Technology continues to advance at anaccelerated pace with the development of lean manufacturing processes, the growth of the Internet of Things (IoT), and the demand for integrated, automated systems. This intersection of technology and industry development has led to a turning point — a point where technology can now manage process variables, enhance productivity, and contribute to seamless manufacturing operations. It’s a turning point that’s also drastically impacting the advancement of the thermal processing industry.
Integration of Lean Manufacturing and the Internet of Things
One of the primary tenants of the lean manufacturing movement is to increase productivity by reducing the work-in-process inventory. However, it is important to note that as the supply chain and manufacturing process become leaner, it is even more essential that production interruptions caused by equipment breakdowns are prevented. This is where the growth in the IoT and predictive maintenance come into play.
Take industrial applications, such as gear manufacturing, for example. Currently, there are multiple steps and physical devices that make up the process of manufacturing a load of gears — heat treatment, machining, molding, and others. However, with the application of the IoT, all of these processes and systems will become interconnected. In the near future, we will be able to start with a piece of material that knows who the end customer is, and once it is put into a machine, any abnormalities or changes from the standard process will be recorded. The technology will move the piece from one process to the next as part of an automated system, and each integrated machine will track the necessary information. All of this data will then be accessible in a central location so the IoT system can analyze the manufacturing process and determine ways to reach peak efficiency and lean manufacturing objectives.
Predictive Maintenance Capabilities
An example of the ability to achieve enhanced control and operation of today’s equipment is predictive maintenance technology, which is emerging as a powerful tool within the heat treatment industry for analyzing performance and efficiency.
One advanced predictive maintenance tool is Ipsen’s PdMetrics™ software platform. PdMetrics was developed as a way for companies to create value from the wealth of data that is generated by their equipment and processes ran in the heat-treating system. With sophisticated monitoring and diagnostics, the PdMetrics software platform integrates with critical systems to provide insights never before seen in the thermal processing industry (see Figure 1). This innovative system securely connects to a network of integrated sensors on the furnace to gather data, analyze it, and provide real-time diagnostics that improve the health and integrity of the equipment.
The PdMetrics platform also provides several advantages, including the ability to:
- Leverage Ipsen’s experience through automated analysis performed by the PdMetrics algorithms
- Experience real-time furnace visibility for faster, better decision-making — from monitoring dashboards at the furnace, on an office PC, smartphone, or tablet, to sending urgent alerts by text or email
- Achieve smart factory integration with furnace fleet analytics that show the health of all furnaces at all facilities
PdMetrics is available as a retrofit or with the purchase of a new furnace, and it is not integrated with the PLC. It also functions as a furnace add-on, meaning it can be quickly retrofitted to the global installed base, including non-Ipsen brand furnaces.
By monitoring the furnace, its performance, and other parameters, predictive maintenance provides key data that can be analyzed to determine when maintenance should be, or will need to be, performed. This data can then be used to augment the furnace’s performance, efficiency, and reliability. Predictive maintenance also allows for an all-encompassing planning of available resources, thus helping to minimize unnecessary personnel, storage, and spare parts costs. In addition, it is effective at identifying problems that occur between scheduled inspections.
The integration of predictive maintenance also provides a smart, connected furnace capable of monitoring in-service equipment to capture data that assists in refining furnace operations and reporting when service will be needed. Through analysis of the critical furnace data, predictive maintenance software can identify maintenance trends, deteriorating conditions, and more. In turn, this helps with planning and scheduling maintenance and ensuring the required furnace parts are in stock.
The Evolution of Low-Pressure Vacuum Carburizing
In addition to the use of technology and equipment that contribute to the achievement of lean manufacturing objectives, there has also been a substantial increase in demand for leaner and more environmentally friendly heat treatment processes that help streamline and shorten the production cycle. With this increase, there has been marked growth around low-pressure carburizing (LPC), and it is estimated that LPC technology has much more room to grow in the near future.
According to industry estimations, currently 25 to 30 percent of gears are vacuum carburized, and assuming that the low-pressure vacuum carburizing market penetration reached that percentage in 2015, there is sure to be an exponential increase in demand for vacuum furnace systems with LPC technology. This not only applies to traditional automobile transmission components and fuel injection nozzles, but also to bearings, PM parts, and tool parts. As LPC equipment and processes continue to be refined, companies gain the ability to further optimize the manufacturing process, which ultimately results in the production of high-quality gears with lower cost per part.
As technology has developed and evolved over the years, so has the LPC process. In the 1960s, development work began to provide an LPC technology that was fully competitive with gas carburizing. At that time, LPC offered a number of benefits with respect to process time, component quality, and minimized fluid burnoff and heat emissions, but it still had a high amount of soot forming in the furnace. In addition, there were high maintenance requirements when propane was used as a carburizing gas with relatively high partial pressures. However, in the mid-nineties, acetylene was discovered to have superior qualities as a reactive gas in vacuum carburizing.
Ipsen’s AvaC® process (acetylene vacuum carburizing) produces twice the carbon availability as compared to traditional carburizing agents, resulting in excellent carbon transfer into the parts. AvaC also has the advantage of producing an oxidation-free surface microstructure while allowing complex geometry components to be evenly carburized. Wherever possible, it is used in combination with dry, high-pressure gas quenching as the hardening step. This provides the industry with a case-hardening process that is safe, environmentally friendly, clean, and flexible — and it has a potential for reducing distortion and improving case-depth uniformity when compared with oil quenching.
Understanding the AvaC Process
The AvaC process involves alternate injections of acetylene (boost) and a neutral gas, such as nitrogen, for diffusion. During the boost injection, acetylene will only dissociate when in contact with metallic surfaces, thus allowing for uniform carburizing. At the same time, it almost completely eliminates the soot and tar formation problem known to occur from earlier propane carburizers.
