Determination of casting process parameters for casting parts of support table

1 Machining allowance

In order to ensure the size and accuracy of the machining surface of the parts, the thickness of the metal layer left on the machining surface and ready to be cut is called machining allowance in the casting process design. Too large or too small machining allowance will affect the quality of parts. When selecting machining allowance, the influence of casting alloy type, casting process, production batch, level of equipment and tooling, pouring position of machining surface, basic size of casting and structure should be considered.

The parts of the support platform are manually molded by sand mold with the maximum outline size of 630-1000 and the basic size of 160mm and 200mm. According to table 1, table 2, table 3 and table 4, the machining allowance grade is F-H, the dimensional tolerance grade is CT (11-13), and the machining allowance is 7.5mm.

Table 1 typical machining allowance grades of rough castings (GB / T6414-1999)

 

Method

Required machining allowance grade

Casting material

Cast steel

Gray cast iron

Ductile iron

Malleable iron

Copper alloy

Light metal alloy

Hand molding of sand mold

G-k

F-H

F-H

F-H

F-H

F-H

Sand machine or shell

E-H

E-G

E-G

E-G

E-G

E-G

Metal mold or low pressure casting

 

D-F

D-F

D-F

D-F

D-F

Pressure casting

 

 

 

 

B-D

B-D

Investment casting

D

D

D

 

E

E

Table 2 casting machining allowance required (GB / T6414-1999)           Unit (mm)

Maximum size 

Required machining allowance grade

C

D

E

F

G

H

J

K

≤40

0.1

0.1

0.2

0.3

0.4

0.5

0.5

0.7

1

1.4

>40-63

0.1

0.2

0.3

0.3

0.4

0.5

0.7

1

1.4

2

>63-100

0.2

0.3

0.4

0.5

0.7

1

1.4

2

2.8

4

>100-160

0.3

0.4

0.5

0.8

1.1

1.5

2.2

3

4

6

>160-250

0.3

0.5

0.7

1

1.4

2

2.8

4

5.5

8

>250-400

0.4

0.6

0.9

1.3

1.4

2.5

3.5

5

7

10

>400-630

0.5

0.7

1.1

1.5

2.2

3

4

6

9

12

>630-1000

0.6

0.8

1.2

1.8

2.5

3.5

5

7

10

14

>6300-10000

 

1.1

 

1.5

 

2.2

 

3

 

4.5

 

6

 

9

 

12

 

17

 

24

① The maximum profile size of the casting after final machining.

② Grades A and B are only used for special occasions, for example, when the supplier and the demander have agreed on batch production of pattern equipment, casting process and machining process for clamping surface and datum plane or datum target.

Table 3 tolerance dimension grade of rough casting produced in small batch or single piece

 

Casting method

 

Molding material

Tolerance grade

Casting material

Cast steel

Gray cast iron

Ductile iron

Malleable iron

Copper alloy

Light metal alloy

Nickel based alloy

Cobalt based alloy

Sand  casting

Clay sand

13-15

13-5

13-15

13-15

13-15

11-13

13-15

13-15

Manual modeling

Chemical binder sand

12-14

11-13

11-13

11-13

10-12

10-12

12-14

12-14

Table 4 dimensional tolerance values of castings        Unit (mm)

Basic dimensions of rough castings

Casting dimensional tolerance class CT

Greater than

To

1

2

3

4

5

11

12

13‚

10

0.09

0.13

0.18

0.26

0.36

2.8

4.2

10

16

0.10

0.14

0.20

0.28

0.38

3.0

4.4

16

25

0.11

0.15

0.22

0.30

0.42

3.2

4.6

6

25

40

0.12

0.17

0.24

0.32

0.46

3.6

5.0

7

40

63

0.13

0.18

0.26

0.36

0.50

4.0

5.6

8

63

100

0.14

0.20

0.28

0.40

0.56

4.4

6

9

100

160

0.15

0.22

0.30

0.44

0.62

5.0

7

10

160

250

0.24

0.34

0.50

0.72

5.6

8

11

① The thickness of the wall shall be subject to the coarse tolerance of grade ct1-ct15.

② For dimensions up to 16 mm, the general tolerance from ct13 to ct16 is not used. Data not found in this design are omitted in this table.

2 Determination of lift off angle and fillet

The angle of lift off refers to that a certain angle is reserved in the direction of lift off of pattern and core box for the convenience of lift off of pattern or take out of sand core, so as to avoid damage to sand pattern or sand core. Due to the thick flange at both ends of the casting, the machining allowance of 1mm can be reduced far away from the parting surface, and the lift angle is 1 degree.

Casting fillet refers to the angle between two adjacent walls of the casting, in order to prevent shrinkage cavity, angle missing due to sand punching, cracking due to concentrated force and other defects. Generally, it is 1 / 3-1 / 2 of the average thickness of the two intersecting walls. Here, r5mm [3] is taken.

3 Casting hole

For the size of 8 small holes on the support table parts, according to the possibility of casting technology and the necessity of use. The small batch hole diameter is 30mm-50mm, while the design part hole diameter is 20mm, and if it is to be cast, it will increase the number of cores, and it is not easy to place, so it is not necessary to cast, but directly drill on the drilling machine with a drill.

4 Core and core head selection

The hole cavity on the casting shall be cast out with core mold, which shall be supported, positioned, vented and desanded by the core head, which is the extension part of the core and plays an auxiliary role. Shape and size of core head: generally, the same inner cavity is cast with an integral core. When the inner cavity is simple, it can be molded with its own sand core instead of core. When complex, the core can be divided into several pieces. The core head is divided into vertical core head and horizontal core head. The vertical core head must keep a certain slope to enhance the stability of the core in the mold. The horizontal core head generally has two core heads on the left and right, and enhances the stability of the core. Generally, the core head is increased or increased to make the core stable and increase the air permeability.

The central inner cavity of the support platform parts is a tapered hole, which is suitable for the use of integral core and large core head, so as to facilitate the closure of the box, to facilitate the stability, positioning, exhaust and sanding. According to the basic dimension, the core length is 200 mm. The vertical core head is selected. Generally, the length of small and medium core heads is 20 mm-80 mm. It is determined that the length of core heads is 50 mm, the diameter of large end core heads is 90 mm, and the diameter of small end core heads is 50 mm. The clearance of core head is 1mm according to table 5.

Table 5 clearance between vertical core head and core seat

 

Casting type

D or(A+B)/2

≤50

51-100

101-150

151-200

200-300

301-400

401-500

501-700

701-1000

1001-1500

>2000

Wet type

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

2.5

3.0

Dry type

0.5

1.0

1.5

1.5

2.0

2.5

3.0

3.5

4.0

5.0

7.0

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