Week 3:- BiW Fixture Design Methodologies Challenges

Q.1. What is Design Methodology?

Design Methodology is sequence of steps which we have to follow while doing design.

1. Purchase Order:  We start designing after customer gives us purchase order. So, basically it is indication to start designing of particular fixture.
2. Inputs from Customer: Customer gives us requiremements or specifications of fixture before starting actual design work. So, we have to design fixture by considering all the points of customers.
3. Percentage Completion Criteria: To complete design in time we have to create schedule or time plan called Percentage Completion Criteria. In this we mention all activities related to design and time required to complete that task like concept design, final finished design and 2D of all units in fixture etc.
4. Design Output: Design Output consist of lots of data like 3D and 2D documents, VMC IGS files, STEP files, gas-cut or laser-cut files in dwg format and BOM, etc. We have to give these data to our customer as design output.

Q.2 – What are the inputs required from the customer to start designing a fixture?

The inputs required from the customer to start designing a fixture:

1. Fundamental requirements.
2. Preferred standard components.
3. Car products.
4. Layout.
5. Ergo – data.
6. Weld study.
7. Standard detailing templates

Functional Requirements:

The purpose or the function of the fixture will be given as inputs from the customers like what are the process the fixture is going to do i.e welding(spot or seam weld), gluing, riveting, hemming or whether it is a checking fixture or a storage racks etc.

It is one of the basic requirements to get from the customer to start designing a fixture.

2. Preferred standards:

As we know different companies follow different standards, we will be following the standards, we will be following the standards followed by the customers. By following standards the time of designing and manufacturing of parts will be saved, which will be automatically minimizing the time of the projects.

As for the standards parts, it can be easily replaced from the used fixture to the new fixture which reduce the cost.

Some of the preferred standard components used in BIW fixtures are given below,

1. Standard like ABB, NAAMS, DESTACO, ZYTRAN, TUNKERS are used in design & manufacturing of fixtures.
2. Standard parts like Risers, L-blocks, retainers, pins, NC blocks, Shims, etc.
3. Components like clamps, cylinders, slides, switches, sensors, etc.
4. Weld guns, Tip dressers, Tool changers, etc. tip dressers are to sharpen the tip of the tools whereas tool changes are used in robots to do various process. As robots are too costly, tool changers are used.

ABB – It is a Robots manufacturing company.

Some example of description of standard robots are, Robust IRB 7600 robots, which can, hold the panels securely and accurately in place while IRB 6640 robots perform the welding.

The below picture shows the welding line is installed at great wall motors (GWM) recently opened and internationally acclaimed automotive plant in Tianjin, china. One of the factory’s most highly publicized and productive manufacturing lines is the ABB welding line, which comprises among other things a fleet of ABB robots and patented ABB framing and hemming technologies.

3. Car Products:

The inputs we get from car products are: GD&T, part list, Cad files of car part, Clamp plan, product assembly process sheet.

1. GD&T: It provides information of locating pins, rest, clamp, damp & slide unit informationof each station. Also includes the information of sequence of openings of clamps, dumps & slide stroke information.
2. Part lists: It gives the lists of parts which are going to assembled in the fixture. The list contains the information of part number, part name, revision of fixture, part thickness, etc.
3. Clamp plan: Clamp plan provides the information of location of pins, Rest units, clamp unit, dump etc. It is the important input from customer. The clamp plan/position should not be changed without the knowledge of customer.
4. 3D cad file: The 3D model of the car part will be given from customer. From that 3D model we will be developing our fixture design process. The 3D cad file will be in the format of step file (stp) or IGES file (igs).
5. Product assembly process sheet: It gives the information of stage wise assembly process like how the parts move from one assembly process like how the parts move from one assembly station to other after the completion of joining process. 

4. Layouts:

Layout shows the entire assembly plan to understand the process.

Layout provides the information of flow of parts, station pitch, robot stations, accessories like tool changers & tip dressers, sub assembly links, plan form height, loading/unloading sequence/height.

