Posted by Andy Marin on | Comments Off on Should Vacuum Impregnation Be Done Before or After Finishing?
Powder coat, paint, chromate conversion, or anodizing, are common finishes applied to die cast parts to improve their performance or appearance. In some die casting applications, components must also be pressure tight to hold pressurized fluid or gases. Companies use vacuum impregnation to meet these requirements by sealing the internal leak paths without impacting any other features of the casting.
A common question asked about vacuum impregnation is “Should vacuum impregnation be done before or after finishing?”
Should Porosity Be Sealed Before or After Finishing?
The general rule is that vacuum impregnation should be done before any surface finishes. This will seal the porosity and eliminate any failure mode that could develop from outgassing, chemical compatibility or bleed out of pretreatments. Below are examples of failure modes that can occur if impregnation is done after the finish is applied.
Paint Finish
The painted part will be exposed to sealant, and certain minerals and alkalis in the water. The sealant can react with paint and degrade the quality of adhesion of the paint with the part surface. During impregnation the painted part is heating to 195 F in hot water. The water or residual minerals in the water may leave water spots, or in the worst case, alter the color hue in color or degrade the finish (Image 1).
Image 1: The water or residual minerals in the water may leave water spots, or in the worst case, alter the color hue in color or degrade the finish
Chemical Finish
Many chemical finishes require aggressive liquid pre-treatments for the finish to ‘bond’ to the casting surfaces. These pretreatments may penetrate the near surface porosity and remain in the pore even after the finish is completed. During the impregnation process, the vacuum will pull these chemicals from the porosity and into the finish may lead to corrosion and a defect known as “blooming” .
Chromate Finish
If a chromate finish is applied to a part prior to impregnation, the heat required to cure the vacuum impregnation sealant (195 F) will degrade the quality of the coating. This will lead to a premature failure of the coating and be the cause of part oxidation.
Finally, regardless of the type of finish, the part can be damaged or scratched from handling and processing (Image 2).
Image 2: If not properly fixtured, the parts can shift during the impregnation process and become damaged or scratched.
Vacuum Impregnation Eliminates Powder Coating Out Gassing
Vacuum impregnation not only seals the porosity but may prevent cosmetic defects in powder coating. If not sealed, the pores would otherwise hold air. This air may expand and out gas during the curing stage. The air escapes through the powder, causing holes or bubbles, called pin holes, in the finish (Image 3). These pinholes are not only unattractive, they also allow in moisture and corrosion to damage the part. Vacuum impregnation prevents this issue from happening by removing the air and filling the porosity with sealant.
Image 3: If not sealed, the pores would otherwise hold air. This air may expand and out gas during the curing stage, causing pin holes.
What if the Parts are Machined?
If parts are machined after finishing, then the parts should be sealed after machining. This is because a machine tool may expose or open porosity when it cuts into the part’s surface.
The new inter-connected porosity will create a leak path. The leak path will cause fluids and gases to leak from the casting, causing it to be non-conforming, and in many cases unusable. Unfortunately, this occurs precisely at the wrong time, since the non-conforming part has already been manufactured. All the value has been added to the non-conforming part.
In Summary
Vacuum impregnation is the most effective way to seal casting porosity, but it must be performed at the correct stage of the production process. Performing vacuum impregnation prior to finishing will ensure that all leak paths are sealed while safeguarding and enhancing the quality of the final finish.
Posted by Andy Marin on | Comments Off on Case Study: How Portable Equipment Solved Production Capacity Issues
The casting industry is in a transitional period adjusting to new trends and products. Manufacturers require flexibility in their equipment to account for shorter program life cycles while still being able to be competitive. In many instances this requires assets to be spread across multiple programs. It is a landscape that rewards companies who identify opportunities to adapt to the changing circumstances. One example is a case where vacuum impregnation requirements unexpectedly and suddenly increased in one manufacturer’s location while another of its locations had underutilized impregnation capacity.
The Challenge
The company operates multiple locations in the United States and one in Mexico. One site in the USA was operating at maximum capacity. Due to issues beyond its control, this facility saw an increase in castings that failed leak test. With this increase in fallout their vacuum impregnation hit full utilization, and more capacity was needed.
