Injection Molding Screw Drive 1.1

Calculate and size an injection molding machine online

With this online calculation tool you can calculate key parameters of an injection molding machine for plasticizing, metering, screw drive and injection. Based on screw geometry, material data and process parameters, the tool determines plasticizing capacity, screw torque, motor power, dosing time, injection force and hydraulic power, among other values.

The tool is suitable for rough sizing and technical evaluation of plasticizing and injection units as well as for comparing variants. By considering plasticizing, drive and injection separately, the respective power requirements can be assessed transparently.

What can be calculated with the tool?

The calculation combines screw geometry, material properties and operating parameters into a technical model of the plasticizing and injection unit.

• Q_plast, ṁ_plast — plasticizing capacity and mass throughput
• M_screw,calc — screw torque
• P_motor,req — required motor power
• t_recovery,est — metering and plasticizing time
• U_ret,est — screw retraction speed
• F_inj, P_inj — injection force and injection power
• Q_inj, P_el,inj — hydraulic volume flow and power demand
• i, torque reserve — gear ratio and torque reserve
• Machine limits and power reserves

Plasticizing capacity of the injection screw

During plasticizing, the screw rotates and conveys the polymer through the feed, compression and metering zones. The calculation model takes into account the actual zone layout L_f → L_c → L_m as well as the change in channel depth in the compression zone.

From screw diameter D, pitch t, channel depth H, speed n, back pressure p_back, viscosity η_eff and other inputs, the volumetric throughput Q_plast and the resulting mass throughput ṁ_plast are determined.

Calculate screw torque and drive

For screw-drive sizing, the required torque is determined from the loads in the different screw zones. The melt, solids conveying and compression zone are considered separately and then combined into the polymer torque.

Taking the mechanical efficiency η_mech, service factor and load type into account, service and design torque are derived.

• M_melt — Schmelzedrehmoment
• M_solid — Feststoffdrehmoment
• M_compression — torque of the compression zone
• M_screw,calc — calculated screw torque
• M_service, M_design — service and design torque
• P_motor,req — required motor power
• n_motor, M_motor,req — motor speed and motor torque
• Getriebeverluste
• torque and power reserves

Estimate dosing and plasticizing time

From dosing stroke S_dose, screw cross-section A_s and calculated plasticizing flow Q_plast, the theoretical dosing volume V_dose is determined. This yields an estimate of the required recovery or dosing time t_recovery,est.

This calculation supports comparing different screw diameters D, speeds n, dosing strokes S_dose and material parameters and helps assess whether the required plasticizing capacity is fundamentally achievable for the planned cycle time.

Injection pressure, injection force and hydraulics

The injection phase is calculated separately from the rotating plasticizing process. The specified injection pressure p_inj acts on the screw cross-sectional area A_s and determines the required axial injection force F_inj.

From injection speed v_inj and screw diameter D, the volumetric flow Q_inj and hydraulic output power P_inj are calculated. If the hydraulic pressure p_hyd is specified, the required cylinder area A_cyl can also be estimated.

• F_inj — injection force
• Q_inj — injection volume flow
• P_inj — injection power
• P_el,inj — electrical power demand considering hydraulic efficiency η_hyd
• t_inj — injection time
• t_inj,min — minimum achievable injection time from machine limits

What inputs are required?

Screw geometry

• D — screw diameter
• d — Kerndurchmesser
• L_f — length of the feed zone
• L_c — length of the compression zone
• L_m — length of the metering zone
• H_f, H — Kanaltiefen
• t — screw pitch
• e — Stegdicke

Process parameters

• n — screw speed
• p_back — plasticizing back pressure
• S_dose — metering stroke
• T — Massentemperatur
• p_inj — injection pressure
• S_inj — injection stroke
• v_inj — injection speed
• p_hyd — Hydraulikdruck

Material data

• η_eff — effective melt viscosity
• ρ — Schmelzedichte
• T — Referenztemperatur
• f_b, f_s — optionale Reibungsparameter

Drive and machine data

• i — gear ratio
• η_G — Getriebewirkungsgrad
• η_mech — mechanischer Wirkungsgrad
• P_nom, n_nom — motor power and motor speed
• M_nom, M_max — rated and maximum torque
• S_max, V_max — maximum stroke and shot volume
• Q_inj,max, v_inj,max — maximum injection volume flow and injection speed
• P_motor,hyd — hydraulic pump power

What results are output?

Plasticizing and metering

• Q_plast — plasticizing flow
• ṁ_plast — Massendurchsatz
• M_screw,calc — screw torque
• P_screw,calc — screw power requirement
• F_back — Staudruckkraft
• U_ret,est — retraction speed
• t_recovery,est — estimated dosing time
• Pressure and zone characteristic values of the solids and compression sections (p(l), k_s, …)

Drive sizing

• M_service — Service-Drehmoment
• M_design — Auslegungsdrehmoment
• P_motor,req — required motor power
• n_motor — motor speed
• M_motor,req — required motor torque
• Getriebeverluste
• power and torque reserves

Injection and hydraulics

• F_inj — injection force
• Q_inj — injection volume flow
• P_inj — hydraulic injection power
• P_el,inj — elektrischer Leistungsbedarf
• t_inj — injection time
• Check of shot volume, speed, volumetric flow and power limits

Machine limits and variant comparison

In addition to the theoretical calculation results, important machine limits can be taken into account. These include maximum screw stroke S_max, shot volume V_max, injection speed v_inj,max, volumetric flow Q_inj,max and available hydraulic power P_motor,hyd.

This makes it possible to compare different screw diameters D, geometries, speeds n, back pressures p_back and injection parameters. Note that the maximum pressure and flow values p_max and Q_max of a machine are not necessarily available at the same time in practice.

What tasks is the calculation suitable for?

• Preliminary sizing of a plasticizing unit
• Sizing of screw motor and gearbox
• Estimate the required hydraulic power
• Comparison of different screw diameters D
• Study of speed n and back pressure p_back
• Estimate plasticizing and dosing times t_recovery,est
• Assessment of injection pressure p_inj and injection speed v_inj
• Comparison of a calculated unit with existing machine data

Model limits and notes

The calculation model is intended for technical preliminary sizing and variant comparison. It does not replace a full time-dependent simulation of the entire injection molding cycle.

Barrier and mixing screws, flight leakage, partially filled screw channels and the complete temperature- and shear-rate-dependent non-Newtonian rheology across the entire process are not yet fully represented.

The effective viscosity η_eff is not a constant material property and must be selected to match the material, temperature and shear rate. Calculation results should therefore be compared with manufacturer data and practical process values before any design or machine-related decision.

Calculation model

The current model version Injection Molding Machine 1.4a takes into account the screw feed, compression and metering zones (L_f → L_c → L_m) as well as the pressure build-up and additional torque M_compression in the compression zone. Plasticizing and injection are treated as separate operating phases.

A more advanced energetic description of the melting process and time-dependent modelling of the complete injection molding cycle are planned for extended model stages.