78: Bringing his wife and children to Harbin Institute of Technology

Chapter 141, Batch 1 of Returns

On the fifteenth day, the rough steel mold blank was delivered.

Two large iron blocks, shaped similarly to the product's outline, but with rough surfaces, leaving room for fine finishing.

Master Li moved the two iron blocks onto the milling machine and clamped them.

The blueprints were spread out beside him, and he took calipers and measured bit by bit, drawing lines on the iron block.

After the markings are completed, start the milling machine.

The milling cutter spun and made a screeching sound when it hit the iron block.

Iron filings flew everywhere. Wearing safety goggles, Master Li kept his eyes fixed on the milling cutter and cranked the feed handwheel, pushing it forward again and again.

After making one cut, stop, take calipers to measure, and then make the next cut.

He spent an entire morning milling a single curved surface.

After milling, I compared it with a standard block and looked at it against the light. The surface was flat, but it was still a little short of ▽7.

Master Li then switched to a finer milling cutter and went through the process again.

The surface that came out this time was much smoother.

Chen An measured it with a roughness tester, and it was close to ▽7.

"Master Li, that's about it."

Mr. Li took off his goggles and wiped his sweat.

"Okay, then we'll use it for now."

The precision machining of the steel mold took five days.

Master Li mills until midnight every day. When he gets tired, he sits down next to the milling machine to rest for a while, and then continues working.

On the twentieth day, the steel mold was finally completed.

The two halves fit together perfectly, with a surface finish of ▽7.

Liu Xiaojun moved the steel mold onto the press and tested the pressure.

As soon as the first item came out, Chen An quickly took measurements.

All dimensions are up to standard, the surface finish meets the requirements, and when held up to the light, a person's reflection can be seen.

"It's done!" Liu Xiaojun shouted.

Master Li stood to the side, looked at the sample, and smiled.

But after laughing, his expression turned serious again.

"Ten days left, 80 items, is that enough time?"

No one answered.

Starting from the twenty-first day, the factory went all out to sprint ahead.

The steel mold presses two pieces at a time, each mold takes sixty minutes, and it runs 24 hours a day, producing 48 pieces.

However, this is a theoretical value. In actual production, the time required for layup, mold closing, and inspection must also be considered.

Chen An rearranged the work schedule: 16 pieces for the day shift, 16 pieces for the night shift, 32 pieces per day, and 320 pieces in ten days.

Production capacity is sufficient, but testing cannot keep up.

Every piece had to be measured for size, smoothness, and internal defects. Zheng Shuyun and Chen An would measure 32 pieces a day, from morning till night, even eating right next to the testing station.

An'an was taken to the factory after school, where she sat in the office to draw. After finishing a drawing, she would run to the workshop to find someone to look at it.

Liu Xiaojun looked at her painting and said:

"An'an, your drawing of the mixer is even more beautiful than the real one."

An'an was delighted: "Then I'll draw another one."

On the twenty-fifth day, 60 pieces had already been made.

All are qualified; dimensions and surface finish meet standards.

Chen An posted the data on the wall; the pass rate line was always 100%.

Ye Bingwen felt a little more at ease after looking at that line every day.

But they hadn't been at ease for more than a few days when the accident happened on the twenty-seventh day.

That afternoon, Engineer Sun arrived, three days earlier than the agreed time.

He didn't call ahead; he just showed up.

Ye Bingwen was inspecting the day's finished products in the workshop when he saw Engineer Sun walk in, and his heart skipped a beat.

Engineer Sun maintained the same expression, said nothing, and walked to the testing station.

Zheng Shuyun was testing a finished product when she saw Engineer Sun and paused for a moment.

Engineer Sun picked up a finished product that had already been measured and examined it from all angles.

Then they picked up the second item, and the third item.

After looking at them, he put the finished products back on the table.

"Director Ye, there's something wrong with these items."

Ye Bingwen walked over: "What's the problem?"

"The surface finish does not reach ▽7."

Chen An quickly took a roughness tester and measured it. The data showed that it was half a grade lower than ▽7.

His expression changed: "All the previous tests were up to standard, how come these few..."

Engineer Sun looked at him:

"The previous ones are the previous ones, these few won't do."

