Week 3:- BiW Fixture Design Methodologies Challenges

Q1 What is design methodologies?

Various design methodologies is nothing but the steps followed during the concept designing stages of fixture design.

Design methodology is divided into four sub categories:

• Purchase Order.
• Inputs from Customer.
• Percentage Completion Criteria.
• Design Output

Purchase order :

A purchase order is basically confirmation from the customer side that we are ready to start work. A purchase order (PO) is a commercial document and the first official offer issued offer issued by a buyer to a seller indicating types, quantities and agreed prices for products or services. It is used to control the Purchasing of Products and services from external suppliers. Purchase orders can be an essential part of enterprise resource planning system orders. Indent is a purchase order often placed through an agent (indent agent) under specified conditions of sale. the issue of a purchase order does not itself form a contract. if no prior contract exists then it is the acceptance of the order by the seller that forms a contract between the buyer and seller.

Input from customer:

• First understand the scope of the work. this means what is expected by the customer. Every customer has its specific requirements and it may have its' own raw material, electric, pneumatic, CAD, design standards. Every customer also gives different inputs and expects output ex- 2D drawing, Process sheet in Xls, pdf, CAD format of design, layout format, OLP.
• BOM of the components to be welded - spot welding.
• CAD panel data or at least 2D drawing of assembly and individual panel data.
• Sheet metal panel thickness plays a major role to decide 2 metal or 3 metal welds.
• Spot detail information like total no. of spots and spacing between the spots.
• Weld information clarity from drawing like 2 metal or 3 metal welding
• PLP ( PRINCIPLE LOCATION SCHEME ) of the individual panel and total assembly.
• Cycle time if calculated or can be found out as per manual or robotic welding process.
• Process sheet if process engineering is done - where loading sequence, no. of clamp data and gun data is mentioned.
• All clamping cylinder and fixtures standards.
• CAD-software guidelines.
• Raw materials standards.
• Design guidelines
• Bought out item (purchase parts) standards like pneumatic items, toggle clamp, bearing, screw, dowel etc. company information

Percentage completion Criteria :

• It consists planning of the completion of the total project how many days the project will take to complete.
• It is followed in the designing stages and dispatch stages of the welding fixtures.
• It ensures that how many tasks that we have decided to complete within the stipulated time is complete or not in a given time.

Design output :

• The output consists of 3D models, a 2D drawing which is the detailing part, BOM and other related documents.
• There are some tools which are multiple units on a common base are called unitized tools for example a fixture which includes no. of units on the same base.
• They required two types of drawing sheets as follows

1- Key sheet - It shows the index of the unit and its placement on the tool base.

2- Layout sheet - It is the detailed drawing of an individual unit to include all its' components. Non unitized tools which can be completely detailed on the layout sheet.

Q2 What are the inputs required from the customer to start designing a fixture?

Inputs required from the customer:

To start designing a fixture the following are the inputs required for designing a fixture.

• Functional requirements
• Preferred standard components
• Car products
• Layout
• Ergo Data
• Weld study
• Standard detailing Templates.

Functional requirements:

The purpose of the function of the fixture will be given as input from the customers like what are the function fixture is going to do i.e, Welding, Riveting, Gluing or whether it is a checking fixture etc.

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

Preferred standards:

As we know different companies follow different standards. we will be following the standards , followed by the customers. By following the standards in the time of designing and manufacturing of parts we will be saving the time and cost which will be automatically minimizing the time of the projects. As per the standard parts, It can be easily replaced from the used fixture to the new fixture which reduces cost.

some of the preferred standard components used in BIW or stated below:

• Standards like ABB, NAAMS ( North american association for mechanical standards) DESTACO, ZYTRAN, TUNKERS.
• Standard parts like Risers, L- Blocks, Retainers, pins.
• Components like Clamps, Cylinders, Slides, Switches, Sensors.
• Weld guns, Tip dressers, Tool changers. Tip Dressers are used to sharpen the tip of the tools which are used in robots in various process.

Car Products:

GD&T- Geometric diemensioning and tolerance.

