The night the experiment failed, Liu Li barely slept. Instead of returning to her dormitory, she found a bench in the corner of the workshop, wrapped herself in a cotton coat, and, under the dim light of the chandelier, repeatedly reviewed the experimental records.
The paper was filled with notes: the value of prestress, the turning speed and feed, the dial gauge readings at each time point, and fragmented observations she made by touch, such as "the vibration was obvious when the tool tip made contact" and "there seemed to be a slight tremor in the middle of the aluminum plate".
Just looking isn't enough. So she got up, put the failed workpiece back onto the fixture, and without turning on the power, used her hands to simulate cutting force to push and press, feeling the deformation of the workpiece and the fixture, and recording and studying the process.
As dawn approached, Fu Jingchen arrived, carrying two steamed buns. "I knew you'd be here." He handed her the buns, looking at her bloodshot eyes. "Don't force yourself, eat something first."
Liu Li shook her head, refusing the steamed bun, and shoved the notebook into his hand, pointing to several data points: "Jingchen, look here. The prestress I applied was taken at 70% of the theoretical maximum value, thinking of leaving some margin. But during actual cutting, the dial indicator showed that the deformation was very small in the initial stage, even a little reversed, but after cutting for a few seconds, the deformation suddenly increased."
Fu Jingchen took the notebook and looked at it carefully, his brows furrowing: "Initial reverse... this means the prestress you applied did work. But the subsequent increase... could it be due to the heat from cutting? Aluminum conducts heat quickly, causing localized temperature rise, softening the material, reducing its stiffness, and making the original prestress insufficient?"
“That’s possible!” Liu Li’s eyes lit up, as if she had grasped something. “Also, I can feel the middle section of the aluminum plate trembling. Could it be that the support point of the clamp wasn’t selected correctly? Is the middle part becoming a weak point that’s ‘suspended’?”
In the dim light of dawn, the two huddled together, analyzing the situation. Fu Jingchen took out his slide rule and draft paper, and based on the data recorded by Liu Li, re-estimated the temperature rise and material property changes that might be caused by cutting heat. He also drew a force diagram to analyze the rationality of the fixture support point layout.
“Look,” Fu Jingchen drew on the draft paper, “if the support points are close to both ends and the span in the middle is too large, it’s like a carrying pole carrying a heavy load; it’s most likely to bend in the middle. Your prestress is mainly applied near the support points, and it may have weakened by the time it reaches the middle, making it unable to resist the cutting force.”
"So, not only does the magnitude of the prestress need to be adjusted, but the location and method of application also need to be optimized?" Liu Li pressed.
“Yes! And we need to consider the impact of thermal deformation. Perhaps... we shouldn’t aim for perfection in one go, but could try applying it in stages? First, apply a basic prestress to offset most of the elastic deformation, and then in the final stage of finishing, make fine adjustments based on the actual situation to compensate for thermal deformation?” Fu Jingchen proposed a new idea.
This idea suddenly dawned on Liu Li. She had previously thought of using a fixed force to counteract all deformations, which was clearly too idealistic. Processing is dynamic; force, heat, and vibration are all changing, and compensation should also be dynamic and more precise!
She snatched the draft paper and quickly sketched the revised fixture on it, adding support points, optimizing the force application mechanism, and also marking possible "secondary fine-tuning" interfaces.
"I'll try again!" She raised her head, her eyes shining brightly once more, though exhausted. "This time, we'll divide the cutting parameters into several levels, recording complete deformation data for each level. We'll change the support points and apply the prestress in stages! I refuse to believe we can't peel this skin off!"
The disappointing data didn't defeat her; instead, it served as a treasure map, guiding her to a clearer direction for further exploration. She learned where to focus her efforts and how to adjust her strategy.
This time, she observed more closely and thought more deeply. Data became her most powerful weapon.
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