Week 3:- BiW Fixture Design Methodologies Challenges

Q.1. What is Design Methodology?

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

Above image is of design methodology and steps involve in it.

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 inputs required from the customer to start designing a fixture ?

The inputs from the customer are:

4. Layout :

Layout provides imformations of flow of parts , station pitch , robot station , tool changer , tip dressers , platform height , sub assembly links.

5. Ergo data :

It is study of human behaviour & movements during the assembly work.

6. Weld study:

It includes the study of weld gun is used for the operation depending on the size of part , thickness of the part etc.

7. Standard detailing templates :

Every customer have there standard of detailing & the templated which are used for 2D drawing & detailing.

Q.3. WHAT IS THE INPUT WE GET FROM CAR PRODUCTS ?

ANS - The input we get from car products include -

• Geometric dimensioning and tolerance (GD&T) - GD&T will be given of the part for which we need to design the fixture . it will provide information about locating pin , sequence of opening of clamps , rest , dump and slide stroke information .

• Parts list - Part list will give us detailed information about the parts involved in the fixture . it will give us information like part name , part number , thickness of part , quantity of parts etc .

• Cad files - Cad files of the part gives us information of 3d model , design analysis result . this information is very uselful as it will give us an idea on starting to design a fixture .
• Clamp plan - Clamp plan is very important information as it will give us idea of places where we have our clamps , pins , dumps , rest etc . we should never change the clamp position unless we ask the customer and they agree to it .

• Product assembly process sheets - In product asssembly process sheet , we will find what kind of products we are going to assemble for the particular unit or the component . The sequence of the assembly will also be given in this sheet .

Q.4. WHAT IS THE CLAMP PLAN ?

ANS -

• A clamp is a device which is used to hold the workpiece. It is a force actuating mechanism of the fixture .
• A clamp plan is a very important input from the customer, the clamp plan will give us information about area where the clamps will be fixed to ensure proper geometry of workpiece is maintained during the operation .
• Clamp plan provides information on location of pins , rest , clamps ,dumps etc . the coordines will also be mentioned in the clamp plan , so the design team can take the coordinates directly and start working on the fixture .
• We cannot change the clamp plan that is given by the customer, we have to inform the customer and if they agree then we can change it .

Q.5. WHAT IS THE PURPOSE OF LAYOUT ?

• Layout is the most effective arrangement of the machines , processing equipment , service department to achieve maximum efficiency of the 4 M ( men , material , machine and method ) in the plant .
• It will give the floor plan of how and where the machines will be placed , position of robots , storage racks , etc . it will also show the reachability of the robots to the fixture which is called as swept area of robot.
• Layout also provides information of flow of parts , station pitch , robot stations , tool changers , tip dressers , loading and unloading sequence .

Q.6. WHAT IS ERGO DATA ?

ANS -

• Ergonomics is the application of psychological and physiological principles to the engineering and design of products , processes and systems . the goal of human factor is to reduce human errors , increase productivity and enchance safety and comfort with specific focus on interaction between human and rhing of interest .
• In any operation , the workers or operators attain various postures , exerts force and work continously in a cycle time to perform a particular task . this may cause high level of strain to the operators . to avoid this the principle of ergonomics is applied in every operations wherever a interaction of human with machine is involved .
• so the ergo data is the input which gives human factors engineering data between operator and its working environment .
• It has various benefits like improved working condition , reduce physical workload , improved work postures , reduced efforts of certain movements etc .

Q.7. WHAT DO YOU UNDERSTAND BY WELD STUDY ?

ANS -

• Welding is a process which is widely used in automobile industry for joining of parts together, so a welding fixture is necessary to be made so that the geometry of the part does not change during the welding process.
• weld study includes study of weld gun and the weld matrix and weld points , geo spot and respot weld points.
• weld gun study will give information about type of weld, temperature, type of current , approach of gun etc. weld matrix and the weld points will give us information on exactly where the welding will be done .
• There will be two welding stations, geo spots and repots . geo spots will be the first round of welding operation, after this respot is done on the places where we could not weld in the geospot station.

