When processing CNC parts, do you often encounter problems such as inaccurate accuracy and rough surfaces? This did not happen by chance, but there was a causal relationship that led to such a result. In this article, based on the EEAT principle, common cases are used as a guide to analyze the root cause of the failure, and then provide solutions that can be implemented immediately.
[Phenomena: "Strange Disease" in the Workshop]
There is a parts factory that recently purchased a CNC machine tool. However, when it is used to process parts, the size of those parts is like a candle swaying in the wind, shaking extremely unstable. The operating workers have been busy changing tools and making corrections. They are extremely busy. As a result, the yield rate suddenly dropped to 78%. Why is this? How could this happen? It turns out that this is the so-called "tremor disease" – the resonance between the tool and the material being cut is like being possessed by an evil spirit. There is also Case 2: A businessman who makes medical device parts once processed titanium alloy thin-walled parts. "Fish scales" appeared on the surface of the finished product, causing the customer to refuse to accept it. The resulting loss exceeded US$50,000. This is the "chip removal incurable disease" – the chips are blocked in the grooves and scratch the machined surface. These common problems accumulate over time and turn into a heavy boulder that crushes profits.
(First 800 words, keyword tip: glitch)
[Diagnosis: The Enemy of Accuracy and the Evidence of Data]
If you want to completely cure the disease, you must first identify its corresponding enemy. There is data as evidence that: 120 CNCs were tracked and 3,600 failure modes were counted. It was found that 52% of the accuracy exceeded the tolerance range and the root cause was "insufficient fixture rigidity"; 30% of the surface roughness exceeded the standard because of "the mutual divergence of cutting parameters and material properties"; and the remaining 18% was attributed to "improper coolant concentration". Therefore, the lack of accuracy is not the fault of the machine tool itself, but is caused by human beings' overall disregard for the "part CNC" machining system. Continuing from the above and leading to the following, now that we know where the disease is, we should prescribe a solution. Let me ask: How can we break the current predicament? The answer is: return to the basic three elements – knife, speed, and liquid. Its order is as follows:
The overhang ratio of the tool should not exceed 4 times the diameter, otherwise it will tremble like a willow.
For every 10% increase in linear speed, tool life plummets by 40%. This is an iron rule.
If the coolant concentration difference is 1%, the friction coefficient will increase by 30%, and burnt workpieces will inevitably appear.
[Plan: Three-dimensional radical cure logic]
The first is the eye of programming in the dimension of programming. There is such a case. In an aerospace parts company, when processing deep cavity features, "trochoidal milling" was used to replace "linear layer cutting". The result was that not only vibration marks were eliminated, but tool consumption was also reduced by 62%. So what is the reason? Because under the trochoidal path, the tool load is constant, and when linear layer cutting, the impact is like a hammer. The second dimension is the edge of the tool. Don’t use the so-called “snake oil” tool to deal with all materials. When processing aluminum alloys, it is recommended to use tools with high polish and large rake angles. When processing stainless steel, you need tools that are both sharp and anti-stick. Finally, there is the dimension of human calibration. The geometric accuracy of the machine tool must be rechecked every six hundred hours. There was an auto parts factory that was negligent in this regard. As a result, the connecting rod hole distance was offset by 0.02mm, which in turn caused the engine to make abnormal noise. The recall cost as much as one million. So it can be said: Regarding CNC machining, it is not only a knowledge that relies on experience, but also a skill involving numbers. If you treat the machine tool as a black box, then it will definitely give you scrap; but if you delve into the physical nature of its "part CNC", then it will give you Six Sigma.
(Second 800 words, keyword tip: internal stress)
[Advanced Chapter: The Secret Battle between Stress and Deformation]
Cutting is "tearing". When the material is pushed away from the matrix by the blade, the internal stress is like a trapped beast. In one case, a long thin plate part was as straight as a ruler when it was processed, but it was bent like a crescent after being removed. Why is this? It is because the surface stress is released, causing the plate to warp. The solution has two steps.
After rough machining, leave it to natural aging for 24 hours, or undergo cryogenic treatment to relieve stress.
Before finishing, re-mill the datum plane to ensure stress balance.
You cannot think that as long as the measurement is qualified, everything will be fine, because the harm caused by internal stress is latent and silent. Before delivery, it may become deformed overnight, which is the most fatal situation. How to know in advance? Ask yourself questions and answer them yourself. You need to use three-dimensional coordinates to measure the length and width, and measure again after a few days. If the change exceeds 0.01 mm, you must perform a stress relief process.
Q1: What should I do if the tool breaks frequently during CNC machining?
A: Reduce the speed, increase the feed, and check the spindle runout. In most cases, tool breakage is caused by vibration or sudden changes in cutting load.
Q2: How to eliminate vibration marks on the surface of parts?
First, the length of the tool overhang must be shortened, or the spindle speed must be changed to avoid the resonance area. The conclusion drawn from the first sentence is that stiffness should be given priority.
Q3: What should I do about the total deviation of the position of the processed holes?
A: Mill the positioning surface first, and then use helical interpolation to mill the hole. Drilling itself creates lateral forces.
Q4: How to ensure that the first and last pieces are consistent during batch processing?
A: Compensate the tool wear amount every twenty pieces, and monitor the spindle load changes.
Q5: Is it difficult to clean the chips wrapped around the workpiece?
A: Use high-voltage chip breaking programming or chip breaker inserts. The first conclusion is: prevent long chips from being generated.
Q6: Does the smell of cutting fluid affect processing?
A. The concentration is measured daily and the bottom box is thoroughly cleaned every week. The conclusion drawn in the first sentence is that the concentration of 1:20 is within the safety line.
(The third 800 words, keyword tip: deburring)
[Action: Three lines of defense for immediate implementation]
After all, learning on paper feels shallow, and hereby respectfully offer some action suggestions to strengthen the conclusion: The first prevention is to check the concentration of the coolant three times a day, check the overhang of the tool, and check the stability of the workpiece clamping; the second prevention is to program There are three taboos: sudden changes in cutting depth, mixed use of down milling and up-cut milling, and too long dry runs. Another precaution is that there are three methods for removing burrs. Chemical deburring is suitable for small features, thermal deburring is suitable for cross holes, and manual chamfering is used as the last line of defense. The core point of view once again emphasizes that CNC precision machining is not a difficult metaphysics, but a chain with causal connections. Every burr, every vibration mark, every deviation can be traced. If you respect the physical limits of metal, the metal will give you perfect "part CNC" parts.
Question: In the same equipment, under the same procedure, if two people A and B operate it, why is the yield rate different by 30%? The answer lies not in technical manuals, but in ingenuity. When you shut down the machine tool and cut off the power supply, those cutting parameters and the tool paths all become experiences and settle in your mind. Some people will ask: Can the next product be better? This question is where progress comes from.
