Technical Requirements For Nylon Machined Parts

Nylon products is a new type of engineering plastics, because of its excellent comprehensive performance, make it in the engineering plastics in the status of the rapid rise, become an important material, the use of the expanding, so what are the technical requirements of nylon processing parts? What are the factors affecting nylon processing parts?

Technical requirements of nylon processing parts

1. Rheological properties of nylon

Most of the nylon is crystalline resin, when the temperature exceeds its melting point, its melt viscosity is small, melt fluidity is very good, should prevent the occurrence of overflow. At the same time, due to the rapid condensation of the melt, the material should be prevented from blocking the nozzle, runner, gate and other products caused by the phenomenon of insufficient. Mould overflow value of 0.03, and the melt viscosity of the temperature and shear changes are more sensitive, but more sensitive to temperature, reduce the melt viscosity from the barrel temperature to start.

2. Water absorption and drying of nylon

Nylon's water absorption is large, wet nylon in the molding process, the performance of a sharp drop in viscosity and mixed with bubbles appear on the surface of the product silver wire, the mechanical strength of the product decreased, so the material must be dry before processing.

3.Crystallization

In addition to transparent nylon, nylon is mostly crystalline polymer, high crystallinity, product tensile strength, abrasion resistance, hardness, lubricity and other properties have been improved, the coefficient of thermal expansion and water absorption tends to decline, but on the transparency and impact resistance is not good.

Mold temperature has a greater impact on crystallization, high mold temperature crystallinity is high, low mold temperature crystallinity is low.

4.Shrinkage

Similar to other crystalline plastics, nylon resin shrinkage problem, the general shrinkage of nylon with the crystallization of the relationship between ******, when the crystallinity of the product products will increase the contraction of the product, in the molding process to reduce the mold temperature \ to increase the injection pressure \ to reduce the temperature will reduce the contraction of the product, but the products of the increase in the internal stress of the easy to deform. For example, non-glass fiber reinforced Pa6 and Pa66 shrinkage in 1.5-2%, after adding glass fiber can make the shrinkage rate reduced to 0.3% to 0.8%.

5. Molding equipment

Nylon molding, the main attention to prevent "nozzle salivation phenomenon", so the processing of nylon materials generally use self-locking nozzle. In addition, it is best to choose the injection molding machine with a larger plasticizing capacity.

6. Products and molds

Wall thickness of products

Nylon flow length ratio of 150-200, nylon products wall thickness is not the bottom of 0.8mm in general between 1-3.2mm to choose from, and the contraction of products and products related to the wall thickness, the thicker the contraction of the wall thickness is greater.

Factors affecting nylon machined parts

1.Clamping

Usually, in the workpiece clamping, the clamping force will make the workpiece deformation, unloading clamping force, the workpiece elastic deformation automatically recover, resulting in the workpiece free of stress under the conditions of size and processing size is not the same. If the clamping force is too large, will exceed the yield limit of the material, a long time clamping will make the workpiece plastic deformation, after processing the clamped part of the part and the processing of the size does not match; on the other hand, it will lead to the clamping is not tight, the vibration of the machining process is large, affecting the final machining of the size of the quality. Nylon materials and metal materials are different in nature, with a small density, easy to deform and easy to process the characteristics of the clamping process, it is more likely to be deformed due to the clamping; processing is completed after the elasticity of the recovery, so that the size and shape of the changes, and the larger the clamping force, the greater the deformation after processing is completed. Therefore, in the nylon thin-walled parts processing, should be taken vigorously clamping primary processing, light clamping finishing processing order to ensure that the clamping force does not affect the size of the machining accuracy.

2.Cutting tool

Cutting nylon material should avoid the tool itself to bring too much pressure, club cutting process in the constant movement to the inside of the material, in addition to the lateral cutting of the tool on the material, there is a direct propulsion pressure. If the propulsion pressure is too large, will not only affect the stability of the workpiece clamping, but also directly cause the deformation of the workpiece, resulting in the elastic deformation of the workpiece to recover after the size deviation is too large.

Stiffness of the tool relative to the stiffness of the weak tool, its own elasticity is poor, more likely to produce the workpiece processing propulsion, resulting in workpiece color, so the use of relatively weak stiffness of the alloy knife machining accuracy is better.

Edge of the sharpness of the degree of its machining accuracy has a considerable impact, the sharper the edge of the tool, the smaller the cutting resistance, the smaller the propulsive force on the material, the smaller the deformation of the workpiece, the smaller the rebound phenomenon, the better able to ensure the dimensional accuracy; therefore, the use of alloy knife processing nylon materials, triangular knife than the quadrangular knife is good and in the finishing of the workpiece, in the case of ensuring the roughness of the surface, the use of a new blade than the old blade is more able to Ensure dimensional accuracy, and even a certain amount of grinding can be carried out on the knife edge, so that the sharp angle of the knife edge becomes smaller.

3.Cutting heat

A very important factor affecting the accuracy of workpiece processing is cutting heat. Parts processing will produce a lot of heat, such as milling elastic deformation and plastic deformation, chip separation and tool and workpiece friction consumed energy, most of which will be converted to thermal energy, and these thermal energy a small part of the chip away or air radiation, a large part of the workpiece is absorbed, these thermal energy in the formation of thermal stress within the workpiece, with the continuous advancement of the processing, and constantly generate thermal energy, thermal stress, and ultimately make the workpiece occur. With the continuous advancement of processing, heat energy is constantly generated and thermal stress is constantly changing, which ultimately makes the workpiece deformed, distorted, and even cracked. For nylon material, its own thermal stability is extremely weak, a little heat absorption, will lead to deformation.

4.Material original internal stress

The workpiece material itself exists within the internal stress. In the machining process, due to the removal of excess parts, changing the overall structure of the workpiece correlation, resulting in the internal stress balance of the material is broken, the need to find a new balance of internal stresses, resulting in deformation of the material in the cutting; therefore, in the processing of metal materials should be used to eliminate internal stresses such as tempering and vibration aging, so that the internal stresses of the material and the structure of the material as much as possible tend to be stabilized to reduce the machining of the Deformation.

Nylon material in the casting production, often appear or large or small pores or holes. When the mold temperature is too high, nylon products are prone to shrinkage; Conversely, due to the instantaneous separation of the polymer in the monomer is not completely dissolved, and easy to cause microporous. In addition, nylon reactants will be more or less mixed with volatile or decomposable material, casting will produce volatile products, the formation of products in the bubble or hole, these holes in a large extent caused by the instability of the nylon material, - once the structure is changed, the internal stresses to re-balance, the material is easy to produce deformation.