Optimizing precision fluid dispensing in the assembly of automotive components

Looking to optimize fluid dispensing in your auto assembly operation?

According to Today’s Motor Vehicles:

Automotive component manufacturers face production challenges. Among the most vital is maintaining a high level of product quality, supported by consistent production throughput with systems that ensure profitability. A key function is assembly, especially as the demand for more automated sensing and control devices, connectivity, infotainment, and green initiatives like electric vehicles, continue to push the need for more complex assembly requirements.

The need to manufacture more complex assemblies poses challenges for process engineers in their manufacturing and assembly functions. Automotive component manufacturers are mandated by stricter requirements to document quality assurance of their manufactured products along each step of production.

Fluid dispensing

Critical to meeting strict requirements is the need to deposit very small and precise amounts of fluid – such as adhesives, greases, silicones, and lubricants – to the component parts during the assembly process. These deposited fluids can also provide the added benefits of mechanical strength, thermal conductivity, dielectric strength, and chemical inertness throughout the life of the assembly.

The tiny amounts of adhesive, silicone, and other fluids must be dispensed reliably and accurately in dosage and placement. The precise positioning and quantity of these fluids deposited on the parts is critical to these products’ assembly, function, quality, appearance, and viability.

This technique of depositing tiny volumes of liquid spans assembly applications in automotive component manufacturing that require the precision dispensing of oils, grease, and lacquers.

The ability to deposit very small and precise amounts of fluid is a challenge for automotive manufacturers of tiny micro-electronics and other minuscule parts. Substrates are becoming more crowded and uneven in nature. Such is the case with printed circuit board (PCB) assembly.

Dispensing fluids onto hard-to-access areas, uneven or irregularly shaped surfaces, or delicate substrates are key factors that need to be carefully assessed as they can considerably impact assembly production. They directly affect the Z-axis movement of the dispensing system, influencing its ability to move over uneven surfaces and dispense the correct volume of fluids in the right locations. Cycle times for fluid dot deposition and throughput rates are regulated to some extent by the substrate surface topography.

The variety of fluids and fluid viscosities that can be dispensed in automotive assembly spans a considerable range – encompassing epoxies, adhesives, silicones, greases, oils, flux, lacquers, solder paste, and solvents. There are many formulations of fluids, each specially manufactured for different application techniques.

The fluid dispensed must readily flow through the dispensing heads. Once the fluid reaches the part, it must have the ability to restructure and recover to keep it from spreading and contaminating other components.

Other properties of the fluid that must be considered for dispensing include its density and weight, whether it has abrasive fillers, and whether it is safe to dispense or combustible. The fluid properties can also be modified by the dispensing process. Temperature variation within the environment of the dispensing system can change the viscosity of the fluid, affecting the fluid pressure and line speed.

Whether applying UV cure glue to a sensor PCB, grease or lubricant into automotive switches, anaerobic glues into connectors, or high-viscosity grease into multiple surfaces of an automotive part, characterizing different fluids and determining the best dispensing parameters for a specific application are important factors for implementing a successful dispensing process for any automotive component assembly.

Parameters for precision fluid dispensing in automotive parts assembly

Fluid dispensing in the assembly of automotive components encompasses a range of methods that can accommodate specific fluid application processes with a wide scope of functionality. The latest benchtop and robotic dispensers provide a high degree of process control, capable of dispensing adhesives, solder pastes, lubricants, and other assembly fluids with high consistency.

Handling fluid dispensing of dots, beads and fills under a broad range of conditions, these units are equipped with multiple capabilities to refine the dispensing process. From precision benchtop fluid dispensers, pneumatic valve systems, piezoelectric jetting valve systems and in-line robotic dispensing systems, there are factors that would support adopting a more efficient and controlled dispensing method in the assembly of automotive components:

  1. Shot-to-shot repeatability and accuracy are considerably improved as a more automated and controlled dispensing approach is employed.
  2. Increased productivity is clearly a benefit that comes with increased automation.
  3. Part quality improves when switching from manual squeeze bottle dispensing to air-powered dispensing, and further along to in-line automated dispensing, because operator-to-operator variance is significantly reduced. The ability to set the time, pressure, and other dispensing parameters for an application improves process control and ensures the right amount of fluid is placed on each part.
  4. Rework and reject rates lessen when upgrading to more automated dispensing solutions, thus improving the yield of the manufacturing lines and greater profitability to the manufacturer.
  5. The amount of assembly fluid used decreases significantly when using a more controlled method of dispensing.

It is important to consider each of these five points, as they represent the actual cost-to-benefit factors influencing fluid dispensing processes in automotive parts assembly.