5. Ergo Data:

As same as preferred standards, different companies follow different standards of ergo data. We have to follow the customer standards of ergo data.

The inputs of ergo data will given by the customer mostly in case of manually operated fixtures/manual fixtures.

The ergo data is mainly used to make the operator comfortable which may leads to improve the efficiency in cycle time & production.

Ergo data provides inputs like platform height, maximum & minimum reach from operator to fixture, maximum & minimum height of the fixture, whether the child parts/assemblies are visible while clamping or loading & unloading.

Also provides informations like loading height, working safety zone of operator, etc.

6. Weld Study:

Weld study is the important inputs given by the customer. It gives details about the study of particular gun that we use for welding.

Also the datas like No. of weld, position of weld in the components will be given. In short, weld study includes weld gun details, weld matrix & weld points. Generally weld points will be given in spheres.

7. Standard detailing templates:

This inputs include the detailing of 2D cad drawing as per the customer standarrds.

So we have to follow the detailing templates as per the customer standards.

What is the input we get from the "Car Products"?

ANS.  The inputs we get from the Car Products are as follow:

1. GD & T: GD & T stand for Geometrical Dimensioning and Tolerance. GD & T of each part is given in car product in which information of locating pins, clamps, rest and slides are mentioned. Image provided below shows how GD & T is apply for particular part.
2. Part List: It states about the parts and assembly style. Part list consist of unique part names of each and every parts in assembly and each part has its own part number which helps while assembly process to identify each and every part in assembly.                                                                                                                                                                                                 
3. Cad Files of Car Part: 3D cad files of parts are necessary while designing fixture.                                                                    
4. Clamp Plan: It is one of the important data while designing fixture because clamp plan mentions location of clamps in which component is going to clamp.     
5. Product Assembly Process Sheet: In product assembly process sheet, sequence or stages of assembly of components are given.                                     

4).What is Clamp plan?

Ans. Clamp plan provides the information of location of pins, Rest units, clamp unit, Dumps etc. It is the important input from customer. Clamp Plan is a document that contains the panel drawing mentioning all the places where clamps and rests are to be given. It gives exact location in X, Y, Z co-ordinate values to start designing. We should never change clamp position without permission of customer. Clamps are nothing but a mechanism or component used to hold or clamp job in fixture securely. Clamps are manual type, hydraulic type or pneumatic type depending on customer requirement. Clamp plan mentions or gives the location of clamps in which component is going to clamp.

A clamp is a force-actuating mechanism of a fixture. The forces exerted by the clamps hold a part securely in the fixture against all other external forces. Clamping surfaces are subjected to the clamping forces for obtaining invariant location. To fix a part at a particular position, we use 3-2-1 principle in all types of fixtures to restrict degrees of freedom. Each Panel is fixed keeping 3-2-1 principle in mind. This principle requires us to use minimum 3 rests, 2 pins and 1 clamp to fix a panel

Q5.What is the purpose of a layout?

Ans. Layout is basically an layout of the entire assembly line to understand the process and the flow of work.Layout sheet will give you information about all the fixtures are placed the robots are going to work on it.

Layout Provides information of

• Flow of parts
• Station Pitch
• Robot Stations
• Accessories like Tool changer and tip dresser
• Sub assembly links
• Platform height
• Loading/Unloading Sequence/heights

Q-6 What is Ergo data?

 Every company have standard ergo data and they provide it to fixture designer to design fixture considering that points Ex. height of

fixture is decided according to ease while working on fixture. So, we have to design a fixture by considering safety,easy and fool proof design.

Ergo Data is used to reduce human errors, increase productivity, human comfert and safety.

