A plastic injection molding machine is one of the largest investment items in a production plant. A wrongly chosen machine either wastes energy and money by running below its capacity or falls short and causes quality problems. In this guide we explain, step by step, what you need to look at when choosing the right machine.
1. Clamping Force (Tonnage) Calculation
The first and most important step in choosing a machine is to determine the clamping force suited to the part you will produce. Clamping force is the force that keeps the mold from opening during injection and is expressed in tons.
The practical calculation is done as follows:
Required tonnage = Projected area of the part (cm²) × Cavity pressure factor (0.3–0.8 ton/cm²)
To do this calculation with your own part data and see the machine models that suit the result, you can use the [plastic injection molding calculators](/en/calculators).
- For thin-walled parts that are hard to fill (packaging, caps) the factor rises to 0.5–0.8
- For thick-walled technical parts 0.3–0.5 is sufficient
- For multi-cavity molds the total projected area of all the cavities is used
A 10–20% safety margin is added on top of the calculated value. For example, for a cap part with a projected area of 100 cm²: 100 × 0.6 = 60 tons, and with the safety margin a machine of roughly 70–90 tons is suitable.
Choosing a machine that is larger than necessary is also a mistake: a large machine consumes more energy, small molds can close unevenly between large platens, and the cycle time becomes longer.
2. Injection Volume and Screw Diameter
The second step is to choose the injection unit suited to the part weight. As a rule, the part weight (including the runner) should stay within 20–80% of the machine's maximum injection capacity.
- If you stay below 20%: the material waits in the barrel for a long time and there is a risk of thermal degradation. This is especially critical with sensitive materials such as PVC and POM.
- If you go above 80%: the screw cannot plasticize sufficiently, metering becomes inconsistent and the risk of short shots increases.
The same machine body is usually offered with different screw diameters, labeled A/B/C. A small diameter gives higher injection pressure and precise metering; a large diameter offers higher volume and plasticizing capacity. DKM injection molding machines come with more than one screw option at each tonnage, and the tables are on every product page.
3. Drive System: Servo Hydraulic or All-Electric?
Today there are three main drive technologies, and the choice is made according to your production profile:
Servo Hydraulic
A servo motor runs the pump only when it is needed. It provides 30–60% energy savings compared with conventional hydraulic machines and is today the standard for general-purpose production. With its wide tonnage range (130–3350 ton SV Servo Series) and reasonable investment cost, it is a balanced choice for most applications.
High-Speed Hydraulic
For thin-walled packaging, caps and disposable products, injection speed is decisive. Machines such as the DFS thin-wall series and the HH high-speed series reach injection speeds of 400–600 mm/s, delivering short cycle times.
All-Electric
All-electric machines, driven directly by servo motors, offer 0.01 mm repeatability and energy efficiency above 95%. Because there is no hydraulic oil, they are indispensable for medical, optical and clean room applications. The investment cost is higher, but they give a total cost advantage in precision part production.
4. Tie Bar Clearance and Mold Dimensions
Your mold has to fit into the machine physically. The dimensions to check:
- Tie bar clearance: The width and height of the mold must be able to pass between the tie bars
- Minimum / maximum mold height: The mold thickness must stay within this range
- Opening stroke: An opening of at least 2–2.5 times the part depth is needed; critical for deep parts
- Ejector stroke and number of ejectors: Must be sufficient for the part to come out of the mold safely
All of these values are given in the clamping unit table on the "Technical Details" tab of our product pages.
5. Material-Specific Series
Some raw materials cannot be processed efficiently on a standard machine:
- For PET preform production, the PET series: a special screw with a high L/D ratio, a low AA (acetaldehyde) value
- For PVC processing, the PVC series: corrosion-resistant screw and barrel, heat control specific to PVC
- For medical production, the MX series and the EH series: clean room compatibility, high precision
- For large parts, the TP two-platen series: a compact machine length in the 600–4000 ton range
6. Energy Consumption and Operating Cost
The purchase price of the machine is usually less than a third of the total cost of ownership. The rest is energy, maintenance and downtime costs. When comparing:
- Ask for the specific energy consumption (kWh/kg of material processed)
- 0.35–0.55 kWh/kg is typical for servo hydraulic systems, 0.25–0.40 kWh/kg for all-electric
- Multiply by your annual operating hours to calculate the real operating cost
7. Pre-Purchase Checklist
1. Has the tonnage been calculated from the projected area of the part? (+10–20% margin) 2. Is the part weight within 20–80% of the injection capacity? 3. Do the mold dimensions fit the tie bar clearance and the mold height range? 4. Does your material require a special series (PET, PVC, medical)? 5. Have the energy consumption values been compared? 6. Are spare parts and technical service support available locally? 7. Have the auxiliary equipment items (dryer, dosing, mold temperature control, robot) been planned?
Let's Choose the Right Machine Together
As Teknik Part, we are the Turkey distributor of DKM injection molding machines from 90 tons to 4000 tons. We provide free machine selection consulting based on the technical drawing of your part and your target production quantity. For a complete line solution including drying, dosing and mold temperature control, get in touch with us.