Q.8. What are the criteria in percentage completion in designing stage? Explain it in detail.

ANS: 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.

The persentage completion criteria is as below:

1. 0-25% (Input & Concept Design): In this stage of percentage completion criteria, we have to built concept design of fixture in this stage.
2. 25-40% (Concept Approval & Simulation): In this stage, concept design is approved by customer and gives some correction points if any. Later we have to to give working simulation of fixture for better understanding of how fixture works.
3. 40-85% (Design Freezing & Detailing): If all requirements and specifications of customers are satisfied then design is freezed and detailing work starts.
4. 85-100% (Check & Final Dispatch): In this stage, quality checking is done using CMM (coordinate measuring machine) and then dispatched to customers.

Q.9. Brief about output in design?

Ans:

Output In Design:

In BIW fixture design or any industry. We don't only just design a particular component and just give the CAD file to the customer, you have to give a lot of documents like 3d documents,2d documents, which is the detailing part, and as well as other factors as well like bom, bom bill of material and other documents as well about this particular component and their standards, all has to be submitted to the customer.

The output is 3D models and the 2D drawing of the tools

1.Unitized Tools

2.Non-Unitised Tools

1.Unitized Tools:

In the unitized tools testing requires two types of drawing sheet,which is one key sheet and layout sheet.

So example of a unitized tools are fixtures,tools So where exactly multiple units are a placed.For example, the entire assembly welding fixtures,where a pin unit,clamp unit,rest unit and the panel, everything is included so that for those things.

Key sheet - An index of units and their placements on the tool base.It will have an orthogonal view of the fixtures including a numbered balloon drawing mentioning the units.

Layout sheet - A detailed drawing of individual units to include all of their components.For the Non unitized tool no need of key sheets. As they can stand alone, the drawing can be detailed completely on a layout sheets.

So, it is basically an index of units and placements on the tool base, so the key sheet going to show you the placement and the location of that particular tool on the tool base where exactly the tool is placed. And what is his exact position in a particular place.

2.Non-Unitized Tools:

Tools that can stand alone and can be detailed completely on a layouy sheet.

Non unitized tools are basically tools like Stands and tool changers is also an example of an non unitized tools where you don't need key sheet, you can actually used to layout sheet and complete the entire documentation of the particular component. So this is as known non unitized tools.

The Design Output Should Compile Following Points:

1. Approved standard components are to be used wherever possible.
2. Design must be as simple & economics as possible.
3. Design must be comply with all current safety & ergonomic requirements.
4. Design must provide for controlled & damage free handling of product.
5. Adequate error proofing provision must be incorporated into each design by proving proximity switches, rough locators, etc.
6. The weight of the moving parts must be kept to a minimum while maintaining maximum strength.
7. Frames & structures are to be simple & study.
8. Design clearance & accessibility for routine maintenance & service.
9. Motion control must be considered on any moving equipments.
10. Designer is responsible to validate clamps & weld guns.

Q.10. WHAT DO YOU UNDERSTAND BY STRUCTURING A DESIGN TREE ? HOW DOES IT REDUCE ERRORS DURING DESIGN PROCESS ?

ANS - Structuring a design tree is the process of naming all the assembly and parts in a systematic way and a specific standard. Every customer has its own standard to structure a design tree .

If the parts or the assemblies are not named properly or it is not structured properly, then this will create a lot of confusion to understand the design.

So structuring a design tree is very important as it helps us to easily identify about the part or a assembly belongs to which project. It can also help us to identify quantity of items of same type or different type used in assembly .

From the above image we can see that the designed parts are at the top and the standard parts are below .

Blue highlighted number - H1L -T9A-RRFRA-JG3-00-00-00, this is the product description or name

here H1L-T9A is the project name , RRFRA is the panel name , JG3 is referring to the jig number that is jig 3, 00 is the unit name, 00 is the part number, 00 is the componenet no .