The company considered three options to create more capacity:
Outsourcing-The company considering outsourcing excess requirements to an impregnation service center. After evaluating the logistics costs, and the quality risks associated with two supply lines, outsourcing was quickly discarded.
Purchasing a New Vacuum Impregnation System-Lead times made buying a new system unfeasible and the cost would be prohibitive, especially for what may be a temporary problem.
Recommissioning a Used Batch System-Purchasing, moving and recommissioning a nearby used batch impregnation system would be no simple task. It required weeks of planning and alterations in infrastructure for equipment pits, platforms and overhead cranes. That was not an option, time was of the essence.
The facility in Mexico had a delay in a product launch, which led to idle capacity. This inactive impregnation system was what was needed in the USA. Most discounted this option as far too complicated given customs, border crossings and transportation.
The Solution
Fortunately, the company standardized on Godfrey & Wing’s lean front-loading vacuum impregnation systems. The USA facility operated a fully automated Continuous Flow impregnation (CFi) system and the Mexico facility employed two High Value Low Volume (HVLV) systems (Image 1). The CFi is a lean, front loading vacuum impregnation system that uses a robot for part handling and transfers between modules. The HVLV is the same impregnation technology but utilizes automated process control and manual material handling.
Image 1: The HVLV is a front loading system that uses automated process control and manual material handling.
Despite initially discounting moving an HVLV system from Mexico, the customer’s operations team decided this was the best option and quickly started assembling data.
The team discovered:
No Infrastructure Changes-The HVLV system did not require infrastructure changes.
Modular Footprint-With a footprint of 96 square feet the HVLV system was easily transportable and did not require riggers and special handling equipment.
No Interconnecting Wires-It would be a fast de-commission and a “plug and play” installation. No interconnecting wires needed to be removed or reinstalled. Single point connections for electricity, water and air were standard on the HVLV (Image 2).
Easy Customer Approval-Customer approvals would be easy as the HVLV used the same impregnation process as the CFI.
No Quality Issues-Quality was not a concern as the wash and cure stations in the CFi and HVLV were identical.
Image 2: The HVLV requires no interconnecting wires to be removed or reinstalled.
The team reached the conclusion that shipping the idle vacuum impregnation system from Mexico was the best solution to the capacity problem in the USA. Within three hours on a Friday morning, the HVLV was decommissioned and placed on a truck. The unit arrived at its USA destination, 1700 miles away, on Monday, qualified on Tuesday, and was sealing parts on Wednesday.
The Results
The data clearly shows that transporting the HVLV achieved the company’s capacity goals. The results included:
Increased Throughput-Operating the HVLV alongside the CFi increased throughput by 40%, easily accommodating the spike in requirements (Image 3).
Minimal Installation and Shipping Costs-The HVLV was transported and installed for $11,000. This represents less than one week of freight costs if the parts were outsourced.
Piece Cost– The HVLV system was the least expensive option of the three considered.
Image 3: The HVLV easily accommodated the spike in capacity requirements by increasing throughput by 40%.
The HVLV is projected to operate in the USA for six months. At that time, the HVLV will be reinstalled back in Mexico for the launch of a new casting program.
In Summary
Godfrey & Wing’s HVLV is the only system that can meet these demands with ease. The company found great value in operating their vacuum impregnation equipment as a flexible, portable system. The company now considers this HVLV not tied to a specific program, but rather as a piece of its infrastructure. That HVLV will now be sent to whichever location that has capacity issues.
Posted by Andy Marin on | Comments Off on Case Study: How One Company Overcame Their Casting Porosity Challenge
Manufacturing activities are being shaped to an increasing degree by the demands of consumer taste. Consumer’s expectations of quality and performance define product design, which further determines the requirements of the supply chain. This is a landscape that rewards suppliers who identify opportunities to adapt to the changing circumstances. One example is a vacuum impregnation service center that seals a variety of aluminum die castings for various automotive and industrial OEMs, Tier 1, and 2 suppliers.
The Challenge
The company primarily uses in-house batch impregnation systems to process the die castings. The batch systems aggregate various parts and process them in large batches. Despite being well versed in vacuum impregnation, the company could not reliably process the high value and complex castings due to the limitations of their batch systems. The company realized that the following challenges needed to be answered:
Contamination-Cured sealant remained in the through and blind tape holes.
