Most people in the plastic mold industry may have the same question: how to calculate the tonnage of an injection molding machine or how to calculate the clamping force in injection molding? Before answering the question about the calculation of the clamping force, we should first clarify some basic definitions of the molding tonnage of the injection molding machine.
What is the tonnage of injection molding machine?
The so-called tonnage of an injection molding machine generally refers to the size of the clamping force, which is an important parameter when designing a mold or selecting an injection molding machine. Injection molding machines usually have two sayings to distinguish the size:
1. Tonnage refers to the maximum clamping force of the injection molding machine. The clamping force is to see whether the injection molding machine can withstand the pressure on the projected area of the product in the mold. For example, a 120-ton injection molding machine refers to an injection molding machine with a maximum clamping force of 120 tons
2. Gram refers to the maximum injection weight of the injection molding machine with PE as the raw material, such as a 200-gram injection molding machine, which means that the maximum injection weight with PE as the raw material is 200 grams
Part 1: Empirical Calculation for Clamping Force Calculation
Empirical formula 1: the key idea - to calculate the clamping force through the clamping force constant
Calculation formula: clamping force = clamping force constant x projected area of the product
That is, P=KpS where P-clamping force (T); Kp-clamping force constant (t/cm2); S-projected area of the product on the template (cm²)
Mode-locking constant kp value：
PS/PE/PP – 0.32;
ABS——0.30~0.48;
PA——0.64~0.72;
POM——0.64~0.72;
Add glass fiber - 0.64~0.72;
Other engineering plastics - 0.64~0.8;
Empirical formula 2: key ideas - calculate the clamping force by estimating the cavity pressure, that is: 350 (kg/cm2) multiplied by the projected area of the product (cm²) divided by 1000
Note: Divide by 1000 to convert KG into tons
Part 2: Accurate Calculation of Clamping Force
The clamping force required for molding can be precisely determined through precise calculation formulas or through Moldflow analysis.
3.1 Accurate formula calculation:
Grouping Group 1: GPPS HIPS TPS PE-LD PE-LLD PE-MD PE-HD PP-H PP-CO PP-EPDM
Group 2: PA6 PA66 PA11/12 PBT PETP
Group 3: CA CAB CAP CP EVA PEEL PUR/TPU PPVC
Group 4: ABS AAS/ASA SAN MBS PPS PPO-M BDS POM
Group 5: PMMA PC/ABS PC/PBT
Group 6: PC PES PSU PEI PEEK UPVC
3.2 Viscosity grade
Each of the above groups of plastics has a viscosity (flowability) grade. The relative viscosity grades of each group of plastics are as follows:
Group multiple (K)
Group 1*1.0
Group 2*1.3～1.35
Group 3*1.35～1.45
Group 4*1.45～1.55
Group 5*1.55～1.70
Group 6*1.70 ～1.90
There are two important reasons for calculating the clamping force: (1) Projected area (2) Cavity pressure
(1) Projected area (S) is the largest area viewed along the mold opening and closing
(2) Cavity pressure (P)
Cavity pressure is affected by the following reasons:
(1) Number and location of gates (2) Gate size (3) Wall thickness of product (4) Viscosity characteristics of plastic used (5) Injection speed
3.1.1 Grouping of thermoplastic flow properties and viscosity grade (flow capacity)
3.1.2 Membrane cavity pressure determines wall thickness, ratio of process to wall thickness and viscosity grade constant (k)
The basic pressure (PO) of the cavity depends on the ratio of wall thickness, process and wall thickness (as shown in the figure).
Cavity pressure P=PO*K. Clamping force F=P*S=PO*K*S