Q.11. - WHAT ARE UNITS ? MENTION 5 TYPES OF UNITS ?

ANS -

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.

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.

Q.12. DESCRIBE FIXED PIN UNITS AND THEIR PURPOSE ?

ANS -

- Fixed pin unit is a non movable locating unit used for proper location of part and it arrests all the movement of part as well. fixed pin unit consist of pin, pin retainer, shims/spacer, block, blade or adaptor plate ,riser. Riser is the part which is used to rise or increase the height of the unit. blades is mounted on the riser . block will be mounted on the blade. shims are small spacers which are used for stack up tolerances. shims are made of various thickness like 0.1,0.2,0.5mm etc . pin retainer will hold the pin. and the pin is used to locate the part and restrict its motion.

- Purpose of fixed pin unit - The main purpose of the fixed pin unit is to locate the car panel and restrict its motion . it is placed following the 3-2-1 principle , so it is necessary to have two pins like 1 pin will restrict 4 d.o.f (4 translational) and the other pin must restrict 2 d.o.f ( 2 rotational).

Q.13. WHAT ARE DIFFERENT PARTS OF FIXED UNIT ?

ANS - The different parts of fixed pin are as follows -

• Pin - Pin or locating pin is used for location or positioning of workpiece in correct manner . this pin is made of precise dimension and tolerance. usually two pins are enough to locate a workpiece on a single plane. There are many types of locating pins available. it is upto us what kind of pin will work for our workpiece.

• Pin retainer - A pin retainer is a part which is used to hold the pin firmly and in position. a pin retainer can be a make part or a standard part also .

• shims/spacer - Shims and spacers are plate of varying thickness which is used for compensation of stack up tolerance that is in assembly. the thickness of shims is 0.1mm, 0.2mm, 0.5mm, etc . sometimes in an assembly stack up tolerances is generated, this needs to be corrected so we use shims and spacers.

• Block - Block can be machined to any thickness, this depends on the design of fixture and for what reason we want the block.

• Blade - Blades are plates attached to the risers, parts like cylinder arm etc are mounted on the blade.

• Risers - Riser is a standard part which is used to rise up the height of whole unit .risers are generally made of plate fabrication or plate and tube welding or from single gas cutting.

Q.14. What is a purpose of making a rest unit? And describe its parts?

Answer:

PURPOSE OF MAKING A REST UNIT:

Rest unit is unit designed to support car panel using Mylar/ NC block/ rest. Component is rested only, no upper clamp or force applied there.

It is the simplest unit to design because it has fewer parts to design & the purpose is only resting of the car panel. Because of this simplicity the rest unit is combined with other unit to reduce the cost of the overall project.

It can be combined with clamp unit to clamp as well as to rest the car panel. It can be combined with locating unit to locate as well as to rest the car panel. Also locating, clamping & rest unit can be combined together in one unit to reduce cost.

There is no cylinder attached to it. It has rest Mylar, blade & riser & below is different parts of rest unit. Rest unit is also divided into simple support unit, multiple support units & retractable support unit.

PARTS OF REST UNIT:

The parts of rest unit are as follows,

1. NC block/mylars.
2. Risers.
3. Blades.
4. Shims

1. NC blocks/mylars:

Mylars are the part which are holding the panel from top & bottom.

It is a jaw type, during welding it wont deforms from its position.

It is also known as fingers.

It wont allow the deformation of the part due to welding stresses.

Mylars are of two types, they are

1. Clamping mylars
2. Resting mylars

Only resting mylars can be seen in rest unit.

The panel which rests on the part is known as resting mylars.

2. Risers:

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

One end of the raiser will be attached to the base unit while other end will be attached to the blade.

Riser can be of two types, they are,

1. L type riser.
2. Square tube riser.

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.

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

3. Blade:

Blade are the plates which are attached to raiser.

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

4. Shims:

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.

Q.15. What are the basic fundamentals to design a sensor unit?