One of the most important advantages of this process, though, is the high carbon availability. This helps ensure extremely homogenous carburizing — even for complex geometries and very high load densities. Overall, AvaC is a fairly diverse process, capable of processing parts with simple and complex geometries; wrought and powder metal materials; dense loading arrangements; variations in section size; and shallow, medium, and deep case-depth requirements.
As shown in Figure 2, once the carburizing temperature is reached, the first carburizing step is initiated by injecting acetylene into the furnace to pressures between 3 and 5 Torr. The carbon transfer is so effective that the limit of carbon solubility in austenite is reached after only a few minutes. As a result, the first carburizing step must be stopped after a relatively short time by interrupting the gas supply and evacuating the furnace chamber.
Deactivation of the boost event and evacuating the furnace chamber initiates the first diffusion step. During this segment, the carbon transferred into the material as well as the surface carbon content decrease until the desired surface carbon content is reached. Depending on the specified material case depth, further carburizing and diffusion steps may need to follow. Once the specified case depth has been obtained, the next step applied is quenching. This typically involves reducing the load temperature and quenching the load in the same chamber.
Control of the AvaC process for LPC involves an understanding of the variables that influence carbon transfer and diffusion. These include time (total boost or carburizing time, total diffusion time, and the number/duration of carburization and diffusion steps); temperature; and gas parameters (type, pressure, and flow rate). Depending on the part’s surface area, geometry, and steel chemical composition, the aforementioned parameters are determined as constants resulting in homogeneous carburization.
The Use of Low-Pressure Carbonitriding
In addition to LPC, low-pressure carbonitriding is also commonly used in the heat treatment and machining of gears. For vacuum carbonitriding (such as Ipsen’s AvaC-N process), an ammonia gas train is incorporated into the process gas system. In vacuum carbonitriding with acetylene and ammonia, carburizing pulses with acetylene alternate with diffusion/nitriding phases with ammonia (see Figure 3). The partial nitrogen pressure is not required in vacuum carbonitriding as the diffusion phases are run with ammonia as the nitriding gas.
Overall, LPC and low-pressure carbonitriding are marked by their ability to provide precise process control, which helps result in uniform part microstructures, process repeatability, and a reduction in manufacturing and maintenance costs. For example, precise process control leads to minimized distortion, and as a result, a reduction in the grinding process thereby contributing to a decrease in hard machining costs.
Refining Operations with LPC Technology
The use of advanced LPC equipment and technology also has a significant impact on refining operations and allowing manufacturers to reduce unnecessary processes and actions. With an increased focus on using the IoT to optimize operations through data collection, data computation, and production maximization, this mode of operation increasingly requires the use of sensors to adjust the furnace’s operational parameters.
Accompanying this shift in operation requirements is a need for vacuum heat-treating systems that are able to provide an equipment design that incorporates integrated technology and meets these new criteria. This has contributed to the development of new technology for multi-chamber LPC, specifically, a modular furnace design that allows the heat treatment process to be seamlessly incorporated into the overall production process. It is important to note that the heat-treating equipment used with LPC plays a significant role in achieving precise process control.
Achieving Exceptional Hardness Results with Nitrogen Quenching
Ipsen’s Argos heat-treating system represents a significant milestone in the growing trend to operate LPC lines in combination with inert gas quenching. Using the AvaC process in combination with 20-bar nitrogen quenching, the Argos system provides metallurgical properties never before seen in gas quenching systems — even those utilizing 20-bar helium quenching.
An initial test was performed on a vacuum carburized component that is one of the most difficult to quench: layshafts for large gears. Until now, helium gas, which is both expensive and declining in availability, was required to fully transform parts with very high cross-sectional thicknesses. Test outcomes showed that the shafts processed in the Argos system with 20-bar nitrogen quenching achieved surface hardness and core hardness values comparable to shafts processed in existing vacuum heat-treating furnaces that use 20-bar helium quenching.
Increasing Production Flexibility
With the demand to meet lean manufacturing objectives, reduce cycle times, increase process flexibility, and maximize furnace uptime, it becomes clear that production flexibility is also an essential component of thermal processing equipment. The modular structure and software flexibility of multicell systems, such as the Argos furnace line, make them adaptable to a variety of plant configurations and changing production processes. For instance, it is possible to selectively isolate modules using Ipsen’s AutoMag® lights-out automation system, thus allowing the user to perform maintenance work on individual modules without affecting the entire production process. It is also easy to set up and take down individual modules without affecting the operation of the plant as a whole. As such, production capacity can easily be expanded or minimized as needed.
Based on specific process and industry needs, available modules can include nitriding, subzero, and/or high vacuum chambers, as well as a washer, pre-oxide furnace, LPC furnace, and tempering furnace. This new generation of multi-chamber furnaces also offers several distinct operational advantages in manufacturing. With synchronized movement between each process and real-time sensors implemented in each process stage, the intermediate buffers between heat treatment operations can be eliminated, and the transfer of loads between different modules (e.g., washing, carburizing, hardening, and tempering) can be monitored. As a result of this flexibility, the Argos heat-treating system provides several solutions that address a diverse range of user needs and easily integrates with technology that aligns with the Industry 4.0 and lean manufacturing movements.
As the demand for leaner, more streamlined operations continues to grow, thermal processing systems and applications will increasingly intersect with the latest advancements in technology if they are to provide the necessary solutions. Bridging this gap between the new generation of multi-chamber LPC heat-treating systems and the integration of furnace operations with the entire manufacturing process is Industry 4.0. As companies utilize the IoT in the form of sophisticated software that analyzes key data, gear manufactures can continue to work toward meeting lean manufacturing objectives, as well as enhancing overall production speed and process quality.