It provides information of locating pins, rest, clamp, dump and slide unit information of each station also includes the information of sequence of opening of clamps, dumps and slide stroke information.

Importance of tolerance

Assmblies : Parts will often fit together if their diemensions do not fall with in a certain range of values.

Interchangeability : If a replacement part is used, It must be a duplicate of the original part within certain limits of deviation.

The relationship between functionality and size or shape of an object varies from part to part.

Layout:

Purpose of layout is to understand the information about where the fixture and robots are been placed, working area covered by the robot what are the fixtures assigned for the robots to do the process etc. layout shows the entire assembly plan to understand the process.

• Flow of parts.
• Station pitch.
• Sub assembly link.

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 of manaual operator / operation.
• Ergo data will be given from customer as per their standards. Every customers follow different ergo dat astandards.
• As per customer standards, we have to consider the ergonomics in the fixture while designing.
• From ergo data we get the details or inputs related between the operator and his working fixture.
• The ergo data is mainly used to make the operator comfortable which may leads to improve the efficiency in cycle time and production.

Weld study

Weld study is the important input from the customer. It gives the study of particular gun that we use for weld, no. of spots to be welded, sequence of weld, position of weld in the components. In short, weld study includes weld gun details, weld matrix and weld points.

Standard detailing template:

These inputs include the detailing templates of 2D CAD drawing as per the customer standards so we have to follow the detailing templates as per the customer standards.

Q3 What is the input we get from " Car Products"?

Inputs we get from car products includes:

1- GD&T.

GD&T- Geometric diemensioning and tolerance.

It provides information of locating pins, rest, clamp, dump and slide unit information of each station also includes the information of sequence of opening of clamps, dumps and slide stroke information.

Importance of tolerance

Assmblies : Parts will often fit together if their diemensions do not fall with in a certain range of values.

Interchangeability : If a replacement part is used, It must be a duplicate of the original part within certain limits of deviation.

The relationship between functionality and size or shape of an object varies from part to part.

When to use GD and T:

When part features are critical to a function or interchangeability.

When functional gauging is desirable.

When datum references are desirable to ensure consistency between design.

When standard interpretation or tolerance is not already implied.

When it allows a better choice of machining processes to be made for production of a part.

Datum refernce in GD&T

A datum is a plane, a straight line, or a point that is used as a reference when processing a material or measuring the dimensions of a target.

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- 3D cad files.

• The 3D model of the car part will be given from th ecustomer 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.) or sometimes it may be in part file (prt.).

4- Clamp plan.

• It provides the information of location of pins, rest units, clamp unit and dump unit etc.
• It is the important input from the customer. The clamp plan/positions should not be changed without the knowledge of customers.
• It gives the detail of the exact position of the clamping units.

5- Product assembly process sheet.

It gives the information of stage wise assembly process like how the parts move from one assembly to other after the completion of joining process.

It shows the sequence of operations / process to be done in a part or a panel.

also what are the parts to be joined with the panel will shown in sequence.

From this sheet we can trace out the pending process which has to further go on for completion of parts.

from this product assembly process sheet designer can understand the sequence for designing the fixtures.

Q4 What is the Clamp plan?

A clamp can be defined as a device for providing an invariant location with respectto an external loading system. In other words, the process of clamping induces a locking effect which, through frictional or some other forms of mechanism, provides a stability of location which cannot be changed until and unless external loading is able to overcome the locking effect. Hence, when a cutting force is producing a load or moment on the workpiece, it is necessary that a sufficient clamping force must be exerted to withstand such actions.

Requirements of clamps:

1- Workpiece must be held rigid while undergoing operations.

2- The time requirement for loading / unloading the tool must be as short as possible, which means the clamping device must be quick acting.

3- When subjected to vibration, chattered , heavy pressure the clamping must be positive .

4- The clamp must not damage the workpiece.

CLAMP PLAN:

Clamp plan provides the information of location of pins, test units, Ciamo unit clamp etc.

It gives the detail of the exact position of the clamping units by mentioning a coordinates the particular position.

Clamp plan is very important input that we get in the car products 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 modify our design while taking care of the input design data about th eclamp position or the pin position.

