PTJ products involve technology and electronic products, Shenzhen plastic molds, auto parts, exquisite gifts, audio-visual office supplies, civilian plastic machining products, exquisite toy products and many other industries. Put forward higher requirements for manufacturing 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, generally 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 employee quality of mold manufacturers.
The so-called inspection design level of precision molds is whether the rationality of the design and the optimization of the complexity into simple are the best. This point is still very different 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. At present, the world’s advanced mold manufacturing equipment can be seen in China. The general Chinese mold maker is basically ok in equipment.
For the management level and quality assurance system. It can only be said that more and more companies realize its importance.
Here, I will focus on some experience of meeting this requirement in the machining technology.
First of all, finish machining the mold parts after 3-4 hours of working 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 machining, so as to minimize the deformation during machining.
During the cutting of mold parts, due to the machining tools, electrodes, cutting wires, changes in cold and heat, and the force exerted on the material by the fastening tools, the internal stresses generated by the processed materials are continuously accumulated; at the same time, internal Stress is constantly accumulating in an attempt to release. When the accumulated internal stress reaches a considerable degree, the rigidity of the material is overcome, the shape of the workpiece is changed, and the deformation occurs. It is inevitable for the processed material to accumulate internal stress during the cutting process, so it is inevitable that the internal stress will cause the mold parts to deform. We know that the most internal stress accumulates in the mold parts is the deep hole, grinding, roughing and electrical machining stages, as well as the welding machining stage.
Overcome the deformation caused by internal forces in the mold parts. There are only two ways: elimination of internal stress and mechanical remachining or a combination of the two.
Elimination of internal stress is generally to adopt the method of heat treatment, which is what we usually call “correspondence treatment”. After the general steel parts enter the furnace, they will gradually heat up to about 590°C within 6-12 hours, keep them warm for 2-6 hours (depending on the size and thickness of the workpiece, but also according to the local seasonal temperature at the time), and then cool down with the furnace. This process generally takes 24-48 hours. Generally, after the aluminum parts enter the furnace, the temperature is gradually increased 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 the time), and then cooled with the furnace. This process generally takes 24 hours.
During mechanical machining, especially rough machining, the force of the fastening tool must be even. Generally, multi-pass, diagonal fastening, tight-loose-tight method is adopted. The machining method we are generally used to is to identify a reference surface, which remains unchanged from beginning to end during the machining process, and uses it as a reference to process other parts. In fact, due to the deformation caused by the accumulation of internal stress during cnc machining, this reference plane is also deforming. The deformation of the reference plane will cause many changes in other shapes. Through trimming during assembly, many changes have been produced, and these accumulations will 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 to overcome the deformation caused by the internal stress during the machining.
We generally select several surfaces in different directions as the observation surface for self-checking the degree of three-dimensional deformation during rough machining. If there is no ready-made one, you can attach it and cut it out when finishing. The additional observation surface should not be too small, and the observation is not accurate if it is too small. The principle is: big can be big, easy to remove. For example: on a part with a three-dimensional size of 1000×800×300mm, it is generally best to set the observation surface length not less than 900mm, 600mm, or 260mm. The smaller the observation surface, the greater the error between the measured value and the actual value. 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 length.
When rough machining is completed, after measuring the conditions of each observation surface and recording 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 phases. , Generally you can know the deformation of the processed workpiece.
Twice tightening: tighten the tightening tools again until they will not move during machining. 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 datum (commonly known as the transition datum).
Workpiece turning over: According to the deformation data measured after rough machining, when trimming the original reference surface, the work piece must be leveled. If it is processed without leveling, other parts will have a shape shift, causing some parts to cut too much, and some parts have no cutting volume or even negative recesses. This process is to overcome the deformation of the reference surface, so that it can continue to play the role of the first reference surface. After the first “correspondence machining” (after rough machining), rework the datum plane. It is different from the following process. The machining of the first datum surface causes errors between it and other surfaces. In order to solve this contradiction, the workpiece is turned over and tightened again: this time the tightening, the workpiece is best placed in place. Re-test each original testing surface that has been processed twice. The error from the new reference plane is generally caused by over-tightening during the second tightening. With the accumulation of experience, this error will become smaller and smaller. Semi-finishing the original machining parts. After finishing, inspect. There is no problem in the inspection and transfer to the next process.
If appropriate machining allowance is reserved on the parting surface in advance, before polishing, use a coordinate machine to measure the three-dimensional reference of the cavity (space 0), and then perform the third machining on the reference surface and the parting surface. Here, one issue needs to be emphasized. We are now using 3D software very popular. However, there are two design benchmarks we use: center 0-position benchmark and corner 0-position benchmark. The former is popularized with the development of CAD. For beginners, it is slow to get started, 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 “measure the cavity three-dimensional datum (space 0-position) with a three-coordinate machine”, which refers to the design and inspection using the “center 0-position datum”. Everyone will understand what I mean. Generally, if you do this procedure, you can overcome the deformation caused by the internal stress caused by the cnc machining. The parting surface can avoid the manual leveling process.