Applications Focus: Vacuum Impregnation Enables Lightweight Material Use

OEMs are redesigning parts and bringing vacuum impregnation systems in-house to meet the demand for aluminum.

By Andy Marin, Godfrey & Wing

Recent decades have seen aluminum castings used much more in car manufacturing. Aluminum has been a key material in car manufacturing since the beginning. The first sports car featuring an aluminum body was unveiled at the Berlin International Motor Show in 1899. Karl Benz developed the first engine with aluminum parts two years later.1 Since that time, aluminum has become the leading material for various components and car models. Aluminum use now ranges from mass-market to luxury vehicles.

As this surge happened, vacuum impregnation became the primary method for eliminating the porosity inherent in aluminum castings.

CAFE Standards

Due to new federal fuel-efficiency regulations, automakers must meet Corporate Average Fuel Economy (CAFE) standards. The CAFE standard for 2017 passenger cars is 38.13 mpg. For light trucks, it is 30.67 mpg. These required averages will increase to 53.34 and 40.29 respectively by 2025.2

According to the U.S. Department of Energy, reducing a car’s weight by 10 percent will improve fuel economy by 6 to 8 percent.3 OEMs are investing in lightweighting frames and powertrains to meet these standards.

Lightweight Material

This investment means a greater use of aluminum. Incorporating aluminum has grown continuously to not only meet CAFE standards, but to also improve automotive performance. A vehicle with lower weight has better acceleration, braking and handling. Lighter vehicles can tow and haul large loads because the engine is not carrying unnecessary weight. Even though aluminum is light, it does not sacrifice strength. Aluminum body structure is equal in strength to steel and can absorb twice as much crash-induced energy. The rigors of aluminum structures give a better feel and precise control on the road. Aluminum means better fuel efficiency and driving stability.

But that presents a new challenge: porosity, which is inherent in the material. If the porosity is not sealed, fluids or gases will seep from the part when under pressure. Parts that leak fluids or gases are typically rejected, increasing costs and production delays.

Oil flowing in this channel is seeping through the porosity.

Vacuum impregnation seals the porosity (highlighted in green) so that the part will function properly without seeping oil.

Vacuum Impregnation

Vacuum impregnation seals metal porosity. The process was developed in the 1940s and has evolved in recent years to be safer, more efficient and more effective. Generally, the process has four steps.

Step 1
The part is placed in an impregnation chamber where a deep vacuum is created to evacuate air from the leak path.

Step 2
The evacuated leak path is filled with sealant by covering the part and applying pressure.

Step 3
The part is moved to a wash/rinse station. Here, residual sealant is removed from the part’s internal passages, taps, pockets and features where sealant is undesirable.

Step 4
The part is moved to a cure station. Here, the impregnated sealant is polymerized in the leak path with hot water.

Aluminum Vacuum Impregnation                          

Vacuum impregnation seals porosity without changing the castings’ dimensional or functional characteristics. This means manufacturers can use parts that would otherwise have been scrapped. It is a simple method and is approved by OEMs for a variety of components.

Two examples include:

Lower Crankcase                                                            

The crankcase shown in Figure 3 supports the crankshaft in the middle of the cylinder block. Made from cast iron, it would weigh approximately 45 pounds. Made from aluminum, it weighs just 18 pounds.

With vacuum impregnation, this lower crankcase retains its intended use without losing any dimensional or functional characteristics.

While the frame is aluminum, the bearing caps are steel. These steel bearing caps see increased force and pressure from supporting the crankshaft and bearings. So, they must be made from a denser, stronger material.

This case has passages that feed the bearings with oil. If the porosity in the aluminum is not sealed, oil will leak from the part. Vacuum impregnation enables this lower crankcase to retain its intended use without losing any dimensional or functional characteristics.

Cylinder Block

Another example of aluminum parts that use vacuum impregnation is the cylinder block. Made from cast iron, the block weighs approximately 185 pounds. Made from aluminum, it weighs about 70 pounds.

This cylinder block is made from aluminum, while the cylinder bores have steel liners. It weighs more than 100 pounds less than a cast-iron version, and the vacuum impregnation process enables the part to be pressure tight and fully functional.

 

The cylinder block shown in Figure 4 is manufactured from aluminum while the cylinder bores have steel liners. The bores would not be able to withstand the wear or heat force if they were in aluminum.

Fluids and gases flow through this part while in use and can seep from any porosity in the aluminum. Once again, vacuum impregnation keeps the part pressure tight and fully functional.

As part designs have changed, so, too, has the use of vacuum impregnation.