In the clamp plan there is clamp unit, pin unit and it is more detailed it also gives the exact location of Y and Z coordinates designing as well you can just input these 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 gives mistake as well it happens that another thought position also given very close to the clamp or the clamp location, so always ask whether you have to changed the clamp position.

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

Q5 What is the purpose of a Layout?

Purpose of layout is to understand the information about where the fixture and robots are been placed, working area covered by the robot what are the fixtures assigned for the robots to do the process etc. layout shows the entire assembly plan to understand the process.

The circle around the robot is the swept area of the particular robot which shows the reachability of the robots particularly with the confined circle.

Layout provides the information of flow of parts, station pitch, robot stations, accessories like tool changers and tip dressers, subassembly links, platform height, loading / unloading sequence / height.

Layout sheet will give you information about all the fixtures are placed, the robots are going to work on it.

In layout sheet the circle around the robot is called Trapped area of that paricular robot so this is basically the reachability of the robot which is confined to the particular circle.

Flow of parts: It shows the flow of the parts / panel in the assembly line or shop floor like how cmponent move from one station to other station after the completion of process.

Station pitch : The distance between the two stations is known as station pitch. It shows the space constraints between the two stations, which shows in layout.

Sub assembly linkSub assembly link : Subassembly link is nothing but the link between the assembly fixtures and the main assembly line. It shows that how the subassembly fixtures are linked with the main assembly line.

The layout providing the above information like flow of parts, Station pitch, robot stations etc. used to understand the working process of robots what are the fixture assigned for the robots, space contraint etc.

By considering the layout, the designer can develop the concept sketches of fixtures without any clash in the assembly lines.

One of the main purpose is to get the information about the space constraint which helps to develop the robotic cell without any clash during working.

Q6 What is Ergo data?

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 of manaual operator / operation.
• Ergo data will be given from customer as per their standards. Every customers follow different ergo dat astandards.
• As per customer standards, we have to consider the ergonomics in the fixture while designing.
• From ergo data we get the details or inputs related between the operator and his working fixture.
• The ergo data is mainly used to make the operator comfortable which may leads to improve the efficiency in cycle time and production.

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

Ergonomists performed a series of ergonomic assessments of fixtures currently on the assembly line, and discussed concerns with workers. A list of 28 concerns

resulted. The challenge was then to determine how to translate an “ergonomic concern” into a “design guideline” in such a way that engineers would understand and

address the concern. For example, one concern observed was sustained forward neck flexion required when using some fixtures. The neck flexion is a result of visual

requirements, both of the fixture as well as the angle of attachment of the part. A guideline suggesting neck flexion should be minimized is not useful for a fixture

design engineer, since their focus is primarily on the function and performance of the actual device – not the operator’s posture. To translate concerns into guidelines, a

two hour workshop was held with nine design engineers. Ergonomists presented the concerns with pictures indicating the problem to be solved. Engineers assisted in

developing the language for the guidelines that would help minimize the concern.

Ergonomics involves the design:

• A workplace suitable for the worker.
• Machinery and controls so as to minimize physical strain on the worker to enable the improvement in the efficiency.
• An environment for performing a task most effectively and conducive.
• A conducive task and worl organization.

Benefits of Ergonomics:

• Improved working condition.
• Reduce physical workload.
• Improved work postures.
• Better reading instrument displays, handling of machine levers and controls.
• Reduced unnecessary information recall efforts.

Q7 What do you understand by Weld study?

Weld study is the important input from the customer.

It gives the study of particular gun that we use for weld, no. of spots to be welded, sequence of weld, position of weld in the components.

In short, weld study includes weld gun details, weld matrix and weld points.

Generally the weld points will be given in spheres.

Red sphere : Geo spot weld points.

Green sphere: Respot weld points.

1- Geo weld points:

These points are planed in Geo fixture.

These weld will determine the position of the panels as per the given data in drawing.

The Geo weld points are represented in red sphere in the weld study inputs given by the customers.

2-Respot weld points:

The respot weld points are planned in the repot tool.

These weld will determine the strength / stiffness of the panel / components.