Handling Damage-Despite being sealed, some parts were scrapped due to damage to machined features from handling in the batch system (Figure 1).
Floor Space-The batch systems consumed a lot of floor space, which prohibited efficient work flow and increased Work-In-Process (WIP).
Figure 1: Despite being sealed, some parts were scrapped due to damage to machined features from handling in the batch system.
The Solution
To meet their customer’s quality and production requirements, the company realized that they needed to install an effective impregnation process in their manufacturing environment. Working with Godfrey & Wing, the company laid out their vision. Godfrey & Wing responded with its Continuous Flow impregnation (CFi) system (Figure 2). The system would be customized to answer the customer’s challenges.
Figure 2: The CFi system uses Dry Vacuum and Pressure (DVP) and recoverable sealants to be the most effective impregnation process in the world. Its use of automation means it seals porosity at a higher rate, in a shorter cycle time and with minimal labor.
The CFi uses the patented Dry Vacuum and Pressure (DVP) process, and 95-1000A or 95-1000AA recoverable sealant. Demonstrated to be the most effective vacuum impregnation process in the world, the CFi with the DVP process incorporates a fast, deep vacuum to evacuate the air from the porosity. Then after moving sealant to the part, the system applies high pressure to allow the sealant to thoroughly penetrate deep in the casting walls.
The castings are in custom designed fixtures to maximize the amount of castings per cycle, flush sealant from blind holes, and protect critical machined features. The fixtures are delivered to the CFi via a conveyor; the CFI takes over and automatically moves the fixtures through the process. This allows the castings to be processed within the fixture without damage (Figure 3).
Figure 3: The fixtures are delivered to the CFi via a conveyor; the CFI takes over and automatically moves the fixtures through the process. This allows the castings to be processed within the fixture without damage.
The CFi system is fully self-contained for quality. The robot and PLC would work together to ensure that fixtures do not leave the system until meeting all of the pre-determined conditions. If acceptable, then the robot will move the fixtures from the CFi to the next process.
The customer relayed to the Godfrey & Wing engineering team where they wanted to place the system on the floor. With this knowledge, the engineering team designed the layout and maintenance access to be integrated with the existing manufacturing flow.
The Results
The data clearly shows that the Godfrey & Wing CFi system achieved all of the customer’s goals. The results included:
Improve Casting Recovery-Scrap from porosity has been virtually eradicated with the CFi delivering a First Time Through (FFT) rating of near 100%. Historically, batch systems recover approximately 85% of castings. The CFi represents nearly a 15 point improvement over the previous impregnation methods.
Eliminate Contamination Handling Damage-The CFi has completely eliminated damage and sealant contamination and runs at 0 PPM. The part flow and fixture design flush sealant from the through and blind tap holes and machined features. This ensures that sealant residue is not on any critical features.
Reduce Floor Space-The CFi processes 40 cycles per hour, and requires 800 square feet with no infrastructure changes. The system maximizes production, eliminates WIP, and reduces floor space.
In Summary
This company found great value in searching for a new way to meet their customer’s ever-changing quality and performance demands. Godfrey & Wing’s automated CFi system is the only system that can meet the stringent demands. The CFi demonstrates that manufacturers can take control of the porosity sealing step and integrate vacuum impregnation into their production flow, to ensure product quality and productivity.
Posted by Andy Marin on | Comments Off on Should Porosity Be Sealed Before or After Machining?
The goal of a foundry is to produce high quality die castings that meet or exceed the customer’s specifications at a competitive cost. In some die casting cases, those specifications require that the part must hold pressurized fluid or gasses.
Companies use vacuum impregnation when the part must hold fluids or gasses under pressure. Vacuum impregnation is a proven process that seals internal porosity without impacting any other features of the manufactured part. A common question asked about vacuum impregnation is “Should vacuum impregnation be done before or after die casting machining?”
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. Some metal casting porosity can affect the part’s structural integrity, creating a failure point. More commonly, porosity prevents the part from being pressure tight. This will impact performance if the part is designed to hold gases or fluids.
