A Look Back, Forward at Process Control
Looking at past equipment purchasing decisions from our current vantage point makes us wonder about future purchases. This article looks at that dilemma.
I currently work for a supplier of instrumentation to the heat-treatment industry and was intrigued by a question asked by a long-standing customer: If I had the job to specify an entire heat-treatment cell, what would I personally invest in? Knowing that this decision would impact the fortunes of a business over the next 20 years (a typical financial time-frame for a furnace purchase) and that the world is not as predictable as it once was, what questions would I ask myself (or others) today to make a decent selection?
For arguments sake, let’s decide this would be a batch carburizing process for treating gearbox components. It just so happens that I have some experience in this area, and nearly 20 years ago, I had my first opportunity to specify, purchase and run a brand new heat-treatment cell to supply gearbox components to a major premium-brand automotive OEM.
Would I decide to select the same path today as I chose 20 years ago?
The short answer is no.
It is almost impossible to make the same decision as 20 years ago because the technology of the day then is not available today. A mix of technology developments, regulations and environmental issues, and a growing concern with environmental sustainability (RoHS compliance, etc.) has definitely impacted the direction of furnace technology.
The world has changed its view about manufacturing over the past few years. China was a favorite destination, but now there is more of a seesaw experience about plant location decisions between BRIC countries and the more established nations. Current conflicts around the world also cloud an already murky picture.
It would be fair to say that a new furnace installation today and into the future could likely move locations (even countries!) once, if not a couple of times, throughout its financial 20-year life. For this reason, some manufacturers have deliberately created more portable versions of their furnaces. This situation was not the case 20 years ago, and less thought had to go into plug-and-play. But it is definitely a decision that needs to be taken into account now.
Over the lifetime of the furnace, the furnace process might even change. This is perhaps easier to address in batch integral-quench furnaces where it is possible to change between case-hardening and neutral hardening. Developments of new alloys and different plating or coating technology may reduce the reliance on the carburizing process in the future. So, a gearbox-component batch-carburizing process today may become a shorter-cycle, direct-hardening process in the same piece of equipment. This requires the control system to be flexible and adaptable.
Then there is the question about vacuum or atmosphere processes. Certainly, vacuum processes are more favored today for gearbox components, but this process does come with a higher price tag. This financial burden can be mitigated by reduced running costs, depending on the process allowed. Vacuum processes can lend themselves to higher-temperature carburizing, but the steel type may dictate the extent of the increase in order to avoid issues with impairing fatigue life due to grain growth.
Labor costs have increased worldwide and are definitely rising at a steep pace in China and India. Wage inflation is pretty sluggish in the U.S. currently, but the so-called experts are scared of a potential uptrend, which will push inflation out of a comfortable/manageable window. As a supplier of automation products (full disclosure), I am obligated to point out that you need to improve the productivity of your setup to mitigate these higher personnel costs. One way to do this is to increase the automation in the process cycle.
What is the automation difference for the heat-treat cell started 20 years ago?
Operator or support personnel involvement is still needed in the jigging process to orientate the workpieces within wire baskets or cast grids. This process has been coming under scrutiny and in some cases has attracted robotic automation with some standard setups being operated entirely by robots. Special jigging robots will eventually be available that can “learn on the job.” The investment cost of robotics has dramatically decreased over time. Programming technology has been made easier, but this type of automation is definitely still in its infancy in the heat-treat world.
Time, temperature and atmosphere are the key elements to control during a heat-treat process. Certainly, the microprocessor-based discrete controllers 20 years ago were competent to provide complete setpoint programming (e.g., ramp, preheat, boost, diffuse, equalize and quench). The process was run to a large extent, however, on push-button logic control to provide the movement between chambers. Internal movement in a furnace is now largely replaced by PLCs. These PLCs can “talk” to each other and also control the movement of items within the overall heat-treatment cell. Operator involvement in providing the control around movement of items – between process types (e.g., furnace, washer, temper/draw furnace) – has largely been made redundant.
