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A commonly asked question is “What size of porosity can vacuum impregnation seal?” What seems like a simple, straightforward question is actually a complicated one. This blog will address the topic by describing the basics of die casting porosity, and what vacuum impregnation will seal.
Porosity
While some refer to porosity as a defect, it occurs naturally and is found in most materials, both man-made and in nature. In metal castings, porosity is typically considered any void found in the casting. Casting porosity can be caused by gas formation or solidification while the metal is being moved from a liquid state to a solid state. This porosity can range in size, from sub-micron to voids greater than 10 mm, depending on the casting.
Metal casting porosity can affect the part’s structural integrity, creating a failure point. Porosity can also prevent the part from being pressure tight. This will impact performance if the part is designed to hold gases or fluids.
What Does Vacuum Impregnation Seal?
Vacuum Impregnation is a process that seals metal casting porosity. Specifically, it seals the internal, interconnecting path of porosity, which breaches the casting wall. The process is not a surface treatment, so it does not seal open pores found on the casting surface. Nor is it intended to seal casting structural defects such as cracks or open knit lines.
Understanding Die Casting Porosity
It’s difficult to pinpoint a generic porosity range that vacuum impregnation seals because, generally speaking, one pore does not cause a leak path. A leak path is created through a series of interconnected pores. For example, a breach caused by a 5mm pore interconnected with a series of smaller pores will be easily sealed (Figure 1).
Figure 1: This sectioned casting shows a 5 mm pore that is interconnected to a series of smaller pores. Vacuum impregnation can seal this leak path.
Conversely, if the same 5mm pore breaches a 5mm wall it will be difficult, if not impossible, to seal as there is little casting material for the sealant to adhere (Figure 2). A pore of that nature has characteristics similar to surface porosity which is not a candidate for sealing through vacuum impregnation. The large open pore breaches the both casting walls and is sometimes called “see through” porosity. One needs to view the porosity in three dimensions to see how it is interconnected, not simply analyze individual pores.
Figure 2: Vacuum impregnation will not seal this surface porosity. There is not enough casting material for the sealant to adhere.
In Summary
The wide range of casting parameters creates a limitless array of shapes and sizes of porosity possibilities. Despite this, vacuum impregnation can seal porosity of any size. While vacuum impregnation can seal porosity of any size, it is important to realize that the leak path is the key characteristic to evaluate and not pore size. A leak path is created through a series of interconnect pores, and not a single pore. Instead of asking “What size of porosity can vacuum impregnation seal?” one should ask “Can vacuum impregnation seal the leak path?”
A future blog will discuss the topic of leak rates.
A global automotive part manufacturing company produces aluminum engine blocks, cylinder heads, and transmission cases. The company is a Tier 1 supplier to automotive OEMs, and has facilities through the world. As such it was actively looking for opportunities to increase its efficiency and output.
The Challenge
This company received a contract for a new large scale, engine block program from an OEM at one of its European facilities. The program’s quality standards forced the need for vacuum impregnation to seal the casting porosity. If the porosity is not sealed, then automotive fluids will leak from the part, causing a field return.
Previously the customer outsourced any impregnation projects to an outside vendor. Due to this country’s poor logistics and limited number of vacuum impregnation vendors, this approach was not feasible with this new program. These factors translated into three specific challenges for the customer:
- High Freight Costs– The freight costs associated with moving these parts to and from the outside source would be high.
- Increased Handling Damage–Previous impregnation vendors utilized a batch impregnation system. This style of system has a history of damaging machined features.
- Work in Process (WIP)–The transit time between the company and the impregnation vendor would cause the company to miss shipments to the OEM.
The company realized that it had to implement an impregnation strategy that would address these three challenges to reduce waste in the supply chain.
The Solution
Godfrey & Wing determined that the implementation of in-house vacuum impregnation technology would alleviate these challenges. The company proposed its High Value Low Volume (HVLV) single piece flow impregnation system for installation at the customer’s facility.
The HVLV uses the Dry Vacuum and Pressure (DVP) process, and Godfrey & Wing’s 95-1000AA recoverable sealant. The DVP process pushes the sealant deep into the micro porosity in order to improve sealing effectiveness. The 95-1000AA recoverable sealant is easy to use and remains stable and pure.
The proposed HVLV solution outlines multiple benefits to the customer:
- The system is a viable in-house solution that can easily be installed into the customer’s facility without any infrastructure changes.
- The single piece flow eliminates excessive handling, and handling damage.
- With a small footprint of 96 square feet, the HVLV system would integrate with other operations achieving continuous part flow. This allows the customer to meet production demands and eliminate WIP.
