Week 3:- BiW Fixture Design Methodologies Challenges

• What is design methodology?

Design methodology is nothing but steps followed during the concept of designing stages of fixture design. The conceptualisation of the design is done during this process.

1. Purchase order: This step is nothing but a go ahead signal from the customer to design the fixture.
2. Inputs from customer: Major inputs from the customer given.

Some of the important inputs are:

Functional requirements: Major function of the fixture is given like if the fixture is used for welding.

• Preferred standard components: Some components will already be there with the customer as a standard part. We need to design our fixture according to the standard components which are already there with the customer. The customer won't change these standard parts. We need to change the design according to these parts.

• Car products: In this step the tolerances are specified and the PLP points are also specified.
• Layout: This gives the layout of the entire assembly line. The robot swept area and station pitch are specified.
• Ergo Data: This information gives the data following which the customer will know how to use the part safely. This is the study of human behaviour and movements.
• Weld study: This gives the information about the position and type of weld we are about to do.

2) What are the inputs required from customers to start designing a Fixture?

Inputs from customer: Major inputs from the customer given.

Some of the important inputs are:

Functional requirements: Major function of the fixture is given like if the fixture is used for welding.

• Preferred standard components: Some components will already be there with the customer as a standard part. We need to design our fixture according to the standard components which are already there with the customer. The customer won't change these standard parts. We need to change the design according to these parts.

• Car products: In this step the tolerances are specified and the PLP points are also specified.
• Layout: This gives the layout of the entire assembly line. The robot swept area and station pitch are specified.
• Ergo Data: This information gives the data following which the customer will know how to use the part safely. This is the study of human behaviour and movements.
• Weld study: This gives the information about the position and type of weld we are about to do.

3) What is the input we get from car products?

GD & T:

Geometric dimensioning and tolerance of the part for which the fixture has to be designed. GD and T provide information about Locating pins. Rest. clamp, dumps and slides information of each station and sequence and opening of clamp dumps and slide stroke information.

Part list:

Part list is nothing but listing down all parts of assembly. It includes information about the part name, number, tooling revision, part thickness etc. Suppose the first assembly has gone between hood inner panels and latch which is going to attach the next hinge going to be attached. So, there are different lists of assembly we are going to perform. So every assembly will have a different fixture unit.

CAD file:

3D file of that car product required from the customer. The 3D model file of the car part is given to the customer to study on it. The car part is designed by using 3D modelling software. From this we can get some conceptual idea of design in fixtures. The model is going to be the base of the fixture design.

Clamp Plan: It provides information about the position of the clamp unit,pin unit, rest unit, dump unit etc. This is major input from the customer and it should never be changed without permission of the customer. Clamp plan provides exact location of pins, rest, clam etc. It is in more detail. It gives the exact location in X,Y,Z coordinates value to start designing.

Product assembly process sheet: It gives a detailed process of the completion of the part from scratch to the finished product assembly.It will give a detailed plan of the component, how the weld is done as well as how the product is moving from one assembly to the other.

4) What is the clamp plan?

• Clamp plan is a very important input that we get in car products. It is where exactly we can place those clamping units are the particular pin units.
• We should never change the position of the particular clamp or the pin, which is given in these data.

• We can change our design a little bit here or there but we should not change the input design data about the clamp position or the pin position.
• In the clamp plan there is a clamp unit, pin unit and it is more detailed. It also gives the exact location of y and z coordinates and you can start designing from there.
• If the three coordinates, whole diameter and everything is already given to design the entire future design phase and it sometimes ministry as well. It happens that another thought position is also given very close to the clamp, or the clamp location. So always ask whether you have changed the clamp position.

• You should never change the vent position or the clamp position without asking it so always be varying about these situations. So the tool might get damaged or the department gets damaged so for that itself need to clarify once again before doing any changes in the clamp.

5) What is the purpose of a layout?

