glossary
Definitions and explanations of common technical injection moulding terms and manufacturing processes.
Additive Manufacturing
Layer-by-layer fabrication processes such as 3D printing. Useful for early-stage prototyping to assess form and basic function, but the resulting parts do not replicate the material behaviour, shrinkage, or surface finish of production injection mouldings and should not be used as a substitute for process validation.
Aluminium Tooling
Mould tools machined from aluminium rather than hardened steel. While historically considered faster and cheaper to produce, aluminium is susceptible to damage and wear under sustained production pressures. Hymid does not use aluminium tooling, preferring hardened steel for its durability and dimensional stability.
Annealing
A post-moulding heat treatment process applied to reduce residual internal stress in moulded components, improving dimensional stability and reducing the risk of warpage over time
Auto-ejection
A mould feature that automatically removes a moulded part from the tool cavity at the end of each cycle without manual intervention, enabling fully automated high-volume production.
Back Pressure
The hydraulic resistance applied to the injection screw during the plasticising phase. Higher back pressure improves melt homogeneity and colour mixing but increases cycle time and can degrade heat-sensitive polymers if set incorrectly.
Barrel
The cylindrical housing of an injection moulding machine that contains the reciprocating screw. Polymer granules are fed into the barrel, melted, and homogenised before being injected into the mould.
Boss
A raised cylindrical feature on a moulded part, typically used to receive a fixing screw, threaded insert, or locating pin. Boss design must account for wall thickness ratios to prevent sink marks on adjacent surfaces.
Burn Marks
Dark discolouration or charring on a moulded part's surface, typically caused by trapped gas that is compressed and ignited as the melt front advances. Resolved through venting improvements, reduced injection speed, or gate repositioning.
CAD (Computer-Aided Design)
Digital three-dimensional modelling of components and assemblies. CAD data (provided in native file format) forms the starting point for Hymid's DfM review and subsequent tool design.
Cavity
The negative impression within a mould tool that defines the external geometry of the moulded component. Multi-cavity tools contain two or more identical impressions to increase output per cycle.
Clamping Force
The force, measured in tonnes, applied by the injection moulding machine to keep the mould closed against the injection pressure of molten polymer. Insufficient clamping force causes flash; over-clamping can damage the tool.
Collapsible Core
A complex mould mechanism that collapses inward upon ejection to release internal undercuts or threaded features that would otherwise prevent part removal. Collapsible cores add cost and maintenance requirements and are subject to DfM review to explore whether design alternatives can eliminate the need.
Component Geometry
The overall three-dimensional form, features, and proportions of a moulded part as defined by the CAD model. Geometry directly influences tool complexity, mould flow behaviour, and the selection of gating and ejection strategies.
Core
The male portion of the mould that forms the internal surfaces or cavities of a moulded part. The core and cavity work together to define the complete part geometry.
Cooling Channel
Passages machined into the mould tool through which temperature-controlled water circulates to remove heat from the molten polymer. Efficient cooling channel design reduces cycle times and minimises residual stress and warpage in the finished part.
Cooling Time
The portion of the injection moulding cycle during which the part remains in the mould to solidify sufficiently before ejection. It is typically the longest phase of the cycle and is strongly influenced by wall thickness, polymer grade, and coolant temperature.
Cosmetic Requirements
The surface quality, appearance, texture, and finish standards specified by the customer for a moulded component. Cosmetic requirements directly influence parting line placement, gate location, draft angle selection, and mould surface treatment.
Cycle Time
The total time required to complete one injection moulding cycle, encompassing mould closing, injection, packing, cooling, and ejection phases. Cycle time is a key driver of production cost per part.
Design for Manufacture (DfM)
A systematic engineering discipline in which a product's design is reviewed and refined specifically for efficient, reliable, and cost-effective manufacture using injection moulding. DfM identifies potential issues, such as wall thickness inconsistencies, undercuts, or poor gating, before tooling manufacture begins, avoiding costly downstream changes. Approximately 70% of a product's manufacturing cost is determined during the design phase, making early DfM engagement critical.
Design Intent
The functional, aesthetic, and performance objectives that a product design must fulfil. During DfM, Hymid's engineers work to satisfy all aspects of design intent while adapting geometry and features for production feasibility.
Dimensional Stability
A material's or component's ability to maintain its specified dimensions over time and across varying environmental conditions such as temperature and humidity. Dimensional stability is influenced by polymer selection, part design, mould cooling strategy, and processing parameters.