The Respot weld points are represent in green spheres in the weld study inputs given by the customers.

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

The percentage completion criteria is followed in the designing stages and dispatch stages of 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 the projects to them.

Also it help us to identify the stages in the projects like how much the project is completed and what are the further stages 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 of the completion of work.

The four stages of percentage completion criteria are as follows:

1- Input and concept design:

Here the project completion criteria of the object will be between (0 - 25) %

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

2- Concept approval and simulation check:

Here the percentage completion criteria of the project will be between 25 to 40 percent.

3- Design freezing and detailing :

Here the percentage completion criteria of the project will be between 40 to 85 percent.

4-Check and final dispatch:

Here the percentage completion criteria of the project will be between 85 to 100 percent.

After the check the project will be finally dispatched successfully to the customer.

Q9 Brief about "Output" in design?

OUTPUT DESIGN:

In BIW fixture design or any industry we do not only just design a perticular 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 like BOM, 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 drawings of the tools

1- Unitized tols

2- Non unitized 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 palced for example the entire assembly welding fixtures where a pin unit and clamp unit, rest unit and the panel, everything is included so that for those things.

Keysheet - An index of units and their placements on the tool base. It will have an orthogonal view of the fixture sincluding a numbered ballon 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 keysheets,as they can stand alone, the drawing can be detailed completely on a lay out sheets.

so, it basically an index of units and palcements on the tool base so the key sheet going to show you the placements and the location of that particular tool on the tol base where exactly the tool is palced and what is his exact position in a perticular 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 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 known as non unitized tools.

Design output should satisfy the following points:

1- Approved standard components are to be used where ever possible.

2- Design must be simple and economic

3- It must provide knowledge for controlled and damage free handling of product.

4- It must meet all current safety and ergonomics requirement.

5- Adequate error proofing provision must be incorporated into each design by providing proximity switches, rough locators etc.

6- The weight of the moving parts must be kept to a minimum while maintaining the maximum strength.

7- Frames and structures are to be simple and easy.

8- Design clearance and accessibility for routine maintenance and service.

9- Motion control must be considered on any moving equipments.

10- Designer is responsible to validate clamps and weld guns.

Q10 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 to process where all the assemblies and parts are named in a specific standard. Different customer will have different set of standards to structure a design tree.

It is a 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.

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

While start designing a fixture, the first unit will be the base unit.

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

Structure tree helps to study or understand the parts in the assemblies easily.

Steps to structuring a design tree:

Step1: Create new product and click ok (by clicking ok now you will enter into a product window).

Step2 : Then right click product in a structure tree a nd go to the properties and rename in part number ( as we created a product we have to mention the total assembly name of the fixture) and click okay.

The naming of the assemblies/parts/ units have certain standard procedures which i have clearly explained below.

the product name is title of the fixture. the renamed titled should be P001_Z03_ST09_00_00_R

P001- REPRESENT THE PRODUCT NAME.

ZO3 - Zone name

Panel name will also be mentioned in some case.

ST09 - Station name/ J03 - jig name will be mentioned sometimes.

00 - Unit name.

00 - Part number.

R/L- Is representing the right hand side/ left hand side of the panel.

The other renamed title explained in video is

H1L _ 19A_ RRFRA_JG3_00_00_R.

H1L _ 19A - Project name

RRFRA - panel name.

JG3 - Jig name / number.

00 - unit name

00 - part number

R - Indicates right side.

Q11 What are Units? Mention 5 types of units.

Units

A unit is a device that have particular function, especially one forming art of a complex mechanism, multiple unit are joined together in order to form a fixture and are attached to a common base which serves as a common support to the units where they are fixed.

A turning fixture is a assembley of different types of units.

Each units have there own functions and purposes

It is classified into two types:

• Unitised tools
• Non unitised tool

1- Unitised tools:

Unitised tools are basically tools which are a part of multiple units or multiple tools inside of it. These are the tools which has to be represented by two formats that is, keysheets and layout sheets.