The temperature controller is still predominantly a discrete controller because of the designed accuracy levels in those devices and the specifications required by many regulatory standards (Nadcap/AMS 2750E, CQI-9, etc.). It is noticeable over the last 20 years that the pyrometry standards referenced by both the automotive and aerospace industries have tightened their accuracy requirements, making it difficult for older instruments to meet the current standards. A new type of PLC was launched at Furnaces North America that bridges the technology gap between conventional PLCs, discrete controllers and chart recorders. As a result, the requirement for interface/communication technology to link multiple devices together is reduced as is the programming complexity and number of interfaces of potential failure.
Atmosphere Control (Batch Integral Quench)
The atmosphere control in batch integral-quench applications historically moved from manually controlled fixed gas flows to automatic oxygen-probe control. Oxygen-probe/zirconia technology has been well established now for over 20 years. Over the past 20 years, there have been movements to and from gas infrared technology to provide a more accurate picture of the furnace atmosphere (by utilizing 3GasIR with additional sensors for carbon monoxide, carbon dioxide and free methane). Constant maintenance requirements to enable these systems to operate at optimum levels have always created doubt in the mind of the heat treater as to whether this additional effort and expense is worthwhile. Low-cost and more robust IR units are now being used by different industries, and it will be interesting to see the migration of these setups into heat treatment.
Online carbon-diffusion algorithms come to the rescue of the 3GasIR units. These algorithms are more accurate when they are fed precise atmosphere information. They can ultimately offer cost savings through tightening of process specifications and improving overall quality output by modeling the carbon activity in real time and adjusting the cycle time to achieve the best nominal case depths.
Twenty years ago, the vacuum processes for carburizing were still in their infancy and not widely used. Low-pressure (or plasma) with carbon supply from methane, propane, acetylene or mixtures thereof have now been successfully used in many automotive applications. This is fast becoming the preferred route to vacuum carburize gearbox components because it eliminates the potential of oxidizing key elements (e.g., chromium in the case of endothermic atmospheres in batch integral-quench furnaces), which can form intergranular oxidation and lead to compromised fatigue performance.
There is still a bit of an issue with carbon control in irregular batches in vacuum carburizing and matching surface areas to create process requirements, but I am sure the math geniuses will eventually solve this and provide robust process-control solutions no matter the makeup of the batch.
A View into the Future (not far away)
Here are several points to keep an eye on in the years to come.
1. Other algorithms that can adjust the time at temperature based on operating conditions rather than rely on 100-year-old rules of thumb (e.g., 1 hour per inch) will definitely start to impact furnace productivity in the years to come. Predictive technology on furnace furniture that alerts when a repair or replacement is due based on actual running conditions (not just hours run) will also improve uptime and overall productivity.
2. Reducing operator errors through error-proofing software and improving off-machine training programs are already being used in a number of industries. 3D virtual-reality systems are already used in the oil and gas industry to train operators on furnaces. Providing clear alarm and action procedures if faults occur will help reduce the unwanted issues that arise from inexperienced or poorly trained personnel.
3. Providing interfaces to control instrumentation that are comfortable for the electrical engineer, maintenance engineer and operator to pick up quickly and easily will become more of a criterion for purchase of new technology.
4. External software planning systems that seamlessly integrate with each piece of equipment to avoid machine queues and prioritize batches will also improve the success of the supervisor or production manager and timely turnaround of heat-treated workpieces.
5. Energy-management systems that are linked to equipment can provide contextual information to the data points recorded, allowing analysis and improvement that results in tangible cost savings.
6. Sharing information electronically between different systems – typically now using an Ethernet backbone – brings in the issue of plant security. This is a concern shared by all automation vendors who are working on technology to aid security in this more open environment.
7. There are other advances in display technology, wearables, augmented reality, etc., that will impact the lives of a heat treater over the next 20 years to a greater or lesser extent.
Following the number of points raised in this article, I think that even more careful consideration is required in your next furnace purchase (new or refurbished). The system selected is not like the fixed technology of 20 years ago but has far more freedom to flex and grow to cater for continuous improvement and unanticipated future challenges. Good luck with your next purchase. IH