基于三維的蓋板復(fù)合模的設(shè)計與裝配【說明書+CAD+PROE】

基于三維的蓋板復(fù)合模的設(shè)計與裝配【說明書+CAD+PROE】,說明書+CAD+PROE,基于三維的蓋板復(fù)合模的設(shè)計與裝配【說明書+CAD+PROE】,基于,三維,蓋板,復(fù)合,設(shè)計,裝配,說明書,仿單,cad,proe Cavity pressure measurements and process monitoring for magnesium die casting of a thin-wall hand-phone component to improve quality K.K.S. Tong * , B.H. Hu, X.P. Niu, I. Pinwill Precision Metal Forming Group, Gintic Institute of Manufacturing Technology, Singapore, Singapore Abstract The die casting of thin-wall magnesium components free of voids and having complete filling, resulting in high strength, can only be achieved under optimum cavity pressure. The pressure peaks occurring in the cavity are an important criterion for the consistent quality of these parts. The results from the measurement and monitoring of the cavity pressure can achieve minimum scrap and ensure constant quality. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Cavity pressure; Die casting; Thin-wall hand-phone component; Magnesium 1. Introduction The cavity pressure during the casting of a magnesium thin-wall hand-phone component is one of the critical factors in determining the quality of the part. The common traditionally measured parameters in die casting are the temperature, the plunger velocity and the machine hydrau- lic pressure. However, the cavity pressure, the obviously deciding parameter, was never really looked at in the past, mainly because of the lack of reliable pressure sensors to withstand the hostile environment of die casting. In this investigation, indirect piezoelectric cavity pressure sen- sors with a miniature 4 mm diameter pin are utilised because of the geometry and size of the component. The metal pressure at the runner and cavity were measured during casting. The measured metal pressure profiles can determine early close-off of the gate due to freezing, which will result in improper liquid metal flow into the cavity, lack of pressure transmission from the machine injection system to the casting and reduction in gate freezing time 1. The effect of process parameters on the gate freezing time such as the hydraulic pressure and metal velocity were studied. 2. Process monitoring development and description 2.1. Hand-phone die, pressure sensors and temperature sensors The experiments were conducted using a thin-wall hand- phone component die; Fig. 1 shows the fixed and moving die halves. In order to measure the metal pressure and temperature variations during the casting process, pressure and tempera- ture sensors were incorporated into the die. Due to the small hand-phone size, direct pressure measurement was physi- cally limited because the minimum diameter of sensor available commercially was 15 mm. Therefore, an indirect pressure measurement was used with a 4 mm ejector pin placed in the cavity with a quartz force sensor behind the ejector pin. The sensor and the details of the specification are shown in Fig. 2 and Table 1, respectively. The temperature sensor used was a normal K-type thermocouple of 2 mm diameter, inserted in the die 10 mm away from the cavity surface. The temperature sensor was to ensure that the die temperature was main- tained during the casting process. The indirect pressure sensors were placed at the runner area (before the gate) and in the cavity (after the gate), the objectives are to evaluate the gate freezing behaviour and the gate freezing time during the casting process, which will effect the behaviour of the metal pressure profiles of the cavity and the runner 2. Journal of Materials Processing Technology 127 (2002) 238241 * Corresponding author. E-mail address: stevengintic.gov.sg (K.K.S. Tong). 0924-0136/02/$ see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0924-0136(02)00149-8 2.2. Die casting process The magnesium hand-phone component was cast using an 80 t hot-chamber machine. Various casting conditions were used to obtain an acceptable quality component. The con- ditions used for the die casting of the magnesium thin-walled hand-phone component are given in Table 2. The settings given were as displayed in the machine: the actual values can only be obtained from the monitoring curves of the machine. 3. Results and discussion 3.1. Metal pressure during casting Two cavity pressure sensors were placed into the die; one in the runner just before the gate and one after the gate at the cavity, for measurement of the pressure variations during casting. Fig. 3 shows typical pressure profiles measured during the casting. The pressure variation during the casting can be characterised as three distinct stages, as indicated in the figure. Stage 1 is associated with the melt flow through the sprue post and runner. The pressure initially is almost zero because of the very low resistance to the metal flow. The presence of a small pressure peak (approximately 50 bar, arrowed) indicates the melt reaching the gate. The slight increase in pressure is due to the cross-sectional reduction towards the gate. Upon further filling to the cavity, the pressure is established rapidly. As soon as the cavity is filled, there is a relatively stable stage (stage 2) to maintain the high pressure to be transmitted from the hydraulic system to the cavity. After this period, the pressure at the cavity decreases, whereas the pressure in the runner increases (stage 3), indicating that the gate has been frozen, resulting in a high resistance to the metal flow in the runner. This metal pressure behaviour is very similar to that reported by Komazaki 3. 