Draft Angle
A deliberate taper applied to vertical walls and features of a moulded component to facilitate clean ejection from the mould without drag marks or distortion. Draft angles of 1° to 3° are typical for smooth surfaces; textured or grained surfaces require greater angles to avoid surface damage upon ejection.
Ejection
The phase of the injection moulding cycle in which the solidified part is removed from the mould cavity, typically using ejector pins, blades, or stripper plates. Ejection design must account for part geometry, draft angles, and fragile features to avoid damage.
Ejector Pins
Hardened steel pins that advance through the mould during ejection to push the solidified part out of the cavity. Pin placement must be carefully considered during tool design to avoid witness marks on cosmetic surfaces and to distribute ejection force evenly.
Feature Geometry
The specific three-dimensional characteristics of individual design elements such as ribs, bosses, snap-fits, and holes. Each feature is assessed during DfM for its mouldability, ejection implications, and potential impact on cooling and flow behaviour.
Fill Pattern
The path and progression of molten polymer as it flows from the gate through the mould cavity. An optimised fill pattern ensures the cavity fills uniformly, minimising weld lines, air traps, and flow-induced stress.
Flash
A thin film of excess material that forms along the parting line or at mould features when polymer forces its way into any gaps between mould surfaces. Flash is caused by insufficient clamping force, excessive injection pressure, or mould wear, and constitutes a dimensional and cosmetic defect.
Flow Characteristics
The rheological behaviour of a molten polymer as it moves through gates, runners, and mould cavities. Flow characteristics are influenced by polymer grade, melt temperature, injection speed, and part geometry, and are assessed during mould flow simulation.
Gate
The point at which molten polymer enters the mould cavity from the runner system. Gate type, size, and location are critical DfM considerations that affect fill pattern, weld line position, surface appearance, and residual stress within the moulded part.
Gate Location
The specific position on a component at which the gate is placed. Gate location is chosen to optimise fill balance, minimise weld lines, and position any gate vestige where it is least cosmetically or functionally impactful.
Gating Strategy
The engineering decision-making process by which gate type, size, number, and location are determined for a given component and tool design. An effective gating strategy balances fill efficiency, cosmetic requirements, and tool complexity.
Gold Sample
A retained production-approved reference part, held by Hymid, used as a benchmark for ongoing quality comparison throughout the life of the programme. Gold samples are established during the UK validation and production approval stage.
Hardened Steel
High-grade steel that has been heat treated to achieve a specific hardness (typically 48–54 HRC for mould tooling), providing long-term wear resistance, dimensional stability under repeated thermal cycling, and extended tool life. Hymid specifies hardened steel for all production tooling.
Hot Runner System
A manifold system built into the mould that maintains the polymer in the molten state within the runner channels between shots, eliminating runner scrap and enabling cleaner, more efficient gating. Hot runners are common in high-volume applications and multi-cavity tools.
Initial Sample Inspection Report (ISIR)
A formal document produced following the first tooling trial (T1) that records dimensional measurement data, visual inspection results, and a comparison against the approved component specification. ISIRs are used to assess whether the tool and process are performing within tolerance before progressing to subsequent trials.
Injection Moulding
A high-volume manufacturing process in which molten thermoplastic polymer is injected under pressure into a closed mould tool, where it cools and solidifies to form a precise, repeatable component. The process is highly scalable and capable of producing complex geometries with tight tolerances.
Injection Pressure
The pressure applied by the screw or plunger to force molten polymer into the mould cavity. Injection pressure must be sufficient to fully fill and pack the cavity but must not exceed the tool's or machine's rated limits.
Injection Speed
The rate at which molten polymer is injected into the mould cavity. Injection speed influences fill patterns, shear heat generation, surface finish, and the propensity for defects such as burn marks or jetting.
Insert (Metal Insert)
A metal component, such as a threaded bush or nut, that is incorporated into a moulded part either by being placed in the tool prior to moulding (insert moulding) or pressed in after moulding. Inserts provide robust mechanical attachment points in plastic components.
Knit Line (Weld Line)
A visible or structural line on a moulded part where two melt fronts meet and fuse. Knit lines can be cosmetically unacceptable and may represent a point of reduced mechanical strength. Their position is predicted during mould flow simulation and influenced by gate location and wall thickness.
Lead Time
The elapsed time from project initiation or purchase order placement through to the delivery of a finished tool or moulded component. Tooling lead times at Hymid typically span six to eight weeks for manufacture, plus trialling and validation phases.
Lifter
An internal mould mechanism that moves at an angle during ejection to release internal undercut features. Lifters add complexity to tool design and are reviewed during DfM to assess whether design modifications could eliminate the need.
