Ultrasonic welding
- Continuous joint that follows every turn
- No extra parts, and nothing to loosen
- Permanent, so the manifold cannot be opened
Molded part guide: manifolds
Injection Molded Manifolds
A manifold takes one inlet and feeds several outlets, which means internal passages that branch, turn, and cross each other. Almost none of that can be formed by cores that pull straight out of a tool. So a molded manifold is usually two parts that become one, and the joint between them is the design.
Two halves
Passages that no core can reach
Fluid manifolds, air manifolds, distribution blocks, and cooling plates.
A core has to be able to come out. That means every passage a core forms must run along the direction the tool opens, with nothing in the way. A manifold breaks that rule immediately: its passages branch sideways, turn corners, and often pass over and under each other. A few side actions can rescue a simple case, but a branching network cannot be built that way.
So the manifold is split along the passages. Each half is molded as an open channel, which cores can reach easily, and the two halves are then joined so the open channels become closed passages. Suddenly the hard part is not the passages at all, it is making a joint that holds pressure everywhere along a long, winding seam.
Ultrasonic welding is the usual method. A small raised ridge along the joint on one half melts under vibration and fuses into the other half, giving a continuous bond that follows the passage wherever it goes. The joint has to be designed so that melted material is contained rather than squeezed into the passage, where it would restrict flow or break off later.
Ports are the other weak point. Melt flowing around a port opening splits and closes again on the far side, and that closing line is weaker than the material around it. Under pressure those lines are exactly where a manifold splits. Feeding the part so the lines fall between ports rather than across them, and adding material around each port, keeps them out of trouble.
Features
Manifold features and what each one needs
Split construction turns a tooling problem into a joining problem.
| Feature | Purpose | Design note |
|---|---|---|
| Open channels | Molded passages before joining | Cores reach them easily in each half |
| Weld joint | Closes the passages | Raised ridge with a place for melted material to go |
| Ports | Inlet and outlets | Extra material, flow joints kept between them |
| Mounting points | Holds the manifold | Kept off the seam and off the passages |
| Pressure test feature | Checks the joint | A blanked port or a test boss for leak testing |
Joining
A welded seam has to hold along its whole length
A manifold seam follows every branch and turn of the passage.
- Vibration melts a raised ridge on one half so it fuses into the other
- The joint must contain the melted material instead of pushing it into the passage
- Loose material inside a passage restricts flow or breaks off later
- Both halves need matching fit along the whole seam, not just at the ends
Joining method
Ultrasonic welding or screws with a gasket
Permanent and serviceable joints suit different products.
Screws with a gasket
- Can be opened for cleaning or service
- Sealing force set by the fasteners
- More parts, and a groove around the whole passage
Drawing
What to send with a manifold
The passages and the joint plan decide everything.
Manifold CAD with the passage network shown
Working pressure and fluid
Port sizes and how each one connects
Whether the manifold must be serviceable
Leak test method you plan to use
Expected annual volume
Keep reading
Related guides
Other fluid parts, welded joints, and the lines that leak.
Valve bodies
Cored passages and side actions.
Valve bodiesPump housings
Casings around a rotor.
Pump housingsDucting
Large air paths and seams.
DuctingIrrigation fittings
Barbs and thread sealing.
Irrigation fittingsWeld lines
Where flow closes behind a port.
Weld linesAssembly features
Designing a joint to be joined.
Assembly featuresGlass filled PBT
A stiff, chemically steady option.
Glass filled PBTIndustrial and transportation
How we support industrial programs.
Industrial and transportationMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded manifolds
Why can a manifold not be molded in one piece?
Cores have to pull straight out, and a branching passage network gives them nowhere to go. Splitting the manifold into open channels that are joined afterward solves it. Splitting along the passages also makes each half easy to inspect before the two are joined.
Where do welded manifolds usually leak?
At a corner or a branch, where the two halves fit least well. Checking each half against its mate along the whole seam, rather than at a few points, catches this early. A short pressure test on every assembled manifold is the usual way to catch a joint that did not fuse properly.
Why did the manifold split at a port?
Flow closes behind the port opening and leaves a weaker line there. Feeding the part so those lines fall between ports, and adding material around each port, is the fix. Adding a collar of material around each port costs little in the tool and removes most burst failures.
Can a manifold be made serviceable?
Yes, with screws and a gasket instead of a weld. It adds parts and a groove around the passage, but the manifold can then be opened and cleaned. A serviceable manifold also needs enough room around the fasteners, which usually makes the body a little larger.
Next step
Quote a manifold as two halves
Upload the manifold and its passage network. DFM feedback covers the split line, weld joint design, port flow joints, and leak testing.