Week 3:- BiW Fixture Design Methodologies Challenges

DESIGN METHODOLOGIES:

In this methodology we learn about three design processes, we're going to study how do we proceed while doing a design. And one of the things that we take care of structuring or design tree so we'll be learning how to structure the design tree, and how to name the particular component or particular assembly, or the part of an assembly, which is very easy to read and very easy to understand

Purchase Order:

A purchase order (PO) is a commercial document and first official 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. Purchase order is a order from customer for start of the work. After offer has been finalized customer will be releasing the LOI/PO(Purchase Order).Once PO is released we have to start the work. After PO from the customer we have to prepare the schedule.Purchase order is the confirmation document from customer to proceed the committed work for them.

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.

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.

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.

 

Customer Inputs

Functional Requirements: 

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

Preferred standards:

As we know different companies follow different standards, we will be following the standards, we will be following the standards followed by the customers. By following standards the time of designing and manufacturing of parts will be saved, which will be automatically minimizing the time of the projects. As for the standards parts, it can be easily replaced from the used fixture to the new fixture which reduce the cost.

Car products: 

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

Layout:

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

Ergo Data:

As same as preferred standards, different companies follow different standards of ergo data. We have to follow the customer standards of ergo data. The inputs of ergo data will given by the customer mostly in case of manually operated fixtures/manual fixtures. The ergo data is mainly used to make the operator comfortable which may lead to improve the efficiency in cycle time& production. Ergo data provides inputs like platform height, maximum & minimum reach from operator to fixture, maximum & minimum height of the fixture, whether the child parts/assemblies are visible while clamping or loading & unloading. Also provises information like loading height, working safety zone of operator, etc.

Weld study: 

Weld study is the important inputs given by the customer. It gives details about the study of particulars gun that we use for welding. Also the dates like no/ of weld, position of weld in the components will be given. In short, weld study includes weld gun details, weld matrix & weld points.

Standard detailing templates:

This 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.

Car Products:

GD&T: It provides information of locating pins, rest, clamp, damp & slide unit informationof each station. Also includes the information of sequence of openings of clamps, dumps & slide stroke information.

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.

Clamp plan: Clamp plan provides the information of location of pins, Rest units, clamp unit, dump etc. It is the important input from customer. The clamp plan/position should not be changed without the knowledge of customer.

3D cad file: The 3D model of the car part will be given from customer. From that 3D model we will be developing our fixture design process. The 3D cad file will be in the format of step file (stp) or IGES file (igs).

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

 

Clamp plan

A clamp is a fastening device used to hold or secure objects tightly together to prevent movement or separation through the application of inward pressure

Clamp Plam 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 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 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 we 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, also given very close to the clamp, or the clamp location. So always ask to whether you have changed the clamp position.
• we should never change the vent position or the clamp position without asking it So always be vary about these situations So the tool might get damaged or department get damaged so for that itself need to clarify once again before doing any changes in the clamp.

Purpose of the layout

The purpose of the layout is to understand the information about where the fixture & 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 confine circle.

 

Layout provides the information of flow of parts, station pitch, robot stations, accessories like tool changers & tip dressers, sub assembly links, plat form 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 particular robot, this is basically the reachebility 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 component move from one station to other station after the completion of process.

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

Robot stations: It shows the position where the robots & their accessories placed, which is shown in the layout.

Sub assembly link: Sub assembly link is nothing but the link between the assembly fixtures & the main assembly line. It shows that how the sub assembly fixtures are linked with the main assembly line.

The main purpose of the layout is to understand the entire plan of the 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 fixtures assigned for the robots, space constraint, etc.

By considering the layout, the designers 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.

Ergo-data

Ergo data is nothing but the data or inputs which gives the human factors engineering data, between the operator & his working environment. Before detailing about ergo data we should know about ergonomics in detail.

Ergo data is nothing but the data or inputs which gives the human factors engineering data, between the operator & his working environment.

Ergo data is mostly needed while there is a need of manual operator/operation.

Ergo data will be given from customer as per their standard. Every customers follow different ergo data standards.

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 & production.

 

WELD STUDY:

 

Weld study is the important inputs 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 & weld points. Generally the weld points will be given in spheres.The weld points are classified as, 

Geo weld points: The Geo weld points are which is planned in the Geo fixture.
These weld will determine the position of the panels as per the given data in drawing.
The geo weld points are represents in red sphere in the weld study inputs given by the customers.

Respot weld points: The respot weld points are planned in the respot 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.

 

Criteria for percentage completion in the designing stage

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:

0-25% (Input & Concept Design):  In this stage of percentage completion criteria, we have to built concept design of fixture in this stage.

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. 

40-85% (Design Freezing & Detailing): If all requirements and specifications of customers are satisfied then design is freezed and detailing work starts.

85-100% (Check & Final Dispatch): In this stage, quality checking is done using CMM (coordinate measuring machine) and then dispatched to customers.