• Layout is basically a layout of the entire assembly line to understand the process and flow of work.
• Layout sheet will give you information about all the fixtures that the robots are going to work on.
• In the layout sheet the circle around the robot is called the trapped area of that particular robot.
• So this is basically the reachability of that robot and which is confined to the particular circle.
• For example, Robot is going to work on the fixture. Details also mentioned the geo 250 and then number is given 250, and you can see.This fixture is going to rotate. And then it will come to and these two robots are going to work on the other side of the fixture. Similarly this robot is also going to work on the particular component as well.
• Entire sheet will give you in that plan the layout of what are the constraints that are there from the customer side itself.
• If you want to do any changes for example , you are changing the geo fixture design and it's going to exceed a little bit bigger or smaller inside you have to inform the customer and you have to get the customers permission to do that so that he will also be able to change the design if we present him with anything.

6) What is ergo data?

-Human factors and ergonomics ( commonly referred to as human factors). It is the data or inputs which gives the human engineering data, between the operator and his working environment. Before detailing ergo data we should know about ergonomics in detail.

Ergonomics:

Ergonomics also known as human engineering and human factors engineering is the scientific study of the relationship between man and his working environments.

Objectives of ergonomics:

• The fundamental objective of the study of ergonomics is to optimise the integration of man and machine so as to improve productivity and accuracy.
• In short the objective of the ergonomics is designing for human use to optimise working and living conditions.
• The two main objectives of ergonomics are:
• To enhance the efficiency and effectiveness with which the work is carried out so as to increase the convenience of use, reduce errors and increase productivity.
• To enhance certain desirable human values including safety, reduced stress and fatigue and improved quality of life.

Ergonomics involves the design:

• A work place suitable for the worker.
• Machinery and controls so as to minimise physical strain on the worker to enable the improvement in efficiency.
• An environment for performing a task most effectively and conducive.
• A conducive task and work organisation.

Benefits of ergonomics:

• Improved working conditions.
• Reduce physical workload.
• Improved work postures
• Reduced efforts of certain movements.
• Better reading instrument displays, handling of machine levers and controls
• Reduced unnecessary information recall efforts
• Below, I have given a basic example of ergonomics in the workstation.

Ergo data:

• Ergo data is nothing but the data or inputs which gives the human factors engineering data, between the operator and his working environment.
• Ergo data is mostly needed while there is a need for manual operators.
• Ergo data will be given from customers as per their standard. Every customer follows different ergo data standards.
• As per customer standards, we have to consider the ergonomics in the fixture while designing.

7) What do you understand by weld study?

Weld study:

Weld study is the important input from the customer.It gives the study of a particular gun that we use for welding, number of spots to be welded, sequence of theweld, position of the weld in the components. In short it gives weld gun details , weld matrix, and weld points.

The shape of weld points is sphere.

Red Sphere: Represents the geo spot weld points.

Green Sphere: It denotes that it is re-spot weld points.

Classification of weld points:

Geo weld points: The geo weld points are planned in geo fixtures.

These welds will determine the position of the panels as per the given data in the drawing. The geo weld points are represented in the red sphere in the weld study inputs given by the customers.

Respot weld points: The re- spot weld points are planned in the re spot tool. These welds will determine the strength or stiffness of the panel / components; the re-welded points are represented in green spheres in the weld study inputs given by the customer.

8) What are the criteria for percentage completion in the designing stage? Explain in detail?

The percentage completion criteria is followed in the designing stages and dispatch stages of the welding fixtures.

This percentage completion criteria is followed to trace the project whether it matches the committed date given to the customer for hand over of the projects to tehm.

Also it helps us to identify the stages in projects like how much the project is completed and what are the further stages which are in pending, to complete which helps us to complete the projects on the committed time and date.

The percentage completion criteria is divided into four stages to identify the percentage completion of work.

The four stages of percentage completion criteria are as follows:

• Input and concept design
• Concept approval and simulation check
• Design freezing and detailing
• Check and final dispatch.

