design the rough locators, which help to load a panel in correction orientation.
• Design the pneumatic lay outing for pneumatic connection.
• Gun study is a major and most important part of 3d finishing.
• Selection of sensors, Solenoid valves as per the requirement and implementation in design.
• Fasteners are implemented as per the hole size and the standard color codes as per the customer requirement are applied to differentiate the type of hole whether it's a dowel hole, Threaded hole, or clearance hole.
• Renaming of the assembly and the part is done to give every part a different identity so everyone can identify in which assembly this part is going to fit.
• After doing all these things the model is sent for simulation and 2d detailing.

Points Need to Be Taken Care of While Finishing the Design:

The following are the points taken into consideration while finishing the design.

1. Hole Concentricity and Hole Sizes:- All part holes concentricity and hole sizes are checked for easy assembly while finishing the parts.

2. Machining Area:- The machining area in every part should be defined and the machining area should be highlighted by using a standard color code. Machining is to be done on parts to properly Mount with mating parts. Machining only on desired faces reduces cost and saves time. And also Machining increases the accuracy of dimension. So before going to simulation or detailing machining area should be defined.

3. Nominality:- All unit’s dimensions should be maintained nominal to facilitate easy assembly of the unit.

4. Holes Colouring Standard:- In a 3D finish hole coloring should be done because it helps to identify what type of hole it is. It depends on customer standards. Customer-specific colors like:

Dowel hole should be given blue color.

The threaded hole should be colored yellow.

Counterbore, the open hole should be given cyan blue color.

The machining Surface should be in Orange color

5. Pneumatic Lay Outing:- Pneumatic lay outing is a collection of different pneumatic pipes which work as an inlet to the pneumatic cylinder. It should be done properly for the proper functioning of the units.

6. Gaps Checking:- The gaps between the different units are checked to ensure the proper individual working of different units.

7. Fasteners Implementation:- Fast should be implemented in all the units as per the requirement and load on the part.

8. Avoiding Clash Between Different Parts:- Proper gap should be maintained between units to avoid clashes between the different units.

9. Mylar Splitting as Per Panel Profile:- Mylar splitting for the panel profile should be confirmed while finishing the design.

10. Proper Renaming of Parts or Assemblies as Per the Standards:- Proper renaming of parts and assembly should be done while finishing the design and hence we can identify every part easily with Unique Identification.

ROUGH LOCATORS:

• A rough locator is designed to guide the panel and locate the car panel onto the pins accordingly. A rough locator can be of standard part or a make part.
• Rough locators also work as Poka-yoke. Poka-yoke is a Japanese concept used for mistake-proofing.
• Rough locators are also used to help to locate the workpieces in the automation process. Locating refers to the desired location where you want the workpiece to be when it is getting worked on either by a person or a team or a robot.
• The accuracy of the locating components directly affects the consistency and how the final product will come out. This is why these components are essential to our setup.
• It can be also called fool proofing method. Because without a rough locator, the part cannot be loaded in the correct position.
• The rough locators are set accordingly to the angle of the respective panel and hence the part can be loaded in a defined direction and orientation only.

Fig 01: Rough Locator

Points Needed to Consider While Designing A Rough Locator:

The following are the points needed to be considered while designing the rough locator.

• Rough locator should be placed at the edges of the car panel, which it has to guide.
• Applicator has to be placed at the same angle as the car part edge with a minimum distance of 2-5 mm from the edge of the car part.
• Prof locator should guide the panel in pin arresting direction.
• Rough locator should start guiding the panel 10 to 15mm to the start of the pin engagement.
• Applicator should be designed with an entry angle for the car panel. Generally, it ranges between 30-45 degrees.
• Rough locator should be designed with two slots to mount the easy adjustment.
• The slot should be in the direction of the car part guiding.

 

Fig 02: Rough Locator

Positioning of rough Locators on the Base Plate:

Fig 03: Rough Locator arrangement 

Fig 04: Rough Locators with Panel

Fig 05: Rough Locators with Panel (Top view)

GUN STUDY:
Welding is predominantly used in automobile industries and requirements for fixtures that ease the welding process is a continuous development task in any industry. Car Body-In-White (BIW) is a complicated steel structure including 300~500 sheets with complex shapes and is assembled by means of welding in a high rhythm through 55~75 robotic work-stations. The foremost step taken before starting the design of the welding fixture is to arrive at the spot weld locations. The location and orientation of other critical units of the fixture including clamps, locators, etc., are decided based on the weld spot distribution. The weld spots for the Front door inner panel and Side bracket assembly are located as shown in Table 1 with respect to the body line of the car. It includes the study of the weld gun (A portable device for semiautomatic welding of parts of various articles) which is going to be used for the operation depending on the size of the part, Thickness of the part, etc. It includes the study of the weld matrix & the weld point positions. There are two types of weld point one is geo weld points which ensures the geometry of the assembly & second is the Re spot weld points which adds strength to the already welded part.