3.2. Metal pressure profiles against casting defects (part quality) The metal pressure profiles in the runner and cavity can be used to determine various casting defects. These defects or inconsistencies are pre-freezing of gate before cavity fill, sprue and nozzle blockages, incomplete filling, insufficient metal flow, severe turbulent flow due to the jerking effects of plunger, flow lines, insufficient pressure build-up in the runner, separation of liquid metal from the main stream and incorrect settings of the machine 4. Examples of this phenomenon (casting defects) with the metal pressure Fig. 1. Fixed and moving halves of the thin-wall hand-phone die. Fig. 2. The Schlaefer quartz force sensor used in the experiments. Table 1 Specification of the force sensor Type Range (kN) Sensitivity (pC/N) Linearity (%) Temperature (8C) Quartz force sensor 010 4.00 C62 400 Table 2 Die casting conditions for the 80 t hot-chamber machine Stroke (mm) Plunger slow speed, first stage (%) Plunger fast speed, second stage (%) Hydraulic pressure (%) 76 210 2045 7590 Fig. 3. Typical measured cavity and runner pressure profiles during casting. K.K.S. Tong et al. / Journal of Materials Processing Technology 127 (2002) 238241 239 profiles are shown in Figs. 46. Fig. 7 shows an optimum metal pressure profile to obtain a part of reasonable quality. The pressure profiles can be used as a reference process signature to verify any inconsistencies in the process settings and part quality. 3.3. Estimated gate freezing time The behaviour observed in stage 2 of the measured metal pressure profile (Fig. 3) is very interesting as it is closely related to the gate freezing which is important for the Fig. 4. Pressure profiles of insufficient metal flow into the cavity because of nozzle blockage resulting in low metal pressures. Fig. 5. Partial runner and gate blockage resulting in the runner pressure at the sensor location not building-up. The higher cavity pressure was probably the result of the unblocked gating and transferring of the pressure from the hydraulic system. The result for the part will be incomplete part filling and pre- solidification. Fig. 6. Jerky flow of the metal resulting from inconsistency in the movement of the plunger. This will result in the liquid metal separating from the main stream. The part will consist of flow lines and turbulence effects characterised by irregular flow patterns. 240 K.K.S. Tong et al. / Journal of Materials Processing Technology 127 (2002) 238241 pressure intensification stage. It is assumed that, particularly for the sensor located just after the gate, the pressure should continue to increase or to be maintained at a high pressure as long as the pressure applied from the hydraulic system can still be transmitted to the cavity 5. The starting of the pressure drop at the sensor after gate indicates the freezing of the gate and that the pressure from the hydraulic system is no longer being applied to the cavity through the gate, resulting in the pressure build-up at sensor in the runner (located before the gate). These significant findings lead to the estimation of the gate freezing time from the start of the cavity fill to the drop in pressure seen in sensor in the cavity. The gate freezing time, the metal pressures in the cavity and gate speed were obtained from the series of plots for each casting condition. Figs. 8 and 9 show the estimated gate freezing time with respect to the metal pressure and the gate speed, respectively. It is seen that the gate freezing time could be prolonged by applying a higher pressure and a higher gate speed. The results indicate that the higher pressure and gate velocity help to keep the gate open longer by offering the possibility to remove any partial gate block- age during cavity filling with a higher momentum of metal flow through the gate. The present finding is significant for process design, as free flowing of the in-gate facilitates material feeding during filling and solidification, which is important in producing high integrity component. 4. Conclusions 1. Capabilities for the monitoring of cavity pressure in thin-wall magnesium die casting have been successfully developed. The measurement of the metal pressure will ensure optimum and high integrity part quality. 2. A relationship between the gate freezing and the process variables has been identified. 3. The process signature (finger printing) technique against the reference metal pressure for each casting cycle can ensure consistent part quality. References 1 X.P. Niu, K.K.S. Tong, B.H. Hu, I. Pinwill, Cavity pressure sensor study of the gate freezing behaviour in aluminium high pressure die casting, Inst. J. Cast Met. Res. 11 (1998) 105112. 2 X.P. Niu, K.K.S. Tong, Net shape casting, Gintics Internal Report, C96-P-136A, 1997. 3 T. Komazaki, Effects of molten metal pressure transfer in a die cavity on quality of Al die casting, JD94-09, Japan Die Casting Association, 1994, pp. 7483. 4 F. Klein, Pressure die casting defects catalogue, Project Be 3636 (89), Vol. VI, No. I, Brite/Euram, 1993. 5 B. Upton, Pressure Die Casting, Pergamon Press, Oxford, 1982. Fig. 7. Metal pressure profiles of an optimum part quality showing an acceptable trace. The profiles can be used as a reference process signature to monitor any inconsistencies in the process settings. Fig. 8. Gate freezing time as a function of the measured cavity metal pressure. Fig. 9. Gate freezing time as a function of the gate speed. K.K.S. Tong et al. / Journal of Materials Processing Technology 127 (2002) 238241 241