He took a piece of paper out of his briefcase; it was a return order.

The label reads: "The first batch of 20 pieces was delivered, but 12 pieces failed the surface finish test and were therefore returned."

Ye Bingwen looked at the return slip without saying a word.

Engineer Sun ignored Ye Bingwen's emotions and simply placed the form on the table:

"You have three days left. 100 items, not one less, not one missing."

After finishing his sentence, Engineer Sun left without delay.

After Engineer Sun left, the workshop became eerily quiet.

Seeing that something was wrong, Mr. Li went over to take a look at the returned samples.

"Were these made using steel molds or wooden molds?"

Chen An flipped through the records:

"Made with steel molds, batch from day 23 to day 25."

"How could something made with a steel mold not have a smooth finish?"

Chen An was also confused. He tested it again, and the data was indeed insufficient.

He compared the previously qualified samples with the samples and found that the qualified ones had a brighter surface, while the unqualified ones had a very fine hazy texture.

Liu Xiaojun squatted down and examined it for a long time: "Is the surface of the steel mold worn?"

Master Li disassembled the steel mold and used a magnifying glass to examine the inner surface.

Sure enough, there were several very fine scratches on the surface, which were not noticeable unless you looked closely, but the pressed product would have a hazy texture on the surface.

"How did these scratches get there?"

After thinking for a long time, Liu Xiaojun deduced:

"It was probably pried open with a metal tool during demolding, which damaged the surface of the mold."

Master Li frowned and said to Ye Bingwen:

"The steel mold needs to be repolished, which will take at least a day."

Ye Bingwen didn't speak, but looked down at his watch.

With three days left, I need to remake 12 returned items and finish the remaining 40, for a total of 52 items.

Polishing takes one day, leaving only two days for production. It's impossible to make 52 pieces in two days.

Chen An lowered his head, thinking of a solution, when suddenly he looked up:

"Director Ye, let's use wooden molds instead. Although the parts made from wooden molds are not as smooth, we've tested them before, and some batches have met the standards."

"Mr. Sun just returned a batch of parts that weren't smooth enough. If you give him the wooden mold parts now, will he accept them?"

Ye Bingwen stood in the workshop, looking at the pile of returned samples, his mind racing as he thought of a solution.

At this moment, Master Li walked over:

"Xiao Ye, how about we polish them by hand? After each piece comes out, we can run it through with fine sandpaper again to improve the smoothness."

"52 pieces, polishing each one individually, is that enough time?"

"Old Hu and I can process about twenty pieces a day, and forty pieces in two days, that's about right."

Chen An shook his head after listening:

"Uneven hand-polishing can cause the dimensions to shift if too much polishing is done in some areas, making it even more difficult to guarantee the yield rate."

After he finished speaking, the workshop fell silent again as everyone pondered a solution.

Liu Xiaojun squatted next to the old mixer, holding the returned sample in his hand, examining it over and over.

Suddenly he stood up:

"Uncle Ye, the problem isn't with the mold, it's with the materials."

Everyone who heard this turned to look at him.

Liu Xiaojun held the sample up to the light:

"Look, this hazy texture isn't caused by scratches or pressure marks; it's caused by uneven surface shrinkage during resin curing."

Then they held up the previously qualified sample and compared the two.

The one that meets the standard has a brighter surface and finer texture.

The one that didn't meet the standard had a very fine orange peel texture on its surface.

"The temperature distribution on the surface of the steel mold is uneven. Some areas heat up quickly while others heat up slowly. As a result, the resin curing shrinkage is different, which causes textures to appear on the surface."

After hearing what Liu Xiaojun said, Chen An quickly checked the temperature records of the compressor.

Sure enough, the temperature fluctuation of the press in the batches from day 23 to day 25 was two degrees greater than before.

"The heating element is old," Liu Xiaojun said.

Master Li looked at Ye Bingwen:

"How long does it take to replace the heating element?"

Liu Xiaojun's tone was firm:

Two hours.

"Then let's change it."

Ye Bingwen still looked at Liu Xiaojun with great concern:

"Will the previous problems be resolved after the replacement?"

"Yes, but the 12 pieces that have already been made cannot be salvaged."

Ye Bingwen made up his mind and said: