Evaluating Hydraulic, Electric, and Hybrid Plastic Injection Moulding Processes

Design engineers face a spectrum of options when selecting a plastic injection moulding process tailored to their specific applications. The three primary methods—hydraulic, electric and hybrid—each present distinct advantages and drawbacks. To facilitate an informed decision for your project, it is imperative to possess a comprehensive understanding of the disparities among these methods and the unique contributions they bring.

Hydraulic Plastic Injection Moulding

Originating in the late 1930s, hydraulic plastic injection moulding machines (IMMs) once held sway in the market. However, their dominance waned with the advent of all-electric machinery in the 1980s. Nonetheless, depending on specific needs, electricity costs and personal preferences, hydraulic machines may still prove optimal for certain tasks.

These machines employ hydraulic cylinders to forcefully unite two halves of a mould. High pressure is applied during this process. Subsequently, plastic substrate pellets undergo melting and the resulting liquid is injected into the mould cavity. After the plastic cools and solidifies, the mould halves part ways, allowing for the extraction of the finished part, and the cycle repeats.

To prevent the mould from unintentionally opening due to injection pressure, leading to an excess of material “flash” around the components, the clamping unit must supply an ample locking force to ensure the mould remains sealed during injection. For components with thin wall sections and deep draw depths, a requirement of around 3-4 tons of clamp force per square inch of the cavity exists. In contrast, for components with thick wall sections and shallow draw depths, approximately 2 tons per square inch is deemed sufficient.

Modern hydraulic IMMs boast the ability to control clamp forces surpassing 8,000 tons, producing parts weighing over 22kg. Notably, hydraulic moulding finds favour in the automotive industry, tasked with manufacturing large, weighty components like bumpers.

Advantages

Hydraulic injection moulding excels in actuating core pulls, ejectors and valve gates. It particularly suits thick-walled parts with extended hold times. The following are the merits you’ll experience in injection moulding projects at Goodfish:

• Ample clamp force for large parts

• Enhanced injection rates

• Heightened resistance to wear and tear

• Increased shot size

• Improved ejection capability

• Availability of gas accumulators to compensate for slower clamp movements

• Lower initial purchase price

• Cost-effective availability of replacement parts, leading to reduced maintenance expenses

• Manageability for high-level projects

• Abundance of units on the used market due to widespread adoption

Disadvantages

The potency of hydraulic machines comes at the expense of substantial energy consumption, even during idle periods. While a typical electric machine consumes around 2.55 kWh during an injection moulding process, hydraulic machines may consume 5.12 kWh. They demand higher moulding temperatures and prolonged cooling times, rendering them unsuitable for clean rooms due to fluid leakage risks.

Hydraulic IMMs also exhibit greater noise levels and diminished precision compared to all-electric presses. Nevertheless, as clamp forces escalate and control systems advance, hydraulic machines enhance their precision performance.