Unitized tools are basically two types

a) Simple units:

These units have very simple design and manufacturing of it is very simple, It is classified as:

Rest unit : It is a unit used for testing the component there is no upper clamp to it, there is no force application to it , no cylinder attached to it usually it will have a riser, a blade and a few rest mylars.

Fixed pin unit : A unit in which pin is fixed it cannot be move.

Retract pin unit : Opposite to fixture which can be moved up and down using a retractable pneumatic cylinders , so it can be retraced to a certain distance.

Rough locator : It is a part design to guide the operator, to locate the car panel on the pins accordingly. a rough locator can be of standard part or make part.

Sensor unit : It is used to sense that whether the panel or a particular component is there or not. for example if we are assembling the component of 10 parts, each part will have a sensor attached to it.

Base unit: It is designed to mount all other units.

b. Complex units:

Slide unit is an example of complex unit here there design are little complicated

a) Slide unit : Here sliding mechanism is involved.

b) Dump unit : It is just like the conveyor where we assembled a component if we have a particular constraint.

2- Non unitized tools:

Non unitized tools are basically one unit itself, which is basically do not have any process functionality to it, it is just to keep component on it as a stable

like grippers turntable stands etc. non unitized tools are

• Stands.
• Take out trolleys.
• Conveyor.
• Turn tables.
• Some grippers.

Q12 Describe Fixed Pin units & their purpose?

These are used to locate car panel using pins. It is already fixed and it cannot move up and down, these are composed of

• Pin.
• Pin retainer.
• Shims / Spacers.
• Block.
• Blade/Adapter plate.

Pin unit have bidirectional shim. the block is used to mount entire pin unit. shims are used to avoid stackup tolerance while assembling entire component

Shims come in pack of 0.1, 0.2 and 0.5 cm.

Purpose

It is the important part of fixture used to resist the translational and rotational degree of freedom of that particular component. purpose of fixed pin unit is to fix the panel translation motion along the two axis and to prevent rotation of panel in the axis oof panel.

Q13 What are the different parts of a fixed unit?

Different parts of a fixed units are:

• Locating pin
• Pin retainer
• Shims
• Blade
• Riser

Locating pins:

• It is used for controlled , fine tolerancing of a workpiece.
• Usually two locating pin are enough to properly locate the workpiece.
• Drill two holes opposite to each other in each part, install a cylindrical locating pin, parts are aligned exactly the way we want.
• If we have some misalignment issues with using just bolts or other fasteners, a locating pin can be a great way to firm up our assembly.

Retainer:

It is used to support the pin it ensure that there is no motion of the pin.

it can be either

a) Make part

b) Standard part

Shims :

Shims are used in jig and fixture construction for filling gaps and to compensate for manufacturing tolerances. They are mainly used for adjusting the clamping points on tools or fixtures e.g. in the automotive or aerospace industry. A clamping point is used to fix one or more components.

Blade:

It is a plate which is attached to the riser, here parts like cylinder, arms etc. are mounted on the blade, chamfer is given to straighten th e blade.

Risers:

• It is used to mount the toggle clamp and rest clamp, mylars and location pin.
• It is not necessary that to have one riser where all the parts of clamp or rest or location units are mounted.
• Generally risers are either made of plate fabrication or plate and tube welding together or from single gas cut plate.
• These are generally manufactured to give height to the assembly.

Q14 What is the purpose of making a Rest unit & describe its parts?

Rest unit is unit designed to support car panel using MYLER / 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 and the purpose is only resting of the car panel.

Because of the 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 and test unit can be combined together in one unit to reduce cost.

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

The different parts of a rest unit are:

• NC BLOCKS / MYLARS
• SPACERS
• BLADE
• RISER

NC BLOCKS / MYLARS:

Mylars are the parts which are holding the panel from top and 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

• Clamping mylars
• Resting mylars

only resting mylars are seen in resting unit. The panel which rests on the part is known as resting mylars.

Risers:

• Riser is a structure generally used to mount the toggle clamp and rest, clamp mylars and locatin pin.
• It is not necessary to have one riser where all the parts of clamp or rest or location units are mounted.
• Generally risers are either made of plate fabrication or plate and tube welding together or from single gas cut plate.
• These are generally manufactured to give height to the assembly.