Having never qualified the HVLV, the customer ran samples at Godfrey & Wing’s technology center, located in Untergruppenbach Germany. The results clearly showed the HVLV’s DVP process created superior sealing results:
- 0% part damage
- 100% part recovery
- 0% part contamination
The customer also found the system simple and safe to use. The part fixtures and platform allows the operator to easily move a part from station to station. Each station starts with a push of a single button. The man-machine interface keeps the operator safe at all times. Light curtains, insulated panels, and ventless exhaust ensure ongoing operator safety.
The Results
The customer purchased two HVLVs. One HVLV is stationed at the customer’s foundry to seal parts after pre-machining (also known as hyper cubing), and the other system is stationed at the OEM to seal any parts that may leak after final machining.
The two facilities are 500 miles apart so the two in-house systems eliminate any production disruptions. After pre-machining, fix-on-fail parts are impregnated at the foundry. When the parts arrive at the OEM for final machining and assembly, only a reduced amount of material is removed. Since the impregnation at pre-machining has already sealed porosity, the opportunity to open an interconnected leak path is reduced. Any parts that don’t conform to standards after machining can be easily impregnated without disrupting production.
The HVLVs are making a significant impact by answering the following challenges:
- Reduce Freight Costs–The modular design allows the company to integrate the HVLVs directly into production, and eliminate outsourcing.
- Remove Handling Damage–The single piece flow eliminates the chance of damaging critical features.
- Eliminate WIP–The parts continuously flow from each in-house operation, enabling the customer to meet production demand.
In Summary
Godfrey & Wing’s HVLV proved that vacuum impregnation is a viable, in-house solution for producing pressure tight components. Throughout the supply chain, the HVLV is the perfect solution to eliminate production delays caused by logistics.
Vacuum impregnation is a process that seals porosity in metal castings. If left untreated, then the porosity creates a path for fluids and gasses to leak from the part. When performed properly, vacuum impregnation seals the porosity, but it is undetectable on the surface or in the machined features of the casting.
Before vacuum impregnation is applied in production, operators often request indisputable evidence that the process is capable. This is done by measuring key process characteristics of the vacuum impregnation process. Common processes that are tested are:
- Sealant gel time
- Sealant viscosity
- Vacuum level achieved and time
- Pressure level achieve and time
- Wash time
- Curing temperature and time
The sealant gel time test produces a test slug. Often the sealant slug is discarded after the sealant gel time. But before it is discarded, the operator should examine the slug’s color and clarity for other conditions. What is optimum is to have the sealant coming out of the system looking like the clean, clear sealant that originally went into the system. Below are three common reasons why the sealant may not match its original state:
- Dark
This is a result of varying amounts of contaminants that come from the impregnated parts, which consists of marker ink, carbon, dirty cutting fluids, dirty test fluids used to pressure test the parts, etc. 
- Cloudy
Too much water will cause the slug to be opaque or cloudy. Sealant can absorb water, but it cannot have too much water.
- Excessive Amount of Crazing
If the slug has an excessive amount of crazing, then this is a result of being over or under catalyzed. Crazing can cause the slug to easily fracture or crumble.
If any of these occur, then the possible action plan can include:
- Filter the sealant to ensure that it is free of contamination.
- De-gas by running additional vacuum cycles
- Add new catalyzed sealant to reduce crazing.
In Summary
Vacuum impregnation is a process that seals internal pores in metal castings. Sealing the porosity allows the part to hold gas and fluid under pressure. Measuring the key process characteristics and the sealant slug provide traceable, quantifiable and actionable data to keep the vacuum impregnation process effective.
One of the largest aluminum casting facilities in United States produces engine blocks and transmission cases for an automotive OEM. This facility supplies the vast majority of powertrain castings in support of the OEM’s assembly operation throughout North America.
The Challenge
The casting standards and aluminum characteristics forced the need for vacuum impregnation. The program was launched with a vendor that utilized a Dry Vacuum (DV) process in an older batch style vacuum impregnation system. Unfortunately, the system and process could not meet the quality demands of the foundry or the OEM.
The main challenges were:
- Poor recovery– 14% of the parts still leaked after impregnation.
- Contamination– Cured (solid) sealant remained in through and blind tapped holes.
- Part Damage– Damage to machined features from handling and the impregnation process.
These challenges caused missed shipments, quality alerts and increased rework costs. A better process was needed to deliver a higher quality parts.