Shot-to-shot repeatability & accuracy

Shot-to-shot repeatability and accuracy are critical factors in fluid dispensing, and with particular importance in the manufacture of automotive components. Depositing the right amount of fluid has a compounding consequence of maintaining product integrity and keeping downstream production moving. In a bonding application, if too much fluid is applied, it can take longer to cure, which will delay production downstream. If too little fluid is applied, the part will not properly bond, again interrupting downstream assembly or causing a failure in the product. Precision dispensing systems apply shot-by-shot repeatable amounts of virtually any manufacturing fluid, by using digital timers and precision air regulators to determine the amount of material applied.

The latest generation of fluid dispensers can distribute practically all assembly fluids from thin solvents, thick silicones, and brazing pastes with greater accuracy. They deliver exceptional throughput and process control, with consistent deposits from the beginning to the end of the fluid reservoir.

For the precise application of adhesives, lubricants, paints, solder pastes, two-part epoxies, UV-cure adhesives, and other assembly fluids, precision dispensing systems enable optimal results.

The consistency and repeatability of precision dispensing systems goes beyond the actual dispensing equipment itself and is also dependent upon the quality and proper usage of the system components. These consumable plastic components such as syringe barrels, adapter assemblies, pistons, caps, and dispense tips are designed to meet the requirements of different types of fluids and applications, and to dispense the most precise fluid deposit possible.

To achieve the highest level of performance from these dispensing systems, several requirements need to be inherent in their manufacture and usage:

  1. Each of the consumable plastic components should be designed as part of a complete, integrated system. This will improve yields and reduce costs by producing the most accurate, repeatable fluid deposits possible. Mixing and matching components from different systems or suppliers is a recipe for diminishing performance.
  2. Maintaining precision shot-to-shot repeatability in dispensing starts with quality manufacturing of the components. For best performance, all components should be certified that no silicone mold-release agents are used in the precision molding process, or at any other time during the production of the dispensing components.
  3. The dispensing components should always be used as single-use consumables. In high-precision dispensing systems, barrel internal diameters (IDs) and piston diameters, as well as dispensing tips, are manufactured with tolerances that make any residue from prior dispensing residing in the barrel, piston or tip degrade dispensing repeatability performance. Once the piston reaches the bottom of the barrel, the barrel, piston, and tip should be discarded.

Process control

The ability to set the time, pressure, and other dispensing parameters for an application improves process control and ensures the right amount of fluid is placed on each part.

The latest generation of fluid dispensers provides a high degree of process control for dispensing applications in the assembly of automotive components, capable of dispensing adhesives, solder pastes, lubricants, and all other assembly fluids with high consistency.

Fluid dispensing of dots, beads, and fills can be achieved with dispensing equipment features such as a 1-100 psi air pressure regulator, timed-shots, vacuum control to keep thin fluids from dripping, digital time/pressure displays and electric foot pedals. Time adjustments can be as fine as 0.0001 seconds, and constant-bleed air pressure regulation will provide reliable control when dispensing any type of fluid.

Some of the latest fluid dispensers allow programmable sequencing to automatically adjust dispensing parameters, making them ideal for applications that involve two-part epoxies and other fluids that thicken over time or get thinner as ambient temperatures rise.

Another feature supporting precision dispensing, which is particularly applicable for automotive component manufacturers, is Automated Optical Inspection (AOI). When coupled with CCD cameras and confocal lasers, Nordson EFD vision-guided automation platforms provide optical assurance of fluid deposit volume and placement accuracy, ensuring a conforming deposit.

With robotics, using the robot’s existing vision systems, the AOI software verifies fluid deposit widths and diameters. With the AOI confocal laser, the system measures the height of a fluid deposit in addition to the width and diameter, providing 3D deposit verification and determines if dispense requirements have been met. The confocal laser detects deposit height measurements regardless of the transparency of the fluid, which can sometimes distort quality data. Constant closed-loop feedback delivers automated quality control data, saving automotive component manufacturers time and costs.

Fluid dispensing challenges with automotive components

The following examples represent key applications where fluid dispensing challenges exist for automotive component manufactures, and solutions to improve product quality and assembly productivity.

EV battery module assembly

Jet valves, dispense valves and automated dispensing systems help manufacturers produce high-performance, defect-free batteries at faster production speeds by applying precise amounts of assembly fluids within tight deposit size and positional tolerances. Several types of dispensing solutions are used to produce the Lithium-ion (Li-ion) battery cells and hydrogen fuel cells used to power electric vehicles.

Battery module dispensing applications require various low- to medium-viscosity adhesives to glue components together in battery module assemblies for electric cars. Within the battery management board of EV battery packs, precision valves are required to dispense extremely precise amounts of solder paste, UV-cure adhesives, and other assembly fluids.