Spacers/ Shims :

Metal shims are used to finely adjust the location of how he fixture holds the product so that it is welded together with in the diemension set for the product to work well. A pack of thin metal shim is placed between wo components in the fixture. The first component is fixed in place and the second component is attached to the first component with the pack of shims in between. removing one shim or adding one shim slightly adjusts the location of the second component. this is important to manufacturers who want to have their product's parts assemble easily being welded.

Blade:

Blades are the plates attached to the riser, other parts like cylinder, arms etc. are mounted on the bklade. chamfer is given here to strengthen the blade.

Q15 What are the basic fundamentals to design a Sensor unit?

Sensor unit:

It is a device that measures physical input from its environment and converts it into data that can be interpreted by either a human or a machine. Most sensors are electronic ( the data is converted into electronic data) but some are more simple such as a glass thermometer which presents visual data. People use sensors to measure temperature, gauge distance, detect smoke, regulate pressure and a myriad of other uses.

Types of sensors used in general are:

• Proximity sensors.
• Photo electric sensors.
• Laser sensors.

Proximity sensors:

A proximity sensor is a non-contact sensor that detects the presence of an object when the target enters the sensor's field.Depending on he type of proximity sensor, sound, light, infrared radiation (I.R) or electromagnetic fields may be utilized by the sensor to detect a target. Proximity sensors are used in phones, recycling palnts, self-driving cars, anti-aircraft systems and assembly lines. These are many types of proximity sensors and they each sense targets in distinct ways. the two most commonly used proximity sensors are the inductive proximity sensor and the capacitive proximity sensor.

An inductive proximity sensor can only detect metal targets, this is because the sensor utilizes an electromagnetic field. When a metal target enters the electromagnetic field, the inductive characterstics of the metal change the field's properties, thereby alerting the proximity sensor of the presence of a metallic target depending on how inductive the metal is, the target can be detected at either a greater or shorter distance.

Capacitive proximity sensors, on the other hand, are not limited to metallic targets. these proximity sensors are capab;e of detecting anything that can carry an electrical charge. Capacitive sensors are commonly used in liquid-level detection.

Photoelectric sensors:

Photoelectric sensors detect objects, changes in surface conditions and other items through a variety of optical properties, A photoelectric sensor consists primarily of an emitter for emitting light and a receiver for receiving light. When emitted light is interrupted or reflected by the sensing object,it changes the amount of light that arrives at the receiver. The receiver detects this change and converts it to an electrical output. The light source for the majority of photoelectric sensors is infrared or visible light (generally red, or green/blue for identifying colors).

Laser sensors:

Laser sensors can be used to measure distances to objects and their related parameters (displacements, position, surface profiles and velocities). Laser sensors are based on many different optical techniques, such as triangulation, time-of-flight, confocal and interferometric sensors. As laser sensor technology has improved, the size and cost of sensors have decreased, which has led to the widespread use of laser sensors in many areas. In addition to traditional manufacturing industry applications, laser sensors are increasingly used in robotics, surveillance, autonomous driving and biomedical areas

These laser distance sensors use a focused, coherent light to measure distance to a target object. In factory automation applications, the target is usually a product.

Fundamental of sensors design

• Every single loose panel, which are being welded in a tool should be sensed.
• Each panel should be sensed by one or two sensors depending on the size of the panel preferred to be in diagonally opposite ends of the panel.
• If a component is really small, we need not use two or three sensors for that you can use one sensor to detect the particular panel.
• If the panel is really big, we will use two sensors in opposite directions to sense the panel.
• So every sensor should be mounted in three directionaladjustable ways in general.
• Sensor manufacturers are IFM, Peperl-Fuchs, OMRON etc.

Q16 What is a Rough locator unit & what are the basic fundamentals to consider while designing it?

Rough locators are elements that aid the operator to guie the car panels while loading onto the fixture and ensure a fool-proof assembly.

It is used a fool proofing method because due to the rough locator part cannot be located in correct position. The rough locators are set according to the respective panel hence it can only be loaded in defined direction and orientation.

