Week 3:- BiW Fixture Design Methodologies Challenges

                  - Usually two locating pins are enough to properly locate the work piece on one plane.

                  - There are dozens of styles of locating pins that can be utilized in a design. We will explain the structure and show an example of how each style can be applied.

                  - One of the most common pins is a stepped pin with either small or large head.

Q-15 What are the fundamental to design a sensor unit.

        Adding Sensors To Weld Fixtures.

       The conversation about whether to put sensors in weld fixtures is one we are having more frequently as manufacturers continue to invest in automating weld processes. There are several types and options           when it comes to sensing. But before getting into details, the first question to be asked is “what problems are you trying to solve?” Adding sensors can help control quality and manufacturing issues, but it             can also add unnecessary complexity and maintenance costs. Before assuming it is the magic bullet for solving quality and manufacturing issues, make sure you are aware of the downsides of adding                   sensors to your tooling as well.

       Below we’ll outline some applications and options for incorporating sensors, along with some of the pros and cons with sensing in weld tooling. However, please note that incorporating sensors into weld                 fixtures has countless nuances and variables that can’t be covered in a blog article. This is just a basic overview to explain some of your options. If you would like to learn more about leveraging sensors for           your next fixture project, we encourage you to reach out to one of our project managers to review your specific application.

        Weld Fixtures and Proximity Sensors 101

Proximity sensors are one of the most common ways to incorporate sensing into weld fixtures. These sensors can be used in a variety of applications including part presence, poka-yoke, or even position verification.

Proximity sensors are categorized two ways – normally open or normally closed. Another way to think about this is the sensor verifying something is either present or not present. Both applications are used in weld fixtures. Other proximity sensors including capacitive proximity sensors, photoelectric sensors, and inductive proximity sensors. The materials and applications determine the type of sensor required. Proximity sensors also have a variety of field or beam specifications.

Typically, sensors are tied into an I/O (input/output) block or stand-alone PLC (Programmable Logic Controller) on the fixture. If they are tied into an I/O block, you can connect the sensors on the fixture to your robot. This allows robot programming to incorporate logic into the weld sequence like, “don’t start welding if all the parts are not present” or “make sure this hole is in the right spot before welding” or “open this clamp once this weld is complete”.

If the sensors are tied into a PLC on the fixture there is usually an HMI (Human-Machine Interface) as well. You can simplify the logic by just having red light/green light indicators, but if you are investing in sensing it usually makes sense to have an HMI as well. An HMI will give you a wide range of control and numerous options for using the proximity sensors. We are not getting into that level of detail in this article, but if you would like to discuss the options and details our team would be happy to assist you.

Part Presence Sensors

Incorporating proximity sensors for part presence is one of the most common applications when adding sensors to your weld fixture. The sensor will sense whether a part present or not – pretty simple (in theory). The obvious benefit of part presence sensors is you can verify all the component parts are loaded before either clamping or starting the weld sequence. This keeps you from welding your fixture if something is missing, which is a good thing.

You don’t necessarily need to sense every component part in the fixture in every application. Sometimes there is only one or maybe just a few critical component parts that require part presence sensing. Complex and/or high cost weldments are typically good candidates for part presence sensors.

One major downside to adding part presence sensors to your weld fixture is restriction of weld access. Not only do you need space for the proximity sensors, but the components to hold the sensors, as well as weld and spatter protection for both the sensor and the cables. This adds potential maintenance issues and costs.

Poka-Yoke

Poka-yoke is another common application for proximity sensors. The term comes from the Japanese phrase for helping a machine operator avoid mistakes (poka yokeru). Poka-yoke applications can verify the addition of left hand vs. right hand parts or indicate if a part is loaded backwards. Adding proximity sensors for poka-yoke applications can help reduce operator errors and decrease scrap rates.

Verifying secondary processes on incoming component parts, like checking for holes and location, is another common application. These applications keep the welder or robot from welding components with missing holes or secondary processes like forming, punching, etc. Of course, it’s better to check these component parts at the source, which will be another article. But whenever you catch them, it’s better to notice these types of mistakes before adding weld cost, having to grind welds off, or scrapping the parts all together. Anyone who has ever has to grind welds knows that should be avoided at all costs!

Position Verification

Position verification is another application for sensors. This is especially common when using multiple sub-assemblies and changeovers to accommodate similar but slightly different weldments using the same base fixture.

Options range from using proximity sensors to verify the correct sub-assembly is mounted to the base fixture in the correct spot to calling up the corresponding weld program according the relative sub-assembly. This can also be a great tool for verifying multiple length parts in an assembly or accommodating multiple lengths by using a linear rail. Sensors can verify the position of the linear rail quickly and reliably.

Of course, this can add complexity and cost to the fixture, so the cost benefits have to be weighed in each application.

Clamp Open/Closed

Verifying clamp open, clamp closed, or both is also a very common sensing application. Again, these are usually tied into either an I/O block or PLC on the fixture.

