Clamp

Clamp close is the stage of the molding cycle where the clamp advances the moving platen to bring the mold halves together and lock them up before injection. It is the first motion of every cycle. ## The three speed phases 1. Fast approach: the platen moves quickly across most of the stroke to save cycle time. 2. Slow / mold protection: near touch it slows to a low-pressure creep so the controller can detect an obstruction — a stuck part or misplaced insert — before metal hits metal. This is "mold protect". 3. High-pressure lock-up: the toggle or ram builds full tonnage, applying the clamp force tonnage that holds the mold shut against injection pressure. ## Why it matters - Mold protection prevents expensive damage: if a part did not eject, the low-pressure phase senses the resistance and stops instead of crushing the tool. - The speed profile trades cycle time against safety — too aggressive a close risks the mold, too slow wastes time. - Only after lock-up do the injection stages begin. ## Related terms - See also: clamp, clamp force tonnage, molding cycle, injection stages, part ejection ## What is clamp close in injection molding? It is the cycle stage that closes and locks the mold before injection, in three phases — fast approach, slow mold-protection, and high-pressure lock-up to full tonnage. ## What is mold protection during clamp close? A low-pressure, slow phase just before the mold touches, so the machine can sense an obstruction (an unejected part or insert) and stop before damaging the tool. ## What happens after clamp close? Once full clamp tonnage is reached, the injection stages begin — first-stage fill, then pack and hold.

Clamp force (clamping force or tonnage) is the force the machine applies to hold the mold halves shut against the pressure of the melt during injection and pack. If it is lower than the force trying to push the mold open, the parting line separates and the part flashes — that is why sizing it correctly is a first-step machine-selection decision. ## How to calculate clamp tonnage The standard estimate: Clamp force = projected area × clamp factor - projected area is the part-plus-runner area seen along the mold-opening direction (in² or cm²). - The clamp factor (see tonnage factor) is an empirical pressure in tons per in² (or bar of cavity pressure). Example: a 50 in² projected area at 3 tons/in² needs 50 × 3 = 150 US tons; add ~10 % margin and pick a press rated near 165–200 tons. ## Typical clamp factors | Resin / situation | Clamp factor (tons/in²) | |---|---| | Easy-flow commodity (PE, PP) | 2–3 | | General engineering (ABS, PA, PC) | 3–5 | | Thin-wall, long-flow, glass-filled | 5–8 | Metric rule of thumb: clamp force in kN ≈ projected area (cm²) × cavity pressure (bar) ÷ 10. ## Why it matters - Too little: flash, dimensional drift and the mold opening during pack — see flash. - Too much: crushed vents and shutoffs, faster mold wear, wasted energy and ruling out otherwise-suitable presses. Most shops size the press from the estimated tonnage required plus a safety margin, without overspending on an oversized machine. ## Related terms - See also: projected area, tonnage factor, estimated tonnage required, flash, injection molding machine imm ## What is clamp force in injection molding? It is the force that keeps the mold closed against injection pressure, quoted in tons (or kN). Too little lets the mold open and the part flashes. ## How do you calculate clamp tonnage? Multiply the projected area by a clamp factor (tons/in²) and add ~10 % margin. A 50 in² part at 3 tons/in² needs about 150 tons, so you would choose a press around 165–200 tons. ## What happens if clamp force is too low? Melt pressure forces the parting line open, giving flash, heavier and dimensionally unstable parts, and eventually damage to the shutoff faces of the mold.

Clamp open is the phase of the cycle in which the two halves of the mold separate after part solidification, to allow ejection. It is the first visible mechanical motion after injection and cooling. ## How it works Once cooling time is up, the controller releases the clamp lock and moves the moving platen along a programmed velocity / position profile: - Fast open: long stretch at high speed, away from the part - Slow open: near the part, to minimize shock or tear ## Typical parameters - Total stroke: 200 – 1500 mm depending on part - Fast velocity: 300 – 600 mm/s - Slow final velocity: 50 – 100 mm/s - Total time: 0.5 – 1.5 s on modern machines - Final open position: typically 1.2 × part height ## Importance in the cycle Every tenth of a second of opening multiplies by thousands of cycles per day. Open accounts for 5 – 10 % of cycle time and is the first optimization target alongside ejection. ## Common issues Excessive over-opening that lengthens the cycle, part tearing from too-fast opening, jamming from poor robot positioning, and non-parallel motion from misaligned tie bars.

Hydraulic pressure (Hpsi) is the oil pressure the machine's hydraulic system applies to the back of the injection ram or screw — the machine-side pressure shown on the controller, distinct from the much higher plastic pressure ppsi acting on the melt at the screw tip. On a hydraulic press it is the setting the operator actually dials in; the screw then multiplies it. ## Hpsi vs Ppsi The two are linked by the intensification ratio (IR): > Ppsi = Hpsi × IR A hydraulic gauge reading of, say, 1,500 psi with an IR of 10:1 means about 15,000 psi of plastic pressure on the melt. So Hpsi alone does not describe what the plastic feels — you must know the IR (which depends on the screw / ram area, i.e. the barrel diameter) to compare machines. ## Why it matters - Setpoints: on hydraulic machines, injection pressure, pack and hold pressure limits and back pressure are usually entered as Hpsi. - Machine comparison: the same Hpsi gives different plastic pressure on machines with different IR, so a process can't be copied by Hpsi alone — convert to Ppsi. - Electric machines: report force/plastic pressure directly and have no hydraulic oil pressure, which is one reason processes are documented in Ppsi for portability. ## Related terms - See also: plastic pressure ppsi, intensification ratio, injection pressure, hold pressure, back pressure ## What is hydraulic pressure (Hpsi) in injection molding? The oil pressure the hydraulic system applies behind the screw or ram, shown on the machine controller; it is the machine-side number the operator sets, which the screw then intensifies into plastic pressure on the melt. ## What is the difference between Hpsi and Ppsi? Hpsi is the hydraulic oil pressure behind the screw; Ppsi is the actual pressure on the plastic. They are related by the intensification ratio: Ppsi = Hpsi × IR, so Ppsi is always much higher. ## Why convert hydraulic pressure to plastic pressure? Because the same Hpsi produces different plastic pressure on machines with different intensification ratios; converting to Ppsi lets you compare machines and transfer a process reliably.

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).