 

Output in design

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. The basic output are 3D models and 2D drawing of fixture. Output are classified as below:

Unitised Tool: This tool consist of two type of sheets, they are as follow:

   Key Sheet: Key sheet mentioned or shows the location of every units in fixture.

   Layout Sheet: Layout sheet is detail drawing of particular unit in fixture.

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

 

Structuring design tree

Structuring a design tree is very necessary while designing fixture because it help to identify all manufactured part in whole fixture. Every customer company have there own standard. This will help us during design study, manufacturing and inspection to avoid errors. If we ignore structuring a design tree it will create confusion to understand design and may errors will appers in fixture.

 

Units

Unit is nothing but a assembly having specific function like clamping, location or resting. In fixture there are number of units. According to 3-2-1 principle of location fixture is designed having two major purpose of clamp and locate the component for which fixture is designed.

Fixed Pin Unit: Fixed Pin Unit is non movable locating unit which arrest movement of component in fixture.

Retract Pin Unit: Retract Pin Unit having retracting unit which is used to move pin to ensure proper loading and unloading of component.

Rough Locator Unit: This unit help operator for correct loading of component.

Rest Unit: As name suggest, rest unit is used to rest the component.

Base Unit: All the units in fixture are placed on this base unit.

 

Fixed Pin Unit

Fixed Pin Unit is non movable locating unit which arrest movement of component in fixture. Fig. shows an example of fixed pin unit. It consist of pin, pin retainer, blade, two way shims or spacer which control X, Y direction adjustment, block and riser.

Purpose of Fixed Pin Unit are as below:

Main purpose of fixed pin unit is to locate component

This unit is used arrest 6 degrees of freedom of component

Two pins are used to locate component. First pin restricts  4 translational motion and other one restricts 2 rotational motion. 

 

Different parts of fixed pin unit

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

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

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

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

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

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

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

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

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

Blade: Blade are the plates which are attached to raiser. Blade is also attached or mounted with cylinders, arms etc.

 

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 units are

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.

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,

Blade: Blade are the plates which are attached to raiser. Blade is also attached or mounted with cylinders, arms etc.

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.

 

Basic fundamentals to design a sensor unit

A sensor unit is a unit designed to sense the car panel by using electrical sensors. This signals from the sensors will be fed to the PLC and so the next process will be executed by the signal.

FUNDAMENTALS TO DESIGN A SENSOR UNIT:

Every single loose panel which are being welded in a tool should be sensed.
Each panel should be sensed by 1 or 2 sensors depend on the size of the panel, preferred to be in diagonal opposite ends of panel.
Every sensor should be mounted in a 3 direction adjustable way in general.
We should try to minimize the size of sensor as much as possible.
Some major sensor manufacturers are IFM, Pepperl – fuchs, sick, OMRON, etc.

 

Rough locator unit

Rough locator unit is a unit designed to guide the operator to locate the car panel on the oins accordingly. A rough locator can be standard part or make part.

THE BASIC FUNTAMENTALS TO CONCIDAR WHILE DESIGING A ROUGH LOCATOR:

Rough locator should be placed at the edges of the car panel, which has to guide.
Rough locator should be placed in the same angle of the car part edge with a minimum distance of 2 – 5 mm from the edge of car part.
Rough locators should guide the panels in a pin assemble direction in general.
Rough locators should start guiding the panel before 10 t0 15mm to the start of the pin engagement.
Rough locators should be designed with entry angle for car part entry as shown in the above figure.
Rough locators should be designed with two slots to mount for easy adjustment in general.
The slots should be in the direction of car part guiding.

 

Base unit

Base unit is the unit designed to mount all the other 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.

Parts of base unit

Valve box: Valve box is basically a box which supplies air to all the pneumatic cylinders assembled in the fixture.
Valve box consist of one solenoid valve is used to collect the air from the pneumatic cylinders to 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 cover: In the measuring hole cover the coordinates points are engraved on it.
The hole which mention the coordinates gives the position & placements of the particular units.
The measuring hole helps in CMM inspection & QC inspection.

Eye bolt: An eye bolt is a bolt with a loop 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 for lifting purpose. Eyebolt is used to frag or lift the base unit while relocating.

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

Floor plates: Floor plates is used to mount the entire base with the floor.
Also it helps to achieve the flatness of the fixture.

 

Dump unit

Dump unit is where you assemble component if you have certain constraint. Here you will have clamp unit, pin unit attached & panel will be assembled. So if you have certain constraint you cannot assemble in normal way.

Dump unit is used in different way. It has dump cylinder & complex design. It consists of dump cylinder to perform the operation of clamping & unclamping car panel. A dump unit can have more than one cylinder to perform such operation.

The first cylinder dumps the assembly carrying clamp mylars, pins and then this assembly performs the required operation. In this unit, we should make sure that in the open position of panel, we should be able to remove the panel. Below fig show dump unit.

 

Slide units

Slide Units are positioning units used to posiotion fixture, units, weldgun and robots. This unit consist of sliding rail on which entire unit is slide in direction of rails for further operation. Sliding unit consist of open and close position. These sliding unit is commonly used in automotive industry for different similar components.