More knowledge.

In the injection molding process, the plastic melt is guided into the cavity through a runner and distribution system. A distinction is made between two basic systems:

Cold Runner System: The runner and sprue solidify together with the molded part. The solidified material (cold runner) must be removed manually or automatically. It can be recycled as regrind and reused. Cold runner systems are cost-effective to manufacture and easy to maintain. They are particularly suitable for small production runs, material changes and sensitive materials.

Hot Runner System: The manifold block is electrically heated and maintained at the processing temperature of the plastic. The melt remains permanently molten within the runner system, eliminating runner waste. Hot runner systems enable shorter cycle times, gentle material processing and are more economical for high-volume production. Their disadvantages are higher initial investment costs and increased maintenance requirements. For sensitive or highly filled materials, the selection and design of the hot runner system require particular care.

New design possibilities for lightweight construction. By combining high-strength metals with plastics, stable components with a high degree of design freedom can be produced. The advantages of both materials – plastic and metal – are combined and enhanced.
In contrast to insert and outsert technology, hybrid technology integrates both materials into a single, cohesive component with different functional properties.
Most applications are found in the automotive industry. However, the use of hybrid technology is also increasing in sectors such as household appliances (“white goods”) and the furniture industry.

The most widely used injection molding process (often referred to colloquially as injection molding or the injection molding process) is thermoplastic injection molding. This process allows both simple and highly complex geometries to be produced in a single operation. A key advantage of injection molding is its suitability for mass production, due to short cycle times and minimal post-processing. Injection-molded parts can range in weight from a few milligrams up to approximately 50 kg. The process enables the production of components with high precision, and surface finishes can be defined almost freely. Smooth surfaces for optical applications, textured surfaces for improved grip, as well as patterns and engravings can all be realized.
The combination of plastic and metal is also commonly used in injection molding. In such cases, threaded inserts, contact units, stamped grids, or continuous strips are overmolded. Processes such as insert/outsert technology as well as reel-to-reel (insert molding on strip) are also implemented in our facility.
Thermoplastics are often modified with fillers and additives to suit specific applications, including materials such as glass beads, glass fibers, and minerals.

Function of an injection molding machine: Plastic granulate is fed into the plasticizing unit via a hopper or a material handling system. A screw conveys the material to the injection nozzle while heating it to a molten state. The maximum amount of plasticized material is determined by the stroke of the reciprocating injection unit. The melt flows through the sprue channel into the mold. The mold is kept closed under pressure in the clamping unit and is temperature-controlled depending on the application. The molded part solidifies under holding pressure within the mold, during which shrinkage occurs. Each material has its own shrinkage factor. Once the mold opens along the main parting line, the molded part is ejected. The process then begins again.

Also known as reel-to-reel processing. In this process, a stamped metal strip is unwound from a reel and fed into the injection mold. After the molding process, the strip is rewound onto empty reels. Pre- and post-processing steps such as cutting and bending operations can also be integrated. This allows products to be supplied to the customer on reels or in trays.

Insert technology refers to the integration of metal components into plastic parts. In this process, metal elements (e.g. threaded inserts, shafts) are placed into the injection mold and overmolded with plastic.

Moldflow simulation is a computer-aided method for predicting the behavior of the plastic melt inside the injection mold. It includes the simulation of filling (Fill), packing (Pack), cooling (Cool), as well as shrinkage and warpage (Warp).

The simulation enables the following parameters to be optimized before the actual mold is manufactured:

• Gate location and gate geometry
• Wall thickness distribution and weld lines
• Cooling channel geometry and temperature control strategy
• Shrinkage and warpage behavior

By identifying potential issues such as air traps, weld lines or uneven filling at an early stage, costly mold modifications can be reduced or avoided altogether.

The simulation is an essential part of the concurrent engineering process and provides valuable data for component and mold design.

At Gindele, the CADMOULD software from Simcon is used.

In multi-component injection molding, two or more plastics are processed within a single mold during one production cycle. The components are joined either by material bonding (through adhesion or mutual melting) or by mechanical interlocking (through undercuts).

A distinction is made between the following processes:

• Overmolding: A previously solidified component is placed into a second mold and overmolded.
• Rotary Table Process: The semi-finished part remains inside the mold and is transferred to a second cavity by means of a rotating table.
• Index Plate Process: The cavities are alternated within the mold by means of an indexing plate.

Typical applications include hard-soft combinations (e.g. PP + TPE for ergonomic handles and sealing lips), multi-colored components without secondary processing, and parts with integrated sealing or damping elements.

The process is particularly economical because assembly steps are eliminated and the bond strength is often higher than that of mechanically assembled components.

Applications: Medical technology, consumer goods, electrical engineering and the automotive industry.

In outsert technology, a metal carrier, typically a stamped grid or lead frame, is partially overmolded with plastic. Unlike insert technology, where a metal part is completely embedded in a plastic matrix, the metal part remains the primary carrier of the assembly in outsert technology. The plastic specifically provides guiding, sealing, fastening or electrical insulation functions. This process enables the cost-effective integration of several functions into a single component, as complex assembly and joining steps are eliminated. It is frequently used in electrical engineering (connectors, sensors), medical technology (diagnostic and therapy devices) and the automotive industry. In combination with the reel-to-reel process (strip overmolding), very high quantities can be produced economically.

Pad printing enables the printing of shaped parts, including convex and concave surfaces. This means that components without flat printing areas – which are difficult or impossible to print using screen printing – can be processed effectively. The ink is transferred from an etched printing plate (cliché) onto an elastic silicone pad. By lowering the pad onto the cliché, it adapts to the surface and picks up the image, which is then transferred onto the component. This process is known as indirect printing.

Shrinkage refers to the reduction in volume of a plastic part as it cools after injection molding. It results from the thermal contraction of the polymer chains and, in semi-crystalline materials, from volume densification caused by crystallization.

The shrinkage factor is material-specific and is, for example, approx. 0.4–0.7% for PC, 0.5–2.0% for PA and 1.0–2.5% for PP. It is taken into account in mold design by applying a corresponding allowance to the cavity.

Warpage occurs when shrinkage is uneven within the component. Causes include non-uniform wall thicknesses, different cooling rates on the core and ejector sides, fiber orientation in glass-fiber-reinforced materials or uneven gate positions.

Warpage leads to dimensional deviations, which can be minimized in precision components through Moldflow simulation, targeted temperature control strategies and adjusted processing parameters.

Viscosity is a measure of the resistance of a fluid or non-solid substance to flow. The reciprocal of viscosity is fluidity, which describes how easily a fluid flows. The higher the viscosity, the thicker (less flowable) the fluid; the lower the viscosity, the thinner (more flowable) it is. The term viscosity is usually associated with shear viscosity, although extensional viscosity can also be measured. In more viscous fluids, particles are more strongly bound to each other and therefore less mobile, which is why viscosity is often described as internal friction. This results not only from the cohesive forces between the particles of the fluid. In the case of solids, properties such as ductility, brittleness, and plasticity are used instead. The term “viscosity” originates from the Latin word viscum, referring to the sticky sap of mistletoe berries, from which birdlime was once produced.