Automating Large Autoclaves for Complex Parts

Herbert Chelner, CEO and Chief Scientist

Dr. Robert A. Mueller, President and General Manager

 Abstract

Micron Instruments has been a leader in design and manufacturing of high-precision semiconductor strain gages. The benefits of semiconductor strain gages are discussed in Compelling Benefits or Micron Instruments Semiconductor Strain Gages. With wireless sensing rapidly becoming the data acquisition method of choice, Micron Instruments is also creating a new line of strain gages that are especially effective in passive wireless implementations.

In this paper we discuss the automation of autoclaves for precise processing of complex parts and show how the judicious use of Micron Instruments’ sensors can lead to much higher production efficiency.

The Challenge

Autoclaved parts are normally time, temperature, and humidity dependent. There are times when the cure cycle is perfect but the part does not meet the performance requirements.

This scenario occurred recently in a solid propellant manufacture. Ten motors were poured and the time temperature cure was proper - yet all ten failed. Why? How?

Sensor-Based Automation

There was a bond stress sensor in the bottom of the mold and, when interrogated, it showed that the grain was not fully cured. The process has now been automated so that it will not complete the cure until the bond stress is within acceptable limits. Since this has been initiated, no motor failures have occurred.

Similarly, a stress response test sensor can be added to the above and used to test the part or parts during autoclave curing to continue the cure cycle until all testing during the cure shows the stress is within limits - insuring that the part is good.

Fully automating the process means that the system will not only run autonomously, but also will automatically detect and notify responsible person or persons of a malfunction. When faults are detected, the system would shunt down the process to avoid damage and make intelligent decisions on time and temperature to maximize good parts.

Even when the chemicals and materials meet all specifications, the cure cycles can change due to small amount of uncertainty in all materials. Minor alterations in the curing can save these parts.

Micron Instruments can make bond stress and resiliency sensors for this type of automation. Micron presently makes and has on the shelf, bond stress and temperature sensors in a single casing. Resiliency sensors are usually application sensitive and designed for the specific part or parts.

The Role of Wireless Communication

 It’s pretty obvious that wires are a significant problem in many applications, which has given rise to dramatic advances in wireless communication technologies and standardization. The elimination of wires, wire connectors, and the associated mechanical support and holes, offers numerous benefits. These benefits include reduced cost, minimal physical space needs, safety, capability, performance, and reliability.

It’s also well known that sensors are becoming ubiquitous, and as sensor use proliferates so do the problems with wired communication. So, again, we see a rapidly growing demand for wireless sensing. However, the challenges for wireless sensing can be quite different than those for wireless voice or data communication. Sensors often must be placed in locations that are unfriendly to RF transmission, or even in applications where wireless communication can present a safety hazard. And, when it is advantageous to operate without batteries, passive wireless sensing offers many benefits but introduces further challenges. Micron Instruments is addressing these challenges as it extends its line of semiconductor strain gages to support passive wireless sensing.

In the context of process automation, sensors and wireless communication both play key roles. Consider the conceptual transformation model, shown below:

The process always starts with acquiring appropriate, accurate, and reliable data. In many applications, users are not generally interested in the data, but rather information provided by the data. For example, the user may only be interested when data is out of range. Examples of this span from environmental limits (e.g., temperature or humidity thresholds), to exposure limits (e.g., excessive shock or vibration levels), to “geo-fences” (where GPS data can be used to determine a vehicle is traveling outside prescribed geographical boundaries). These are all considered “exceptional” situations.

Exceptional situations that are interpreted in context or with semantic information (e.g., ontologies) can transform information into actionable knowledge.

When wireless sensing is used to both acquire and transmit data and information, we can achieve autonomous systems that provide real-time notifications, alerts, and alarms. Given today’s highly interconnected world, this can provide users with immediate knowledge of process status or exceptional conditions, anytime and anywhere.

Want to Learn More? Interested in Collaborating?

 Whether you’re interested in pursuing this type of design, or another measurement related application or design, please contact us for a free, confidential consultation either by email using our Contact Us Form or phone (805-522-4676).

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