Application of the hottest deformation pre compens

Application of deformation pre compensation in fan injection mold design

in the process of injection mold design, the deformation of products is an important factor that mold engineers must consider. High temperature plastic melt will inevitably deform in the process of cooling and shaping in the injection mold and cooling outside the mold, which will affect the molding accuracy of products, resulting in the emergence of a large number of waste products

there are two main forms of deformation of plastic products: shrinkage deformation and warpage deformation. Shrinkage deformation refers to the difference between the product size and the mold cavity size; Warping deformation refers to the deviation of the shape of the product from the shape of the mold cavity

in order to reduce the shrinkage deformation of products, mold engineers often compensate the shrinkage of molding materials into the product model before dividing the mold cavity, so as to make the product size as close to the design size as possible after deformation. At present, many large-scale injection mold CAD commercial software have the function of setting shrinkage, and can set shrinkage in different directions according to different situations. The essence of this method is to carry out inverse pre compensation for the shrinkage deformation of products. The author believes that this method can also be used to reduce warpage deformation

1 deformation characteristics of automobile fan

the shape of automobile fan is shown in Figure 1. The fan is composed of inner ring, outer ring and six blades, and the overall structure is in the shape of spokes. There is a large ventilation area between the blades connecting the inner ring and the outer ring, which makes the material distribution uneven. Therefore, whether it is on the inner and outer rings of the products in process, or on the blades with uneven wall thickness, shrinkage deformation and warpage deformation will occur in a very wide range of disciplines

in contrast, the warpage deformation on the inner and outer rings is smaller, and the main form of deformation of these two parts is shrinkage deformation. Like the inner and outer rings, the blade has both shrinkage deformation and warpage deformation, which is the largest part of the fan warpage deformation. Therefore, when considering the deformation of the blade, the shrinkage deformation and warpage deformation must be considered at the same time

according to the structural characteristics of the fan, the gate is set at the center of the product. The molding material is pa66/gf30, which is an engineering plastic prone to warpage and deformation. Data shows that [1], a piece of 200mm × 200mm × The maximum warpage deformation of 2.5mm pa66/gf30 flat parts can reach 10.9mm. Because of excessive warpage and deformation, the mold of this product has been designed twice. In the first mold design process, only the shrinkage deformation of the product was pre compensated, and the expected treatment of blade warpage deformation was not carried out. As a result, the warpage deformation of the front and rear edges of the blade was too large to meet the design requirements of the customer's drawings. This product is a key component in the cooling system of an automobile engine. It is produced in large quantities and has strict quality requirements. After more than a year of mold repair, the plastic recycling granulator reprocesses the waste plastics in daily life to generate the plastic raw materials and test molds required by the enterprise. The molding accuracy of the final products is still not ideal. Even in the process of mass production, the qualified rate of products is only 86%

Figure 1 fan outline drawing

2 data processing of deformation pre compensation

2.1 principle of deformation pre compensation

the principle of deformation pre compensation is very simple, that is, the area with reduced WIP size will increase a deformation amount, and the area with increased WIP size will decrease a deformation amount

arbitrarily select a curve f on the product, which is located at f before deformation. Select any point R on the curve F, and the displacement vector before deformation is. After deformation, the position of curve f becomes F1, and the displacement vector of point R is. The deformation vector of point R is

curve F2 is the deformation pre compensation curve of curve F, and the displacement vector of point R on the curve is. Relative to the undeformed curve F0, the deformation of point R is

after being known, move the position of curve F0 to F2, and meet the following relationship

will be compensated to curve F0, so that it coincides with the position of F2, reconstruct the product model and design the mold, then the deformation of the product can be reduced to the minimum

