Week 3:- BiW Fixture Design Methodologies Challenges
What is design methodology?
Design methodology is sequence of steps which we have to follow while doing design.
Above image is of design methodology and steps involved in it.
1. Purchase Order: We start designing after customer fives us purchase order. So, basically it is indication to start designing of particular fixture.
2. Inputs from customer: Customer gives us requirements 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: It consists of lots of data like 3D and 2D documents, VMC IGES files, STEP files, gas-cutter or laser-cut files in dwg format and BoM etc. We have to give these data to our customer as design output.
Q2. What are the inputs required from customer to start design a fixture?
Following are the inputs required from customer to start design work:
1. Function requirement: Generally, function requirement means for what purpose we are going to design fixture like welding, gluing or riveting fixture and inspection fixture.
2. Preferred standard components: While designing fixture, we have to use standard components as much as possible to save time, money and efforts to design, manufacture that non-standarrd components.
3. Car product: It consist of 3D, read files, geometric tolerance and PLP (Principle locating points) of fixture.
4. Layout: Layout is nothing but management of space which helps to understand process or flow of work of entire assembly line.
5. Ergo data: Every company have standard ergo data and they provide it to fixture designer to design fixture considering that points. Example: Height of fixture is decided according to ease while working on fixture. So, we have to design a fixture by considering safety, easy and fool proof design.
6. Weld study: In this input, customer specify which type of welding is required to join components according to which we have to design fixture.
7. Standard detailing template: Customer gives us standard detailing template, so we can use that to detail or dimensioning components according to that template.
Q3. What is the input we get from the ‘Car Products’?
1. GD&T: GD&T of each part is given in car product in which information of locating pins, clamps, rest and slides are mentioned.
2. Part list: It states about the parts and assembly style. Part list consist of unique part names of each and every parts in assembly and each part has its own part number which helps while assembly process to identify each and every part in assembly.
3. Cad files of car part
4. Clamp plan: It is one of the important data while designing fixture because clamp plan mentions location of clamps in which component is going to clamp.
5. Product assembly process sheet: In product assembly process sheet, sequence or stages of assembly of components are given.
Q4. What is clamp plan?
Clamps are nothing but a mechanism or component used to hold or clamp job in fixture securely. Clamps are manual type, hydraulic type or pneumatic type depending on the customer requirement.
Clamp plan mentions or gives the location of clamps in which component is going to clamp. We can’t change clamp location without customer’s approval. Clamp plan also provide information regarding location of pins, rest, clamps and dumps.
Q5. What is the purpose of layout?
Layout is nothing but management of space which helps to understand process or flow of work of entire assembly line. Below image is one of the example of layout.
Layout is used to achieve more efficiency or coordination of 4 M’s (Men, Material, Machines and Methods). Plant layout is simply floor plan for arranging machinery and equipment present in plant and these things are arranged according to its usage, easy for everyone to use particular equipments or machinery, should not disturb flow of material. Actually, layout is very helpful to save time and money in plant.
Q6. What is ergo data?
Every company have standard ergo data and they provide it to fixture designer to design fixture considering that points. Example: Height of fixture is decided according to ease while working on fixture. So, we have to design a fixture by considering safety, easy and fool proof design. Ergo data is used to reduce human errors, increase productivity, human comfort and safety.
Q7. What do you understand by Weld study?
Weld study is nothing but a study of welding gun that we are going to use in welding fixture and where we are going to weld. It consists study of welding gun details, weld matrix, weld point, geo weld points and re spot weld points etc. Weld study consists of study of following points:
1. Weld gun details
2. Weld matrix and weld points (Weld spots)
3. Geo weld points and re-spot weld points – Weld points are divided using color code, one of them is red color points and remaining points has green color. In these, red color points indicate geo weld points which are going to weld in geo tool and green color points indicate re-spot weld points which are going to weld in re-spot tool.
Q8. What are the criteria in percentage completion in designing stage? Explain it in detail.
To complte 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 percentage completion criteria is as below:
1. 0-25 % (Input & concept design): In this stage of percentage completion criteria, we have to build concept design of fixture
2. 25-40% (Concept approval and simulation): In this stage, concept design is approved by customer and gives some correction points if any. Later we have to give working simulation of fixture for better understanding of how fixture works.
3. 40-85% (Design freezing and detailing): If all requirements and specifications of customers are satisfied then design is freezed and detailing work starts.
4. 85-100% (Check and final dispatch): Quality checking is done using CMM and then dispatched to customers.
Q9. Brief about output in design?
Design output consist of lots of data like 3D & 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:
1. Unitised tool: This tool consist of two types of sheets, they are as follows:
a. Key sheet: It contains the location of every units in fixture
b. Layout sheet: Layout sheet is detailed drawing of particular unit in fixture
2. Non-unitised tools: These tools don’t require key sheet, Ex. Stands and tool changer. Tools that can stand alone and details in layout sheet.
