1.Analysis of process characteristics
Pancake iron castings (diameter and thickness) δ Although the shape of the casting is simple, it is difficult to carry out feeding in the casting production due to the large upper plane, and the defects such as shrinkage cavity and porosity often appear. The production size is (425 × For example, the traditional(see Fig. 1 for the process diagram) was adopted at the beginning to cast the 35.5kg thin discus workpiece, which has shrinkage cavity and porosity at the root of riser, and the qualified rate of cast iron can only reach about 70%. According to the theory of proportional solidification and the principle of limited feeding, the improved casting process is adopted, which consists of a sprue, a runner and a blank holder riser.
2.Determination of specific process parameters
The key process parameters to be determined are: the size of blank holder riser, the width of blank holder gap, the section size of sprue and runner.
2.1 size of blank holder riser
(1) Calculation of casting modulus MC
Mc=Vc/Sc= π r2h/ （2 π r2+ π Dh）=42.52 × 3.5/4 （2 × 42.52/4+42.5 × 3.5）=1.5（cm）
(2) Calculation of riser modulus Mr
MR=1.08Mc=1.08 × 1.5=1.62（cm）
Therefore, A-7 riser is selected, and the specific dimensions are: a = 100 mm, B = 100 mm, H = 100 mm. In order to facilitate the modeling in actual production, the riser body adopts a cylinder of 100, GR = 5.6 kg.
2.2 selection of section size of sprue
G runner is 15% of casting weight.
Σ gtotal = GC + GR + G runner = 35.3 × 2+5.6+35.3 × 15%=81.5（kg）
At this time, the diameter of the sprue is 28mm and the cross-sectional area (a straight) is 6.1cm2.
2.3 selection of cross section size of runner
A transverse = 0.8A straight = 6.1 × 0.8=4.9（cm2）
The specific size of the runner is 28 mm × 36mm, 15mm high. In addition, according to relevant data, blank holder gap e = 5mm.
2.4 calculation of process yield
According to the process route shown in Fig. 1 and Fig. 2, the casting size is 90 mm, H ′ = 100 mm. In the calculation, the mass conversion was carried out based on the specific gravity of discus casting, and the yield of traditional process and proportional solidification process was compared.
Figure 2 is used to get the yield of proportional solidification process η： η= GC / ∑ g total = 35.3 × 2/81.5 × 100%=86.7%
By calculating the quality of a single casting and calculating the process yield, the yield of the traditional process shown in Figure 1 is obtained η′： G′R= ρ iron π r′2h′=7.1 × three point one four ×（ 90/2）2 × one hundred × 10-6=4.52（kg）
η′= GC ′ / ∑ g ′ = 35.3 / (35.3 + 4.52 + 35.3) × 15%） × 100%=78.2%
Comparison of production rate:
（ η-η′）/η′=（ 86.7- 78.2）/78.2 × 100%=11%
According to the above proportional solidification process, a batch of iron cakes with the thickness of 425mm and 35mm were produced, and the qualified rate after machining reached 98%.