 

 Q-7 What do you understand by Weld study

Weld Study is nothing but a study of welding gun that we are going to use in welding fixture and where we are going to weld. It consist study of welding gun details, weld matrix, weld point, geo weld points and re-spot weld points, etc. Weld study consist of study following points:

• Weld Gun Details: In this we are going to study which type of gun is suitable for particular fixture and selected gun 

• Weld Matrix and Wel d Points: Weld points are the points where welding is to be

• Geo Wel d Points and Re-sP-ot Wel d Points: Weld Points are divided usingcolor code, one of them is red color points and remaing points has green col In these, red color points indicate geo weld points which are going to weld in geo tool and green color points indicate re-spot weld points which are going to weld in re-spot tool.

Q8. What are the criteria for percentage completion in the designing stage? Explain it in detail

Ans It is used in the design and dispatch stages of the welding fixture. It shows the number of tasks completed in the project and we can make sure whether the work is being done as per the planned schedule.

Different stages in a project have a different percentage as follows

Input and concept design 0-25%

Concept approval and Simulation check 25-40%

Design Freezing and detailing 40-80%

Check and Final Dispatch 80-100%

 Input and concept design 0-25%

 It is the initial stage of the project where we get all the design inputs from the customer and based on those inputs a design concept of the project will be created.

Concept approval and Simulation check 25-40%

Once the concept is designed it is sent to the customer for approval and the simulation checks are done for the given design and looked for the feasibility of the design.

Design Freezing and detailing 40-80%

The changes are done to the design if the results of the simulation checks force us to do or if there any changes suggested by the customer. After all these changes are done the design is fixed and the detailing to the design starts

Check and Final Dispatch 80-100%

After the detailing, it is sent for the quality inspection and finally dispatched to the customer.

-9 Brief about "Output" in design?

Design Output consist of lots of data like  30 and 20 documents, VMC IGS files, STEP files, gas-cut or laser-cut files in dwg format and BOM, etc. We have to give these data to our customer as design output. The basic output are 30

models and 20 drawing of fixture. Output are classified as below: Uni tised Tool: This toolconsist of two type of sheets, they are as follow:

• keY. Sheet: Key sheet mentioned or shows thelocation of every units in fixture.
• LaYout Sheet: Layout sheet is detail drawing of particular unit in fixture.

• Non-unitised Tools:This type of tools don't require key Ex. stands and tool changer. Tools that can stand alone and details in layout sheet.

10. What do you understand by structuring design tree? How does it reduce errors during design process?

ANS.  Structuring a design tree is very necessary while designing fixture because it help to identify all manufactured part in whole fixture. Every customer company have there own standard. This will help us during design study, manufacturing and inspection to avoid errors.

          If we ignore structuring a design tree it will crete confusion to understand design and may errors will appers in fixture.

Question No. 11 – What are units? Mention 5 types of units?

Answer:

Units:

A unit is a device that has a specified function, especially one forming part of a complex mechanism.

A welding fixture is assembly of different types of units.

As name refers, the different units will be only seen in the unitized tool.

A units are classified into two, they are,

Simple unit: In a simple welding fixture, the combination of these different units will be seen.

1. Rest unit.
2. Fixed pin units.
3. Retract pin units.
4. Rough locator unit.
5. Sensor unit.
6. Base unit.

Complex unit: In a complex welding fixture, in addition with some of the simple units these complex units will also seen

1. Slide unit.
2. Dump unit.

Five Types Of Units:

1. Base unit:

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

2. Fixed pin unit:

Fixed pin unit is a unit designed to locate the car panel using pins.table

Pin, pin retainer, shims, blocks, blade, riser are the part of fixed pin units.

Pin retainer is used to hold the pin firmly.

Typically, the locating pins are used to locate a body part in a position sufficiently accurate to execute a welding process.

The body part is constrained by a set of appropriately locating pin so total constraint by locating pin should be fully constrained at all times to prevent any movement.

3. Retractable pin unit:

retractable pin unit is unit designed to locate the car panel using pins, but the entire pin package parts will be mounted on the retractable pneumatic cylinder as shown in below fig 3.

Retractable pin unit is the opposite of fixed pin unit which can be moved up & down also which can be retracted till certain distance.

It is mainly used for unloading the complex panel after welding.