Material Selection
The process of choosing the most appropriate thermoplastic polymer for a component based on its functional requirements, environmental conditions, cosmetic specification, processing behaviour, and regulatory obligations. Material choice directly influences tool design, processing parameters, and component performance.
Melt Temperature
The temperature at which a polymer is processed in its molten state within the barrel of the injection moulding machine. Each polymer has an optimal melt temperature range; deviating outside this range causes degradation or poor flow.
Mould Flow Simulation
Computer-aided engineering software that simulates the injection moulding process digitally, predicting melt flow, cooling behaviour, shrinkage, warpage, weld line formation, and potential defects before the tool is manufactured. Hymid uses mould flow simulation as a key element of its DfM process to validate design decisions with evidence.
Mould Tool
The precision-engineered steel tool that defines the shape and surface finish of an injection-moulded component. The tool is the physical embodiment of all design and engineering decisions made during product development and represents a strategic long-term manufacturing asset.
Mouldability
The degree to which a component's design is compatible with reliable, efficient production using injection moulding. A DfM review assesses mouldability across factors including wall thickness, draft angles, gating options, ejection, and material flow.
Multi-Cavity Tool
A mould tool containing two or more identical cavities that produce multiple parts per cycle. Multi-cavity tools increase production output and reduce the cost per part, but require careful balancing of runners and gates to ensure consistent fill across all cavities.
Packing Phase
The injection moulding stage following cavity fill in which additional polymer is injected at reduced pressure to compensate for material shrinkage as the part cools. Insufficient packing leads to sink marks and dimensional inaccuracy; excessive packing causes flash or moulded-in stress.
Parting Line
The line on a moulded component where the two halves of the mould tool meet. Parting line location influences ejection direction, cosmetic appearance, flash risk, and the need for side actions or other complex tooling features.
Plasticising
The process by which solid polymer granules are melted and homogenised by the rotating screw within the barrel before injection. Effective plasticising ensures a consistent melt temperature and uniform material properties across each shot.
Polymer
A large-molecule material formed by the repetition of monomer units. In injection moulding, thermoplastic polymers, which soften when heated and solidify when cooled, are used. Common examples include ABS, polypropylene, nylon, and polycarbonate.
Precision Tooling
The design and manufacture of mould tools to exacting tolerances, using high-quality steel and precision machining, to produce moulded components that consistently meet specification throughout the production life of a programme. Hymid's precision tooling process is built around a 'right first time' philosophy.
Production Approval
The formal sign-off that confirms a tool and its associated moulding process have met all dimensional, cosmetic, and functional requirements and are ready to enter sustained production. At Hymid this follows UK-based pre-production trialling and validation.
Production Volume
The anticipated number of parts to be produced over a programme's lifetime, typically expressed as an annual quantity. Production volume is a key input for DfM decisions around tool material, cavity count, hot or cold runner selection, and tooling investment level.
Prototype Injection Mould
A production-intent or simplified tool manufactured specifically to produce representative moulded samples at an early stage of development. Prototype injection mould tools are more effective than 3D-printed parts at replicating the material behaviour, surface finish, and potential defects of volume production.
Repeatability
The ability of an injection moulding process to consistently produce components within specification, cycle after cycle, over the long-term life of the programme. Repeatability depends on the quality of the tool, stability of the moulding process, and consistency of material supply.
Rib
A thin vertical wall feature used to increase the stiffness of a moulded component without adding excessive wall thickness. Ribs should typically be 50–70% of the adjacent nominal wall thickness to avoid sink marks on the opposite face.
Right First Time
A manufacturing philosophy centred on preventing defects and avoiding rework by thoroughly analysing and resolving potential issues before and during production, rather than inspecting and correcting after the fact. Hymid's tooling process is explicitly built around this principle.
Runner System
The network of channels within the mould through which molten polymer flows from the machine nozzle to the gate(s) and into the cavity or cavities. Runners can be cold (requiring removal as scrap) or hot (maintained in a molten state via a heated manifold).
Sample Submission Report
(SSR)
A formal quality document prepared during Hymid's UK pre-production approval stage, accompanying moulded sample parts submitted for customer or internal approval. The SSR records process parameters, dimensional data, and any deviations from specification.
Shrinkage
The reduction in dimensions that occurs as a moulded part cools and solidifies. Shrinkage varies by polymer type and grade, wall thickness, and processing conditions, and must be accounted for in tool design through application of an appropriate shrinkage factor.