The device used to make spot welding on the panel is called a Gun. The Gun may differ depending on the application. Fixtures will be designed by considering the weld spots on the panel. After designing the Fixture, the CAD file of the gun is placed on the weld spots to check whether the Gun is clear with the Fixture. After adjusting the Fixtures, the coordinates of the welds be taken for further operations of the Weld Gun.

Points needed to consider during the gun study:

Weld gun study is a very time-consuming process, the entire welding cycle time study depends on the no. of spots & weld gun study.

The following are the points that need to consider during the gun study.

• The axis of the weld spot along the welding direction must be normal to the weld surface.
• The no. of weld spots for the panel, the time required to spot each weld & the total time required to complete all weld spots.
• If we have one or more device models & we want to program, the behavior of each model in the work cell can be simulated over time. Instructions for each device are coded by giving sequences. The sequence defines the motion, manipulation & action of the devices. Based on the distance of each tag point from the home position, motion type, speed & acceleration one can obtain cycle time for each device assigned with sequences. This way robot cycle time is precisely calculated.
• After sequencing all the devices, a simulation is run with “collision check” ON & made sure that the welding operation is collision-free.

IXTURE ASSEMBLY:

Renaming and structuring of the design tree:

Renaming of the design tree is done. and structuring design tree in a way that is simple to identify the units. some units use multiple times that are easy to identify by its name.

Fig 06: Desing Tree

Base unit:- It is a 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 a pneumatic valve box, trunking cable path will be mounted on to a base unit.

Fig 07: Base Unit

The base unit is the fundamental component of the fixture because all other components are mounted over it so every fixture has a base unit. The base unit design is different according to the panel design of the clamp system, location system, etc.

Parts of the Base unit

• Base Plate
• Pedestal
• Valve Box
• Measuring Hole Cover
• Eyebolt
• Floor Plate
• Weld Bar

Base Plate:- The base plate is a machined plate of 25 to 40 mm thickness made of steel & aluminum, on which the holes are drilled to mount the individual units like clamp units, pins, etc., of a tool.

Fig 08: Base plate

Pedestal:- A pedestal is a part that connects the base plate to the floor plate. A pedestal is a standard part in general & in some cases, it can be a welded frame integrated with the base plate. Pedestals are used for leveling the base unit

Fig 09: Pedestal

A standard pedestal can be of different heights & different sizes.

Depending on the base plate’s size, the number of pedestals varies for load distribution.

A pedestal is of different types with different inclinations.

Trunking Channel:- A trunking channel is a duct that accommodates all the pneumatic & electrical hoses and wires for the units of the tool. It has a thickness of a few millimeters.

Fig 10: Trunking Channel

Valve box:- Valve box is a standard part that will accommodate all the pneumatic valves for the units. The valve box is the box that includes different solenoid valves. The pneumatic fixtures work on air pressure provided to it. So the arrangement of the air pressure inlet & outlet is done within this valve box. The trunking channel includes all the pressure inlet cables going to pneumatic parts of the fixture & protects them from damage while the operation is in process.

Fig 11: Valve Box

Eyebolt:- Eye bolts are used for the transporting of the tool, using lift hooks, forklift holes will also be provided in some cases for transporting purposes. For example, we usually use M20 bolts that are bolted on the base plate.

Fig 12: Eyebolts

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

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

Points need to account for while designing a Base unit

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.
• If the base structure is made with a base plate having a tubular structure welded below it. We can reach a height of 100mm to 250mm. in this case to reach the working welding height we need to provide additional leg structure which may have top & plate welded to the tube.
• As a designer, it is important to know how big base plates or bigger base welded structures will be handled during the fabrication & handling process. The special case needs to take care of flatness if the base size is very long.
• Depending upon the weight eyebolts size is selected for lifting holes on the base plate. Generally, 4 eye bolt 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 nearby.
• Most of the OEM makes 4 dowel holes & puts a small aluminum plate marking the X, Y, & Z coordinates of dowel holes. If the base length is too long few OEMs follow the methodology of having holes at a 500mm distance.
• The best unit of the fixture must be strong enough so that the deflection of the fixture is as minimum as possible. This defection of a fixture is caused because of forces of welding, and clamping of the workpiece.
• The base unit of the fixture should have the mass to prevent vibration & chatter.
• The base unit may be built from a simple section so that other units may be fastened with screws or welded as 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.
• The base unit should be parallel to the floor, to adjust this there should be the provision of the height adjusting mechanism.