4. Clamping unit:

Clamp unit is a unit designed to clamp or hold the car panel with NC block / Mylars by using a pneumatic clamp cylinder.

Clamping unit is used to clamp the part which is to be welded after location using pin unit.

Clamping is achieved with the help of pneumatic cylinders and clamp arms.

Clamping arm, finger, rest, shims, standard riser, pneumatic cylinder are the parts of clamping unit in general.

5. Slide unit:

Slide unit is found mostly in complex fixture, where the sliding mechanism will be involved.

This type of unit used when there is some space constraints.

Guide block, guide rail, position lock unit, stopper block, sensors are the parts of slide unit in general.

Guide block & guide rail helps to the guide the slide unit. The rail should always be covered to protect against weld spatter & dust by a bellow or a sheet metal cover.

Position lock unit helps the slide to be locked/clamped in the working position.

Stopper block helps to stop/control the entire moving of a slide unit from certain distance, which is placed at the end of the guide rail.

Sensors – The two end limits to be sensed externally by a proximity sensor.

Question no. 12 –Describe fixed pin unit & their purpose?

Answer:

Fixed pin unit:

Fixed pin unit is a unit design to locate the car panel using pins.

Pin, pin retainer, shims, blocks, blade, riser are part of fixed pin unites in general.

Pin retainer is used to hold the pin firmly.

PURPOSE OF FIXED PIN UNIT:

As by 3-2-1 locating principle, the introduction of two pins helps to arrest the 6 degrees of freedom (4 axial & 2 radial movements) whereas other 6 degrees of freedom are arrested by introducing minimum three supports.

Typically, the locating pins are used to locate a body part in a position sufficiently accurate to execute a welding process a welding process.

The body part is constrained by a set of appropriately locating pin so total constraint by locating pin should be fully constrained at all times to prevent any movement.

Question No.13 – What are the different parts of the fixed pin unit?

Answer:

DIFFERENT PARTS OF THE FIXED PIN UNIT:

The different parts of the fixed pin units are as follows,

1. Pin.
2. Pin retainer.
3. Shims.
4. Blade.
5. Riser.

1. Pin:

It is used for the location purpose of the panel. Typically, the locating pins are used to locate a body part in a position sufficiently accurate to execute a welding process.

The body part is constrained by a set of appropriately locating pin so total constraint by locating pin should be fully constrained at all times to prevent any movement.

There are dozens of styles of locating pins that can be utilized in a design. One of the most common pins is a stepped pin with either small or large head.

Round Pins:

These can be Screw secured (PNRS) or Grub Screw secured (PNRG) or Thread secured (PNRT) for Prototype build only. One of the most common pins is a stepped pin with either small or large head.

Diamond Pins:

The Diamond Shape is a critical feature that helps with machining inaccuracies and smoother locating operation. When two round head pins are installed onto one plate, the distance between two mounting holes must be extremely precise and even then, the work piece will not be placed on the base as easily as it would with the use of a diamond shape pin. These can be Screw secured (PNDS) or Grub Screw secured (PNDG) or Thread secured (PNRT) for Prototype build only.

2. Pin Retainer:

Pin retainer is used to hold the locating pins firmly. Pin retainer is designed to hold the pin in its place and is also used as a rest for the pin. A counter hole drilled on which pin is fit. 

3. Shims:

In general, a shim is a thin and often tapered or wedged piece of material, used to fill small gaps or spaces between objects.

Shims are typically used in order to support, adjust for better fit, or provide a level surface.

Shims may also be used as spacers to fill gaps between parts subject to wear.

Shims are the small parts which comes with the thickness of 0.1mm, 0.2mm, 0.5mm, 1.0mm etc.

These will compensate the stack up tolerance which reflects at the mylars.

We give tolerances to all parts of the fixture. Due to this tolerance the mylars will either lift up moves down from its defined position. To adjust the mylars for getting the defined position we use shims.

Shims will be added above the mylar for adjusting according to tolerance.

