THE CALCULATIONS OF TEMPERATURE FIELDS OF THE FORMING MACHINES

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1 THE CALCULATIONS OF TEMPERATURE FIELDS OF THE FORMING MACHINES ABSTRACT Ing. Zdeněk Chval West Bohemia University, Univerzitni 8, Pilsen, Czech Republic At the present time is placed increasing emphasis on product quality. This brings increasing demands on the construction of a forming machine. An important factor, among other things, is the thermal effects, especially for technology operations with high temperature (1200 C). The paper deals with the temperature effect of the press CKV 84/105. INTRODUCTION Nowadays the quality of products is very important and design demands of forming machines are still higher. Quality and competitiveness of products manufactured on the forming machine is influenced by many factors, such as stiffness of the workspace, the strength of the frame, energy balance, etc. Temperature effect on structure is one of the important design factors, especially in technology operations with a high temperature of semiproduct (up to 1200 C). Each type of forming machine is somewhat special, and it is necessary to analyze the heat effect on each machine type separately. KEYWORDS forming machines, forging, FEM, thermal measurement MEASUREMENT OF TEMPERATURE RISE OF HYDRAULIC FORGING PRESS CKV 84/105 Press CKV 84/105 was the first forming machine, where warming has been analyzed in various parts of the machine workspace. It is a thermal effect on hydraulic press due to radiation in the technological process of forming. First, it was measured at the smithy in the company PILSEN STEEL s.r.o. during the hot forming. Subsequently, a mathematical model was developed and started calculating on machine parts affected by the emission of semiproduct by FEM method. CHARACTERISTICS OF THE PRESS CKV 84/105 It is a hydraulic forging press with a top drive, vertical, four columns construction. The drive is realized by three hydraulic plunger cylinders working at the top cross beam. Working fluid is an emulsion of water with oil. Nominal power of the press is 28/56/84 (MN), with multiplication 105 (MN). MEASURING EQUIPMENT Fluke Ti30 thermal imager, Thermal imager, USA 2005 (working range of 0 to 255 [ C]) Fig.1 Press CKV 84 /105 MN

2 MEASUREMENT OF TEMPERATURE FIELDS IN DIFFERENT PARTS OF THE MACHINE WORKSPACE IN HOT FORMING The aim of measurement was analyzed temperature field of each part of the workspace of the press CKV 84/105 by thermal imager during the technological process of hot forming. The initial temperature of the forming semiproduct was 1150 ( C) - this is the temperature of the semiproduct when it is removed from the oven. The critical points were identified on structure (Fig.2) and measurement was made at five locations of the press (Fig.3). Fig.2 Thermally affected area, hydraulic forging press CKV 84/105 Fig.3 CKV 84/105 before inserting semiproduct, marked points for measurement by thermal imager MEASUREMENT First, the ambient temperature was measured. Subsequently, the temperature was scanned in five measuring points (Fig.3) and always three times in quick succession to eliminate measurement errors. Accuracy of these measurements was verified using touch sensing device (in the shields, because the other points were too high). Total measurement time was 132 min. which is divided by technological break to two parts 37min and 40 min. Diameter of the semiproduct was 1900 mm and weight was 95t. Fig.4 CKV 84/105 during the forging

3 The tables 1 and 2 shows an increase of surface temperature on the inside surface during the free forging. After removing the semiproduct there is a very rapid cooling from 103 C to 42 C in 5 minutes. During a break lasting 26 minutes it was cooled down up to 35.8 C, which is comparable to the baseline temperature (32 C). Table 1 - Measurement results (first part) temperature/ time t 1 =0 t 2 =+14 t 3 =+21 t 4 =+28 t 5 =+35 t 6 =+40 t 7 =+1.06 before start die forging free forging brake brake point 1 ( C) 32 63,7 59,6 60,7 103,2 42,1 35,8 point 2 ( C) 31,8 48,6 34,1 33,8 48,9 30,3 30,1 point 3 ( C) 33,8 109, ,3 61,6 55 point 4 ( C) 32,6 36,15 35, ,67 29,5 32,7 point 5 ( C) 34,7 55,4 46,47 47,7 55, ,45 In the second part of measurements we recorded a significant increase in surface temperature on the inner side of the column and in the middle point of the slide. There was a significant temperature difference between the pairs of columns and the opposite sides of the slide, caused by different heating from long semiproduct. This difference is up to 64 C, on the column and up to 69 C on the slide. temperature/ time t 8 =+1.20 t 9 =+1.30 kování (začátek t 7 =+1.17) Table 2 - Measurement results (second part) t 10 =+1.40 t 12 =+1.50 t 13 =+1.55 t 14 =+2.05 free forging t 15 =+2.12 press side L L L R L R L R L R L R point 1( C) 55,3 59,5 55, ,5 70,8 74,5 49,2 point 2( C) 35,8 36,2 36,7 32,5 35, point 3 ( C) 76 82, , , point 4 ( C) 28,3 26,7 33,7 35, ,5 34,5 29,5 26,5 32 point 5( C) 34,8 36,5 35, ,9 81,5 35,4 101,5 36,5 72,5 32,5 66,1 end Fig.5 Comparison of surface temperatures on the left (35 C) and the right side of the slide (104 C)

