A formed part is a component with a three-dimensional geometry that is not made up of a flat contour. At GOBA, formed parts are made from electrical insulating materials in flat stock: polyester films, aramid papers, laminates and pressboard in thicknesses from 0.023 to 3.0 mm. Shaping is done under heat in the tool, complemented by folding and embossing. This page separates the formed part from flat stock from the injection moulded part, shows the processes and their limits, clarifies the distinction from stamped and bent parts, and answers when the effort pays off.
Formed parts from flat stock and from injection moulding are two different worlds
Most searches for formed parts lead to plastic injection moulding. There the geometry is created from the melt in a closed tool, the part is solid and the wall thickness freely chosen. Insulating formed parts arise differently: the starting point is a uniformly thin web that is cut and then shaped. The wall thickness remains the material thickness across the whole part, and the geometry is limited to what can be developed from a surface.
This has concrete consequences for purchasing. An injection mould costs a multiple and only pays off at high volumes. A formed part from flat stock is considerably cheaper at small and medium volumes and available at shorter notice. In exchange, ribs, bosses and varying wall thicknesses are not feasible. Anyone needing a thin, electrically separating geometry is in the right place with insulation and moulded parts from flat stock. Anyone needing a load-bearing plastic component belongs with an injection moulder.
Three routes from surface to three-dimensional shape
Which process applies depends on the depth of the geometry and on whether the part is rotationally symmetrical.
| Process | Principle | Suited to | Limit |
|---|---|---|---|
| Hot forming | Under heat in the tool the material takes the shape permanently | Caps, shells, trays and geometries with depth | Cooling has to be controlled, otherwise the part distorts |
| Folding and embossing | Cold forming along defined lines, embossing creates beads and structures | Flat geometries with edges, stiffeners and locating features | Three-dimensional curvature cannot be reached this way |
| Winding | The web is laid around a mandrel and bonded | Sleeves, tubes and caps closed on one side | Rotationally symmetrical shapes only, separate production line |
At GOBA the focus lies on the first two rows. We form insulating materials under heat when the geometry cannot be reached cold, working so that the surface and structure of the material remain undamaged. That is the real difference from forming sheet metal: an insulating material loses its function as soon as the surface tears or the structure breaks open. Which groups of DIN 8582 apply here at all is set out in the article on forming technology. How that looks in practice is described on our stamping and forming page.
Insulating materials that can be formed
Not every material takes a three-dimensional shape. What matters is stretchability under heat and whether the material stays in shape after cooling.
- Polyester films hot form well and hold their shape after cooling
- Polyimide films withstand high temperatures and suit tight radii
- Aramid papers form to a limited degree, they break along the fibre at tight radii
- Technical laminates follow the weakest partner in the composite
- Pressboard is folded and embossed, deep draws are not possible
- Glass fabric and mica products stay largely dimensionally stable and are joined mechanically
Which thermal class and which dielectric strength the finished part carries is decided by the material, not by the process. The overview of the groups is on our insulating materials page, the assignment to temperatures in the article on thermal classes of insulation.
Stamped part, bent part, formed part: where the line runs
The three terms describe increasing depths of manufacture. A stamped part leaves the tool flat. A bent part has at least one edge and is processed a second time after cutting. A formed part has a geometry that is not made up of straight edges, such as a cap, a tray or a shell.
For costing this means: every edge is an operation, every three-dimensional shape needs a forming tool and usually a heat process. The step from bent part to formed part is therefore the most expensive in this sequence. It pays off when the geometry serves a function that edges cannot deliver, such as tightly enclosing a component or a tray that retains liquid.
When a formed part beats a bent part
The most common objection from design is that a folded part would do. That is often true, and we say so. A formed part justifies its premium in three cases. First, when the contour has to be closed all round and a folded edge would leave a gap. Second, when assembly saves time because one formed part sits in a single motion where two bent parts would otherwise be joined. Third, when the geometry stiffens the part and allows a thinner material.
Against a formed part speaks a geometry that is still going to change. A forming tool is harder to adapt than a steel rule die. In that situation we recommend starting with a folded sample and only moving to the formed part after design release.
Formed parts in apparatus engineering and electronics
In apparatus engineering, insulating formed parts separate live assemblies from the housing. Typical examples are cover trays over terminal blocks, caps over connections and linings that extend a creepage distance without costing installation space. In electronics, formed insulating parts serve as shielding carriers, as a separating shell between board and housing, or as a holder that insulates and locates at the same time.
Electric motor manufacturing is the third large block. There insulating parts are fitted into the lamination stack so they do not compress during assembly. For complex geometries we form under heat so the part reproduces the slot contour cleanly. Applications in electromobility come on top, above all as cell and module insulation with a tight fit.
What belongs on the drawing of a formed part
For a formed part, the flat development is not enough. Four details decide whether the first sample lands.
- Draw depth and the tightest radii of the geometry
- Which dimensions are functional, meaning they meet a mating part
- Permissible wall thinning, because the material thins out during drawing
- Temperature class of the application, which rules materials in or out
Wall thinning is the detail most often missing from drawings. A formed part is thinner at the point of greatest deformation than the original web. Where insulation is required at that point, the starting thickness has to be chosen accordingly. For all dimensions without an individual tolerance, the general tolerance to DIN ISO 2768 applies.
Delivery format belongs in the design
Formed parts are bulkier than flat ones, they stack less well and interlock more easily. Noticing that only at goods-in costs assembly time. On request we therefore deliver insulating parts stacked or packaged, with individually defined pack sizes, so automated downstream processing at the customer works.
On individual customer projects we additionally apply marker lines to the insulating parts. Sensors in the customer assembly use them to detect the position and orientation of the part. Such details belong in the discussion early, because they can influence the geometry. For recurring requirements with varying call-off quantities we offer customer-specific production with stockholding.
GOBA conclusion: the three-dimensional shape is the costly step, check it first
A formed insulating part costs more than a bent part and considerably less than an injection moulded one. Before commissioning a forming tool, check whether the function can also be reached with edges. If it stays a formed part, state the draw depth, the tightest radii and the permissible wall thinning, because at the point of greatest deformation the material is thinner than the original web. Settle the delivery format before series start as well, since stacked or packaged delivery drives assembly time at your end. Which material can be formed and which thermal class it carries we agree in advance: our material range covers films, papers, laminates and pressboard.