Input and concept design: If the project is in the stage of input and concept design then the percentage completion criteria of the project will be between 0-25%

After the completion of concept approval and simulation check which is the second stage in percentage completion criteria.

Concept approval and simulation check: If the project is in the stage of design freezing and detailing then the percentage completion criteria of the project will be between 25%-40%.

After the completion of the concept approval and simulation check then the project will be moved to design freezing and detailing which is the third stage in percentage completion criteria.

Design freezing and detailing:

If the project is in the stage of design freezing and detailing then the percentage completion criteria of the project will be between 40%-85%.

After completion of the design freezing and detailing the project will be moved to check and finally dispatch which is the fourth and last stage in percentage completion criteria.

Check and final dispatch: If the project is in the stage of check and final dispatch then the percentage completion criteria of the project will be between 85%-100%. After the check the project will be finally dispatched successfully to the customer.

9) Brief about output in design

The output should compile the following points:

• Approved standard components are to be used wherever possible.
• Design must be as simple and economical as possible.
• Design must comply with all current safety and ergonomic requirements.
• Design must provide for controlled and damage free handling of the product.
• Adequate error proofing provision must be incorporated into each design by providing proximity switches. Rough locators etc.
• The weight of the moving parts must be kept to minimum while maintaining maximum strength.
• Frames and structures are to be simple and sturdy.
• Design clearance and accessibility for routine maintenance and service.
• Motion control must be considered on any moving equipment.
• Designer is responsible for validating clamps and all weld guns.

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

• Unitized tools
• Non-unitized tools

Unitized tools:

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

So examples of unitized tools are fixtures. So where exactly multiple units are placed. For example the entire assembly welding fixtures where's 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 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 there is no need for key sheets.As they can stand alone, the drawing can be detailed completely on 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 location of the particular tool on the tool base where exactly the tool is placed and what is its exact position in a particular place

2. Non- unitized tools:

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

Non unitized tools are basically tools like stands and tool changers where you don't need a key sheet, you can actually use a layout sheet and complete the entire documentation of the particular component. So this is known as non-unitized.

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

Structuring a design tree:

Structuring a design tree implies a process where all the assemblies and parts are named in a specific standard. Different customers have different sets of standards to structure a design tree.

It is an important process which helps us to identify a specific part or assembly as to which project, tool/unit it belongs to.

This helps us to avoid the errors during design, manufacturing, assembly, inspection, etc.

If the parts or assemblies are not named properly or the design tree is not structured properly, it will create confusion to understand the design and may create major possibilities of making an error.

Naming of a fixture or a unit or a part gives information as to which project or zone or assembly they belong.

It can help us to identify the quantity of items of the same types or different types that are being used in the assembly.

While starting to design a fixture, the first unit will be the base unit.

In the structure tree all manufacturing parts should be first and standard parts should be at last.

Structure trees help to study or understand the parts in the assemblies easily.

11) What are units? What are the 5 types of 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. Units are classified into two. They are:

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

• Rest unit
• Fixed pin units
• Retract pin units
• Rough locator unit
• Sensor unit
• Base unit

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

• Slide unit
• Dump unit

Five types of units:

Rest unit: It is a unit on which the panel is rested.It consists of a blade and a riser along with a few mylers which also vary depending on requirement. Rest unit is used to arrest vertical translational motion in downward direction.

Retractable Pin unit: Retractable pin unit is a unit designed to locate the car panels using pins in which the entire pin package is mounted on a retractable cylinder.

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 the base unit.

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 pins so total constraint by locating pin should be fully constrained at all times to prevent any movement.

Sensor Unit: It is a unit used to sense the car panels by mounting electric sensors on it. Sensors send a signal to the PLC if the panel is present or not and then the process will be executed based on this signal. Sensor unit has a sensor mounted on it. This is done for mistake proofing in the panel welding process.It is attached to the blade of rest clamp, pin units to sense panels.

12) Describe Fixed Pin units & their purpose?