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.
In general, there are three casting porosity classifications:
Blind Porosity: From one surface only and therefore not forming a continuous passage for liquid (highlighted in blue in figure 1).
Through Porosity: Stretching from one side of a casting to another (highlighted in red in figure 1).
Fully Enclosed Porosity: Enclosed within the casting, and has no passage to the surface (highlighted in green in figure 1).
Figure 1: There are three types of casting porosity: blind porosity, through porosity, and fully enclosed porosity.
Blind and through porosity cause immediate casting problems. Blind porosity can cause internal corrosion; while through porosity will create a leak path and allow gas and liquids to seep through the casting (Figure 2). In addition, blind porosity can cause defects on the part surface when secondary treatments, like powder coating or anodizing, are done. This is because solutions used to clean the castings prior to the treatment will leech out of the voids after the surface finish process.
Should Porosity Be Sealed Before or After Machining?
Figure 2: Blind porosity can cause internal corrosion; while through porosity will create a leak path and allow gas and liquids to seep through the casting.
When a machine tool cuts into the surface or “skin” of a casting, it can expose or open porosity (Figure 3). The porosity may be either blind porosity or existing blind and enclosed porosity may be opened and become through porosity.
Figure 3: When a machine tool cuts into the surface or “skin” of a casting, it can expose or open porosity.
The new inter-connected porosity (highlighted in green) will create a leak path (Figure 4). The leak path will cause fluids and gases to leak from the casting, causing it to be non-conforming, and in many cases unusable. Unfortunately, this occurs precisely at the wrong time, since the non-conforming part has already been cast, cubed (pre-machined), washed, tested, shipped, fully machined, washed and tested again. All the value has been added to the non-conforming part. In the worst-case scenario if the problem occurs frequently, the manufacturer may have maxed-out their production and may be unable to replace the non-conforming castings with functional parts, delaying shipments and significantly increasing costs.
Figure 4: The new inter-connected porosity (highlighted in green) will create a leak path. This leak path will cause fluids and gases to leak from the casting, causing it to be non-conforming, and in many cases unusable.
Impregnating 100% of castings after final machining is the best way to insure leak free castings at build. If prior to assembly, a final leak test of individual parts is incorporated into production, leak testing fully machined casting and impregnating only the non-conforming parts (often referred to as fix-on-fail) is an excellent alternative.
Another approach is that manufacturers have chosen to increase the machining content at the pre-machine stage (cubing) thus maximizing the exposure of blind and through porosity prior to the parts reaching the final production line. After pre-machining 100% of all parts are impregnated and tested. Only conforming parts are sent through to production when the parts are fully machined in production only a reduced amount of material is removed. Since the impregnation at pre-machining has already sealed both the blind and through porosity, the opportunity to open an interconnected leak path is substantially reduced. In some cases, any non-conforming parts that make it to final test can be easily impregnated without disrupting production on a “fix-on-fail” basis.
In Summary
Because machining may potentially uncover additional casting porosity, vacuum impregnation should be done after machining. Performing vacuum impregnation after machining is the only way to seal all leak paths. However, some castings may be pre-machined or cubed. Impregnating 100% of production castings after cubing will seal the exposed porosity. In this case, impregnation is still very effective in reducing non-conforming parts at final assembly.
Posted by Andy Marin on | Comments Off on Case Study: How One Turf Care Company Solved Their Casting Porosity Challenge
The commercial turf care market is expected to reach USD 38.2 billion by 2025. The growing trend toward investing more time in one’s home leads to a higher interest in outdoor & gardening-related activities.
The Challenge
In an effort to meet this growing demand, a turf care engine manufacturer developed a plan to expand its engine manufacturing facility. This facility manufactures aluminum crank cases and cylinder heads.
The engine, crank case, and cylinder heads are die casting aluminum castings, and therefore have porosity. Interconnected pores will cause a leak path causing fluids to seep from the crank cases and cylinder heads. These parts need to be pressure tight in order to function properly. The manufacturer seals the leak paths through vacuum impregnation.
