Mid term Review Questions P a g e 1 CASTING

Transcription

1 Mid term Review Questions P a g e 1 Q1: Define the casting process? CASTING A1: Casting is the process of pouring molten metal into a mould containing a cavity, which represents the required product shape Q2: State the advantages of casting process A2: Answer: Can create complex part geometries Can create both external and internal shapes Some casting processes are net shape; others are near net shape Can produce very large parts Some casting methods are suited to mass production. It is economical to use. Q3: State the disadvantages of casting process A3: Answer: Limitations on mechanical properties Poor dimensional accuracy and surface finish for some processes; e.g., sand casting Safety hazards to workers due to hot molten metals Environmental problems Q4: Draw the sand mould? A4: Answer

2 Mid term Review Questions P a g e 2 Q5: Identify each part of the following sand mould A5:

3 Mid term Review Questions P a g e 3 Q6: Identify the function of each of the following sand mould elements: A6: Answer Core Flask Drag Cope Riser Pouring basin vent cavity Is placed in the cavity to form holes. The container carrying the sand The lower part of the flask two halves The lupper part of the flask two halves is an extra void created to contain excessive molten metal. The purpose of this is to feed the molten metal to the mold cavity as the molten metal solidifies and shrinks. To form the entrance of molten metal to the cavity To escape gases and vapors Form the geometry of the part shape Q7: Compare between sand and die mould A7: Comparison Comparison Item Sand Die Mould material Sand Metal No. of product per mould One many Mould cost Cheap Expensive Product cost According to the No. of products Product accuracy Low High Product complexity Complex Not complex Product volume Big parts Small parts Force required No force, gravity only Force required Q8: State three different properties required in casting sand? A8: The properties required are: 1. Permeability 2. Strength 3. Refractoriness

4 Mid term Review Questions P a g e 4 Q9: State and describe the properties required in mold sand? A9: The properties required are: Permeability :النفاذیة posrosity of the sand enables the escape of gas and steam formed in the mold. Strength: sand must be cohesive to the extent that it has sufficient bond; both water and clay content affect the cohesive properties. Refractoriness: Sand must resist high temperatures without fusing. Grain size and shape: Sand must have a grain size commensurate with the surface to be produced, and grains must be irregular to the extent that they will have sufficient bonding strength. Q10: State the three pattern allowances A10: the pattern allowances are 1- Shrinkage allowance 2- Machining allowance 3- Draft allowance Q11: Write the allowance name which match each of the following purposes No. Pattern Purpose allowance type 1 To facilitate pattern withdrawal 2 To compensate volume reduction due to shrinkage during solidification 3 To compensate volume loss due to chip formation A11: No. Pattern Purpose allowance type 1 Draft To facilitate pattern withdrawal

5 Mid term Review Questions P a g e 5 2 Shrinkage To compensate volume reduction due to shrinkage during solidification 3 Machining To compensate volume loss due to chip formation Q 12: Discuss the correctness of the following statements. ( State true of false, then describe the reasons in detail) 1 The riser has to be solidified before the product solidification. 2 Sand casting is required when good surface quality is required 3 Draft allowance is added to facilitate product extraction 4 In die casting, the metal fills the cavity under gravity force. 5 Core is used in die casting to form the internal cavities A12 Answer 1 The riser has to be solidified before the product solidification. X Must solidify after the product 2 Sand casting is required when good surface quality is required X Die casting 3 Draft allowance is added to facilitate product extraction X Facilitate pattern extraction 4 In die casting, the metal fills the cavity under gravity force. X In sand casting 5 Core is used in die casting to form the internal cavities X In sand casting

6 Mid term Review Questions P a g e 6 Q13: Explain the reasons of each of the following: Using pattern instead of final product in sand molding A Using die mould to produce high no of products adding draft in sand molding A13: Using pattern instead of final product in sand molding Pattern is an exact copy of the required casting made from wood and sometimes from metal. It is removed to leave the mould cavity. It has bigger size than product to overcomes the allowances, Ii is made from two or more parts to be easily removed from the mould. Its material should be cheap and easily formed. Adding draft in sand molding To facilitate pattern extraction from mold without tearing the sand on boundaries Using die mould to produce high no of products It will cheaper Q14: Compare between Product and pattern A14: Comparison Final Product Pattern No of pieces Only one At least two parts Material Any material, the required product material Cheap material and easily formed

7 Mid term Review Questions P a g e 7 Size Exact final size Has extra size to compensate loss of volume during casting process Hole May has hole Never has hole The hole is formed using another item called core Q15: Identify the steps required to cast the following sample product Drawing Drawing Pattern made with its three allowances; shrinkage, machining and draft. A core prints are added to hold the core in place. Core boxes produce core. The core will be used to produce the hollow area of the part shown. Molding Preparation Drawing Description

8 Mid term Review Questions P a g e 8 Half of the pattern have been mounted on plate inside the drag. The drag is filled with casting sand. The drag is inverted. The half pattern can easily be removed Drag is filled with sand. The full pattern is inserted The cope is ready for sand Cope and drag are filled with sand. The pattern is withdrawn. The riser, sprue and vent holes are made inside the sand in the cope Core is set in place. Cope and drag assembled ready for pouring. May be summarized into six steps as follows: 1. Place a pattern in sand to create a mold. 2. Incorporate the pattern and sand in a gating system. 3. Remove the pattern. 4. Fill the mold cavity with molten metal. 5. Allow the metal to cool.

9 Mid term Review Questions P a g e 9 6. Break away the sand mold and remove the casting. Q16: Using sketch illustrate the sand casting defects? A: Sand casting defects are: Mis run Cold Shot Shrinkage Cavity Sand Blow Mold Shift