Basic knowledge of plastic cutting

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Basic knowledge of plastic cutting

plastic parts used in industry are mostly made by injection molding. However, in the following cases, cutting is required to obtain more accurate and complex parts to meet the use requirements

(1) raw materials supplied by plates, bars and tubes need to be cut and cut before they can become parts

(2) when the product batch is small and the cost of designing and manufacturing injection molds and molding molds is high, it is more appropriate to use cutting methods to process parts instead of traditional forming methods. In some cases, it is even cost-effective to obtain plastic parts completely by machining, because existing metal cutting equipment can be used in this way

(3) only by cutting with car cutting, drilling, reaming, grinding and tapping, can the dimensional accuracy and surface roughness required by machine parts be achieved, which is the product value of some foreign manufacturers

(4) clean the gate, riser, flash, burr and scar produced during injection molding of plastic blank, which can be repaired only by mechanical processing

The machining of plastic products or products can be divided into two categories: single edge tool processing and multi edge tool processing. Single blade tool processing includes turning, planing, toothless sawing, etc. The processing of multi blade tools includes cutting, milling, punching drilling, tapping thread, toothed saw processing, etc

(I) formation process of plastic chips

the formation process of plastic chips is extruded by cutting tools, as shown in Figure 1

(II) factors affecting cutting force

cutting force is generated by deformation and friction, so all factors affecting deformation and friction in the cutting process will affect cutting force

Figure 1 formation of plastic chips

1 - workpiece; 2 - cutting tool; 3 - fixture; 4 - cutting prolongs the service life of the equipment and improves the safety; 5 ― indenter

1. plastic type

the higher the strength and hardness of the workpiece material, the greater the deformation resistance and the greater the cutting force. If the strength and hardness of the material are similar, the greater the plasticity, the greater the cutting force because of the large friction between the chip and the rake face. Experiments show that the cutting force for cutting plastics is generally 1/6 ~ 1/7 of that for cutting steel

2. The influence of cutting parameters

the increase of back feed P and feed f will increase the cutting force, but the degree of influence of the two is different. The influence of the two on the main cutting force FZ is shown in Figure 2

operate according to the actual utilization

Figure 2. The influence of cutting depth P and feed rate f on the main cutting force FZ

the same pp/epdm T20 is used for different parts. The influence of cutting speed V on the main cutting force FZ is shown in Figure 3. Back feed p=1.5mm, feed f=0.2mm/r. It can be seen from the figure that the cutting speed V has little effect on the cutting force

Fig. 3 Influence of cutting speed V on main cutting force FZ

3. Influence of tool angle

FIG. 4A is the influence of tool rake angle 0 on cutting force when cutting polycarbonate plastic; Figure 4B shows the influence of rake angle 0 on the cutting force when cutting phenolic paper-based laminated plastics. The solid line and dotted line in the figure represent the changes of main cutting force FZ and radial force FY respectively. From the experimental results, it can be seen that the front angle 0 increases and the cutting force decreases

a) b)

Figure 4 Effect of front angle 0 on cutting force

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