The Solution
Based on the customer’s requirements and production quantities, Godfrey & Wing proposed the Dry Vacuum and Pressure (DVP) Continuous Flow vacuum impregnation (CFI) process for the customer’s parts. The CFi seals high volumes of parts in a short cycle time with minimal labor. The system uses a recoverable sealant, maintaining the sealant in is original and purest state, which allows for repeated use.
Godfrey & Wing’s solution was designed to address each of the customers concerns:
- Dry Vacuum and Pressure (DVP) process– Godfrey & Wing’s data indicated a meaningful improvement in recovery would be found using the DVP process. The previous vendor used a vacuum only process.
- Single fixture part flow- Using single part flow systems allows parts to be fixture in a manner that promotes repeatability and consistent processing. The previous impregnation vendor stacked parts side by side in a random manner in large steel baskets leading to multiple failure modes.
- Automation– Material handling would be done with a robot instead of manual labor. This insures all parts are processed correctly and in sequence. The previous vendor’s batch system is manually controlled where the large baskets could be packed or processed incorrectly.
Having never qualified the DVP process, the customer ran a sample to determine how much more effective it would perform compared to its existing DV process. The results clearly showed the DVP process surpassed the existing sealing results:
- 100% part recovery– The customer’s part recovery rate increased to 100% with the DVP. This was a 14% improvement over the average rate with their existing process.
- 0% part contamination– Using the DVP process, the customer’s rate of part contamination dropped to virtually zero.
- 0% part damage– The customer experienced no part damage with the DVP process.
Impressed with the results, the customer moved production to Godfrey & Wing.
The Results
During the first year of production, the CFI impregnated over 16,000 parts. The First Time Through (FTT) rate remained at 100% without any contamination or damage. The impregnation process continues to achieve 100% recovery without any contamination or damage. The process seals the parts at 150 cc.
Godfrey & Wing’s CFi with the DVP process solution answered the following challenges:
- Improve Recovery-The DVP process pushes the sealant deep into the micro porosity, which delivers near 100% recovery in a single cycle. The process thus delivers improved sealing efficiency.
- Eliminate Contamination-Instead of packing the parts in a basket; the parts are placed in fixtures that hold either one or two parts. This allows excess sealant is effectively washed from the part during the cycle.
- Eliminate Part Damage-The CFI system is fully robotic; the attendant interacts with the system through the HMI panel. The system’s robotic arm moves the castings between stations, which allows for a shorter cycle time and eliminates operator errors.
In Summary
As companies continue their search for ways to reduce costs and increase quality, it will be necessary to challenge the status quo. This company realized that the DV recovery rates were no longer valid for today. With Godfrey & Wing’s technology and processes, this company maximized casting recovery, reduced costs and improved quality.
The definition of porosity is any void or hole in a casting. But this definition does not describe or give direction on the root cause of porosity. Casting porosity can be caused by gas formation or solidification shrinkage while the metal is a liquid. If a casting needs to be pressure tight, then the porosity can allow gas and fluids to seep from the part. In addition, the porosity can weaken the casting. In this blog, we will discuss the difference between gas and shrink porosity, and the best solution to seal porosity.
Gas-Related Porosity
What is it?
Gas-related porosity is caused by trapped mold or core gases in the liquid metal. Air is present in the tool cavity, and is easily trapped as metal fills the cavity. The air dispersed as small sphere of high pressure air when the metal fills the cavity.
What does it look like?
Gas-related voids generally look like bubbles with a smooth interior. Gas porosity is always buoyant and will be near the top of the casting.
Shrinkage-Related Porosity
What is it?
When a casting solidifies inside the tool, it always shrinks in size. Shrinkage-related porosity is caused by sections of a casting that solidify later than the surrounding sections, and do not have enough metal flow into the section to completely fill.
What does it look like?
Shrinkage porosity will have a jagged or linear appearance. Shrinkage porosity usually occurs in either the cope or drag portion of the casting and below the surface.
Problems of Porosity
As the amount of porosity increases in an aluminum or iron casting, it can become inter-connected and cause a leak path. The porosity makes the casting unusable for holding pressure in applications like pumps, compressors, transmissions and plumbing fixtures.
Porosity in powdered metal parts can cause severe plating problems where the plating chemicals are trapped in the pores. The entrapped plating chemicals expand with enough force to cause spotting on the plating.
How to Stop Casting Porosity
The most economical and successful approach to stop casting porosity is through vacuum impregnation. Vacuum impregnation is a method that seals the casting resulting from porosity. The impregnating sealant is introduced into the voids within the wall thickness of the casting through vacuum and/or pressure methods. This method is a cost effective and permanent solution to casting porosity. There is no limit to the size of castings which can be impregnated. Since the impregnation process occurs within the part, the vacuum impregnation process does not distort, discolor, or affect the casting.