This application is very common in robotic weld tooling. Verifying clamps are closed helps prevent the robot(s) from crashing into open clamps. Creating weld programs that avoid both open and closed clamps is an obvious work around, but this can add complexities and programming time, not to mention inefficient robot paths.

Another application for clamp closed sensing is when you are rotating the fixture upside down (usually for weld access on the backside). Having sensors for clamp closed adds a level of safety and prevents the operator or robot from rotating the fixture and having parts fall out. This can be a major safety concern, especially when dealing with heavy parts.

Clamp open sensing has many applications and benefits as well. Verifying clamp open is tremendously beneficial when incorporating part ejection, as you can imagine. Hard to eject a part when it is still clamped! It is also crucial when integrating any sort of automated part tending or load/unload automation.

Pros and Cons

While there can be a lot of benefits to using sensors in your weld fixtures, there are also added costs, the possibility of increased maintenance requirements, and other potential issues that can compound in the process. If you can clearly ask “What problems am I trying to solve?” and state a solution that incorporated sensors can solve, then yes, it’s a good idea to look at the options. However, in our experience, if you cannot definitively say WHY you need sensors, adding them can cause just as many – if not more – problems than it solves.

There are also other options for verifying and controlling processes that are more mechanical in nature, for instance, incorporating logic into your pneumatic or hydraulic systems. We do this routinely for many applications. Logic can verify parts are located and/or seated correctly, check to make sure a hole is present for a poka-yoke application, or ensure clamps are open before parts are ejected pneumatically. Stay tuned for a more in-depth discussion of this in a future blog post!

Again, incorporating sensors into weld fixtures has countless nuances and variables that can’t all be covered here. This is just a basic overview to know some of your options. If you would like to learn more about leveraging sensors for your next fixture project, I would highly encourage you to reach out to one of our project managers to review your specific application. We would be happy to help any way we can.

Q-16 What is rough locator unit ? What are the fundamental to consider while designing it.

      - Rough locators helps to locate workpieces in the automation process. Locating refers to the desired location where you want the workpiece to be when it is getting worked on either by a                                        person, team, or robot.It is a device to establish and maintain position of a part in a jig or fixture.

        The basic fundamental to consider while designing :

        - Rough locators should be placed at edges of the car panel which has to guide.

        - Rough locators should be placed at the same angle of the car panel edge with min. distance of 2-5 mm from the edge of the car panel.

        - Rough locators should guide the panels in pin assembly direction in general.

        - The slot should be in direction of car part only.

Q-17 What is a base unit ? Describe its parts.

       - 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 of base unit :

       1. Valve box

       2. Truncking channel.

       3. Measuring hole cover.

       4. Eyebolt 

       5. Pedestal

       6. Floor plates.

      1. Valve box.

         - A valve box is a box that supplies air to all the pneumatic cylinders assembled in the fixture valve box consists of one solenoid valve with one inlet & one outlet. The outlet in the solenoid is used to

           supplies air to the pneumatic cylinders from the valve box whereas , the inlet in the solenoid valve is used to collect the air from pneumatic cylinders to the valve box.

       2. Truncking channel.

         - Tuncking channel is kind of cable duct. Which helps to guide & protect the wiring / tubes used in the fixture.

         3. Measuring hole cover.

           - In the measuring hole cover the co-ordinates points are engraved on it. The hole which mentions the co-ordinates gives the position & placements of the particular units.

           - The measuring hole helps in CMM & OC inspection.

         4. Eyebolt.

           -  The eyebolt is bolt with loop at one end , they are firmly attach a securing eye to structure so that ropes or cable may then be tied to it for lifting purpose.

           -  Eyebolt is used to drag or lift the base unit while relocating.

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

           6. Floorplates.

              - Floor plates are used to mount the entire base unit with floor.

              - also it helps to achieve flatness for the future.

Q-18 What is dump unit & what are its function ?

       - Dump unit is the complex unit to design due to space constains there is less space avilable & have to adjust all the parts in available space. It consist of dump cylinder to perform the operation of clamping           & unclamping car panel.

        Function of dump unit :

        - To ensure proper resting of the panel being welded and to restrict its motion. To ensure there are is no rotation in the panel and to fix it either by pins or side blocks or magnets.

Q-19 What is a slide unit ? mention were slides unit are commonly used.

         - Slide units are positioning units , which are used to position of the car part or panel units weld gun , slots for further operations.

         - Slide units may be classified into two types :

           1. Handed guideway.

           2. LM guideway.

          - Slide units may be further classified into three types based on prime movers :

            1. Manual slides

            2. Hydraulic / pneumatic slides.

            3. CNC slides 

           - It may also classified depending on applications :

            1. Horizontal slide unit.

            2. Vertical slide unit.

            3. Angular slide unit.

          Fundamental of slide units design :

          1. Reverse stroke of 10 mm to be consider in both forward & retracted conditions.

          2. Cylinders & LM guides to be validated for load & stroke.

          3. LM guide rail length to be standard & more than the actual stroke.

          4. Master guideway should be constrained & the subsidiary guideway to be free.

          5. Mechanical hard stop to be considered for both extented & retracted condition.