The core and cavity of the mold often have a variety of free-form surfaces, making them ideal for machining on CNC machines. The process of CNC machining is quite different from the ordinary machining process. This paper combines the CNC machining technology of the mold core of children's product decoration.
The CNC machining process refers to the sum of various methods and technical means used when machining parts by CNC machine tools, and is applied to the entire CNC machining process. Because CNC machining has the characteristics of high processing efficiency, stable quality, relatively low technical requirements for workers, and the ability to process complex curved surfaces in one setup, CNC machining is becoming more and more widely used in the mold manufacturing industry. The more important. The quality of CNC process design will directly affect the dimensional accuracy and surface quality of CNC machining dimensions, the length of processing time, material and labor costs, and even directly affect the safety of processing. The following is an example to analyze the CNC machining technology of typical mold forming parts.
First, product analysis
The product exemplified in this article is a decoration for children's products, the material is ABS. The structure of the product is relatively simple, the surface is flat, the side has a semi-circular hole, and the top has a plurality of round holes. Since the product is an ornament and is not a delicate structural member, the appearance quality of the product is high and the dimensional tolerance requirements are not strict.
Second, the structure and analysis of molded parts
After obtaining the solid shape or engineering drawing of the product, the mold can be designed using the CAD function in Pro/ENGINEER, NX or MasterCAM. The designed mold core is shown in Figure 2.
The mold core has the following characteristics:
(1) The core blank size is 200 × 170 × 65 mm, and the processed size is 160.8 × 126.6 × 35.8 mm, and the material is S136 steel.
(2) The height of the core glue is 35.8mm, and the corners where the ellipse and the triangle face intersect are small, only R1mm. These positions are difficult to machine directly with a milling cutter, and can be achieved by electric discharge machining.
Since the dimensional tolerance of the product is not high, the core can be directly machined using a CNC machine.
Third, process analysis
There is a certain difference between the CNC machining process and the traditional machining process. Since most CNC machine tools do not have the processing capability, every detail of the machining process must be predetermined, and the machining is automatically completed according to the programmed procedure. Therefore, the machining process must be analyzed in detail before programming and the corresponding design is designed. Processing steps.
1. Process benchmark selection
CNC machining often uses the principle of process concentration to process. Therefore, when selecting the process reference, the appropriate reference elements should be selected as much as possible to reduce the number of clamping times, improve the processing efficiency and machining accuracy. At the same time, when selecting the positioning reference, refer to the drawings. It is required to make the process benchmark coincide with the design basis to reduce the error caused by the misalignment of the benchmarks.
In this example, the workpiece blank is a machined rectangular parallelepiped blank, and the parallelism, perpendicularity and dimensional accuracy are guaranteed. Therefore, the opposite direction of the length and width can be selected as the reference in the horizontal direction (XY direction); As a reference for the height direction (Z direction). At the same time, a pair of tool references are found on the machine tool to ensure that the programmed height reference can still be accurately found after the tool change, that is, the Z0 point of the workpiece coordinate system. These datums are no longer processed in the CNC machining process, and as a machining reference, the accuracy of the datum and the uniformity of the front and back can be guaranteed.
2. The choice of clamping method
In the milling process, the clamping method of the workpiece is generally in the form of a clamping plate and a bolt clamping, a machine using a flat jaw clamp, and a special fixture clamping. The mold core belongs to the single-piece order production, generally does not use special fixtures; the size of the mold core is 200×170×65mm, which belongs to small workpieces. Therefore, the machine is selected to be clamped with flat pliers.
When using the machine pliers to clamp, it is necessary to consider that the height of the core is 35.8mm. Therefore, the height of the top surface of the blank after the clamping should be greater than 35.8mm from the jaw of the flat jaw, and the bottom surface can be padded with the same height horn.
3. Processing sequence
Parts processed on CNC machine tools are generally divided into processes according to the principle of process concentration, that is, each process should include as much processing content as possible. The process division method is divided according to the used tool, divided by the number of installations, divided by rough finishing or divided by machining parts. In this case, the mold core is a single-piece production. Therefore, the principle of process concentration is adopted when the processing sequence is arranged to reduce the number of tool changes and improve the processing efficiency.
Whether the processing sequence is arranged reasonably directly affects the processing quality, processing efficiency and processing cost. When selecting the processing sequence, according to the blank condition and the part structure, combined with the positioning reference and clamping method of the part, it is important to consider ensuring that the rigidity of the workpiece during the processing is not damaged, reducing the deformation and ensuring the processing quality.
The blank of the mold core is a rectangular parallelepiped, and the parting surface of the product has a large cutting amount, and must be roughed first, and then semi-finished and finished. After the parting surface is processed, the top surface, the wearing surface and the glue position are finished in order.