Fixed pin unit: This unit consists of riser, blade, block,shims or spacer, pin retainer & pin.

Riser is the standard part which is used to raise up the height of the unit.Blades are plates mounted on the riser.Other parts like cylinder, arms etc are mounted on the blade.

Shims are the small part which comes with the thickness of 0.1mm, 0.2mm, 0.5mm etc. These will compensate for the stack up tolerance which reflects at the panel holding part called Mylars. In fixed pin shims are used to adjust to translational motions.

Pin retainer will support the pin and the locating pin which restricts movement of the car panel.

Purpose of fixed pin unit:

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

The fixed pin unit is the part of the 3-2-1 principle. It restricts 6 degrees of freedom of the car panel.

It is necessary to have 2 pins to locate the car panel. One pin must arrest 4 ways( 4 transitional) and the other must arrest 2 ways (2 rotational) of a car panel.

13) What are the different parts of a fixed unit?

Fixed pin unit consists of a riser, blade, block, shims or a spacer, pin retainer and pin. All parts are described below.

1. Riser- Riser is the standard part which is used to rise up the height of the unit.
2. Blades- these are plates mounted on the riser. Other parts like cylinders, arms etc are mounted on the blade.
3. Shims:These are small parts which come with the thickness of 0.1mm, 0.2mm, 0.5mm etc. These will compensate for the stackup tolerance which reflects at the panel holding part called mylars. We give tolerance to all parts of the fixture. Due to this tolerance the mylars will either lift up or goes down from its defined position.If the mylars go down from the defined height it will make impression or dent on the panel.If the Mylars lift up then there will be a distortion due to welding stress.To adjust the mylars at its defined position we use shims so the panel won't deform and also don't get any impression on it.

• Pin-retainer: It will support the pin.

1. Locating pin- Typically , locating pins are used for controlled, fine tolerance positioning of a work piece. For example, a pallet that is moved along one axis, where the drive mechanism is not accurate and stable enough to place it in a position sufficiently accurate to execute a particular process, the use of locating pins may be the best solution.

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 workpiece will not be placed on the base as easily as it would with the use of a diamond shape pin.

14) What is the purpose of making a rest unit and describe its parts?

The rest units are designed to rest/support the car panel by using NC blocks/Mylars/rest.It is the simplest unit to design because it has fewer parts to design and the purpose is only resting of the car panel.Because of this simplicity, the rest unit is combined with other units 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 and rest unit can be combined together in one unit to reduce cost.

Riser- Riser is the standard part which is used to rise up the height of the unit.

Blades- these are plates mounted on the riser. Other parts like cylinders, arms etc are mounted on the blade.

Shims:These are small parts which come with the thickness of 0.1mm, 0.2mm, 0.5mm etc. These will compensate for the stackup tolerance which reflects at the panel holding part called mylars. We give tolerance to all parts of the fixture. Due to this tolerance the mylars will either lift up or goes down from its defined position.If the mylars go down from the defined height it will make impression or dent on the panel.If the Mylars lift up then there will be a distortion due to welding stress.To adjust the mylars at its defined position we use shims so the panel won't deform and also don't get any impression on it.

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

• Sensor is a device which detects or measures a physical property and records, indicates or otherwise responds to it.
• A unit designed to sense a car panel using electrical sensors is called a sensor unit. The signal from the sensor is sent to PLC so the next process is executed by this signal.
• The sensor is a very sensitive and easily damageable part so sensor cover is provided to the sensor for safety purposes.

