Shot weight of machine is the maximum weight of raw material that an injection molding machine can inject into a mold.
Shot weight is the same as injection weight.
The injection weight of an injection molding machine can be calculated based on parameters such as screw diameter, injection stroke, raw material density, and theoretical injection capacity.
The specific value depends on the material used and the model of the injection molding machine
In practical applications, Haichen’s machine catalogs provide injection shot weight data for specific models of injection molding machines.
The injection weight range of the Haichen K series servo energy-saving injection molding machine varies from 100 grams to 39,950 grams.
Shot capacity of injection molding machine
Calculation of Injection Capacity
Injection capacity can be calculated by the following formula:
Injection capacity = maximum injection stroke x screw cross sectional area
Where the maximum injection stroke is the stroke length of the screw, and the screw cross-sectional area depends on the screw diameter.
Factors affecting injection capacity
Screw Diameter and Stroke: Screw diameter and stroke length directly affect injection capacity. Larger screw diameters and longer strokes provide greater injection capacity.
Material Density: Different materials have different densities, so the actual weight of the same shot capacity in different materials will be different. For example, PVC has a density of 1.52g/cm³, while ABS has a density of 1.04g/cm³.
Mold Design: The cavity volume of the mold also affects the shot capacity. If the mold cavity is small, the injection capacity will be limited.
Injection Pressure: The higher the injection pressure, the higher the injection capacity, but at the same time you need to make sure that the mold can withstand the corresponding pressure.
How do you reduce shot weight in injection molding
In injection molding, the reduction of shot weight can be achieved through a variety of methods, which are mainly related to mold design, process parameter adjustment and material selection.
Optimization of mold design： By reducing the number of cavities in the mold, the amount of material injected per shot can be significantly reduced. This method is suitable for small batch production of plastic products because of the relatively low cost of the mold.
Adjustment of process parameters：Lowering the injection speed reduces shear heat, which reduces material flow and avoids overfilling and waste.
Selection of suitable materials：The use of low-density or low-viscosity materials can reduce injection volumes. For example, selecting a material with a lower melting point can reduce injection pressure and injection volume.
Optimize injection machines and process equipment：Use small injection machines or micro-injection molding machines, which typically have smaller injection volumes and higher precision for producing small parts.
Reduce mold temperature：Lowering the mold temperature reduces the viscosity of the material and therefore the injection volume. However, this approach requires a trade-off between mold cooling time and product quality.
How to Calculate Injection Molding Shot Weight?
The calculation method of the actual shot weight of the injection molding machine needs to consider multiple factors, including the properties of the plastic, the screw structure, the injection force, etc. The following calculation methods can be summarized:
Theoretical shot weight:
First, the theoretical shot weight of the injection molding machine is calculated, which is usually calculated based on the cross-sectional area of the barrel and the injection stroke. The specific formula is:
Theoretical shot weight = injection molding machine barrel cross-sectional area × injection stroke
This step is calculated based on the physical parameters of the injection molding machine.
Actual shot weight:
Since the actual shot weight needs to consider factors such as plastic shrinkage and screw structure, a correction factor K is needed to adjust the theoretical shot weight.
The size of the K value is related to the structure and parameters of the screw (plunger), the outer diameter and clearance, the size of the injection force, the melt flow rate, the size of the back pressure, the mold structure, the shape of the product and the properties of the plastic.
The specific formula is:
Actual shot weight= theoretical injection volume × K
For example, when there is a check valve at the head of the screw, the K value is usually 0.9.
Plastic type correction:
If the material of the product is not polystyrene (PS), the injection volume needs to be converted. The conversion formula is:
Wps=Wx*1.05/Vx
Wx is the weight of the product, and Vx is the specific gravity of a certain plastic.
Calculation of product weight:
Before determining the shot weight, you need to calculate the weight of the product, including the weight of the product itself and the gate system. The formula is W = product weight + gate system weight. This step is to ensure that the injection molding machine has enough injection volume to complete the production of the product.
How do you reduce shot weight in injection molding?
There are seven steps for reducing shot weight in injection molding
- Step1: Adjust process parameters
- Step2: Adjust injection pressure and injection speed
- Step3: Optimize mold temperature and melt temperature
- Step4: Use simulation technology to optimize process parameters
- Step5: Multi-objective optimization design
- Step6: Apply artificial neural network (ANN) optimization
- Step7: Improve mold design
Adjust process parameters:
By optimizing the process parameters of injection molding, the weight of the product can be reduced as much as possible while meeting the quality requirements. For example, adjust the injection pressure, holding time, and the amount of filler masterbatch added.
Adjust injection pressure and injection speed:
Reducing the injection pressure and injection speed can effectively reduce the amount of plastic melt filled in the mold cavity.
For example, by using Moldflow software for simulation analysis, determine the best combination of injection pressure and injection time.
Optimize mold temperature and melt temperature:
Appropriately reducing the mold temperature and melt temperature can slow down the flow rate of the plastic melt, thereby reducing the weight of the molded part.
Use simulation technology to optimize process parameters:
Use CAE (computer-aided engineering) technology and adjust the process parameters based on the simulation results.
This method can predict and optimize molding conditions before actual production to achieve the purpose of reducing injection weight.
Multi-objective optimization design:
The multi-objective optimization design method is considered at the same time to find the most optimized combination of process parameters.
This helps to minimize the injection weight while ensuring product quality.
Apply artificial neural network (ANN) optimization:
The ANN model is used to analyze the impact of different parameters on the molding effect, and the optimal parameter settings are obtained through training. This method can accurately adjust each parameter to achieve a more efficient molding process and lower injection weight.
Improve mold design:
By optimizing the design of the mold, such as increasing the height of the core or ejector, or adjusting the design of the gating system, the problem of overfilling caused by improper design can be effectively reduced, thereby reducing the weight of the finished product.
Shot Weight of Haichen
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Haichen machinery produces highly precise injection molding machines with a clamping force ranging from 50T to 3000 T. The products have a high rigid structure and are equipped with imported hydraulic and electrical elements.
The actual injection volume of the injection molding machine is not only related to the quality and production efficiency of the product but also involves the normal operation and maintenance of the equipment.
Therefore, in the process of setting the injection molding process parameters, various factors must be considered comprehensively to accurately control the actual injection volume to ensure maximum product quality and production efficiency. If there is any demand, welcome to consult us.