Side Action
A mould mechanism, typically a side core or lifter, that moves laterally or at an angle relative to the mould opening direction to form or release features such as holes, slots, or undercuts on the side faces of a component. Side actions increase tool complexity and cost and are subject to DfM optimisation.
Sink Mark
A surface depression or dimple on a moulded part, caused by localised volumetric shrinkage where the part wall is thickest — typically opposite a rib or boss. Sink marks are a cosmetic defect, prevented by maintaining recommended wall thickness ratios and optimising packing parameters.
Snap-Fit
An integral moulded feature designed to engage with a mating component by deflecting during assembly and springing back to lock in place. Snap-fit geometry must be designed with appropriate draft and wall thickness to ensure reliable function and ejection without damage.
Steel Grade
The specific composition and heat treatment classification of the steel selected for mould construction. Common tool steel grades include P20, H13, and S136; the choice depends on required surface hardness, polishability, corrosion resistance, and expected production volumes.
Surface Finish
The texture and visual quality of a moulded component's external surfaces, ranging from high-gloss polish to matte or grained textures. Surface finish requirements influence draft angle specification, parting line placement, gate location, and mould polishing or texturing operations.
T1 Trial (First Tool Trial)
The first formal moulding trial conducted at the tool maker's facility after tool manufacture, using the specified production polymer. The T1 trial produces initial sample components that are inspected via an ISIR to determine whether the tool is performing to specification.
T2 Trial
A subsequent tooling trial conducted after modifications have been made following T1 inspection findings. Further trials (T3 etc.) may follow if additional adjustments are required.
Thermoplastic
A class of polymer that softens and becomes fluid when heated, then solidifies again upon cooling - a process that can be repeated multiple times. Thermoplastics are the primary material type used in injection moulding. Common examples include ABS, polycarbonate, nylon (PA), polypropylene (PP), and PEEK.
Tolerance
The permissible range of dimensional variation from a nominal design dimension, specified on engineering drawings or in a product specification. Tight tolerances increase tooling complexity and cost and must be clearly defined before DfM and tool design commence.
Tool Design
The detailed engineering of the mould tool's geometry, mechanisms, gating, cooling, venting, and ejection systems, governed by DfM outputs and Hymid's proprietary manufacturing standards. Tool design is an iterative, governed process completed before manufacture begins.
Tool General Assembly
(GA) Review
A formal, iterative review stage at Hymid in which shared CAD data for the proposed mould tool design is examined and refined in collaboration with the selected tool maker, in accordance with Hymid's manufacturing standards, prior to release for manufacture.
Tool Life
The number of moulding cycles a tool is designed and expected to sustain before requiring major refurbishment or replacement. Hymid's hardened steel tools are designed for long production lives, with guarantees provided on every tool manufactured.
Toolroom
Hymid's in-house facility equipped for the inspection, servicing, maintenance, and repair of mould tools. The toolroom enables thorough tool assessment, cleaning, and pre-production trialling on import from overseas manufacture.
Undercut
A feature on a moulded component whose geometry prevents straight-line ejection from the mould in the tool's opening direction. Undercuts typically require side actions, lifters, or collapsible cores to release, increasing tool complexity and cost. DfM aims to identify and, where possible, redesign undercuts to simplify tooling.
Uniform Wall Thickness
The design principle of maintaining consistent material section throughout a moulded component to ensure even polymer flow, balanced cooling, and minimised risk of sink, warp, and residual stress. DfM specifically targets non-uniform walls as a primary risk factor.
Validation
The process of demonstrating, through physical trials and documented evidence, that a mould tool and moulding process consistently produce components that meet the specified requirements. Hymid conducts formal validation at its UK facility before any tool enters sustained production.
Vent
A very shallow channel or gap machined into the mould at the end of flow paths to allow air and volatiles to escape as the cavity fills. Inadequate venting leads to burn marks, short shots, and elevated cavity pressure.
Void
An internal air pocket or vacuum bubble within a moulded part, caused by insufficient packing pressure or excessive wall thickness. Voids compromise structural integrity and may not be visible externally, making process control critical.
Wall Thickness
The nominal cross-sectional thickness of the material forming a moulded component's walls. Wall thickness is the single most influential design parameter in injection moulding, directly affecting polymer flow, cooling time, cycle time, shrinkage, sink, warpage, and structural performance. DfM analysis includes a detailed review of wall thickness consistency.
Warp
Distortion of a moulded component from its intended geometry, caused by differential shrinkage or residual stress during cooling. Warpage is predicted by mould flow simulation and mitigated through design changes, material selection, cooling optimisation, and process control.
Weld Line
See Knit Line.