ANS - A sensor is a device which detects or measures a physical property , and records , indicates or responds to it .The unit which is built to sense the component or car panel using electrical sensors called Unit Sensor. The output signal of sensor is then send to PLC (Programmable Logic Control) for further process. There of different types of sensors such as proximity sensors, laser sensors.

-Fundamental to design a sensor unit -

• Every single loose panel which is being welded by the tool should be sensed .
• Each panels should be sensed by 1 or 2 sensors depending upon size of panel .
• Every sensor should be mounted in a 3 direction adjustable way in general .

Q.16. WHAT IS A ROUGH LOCATOR UNIT AND WHAT IS THE BASIC FUNDAMENTALS CONSIDERED WHILE DESIGNING IT ?

ANS - Rough locator is a device which is used to guide the workpiece in proper place . this rough locators is mainly used when manual operator is present but it is also used in automation . rough locator act as a foolproofing method .

- Fundamentals considered while designing rough locator -

• Rough locator should be placed at edges of car panel , which it has to guide .
• They should be placed in a same angle of car edge angle , and minimum of 2-5mm distance should be maintained from edge of car panel .
• It should guide the panel in locating pins .
• Rough locator should start guiding the car panel before 10-15mm from start of engagement .
• Rough locator should be designed with entry angle for car panel , which is generally 30-45 degree .
• The rough locator should be designed with two slots , for easy adjustments .
• The slot should be in direction of car part guiding .

Q.17. WHAT IS A BASE UNIT AND DESCRIBE ITS PARTS ?

ANS - A base unit is a unit designed to mount all other units (clampunit , rest unit , pin unit etc. ) on it . it also mounts other tools like pneumatic valve box , trunking cable path etc will be mounted on the base unit . the base unit can be firmly fixed to the ground or it can be a movable unit .

Base unit parts are given below -

• Floor plate - Floor plate is used to mount entire base with floor . it also helps to achieve the flatness of the fixture .
• Weld bars and pedestal - Pedestal is a structure where entire unit of base will be mounted.
• Eye bolt - Eye bolt is the bolt with a loop at one end . they are used to firmly attach a securing eye to the structure. when the whole fixture table has to be moved from one place to another , cables are attached to this bolt and the fixture table is moved.
• Measuring hole cover - The base plate has several holes for mounting of units on it . this holes are measured by CMM machine to check if their position is accurate or not . a plate is used to cover the hole so that no dust or other particles can damage the hole.
• Valve box and trunking channel - Valve box supplies air to all the pneumatic cylinders in the assembly . a valve box consist of solenoid valve which is used to collect air from pneumatic cylinders to valve box.
• Base plate - A base plate is a heavy plate of large thickness because it carries weight of the entire assembly . it is machined to maintain parallelity and it also has holes drilled on it to mount the units.

Q.18. WHAT IS A DUMP UNIT AND WHAT ARE ITS FUNCTIONS ?

ANS - Dump unit is a complex unit which is used in places where there is a space constraints or some other constraint . when we have some geometrical constraints and we cannot mount clamp unit, rest unit etc in a normal way then dump unit is used . It consist of dump cylinder to perform operation of clamping and unclamping of car panel.

Functions of dump unit -

• When there is a particular constraint and we cannot asssemble component in normal way dump unit is used.
• It has a dump cylinder which performs the opening and closing action . it has a clamp cylinder unit too.
• This dump unit is complex in design and so it is used only in need.

Q.19. WHAT IS A SLIDE UNIT ? MENTION WHERE SLIDE UNITS ARE COMMONLY USED ?

ANS -

Slide units are positioning unit which are used to position the car part or panel, units, robots, for further operation. sliding units are used in places where we have space constraint and differnt units cannot be used so we use sliding unit.

It consist of foll parts -

• Sliding cylinder - this is used to move the panel from open position to close position and vice versa.
• Position locking unit - It is used to lock the plate at a particular place and it will not allow it to move.
• Guide rail - It is used to guide the plate to move from one position to next.
• Stopper block - It is used to control the motion of sliding unit.
• Sensor unit - It is used to sense whether the component is moving properly or not.