Hydraulic Pressure (Hpsi)

The clamp (clamping unit) is the half of an injection molding machine imm that closes, locks and opens the mold and holds it shut against injection pressure — the counterpart to the injection unit that melts and injects the plastic. ## Main components - Platens: the fixed and moving plates the mold halves bolt to. - Tie bars: the four (sometimes two) columns the moving platen slides on; they carry the clamp load. - Clamp mechanism: toggle (mechanical link), direct-hydraulic, or two-platen designs that generate and hold the tonnage. - Ejector: drives the mold's ejector system for part ejection. ## What it does in the cycle 1. clamp close: the moving platen advances and locks the mold. 2. Hold: it keeps the mold shut with enough clamp force tonnage so the melt cannot blow the parting line open. 3. Open & eject: after cooling, it opens and triggers ejection; then the molding cycle repeats. ## Why it matters The clamp's rated tonnage sets the largest part the machine can run without flash. Too little tonnage flashes the part; an oversized clamp wastes energy and floor space. Tie-bar wear, platen parallelism and toggle lubrication all affect part quality and mold life. ## Related terms - See also: injection molding machine imm, clamp force tonnage, injection unit, clamp close, part ejection ## What is the clamp in injection molding? It is the clamping unit — platens, tie bars and a toggle or hydraulic mechanism — that closes the mold and holds it shut against injection pressure. ## What are the types of clamping units? Toggle (mechanical), direct-hydraulic, and two-platen clamps, chosen by tonnage, speed, precision and footprint. ## What is the difference between the clamp and the injection unit? The clamp closes and holds the mold; the injection unit melts and injects the plastic. They are the two halves of the machine.

An injection molding machine (IMM) is the industrial machine that makes plastic parts by melting resin and injecting it under pressure into a closed mold. Every IMM is built from two main units plus a base, drive and controls. ## The two main units - injection unit: melts, meters and injects the plastic — barrel, screw, nozzle and hopper. - clamp (clamping unit): closes, holds and opens the mold, supplying the clamp force tonnage that keeps it shut against injection pressure. ## Drive types - Hydraulic: robust and low-cost, the traditional workhorse. - All-electric: servo-driven — the most precise, repeatable and energy-efficient. - Hybrid: combines electric and hydraulic for a balance of force and efficiency. ## How machines are sized Two numbers define a machine: clamp tonnage (e.g. 50 to 4000+ t — the largest part it can hold without flash) and shot capacity (the maximum shot size). Orientation is usually horizontal; vertical machines suit insert molding. ## Why it matters Picking the right tonnage and shot size for the job is the first decision in molding: too small and you cannot fill or hold the part, too large and you waste energy and over-residence the resin. One full pass of the machine is the molding cycle. ## Related terms - See also: injection unit, clamp, clamp force tonnage, molding cycle, shot size ## What is an injection molding machine? It is the machine that melts plastic and injects it into a mold to make parts, built from an injection unit and a clamping unit plus a base, drive and controls. ## What are the main parts of an injection molding machine? The injection unit (barrel, screw, nozzle, hopper), the clamping unit (platens, tie bars, clamp mechanism), and the base with the drive and control system. ## How is an injection molding machine sized? By clamp tonnage (the force that holds the mold shut) and shot capacity (the maximum amount of plastic it can inject per cycle).

The intensification ratio (IR) is the factor by which a machine's hydraulic pressure is multiplied into plastic (melt) pressure at the screw tip. Because the hydraulic piston has a larger area than the screw cross-section, a modest oil pressure becomes a much higher pressure on the plastic. ## The formula Plastic pressure (plastic pressure ppsi) = hydraulic pressure (hydraulic pressure hpsi) × IR Example: a machine with IR = 10:1 running 2,000 psi of hydraulic pressure delivers 20,000 psi on the plastic. ## Typical values Most machines fall between ~8:1 and 15:1 (some up to 20:1). It is fixed by design — the ratio of the hydraulic-piston area to the screw area — so it changes if you swap the barrel diameter / screw. ## Why it matters - Compare machines fairly: two presses set to the same hydraulic psi can apply very different melt pressures if their IRs differ — which is why a setup sheet should record plastic pressure, not just hydraulic. - Convert settings: it translates the machine's hydraulic display into the real injection pressure the polymer actually sees. - A higher IR gives more available melt pressure (good for thin-wall) at a given hydraulic capacity. ## Related terms - See also: plastic pressure ppsi, hydraulic pressure hpsi, injection pressure, screw, barrel diameter ## What is the intensification ratio in injection molding? It is the multiplier between hydraulic pressure and plastic pressure at the screw tip; plastic pressure = hydraulic pressure × IR, typically 8:1 to 15:1. ## How do you calculate plastic pressure from hydraulic pressure? Multiply the hydraulic pressure by the intensification ratio: e.g. 1,500 hydraulic psi × 11 = 16,500 plastic psi. ## Why does the intensification ratio matter when comparing machines? Because the same hydraulic setting produces different melt pressures on machines with different ratios — transferring a process needs the plastic pressure to match, not the hydraulic.

Plastic pressure (Ppsi) is the actual pressure the melt experiences at the tip of the screw as it is pushed into the mold — the real pressure on the plastic, not the machine's oil pressure. It is the number that matters for filling, packing and part quality, and it is almost always far higher than the hydraulic pressure hpsi the operator sets. ## How it relates to hydraulic pressure The screw acts as an intensifier: a relatively low oil pressure behind a large piston becomes a high pressure on the small melt area at the screw front. They are linked by the intensification ratio (IR): > Ppsi = Hpsi × IR So 1,500 Hpsi at an IR of 10:1 gives roughly 15,000 Ppsi on the plastic. Typical injection machines reach on the order of 15,000–30,000+ psi of plastic pressure. ## Why it matters - The plastic's reality: Ppsi is what fills the cavity and packs the part, so it drives weight, dimensions and defects far more directly than hydraulic pressure hpsi. - Process transfer: because IR differs between machines, two presses at the same Hpsi deliver different Ppsi. Documenting a process in Ppsi (or force on an electric machine) lets it move between machines reliably. - Setpoints: injection pressure, pack and hold pressure are best understood and transferred as plastic pressure. ## Related terms - See also: hydraulic pressure hpsi, intensification ratio, injection pressure, hold pressure, screw ## What is plastic pressure (Ppsi) in injection molding? The real pressure acting on the melt at the screw tip as it fills and packs the mold — much higher than the machine's hydraulic pressure, and the value that actually governs part weight, dimensions and quality. ## What is the difference between Ppsi and Hpsi? Ppsi is the pressure on the plastic at the screw tip; Hpsi is the hydraulic oil pressure behind the screw. The screw intensifies Hpsi into Ppsi: Ppsi = Hpsi × intensification ratio. ## Why document a process in plastic pressure? Because the intensification ratio varies between machines, the same hydraulic setting gives different plastic pressure; recording the process in Ppsi (or force) makes it transferable and repeatable across presses.