Adhering anode, separator, and cathode layers – This process requires small, precise amounts of material to be applied to attach more than 100 thin electrode layers in the production of cylindrical and prismatic Li-ion batteries. The application requires a very fast dispense time between one and four seconds per dot of UV-cure adhesives and epoxy material applied between the anode, separator, and cathode layers of each battery cell.

For this application, jetting systems provide the most control at the high speeds required for this dispensing application. Jetting systems like the Nordson EFD PICO Pµlse jets fluid deposits as small as 0.5 nL at up to 1000Hz (deposits per second) continuously. Since it does not require Z-axis movement, the PICO Pµlse can jet extremely accurate, repeatable deposits over uneven surfaces.

Electrolyte filling – The processmust be able to withstand the corrosive properties of the electrolyte and dispense accurate, repeatable amounts of material to transport the positive lithium ions between the cathode and anode layers.

The solution is a valve with an acetal copolymer fluid body for dispensing corrosive materials, such as electrolytes. One such valve is the Nordson EFD 702V-A Series mini-diaphragm valve, its unique design prevents trapped air and bubbles from affecting the quality and performance of battery cells.

Sealing to prevent short-cuts – Accurate, repeatable amounts of UV-cure adhesive are required to seal the top of cylindrical and prismatic battery cells to prevent short-cuts. Jetting dispensing systems provide the speed and accuracy needed to keep up with the throughput and quality assurance requirements of this application.

Greasing of switches

Applying enough grease to dampen the sound of plastic-on-plastic and metal-on-metal friction, but not too much that would seep out of the control panel, is a critical grease dispensing challenge in the assembly of switches for automotive door locks, windows, mirrors, wiper signals, turn signals and headlamps.

The switches can have varying part tolerances that can cause major process control issues as the dispensing tips may crash into parts that have a variance in thickness, which contact dispense valves cannot accommodate.

A viable solution is non-contact jet valves for the dispensing of greases to switches, which eliminate the need for Z-axis movement, allowing the jet valve to accommodate varying part tolerances. One example is the Nordson EFD Liquidyn P-Jet jet valve, which will dispense low- to medium-viscosity greases in extremely accurate, repeatable beads and lines. Micro-deposits as small as 3 nL can be applied at up to 280Hz. Such non-contact jet valves allow the manufacturer to apply the exact amount of grease needed for the automotive switch application and prevent material from seeping out of the automotive switches.

Lubrication/greasing of moving parts

Automotive manufacturers need to apply consistent amounts of oil and grease to a wide range of automotive parts in final assembly – such as moving parts in armrests, springs in door handles and door trim. These lubricants are applied to facilitate smooth movement and to prevent squeaking.

Sponges and brushes have been used to apply oil or grease to these moving parts, which has led to a significant amount of time required for cleaning up excess fluid on surrounding parts to prevent rejects and quality issues.

The solution is the application of fluid dispensing spray valves, such as the Nordson EFD 781S Series spray valve, which provides exceptional control for reliable, consistent coatings of low- to medium-viscosity fluids. Fluid can be reliably sprayed in microliter to milliliter amounts, in round patterns with diameters ranging from 4.3 mm to 50.8 mm, and in fan patterns up to 165.1 mm wide.

This valve allows for adjustable fluid flow, adjustable nozzle air, and post-air cutoff to provide superior spray control without waste, mess, or overspray. This means fluid goes exactly where it is needed, improving consistency with reduced fluid use and cleanup costs.

Thermal management for ECUs

In the applying of thermal interface materials (TIM) to heat sinks of electronic control units (ECUs), the conventional approach has been to apply thermal tape or thermal gap pads manually instead of thermal grease because of cost reductions. But the pads do not always conform to different gap geometries between the heat sink and the ECU, which does not allow consistent coverage of thermal material on the part.

For some TIM applications, automotive manufacturers use a handheld fluid dispenser to apply fluid manually, which allows coverage that thermal tape and gap pads do not always provide. But dispensed manually, coverage inconsistencies frequently occur due to operator-to-operator variability.

A solution to this issue is progressive cavity pumps, such as Nordson EFD’s model 797PCP progressive cavity pump, which is designed for applying thermal paste into heat sinks that are attached to ECUs. The pump provides a perfectly sealed metering chamber that prevents shear, pulsation, and squeezing of the fluid that can sometimes crush delicate fillers and particles used in thermal pastes.  The pump delivers highly precise fluid volume accuracy and repeatability at +/- 1%, for consistent fluid application. This ensures 80 – 90% coverage of TIM on every part, every time.