Vacuum impregnation achieves the results that casting engineers have sought for centuries: a leak-free and pressure tight casting that is economical and usable in all the applications required.
Schabmüller Automobiltechnik is a leading engineering, machining, and sub-assembly supplier to major automotive OEMs and Tier 1 suppliers. Founded in 1978, the company’s headquarters is in Großmehring Germany, and employs 850 people in four locations.
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Manufacturing castings with the lost foam process enables the foundry to produce castings with many benefits and features not available in other casting processes. This casting process is advantageous for very complex castings that would regularly require cores. It is also dimensionally accurate, maintains an excellent surface finish, requires no draft, and has not parting lines so no flash is formed.
Like all casting processes, lost foam castings may exhibit unwanted shrink porosity in the final product. The lost foam casting shrink porosity is due to the dispersal of the gas from the destruction of the foam cores during the casting process. Many lost foam castings exhibit leaks that prevent the castings from functioning properly. The leaks keep gases and fluids from properly flowing through the casting when under pressure.
The Challenge
With the launch of a new family of three engines using lost foam castings for both cylinder heads and blocks, an OEM began to evaluate the effectiveness of different vacuum impregnation processes. After carefully evaluating results from different vacuum impregnation processes, it was specified that all lost foam should be processed through a Dry Vacuum and Pressure (DVP) process. The plan required 100% impregnation of both the block & head and even with the superior results delivered by the DVP process the OEM needed to ensure the absolute highest seal rates.
The Solution
Godfrey & Wing had been working on a new revolutionary approach to vacuum impregnation- Continuous Flow Impregnation (CFi). Ideally, designed and suited for powertrain manufacturing, the new system would:
- Use DVP processing in a controlled single-piece method, quickly taking each casting to deeper vacuum end-points in order to maximize the processes effect on the target shrink porosity.
- Recover more porous castings increasing the OEM’s first time through pressure test rate to >99%.
- Reduce the average DVP impregnation cycle time from twenty-two minutes to forty-five seconds.
- Use robotics to increase throughput and eliminate handling damage.
- Detect process variations and self-contain any suspect castings allowing for improved repeatability and consistency.
Working with the OEM, Godfrey & Wing initially launched the new CFi process on lost foam cylinder heads. The results were exceptional and the program was expanded to cylinder blocks as new equipment was designed and built.
The Results
The OEM and Godfrey & Wing conducted a massive Production Trial Run (PTR), studying the results on over 450,000 cylinder block castings. Castings were impregnated on Godfrey & Wing’s CFi and batch system, as well as the batch systems of three other vendors. The data in figure 1 shows that the Godfrey & Wing CFi technology surpassed all other traditional batch systems used to impregnate lost foam castings.
Figure 1
In Summary
With years of experience with the impregnation of lost foam castings, Godfrey & Wing has developed processes and systems targeted to meet the unique requirements of lost foam castings.
- The use of DVP in order minimize the fall-out at final test due to shrink porosity.
- The development of the CFi’s rapid single-piece-flow technology, which provides for manufacturing cells that are 100% self-contained for quality and can easily support other quality functions for the OEM such as part data collection and individual part inspection.
Godfrey & Wing has impregnated millions of lost foam castings. Through continuous effort to achieve better results, Godfrey & Wing has been able to reduce the fall-out at final test for LF components for major powertrain programs. Godfrey & Wing approach to systems, like the CFi, have also reduced the risk of non-conforming parts entering the production flow. Godfrey & Wing systems are shipped worldwide to enable our customers to recover more castings and use less resources and overhead than any other vacuum impregnation system in the world.
The Albert Handtmann Metallgusswerk GmbH is the largest lightweight (aluminum) foundry in Germany. The family-owned company has continually endeavored to improve its casting and machining processes to benefit its customers worldwide.
Thus, when Daimler AG awarded Handtmann a contract to cast and machine one third of the entire worldwide production of transmission cases and clutch housings for the Mercedes A-Class, B-Class, CLA-Class, and GLA-Class vehicles, the managing directors and board at Handtmann saw an opportunity. It was an opportunity to build a world-class production facility fully dedicated to automated one-piece flow in the complete machining and post-machining processes of these Mercedes cases and housings.
The Challenge
As a company, Handtmann was expert in almost all of the production processes required as part of this new facility. However, in order to achieve true one-piece flow, Handtmann had to bring inside a critical aspect of quality control that the company had previously hired out, vacuum impregnation.