Types of shim:

Types of shims are,

1. Wood shim.
2. Stone shim.
3. Plastic shim.
4. Metal shim.
5. Paper shim.

4. Riser:

Riser is a manufacturing part used to raise / height the assemblies of fixture.

One end of the raiser will be attached to the blade.

Raiser can be of two types. They are,

1. ‘L’ type risers.
2. Square tube risers.

1. L TYPE RISERS: L type risers are of welded type. Where the stiffner will be added at the centre for support, as shown in the below figure the wedge shaped structure is known as stiffner which is used as a support/to withstand load.

2. Square tube risers: Square tube risers are of frame type.

5. Blade:

Blade are the plates which are attached to raiser.

Blade is also attached or mounted with cylinders, arms etc.

Q-14 What is the purpose of making a Rest unit & describe its parts

rest unit is one of the simplest unit to fixture to clamp the surfaces of he carthe main components of the simple rest unit are riser,blade,shim or spacer,myler

Riser

risers are used for incrrease the Ht of unit to standard parts

Blade

blades are bolted to the unit body

Shim or Spacer

shims are used to compensate tolerance stack up in we need to control two direcio that are XandY using shim

Mylar

mylers are parts in rest unit which are in contact with ca panel or component used to give support to component.

Q-15 What are the basic fundamentals to design a Sensor unit?

sensor is a device which detect  or measure a physical property the unit which is built to sense component or car panel using electrical sensor called unit sensor the O/P signal sensor to PLC

Q-16 What is a Rough locator unit & what are the basic fundamentals to consider while designing it?

rough locator are the parts used to locate components in correctly in the fixture.basically it guide the operator while load component in fixture 

fundamentals

• they are used to guidde the component
• the angle in locator should according to component
• entry angle should to be 30 to 45 degree
• for easy adjustment rough locator mounted on base with two slots in it

Q17. What is a Base unit and describe its parts?

Ans. The base unit is designed to mount all the other units like clamp unit, pin unit, rest unit, etc of the tool, also other parts like pneumatic valve box, trunking cable path will also be mounted on the base unit.

The parts of the base unit are as follows:

Valve box

Trunking Channel

Measuring hole cover

Eyebolt

Pedestal

Floorplates

Valve box: A valve box is used to supply pneumatic cylinders assembled in the fixture.

The valve box consists of solenoid valves with an inlet and outlet which controls the supply of air to the cylinder.

Trunking channel: Trunking channel is a hollow passage that guides and covers the pneumatic and electrical linings.

Measuring hole cover: The measuring hole cover the coordinates of the measuring holes are mentioned. These coordinates are used as references for placing the other units and also for the CMM inspection purposes.

Eyebolts: Eyebolts are placed in the base unit in order to lift the base unit and move it from one place to another.

Pedestal: The pedestal is a stand-like structure where the entire unit of the base will be mounted.

Floorplates: Floorplates are used to mount the entire base on the floor.

Q18.  What is a Dump Unit and what are its function ?

ANS. Dump unit is used due to lack of space on fixture to build a unit. So, this is a complex unit consist of dump cylinder used for clamping or unclamping of car panel or component. Dump unit is found in complex fixture. A dump unit is used when there are geometrical constraints while placing a panel. It consists of a dump cylinder to perform clamping and unclamping operation.

FUNCTION:

Due to space constrain dump unit used in fixture. It has dump cylinder having open and close position for better understanding of design. It also has clamp cylinder used for clamping purpose.Hence this is too complex unit to built.

19. What is a Slide unit? Mention where Slide units are commonly used

Ans. Sliding units are used in a fixture when there are a lot of space constraints, where usage of different units is very difficult in order to design the assembly.

The sliding unit consists of a sliding cylinder to which a panel is attached

The panel moves on the guide rails provided and this motion is due to the reciprocating motion of the cylinder

The position locking units are used to lock the position of  the panels on the guide rails

Sensor units are used to detect the position of the sliding plate, whether it has reached the desired position or not.

A stopper block is used to control the motion of the sliding plate.