A solenoid valve housing that is machined from tube or fabricated from welded sheet starts life with a seam. A deep drawn housing does not. The difference shows up in the leak test, in how uniform the wall is around the circumference, and in how much secondary work the part needs before it can be assembled. This guide explains how the seam is eliminated, what drawing can and cannot do, and how to write the requirement so a supplier can quote it.
How does deep drawing remove the weld seam in a solenoid valve housing?
A deep drawn solenoid valve housing is formed from flat strip into a one-piece cup, so the sidewall is continuous parent metal and carries no longitudinal weld seam - the same part is also described as a seamless or weldless (nahtlos) housing shell. Balford draws these housings on presses from 25 t to 350 t with a maximum drawn diameter of 250 mm. A first draw on mild steel such as DC04 normally stays inside a limiting drawing ratio (LDR) of about 2.0 to 2.2, which for a 40 mm diameter cup means roughly 35 mm of depth before a redraw is needed; deeper shells take two or more draws with interstage annealing. Where a tight wall is specified, the wall is thinned and sized by ironing. The finished shell has one continuous wall, so the only joints on the assembly are the ones added afterwards.
Where a weld seam comes from, and why it matters
A welded housing is normally built from tube, or from sheet that is rolled and joined. Electric resistance or TIG welding leaves a longitudinal seam whose heat-affected zone is softer, more corrosion-prone and geometrically less uniform than the parent metal. In pressure or vacuum duty that seam is a potential leak path, and it is also the place where roundness and wall thickness are hardest to hold, so it is usually either machined away afterwards or inspected as a separate feature. A drawn shell is formed from flat strip in a press, so the wall stays continuous around the full circumference and there is no seam to dress, seal or inspect.
What the drawn route replaces
- Longitudinal weld seam - removed by forming rather than by machining, so there is no post-weld dressing step.
- Heat-affected zone - no local softening or sensitisation band running the length of the wall.
- Post-weld straightening - the shell is formed to shape in the die instead of being straightened after joining.
- Weld-zone leak path - the wall is one piece, so a pressure-decay or bubble test is evaluating the material and the forming.
- Wall variation at the seam - thickness is set by the strip and by ironing, not by weld reinforcement.
When a welded or fabricated housing is still the right answer
Drawing does not win every case. A shell larger than the 250 mm maximum drawn diameter, a rectangular or multi-chamber body, or a single prototype is usually better fabricated from tube or plate and welded - the draw ratio limits set where that boundary sits. Very low volumes rarely justify a deep drawing die at all, and a body that must contain internal baffles or cross-drilled galleries is easier to build in pieces. The question worth asking is where the joint sits: if it falls in a critical pressure or sealing path, drawing removes a risk that welding has to manage for the life of the part.
How to specify a weldless housing
- Give the cup geometry: outside diameter, overall height, bottom and corner radii, and the flange or lip that mates with the valve body.
- State the wall thickness at the functional zone rather than one nominal for the whole part - the wall thins as material flows into the die.
- Name the material and its temper, because formability and the number of draws follow from that choice.
- Define the leak requirement with the test method and the acceptance limit, not just with the word tight.
- Flag the interface tolerances that matter for assembly: concentricity, shoulder height, and the flatness of the sealing face.
Materials that draw into seam-free housings
- DC01 and DC04 mild steel - the default for drawn housings; DC04 draws deeper before a redraw is needed.
- 304 and 316L stainless - chosen for corrosion resistance; harder to form, so expect more draws and more interstage annealing.
- Aluminium 1050A and 5754 - light housings with lower strength and different springback behaviour.
- Copper and brass - where conductivity or a soldered joint drives the material decision.
- Pure iron such as DT4E - for solenoid parts where magnetic behaviour matters more than strength.
What wall thickness and tolerance are realistic
Wall thickness on a drawn housing follows from the starting strip, the number of draws and any ironing step, so the useful specification is a range per zone rather than one tight number applied everywhere. Concentricity between the bore and the outside diameter, the height of the shoulder, and the flatness of the sealing face are the features that decide whether the housing assembles and seals - those are the ones worth tightening. Very fine tolerances in the 0.001 mm class are realistic only on selected machined features where the process, geometry, material and inspection conditions are confirmed from the drawing; they are not a general wall tolerance on a drawn shell.
Leak testing a drawn housing
A weldless shell removes the seam, but it does not remove the need to prove tightness - see how leak-tight deep drawn housings are specified and tested. The test method should be agreed before the first samples are made, because it decides the inspection fixture as much as the part: pressure decay at a defined pressure and dwell time, a bubble or immersion test, or a customer-specified procedure with a documented limit. Drawn housings are also frequently joined to end fittings by brazing or welding after forming; in that case the seam-free shell is the starting point and the added joint becomes the feature to control.
How Balford approaches drawn solenoid housings
Balford is a metal stamping and deep drawing manufacturer in Zhuji, Zhejiang, with manufacturing heritage dating to 2000 through its predecessor toolmaking business. The plant covers 12,000 m2, runs more than 500 machines with 120+ staff and produces over 50 million parts a year; housings are drawn on presses from 25 t to 350 t, and the toolroom holds more than 4,000 single-hit drawing dies built over that history. Quality management is certified to ISO 9001:2015, and the system is aligned with IATF 16949 requirements - Balford does not hold an IATF 16949 certificate and does not claim one. PPAP Level 3 is the normal submission for a new programme. Bulk heat treatment, plating and the other special processes run at qualified partner plants, and that split is declared in the drawing package rather than left implicit. Typical tooling lead time is 15-30 calendar days for a single-operation drawing die and 30-60 days for a progressive or transfer die.
Key point
A seam is a decision, not a detail. If the joint sits in the sealing or pressure path of a solenoid valve housing, deep drawing removes it at the forming stage instead of managing it for the life of the part.
Frequently asked questions
Do deep drawn solenoid valve housings have a weld seam?
No. A deep drawn housing is formed from flat strip into a one-piece cup, so the sidewall is continuous metal with no longitudinal weld. Any joint on the finished part is a secondary operation such as brazing or welding an end fitting, and that joint - not the shell - is the feature to inspect.
What is the maximum size of a deep drawn housing?
Balford draws up to 250 mm in diameter on presses from 25 t to 350 t. Depth is limited by the draw ratio rather than by the press: a first draw on mild steel such as DC04 normally stays within a limiting drawing ratio of about 2.0 to 2.2, so a deeper housing needs two or more draws with interstage annealing.
Can a deep drawn housing be welded to other parts?
Yes. The seam-free shell is often brazed or welded to a fitting, a flange or a tube after forming. State the joint process and the leak requirement in the RFQ, because the added joint has its own heat-affected zone and its own inspection.
Why is a drawn housing more leak-tight than a welded tube shell?
Because there is no longitudinal seam to seal. A welded tube shell carries a heat-affected zone that is less uniform than the parent metal, plus a seam that has to be dressed and inspected; a drawn shell has one continuous wall, so a pressure-decay test is evaluating the material and the forming rather than a weld.
Which material is best for a drawn solenoid housing?
DC04 mild steel is the usual choice where formability and cost drive the decision, and pure iron such as DT4E is used where the magnetic circuit matters more than strength. 304 or 316L stainless is specified for corrosion resistance. Temper matters as much as grade - a harder strip needs more draws and more interstage annealing.