Casting deformation is one of the most common defects in casting. Unfortunately, after more than a dozen processes, you find that you cannot meet the customer’s requirements due to the deformation of the casting. Today, we will generally discuss the causes of casting deformation and their solutions. Hope this article helps you.
Castings often experience varying degrees of deformation, such as bending, warping, twisting, dents, irregular round and oval shapes, and uneven wall thickness, which are called deformations. The degree of deformation of casting is usually relative to the overall deformation. In addition, a situation that does not conform to the drawing size due to the change in the external size is called deformation.
Casting deformation law
It is not difficult to find that deformed products usually have thick walls and are concave inwards. The thin-walled products are mostly convex.
The hazards of casting deformation
The deformation of the casting will cause the size of the product not to meet the requirements of the drawing and affect the processing of subsequent products. Part of the position deformation may also affect the clamping, resulting in deviation after processing. Severe deformation of the casting may lead to insufficient machining allowance, and may even lead to the scrapping of the casting, resulting in loss of roughness and machining.
Causes and Solutions of Casting Deformation
This shows that it is very important to control the deformation of castings. Casting stress is the main cause of casting deformation. Therefore, reducing and preventing casting stress is an effective measure to prevent casting deformation. However, it should be noted that casting stress can only be reduced rather than eliminated.
Causes of casting deformation
1. The wax model is deformed. Since the wax pattern is produced during the production process, it needs to be taken and placed. During this process, if the mold is not installed correctly, the wax mold is easily deformed due to external force when it is not completely cooled. Placement after taking the mold is also very important.
2. Deformation caused by product structure. For some products with uneven wall thickness, there will be a shrinkage process in the wax mold and pouring process. Thick wall locations will shrink more than thin wall locations, causing problems such as sinking and deformation.
3. Deformation caused by placing the mold shell after pouring. The mold shell has just been poured for a long time, and the product is still at a high temperature. If we can’t standardize them and stack them on top of each other, it will put an external force on our casting, and the casting is cooling and solidifying. The performance of the casting is not completely stable, resulting in the deformation of the casting.
4. Deformation caused by workers’ improper operation when cleaning the sand and shaking the shell. Under the high-frequency vibration of the shell vibrator, the casting is unstable, resulting in deformation of the casting.
5. Deformation caused by heat treatment. The main reason is that the strength of the casting is reduced after thermal expansion and softening during heat treatment. The deformation of the casting is caused by its gravity, and it may also be caused by the release of stress accumulated in the structure during the deformation of the structure. This deformation has a great influence on the size and shape of the casting.
6. Deformation caused by welding of wax patterns and group trees. This deformation mainly occurs in products with multiple pouring risers and complex structures. The two gates that should be on the same line appear to be bent due to external forces during the soldering process.
7. When processing the shell, deformation is caused by improper operation of the coated shell. During the shell-making process, there is a problem with mixing and drying the slurry, which causes the product to swell, which is also a deformation.
8. Deformation caused by subsequent processes. During post-processing, excessive shot peening and heavy product stacking can cause casting distortion.
How to prevent casting deformation
1. Reasonably design the product structure to make the product wall thickness more uniform, and the wall thickness should not be too large. During the sample development stage, a casting inspection must be performed on the product structure to reduce the risk of product deformation caused by the structure.
2. Design the anti-deformation amount of the product. Our Besser Casting achieves this by measuring the dimensions of the cast strands and product wax patterns. Of course, obtaining the amount of resistance to deformation and correcting the mold, requires a lot of data to support it.
3. For open castings, our Besser casting company often controls the deformation of the product by adding process ribs at the opening.
4. If the structure of some products cannot be changed, and it is difficult to meet the drawing requirements through molding and other methods, it is necessary to add a sufficient margin to the product and control it through machining.
5. In the wax mold manufacturing stage, there will be a shrinkage process when the wax mold cools. This process can easily cause the wax model to deform. Deformation is usually controlled by proper placement and water cooling. In some cases, shrinkage variables caused by different wall thicknesses are not easily controlled. As a result, the standard block is usually used to control the size of the wax pattern, and the standard block is removed after the wax pattern has cooled.
6. Reasonable placement and process control of castings in subsequent processes.
How to Correct the Distortion of Castings
1. Cold correction
The cold straightening method is based on the dimensions of the deformed casting and the thickness of the profile. Castings can be hammered, impacted, or extruded at room temperature using hand hammers, straightening machines, water (oil) presses, or some simple pressurization methods as correction methods. The practice has proved that when cold straightening is used to correct the deformation of ordinary castings, it is difficult to achieve the desired effect. However, for correcting the deformation of high manganese steel castings, only cold correction (determined by material properties) can be used.
2. Thermal correction
The thermal correction method is to heat the deformed casting above the elastic-plastic temperature zone of the material and restore the deformation of the casting through external forces such as extrusion and support, to achieve the purpose of correction.
There are roughly two types of heating temperatures in the thermal correction method. One is high temperature (ie austenitizing temperature); the other is high temperature. The other is low temperature, that is, the heating temperature for low-temperature annealing or high-temperature tempering. Both heating temperatures have advantages and disadvantages. “High temperature” has high requirements on the operator, and the operation is difficult, but the correction time is short. “Low temperature” has fewer requirements on the operator, simple operation, and high calibration success rate, but the calibration time is relatively long.
Summary
In the production process of castings, it is necessary to fully consider the product structure, materials, and other factors, determine the key characteristics, and take corresponding casting techniques and measures according to the specific situation. All these steps mentioned above help to reduce the occurrence of casting deformation.
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