Figure 2 Schematic diagram of deformation pre compensation

2.2 measurement of deformation data

the source of deformation data can not only measure the injection sample, but also analyze and calculate with the help of finite element software. The former has reliable data but high cost; The latter cost is low, but the reliability of the data depends on the analysis accuracy of the finite element software. With the rapid development of computer hardware and software, the data processing accuracy of finite element software continues to improve. At present, there are more and more cases of measuring product deformation data with the help of injection mold CAE software

Figure 3 radial shrinkage deformation curve of the product

Figure 3 is the radial shrinkage deformation curve of the product, and the average radial shrinkage of the product is = 0.64%

the average shrinkage in the axial direction of the product is 0.5%

Figure 4 deformation data curve of front and rear edges of blades

fan blades are bicubic B-spline surfaces, which are formed by scanning a closed cubic B-spline curve (section curve) along two guide curves (i.e. along the front and rear B-spline curves). The data measurement of blade warpage deformation is also based on the leading curve of front and back edges. The results are shown in Figure 4. From the analysis of the measurement results, the leading edge of the blade is warped downward and the trailing edge is warped upward

2.3 generation of deformation pre compensation model

pre compensation of shrinkage deformation can be realized directly through injection mold CAD software, and the operation is simple. The processing of pre compensation for warping deformation is relatively complex. It is necessary to reverse compensate the two original guide curves according to the size and direction of warping deformation to generate a new pre compensation curve. After the deformation of the product, the displacement of the point on the guide curve is a spatial displacement, and the coordinate value changes not only in the vertical direction (z direction), but also in the horizontal direction (x, Y direction)

in order to simplify the processing process, the coordinate changes of the points on the blade guide curve in the horizontal direction are now attributed to shrinkage deformation, and the coordinate changes in the vertical direction are attributed to warpage deformation. Therefore, when generating a new guide curve, you only need to change the Z coordinate on the guide curve. Because the warping deformation of the inner and outer rings of the product is ignored, the warping deformation of both ends of the blade is also ignored, which means that the section curve of the blade surface is not deformed and does not need to be pre compensated for its deformation

see Figure 5 for the model after deformation pre compensation. The dark color in the figure is the original CAD model, and the light color is the CAD model after deformation pre compensation. The two are overlapped in other areas outside the blade. It is only necessary to set a shrinkage of 0.64% in the radial direction and 0.5% in the axial direction of the model before using CAD software to divide the mold cavity and core

Figure 5 product deformation pre compensation model

3 Fan Injection Mold Design

the design of fan mold is completed by using the Moldwizard module of UGII software. When the shrinkage of the pre compensated CAD model is set, the parting curve and surface can be constructed, and the cavity can be volume divided. Select the standard mold base provided by Moldwizard module, add standard parts such as ejector rod, locating ring, sprue bushing, guide post, reset rod, and then set up the cooling system and pouring system. The assembly drawing of the completed fan injection mold is shown in Figure 6 [2]

Figure 6 assembly drawing of fan injection mold

1 Fixed mold base 2 Fixed mold fixing plate 3 Product 4 Locating ring 5 Sprue bushing 6 Cavity 7 Cooling water channel 8 Top plate 9 Guide sleeve 10 Guide post 11 Support block 12 Reset lever 13 Ejector pin fixing plate 14 Ejector base plate 15 New materials can react to electrical signals, dynamic mold base 16 Ejector rod 17 Core 18 Moving die fixing plate

4 summary

using the model of shrinkage deformation and warpage deformation with deformation pre compensation at the same time, the mold is designed and manufactured again, the mold test time is greatly shortened, and the deviation size is greatly reduced compared with the products formed by the previous mold. After only two small mold repairs, it passed the quality audit of customers, and the qualified rate of products is 99.5%

under the condition that the molding materials and injection process conditions are determined, deformation pre compensation is an effective method to reduce the deformation of injection products

references

[1] Zuo Da Ping Study on warpage deformation of pa66/gf30 products Application of engineering plastics 2005，12:21~23.

[2] left great equality Application of CAD technology in fan injection mold design Mold industry 2006.02:. (end)