FUNDAMENTALS OF ROUGH LOCATOR DESIGN:

• Rough locators should be placed at the edges of the car panel which it has to guide.
• Rough locator has to be placed at the same angle of the car part edge with a minimum distance of 2.5mm from the edge of the car part.
• Rough locator should guide the panel in the pin arresting direction.
• Rough locator should guide the panel before 10-15 mm to start of the pin engagement.
• Rough locator should be designed with entry angle for the car panel, Generally it ranges between 30-45 degree.
• Rough locator should be designed with two slots to mount the easy adjustments.
• The loctaors should be in the direction of car part guiding.

Q17 What is a Base unit and describe it's parts?

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

Different parts of base units

1- Valve box.

2- Trunking channel

3- Measuring hole cover.

4- Eye bolt.

5- Pedestal

6- Weld bars.

7- Floor plates.

VALVE BOX:

It is a box which supplies air to all the pneumatic cylinders assembled in the fixture. It is a device which includesa lot of other solenoid valves, so it will have one inlet and one outlet and from that one inlet, all the other solenoid valves will be attached to it and each solenoid valves will have the inputs, and then again supplied to the seprate cylinder, then again the output wil be collected, while this solenoid valves and again given back to the valve box.

Trunking channel:

Trunking channel is a kind of cable duct, which helps to guide and protect the wirings/tubes used in the fixtures.

Measuring hole covers.

Measuring hole covers is on the base unit which is for measuring purpose.

Eye bolt

It is used to drag the entire unit and relocated.

Pedestal

It is used for standing the entire unit.

Floor plates

It is used to mount the entire base with floor, it also achieve the flatness of the fixture.

Q18 What is a Dump Unit and what are its functions?

Dump units

• Found in complex fixture
• It is used where there is any geometrical constraints while placing the panel.
• It consists of dump cylinder to perform clamping and unclamping.
• It can have more than one cylinder to perform claming and unclamping.

Functions of dump units

• It requires when there is any geometrical constraints while placing the panel.
• Here the first cylinder dump the assembly carrying the clamp mylars, pins and then this assembly perform the required operation, In this unit we should make sure that in the open position of panel we can remove the panel.

Q19 What is a Slide unit? Mention where Slide units are commonly used.

Slide units are positioning units they are used to position the fixture, weld gun, units, robot into the required position for further operations.

Slide units consists of LM GUIDES, LINEAR CYLINDER, FRONT AND REAR STOPPERS, FRONT AND REAR SHOCK ABSORBERS, TWO PROXIMITY SWITCHES / REED SWITCHES (for sensing the two end positions), Bellows and protection (covers for rails).

These are Further divided into two types based on the type of guideways used as

1) Hardened guide way.

2) LM guide way.

These are classified into three types on the base of the prime mover used

1) Manual slide.

2) Hydraulic/Pneumatic slide.

3) CNC slides.

Depending on the orientation these are divided into three types

1) Horizontal slide.

2) Vertical slide.

3) Angular slide.

DESIGN CONSIDERATIONS

• Center trunion/rear clevis mounted cylinders are ideally used for slide unit application as this allows for some float to take up misalignment.
• LM guideways are preferred over Hardened guideways due to the least coefficient of friction.
• 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 the actual stroke.
• Mechanical hard stop to be considered for both extend and retracted condition.
• Shock absorber to be used for both extended and retracted condition to reduce impact load.
• The two end limits to be sensed externally by a proximity switch.
• the shock absorber should be mounted such that it is perpendicular to the pivot at mid stroke oe with in +/- 5 (deg.).
• The LM rails should always be covered to protect against weld spatter and dust by a bellow or sheet metal cover.
• The design to be checked for screw accessability, ease of assembly and machinability of parts.
• LM guide and rail can be ordered separately or as a single pakage based on the customer requirements and the make of LM guide.

USES

• Slide units are found mostly in complex fixture where the sliding mechanism will be involved.
• It is used where there is some space constraints in locating the panel.
• Slide application will be easy for welding.
• Slide unit can be minimized the cost of robot as slide unit provided to move weld gun from one weld spot to other weld spot instead of weld robot.