This company long used an in-house wet vacuum batch impregnation system to process the parts. The batch system aggregated parts from the company’s assembly lines and processed them in large batches. After processing, the parts were dispersed to the next manufacturing step. After much consideration, the company determined the system was not viable for their expansion plans due to:
Poor recovery-Approximately 16% of the parts still leaked after impregnation.
Sealant contamination-Cured (solid) sealant remained in through and blind tapped holes (Figure 1).
Rust-Many parts had cast-in steel liners that would rust in the current process.
Figure 1: Cured (solid) sealant remained in through and blind tapped holes after impregnation causing significant quality issues.
Also, the batch system was a labor-intensive system, requiring operators to move large heavy baskets between stations while on an elevated work platform. Not only did this present a throughput issue, more troublesome was the lack of operator protection from moving pieces of machinery. This was not a safe or viable method to keep up with the growing production.
These issues lead to increased costs, reduced quality and significant safety concerns. The company determined that they needed a more effective, lean and safe porosity sealing solution.
The Solution
The customer contacted Godfrey & Wing to evaluate their manufacturing dilemma. It was determined that the implementation of a modern, front-loading, in-house vacuum impregnation system would alleviate these challenges. After careful consideration, Godfrey & Wing proposed its Advanced Powertrain impregnation (APi) (Figure 2) system with recoverable sealant for installation at the customer’s facility.
Figure 2: The Advanced Powertrain impregnation (APi ) system uses the Dry Vacuum and Pressure (DVP) process to push the recoverable sealant deep into the micro porosity.
The APi 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 APi solution would deliver multiple benefits to the customer:
The system is a viable in-house solution that requires 127 square feet that can easily be installed into the customer’s facility without any infrastructure changes. The modular design enables the customer to achieve cellular manufacturing.
The centrifuge was designed to rotate clockwise and counterclockwise to remove excess sealant. This enables the system to recover residual sealant, reduce sealant carryover to the wash, maintain sealant purity, and preserve part cleanliness.
Fixtures were designed to maximize the amount of parts per cycle, flush sealant from the blind holes, and protect critical machined features.
Water is the biggest variable that causes parts to rust because its properties are always changing. Godfrey & Wing analyzed the customer’s water to determine what properties caused the parts to run. A custom-tailored rust preventative was used in the cure tank to eliminate the parts rusting.
Subsequently, the customer attended a demonstration of a Godfrey & Wing impregnation system at the company’s headquarters in Aurora, OH.
This demonstration gave the customer an opportunity to process parts themselves on Godfrey & Wing’s technology. The customer found the system simple and safe to use compared to their current batch system. The part fixtures and platform allows the operator to easily move a part from station to station. Each station starts with the flip of a switch (Figure 3). The man-machine interface keeps the operator safe at all times. Light curtains, insulated panels, and ventless exhaust ensure ongoing operator safety. (Figure 4)
Figure 3: The customer found the APi system simple and easy to use compared to their current batch system. Each station starts with the flip of a switch.
Figure 4: The man-machine interface keeps the operator safe at all times.
The Results
The customer integrated the APi (Figure 5) into production quickly and efficiently with no infrastructure changes. The APi is now making a significant impact by answering the following challenges:
Improved Casting Recovery-The APi system delivers near 100% recovery in a single cycle. This represents over a 10 point improvement from the previous impregnation method.
Eliminate Sealant Contamination– Cured sealant from tapped and blinded holes is completely eliminated, as the customer runs at 0 PPM.
Eliminate Rust-The use of the tailored rust preventative eradicates rust in the steel liners, thus improving part quality and eliminating unforeseen scrap.
The cost savings realized allows the customer to have a CapEx recovery of less than 18 months.
Figure 5: The APi was integrated into production quickly and efficiently with no infrastructure changes. The company improved casting recovery and eliminated unforeseen costs with an easy to use system.
In Summary
As companies continue their search for ways to meet their customer’s growing needs, it will be necessary to challenge old paradigms. This company found great value in doing so by implementing a modern and lean vacuum impregnation system. The company improved casting recovery, and eliminated unforeseen costs with an easy to use system.
Posted by Andy Marin on | Comments Off on An Introduction to Vacuum Impregnation Equipment Safety
The beginning of the 21st century was a turning point for vacuum impregnation equipment safety, and in less than two decades there have been significant improvements in that technology, a process that had been essentially unchanged for 70 years.