Fundamentals of Base Unit:

• A base plate size should cover all the units with its outer periphery including the opening.
• A base plate is always preferred to be designed concerning BCS coordination.
• A base plate should be drilled with datum holes / measuring holes in line with a pitch of 1000m in general.
• The number of datum holes depends on the size of the base plate.
• Datum holes should be drilled at nominal valves of coordinates and in terms of 50 and 100. Example X=100, Y= -600, Z=250.
• Datum holes should be covered with cover plates.

Fig 13: Base Plate

Fig 14: Base Unit

Fig 14: Base Unit (all views)

REST UNIT:

• A rest unit is a unit that is designed to support or rest the car panel on it.
• Its sole purpose is to rest the panel onto it and thus no force or clamping is done.
• But as it is a simple design, it can be combined with other units to reduce the cost of the overall project.
• For example it can be used along with locating unit to locate and rest the panel or with a clamp unit to clamp and rest the panel.
• Or the rest unit, locating unit, and clamp unit can be used together in one single project.

Components of Rest unit:

• NC block
• Spacer/ Shim pack
• Blade
• Riser

Mylar/NC Block

• NC blocks or popularly also known as Mylar is the ones that hold the panel.
• It prevents the panel from deforming while welding.
• They always come in pairs.
• Top Mylar is known as clamping Mylar and bottom Mylar is known as resting Mylar.

Few points to remember about Mylar:

• Generally, Mylar clamping block clamp cross section (the area in the contact panel) is considered as 20mmx20mm.
• Most of the OEMs/Tier 1 prefer Mylar to have a 5mm allowance material for machining. Most Mylar is CNC machined if it is clamping 3D profile.
• Depending on the angle of the cross-section, Mylar will be shimming either in one direction or in 2 directions.

The general Thumb rule is if the section is inclined more than 15 deg or the clamping surface is a 3D profile then 2-direction shimming is provided. The reason is simple mathematics. The equation of inclined line/ plane will be having 2 parameters to control and we control with shimming in 2 directions. Less than 15 deg does not mean that there are not 2 parameters. These are there but they are neglected if angle is less than 15 deg.

Fig 15:- Mylar/NC Block

Block:- The L-shaped plate is called a Block or L block. This part is used as a connection between the Pin retainer and Blade. Generally, blocks are used to provide shimming. Blocks don't need to be only used for shimming, their uses change as per the requirements, At some places, it is used just to connect one part to another.

Fig 16:- Blocks/L- Blocks

Shim:- Shims & Spacers are some standard parts in general, which are used for adjustments of locators (NC Blocks & pin retainers) for desired values for the precise working of a unit concerning car parts. In general to adjust the design to manufacturing deviation.

Fig 17:- Shim/Spacer

Blade:- The plate which connects Riser to the Block/Clamp cylinder is named Blade. This plate plays an important role in building the unit. The plate can be of any shape. But we need to keep in mind that the plate should be as compact as possible.

Fig 18:- Blades

Riser:- The part which is mounted on the base plate and holds a blade or pin cylinder on it is called Riser. The riser can be a Standard Part or a manufactured part, it varies from project to project. A riser can be a Single part or welded part. Standard risers also have various shapes and sizes.

Fig 19:- Risers

Fig 20:- Rest Unit

Fig 21:- Rest Unit (all view)

Fig 22:- Rest Unit with panel

Pin Unit:- Pin unit is a unit designed to locate the car panel using Pin. The pin unit is used to lock the rotational position of the panel.

Fundamentals of pin unit design

• it is necessary to have 2 pins to locate a car panel & here one pin must arrest 4 way (4 translational) & other must arrest 2 way (i.e. 2 rotational) of a car panel.
• The axis of the car panel hole & the axis of the pin should be the same (in general)
• The pin tolerance for a geo pin will be of closer tolerance i.e. -0.15mm & for a re-spot pin is -0.28mm
• Pin should engage 3 to 5 mm from the car panel entry surface.
• All pins should be accommodated with 2-way adjustable shims irrespective of the direction of arresting.
• Round pins should be used if the hole is round in case of 4-way arresting of the car part.
• Round pins can be used for 2 way arresting of car parts only if the hole is slot.
• Diamond pins should be used in case of 2-way arresting of car part if the hole is round
• Diamond pins should be used in case of 4-way arresting of the car part if the hole is slotted.