Vacuum Impregnation Systems

To meet the increased demand for aluminum components, OEMs have brought vacuum impregnation systems in-house. Aluminum accounts for 400 pounds per car. It is expected to reach 550 pounds by 2025. To meet this growing demand, OEMs are taking advantage of recent redesigns in vacuum impregnation systems.

Until the 2000s, vacuum impregnation typically employed batch systems. Workers would load various parts from the top into a large basket for processing. Batch systems were prone to quality issues. Complex castings were difficult to impregnate. Large batches could not be adequately washed and rinsed, increasing sealant contamination. This rendered many parts unusable or jeopardized assembly.

Additionally, large batch systems increased WIP (work in process), labor and maintenance costs. Floor space to lay down large incoming batches, inspect and pack out impregnated parts was too costly and impractical in today’s machining and assembly plants.

This forced manufacturers to outsource their impregnation requirements. Expensive outsourcing solved the labor and floor space issue, but poor quality (now out of the manufacturer’s care, custody and control), costly transportation and production delays emerged as critical issues.

The redesign of vacuum impregnation equipment offered the following benefits:

Improved Quality

Equipment was redesigned to be front-loading and thus more ergonomic. And they were redesigned to process just single pieces or a small number of castings. This change increased seal rate while decreasing sealant contamination and damage.

Example of an ergonomically designed, front-loading system.

Improved Production

Systems were also redesigned for robotic handling between stations. This reduced cycle times improved overall production time and volumes. The new systems were smaller than batch systems, and their modular design let them integrate into other production operations. There was improved quality while eliminating WIP, unnecessary, costly transportation and production delays.

Modern robotic-handling between production stations reduces cycle times and improves production volumes.

Vacuum Impregnation System at Work

If the lower crankcase and cylinder block were processed in a batch system, the typical failure modes would be:

  • Parts leak after impregnation (poor recovery)
  • Parts damaged during the impregnation process
  • Contamination of parts during the impregnation process

These challenges can quickly cause quality issues and production delays. By impregnating these parts in a modern system, the expected results would be:

  • Near 100-percent casting recovery
  • Zero PPM for handling damage
  • Zero PPM for contamination

This is because single-piece flow packages parts so they are efficiently and effectively sealed. Batch systems stack parts on top of each other. This compromises the effectiveness of the cleaning and potential part damage. Robotics, on the other hand, properly and efficiently move parts between each station. This eliminates the risk of mishandling and sealant contamination.

Today’s programmable logic controller (PLC) and robotic-tended units are self-contained for quality. Working in tandem, the PLC and robot ensure parts that have not been properly impregnated do not move forward into production. Pre-set parameters control every step of the process. Should the system fault and any specified processing parameter is not met, the PLC will signal the robot to contain the suspect component for management’s evaluation.

In the same way, the smaller manually attended units have sensors and a PLC to control the process and alert the attendant to any irregularities.

Where the Action Is

Both the size and the modular design of the new impregnation systems mean manufacturers can locate the units immediately within the machining, testing or build areas, placing the solution right where it’s needed.

This cellular approach further reduces costs and improves production efficiency. Part handling, movement and tracking are reduced or all together eliminated, especially when compared to outsourcing.

Since all systems are PLC controlled, data acquisition, essential in today’s manufacturing environment, can be baked into the process to strengthen the plant’s overall quality-production system. Individual data points on all key parameters are collected and stored with individual part serial numbers. If questions arise, a system audit will provide valuable data on every part that has been impregnated.

Do More with Less

CAFE standards require manufacturers to “do more with less.” Manufacturers are specifying lighter materials and thinner walls with higher performance requirements and lower acceptable leak rates in castings. Vacuum impregnation helps make this possible.

References

  1. Automotive Quick Read. http://www.aluminum.org/product-markets/automotive
  2. (2011) 2017-2025 Model Year Light-Duty Vehicle GHG Emissions and CAFE Standards: Supplemental Notice of Intent. 2017-2025_CAFE-GHG_Supplemental_NOI07292011%20(2).pdf
  3. Brescher, S. (2012) 54.5 MPG and Beyond: Materials Lighten the Load for Fuel Economy. https://energy.gov/articles/545-mpg-and-beyond-materials-lighten-load-fuel-economy

 

ABOUT THE AUTHOR

Andy Marin is the Marketing Coordinator for Godfrey & Wing. He received a B.S. in marketing from John Carroll University and an MBA from Cleveland State University. He joined Godfrey & Wing in 2016, and manages the company’s marketing operations and communication.

 

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