4 TEMPERATURE CALCULATION As the next step in solving thermal problems of the forming machine was carried out FEM temperature calculation. Its aim was to determine the surface temperature of the press CKV 84/105 for comparison with measurements. Its served for further calculation calibration. This knowledge can be used in future calculations for other thermal calculation on forming machine. A simplified model was created by available documentation in the program Gambit for calculation by FEM - Fluent. Boundary conditions Ambient temperature: 30 C The temperature of the semiproduct 1150 C Simplification of the calculation: modelled only a quarter of the press; semiproduct permanently attached to the lower tool; the upper part of the press is fixed in one position; air flow is not considered (only the minimum necessary for the calculation). Fig.6 Model for FEM calculation in the FLUENT Results of calculation Maximum surface temperature on the inner side of the press column reaches 214 C. This is the maximum temperature, which may be on the surface structure - column - warmed to the steady-state of the thermal system. Obr.7 Results of temperature calculation surface temperatures

5 The figure 8 shows the section headed by the center of the column. Warming up the column throughout the thickness of the inner side can be seen in the range of 195 C C. From the outside, up to about half the height of the column temperature is the same, the temperature drops to values between 176 C C. Warming of the slide is in the same relations. THERMAL TIME CALCULATION Fig.8 Results of temperature calculation cross section The next logical step in solving the temperature problem was the introduction time in the temperature calculation. Boundary conditions were maintained the same as for steady-state calculation: temperature 30 C, the temperature of the semiproduct 1150 C. Results of calculation The maximum surface temperature of the column as the middle point of slide reaches C. That result (Fig. 9) represents the state of the system after 38 minutes. This result corresponds to the insertion of the semiproduct in the second part of the measurement (Table 2). The calculation shows that about 40 minutes is too short to heat the larger structures in the existing design. The following section (Fig. 10) shows that this is only the surface temperature and calculating time period is not enough to warm this large body structure.

6 Fig.9 Results of thermal time calculation (38min) - surface temperature Fig.10 Results of thermal time calculation (38min) - cross section

7 Time temperature calculation was subsequently calculated to 100 minutes (Fig. 11). During this time period was increased to a maximum surface temperature to 105 C and the construction of the press began to slowly warm. Maximum temperature of the inner part of the column reached 65 C. CONCLUSION Fig.11 Results of thermal time calculation (100min) cross section Verification of the credibility was carried out of thermal FEM calculation in comparison with the measurement. The results are comparable. Calculating of temperature and temperature measurement at the press CKV 84/105 showed that in this case thermal effect is not significant. Concept of procedure for verifying the thermal effect on forming machines: - use of stationary calculation - determination of the maximum temperature - theoretically possible - verification by the time calculation - if justifiable This knowledge can be used in future calculations for other particular thermal calculation on forming machine. In this particular case, we verified that we are able to FEM analysis of thermal conditions on the forming machines. REFERENCES [1] RUDOLF, B., KOPECKÝ, M. Tvářecí stroje Základy stavby a využití. Praha: SNTL, [2] KOVÁČ, A., RUDOLF, B. Tvárniace stroje. Btatislava: ALFA, [3] SEMIATIN, S, L. Forming and Forging. ASM Handbook, Volume 14. Ohio: Metals Park, 1996, ISBN [4] RUDOLF, B., KOPECKÝ, M. Tvářecí stroje Základy výpočtů a konstrukce. Praha: SNTL, 1982.