In the past after machining, Handtmann had always sent out its transmission cases and clutch housings to vendors to be vacuum impregnated. The company’s experience here was not always pleasant. At external points parts have been damaged during transport or contaminated. To avoid additional handling and costly washing-process, they decided to integrate this process into the (manufacturing) line.
For Handtmann, the challenge was to quickly educate its executives on the detailed aspects of vacuum impregnation, then chose the proper vacuum impregnation equipment to install. This equipment would have to meet Handtmann’s demands to seal casting porosity effectively and to meet production volumes, to do so in a 96-second per piece TAKT time, to fit into a confined space on the facility’s floor, and to fully integrate within the automated processes that would govern the entirety of the plant.
The Solution
Since several of Handtmann’s vacuum impregnation service providers also build impregnation equipment, the company began by soliciting bids from these traditional sources. However, it was apparent immediately on receipt of these bids that the equipment proposed could not possibly be installed as part of a one-piece flow manufacturing line. The big batch systems that were recommended require parts to be manually loaded and unloaded and they carry a high risk for damage and contamination to the machined parts. They require significantly more TAKT time to complete the impregnation process. They also require a tremendous amount of floor space, for both the equipment itself as well as for loading and unloading areas. Hence, the big batch systems proposed early on were completely disqualified. Handtmann needed more advanced technology. Enter Godfrey & Wing.
By chance, a Handtmann engineering executive came across an article about a different process of vacuum impregnation called Continuous Flow Impregnation written by Ralf Versmold, Godfrey & Wing’s sales and service director for Europe based in Germany. As the name itself indicates, Continuous Flow technology was developed by Godfrey & Wing to answer the demand for the vacuum impregnation process to be fast, efficient, and capable of being installed as part of a machining line where floor space is limited.
The Results
After visiting several CFi installations in 2012 and learning firsthand from Godfrey & Wing customers about the effectiveness and efficiency of these CFi systems, Handtmann purchased a multi-station CFi from Godfrey & Wing in early 2013. The system was installed in Handtmann’s new Mercedes one-piece flow manufacturing facility in Biberach, Germany in late 2013 where it operates alongside machining centers, parts cleaning equipment, and pressure test benches in a fully automated environment. This CFi includes a compact impregnation pressure vessel, a high-speed centrifuge, a wash tank, and three cure stations, all serviced by a robotic arm and automated conveyors. Six days per week, 24 hours per day, this CFi vacuum impregnates every transmission case and clutch housing that fails its initial pressure test.
In Summary
Considering the four demands required of it– speed, efficiency, and total automation within a small footprint, Godfrey & Wing’s Continuous Flow Impregnation system has proved to be the perfect solution for Handtmann Metallgusswerk in its dedicated Mercedes machining facility. Today, this CFi plays an integral role in the manufacture of these transmission cases and clutch housings and it does so in one of the most advanced manufacturing facilities in the world.
Production manager Heiko Pfeiffer sees a huge cost/handling and thus competitive advantage due to the direct automatic integration of the CFi-technology. He confirms, that the CFi-technology is actually the only possibility to integrate the impregnation-process into the manufacturing-process within a modern production-environment.
Foundry Management & Technology recently wrote an article about a Godfrey & Wing HVLV vacuum impregnation system that was installed at SEW-Eurodrive. You can read the entire article below.
Sealing equipment specialist Godfrey & Wing has a contract to supply its HVLV vacuum-impregnation system to SEW-Eurodrive, to seal diecast aluminum motor and gear components at its operation in Fordach, France. SEW is a developer and manufacturer of decentralized motor control technology. It also produces large industrial gearboxes, with helical, bevel helical, and planetary gears.
The system will be installed next year. According to Godfrey & Wing, the order also includes its 95-1000AA recoverable sealant and ongoing techni cal support.
Also, according to G&W, the contract resulted from SEW-Eurodrive’s plan to move its vacuum impregnation processes in-house. In-house production will reduce freight costs and production delays that necessitated by outsourcing the part-sealing stage of production.
Godfrey & Wing has published an article in LightWeighting World titled “Vacuum Impregnation Enables Lightweight Material Use”. This article discusses the surge in aluminum use and how vacuum impregnation eliminates aluminum casting porosity. You can read the entire article below.
Recent decades have seen a surge in use of aluminum castings 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. Carl Benz developed the first engine with aluminum parts two years later1. Since this time, aluminum has become the leading material used in various components and car models. Aluminum use now ranges from mass-market to luxury vehicles.
As this surge has happened, vacuum impregnation has become the primary method to eliminate the porosity inherent in aluminum castings. OEMs are redesigning parts and bringing vacuum impregnation systems in-house to meet the aluminum use demand.
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