What wall thickness is achievable on a drawn sensor housing?
On a deep drawn sensor housing the wall thickness is not a single number: it follows the blank thickness in the first draw, thickens slightly at the open rim, thins at the punch nose where the material is bent and stretched, and can then be deliberately reduced by ironing. Typical production walls for drawn sensor housings run from about 0.8 mm to 3.0 mm in copper, brass, pure iron, carbon steel and stainless steel; the achievable minimum depends on the material, the draw ratio and the corner radius, not on the wall thickness specification alone. Because the value changes along the height, a drawing that states only one wall thickness cannot be inspected - the drawing must also state where the wall is measured. Fixing that position is also what lets the drawing review decide the number of drawing stages and whether an ironing pass is needed.
Why one number is not enough
A drawn housing starts as a flat blank and is pulled over a punch. Material that was in the blank has to end up in a taller, smaller-diameter shape, so thickness moves rather than staying constant. The result is a gradient: the wall near the bottom radius is usually thinner than the blank, the straight wall sits close to the blank thickness, and the top rim thickens because material from the flange is compressed into it as the flange shrinks.
That is why a note such as "wall 1.0 mm" on a drawing is not a specification. It does not say where the 1.0 mm applies, so the part can pass one measurement and fail the next while both are taken to the same drawing.
What we run in production
- Drawn wall, copper, brass and pure iron: about 0.8 mm to 3.0 mm
- Drawn wall, carbon steel and stainless steel: about 1.0 mm to 3.0 mm
- Wall reduced by ironing: roughly 10 to 30 percent thinner than the blank per pass, depending on material and the reduction the die set allows
- Maximum draw diameter: Ø250 mm; presses 25-350 t
- Housings are formed on single-hit draw dies and on progressive and transfer dies; more than 4,000 single-hit drawing dies have been built since 2000
The three things that decide the achievable minimum
- Draw ratio - how much the blank has to shrink to reach the finished diameter. A deeper draw ratio needs more stages, and each extra stage costs thickness control.
- Material - stainless steel work-hardens faster than low-carbon steel, so it tolerates less thinning per stage before it needs to be annealed.
- Corner radius and punch nose - the tighter the radius, the more the material is stretched at that point, and the thinner the wall becomes there.
Key point
If the diagram shows one wall figure and no measuring position, add the position before tooling starts. Retrofitting a measuring position after the dies are cut means either a new die or a deviation note.
How to write it on the drawing
- Give the wall as a nominal with a tolerance band, and state the measuring position: distance from the bottom face, or distance below the rim.
- If the wall is measured after plating or coating, say so - the deposit adds to the measurement and the drawing must state whether the figure is before or after finishing.
- Where the wall thins at the bottom radius, give a separate minimum rather than letting one global figure cover it.
- For ironed walls, state the target wall and the surface finish, because ironing sets both at the same time.
How thickness is checked
Wall thickness is checked with outside micrometers at the positions the drawing defines, and cross-checked against the 2.5D optical measuring projector and the instant vision measuring system where the geometry makes a micrometer reading unreliable. Bore-related dimensions are checked with three-point bore micrometers, plug and go/no-go gauges, and a concentricity gauge. Inspection results are recorded per lot and reviewed in the quality routine. Where a feature is critical and the process, geometry, material and inspection conditions allow it, dimensions to 0.001 mm can be agreed in advance - but that is a drawing-confirmed exception for selected machined features, not a standard tolerance for a drawn wall.
What we do not claim
- We are not IATF 16949 certified. Our controls are aligned with IATF 16949 requirements, and we say so rather than claiming the certificate.
- Our quality system is certified to ISO 9001:2015. ISO 14001:2015 has lapsed and is not claimed.
- Bulk heat treatment, slow-wire EDM, passivation, electropolishing, plating, phosphating and liquid painting are subcontracted, with traceable process records. Powder coating is split: large sheet-metal parts run in our own manual booth, small parts are coated by a partner on an automatic line.
- Hot forging, cold extrusion, cold heading, casting and powder metallurgy are bought as near-net pre-forms and finished by machining in-house. We are not a forge, a foundry or a powder-metallurgy plant.
- Walls thinner than the ranges above are possible on specific parts, but only after a drawing review - we do not quote a minimum as a catalogue figure.
Frequently asked questions
What is the thinnest wall you can draw?
It depends on the material, the draw ratio and the corner radius rather than on a fixed catalogue number. For the materials we run most, drawn walls start at about 0.8 mm in copper, brass and pure iron, and about 1.0 mm in carbon steel and stainless steel. Send the drawing and we will tell you whether the wall you need is reachable, and what it does to the number of drawing stages.
Why does the wall thickness change along the height?
Because the material is moved, not added. The flange shrinks into the wall as the part is drawn, so the rim thickens; the material stretched over the punch nose thins. In an ironed wall the thinning is deliberate and set by the die clearance.
How should the wall be dimensioned on the drawing?
As a nominal with a tolerance band plus an explicit measuring position - for example, 12 mm above the bottom face. Also state whether the figure applies before or after plating or coating, and give a separate minimum where the bottom radius thins.
Can you hold the wall thickness after ironing as well as the surface finish?
Ironing sets the wall and the surface in the same operation, so the two are specified together. If both are critical, they need to be on the drawing together, and the die set has to be built for that combination.