Q10. What do you understand by structuring design tree? How does it reduce error during design process?
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.
Q11. What are Units? Mention types of 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.
Types of units:
1. Fixed pin unit: It is non movable locating unit which arrest movement of component in fixture.
2. Retract pin unit: These units having retracting unit which is used to move pin to ensure proper loading and unloading of component.
3. Rough locator unit: This unit help operator for correct loading of component
4. Rest unit: It is used to rest the component
5. Base unit: All the units in fixture are placed on the base unit
Q12. Describe fixed pin unit and their purpose?
Fixed pin unit is non movable locating unit which arrest movement of component in fixture. Figure 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:
• Main purpose of fixed pin unit is to locate the component
• This unit is used to arrest 6 DOF of component
• Two pins are used to locate component. First pin restricts 4 translational motion and other one restricts 2 rotational motion
Q13. What are the different parts of fixed pin unit?
Fixed pin unit is non movable locating unit which arrest movement of component in fixture. Figure 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.
Pin: Pins are main part in this type unit because it is used to locate component. 2 pins are used to restrict 6 DOF. In fixed pin unit, pins are fixed or non movable.
Pin Retainer: These are used support or carry pin in it as shown in fig.
Block: This can be machined in any desired shape according to fixture. It may be simple square or rectangular block or it may be L shaped block as shown in fig.
Shims or Spacer: These are used to compensate tolerance stack up. In pin unit we need to control two direction that are X & Y using shims or space. Shims are generally thin sized plates used in group called shim pack and spacer are used as single plate and can be machined accordingly.
Blade: Blades are bolted on riser as shown
Riser: These are used to increase height of unit and these are standard parts so need not detailed it or designed it.
Q14. What is the purpose of making a rest unit? Describe its parts?
Rest unit is one of the simplest unit in fixture used with myler. As rest unit is simple to manufacture and require low cost, hence rest unit is combine with clamp unit and location unit. Rest unit consist of following parts:
Riser: These are used to increase height of unit and these are standard parts so need not detailed it or designed it.
Shims or Spacer: These are used to compensate tolerance stack up. In pin unit we need to control two direction that are X & Y using shims or space. Shims are generally thin sized plates used in group called shim pack and spacer are used as single plate and can be machined accordingly.
Blade: Blades are bolted on riser as shown
Mylars: These are the parts in the rest unit which are in contact with car panel or component used to give support or rest to the component.
Q15. What are the basic fundamentals to design a sensor unit?
Sensor is a device which detect or measure a physical property. The unit which is built to sense the component or car panel using electrical sensors called Unit sensor. The output signal of sensor is then send to PLC for further process. There are different types of sensors such as proximity sensors, laser sensors.
Each components which are welded in fixture should be sensed. So, we manufactured or assemble component free from errors. Consider an example of car panel having multiple components to assemble using welding. These multiple components are going to be sensed by sensor to assure correct component is placed at correct position.
Q16. What is rough locator unit and what are the basic fundamentals to consider while designing it?
Rough locator are the parts used to locate component correctly in fixture, basically it guide the operator while loading component in fixture.
• They are used to guide the component to load correctly in fixture and placed at the edges of components.
• The angle in locator should be according to component
• Rough locator helps component to placed in pins used in fixture to locate component
• Entry angle should be 30-45 degree and rough locator should start guiding component before 10-15 mm to start the pin engagement.
• For easy adjustment rough locator mounted on base with two slots in it.
• The direction of slots are in the direction of car panel or component.
Q17. What is a base unit and describe it parts?
Base unit is used to provide base for other units such as location unit, rest unit or sliding unit in fixture. These all units are mounted on this base unit.
1. Floor plate: Plate which is used to join fixture and floor called floor plate.
2. Weld bars and Pedestal: Pedestal is support or base on which fixture is mounted.
3. Eye bolt: It is used to move fixture or place fixture on its place using cables or ropes. This threaded eyebolt is sustain 45 deg of angular forces.
4. Measuring hole cover: It is also known as tooling hole from which other holes on base are drilled. So, measuring holes are basically reference holes. These measuring holes are covered using measuring hole cover
5. Base plate: The plate on which all units are mounted called base plate. Base plate Is machined on both to achieve parallelism. Thickness of base plate is too thick to sustain load of all units.
6. Valve box & trunking channel: Pneumatic fixture consist of solenoid valve and these valves are placed inside valve box. Trunking channel protects all pressure inlet tube which are attached to pneumatic devices such as cylinders, clamps.
Q18. What is a dump unit? What are its function?
Dump unit is used due to lack of space on fixture to build an unit. So this is a complex unit consist of dump cylinder used for clamping or unclamping of car panel or component
Function: Due to space constraints dump unit used in fixture. It has dump cylinder having open and close position for better understanding of design. It also has clamp cylinder used for clamping purpose.
Q19. What is slide unit and mention where slide unit are commonly used?
Slide units are positioning units used to position fixture, units, weld gun 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.