There are mainly 2 types of pin units

• Fixed Pin Unit
• Retractable Pin Unit

Fixed Pin Unit Design

Fixed Pin Unit:- The pin’s position is fixed in a Fixed Pin Unit.

Fig 23:- Pin Unit

Retractable Pin Unit:- Retractable pin unit is used to locate the workpiece. It mounts the pin either directly on the cylinder or on the retainer and L-block and this is mounted on the cylinder. As the pin is mounted on the cylinder directly or indirectly, it has the freedom to move down by the maximum distance of the stroke of the cylinder.

Fig 24:- Retractable Pin Unit

There are two types of Retractable pin units

• Single Cylinder/ Inline Retractable Pin Unit
• Two Cylinder/ Offset Retractable Pin Unit

Retractable Pin Unit Design-1

Single Cylinder/ Inline Retractable Pin Unit:- Inline Retractable Pin unit consists of one Pin cylinder which operates the pin in one direction. In this unit Pin is directly mounted on the cylinder and it is a must to have the pin and cylinder in line with the hole or slot of the panel. The pin cylinder is controlled in two directions with the help of shimming.

Pin cylinders have various stroke sizes like 30mm, 40mm, and 60mm. Cylinder. Uses of cylinders depend upon the area and availability while building the fixture.

Fig 25:- Retractable Pin Unit Design-1

Fig 26:- Pin Positions (Design-1)

Two Cylinder/ Offset Retractable Pin Unit:- Offset Retractable Pin unit consists of one Pin cylinder which operates the pin in one direction. In this unit Pin is mounted on the Pin retainer and then the pin is controlled in two directions with the help of shimming. In this unit cylinder can be mounted away from the pin.

These Pin cylinders have various stroke sizes like 30mm, 40mm, and 60mm. Cylinder. Uses of cylinders depend upon the area and availability while building the fixture.

Fig 27:- Retractable Pin Unit Design-2

Fig 28:- Pin Positions (Design-2)

Fig 29:- Pin Units

Fig 30:- Pin Units with Panel

Fig 31:- Pin Units with Panel (all views)

Clamp unit: - A clamp unit is a unit designed to clamp/hold the car panel with NC blocks/ Mylar/ rest by using a pneumatic clamp cylinder & below are different parts of a clamp unit in general. Usually clamp open position is 90°. Fingers are attached to the clamp Mylar. In a clamp unit shimming to one side is more than enough because it will restrict translation motion in upward & downward directions only. There is another type of clamp unit known as the swivel type. There is a pivot pin around which the clamp arm rotates.

CLAMP PLAN:

1. The customer provides the clamp plan which consists of the position of the clamp, pins, rests and dump, etc.
2. It has the exact coordination of these components and in addition, it also has the hole’s dimensions and tolerances.
3. As this is critical input data, it must not be modified.
4. In case the spot for weld and the clamp position is nearby and it may create a problem later and there is a need to change the position of the clamp, the same must be done so with the permission of the customer as it will be easy for the customer to make changes from his side also.

Fig 32:- Clamp Plan

Factors should be considered while designing a clamp unit:

• There should be adequate space between the cylinder & another part like the riser, car panel because the cylinder moves or swing while opening & closing
• Pin clamp unit used where two panels or components are located for welding.
• Clamping is make in such a way that it clamps two car panels at once
• All parts should snap & butt properly to each other.
• Make sure that parts of the clamping unit are 10 to 12 mm away from the car panel so they do not damage the car panel
• Avoid any clash. It will not arise an issue at assembly.

Below are the general parts of the swivel clamp unit.

Fig 33:- Swivel clamp unit

Fig 34:- Clamp units

Fig 34:- Clamp units with panel

Fig 34:- Clamp units with panel (all views)

Fig 34:- Panel with Rest unit, Pin units, Clamp units & Rough locators

Fig 35:- Panel with Rest unit, Pin units, Clamp units & Rough locators

CONCLUSION :

Hence, 3D finishing is performed on the designed Assembly of fixtures & Rough locators were designed for the given panel.