Special topic on precision machining of large workpieces
If an accident occurs in the processing of large parts, it will often lead to serious losses of hundreds of thousands or even millions of dollars. However, the very strange situation is that every relevant construction link is particularly prone to problems or errors. Next, we will explain the six most critical important points in detail and clearly.
If the accuracy is less than one millimeter, it will be scrapped.
The size of large parts is relatively large, so the thermal deformation phenomenon and vibration amplification effect are very obvious. In 2025, a heavy industry workshop in Shenyang processed a wind turbine spindle with a diameter of four meters. As a result, a shape error of 0.02 mm caused the entire product to be scrapped.
The material cost of this product exceeds the 1.2 million yuan. For such workpieces, thermal equilibrium treatment and stress relief operations must be performed before processing. If the preparation time is not enough to challenge the large-scale parts processing technology , then all the subsequent work will be in vain.
Accuracy requirements are also reflected in tolerance superposition. There are more than a dozen key mating surfaces on a large shell. If there is a deviation of 0.01 mm on each surface, it will become a big problem when these deviations are accumulated during assembly. Therefore, the operator must clearly calculate the tolerance chain in advance, and at the same time, the processing sequence and allowance of each surface must be properly arranged.
Repairing after a mistake is extremely costly
For small parts, even if it exceeds the specified value, it can still be repaired, but for large workpieces, that is not possible. In 2024, there was an equipment factory belonging to a mining industry in Hunan, and they went to process a set of tooth plates belonging to a large crusher. During rough machining, an extra 0.5 millimeter was walked.
They want to use surfacing welding method to carry out repair work. As a result, the problem of uneven stress distribution occurs. After heat treatment, this thing cracked directly. The economic loss caused by this failure was approximately 850,000 yuan. At the same time, the entire work period was delayed by two months.
Large workpieces can easily weigh dozens of tons. Repair requires complete hoisting and partial heat treatment. Each step involves additional equipment and space. The time and capital costs are far beyond those of small items. One mistake may result in the loss of half the production line.
If you can't move it, I'll force you to change your craftsmanship.
There is a gear weighing 60 tons. This gear requires a total of three specific operations from rough machining to finishing. During this period, each time a bridge crane with a rated lifting capacity of 250 tons is required to carry out lifting operations. The cost of this hoisting service alone is close to tens of thousands of yuan. For workpieces with obvious centers of gravity, if the lifting point plan is not designed very appropriately, It is very easy to cause a tipping accident. During 2023, a factory manufacturing machine tool equipment in Jiangsu Province had an accident in which the boom was significantly deformed due to the above reasons.
As long as the workpiece cannot be moved, that means it must be processed in situ, the equipment must be moved next to the workpiece, or the workpiece itself needs to be able to be turned over. This regulation directly determines whether you should choose the gantry milling method, the turning and milling composite processing technology, or the five-axis linkage technology. The entire process roadmap needs to be rearranged and laid out.
Composite equipment is an unavoidable choice
The domestic large-scale parts processing trend in 2025 has become very clear, and single-function equipment is becoming increasingly insufficient. If a large rotor is turned on a lathe first, and then goes to a boring machine for two clamping operations of the boring process, the cumulative error will be difficult to control within 0.01 mm. Application special topic on precision machining of large workpieces. However, using the turning and milling composite process can complete the cutting of multiple processes in one clamping, reducing the direct error by half.
However, the price of composite equipment is relatively high. For example, a gantry turning and milling composite machine with a length of 15 meters costs more than 20 million yuan, which not all factories can afford. Under normal circumstances, when faced with small and medium-sized factories, special fixtures are usually used to combine one-time clamping and multi-faceted processing, so as to suppress the resulting errors with force.
Move one hair and move the whole body
The processing chain of large workpieces is very long. Every step is closely connected: design link, blanking link, rough machining link, finishing link, inspection link and assembly link. In early 2026 , due to technical challenges in large-scale parts processing , a shipyard in Shanghai received an order for the production of a marine crankshaft.
During the rough machining process, the reserved machining allowance is calculated to be relatively small, only 0.3 mm less. When it came to the finishing stage, it was discovered that there was not enough material to carry out cutting. This forced the production plan to be rearranged, causing the entire production line to be stagnant for as long as three weeks.
As long as every link changes, the accounts must be calculated again. For example, if the tool path changes, the clamping method must be adjusted accordingly. If the clamping parameters are adjusted, the deformation compensation value must be calculated again. Generally speaking, a set of craft cards for large workpieces is often dozens of pages thick. So if you move a small place, it will affect the whole body and affect the whole situation.
Live data speaks
By 2025, the average one-time pass inspection for large parts in the Yangtze River Delta region will be about 82%. The data for the Northern Heavy Industry Base is only about 78%. Among them, the three main reasons that hold back the most serious problems are as follows. One is that the problem of thermal deformation is not well controlled. The second is the impact of clamping deformation. The third reason is that detection methods have not been able to keep up with development in time.
At present, large enterprises at the forefront of the industry have begun to deploy online testing equipment. In the middle of the processing work, a measurement operation will be performed, and the data generated by the inspection will be directly sent back to the CNC system so that the system can make real-time compensation adjustments based on the data.
After a wind power tower manufacturing factory in Shandong installed this system, the product defect rate was reduced from the original 5% to 1.2%, saving nearly 3 million per year.
When your factory handles large workpieces, the most worrying thing is whether it can achieve accurate accuracy or whether the transportation cost is too high? You can discuss this matter in the comment area, give it a like by the way, and forward it to your colleagues and friends.
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