Developed in the 1950s, the process was adopted quickly in various industries, particularly in automotive and aerospace sectors, and it became the preferred method to seal die casting leak paths to prevent leakage of fluid or gases under pressure.
Until the mid-1980s, most automotive OEMs handled the vacuum impregnation process in-house. They used batch systems, in which workers would load multiple parts into large baskets for processing. To increase productivity the companies would increase the size of the process equipment, but this was accompanied by a reduction in finished product quality and process safety.
Equipment Safety Concerns
As other manufacturing operations (e.g., machining, pressure testing, and assembly) had been modernized, vacuum impregnation remained stagnant. Other operations became more cellular, more automated, more ergonomically sound and safer for operators, and in general more efficient. Vacuum impregnation, however, remained a manual process with significant safety concerns.
Among the safety concerns were:
Open Modules
Open modules would jeopardize operator safety. For example, an operator could be splashed with sealant or fall into an open, 800-gallon container of 195°F water.
Open Tanks
Open tanks would emit hot vapor with elevated Volatile Organic Compounds (VOC) levels, which could cause health problems.
Liquids on the Floor
Since the modules are open; there was the risk that liquids will splash on the floor causing a slipping hazard.
Overhead Equipment
System components like overhead hoist chains, actuating tank lids, locking rings and chain drives could cause injuries.
High Platforms
Operators needed to climb, descend, and stand on elevated platforms to load parts from the top. Operators had the risk of a potential fall and trip hazard.
Bulky and Heavy Baskets
Part baskets were bulky and heavy and moving them could create stress on the operator’s body or cause injury if mishandled.
Re-imagining Vacuum Impregnation
In the early 2000s, many OEMs brought vacuum impregnation in-house, intending to meet the volume demand for lighter, aluminum parts that increased in volume following the introduction of the Corporate Average Fuel Economy (CAFE) standards, and subsequent pressure to produce more fuel-efficient vehicles.
Systems were modernized to meet the demands of the new manufacturing environment. Rather than large, top-loading batch systems new equipment was designed to be front-loading and to process just single pieces or a small number of castings.
Incorporating robotic handling allowed parts to move continuously between each station. The robotics reduced cycle times and improved overall cycle time and production volumes. Operators work outside the robotic cells, interfacing with the system only as needed.
Automated impregnation technology then expanded to compact, manually operated systems, incorporating all the safety features of the fully automated robotic units. This allowed OEMs to bring vacuum impregnation in-house at a fraction of the cost. These new systems were smaller than batch systems and the cellular design enabled them to easily integrate with other production operations.
Now, the operators were safer than ever before as self-contained modules protected them from contact with sealant and hot fluids; mist eliminators collect water vapor in the exhaust and return it through a drain line for re-use and better ergonomics allow the operator to simply slide a lightweight fixture onto the platform for each module, eliminating the risk of injury.
Conclusion
As the 21st Century continues, companies continue to wrestle with challenging design standards, fewer resources and shorter cycle times. Those that thrive will do so by increasing productivity, quality, throughput and cost reduction.
The vacuum impregnation systems of the past are no longer competitive, and the most competitive newer systems are those that will continue to offer safety to the operators, with increasing production volumes and the continuing effectiveness at eliminating casting defects.
Posted by Andy Marin on | Comments Off on Novelis Projects Automotive Aluminum Demand To More Than Double by 2025.
In an interview with Reuters this month, Pierre Labat, vice president of global automotive at Novelis, the world’s largest maker of rolled aluminum products, said that demand for aluminum by the automotive industry is projected to more than double over the next seven years.
Labat said that aluminum is increasingly becoming the go-to metal to replace steel as automakers search for ways to reduce automobile weight.
“Typically what we see is an increase of aluminum percentage of the (automotive) body, which is why we’re projecting to grow from 1.5 million tonnes of aluminum demand this year to 3.5 million tonnes a year in 2025.” he explained. “We will continue to add new products in the years to come which make the value proposition of aluminum very compelling for strength and light weight.”
Labat continued by noting that, of the 1.5 million tonnes of aluminum autobody sheet demand this year, roughly a 10 percent, or about 150,000 tonnes, of it is produced in Asia. But, over the next few years, Asia’s demand is expected to rise significantly, ultimately rivaling Europe’s.
“China and the rest of Asia will almost grow from 10 percent to one third of global demand,” he predicted.
Though aluminum is expected to make significant inroads into the automotive industry for the foreseeable future, Labat concluded by saying that, at least for now, it will not completely replace steel.
“I think we are convinced that the world at least in the next 10 years will be multi-material architecture with aluminum tripling its size.” he opined. Read the entire article on Reuters
Posted by Andy Marin on | Comments Off on Establishing Leak Rate Standards
A previous blog What Size of Porosity Can Vacuum Impregnation Seal?discussed that porosity occurs naturally and that the purpose vacuum impregnation is to seal leak paths created by interconnected pores. This follow up blog discusses how to define what leak paths should be sealed.
It is important to understand that all materials permit leakage over time. In order for vacuum impregnation to effectively seal the leak and maximize the amount of acceptable parts, the manufacturer needs to define the part’s performance requirements, and develop measurable and repeatable standards around those needs. Defining these standards is done through leak rate testing. Vacuum impregnation is then used to seal specific leak paths to achieve the pre-defined leak rate.
Purpose of Leak Rate Testing
The purpose of leak rate testing is to confirm that the manufacturing process is performing to specification and making acceptable parts. Finding defective parts early in the manufacturing process will reduce field failures, minimize unforeseen costs, and improve customer satisfaction (Image 1).
Image 1: Identifying defective parts with leak paths will reduce field failures, minimize unforeseen costs, and improve customer satisfaction.
Setting a Leak Rate Standard
Inspecting die castings requires quantitative, measurable values that define what is and isn’t acceptable given a part’s intended use. The fact is even materials cast with careful processes will allow some leakage, given enough time. Casting manufacturers develop and adhere to leak rate standards. Such standards define the maximum tolerable leakage for a part, typically specified by cc/min at a specified pressure and time duration.
Air vs. Liquid Leak Testing
Most automotive components operate with liquid. However, air is primarily used in leak rate testing for the following reasons:
Air is compressible and has a lower viscosity than liquid. Air can travel through a leak approximately 100-400 times faster than a liquid.
Air has no surface tension. This allows it to escape a leak more easily than a liquid.
Overall, testing methods using air are faster to conduct than those using a liquid.
Understanding Testing Protocols
To save time and resources, most manufacturers use the industry-recognized leak rates that are available for many products. Figure 1 shows typical ranges for existing parts.
Figure 1
At times, industry recognized standards are not relevant for a part’s application. To establish new standards, those parts should be analyzed through the following steps:
Test a large sample of production parts with an air leak tester at the same part working pressure.
Pressurize parts with water at the same working pressure. This testing identifies the approximate hole size (measured by air leak rate) that does not allow fluid to flow through. The part’s resistance to fluid flow is defined by the hole diameter, part length, hole surface finish, fluid viscosity, and surface tension.
Set the reject leak rate at a point close to but below the highest air leak rate that does not allow fluid to leak.
The final leak rate tolerance should be stated as “specified air leak rate at a specified test pressure and time duration”.
It is important to note that even after a casting is sealed and passes the leak test criteria, the casting can still exhibit leaks under more aggressive test conditions. Recall that all materials will leak in varying degrees. If the test standards were established so that the casting would hold oil a 1 bar, it may still exhibit a leak if tested with air or helium at 1 bar. Gasses are thinner than liquids (e.x. sealant, oil, etc.) and will leak through a path that would not pass fluids.
What is the Role of Vacuum Impregnation in this Process?
Once a leak rate is defined, parts within that range can be sealed through vacuum impregnation. Parts outside of the leak rate parameters are typically scrapped.
Vacuum Impregnation is a process that seals metal casting porosity. Specifically, it seals the internal, interconnecting path of porosity, which breaches the casting wall (Image 2). 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.
Image 2: Vacuum impregnation seals this leak path (highlighted in green) so that fluids do not seep from the part.
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?”
Posted by Andy Marin on | Comments Off on What Size of Porosity Can Vacuum Impregnation Seal?
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.
