The parting surface of the precision mold is not allowed to be polished by hand. How to realize it?

Update:18-08-2022
Summary:

Now, many foreign businessmen put forward higher requir […]

Now, many foreign businessmen put forward higher requirements for the manufacture of molds. It is required that the parting surface of the mold provided by the mold manufacturer must not have traces of manual polishing, and many domestic factories cannot meet this requirement. In fact, general mid-range molds (small and medium-sized) should meet this requirement. This requirement is one of the comprehensive indicators to examine the design level, equipment level, process level, management level, quality assurance system and staff quality of the mold manufacturer.

The so-called inspection of the design level of precision molds is the rationality of the design and the optimization of the complex to simple optimization. At this point, there is still a big difference among Chinese mold manufacturers.

The so-called inspection equipment level is to see whether you have formal CNC equipment and use the correct technology to process it. At present, the world's most advanced mold manufacturing equipment can be seen in China. The general Chinese mold maker is basically okay with the equipment.

For management level and quality assurance system. It can only be said that more and more enterprises realize its importance.

Here we focus on some experiences of meeting this requirement in the processing technology.

First of all, finish machining the mold parts after 3-4 hours of work in the machining center, the effect will be the best. Secondly, it is necessary to solve the problem of deformation of mold parts due to internal stress during all processing, so as to minimize the deformation during processing.

During the machining of mold parts, due to the machining tools, electrodes, cutting wires, changes in cold and heat, and the force exerted by the fastening tools on the material, the resulting internal stress is continuously accumulated inside the material being machined; at the same time, the internal stress Stress builds up and tries to release it. When the accumulated internal stress reaches a considerable level, the rigidity of the material is overcome, the shape of the workpiece is changed, and deformation occurs. It is inevitable that the processed material accumulates internal stress during the cutting process, so it is also inevitable that the internal stress will cause the deformation of the mold parts. We know that the greatest accumulation of internal stress in mold parts is the drilling, grinding, roughing and electrical machining stages, as well as the welding stage.

Overcome deformation caused by internal forces in mold parts. There are only two ways: to eliminate internal stress and mechanical reprocessing or a combination of the two.

Eliminating internal stress is generally a method of heat treatment, which is what we usually call "relief treatment". Generally, after the steel parts enter the furnace, the temperature is gradually raised to about 590 ℃ within 6-12 hours, and the temperature is kept for 2-6 hours (depending on the size and thickness of the workpiece, but also according to the local seasonal temperature at that time), and then cooled with the furnace. This process generally takes 24-48 hours. Generally, after the aluminum parts are put into the furnace, the temperature is gradually raised to about 290 °C within 6 hours, and the temperature is kept for 2-4 hours (depending on the size and thickness of the workpiece, but also according to the local seasonal temperature at that time), and then cooled with the furnace. This process generally takes 24 hours.

During machining, especially rough machining, the force of the tightening tool must be uniform. Generally, multiple times, diagonal tightening, and tightening-loose-tightening methods are used. The processing method we are generally accustomed to is to identify a datum plane, which remains unchanged from the beginning to the end during the processing process, and use it as the benchmark to process other parts. In fact, this reference plane is also deformed due to the deformation caused by the accumulation of internal stress during processing. The deformation of the reference plane will cause many changes in the rest of the shape. Through trimming during assembly, there are many changes, which cumulatively affect the quality and life of the mold.

In order to make the performance of the manufactured mold meet the design requirements, we should solve the common problem in the mold manufacturing process of overcoming the deformation caused by the internal stress during the processing.

We generally select several surfaces in different directions as observation surfaces for self-detection of the degree of three-dimensional deformation during rough machining. If there is no ready-made, it can be attached and cut off after finishing. The additional observation surface should not be too small, and the observation will be inaccurate if it is too small. The principle is: the bigger it can be, the bigger it is, and it is easy to remove.

For example, on a part with a three-dimensional size of 1000×800×300mm, it is generally best to set the length of the observation surface to be no less than 900mm, 600mm, and 260mm. The smaller the observation surface, the larger the error between the measured value and the actual one.

In general, if the length of the observation surface is only 50% of the actual workpiece length, the measured value will be 1-2 times different from the actual one.

After rough machining is completed, measure the condition of each observation surface and record the data, try to completely loosen the tightening tool, but do not change the position of the workpiece on the work surface, and then measure the actual data of each observation surface of the workpiece, and compare the two , the deformation of the workpiece to be processed can generally be known.

Secondary tightening: Re-tighten each tightening tool until it does not move during processing. This is the hardest. Then a small amount of cutting is performed on each observation surface so that it can correctly play the true and correct role of the second reference (commonly known as the transition reference).

Turning the workpiece over: According to the deformation data measured after rough machining, when trimming the original datum surface, the workpiece must be leveled. If it is processed without pad leveling, other parts will have shape deviation, resulting in the excessive cutting amount in some parts, no cutting amount or even negative concave in some parts. This processing is to overcome the deformation of the reference plane so that it can continue to function as the first reference plane.

After the first "reaction treatment" (after roughing), the datum is re-machined. It is different from the following procedure.

The processing of the first datum surface causes the error between it and other surfaces. In order to solve this contradiction, the workpiece is turned over and tightened again: this time, the workpiece is best placed in its original position. The inspection is carried out on each original inspection surface that has been processed for the second time. The error between it and the new datum surface is generally caused by over-tightening during secondary tightening. With the accumulation of experience, this error will become smaller and smaller. Perform semi-finishing on each part of the original processing. When finished, check. If there is no problem in the inspection, it will be transferred to the next process.

If an appropriate machining allowance is reserved on the parting surface in advance, before polishing, the three-dimensional reference of the cavity (space 0 positions) is measured with a three-coordinate machine, and then the reference surface and the parting surface are processed for the third time. Here, a problem needs to be emphasized. Our use of 3D software is now very common. But there are two design datums we use: center 0-bit datum and corner 0-bit datum. The former is popularized with the development of CAD. For beginners, the entry is slow, but it is very accurate and not easy to make mistakes. The latter is to follow the traditional design method, which is prone to errors. What I mean here is "measurement of the three-dimensional reference of the cavity (space 0-bit) with a three-coordinate machine", which refers to the design and detection of the "center 0-bit reference". If you experience it, you will understand what I mean.

Generally, according to this process, the deformation caused by the internal stress caused by processing can be overcome. The parting surface can avoid the process of manual flying.

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