There are different types of sensors

1. Proximity sensor
2. Laser sensor
3. Photoelectric sensor
4. Infrared sensor etc.

Fundamentals of sensor unit design:

1. Every single loose panel which is being welded in a tool should be sensed.The assembly of the car panel consists of no.of panels. The location of every panel is fixed. There are some locating units, clamping units, rest units etc.are provided for proper location and operation. The sensor is attached in this unit to sense if the part is loaded or not.If the part is not loaded the sensor will send a negative signal to the PLC controller and operation will not start and vice versa. Hence every single loose part should have at least 1 sensor.
2. Each panel should be sensed by 1 to 2 sensors depending on the size of the panel, preferred to be in diagonal opposite ends of the panel. Sensor is used to sense if the part is loaded or not and starts the operation by sending the positive signal. But if the part is big in size then there will be 2 sensors required because the part will be loaded in the correct position at one end and will not be positioned correctly at the other end and due to which the assembly will not be ok part and gets rejected at QC check stage. Hence to neglect these kinds of situations the part should be sensed by 1 or 2 sensors depending on its size for proper assembly.
3. Every sensor should be mounted in a 3 direction adjustable way in general.Sensor can be adjustable to particular distance from the panel by using these 3 direction adjustable ways. If we use proximity sensors it has a range 5 to 10mm to sense part and for laser sensors the range increases.

16) What is a rough locator unit and what are the basic fundamentals to consider while designing it?

The rough locators are used to guide the operator how to locate the car panel on to the pins accordingly. The rough locator can be a standard or make part.It guides in loading and unloading the panel.

The fundamentals followed while designing rough locator unit are:

• The rough locator should be placed at the edges of the panel so that the panel is guided.
• It should be placed at the same angle of the car panel edge with minimum distance of 2 to 5 mm from the edge of the panel..
• In general it is designed to guide the panel in pin arresting and it also should be in angle parallel to the panel edge.
• The rough locator should be guiding the panel before 10-15mm of the pin engagement.
• The entry angle for the car panel should be considered while designing the rough locator.
• In general it should have two slots to mount for easy adjustments. These slots should be in the direction of the car panel guiding.

17) What is a Base unit and describe its parts?

Base unit: A base unit is the unit designed to mount all the other units( 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.

Parts involved in base plate are described below:

Floor plate- It is the plate which joins the fixture to the floor by using some nuts and bolts. This plate surface is machined for maintaining the horizontal position of the fixture.

Weld bars and pedestal- Pedestal is the base or support on which a fixture is mounted.

Eyebolt- An eye bolt is a bolt with at one end.They are used to firmly attach a securing eye to a structure, so that ropes or cables may then be tied to it.

Machinery eye bolts are fully threaded and may have collar making them suitable for use with angular loads up to45 deg. Eye bolts without a shoulder should not be used for angular loads.

18) What is a dump unit and what are its functions?

• When we have some geometrical constraints then we cannot mount normal 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 constraints. There is less space available and I have to adjust all parts in available space.
• It consists of dump cylinder to perform the operation of clamping and unclamping car panel.

19) What is a slide unit? Mention where slide units are commonly used?

Slide unit : Slide units are positioning units which are used to position the fixture, weld gun, units, robots into position for further operations. Slide units can be classified into two types on the base of the type of guide-ways used as.

• Hardening guide ways
• LM guide way

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

• Manual slides
• Hydraulic/pneumatic slides
• CNC slides.

It may also be classified depending on the application as:

• Horizontal slide
• Vertical slide
• Angular slide

Guidelines to design the slide unit:

• LM guide ways are preferred over hardened guideways due to least coefficient of friction.
• Slide unit essentially consists of LM guide, linear cylinder, front and rear stoppers, front and rear shock absorber, two p[roximity switches/ reed switches for sensing the two end position , bellows or protection cover for rails.
• Centre trunnion/rear clevis mounted cylinders are ideally used for slide unit application as this allows for some float to take up mis-alignment.
• Reverse stroke of 10mm to be considered in both forward and retracted condition.
• Cylinder and LM guides to be validated for load and stroke.

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

• Shock absorber to be used for both extended and retracted conditions to reduce the impact load.
• Mechanical hard stop to be considered.
• The two end limits can be sensed externally by a proximity switch.
• Slide units are used when we have some space constraints. So we don't have space to design different special units and to assemble them. In those cases we use sliding units.