PCB conformal coating and sealing

Coating densely populated PCBs in vital automotive electronic components is critical to waterproof and prevent corrosion and oxidation. This requires precise deposition of fluid, such as HumiSeal conformal coating, into narrow, hard-to-reach areas without over deposits and migrating of the coating, which could lead to contamination of other parts of the board and potential product failure.

Manufacturers commonly use a film coater to selectively apply conformal coatings. To facilitate application with this system, the coating is frequently diluted with a solvent to improve its flow characteristics. Thinning can lead to over-deposits onto areas where coating should not go, potentially reducing the integrity of the coating to effectively protect the board and adding production steps to manage the over-deposits.

Replacing the film coater with a jetting valve, such as the Nordson EFD PICO Pµlse jet valve, allows manufacturers to apply the exact amount of conformal coating needed without diluting the fluid first. The jet valve provides precision dispensing control at high speeds up to 1000Hz (cycles per second), resulting in reduced voids in the dispensing area, increasing first-pass yields.

Window sealing

Automotive window sealing applications are dependent on consistent dispensing of urethanes and sealants. Many of these applications require consistent bead or line widths dispensed within tight tolerances. Defects of any kind become costly scrap or rework. Reliable and low maintenance dispense valves must meet the controlled, high-volume production requirements necessary in the automotive manufacturing industry.

When dispensing high-viscosity urethane, for example, manufacturers face issues with clogging in the dispense valves when sealing windshields and sunroofs, creating excessive downtime for maintenance. Using a high-pressure valve system which is better designed for dispensing high-viscosity fluids not only cuts the need for maintenance but reduces waste by minimizing premature curing of the urethane.

High pressure valves, like the Nordson EFD 736HPA-NV Series, apply uniform amounts of thick materials, like urethanes, at pressures up to 2500 psi. Adjustable stroke control keeps consistent dot profiles and bead widths, prevents drooling between shots, while helping to reduce opening surge and regulate snuff-back cutoff.

Dispensing low- to medium-viscosity fluids, like primer sealants on window trim, require a dispensing valve that delivers fine flow control to create a cleaner, higher quality finished product, while minimizing fluid usage. The Nordson EFD 752V Series is such a valve, providing an open/close stroke that is adjustable from 0.13 mm to 0.64 mm, producing a very fast response and positive shutoff, with valve actuation speeds as short as 5 to 6 milliseconds, and operating with cycle rates as high as 800 cycles per minute.

Robotic dispensing

Robotic dispensing has evolved to support the needs for higher throughput automotive component assembly production by developing specialized dispensing technology for automated inline assembly and manufacturing systems, and for stand-alone production devices.

Many applications involve attaching a valve to a 6-axis robot arm or using the valve with a 3-axis tabletop robot. An example is mounting a PICO Pµlse jet valve on Nordson EFD’s vision-guided 3-axis EV Series dispensing robot for conformal coating in densely populated PCBs. When combined, the exact amount of fluid is applied in the exact location required on the PCB.

The 3-axis EV Series dispensing robot can also be combined with the Liquidyn P-Jet jet valve, which is designed to dispense low- to medium-viscosity greases in extremely accurate, repeatable beads and lines. Because the need for Z-axis movement has been eliminated, manufacturers can react very quickly to lubrication of new and different parts.

A 3-axis fluid-dispensing robot can also be applied for adhering anode, separator, and cathode layers for EV battery production. Robotic dispensing systems, such as the Nordson EFD GV Series gantry dispensing robot, provide the conveyor-fed assembly required by Li-ion and hydrogen fuel cell electric car battery production. The robot’s 3D motion control allows programming of dots, lines, circles, arcs, and compound arcs. Fluid deposit placement and Nordson EFD accuracy is verified with automated optical inspection (AOI) software. When paired with the system’s confocal laser, the AOI system measures the height of fluid deposits, in addition to width and diameter, providing 3D dispense verification.

Manually spraying lubricant on parts, such as door trim, armrests and door handles on the assembly line can be robotically automated with a 6-axis articulated robot. The Nordson EFD 781S Series spray valve, for example, can be applied for either manual use or robotic automation. The robot provides the flexibility, strength and reach needed for the application of lubrication to many types of automotive parts.

Requirements for robotic fluid dispensing are as varied as the differences in production environments. Identifying these requirements will facilitate the selection of the most optimum dispensing and robotics system for the application.

Consult with a fluid dispensing professional

Because so many factors can impact a fluid dispensing process, it is important to consult an experienced fluid application specialist who knows the specifics and priorities influencing dispensing for a particular automotive component application.

Consulting with an application specialist early in a project will ensure the correct fluid dispensing equipment is utilized, and the most optimum process has been put into place.  This will facilitate manufacturing to achieve the desired production throughput, and improve process control, while reducing rework, rejects and fluid waste.

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